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1
Jouanno, Julien, Frédéric Marin, Yves du Penhoat, and Jean-Marc Molines. "Intraseasonal Modulation of the Surface Cooling in the Gulf of Guinea." Journal of Physical Oceanography 43, no. 2 (February 1, 2013): 382–401. http://dx.doi.org/10.1175/jpo-d-12-053.1.
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Abstract A regional numerical model of the tropical Atlantic Ocean and observations are analyzed to investigate the intraseasonal fluctuations of the sea surface temperature at the equator in the Gulf of Guinea. Results indicate that the seasonal cooling in this region is significantly shaped by short-duration cooling events caused by wind-forced equatorial waves: mixed Rossby–gravity waves within the 12–20-day period band, inertia–gravity waves with periods below 11 days, and equatorially trapped Kelvin waves with periods between 25 and 40 days. In these different ranges of frequencies, it is shown that the wave-induced horizontal oscillations of the northern front of the mean cold tongue dominate the variations of mixed layer temperature near the equator. But the model mixed layer heat budget also shows that the equatorial waves make a significant contribution to the mixed layer heat budget through modulation of the turbulent cooling, especially above the core of the Equatorial Undercurrent (EUC). The turbulent cooling variability is found to be mainly controlled by the intraseasonal modulation of the vertical shear in the upper ocean. This mechanism is maximum during periods of seasonal cooling, especially in boreal summer, when the surface South Equatorial Current is strongest and between 2°S and the equator, where the presence of the EUC provides a background vertical shear in the upper ocean. It applies for the three types of intraseasonal waves. Inertia–gravity waves also modulate the turbulent heat flux at the equator through vertical displacement of the core of the EUC in response to equatorial divergence and convergence.
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Holmes, R. M., and L. N. Thomas. "The Modulation of Equatorial Turbulence by Tropical Instability Waves in a Regional Ocean Model." Journal of Physical Oceanography 45, no. 4 (April 2015): 1155–73. http://dx.doi.org/10.1175/jpo-d-14-0209.1.
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AbstractSmall-scale turbulent mixing in the upper Equatorial Undercurrent (EUC) of the eastern Pacific cold tongue is a critical component of the SST budget that drives variations in SST on a range of time scales. Recent observations have shown that turbulent mixing within the EUC is modulated by tropical instability waves (TIWs). A regional ocean model is used to investigate the mechanisms through which large-scale TIW circulation modulates the small-scale shear, stratification, and shear-driven turbulence in the EUC. Eulerian analyses of time series taken from both the model and the Tropical Atmosphere Ocean (TAO) array suggest that increases in the zonal shear of the EUC drive increased mixing on the leading edge of the TIW warm phase. A Lagrangian vorticity analysis attributes this increased zonal shear to horizontal vortex stretching driven by the strain in the TIW horizontal velocity field acting on the existing EUC shear. To investigate the impact of horizontal vortex stretching on the turbulent heat flux averaged over a TIW period the effects of periodic TIW strain are included as forcing in a simple 1D mixing model of the EUC. Model runs with TIW forcing show turbulent heat fluxes up to 30% larger than runs without TIW forcing, with the magnitude of the increase being sensitive to the vertical mixing scheme used in the model. These results emphasize the importance of coupling between the large-scale circulation and small-scale turbulence in the equatorial regions, with implications for the SST budget of the equatorial Pacific.
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Cherian, D. A., D. B. Whitt, R. M. Holmes, R. C. Lien, S. D. Bachman, and W. G. Large. "Off-Equatorial Deep-Cycle Turbulence Forced by Tropical Instability Waves in the Equatorial Pacific." Journal of Physical Oceanography 51, no. 5 (May 2021): 1575–93. http://dx.doi.org/10.1175/jpo-d-20-0229.1.
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AbstractThe equatorial Pacific cold tongue is a site of large heat absorption by the ocean. This heat uptake is enhanced by a daily cycle of shear turbulence beneath the mixed layer—“deep-cycle turbulence”—that removes heat from the sea surface and deposits it in the upper flank of the Equatorial Undercurrent. Deep-cycle turbulence results when turbulence is triggered daily in sheared and stratified flow that is marginally stable (gradient Richardson number Ri ≈ 0.25). Deep-cycle turbulence has been observed on numerous occasions in the cold tongue at 0°, 140°W, and may be modulated by tropical instability waves (TIWs). Here we use a primitive equation regional simulation of the cold tongue to show that deep-cycle turbulence may also occur off the equator within TIW cold cusps where the flow is marginally stable. In the cold cusp, preexisting equatorial zonal shear uz is enhanced by horizontal vortex stretching near the equator, and subsequently modified by horizontal vortex tilting terms to generate meridional shear υz off of the equator. Parameterized turbulence in the sheared flow of the cold cusp is triggered daily by the descent of the surface mixing layer associated with the weakening of the stabilizing surface buoyancy flux in the afternoon. Observational evidence for off-equatorial deep-cycle turbulence is restricted to a few CTD casts, which, when combined with shear from shipboard ADCP data, suggest the presence of marginally stable flow in TIW cold cusps. This study motivates further observational campaigns to characterize the modulation of deep-cycle turbulence by TIWs both on and off the equator.
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Couvelard, Xavier, Patrick Marchesiello, Lionel Gourdeau, and Jerome Lefèvre. "Barotropic Zonal Jets Induced by Islands in the Southwest Pacific." Journal of Physical Oceanography 38, no. 10 (October 1, 2008): 2185–204. http://dx.doi.org/10.1175/2008jpo3903.1.
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Abstract The oceanic circulation entering the tropical southwest Pacific (SWP) is dominated by the broad westward flow of the South Equatorial Current (SEC), which is forced by the trade winds. It has been argued that the numerous islands of the SWP are able to restructure the SEC into a series of deep and narrow zonal jets, which control important pathways connecting equatorial and extraequatorial signals. The primary objective of this paper is to improve the understanding of the structure and dynamics of SWP zonal jets, giving special attention to topographic effects. This study is based on the use of a high-resolution regional oceanic model, whose solution is compared with observations, as well as with solutions from global models and the Sverdrup relation. The model used here indicates that the regional topography drives a general equatorward shift of the SEC, which is beneficial to the North Fiji, North Vanuatu, and North Caledonian jets. A depth-integrated vorticity budget shows that this topographic effect is considerably attenuated by baroclinicity and advection processes, but not to the point of total compensation as often admitted for the interior ocean. The effect of nonlinear advection is to allow flow rectification of the jets fluctuations, taking the form of zonally elongated dipole circulations in the leeward side of the islands.
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Lindstrom, Eric, James Edson, Julian Schanze, and Andrey Shcherbina. "SPURS-2: Salinity Processes in the Upper-Ocean Regional Study 2 – The Eastern Equatorial Pacific Experiment." Oceanography 32, no. 2 (June 1, 2019): 15–19. http://dx.doi.org/10.5670/oceanog.2019.207.
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Ouyang, Yating, Yuhong Zhang, Jianwei Chi, Qiwei Sun, and Yan Du. "Regional difference of sea surface salinity variations in the western tropical pacific." Journal of Oceanography 77, no. 4 (February 27, 2021): 647–57. http://dx.doi.org/10.1007/s10872-021-00598-2.
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AbstractRegional difference of sea surface salinity (SSS) variations in the western tropical Pacific is investigated with Ocean Reanalysis System 5 datasets. Three robust zonal bands of SSS variations have been identified in the northwestern tropical Pacific (NWTP), the western equatorial tropical Pacific (WEqP), and the southwestern tropical Pacific (SWTP), respectively. SSS in the WEqP and the SWTP has a strong interannual variability that is related to ENSO. In the WEqP, SSS variations are mainly controlled by anomalous freshwater flux, while in the SWTP they are governed by both freshwater forcing and oceanic processes. In the NWTP, SSS variations present a low-frequency variability that is correlated with Interdecadal Pacific Oscillation (IPO), which is mostly dominated by the freshwater flux and strongly adjusted by the ocean advection and mixed layer changes. After removing interannual signals, the SSS in all three regions are highly related to IPO, indicating that IPO has a general influence on the western tropical Pacific.
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Johnson, Gregory C. "Generation and Initial Evolution of a Mode Water θ–S Anomaly*." Journal of Physical Oceanography 36, no. 4 (April 1, 2006): 739–51. http://dx.doi.org/10.1175/jpo2895.1.
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Abstract Generation and evolution of an isopycnal potential temperature–salinity (θ–S), or spiciness, anomaly is studied around 20°–23°S, 110°W in the austral winter of 2004. Two profiling CTD floats deployed in the region in January 2004 provide the observations. The anomaly (defined as relative to water properties of the preceding summer) is very large (initially about 0.35 in S and about 0.9°C in θ). It is associated with the winter ventilation of a thick, low-potential-vorticity layer known as South Pacific Eastern Subtropical Mode Water. Regional lateral θ and S distributions at the surface predispose the ocean to formation of this water mass and allow significant anomalies to be generated there with relative ease. The water mass is potentially important for climate in that, after northwestward advection in the South Equatorial Current, it contributes to the Equatorial Undercurrent and eventually resurfaces in the cold tongue of the eastern equatorial Pacific Ocean. The anomaly studied is strong enough to predispose a portion of the water column to salt fingering, increasing vertical mixing. Although lateral processes are no doubt important in evolution of the anomaly, the vertical mixing appears to be sufficiently vigorous to reduce it significantly within 6 months after its formation by spreading it to denser horizons through diapycnal fluxes. By that time the anomaly is most likely sufficiently diffuse so that subsequent evolution from diapycnal fluxes is significantly reduced as it makes its way toward the equator.
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Chen, Gengxin, Dongxiao Wang, Weiqing Han, Ming Feng, Fan Wang, Yuanlong Li, Ju Chen, and Arnold L. Gordon. "The Extreme El Niño Events Suppressing the Intraseasonal Variability in the Eastern Tropical Indian Ocean." Journal of Physical Oceanography 50, no. 8 (August 1, 2020): 2359–72. http://dx.doi.org/10.1175/jpo-d-20-0041.1.
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AbstractIn the eastern tropical Indian Ocean, intraseasonal variability (ISV) affects the regional oceanography and marine ecosystems. Mooring and satellite observations documented two periods of unusually weak ISV during the past two decades, associated with suppressed baroclinic instability of the South Equatorial Current. Regression analysis and model simulations suggest that the exceptionally weak ISVs were caused primarily by the extreme El Niño events and modulated to a lesser extent by the Indian Ocean dipole. Additional observations confirm that the circulation balance in the Indo-Pacific Ocean was disrupted during the extreme El Niño events, impacting the Indonesian Throughflow Indian Ocean dynamics. This research provides substantial evidence for large-scale modes modulating ISV and the abnormal Indo-Pacific dynamical connection during extreme climate modes.
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Wijffels, Susan E., Gary Meyers, and J. Stuart Godfrey. "A 20-Yr Average of the Indonesian Throughflow: Regional Currents and the Interbasin Exchange." Journal of Physical Oceanography 38, no. 9 (September 1, 2008): 1965–78. http://dx.doi.org/10.1175/2008jpo3987.1.
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Abstract Twenty years of monthly or more frequent repeat expendable bathythermograph data are used to estimate the mean geostrophic velocity and transport relative to 750 m of the Indonesian Throughflow (ITF) and its partitioning through the major outflow straits into the Indian Ocean. Ekman transports are estimated from satellite and atmospheric reanalysis wind climatologies. A subsurface maximum near 100 m characterizes the geostrophic ITF, but Ekman flows drive a warm near-surface component as well. A subsurface intensified fresh Makassar Jet feeds the Lombok Strait Throughflow (∼2 Sv; 1Sv ≡ 106 m3 s−1) and an eastward flow along the Nusa Tenggara island chain [the Nusa Tenggara Current (6 Sv)]. This flow feeds a relatively cold 3.0-Sv flow through the Ombai Strait and Savu Sea. About 4–5 Sv pass through Timor Passage, fed by both the Nusa Tenggara Current and likely warmer and saltier flow from the eastern Banda Sea. The Ombai and Timor Throughflow feature distinctly different shear profiles; Ombai has deep-reaching shear with a subsurface velocity maximum near 150 m and so is cold (∼15.5°–17.1°C), while Timor Passage has a surface intensified flow and is warm (∼21.6°–23°C). At the western end of Timor Passage the nascent South Equatorial Current is augmented by recirculation from a strong eastward shallow flow south of the passage. South of the western tip of Java are two mean eastward flows—the very shallow, warm, and fresh South Java Current and a cold salty South Java Undercurrent. These, along with the inflow of the Eastern Gyral Current, recirculate to augment the South Equatorial Current, and greatly increase its salinity compared to that at the outflow passages. The best estimate of the 20-yr-average geostrophic plus Ekman transport is 8.9 ± 1.7 Sv with a transport-weighted temperature of 21.2°C and transport-weighted salinity of 34.73 near 110°E. The warm temperatures of the flow can be reconciled with the much cooler estimates based on mooring data in Makassar Strait by accounting for an unmeasured barotropic and deep component, and local surface heat fluxes that warm the ITF by 2°–4°C during its passage through the region.
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Tchilibou, Michel, Lionel Gourdeau, Rosemary Morrow, Guillaume Serazin, Bughsin Djath, and Florent Lyard. "Spectral signatures of the tropical Pacific dynamics from model and altimetry: a focus on the meso-/submesoscale range." Ocean Science 14, no. 5 (October 24, 2018): 1283–301. http://dx.doi.org/10.5194/os-14-1283-2018.
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Abstract. The processes that contribute to the flat sea surface height (SSH) wavenumber spectral slopes observed in the tropics by satellite altimetry are examined in the tropical Pacific. The tropical dynamics are first investigated with a 1∕12∘ global model. The equatorial region from 10∘ N to 10∘ S is dominated by tropical instability waves with a peak of energy at 1000 km wavelength, strong anisotropy, and a cascade of energy from 600 km down to smaller scales. The off-equatorial regions from 10 to 20∘ latitude are characterized by a narrower mesoscale range, typical of midlatitudes. In the tropics, the spectral taper window and segment lengths need to be adjusted to include these larger energetic scales. The equatorial and off-equatorial regions of the 1∕12∘ model have surface kinetic energy spectra consistent with quasi-geostrophic turbulence. The balanced component of the dynamics slightly flattens the EKE spectra, but modeled SSH wavenumber spectra maintain a steep slope that does not match the observed altimetric spectra. A second analysis is based on 1∕36∘ high-frequency regional simulations in the western tropical Pacific, with and without explicit tides, where we find a strong signature of internal waves and internal tides that act to increase the smaller-scale SSH spectral energy power and flatten the SSH wavenumber spectra, in agreement with the altimetric spectra. The coherent M2 baroclinic tide is the dominant signal at ∼140 km wavelength. At short scales, wavenumber SSH spectra are dominated by incoherent internal tides and internal waves which extend up to 200 km in wavelength. These incoherent internal waves impact space scales observed by today's along-track altimetric SSH, and also on the future Surface Water Ocean Topography (SWOT) mission 2-D swath observations, raising the question of altimetric observability of the shorter mesoscale structures in the tropics.
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Qiu, Bo, and Shuiming Chen. "Multidecadal Sea Level and Gyre Circulation Variability in the Northwestern Tropical Pacific Ocean." Journal of Physical Oceanography 42, no. 1 (January 1, 2012): 193–206. http://dx.doi.org/10.1175/jpo-d-11-061.1.
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Abstract Sea level rise with the trend >10 mm yr−1 has been observed in the tropical western Pacific Ocean over the 1993–2009 period. This rate is 3 times faster than the global-mean value of the sea level rise. Analyses of the satellite altimeter data and repeat hydrographic data along 137°E reveal that this regionally enhanced sea level rise is thermosteric in nature and vertically confined to a patch in the upper ocean above the 12°C isotherm. Dynamically, this regional sea level trend is accompanied by southward migration and strengthening of the North Equatorial Current (NEC) and North Equatorial Countercurrent (NECC). Using a 1½-layer reduced-gravity model forced by the ECMWF reanalysis wind stress data, the authors find that both the observed sea level rise and the NEC/NECC’s southward migrating and strengthening trends are largely attributable to the upper-ocean water mass redistribution caused by the surface wind stresses of the recently strengthened atmospheric Walker circulation. Based on the long-term model simulation, it is further found that the observed southward migrating and strengthening trends of the NEC and NECC began in the early 1990s. In the two decades prior to 1993, the NEC and NECC had weakened and migrated northward in response to a decrease in the trade winds across the tropical Pacific Ocean.
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Travis, Seth, and Bo Qiu. "Decadal Variability in the South Pacific Subtropical Countercurrent and Regional Mesoscale Eddy Activity." Journal of Physical Oceanography 47, no. 3 (March 2017): 499–512. http://dx.doi.org/10.1175/jpo-d-16-0217.1.
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AbstractDecadal variability of eddy activity in the western, subtropical South Pacific is examined using the past two decades of satellite altimetry data. Between 21° and 29°S, there is a band of heightened eddy activity. In this region, the eastward South Pacific Subtropical Countercurrent (STCC) overlays the westward South Equatorial Current (SEC). This vertically sheared STCC–SEC system is subject to baroclinic instabilities. By using the European Centre for Medium-Range Weather Forecasts (ECMWF) Ocean Reanalysis System, version 4 (ORAS4), data and verifying with the gridded Argo float data, low-frequency variations in the state of the ocean in this region are investigated. It is found that the low-frequency changes in the shearing and stratification of the STCC–SEC region simultaneously work to modulate the strength of baroclinic instabilities, as measured through the baroclinic growth rate. These changes in the strength of the instabilities consequently affect the observed eddy activity. Using a linearization of the baroclinic growth rate, the contribution to the variability from the changes in shearing is found to be roughly twice as large as those from changes in stratification. Additionally, changes in the temperature and salinity fields are both found to have significant impacts on the low-frequency variability of shearing and stratification, for which salinity changes are responsible for 50%–75% of the variability as caused by temperature changes. However, the changes in all these parameters do not occur concurrently and can alternately work to negate or augment each other.
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Wilson, Moyra E. J. "Global and regional influences on equatorial shallow-marine carbonates during the Cenozoic." Palaeogeography, Palaeoclimatology, Palaeoecology 265, no. 3-4 (August 2008): 262–74. http://dx.doi.org/10.1016/j.palaeo.2008.05.012.
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Guiavarc'h, C., A. M. Treguier, and A. Vangriesheim. "Deep currents in the Gulf of Guinea: along slope propagation of intraseasonal waves." Ocean Science Discussions 6, no. 1 (January 7, 2009): 57–94. http://dx.doi.org/10.5194/osd-6-57-2009.
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Abstract. In the Gulf of Guinea, intraseasonal variability is large at the equator and along the coast. Current data on the continental slope near 7.5° S show very energetic biweekly oscillations at 1300 m depth. A high resolution numerical model demonstrates that this deep variability is forced by equatorial winds, through the generation of equatorial Yanai waves that propagate eastward and at depth, and then poleward as coastal-trapped waves upon reaching the coast of Africa. Intraseasonal variability is intensified along the coast, especially in the 500–1500 m depth range, with the largest intensification in the 10–20 day period range. The structure of kinetic energy is well explained at first order by a linear model with six baroclinic modes. Along the equator, eastward intensification of energy and bottom intensification are in qualitative agreement with vertically propagating Yanai waves, although the signal is clearly influenced by the details of the bathymetry. Along the coast, vertical modes 3 to 5 are important close to the equator, and the signal is dominated by lower modes farther south. Additional current meter data on the continental slope near 3° N display an energy profile in the 10–20 day period band that is strikingly different from the one at 7.5° S, with surface intensification rather than bottom intensification and a secondary maximum near 800 m. The model reproduces these features and explains them: the surface intensification in the north is due to the regional wind forcing, and the north-south dissymetry of the deep signal is due to the presence of the zonal African coast near 5° N. A 4 years time series at 7.5° S displays intermittencies of the 10–20 day signal near the bottom. This intermittency is not correlated with fluctuations of the equatorial winds and does not seem to be a simple linear response to the wind forcing.
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Guiavarc'h, C., A. M. Treguier, and A. Vangriesheim. "Deep currents in the Gulf of Guinea: along slope propagation of intraseasonal waves." Ocean Science 5, no. 2 (May 18, 2009): 141–53. http://dx.doi.org/10.5194/os-5-141-2009.
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Abstract. In the Gulf of Guinea, intraseasonal variability is large at the equator and along the coast. Current data on the continental slope near 7.5° S show very energetic biweekly oscillations at 1300 m depth. A high resolution primitive equation numerical model demonstrates that this deep variability is forced by equatorial winds, through the generation of equatorial Yanai waves that propagate eastward and at depth, and then poleward as coastally-trapped waves upon reaching the coast of Africa. Intraseasonal variability is intensified along the coast of the Gulf of Guinea, especially in the 10–20 day period range and at depths between 500 and 1500 m. The kinetic energy distribution is well explained at first order by linear theory. Along the equator, eastward intensification of energy and bottom intensification are in qualitative agreement with vertically propagating Yanai waves, although the signal is influenced by the details of the bathymetry. Along the coast, baroclinic modes 3 to 5 are important close to the equator, and the signal is dominated by lower vertical modes farther south. Additional current meter data on the continental slope near 3° N display an energy profile in the 10–20 day period band that is strikingly different from the one at 7.5° S, with surface intensification rather than bottom intensification and a secondary maximum near 800 m. The model reproduces these features and explains them: the surface intensification in the north is due to the regional wind forcing, and the north-south asymmetry of the deep signal is due to the presence of the zonal African coast near 5° N. A 4 years time series of current measurements at 7.5° S shows that the biweekly oscillations are intermittent and vary from year to year. This intermittency is not well correlated with fluctuations of the equatorial winds and does not seem to be a simple linear response to the wind forcing.
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Zhang, Xuebin, Bruce Cornuelle, and Dean Roemmich. "Sensitivity of Western Boundary Transport at the Mean North Equatorial Current Bifurcation Latitude to Wind Forcing." Journal of Physical Oceanography 42, no. 11 (November 1, 2012): 2056–72. http://dx.doi.org/10.1175/jpo-d-11-0229.1.
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Abstract The bifurcation of the North Equatorial Current (NEC) plays an important role in the heat and water mass exchanges between the tropical and subtropical gyres in the Pacific Ocean. The variability of western boundary transport (WBT) east of the Philippine coast at the mean NEC bifurcation latitude (12°N) is examined here. A tropical Pacific regional model is set up based on the Massachusetts Institute of Technology general circulation model and its adjoint, which calculates the sensitivities of a defined meridional transport to atmospheric forcing fields and ocean state going backward in time. The adjoint-derived sensitivity of the WBT at the mean NEC bifurcation latitude to surface wind stress is dominated by curl-like patterns that are located farther eastward and southward with increasing time lag. The temporal evolution of the adjoint sensitivity of the WBT to wind stress resembles wind-forced Rossby wave dynamics but propagating with speeds determined by the background stratification and current, suggesting that wind-forced Rossby waves are the underlying mechanism. Interannual-to-decadal variations of the WBT can be hindcast well by multiplying the adjoint sensitivity and the time-lagged wind stress over the whole model domain and summing over time lags. The analysis agrees with previous findings that surface wind stress (especially zonal wind stress in the western subtropical Pacific) largely determines the WBT east of the Philippines, and with a time lag based on Rossby wave propagation. This adjoint sensitivity study quantifies the contribution of wind stress at all latitudes and longitudes and provides a novel perspective to understand the relationship between the WBT and wind forcing over the Pacific Ocean.
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Ballarotta, Maxime, Clément Ubelmann, Marie-Isabelle Pujol, Guillaume Taburet, Florent Fournier, Jean-François Legeais, Yannice Faugère, et al. "On the resolutions of ocean altimetry maps." Ocean Science 15, no. 4 (August 20, 2019): 1091–109. http://dx.doi.org/10.5194/os-15-1091-2019.
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Abstract. The Data Unification and Altimeter Combination System (DUACS) produces sea level global and regional maps that serve oceanographic applications, climate forecasting centers, and geophysics and biology communities. These maps are generated using an optimal interpolation method applied to altimeter observations. They are provided on a global 1∕4∘ × 1∕4∘ (longitude × latitude) and daily grid resolution framework (1∕8∘ × 1∕8∘ longitude × latitude grid for the regional products) through the Copernicus Marine Environment Monitoring Service (CMEMS). Yet, the dynamical content of these maps does not have full 1∕4∘ spatial and 1 d temporal resolutions due to the filtering properties of the optimal interpolation. In the present study, we estimate the effective spatial and temporal resolutions of the newly reprocessed delayed-time DUACS maps (a.k.a. DUACS-DT2018). Our approach is based on the ratio between the spectral content of the mapping error and the spectral content of independent true signals (along-track and tide gauge observations), also known as the noise-to-signal ratio. We found that the spatial resolution of the DUACS-DT2018 global maps based on sampling by three altimeters simultaneously ranges from ∼100 km wavelength at high latitude to ∼800 km wavelength in the equatorial band and the mean temporal resolution is ∼34 d. The mean effective spatial resolution at midlatitude is estimated to be ∼200 km. The mean effective spatial resolution is ∼130 km for the regional Mediterranean Sea and for the regional Black Sea products. An intercomparison with previous DUACS reprocessing systems (a.k.a., DUACS-DT2010 and DUACS-DT2014) highlights the progress of the system over the past 8 years, in particular a gain of resolution in highly turbulent regions. The same diagnostic applied to maps constructed with two altimeters and maps with three altimeters confirms a modest increase in resolving capabilities and accuracies in the DUACS maps with the number of missions.
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Liu, Lingling, Yuanlong Li, and Fan Wang. "MJO-Induced Intraseasonal Mixed Layer Depth Variability in the Equatorial Indian Ocean and Impacts on Subsurface Water Obduction." Journal of Physical Oceanography 51, no. 4 (April 2021): 1247–63. http://dx.doi.org/10.1175/jpo-d-20-0179.1.
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AbstractChange of oceanic surface mixed layer depth (MLD) is critical for vertical exchanges between the surface and subsurface oceans and modulates surface temperature variabilities on various time scales. In situ observations have documented prominent intraseasonal variability (ISV) of MLD with 30–105-day periods in the equatorial Indian Ocean (EIO) where the Madden–Julian oscillation (MJO) initiates. Simulation of Hybrid Coordinate Ocean Model (HYCOM) reveals a regional maximum of intraseasonal MLD variability in the EIO (70°–95°E, 3°S–3°N) with a standard deviation of ~14 m. Sensitivity experiments of HYCOM demonstrate that, among all of the MJO-related forcing effects, the wind-driven downwelling and mixing are primary causes for intraseasonal MLD deepening and explain 83.7% of the total ISV. The ISV of MLD gives rise to high-frequency entrainments of subsurface water, leading to an enhancement of the annual entrainment rate by 34%. However, only a small fraction of these entrainment events (<20%) can effectively contribute to the annual obduction rate of 1.36 Sv, a quantification for the amount of resurfacing thermocline water throughout a year that mainly (84.6%) occurs in the summer monsoon season (May–October). The ISV of MLD achieves the maximal intensity in April–May and greatly affects the subsequent obduction. Estimation based on our HYCOM simulations suggests that MJOs overall reduce the obduction rate in the summer monsoon season by as much as 53%. A conceptual schematic is proposed to demonstrate how springtime intraseasonal MLD deepening events caused by MJO winds narrow down the time window for effective entrainment and thereby suppress the obduction of thermocline water.
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Chen, Ge, and Haitao Li. "Fine Pattern of Natural Modes in Sea Surface Temperature Variability: 1985–2003." Journal of Physical Oceanography 38, no. 2 (February 1, 2008): 314–36. http://dx.doi.org/10.1175/2007jpo3592.1.
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Abstract A natural mode refers, in this study, to a periodic oscillation of sea surface temperature (SST) that is geophysically significant on a global, regional, or local scale. Using a newly developed harmonic extraction scheme by Chen, which has the advantage of being space–time decoupled and fully data adaptive, a variety of natural modes have been recovered from global monthly SST data for the period of 1985–2003. Among them, the eight most significant modes are identified as primary modes, whose spatial patterns are presented, along with their phase distributions. At seasonal time scales, a 4-month primary mode is uncovered in addition to the well-documented annual and semiannual cycles. At interannual time scales, the dominant El Niño–Southern Oscillation (ENSO) variability is found to be composed of at least five primary modes, with well-defined central periods around 18, 25, 32, 43, and 63 months. At time scales beyond ENSO, a decadal SST signal with an average period of 10.3 yr is observed. A unique contribution of this study is the derivation and presentation of fine patterns of natural SST modes and signals in joint dimensions of time, space, period, and phase, leading to several findings and conclusions that are of potential importance: 1) The degree of separability and regularity of the sub-ENSO modes is surprising, and thus reveals new details on the nature of this event. 2) The midlatitude counterparts of the equatorial interannual and decadal SST modes/signals are found in the two hemispheres with a frequency shift toward longer periods. The “shadows” of the Pacific Ocean’s ENSO modes are also observed with some detail in the Atlantic and the Indian Oceans. All of these provide direct evidence that teleconnections exist between the equatorial and extratropical oceans, as well as among the tropical Pacific, tropical Atlantic, and tropical Indian Oceans, possibly as a result of the “atmospheric bridge.” 3) A sharply opposite anisotropy is observed in the spatiotemporal pattern between the interannual modes and decadal signals, implying that they are potentially of a categorical difference in origin. 4) Locality or regionality is a fundamental feature for most of the SST modes. Treating the interannual or decadal variability as a single ENSO or Pacific decadal oscillation mode appears to be an oversimplification, and may lead to inappropriate interpretations. The results herein represent an improved knowledge of the natural variability in sea surface temperature, which will hopefully help to enhance the understanding of natural fluctuations of the global/regional climate system in the context of ocean–atmosphere interaction.
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Trenberth, Kevin E., and John T. Fasullo. "An Observational Estimate of Inferred Ocean Energy Divergence." Journal of Physical Oceanography 38, no. 5 (May 1, 2008): 984–99. http://dx.doi.org/10.1175/2007jpo3833.1.
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Abstract Monthly net surface energy fluxes (FS) over the oceans are computed as residuals of the atmospheric energy budget using top-of-atmosphere (TOA) net radiation (RT) and the complete atmospheric energy (AE) budget tendency (δAE/δt) and divergence (∇ · FA). The focus is on TOA radiation from the Earth Radiation Budget Experiment (ERBE) (February 1985–April 1989) and the Clouds and Earth’s Radiant Energy System (CERES) (March 2000–May 2004) satellite observations combined with results from two atmospheric reanalyses and three ocean datasets that enable a comprehensive estimate of uncertainties. Surface energy flux departures from the annual mean and the implied annual cycle in “equivalent ocean energy content” are compared with the directly observed ocean energy content (OE) and tendency (δOE/δt) to reveal the inferred annual cycle of divergence (∇ · FO). In the extratropics, the surface flux dominates the ocean energy tendency, although it is supplemented by ocean Ekman transports that enhance the annual cycle in ocean heat content. In contrast, in the tropics, ocean dynamics dominate OE variations throughout the year in association with the annual cycle in surface wind stress and the North Equatorial Current. An analysis of the regional characteristics of the first joint empirical orthogonal function (EOF) of FS, δOE/δt, and ∇ · FO is presented, and the largest sources of uncertainty are attributed to variations in OE. The mean and annual cycle of zonal mean global ocean meridional heat transports are estimated. The annual cycle reveals the strongest poleward heat transports in each hemisphere in the cold season, from November to April in the north and from May to October in the south, with a substantial across-equatorial transport, exceeding 4 PW in some months. Annual mean results do not differ greatly from some earlier estimates, but the sources of uncertainty are exposed. Comparison of annual means with direct ocean observations gives reasonable agreement, except in the North Atlantic, where transports from the ocean transects are slightly greater than the estimates presented here.
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Ferriss, Bridget E., and Timothy E. Essington. "Regional patterns in mercury and selenium concentrations of yellowfin tuna (Thunnus albacares) and bigeye tuna (Thunnus obesus) in the Pacific Ocean." Canadian Journal of Fisheries and Aquatic Sciences 68, no. 12 (December 2011): 2046–56. http://dx.doi.org/10.1139/f2011-120.
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Mercury (Hg) concentrations in high trophic level fish, such as bigeye tuna ( Thunnus obesus ) and yellowfin tuna ( Thunnus albacares ), can often exceed consumption advisories. Here we sampled 444 yellowfin and bigeye tuna to determine whether tuna Hg concentration varies regionally in the eastern and central Pacific Ocean and whether this variation corresponds to environmental characteristics that promote the bioavailability of Hg. Of the five regions sampled, we found significantly higher Hg concentrations in the eastern equatorial region (5°S–5°N; 110°W–120°W) for both species. Hg concentrations in this region were elevated by 0.22 and 0.17 µg·g–1for yellowfin and bigeye tuna, respectively, compared with Hg concentrations in the other regions. Tuna selenium concentrations, which may alter the toxicity of Hg, did not vary by region. Oceanographic data indicated that the eastern equatorial region had elevated chlorophyll a concentrations and shallow minimum oxygen depths, both of which promote Hg methylation. These findings suggest that methylation-promoting mechanisms may translate into regional variation in the Hg concentrations of highly mobile, high trophic level fish.
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Raes, Eric J., Levente Bodrossy, Jodie van de Kamp, Andrew Bissett, Martin Ostrowski, Mark V. Brown, Swan L. S. Sow, Bernadette Sloyan, and Anya M. Waite. "Oceanographic boundaries constrain microbial diversity gradients in the South Pacific Ocean." Proceedings of the National Academy of Sciences 115, no. 35 (August 14, 2018): E8266—E8275. http://dx.doi.org/10.1073/pnas.1719335115.
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Marine microbes along with microeukaryotes are key regulators of oceanic biogeochemical pathways. Here we present a high-resolution (every 0.5° of latitude) dataset describing microbial pro- and eukaryotic richness in the surface and just below the thermocline along a 7,000-km transect from 66°S at the Antarctic ice edge to the equator in the South Pacific Ocean. The transect, conducted in austral winter, covered key oceanographic features including crossing of the polar front (PF), the subtropical front (STF), and the equatorial upwelling region. Our data indicate that temperature does not determine patterns of marine microbial richness, complementing the global model data from Ladau et al. [Ladau J, et al. (2013) ISME J 7:1669–1677]. Rather, NH4+, nanophytoplankton, and primary productivity were the main drivers for archaeal and bacterial richness. Eukaryote richness was highest in the least-productive ocean region, the tropical oligotrophic province. We also observed a unique diversity pattern in the South Pacific Ocean: a regional increase in archaeal and bacterial diversity between 10°S and the equator. Rapoport’s rule describes the tendency for the latitudinal ranges of species to increase with latitude. Our data showed that the mean latitudinal ranges of archaea and bacteria decreased with latitude. We show that permanent oceanographic features, such as the STF and the equatorial upwelling, can have a significant influence on both alpha-diversity and beta-diversity of pro- and eukaryotes.
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Sun, Bingrong, Zhaohui Chen, Bin Wang, and Lixin Wu. "Seasonal variation of the North Equatorial Current bifurcation in regional model: Role of open boundary conditions." Ocean Modelling 145 (January 2020): 101528. http://dx.doi.org/10.1016/j.ocemod.2019.101528.
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Romero-Torres, Mauricio, Alberto Acosta, and Eric A. Treml. "The regional structure of spawning phenology and the potential consequences for connectivity of coral assemblages across the Eastern Tropical Pacific." ICES Journal of Marine Science 74, no. 3 (December 23, 2016): 613–24. http://dx.doi.org/10.1093/icesjms/fsw218.
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The coral reefs of the Eastern Tropical Pacific (ETP) are some of the most geographically isolated of the world. A key to understanding their long-term persistence and population recovery via dispersal (i.e. population connectivity), is knowing when the corals spawn in the region. To this end, we reviewed and synthesized the literature on the reproductive phenology of corals (month of spawning) and their dispersal-related characteristics to infer the potential impact on the region’s functional connectivity. We classified the region into four thermal regimes based on long-term mean sea surface temperature (SST) data: Tropical Upwelling, Thermally Stable, Equatorial Upwelling, and Seasonal. Each regime’s unique spawning seasonality was then explored by quantifying the linear dependence between the number of observed spawning events and SST. Finally, the potential impact of this unique regional mismatch in spawning was illustrated using a biophysical larval dispersal model. We found spawning occurs throughout the year in the Upwelling and Thermally Stable regimes (showing low or no linear dependence with SST); whereas spawning had a strong seasonal signal in the Equatorial Upwelling and Seasonal regimes, occurring primarily in the warm months. Considering the region’s mismatch in spawning phenologies, and unique dispersal traits, the simulations of coral larval dispersal across the ETP result in infrequently realized connectivity between ecoregions, low local retention and high self-recruitment, that combined with low recruitment densities in the field indicates more vulnerable populations to disturbance than previously appreciated. The strong relationship between spawning phenology and SST in some regimes suggests a greater susceptibility of these coral assemblages to extreme El Niño and La Niña events and future ocean warming.
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Wilson, W. Douglas, Scott Glenn, Travis Miles, Anthony Knap, and Cesar Toro. "Transformative Ocean Observing for Hurricane Forecasting, Readiness, and Response in the Caribbean Tropical Storm Corridor." Marine Technology Society Journal 55, no. 3 (May 1, 2021): 90–91. http://dx.doi.org/10.4031/mtsj.55.3.43.
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Abstract The upper ocean in the Western Tropical Atlantic tropical storm corridor—including the Caribbean Sea—is under-sampled and climatologically warming (Figure 1). Regionally varying Essential Ocean Features impacting tropical cyclone dynamics include fresh water upper ocean layers, mesoscale eddies, high Upper Ocean Heat Content values, and inflows from the Subtropical and Equatorial Atlantic. Ongoing research indicates that hurricane intensity forecasts can be improved with expanded and sustained ocean data collection and utilization along the hurricane path.This proposed activity will build supporting physical and social infrastructure and conduct a long-term sampling program in this critical region using gliders, High Frequency Radars (HFR), and developing technologies to provide real-time information resulting in hurricane forecast improvement. Improved forecasts will support new generation of local storm surge/precipitation/wave and coastal impact models and guidance used to directly enhance resilience.The success of this project will depend on the merger of regional scale planning and management AND development of local-level partnerships for implementation. To be sustainable, operational, analytical, and actionable, capability has to exist at the multiple proposed regional system nodes. We will promote expanded education and workforce development using existing partner capabilities, and include an Ocean Observing for SIDS/Developing Economies component. Product and information delivery systems will have local interpretive support and will incorporate local knowledge and expertise.It is our hope that by 2030 our legacy would be successful program to—in the words of the Decade Action Framework—“sustain long-term high-quality observations of marine and coastal environments including human interactions and deliver forecast and decision-support tools.”
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Etourneau, J., R. S. Robinson, P. Martinez, and R. Schneider. "Equatorial Pacific peak in biological production regulated by nutrient and upwelling during the late Pliocene/early Pleistocene cooling." Biogeosciences 10, no. 8 (August 27, 2013): 5663–70. http://dx.doi.org/10.5194/bg-10-5663-2013.
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Abstract. The largest increase in export production in the eastern Pacific of the last 5.3 Myr (million years) occurred between 2.2 and 1.6 Myr, a time of major climatic and oceanographic reorganization in the region. Here, we investigate the causes of this event using reconstructions of export production, nutrient supply and oceanic conditions across the Pliocene–Pleistocene in the eastern equatorial Pacific (EEP) for the last 3.2 Myr. Our results indicate that the export production peak corresponds to a cold interval marked by high nutrient supply relative to consumption, as revealed by the low bulk sedimentary 15N/14N (δ15N) and alkenone-derived sea surface temperature (SST) values. This ∼0.6 million year long episode of enhanced delivery of nutrients to the surface of the EEP was predominantly initiated through the upwelling of nutrient-enriched water sourced in high latitudes. In addition, this phenomenon was likely promoted by the regional intensification of upwelling in response to the development of intense Walker and Hadley atmospheric circulations. Increased nutrient consumption in the polar oceans and enhanced denitrification in the equatorial regions restrained nutrient supply and availability and terminated the high export production event.
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Etourneau, J., R. S. Robinson, P. Martinez, and R. Schneider. "Equatorial Pacific peak in biological production regulated by nutrient and upwelling during the late Pliocene/early Pleistocene cooling." Biogeosciences Discussions 10, no. 3 (March 21, 2013): 5535–54. http://dx.doi.org/10.5194/bgd-10-5535-2013.
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Abstract. The largest increase in export production in the eastern Pacific of the last 5.3 Myr (million years) occurred between 2.2 and 1.6 Myr, a time of major climatic and oceanographic reorganization in the region. Here, we investigate the causes of this event using reconstructions of export production, nutrient supply and oceanic conditions across the Pliocene-Pleistocene in the eastern equatorial Pacific (EEP) for the last 3.2 Myr. Our results indicate that the export production peak corresponds to a cold interval marked by high nutrient supply relative to consumption, as revealed by the low bulk sedimentary 15N/14N (δ15N) and alkenone-derived sea surface temperature (SST) values. This ~ 0.6 million years long episode of enhanced delivery of nutrients to the surface of the EEP was predominantly initiated through the upwelling of nutrient-enriched water sourced in high latitudes. In addition, this phenomenon was likely promoted by the regional intensification of upwelling in response to the development of intense Walker and Hadley atmospheric circulations. Increased nutrient consumption in the polar oceans and enhanced denitrification in the equatorial regions restrained nutrient supply and availability and terminated the high export production event.
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Currie, J. C., M. Lengaigne, J. Vialard, D. M. Kaplan, O. Aumont, S. W. A. Naqvi, and O. Maury. "Indian Ocean Dipole and El Niño/Southern Oscillation impacts on regional chlorophyll anomalies in the Indian Ocean." Biogeosciences Discussions 10, no. 3 (March 26, 2013): 5841–88. http://dx.doi.org/10.5194/bgd-10-5841-2013.
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Abstract. The Indian Ocean Dipole (IOD) and the El Niño-Southern Oscillation (ENSO) frequently co-occur, driving significant interannual changes within the Indian Ocean. We use a four-decade hindcast from a coupled bio-physical ocean general circulation model, to disentangle patterns of chlorophyll anomalies driven by these two climate modes. Comparisons with remotely-sensed records show that the simulation competently reproduces the chlorophyll seasonal cycle, as well as open-ocean anomalies during the 1997–1998 ENSO and IOD event. Results show that anomalous surface and euphotic-layer chlorophyll blooms in the eastern equatorial Indian Ocean in fall, and southern Bay of Bengal in winter, are primarily related to IOD forcing. IOD depresses integrated chlorophyll in the 5° S–10° S thermocline ridge region, even though the signal is negligible in surface chlorophyll. A previously-unreported negative influence of IOD on chlorophyll concentrations is also shown in a region around the southern tip of India. The only investigated region where ENSO has a greater influence on chlorophyll than does IOD, is in the Somalia upwelling region, where it causes a decrease in fall and winter chlorophyll by reducing local upwelling winds. Lastly, we show that the chlorophyll impact of climate indices is frequently asymmetric, with a general tendency for larger positive than negative chlorophyll anomalies. ENSO and IOD cause significant and predictable regional re-organisation of phytoplankton productivity via their influence on near-surface oceanography. Resolving the details of these effects should improve our understanding, and eventually gain predictability, of interannual changes in Indian Ocean productivity, fisheries, ecosystems and carbon budgets.
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Brenes, Carlos, Daniel Ballestero, Rosario Benavides, Juan Pablo Salazar, and Gustavo Murillo. "Variations in the geostrophic circulation pattern and thermohaline structure in the Southeast Central American Pacific." Revista de Biología Tropical 64, no. 1 (March 2, 2016): 121. http://dx.doi.org/10.15517/rbt.v64i1.23421.
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<p>This study was conducted in the southeast region of the Central American Pacific, an area of great oceanographic importance due to the presence of various upwelling phenomena and the direct influence of the ENSO on its waters. Its main objective was to contribute to the knowledge of the main factors that modulate the regional dynamics. We describe the geostrophic circulation and thermohaline features along two transects obtained in October 2010 and March 2011, one from Costa Rica at (84°54’ W - 9°37’ N) to the SW of Cocos Island at (88°19’ W - 3°06’ N), and the second oriented zonally across the island from (88°14’ W - 5°33’ N) to (84°33’ W - 5°33’ N). Surface temperatures ranged from 27°C to 29°C and a near isothermal layer, with an average thickness of 40 m, was apparent above the thermocline centered at 60 m. Surface salinities were between 32 and 32.8, typical values of the Tropical Surface Water. In both years, Cocos Island was located in a region of low surface salinities (~32). The salty core of the Subtropical Subsurface Water (~35) was located at an average depth of 150m. In October the circulation between Cocos Island and the continent was dominated by the presence of the North Equatorial Countercurrent (NECC), with speeds above 40 cm s<sup>-1 </sup>in the upper 50 m of the water column. No flow to the northwest near the coast that could be associated with the Costa Rica Coastal Current (CRCC) in October was observed. The Cocos Island was located in the center of a 150 m deep, 100 km diameter anticyclonic eddy, with surface speeds of 10 cm s<sup>-1</sup>and 20 cm s<sup>-1</sup>. In March the study area was again dominated by an anticyclonic cell, with eastward flow between 50 cm s<sup>-1</sup> and 60 cm s<sup>-1</sup> located between 200 km north and 100 km south of the island. The southern end of this cell, with velocities between 10 cm s<sup>-1 </sup>and 50 cm s<sup>-1</sup> to the northwest, was located 200 km south of Cocos Island. A flow to the NW near the edge of the continental shelf, consistent with the CRCC, was observed in May. Our study contributes to document the oceanography of the eastern end of the Equatorial Current System near the coast of Central America, where regional forcing modifies the zonal flow which prevails west of the study area.</p><div> </div>
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Belmadani, Ali, Nikolai A. Maximenko, Julian P. Mccreary, Ryo Furue, Oleg V. Melnichenko, Niklas Schneider, and Emanuele Di Lorenzo. "Linear Wind-Forced Beta Plumes with Application to the Hawaiian Lee Countercurrent*." Journal of Physical Oceanography 43, no. 10 (October 1, 2013): 2071–94. http://dx.doi.org/10.1175/jpo-d-12-0194.1.
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Abstract Two numerical ocean models are used to study the baroclinic response to forcing by localized wind stress curl (i.e., a wind-forced β plume, which is a circulation cell developing to the west of the source region and composed of a set of zonal jets) with implications for the Hawaiian Lee Countercurrent (HLCC): an idealized primitive equation model [Regional Ocean Modeling System (ROMS)], and a global, eddy-resolving, general circulation model [Ocean General Circulation Model for the Earth Simulator (OFES)]. In addition, theoretical ideas inferred from a linear continuously stratified model are used to interpret results. In ROMS, vertical mixing preferentially damps higher-order vertical modes. The damping thickens the plume to the west of the forcing region, weakening the near-surface zonal jets and generating deeper zonal currents. The zonal damping scale increases monotonically with the meridional forcing scale, indicating a dominant role of vertical viscosity over diffusion, a consequence of the small forcing scale. In the OFES run forced by NCEP reanalysis winds, the HLCC has a vertical structure consistent with that of idealized β plumes simulated by ROMS, once the contribution of the North Equatorial Current (NEC) has been removed. Without this filtering, a deep HLCC branch appears artificially separated from the surface branch by the large-scale intermediate-depth NEC. The surface HLCC in two different OFES runs exhibits sensitivity to the meridional wind curl scale that agrees with the dynamics of a β plume in the presence of vertical viscosity. The existence of a deep HLCC extension is also suggested by velocities of Argo floats.
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Griffies, S. M., A. Gnanadesikan, K. W. Dixon, J. P. Dunne, R. Gerdes, M. J. Harrison, A. Rosati, et al. "Formulation of an ocean model for global climate simulations." Ocean Science 1, no. 1 (September 12, 2005): 45–79. http://dx.doi.org/10.5194/os-1-45-2005.
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Abstract. This paper summarizes the formulation of the ocean component to the Geophysical Fluid Dynamics Laboratory's (GFDL) climate model used for the 4th IPCC Assessment (AR4) of global climate change. In particular, it reviews the numerical schemes and physical parameterizations that make up an ocean climate model and how these schemes are pieced together for use in a state-of-the-art climate model. Features of the model described here include the following: (1) tripolar grid to resolve the Arctic Ocean without polar filtering, (2) partial bottom step representation of topography to better represent topographically influenced advective and wave processes, (3) more accurate equation of state, (4) three-dimensional flux limited tracer advection to reduce overshoots and undershoots, (5) incorporation of regional climatological variability in shortwave penetration, (6) neutral physics parameterization for representation of the pathways of tracer transport, (7) staggered time stepping for tracer conservation and numerical efficiency, (8) anisotropic horizontal viscosities for representation of equatorial currents, (9) parameterization of exchange with marginal seas, (10) incorporation of a free surface that accomodates a dynamic ice model and wave propagation, (11) transport of water across the ocean free surface to eliminate unphysical ``virtual tracer flux" methods, (12) parameterization of tidal mixing on continental shelves. We also present preliminary analyses of two particularly important sensitivities isolated during the development process, namely the details of how parameterized subgridscale eddies transport momentum and tracers.
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Griffies, S. M., A. Gnanadesikan, K. W. Dixon, J. P. Dunne, R. Gerdes, M. J. Harrison, A. Rosati, et al. "Formulation of an ocean model for global climate simulations." Ocean Science Discussions 2, no. 3 (May 20, 2005): 165–246. http://dx.doi.org/10.5194/osd-2-165-2005.
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Abstract. This paper summarizes the formulation of the ocean component to the Geophysical Fluid Dynamics Laboratory's (GFDL) coupled climate model used for the 4th IPCC Assessment (AR4) of global climate change. In particular, it reviews elements of ocean climate models and how they are pieced together for use in a state-of-the-art coupled model. Novel issues are also highlighted, with particular attention given to sensitivity of the coupled simulation to physical parameterizations and numerical methods. Features of the model described here include the following: (1) tripolar grid to resolve the Arctic Ocean without polar filtering, (2) partial bottom step representation of topography to better represent topographically influenced advective and wave processes, (3) more accurate equation of state, (4) three-dimensional flux limited tracer advection to reduce overshoots and undershoots, (5) incorporation of regional climatological variability in shortwave penetration, (6) neutral physics parameterization for representation of the pathways of tracer transport, (7) staggered time stepping for tracer conservation and numerical efficiency, (8) anisotropic horizontal viscosities for representation of equatorial currents, (9) parameterization of exchange with marginal seas, (10) incorporation of a free surface that accomodates a dynamic ice model and wave propagation, (11) transport of water across the ocean free surface to eliminate unphysical "virtual tracer flux" methods, (12) parameterization of tidal mixing on continental shelves.
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Hodkinson, R. A., and D. S. Cronan. "Regional and depth variability in the composition of cobalt-rich ferromanganese crusts from the SOPAC area and adjacent parts of the central equatorial Pacific." Marine Geology 98, no. 2-4 (June 1991): 437–47. http://dx.doi.org/10.1016/0025-3227(91)90115-k.
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Currie, J. C., M. Lengaigne, J. Vialard, D. M. Kaplan, O. Aumont, S. W. A. Naqvi, and O. Maury. "Indian Ocean Dipole and El Niño/Southern Oscillation impacts on regional chlorophyll anomalies in the Indian Ocean." Biogeosciences 10, no. 10 (October 24, 2013): 6677–98. http://dx.doi.org/10.5194/bg-10-6677-2013.
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Abstract. The Indian Ocean Dipole (IOD) and the El Niño/Southern Oscillation (ENSO) are independent climate modes, which frequently co-occur, driving significant interannual changes within the Indian Ocean. We use a four-decade hindcast from a coupled biophysical ocean general circulation model, to disentangle patterns of chlorophyll anomalies driven by these two climate modes. Comparisons with remotely sensed records show that the simulation competently reproduces the chlorophyll seasonal cycle, as well as open-ocean anomalies during the 1997/1998 ENSO and IOD event. Results suggest that anomalous surface and euphotic-layer chlorophyll blooms in the eastern equatorial Indian Ocean in fall, and southern Bay of Bengal in winter, are primarily related to IOD forcing. A negative influence of IOD on chlorophyll concentrations is shown in a region around the southern tip of India in fall. IOD also depresses depth-integrated chlorophyll in the 5–10° S thermocline ridge region, yet the signal is negligible in surface chlorophyll. The only investigated region where ENSO has a greater influence on chlorophyll than does IOD, is in the Somalia upwelling region, where it causes a decrease in fall and winter chlorophyll by reducing local upwelling winds. Yet unlike most other regions examined, the combined explanatory power of IOD and ENSO in predicting depth-integrated chlorophyll anomalies is relatively low in this region, suggestive that other drivers are important there. We show that the chlorophyll impact of climate indices is frequently asymmetric, with a general tendency for larger positive than negative chlorophyll anomalies. Our results suggest that ENSO and IOD cause significant and predictable regional re-organisation of chlorophyll via their influence on near-surface oceanography. Resolving the details of these effects should improve our understanding, and eventually gain predictability, of interannual changes in Indian Ocean productivity, fisheries, ecosystems and carbon budgets.
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Wei, Jun, M. T. Li, P. Malanotte-Rizzoli, A. L. Gordon, and D. X. Wang. "Opposite Variability of Indonesian Throughflow and South China Sea Throughflow in the Sulawesi Sea." Journal of Physical Oceanography 46, no. 10 (October 2016): 3165–80. http://dx.doi.org/10.1175/jpo-d-16-0132.1.
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AbstractBased on a high-resolution (0.1° × 0.1°) regional ocean model covering the entire northern Pacific, this study investigated the seasonal and interannual variability of the Indonesian Throughflow (ITF) and the South China Sea Throughflow (SCSTF) as well as their interactions in the Sulawesi Sea. The model efficiency in simulating the general circulations of the western Pacific boundary currents and the ITF/SCSTF through the major Indonesian seas/straits was first validated against the International Nusantara Stratification and Transport (INSTANT) data, the OFES reanalysis, and results from previous studies. The model simulations of 2004–12 were then analyzed, corresponding to the period of the INSTANT program. The results showed that, derived from the North Equatorial Current (NEC)–Mindanao Current (MC)–Kuroshio variability, the Luzon–Mindoro–Sibutu flow and the Mindanao–Sulawesi flow demonstrate opposite variability before flowing into the Sulawesi Sea. Although the total transport of the Mindanao–Sulawesi flow is much larger than that of the Luzon–Mindoro–Sibutu flow, their variability amplitudes are comparable but out of phase and therefore counteract each other in the Sulawesi Sea. Budget analysis of the two major inflows revealed that the Luzon–Mindoro–Sibutu flow is enhanced southward during winter months and El Niño years, when more Kuroshio water intrudes into the SCS. This flow brings more buoyant SCS water into the western Sulawesi Sea through the Sibutu Strait, building up a west-to-east pressure head anomaly against the Mindanao–Sulawesi inflow and therefore resulting in a reduced outflow into the Makassar Strait. The situation is reversed in the summer months and La Niña years, and this process is shown to be more crucially important to modulate the Makassar ITF’s interannual variability than the Luzon–Karimata flow that is primarily driven by seasonal monsoons.
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Schroeder, Isaac D., Jarrod A. Santora, Steven J. Bograd, Elliott L. Hazen, Keith M. Sakuma, Andrew M. Moore, Christopher A. Edwards, Brian K. Wells, and John C. Field. "Source water variability as a driver of rockfish recruitment in the California Current Ecosystem: implications for climate change and fisheries management." Canadian Journal of Fisheries and Aquatic Sciences 76, no. 6 (June 2019): 950–60. http://dx.doi.org/10.1139/cjfas-2017-0480.
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Elucidating connections between ocean climate variability and change and recruitment of juvenile fishes to adult populations is critical for understanding variability in stock–recruit dynamics. Recruitment to adult rockfish populations in the California Current Ecosystem (CCE) is highly variable, leading to short- and long-term changes in abundance, productivity, forage availability, and potential fisheries yield. We used regional ocean model output, oceanographic data, and a 34-year time series of pelagic juvenile rockfish to investigate the interaction between changes in CCE source waters, as reflected by physical water mass properties, and recruitment variability. Specifically, variability of “spiciness” on upper water isopycnals explains a substantial fraction of the variation in pelagic juvenile rockfish abundance. High rockfish abundances correspond to cooler, fresher waters with higher dissolved oxygen (i.e., “minty”) conditions, indicative of Pacific subarctic water. By contrast, years of low rockfish abundance are associated with warmer, more saline, and more oxygen-deficient (i.e., “spicy”) conditions, reflecting waters of subtropical or equatorial origin. Transport and source waters in the CCE are key factors determining density-independent processes and subsequent recruitment to adult populations.
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Hughes, Geraint Wyn ap Gwilym, Osman Varol, and Mokhtar Al-Khalid. "Late Oxfordian micropalaeontology, nannopalaeontology and palaeoenvironments of Saudi Arabia." GeoArabia 13, no. 2 (April 1, 2008): 15–46. http://dx.doi.org/10.2113/geoarabia130215.
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ABSTRACT The Hanifa Formation in Saudi Arabia consists of a succession of carbonates, over 100 m thick, that were deposited during the Late Jurassic in an equatorial position on the west flank of the Neo-Tethys Ocean. It consists of the Hawtah and overlying Ulayyah members, each of which is considered as a third-order depositional sequence. The Hawtah Member is assigned an ?Early to Mid-Oxfordian age, based on brachiopod, nautiloid and coccolith evidence; ammonite, nautiloid, coccolith and foraminiferal evidence indicate a Late Oxfordian age for the Ulayyah Member. A detailed study of the microbiofacies and lithology of the late highstand succession of the Ulayyah member sequence was conducted in 41 cored wells distributed across Saudi Arabia. The aim of the study was to determine the most likely locations for porous and permeable grainstone lithofacies that host the Hanifa Reservoir in the region. A range of palaeoenvironments has been determined which include shallow-lagoon packstones and foraminiferal-dominated grainstones and deep-lagoon wackestones and packstones with Clypeina/Pseudoclypeina dasyclad algae. In addition, a series of basin-margin, shoal-associated biofacies are present that include stromatoporoid back-bank packstones and grainstones with the branched stromatoporoid Cladocoropsis mirabilis, bank-crest grainstones with encrusting and domed stromatoporoids. A few wells also proved the presence of intra-shelf, basin-flank mudstones and wackestones containing tetraxon sponge spicules, deep-marine foraminifera and coccoliths. The Hanifa Formation demonstrates the high environmental sensitivity of the Oxfordian biocomponents in Saudi Arabia. The study has exploited this feature to interpret the regional Late Oxfordian palaeoenvironmental variations, together with inferred hydrocarbon implications, with a moderately high degree of certainty. This essentially micropalaeontologically based study has revealed the approximate limit of an intra-shelf basin, with an irregular margin, located in the east-central part of the Saudi Arabian portion of the Late Oxfordian Arabian Plate carbonate platform. The basin is flanked by a belt of stromatoporoid banks that pass laterally into a back-bank facies before developing into a lagoonal facies. There is no evidence for shoreline of this basin, although the presence of rare charophytes, wood fragments and quartz grains in the northwest testifies to possible proximity of fluviatile input. The grainstone-dominated basin-margin facies presents good hydrocarbon reservoir facies and its juxtaposition to intra-shelf, potential source-rock basinal sediments provides important new exploration prospects in areas hitherto uninvestigated for hydrocarbon reservoirs, for which the overlying Jubaila Formation provides an efficient regional seal. The study provides a template for low-cost, high-value guidance for the selection of seismic survey sites in remote, under-explored areas where only a few wildcat well samples are available. The study could also be performed using cuttings samples where cores are not available. The varied biofacies within the Hanifa Formation could be applied for biosteering applications should this tool become necessary in coiled-tube, underbalanced horizontal development wells.
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Geert, Konert, Abdulkader M. Afifi, Sa’id A. Al-Hajri, and Henk J. Droste. "Paleozoic Stratigraphy and Hydrocarbon Habitat of the Arabian Plate." GeoArabia 6, no. 3 (July 1, 2001): 407–42. http://dx.doi.org/10.2113/geoarabia0603407.
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ABSTRACT The Paleozoic section became prospective during the early 1970s when the enormous gas reserves in the Permian Khuff reservoirs were delineated in the Gulf and Zagros regions, and oil was discovered in Oman. Since then, frontier exploration has targeted the Paleozoic System throughout the Middle East, driven by various economic considerations. The Paleozoic sequences were essentially deposited in continental to deep marine clastic environments at the Gondwana continental margin. Carbonates only became dominant in the Late Permian. The sediments were deposited in arid to glacial settings, reflecting the drift of the region from equatorial to high southern latitudes and back. Following late Precambrian rifting that formed salt basins in Oman and the Arabian Gulf region, the Cambrian-Devonian sequences were deposited on a peneplained continental platform. The entire region was affected by the Hercynian Orogeny, which climaxed during the Carboniferous. The orogeny manifested itself in a change in basin geometry, inversion tectonics, regional uplift and tectonism along the Zagros fault zone. This deformation caused widespread erosion of the Devonian-Carboniferous and older sections, and was probably caused by collision along the northern margin of Gondwana. The Paleozoic tectonic super cycle ended with the onset of break-up tectonics in the Permian, and the deposition of Khuff carbonates over the newly formed eastern passive margin. A major Paleozoic petroleum system embraces reservoir seal pairs spanning the Silurian to Permian sequences. Hydrocarbons occur in a variety of traps, and are sourced by the Silurian ‘hot shale’. A second petroleum system occurs in areas charged from upper Precambrian source rocks in the salt basins. Hydrocarbon expulsion estimates, taking into account secondary migration losses, suggest that some one trillion barrels of oil equivalent (BOE) may have been trapped from the Silurian ‘hot shale’ alone. However, the long and complex hydrocarbon geological evolution of the basin, combined with low acoustic contrasts between target rock units, difficult surface conditions, tight reservoirs, and deep subsurface environments, posed significant challenges to exploration and development. The critical success factor is the continuous innovative effort of earth scientists and subsurface engineers to find integrated technology solutions, that will render the Paleozoic plays economically viable.
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Reineman, Benjamin D., Luc Lenain, and W. Kendall Melville. "The Use of Ship-Launched Fixed-Wing UAVs for Measuring the Marine Atmospheric Boundary Layer and Ocean Surface Processes." Journal of Atmospheric and Oceanic Technology 33, no. 9 (September 2016): 2029–52. http://dx.doi.org/10.1175/jtech-d-15-0019.1.
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AbstractThe deployment and recovery of autonomous or remotely piloted platforms from research vessels have become a way of significantly extending the capabilities and reach of the research fleet. This paper describes the use of ship-launched and ship-recovered Boeing–Insitu ScanEagle unmanned aerial vehicles (UAVs). The UAVs were instrumented to characterize the marine atmospheric boundary layer (MABL) structure and dynamics, and to measure ocean surface processes during the October 2012 Equatorial Mixing (EquatorMix) experiment in the central Pacific and during the July 2013 Trident Warrior experiment off the Virginia coast. The UAV measurements, including atmospheric momentum and radiative, sensible, and latent heat fluxes, are complemented by measurements from ship-based instrumentation, including a foremast MABL eddy-covariance system, lidar altimeters, and a digitized X-band radar system. During EquatorMix, UAV measurements reveal longitudinal atmospheric roll structures not sampled by ship measurements, which contribute significantly to vertical fluxes of heat and momentum. With the nadir-looking UAV lidar, surface signatures of internal waves are observed, consistent and coherent with measurements from ship-based X-band radar, a Hydrographic Doppler Sonar System, and a theoretical model. In the Trident Warrior experiment, the instrumented UAVs were used to demonstrate real-time data assimilation of meteorological data from UAVs into regional coupled ocean–atmosphere models. The instrumented UAVs have provided unprecedented spatiotemporal resolution in atmospheric and oceanographic measurements in remote ocean locations, demonstrating the capabilities of these platforms to extend the range and capabilities of the research fleet for oceanographic and atmospheric studies.
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Pérez-Cruz, Ligia. "Climate and ocean variability during the middle and late Holocene recorded in laminated sediments from Alfonso Basin, Gulf of California, Mexico." Quaternary Research 65, no. 3 (May 2006): 401–10. http://dx.doi.org/10.1016/j.yqres.2006.02.003.
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AbstractA laminated sequence (core BAP96-CP 24°38.12′N, 110°33.24′W; 390 m depth) from the Alfonso Basin in Bay of La Paz, southern Gulf of California, contains a record of paleoceanographic and paleoclimatic changes of the past 7900 yr. Radiolarian assemblages and magnetic susceptibility are used as proxies of oceanographic and climatic variability. The records provide a regional scenario of the middle and late Holocene, suggesting two major climatic regimes and several millennial-scale events. Conditions relatively warmer and drier than today occurred from ∼7700 to 2500 cal yr BP, promoting the intensification of evaporation processes and the prevalence of the Gulf of California water in the Basin. These conditions correlate with strong droughts in the middle Holocene of North America and with minimal incursion of tropical waters into the Gulf of California. Proxies indicate a warm scenario and the dominance of the Equatorial Surface Water in the Alfonso Basin from ∼2400 to 700 cal yr BP, suggesting the intensification of ENSO cycles. A climatic signal between ∼1038 and 963 cal yr BP may be correlated with global signal of the “Medieval Warm Period.” Several cooling events are recognized at 5730, 3360, 2700, 1280 and 820 cal yr BP and are associated with intensification of northwest winds leading to upwellings and enhanced productivity in the Basin.
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Butt, Jeff, and Eric Lindstrom. "Currents off the east coast of New Ireland, Papua New Guinea, and their relevance to regional undercurrents in the western equatorial Pacific Ocean." Journal of Geophysical Research 99, no. C6 (1994): 12503. http://dx.doi.org/10.1029/94jc00399.
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Ascough, Philippa, Gordon Cook, and Andrew Dugmore. "Methodological approaches to determining the marine radiocarbon reservoir effect." Progress in Physical Geography: Earth and Environment 29, no. 4 (December 2005): 532–47. http://dx.doi.org/10.1191/0309133305pp461ra.
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The marine radiocarbon reservoir effect is an offset in 14C age between contemporaneous organisms from the terrestrial environment and organisms that derive their carbon from the marine environment. Quantification of this effect is of crucial importance for correct calibration of the 14C ages of marine-influenced samples to the calendrical timescale. This is fundamental to the construction of archaeological and palaeoenvironmental chronologies when such samples are employed in 14C analysis. Quantitative measurements of temporal variations in regional marine reservoir ages also have the potential to be used as a measure of process changes within Earth surface systems, due to their link with climatic and oceanic changes. The various approaches to quantification of the marine radiocarbon reservoir effect are assessed, focusing particularly on the North Atlantic Ocean. Currently, the global average marine reservoir age of surface waters, R(t), is c. 400 radiocarbon years; however, regional values deviate from this as a function of climate and oceanic circulation systems. These local deviations from R(t) are expressed as +R values. Hence, polar waters exhibit greater reservoir ages (δR = c. +400 to +800 14C y) than equatorial waters (δR = c. 0 14C y). Observed temporal variations in δR appear to reflect climatic and oceanographic changes. We assess three approaches to quantification of marine reservoir effects using known age samples (from museum collections), tephra isochrones (present onshore/offshore) and paired marine/terrestrial samples (from the same context in, for example, archaeological sites). The strengths and limitations of these approaches are evaluated using examples from the North Atlantic region. It is proposed that, with a suitable protocol, accelerator mass spectrometry (AMS) measurements on paired, short-lived, single entity marine and terrestrial samples from archaeological deposits is the most promising approach to constraining changes over at least the last 5 ky BP.
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Goodwin, Deborah S., Amy N. S. Siuda, and Jeffrey M. Schell. "In situ observation of holopelagic Sargassum distribution and aggregation state across the entire North Atlantic from 2011 to 2020." PeerJ 10 (September 22, 2022): e14079. http://dx.doi.org/10.7717/peerj.14079.
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Between 2011 and 2020, 6,790 visual observations of holopelagic Sargassum were recorded across the North Atlantic Ocean to describe regional distribution, presence, and aggregation state at hourly and 10 km scales. Influences of oceanographic region and wind/sea conditions as well as temporal trends were considered; marine megafauna associates documented the ecological value of aggregations. Holopelagic Sargassum was present in 64% of observations from the western North Atlantic. Dispersed holopelagic Sargassum fragments and clumps were found in 97% of positive observations whereas aggregated windrows (37%) and mats (1%) were less common. Most field observations noted holopelagic Sargassum in quantities below the AFAI algorithm detection limit for the MODIS sensor. Aggregation state patterns were similar across regions; windrow proportion increased with higher wind speeds. In 8 of 10 years in the Sargasso Sea holopelagic Sargassum was found in over 65% of observations. In contrast, the Tropical Atlantic and Caribbean Sea exhibited greater inter-annual variability (1–88% and 11–78% presence, respectively) that did not align with extremes in central Atlantic holopelagic Sargassum areal coverage determined from satellite observations. Megafauna association patterns varied by taxonomic group. While some study regions were impacted by holopelagic Sargassum dynamics in the equatorial Atlantic, the Sargasso Sea had consistently high presence and operated independently. Field observations capture important dynamics occurring at fine spatiotemporal scales, including transient aggregation processes and ecological value for megafauna associates, and therefore remain essential to future studies of holopelagic Sargassum.
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Figueroa, DF. "Environmental forcing on zooplankton distribution in the coastal waters of the Galápagos Islands: spatial and seasonal patterns in the copepod community structure." Marine Ecology Progress Series 661 (March 4, 2021): 49–69. http://dx.doi.org/10.3354/meps13617.
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The oceanographic setting of the Galápagos Archipelago results in a spatially diverse marine environment suitable for a variety of species with different climatic requirements. The goal of this study is to demonstrate that the community of zooplankton in the Galápagos is highly structured by regional differences in productivity patterns and advective sources. Results are mostly based on biodiversity patterns of the copepod community collected over the Galápagos shelf between 2004 and 2006. Two contrasting marine environments were observed: a nutrient-rich upwelling system with a shallow mixed layer and a diatom-dominated phytoplankton community in the west, and a non-upwelling system with a deeper mixed layer, lower surface nutrient concentrations, and a phytoplankton community dominated by small cells in the east. These conditions drive spatial structuring of zooplankton that varies seasonally, with 3 distinct copepod communities separated geographically in western, central, and southeastern regions. The western upwelling region has a high-abundance and low-diversity community, whereas the non-upwelling eastern region has a lower-abundance and higher-diversity community. The eastern community is further differentiated into central and southeastern regions, the former with tropical species advected from the north, the latter with temperate species advected from the south. During the warm season, when the equatorial front moves south, species typical of the central region spread southwest across the archipelago. This is the first taxonomically comprehensive list of copepod species for the Galápagos Islands. A total of 164 copepod species are identified, including 22 species previously unreported from the Eastern Tropical Pacific.
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McGregor, Shayne, Alexander Sen Gupta, and Matthew H. England. "Constraining Wind Stress Products with Sea Surface Height Observations and Implications for Pacific Ocean Sea Level Trend Attribution*." Journal of Climate 25, no. 23 (December 1, 2012): 8164–76. http://dx.doi.org/10.1175/jcli-d-12-00105.1.
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Abstract A number of global surface wind datasets are available that are commonly used to examine climate variability or trends and as boundary conditions for ocean circulation models. However, discrepancies exist among these products. This study uses observed Archiving, Validation, and Interpretation of Satellite Oceanographic (AVISO) sea surface height anomalies (SSHAs) as a means to help constrain the fidelity of these products in the tropical region. Each wind stress product is used to force a linear shallow water model (SWM) and the resulting hindcast thermocline depth anomalies are converted to SSHAs. The resulting SSHAs are then assessed to see how well they reproduce the dominant EOF modes of observed variability and the regional (global mean removed) sea level trend (1993–2007) in each of the three ocean basins. While the results suggest that all wind datasets reproduce the observed interannual variability with reasonable fidelity, the two SWM hindcasts that produce the observed linear trend with the highest fidelity are those incorporating interim ECMWF Re-Analysis (ERA-Interim) and Wave- and Anemometer-Based Sea Surface Wind (WASWind) forcing. The role of surface wind forcing (i.e., upper ocean heat content redistribution) versus global mean sea level change (i.e., including the additional contributions of glacier and ice sheet melt along with ocean thermal expansion) on the recent dramatic increase in western equatorial Pacific island sea level is then reassessed. The results suggest that the recent sea level increase cannot be explained solely by wind stress forcing, regardless of the dataset used; rather, the global mean sea level signal is required to fully explain this observed recent abrupt sea level rise and to better explain the sea level variability of the last 50–60 years.
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Bunzel, Dorothea, Gerhard Schmiedl, Sebastian Lindhorst, Andreas Mackensen, Jesús Reolid, Sarah Romahn, and Christian Betzler. "A multi-proxy analysis of Late Quaternary ocean and climate variability for the Maldives, Inner Sea." Climate of the Past 13, no. 12 (December 13, 2017): 1791–813. http://dx.doi.org/10.5194/cp-13-1791-2017.
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Abstract. As a natural sediment trap, the marine sediments of the sheltered central part of the Maldives Inner Sea represent an exceptional archive for paleoenvironmental and climate changes in the equatorial Indian Ocean. To evaluate the complex interplay between high-latitude and monsoonal climate variability, related dust fluxes, and regional oceanographic responses, we focused on Fe ∕ Al, Ti ∕ Al and Si ∕ Ca ratios as proxies for terrigenous sediment delivery and total organic carbon (TOC) and Br XRF counts as proxies for marine productivity. Benthic foraminiferal fauna distributions, grain size and stable δ18O and δ13C data were used for evaluating changes in the benthic ecosystem and changes in the intermediate water circulation, bottom water current velocity and oxygenation. Our multi-proxy data record reveals an enhanced dust supply during the glacial intervals, causing elevated Fe ∕ Al and Si ∕ Ca ratios, an overall coarsening of the sediment and an increasing amount of agglutinated benthic foraminifera. The enhanced dust fluxes can be attributed to higher dust availability in the Asian desert and loess areas and its transport by intensified winter monsoon winds during glacial conditions. These combined effects of wind-induced mixing of surface waters and dust fertilization during the cold phases resulted in an increased surface water productivity and related organic carbon fluxes. Thus, the development of highly diverse benthic foraminiferal faunas with certain detritus and suspension feeders was fostered. The difference in the δ13C signal between epifaunal and deep infaunal benthic foraminifera reveals intermediate water oxygen concentrations between approximately 40 and 100 µmol kg−1 during this time. The precessional fluctuation pattern of oxygen changes resembles that from the deep Arabian Sea, suggesting an expansion of the oxygen minimum zone (OMZ) from the Arabian Sea into the tropical Indian Ocean with a probable regional signal of strengthened winter-monsoon-induced organic matter fluxes and oxygen consumption further controlled by the varying inflow intensity of the Antarctic Intermediate Water (AAIW). In addition, the bottom water oxygenation pattern of the Maldives Inner Sea reveals a long phase of reduced ventilation during the last glacial period. This process is likely linked to the combined effects of generally enhanced oxygen consumption rates during high-productivity phases, reduced AAIW production and the restriction of upper bathyal environments in the Inner Sea during sea-level lowstands. Thus, our multi-proxy record reflects a close linkage between the Indian monsoon oscillation, intermediate water circulation, productivity and sea-level changes on orbital timescale.
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Gabioux, Mariela Gabioux, Vladimir Santos Da Costa, João Marcos Azevedo Correia de Souza, Bruna Faria de Oliveira, and Afonso De Moraes Paiva. "MODELING THE SOUTH ATLANTIC OCEAN FROM MEDIUM TO HIGH-RESOLUTION." Revista Brasileira de Geofísica 31, no. 2 (June 1, 2013): 229. http://dx.doi.org/10.22564/rbgf.v31i2.291.
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ABSTRACT. The standard REMO (a Brazilian approach towards operational oceanography) model configuration is tested, and results of two numerical simulations with HYCOM are presented and discussed. This configuration consists basically of a high-resolution eddy-resolving, 1/12 degree model for the Metarea V (latitudes from 7◦N to 35◦50’S, and longitudes between 20◦W and the Brazilian coast), nested in a medium-resolution eddy-permitting, 1/4 degree model of the Atlantic Ocean. These simulations aim for: a) creating a basic set-up for implementation of assimilation techniques leading to ocean prediction; b) the development of hydrodynamic bases for environmental studies; and c) providing boundary conditions for regional domains with increased resolution. This is the first time HYCOM is applied in high-resolution and particularly tailored for this region of the ocean. The 1/4 degree simulation was able to simulate realistic Equatorial and South Atlantic large scale circulation, both the wind-driven and the thermohaline components. The high-resolution introduces realistic mesoscale activity, in particular that associated with the dynamics of western boundary currents, and captures also both the continental shelf and the upper-ocean modes of variability associated with atmospheric synoptic forcing. Important issues for the simulation of the South Atlantic with high-resolution are discussed, like the ideal place for boundaries, improvements in the bathymetric representation, and the control of SST bias by the introduction of surface relaxation. In order to make a preliminary assessment of the model behavior when submitted to data assimilation, the Cooper & Haines (1996) method was used to extrapolate SSH anomalies fields to deeper layers every 7 days, with encouraging results.Keywords: numerical simulation, nesting, southwest Atlantic, Brazil Current. RESUMO. Neste trabalho são apresentados e discutidos resultados de duas simulações numéricas realizadas com o model HYCOM e que representam a configuração padrão do projeto REMO (Rede de Modelagem e Observação Oceanográfica), uma abordagem brasileira para a oceanografia operacional. Esta configuração consiste em um modelo em alta resolução (1/12 de grau, que resolve a mesoescala) da região denominada de Metarea V (latitudes de 7◦N a 35◦50’S e longitudes desde 20◦W até a costa brasileira), aninhado em um modelo em média-resolução (1/4 de grau, que resolve apenas parcialmente a mesoescala) do oceano Atlântico. Estas simulações tem como objetivos: a) a geração de um set-up básico para implementação de técnicas de assimilação visando a previsão oceânica; b) o desenvolvimento de bases hidrodinâmicas para estudos ambientais; e c) a geração de condições de contorno para domínios regionais com maior resolução. Esta é a primeira vez que o HYCOM é aplicado em alta resolução e especialmente configurado para esta região do oceano. A simulação em 1/4 de grau simulou de forma realista a circulação de larga escala no Atlântico Sul e Equatorial, tanto a componente eólica quanto a termohalina. A simulação em alta resolução foi capaz de introduzir também de forma realista a mesoescala, em particular aquela associada à dinâmica das correntes de contorno oeste, e de capturar a variabilidade da porção superior do oceano e da plataforma continental associada à forçante atmosférica em escala sinótica. Aspectos importantes para a simulação do Atlântico Sul em alta resolução são discutidos, como o posicionamento dos contornos, a representação da batimetria e o controle de possíveis tendências na TSM pela introdução de um termo de relaxamento para climatologia em superfície. Uma avaliação preliminar do comportamento do modelo submetido à assimilação de dados foi realizada com o método de Cooper & Haines (1996), capaz de extrapolar campos de anomalias de elevação da superfície para camadas mais profundas a cada 7 dias, com resultados promissores.Palavras-chave: simulação numérica, aninhamento, Atlântico sudoeste, Corrente do Brasil.
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Roemmich, Dean, Michele Morris, W. R. Young, and J. R. Donguy. "Fresh Equatorial Jets." Journal of Physical Oceanography 24, no. 3 (March 1994): 540–58. http://dx.doi.org/10.1175/1520-0485(1994)024<0540:fej>2.0.co;2.
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Yu, Zuojun, Julian P. McCreary, William S. Kessler, and Kathryn A. Kelly. "Influence of Equatorial Dynamics on the Pacific North Equatorial Countercurrent*." Journal of Physical Oceanography 30, no. 12 (December 2000): 3179–90. http://dx.doi.org/10.1175/1520-0485(2000)030<3179:ioedot>2.0.co;2.
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Send, Uwe, Carsten Eden, and Friedrich Schott. "Atlantic Equatorial Deep Jets: Space–Time Structure and Cross-Equatorial Fluxes." Journal of Physical Oceanography 32, no. 3 (March 2002): 891–902. http://dx.doi.org/10.1175/1520-0485(2002)032<0891:aedjst>2.0.co;2.
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