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Articoli di riviste sul tema "Ocean circulation"

Autore: Grafiati

Pubblicato: 4 giugno 2021

Ultima modifica: 29 luglio 2024

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1

Cunningham, Stuart A. "Southern Ocean circulation". Archives of Natural History 32, n. 2 (ottobre 2005): 265–80. http://dx.doi.org/10.3366/anh.2005.32.2.265.

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The Discovery Investigations of the 1930s provided a compelling description of the main elements of the Southern Ocean circulation. Over the intervening years, this has been extended to include ideas on ocean dynamics based on physical principles. In the modern description, the Southern Ocean has two main circulations that are intimately linked: a zonal (west-east) circumpolar circulation and a meridional (north-south) overturning circulation. The Antarctic Circumpolar Current transports around 140 million cubic metres per second west to east around Antarctica. This zonal circulation connects the Atlantic, Indian and Pacific Oceans, transferring and blending water masses and properties from one ocean basin to another. For the meridional circulation, a key feature is the ascent of waters from depths of around 2,000 metres north of the Antarctic Circumpolar Current to the surface south of the Current. In so doing, this circulation connects deep ocean layers directly to the atmosphere. The circumpolar zonal currents are not stable: meanders grow and separate, creating eddies and these eddies are critical to the dynamics of the Southern Ocean, linking the zonal circumpolar and meridional circulations. As a result of this connection, a global three-dimensional ocean circulation exists in which the Southern Ocean plays a central role in regulating the Earth's climate.

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2

Ferrari, Raffaele, Louis-Philippe Nadeau, David P. Marshall, Lesley C. Allison e Helen L. Johnson. "A Model of the Ocean Overturning Circulation with Two Closed Basins and a Reentrant Channel". Journal of Physical Oceanography 47, n. 12 (dicembre 2017): 2887–906. http://dx.doi.org/10.1175/jpo-d-16-0223.1.

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AbstractZonally averaged models of the ocean overturning circulation miss important zonal exchanges of waters between the Atlantic and Indo-Pacific Oceans. A two-layer, two-basin model that accounts for these exchanges is introduced and suggests that in the present-day climate the overturning circulation is best described as the combination of three circulations: an adiabatic overturning circulation in the Atlantic Ocean associated with transformation of intermediate to deep waters in the north, a diabatic overturning circulation in the Indo-Pacific Ocean associated with transformation of abyssal to deep waters by mixing, and an interbasin circulation that exchanges waters geostrophically between the two oceans through the Southern Ocean. These results are supported both by theoretical analysis of the two-layer, two-basin model and by numerical simulations of a three-dimensional ocean model.

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3

Smith, H. J. "OCEANS: Tracing Ocean Circulation". Science 288, n. 5474 (23 giugno 2000): 2097e—2099. http://dx.doi.org/10.1126/science.288.5474.2097e.

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4

Olson, Donald B. "Ocean Circulation". Marine Geology 103, n. 1-3 (gennaio 1992): 534. http://dx.doi.org/10.1016/0025-3227(92)90044-i.

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5

Bigg, Grant R. "Ocean circulation". Endeavour 14, n. 2 (gennaio 1990): 101. http://dx.doi.org/10.1016/0160-9327(90)90091-5.

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6

Jansen, Malte F., Wanying Kang, Edwin S. Kite e Yaoxuan Zeng. "Energetic Constraints on Ocean Circulations of Icy Ocean Worlds". Planetary Science Journal 4, n. 6 (1 giugno 2023): 117. http://dx.doi.org/10.3847/psj/acda95.

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Abstract Globally ice-covered oceans have been found on multiple moons in the solar system and may also have been a feature of Earth’s past. However, relatively little is understood about the dynamics of these ice-covered oceans, which affect not only the physical environment but also any potential life and its detectability. A number of studies have simulated the circulation of icy-world oceans, but have come to seemingly widely different conclusions. To better understand and narrow down these diverging results, we discuss the energetic constraints for the circulation on ice-covered oceans, focusing in particular on Snowball Earth, Europa, and Enceladus. The energy input that can drive ocean circulation on ice-covered bodies can be associated with heat and salt fluxes at the boundaries as well as ocean tides and librations. We show that heating from the solid core balanced by heat loss through the ice sheet can drive an ocean circulation, but the resulting flows would be relatively weak and strongly affected by rotation. Salt fluxes associated with freezing and melting at the ice sheet boundary are unlikely to energetically drive a circulation, although they can shape the large-scale circulation when combined with turbulent mixing. Ocean tides and librations may provide an energy source for such turbulence, but the magnitude of this energy source remains highly uncertain for the icy moons, which poses a major obstacle to predicting the ocean dynamics of icy worlds and remains an important topic for future research.

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7

Semtner, A. J. "Modeling Ocean Circulation". Science 269, n. 5229 (8 settembre 1995): 1379–85. http://dx.doi.org/10.1126/science.269.5229.1379.

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8

Ladant, Jean-Baptiste, Christopher J. Poulsen, Frédéric Fluteau, Clay R. Tabor, Kenneth G. MacLeod, Ellen E. Martin, Shannon J. Haynes e Masoud A. Rostami. "Paleogeographic controls on the evolution of Late Cretaceous ocean circulation". Climate of the Past 16, n. 3 (9 giugno 2020): 973–1006. http://dx.doi.org/10.5194/cp-16-973-2020.

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Abstract. Understanding of the role of ocean circulation on climate during the Late Cretaceous is contingent on the ability to reconstruct its modes and evolution. Geochemical proxies used to infer modes of past circulation provide conflicting interpretations for the reorganization of the ocean circulation through the Late Cretaceous. Here, we present climate model simulations of the Cenomanian (100.5–93.9 Ma) and Maastrichtian (72.1–66.1 Ma) stages of the Cretaceous with the CCSM4 earth system model. We focus on intermediate (500–1500 m) and deep (> 1500 m) ocean circulation and show that while there is continuous deep-water production in the southwestern Pacific, major circulation changes occur between the Cenomanian and Maastrichtian. Opening of the Atlantic and Southern Ocean, in particular, drives a transition from a mostly zonal circulation to enhanced meridional exchange. Using additional experiments to test the effect of deepening of major ocean gateways in the Maastrichtian, we demonstrate that the geometry of these gateways likely had a considerable impact on ocean circulation. We further compare simulated circulation results with compilations of εNd records and show that simulated changes in Late Cretaceous ocean circulation are reasonably consistent with proxy-based inferences. In our simulations, consistency with the geologic history of major ocean gateways and absence of shift in areas of deep-water formation suggest that Late Cretaceous trends in εNd values in the Atlantic and southern Indian oceans were caused by the subsidence of volcanic provinces and opening of the Atlantic and Southern oceans rather than changes in deep-water formation areas and/or reversal of deep-water fluxes. However, the complexity in interpreting Late Cretaceous εNd values underscores the need for new records as well as specific εNd modeling to better discriminate between the various plausible theories of ocean circulation change during this period.

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9

Wu, Yang, Xiaoming Zhai e Zhaomin Wang. "Impact of Synoptic Atmospheric Forcing on the Mean Ocean Circulation". Journal of Climate 29, n. 16 (27 luglio 2016): 5709–24. http://dx.doi.org/10.1175/jcli-d-15-0819.1.

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Abstract The impact of synoptic atmospheric forcing on the mean ocean circulation is investigated by comparing simulations of a global eddy-permitting ocean–sea ice model forced with and without synoptic atmospheric phenomena. Consistent with previous studies, transient atmospheric motions such as weather systems are found to contribute significantly to the time-mean wind stress and surface heat loss at mid- and high latitudes owing to the nonlinear nature of air–sea turbulent fluxes. Including synoptic atmospheric forcing in the model has led to a number of significant changes. For example, wind power input to the ocean increases by about 50%, which subsequently leads to a similar percentage increase in global eddy kinetic energy. The wind-driven subtropical gyre circulations are strengthened by about 10%–15%, whereas even greater increases in gyre strength are found in the subpolar oceans. Deep convection in the northern North Atlantic becomes significantly more vigorous, which in turn leads to an increase in the Atlantic meridional overturning circulation (AMOC) by as much as 55%. As a result of the strengthened horizontal gyre circulations and the AMOC, the maximum global northward heat transport increases by almost 50%. Results from this study show that synoptic atmospheric phenomena such as weather systems play a vital role in driving the global ocean circulation and heat transport, and therefore should be properly accounted for in paleo- and future climate studies.

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10

Stanton, B. R. "Ocean circulation and ocean-atmosphere exchanges". Climatic Change 18, n. 2-3 (aprile 1991): 175–94. http://dx.doi.org/10.1007/bf00138996.

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11

Cullum, Jodie, David P. Stevens e Manoj M. Joshi. "Importance of ocean salinity for climate and habitability". Proceedings of the National Academy of Sciences 113, n. 16 (4 aprile 2016): 4278–83. http://dx.doi.org/10.1073/pnas.1522034113.

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Modeling studies of terrestrial extrasolar planetary climates are now including the effects of ocean circulation due to a recognition of the importance of oceans for climate; indeed, the peak equator-pole ocean heat transport on Earth peaks at almost half that of the atmosphere. However, such studies have made the assumption that fundamental oceanic properties, such as salinity, temperature, and depth, are similar to Earth. This assumption results in Earth-like circulations: a meridional overturning with warm water moving poleward at the surface, being cooled, sinking at high latitudes, and traveling equatorward at depth. Here it is shown that an exoplanetary ocean with a different salinity can circulate in the opposite direction: an equatorward flow of polar water at the surface, sinking in the tropics, and filling the deep ocean with warm water. This alternative flow regime results in a dramatic warming in the polar regions, demonstrated here using both a conceptual model and an ocean general circulation model. These results highlight the importance of ocean salinity for exoplanetary climate and consequent habitability and the need for its consideration in future studies.

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12

Barron, Eric J., e William H. Peterson. "The Cenozoic ocean circulation based on ocean General Circulation Model results". Palaeogeography, Palaeoclimatology, Palaeoecology 83, n. 1-3 (febbraio 1991): 1–28. http://dx.doi.org/10.1016/0031-0182(91)90073-z.

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13

Meehl, Gerald A., Julie M. Arblaster e Johannes Loschnigg. "Coupled Ocean–Atmosphere Dynamical Processes in the Tropical Indian and Pacific Oceans and the TBO". Journal of Climate 16, n. 13 (1 luglio 2003): 2138–58. http://dx.doi.org/10.1175/2767.1.

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Abstract The transitions (from relatively strong to relatively weak monsoon) in the tropospheric biennial oscillation (TBO) occur in northern spring for the south Asian or Indian monsoon and northern fall for the Australian monsoon involving coupled land–atmosphere–ocean processes over a large area of the Indo-Pacific region. Transitions from March–May (MAM) to June–September (JJAS) tend to set the system for the next year, with a transition to the opposite sign the following year. Previous analyses of observed data and GCM sensitivity experiments have demonstrated that the TBO (with roughly a 2–3-yr period) encompasses most ENSO years (with their well-known biennial tendency). In addition, there are other years, including many Indian Ocean dipole (or zonal mode) events, that contribute to biennial transitions. Results presented here from observations for composites of TBO evolution confirm earlier results that the Indian and Pacific SST forcings are more dominant in the TBO than circulation and meridional temperature gradient anomalies over Asia. A fundamental element of the TBO is the large-scale east–west atmospheric circulation (the Walker circulation) that links anomalous convection and precipitation, winds, and ocean dynamics across the Indian and Pacific sectors. This circulation connects convection over the Asian–Australian monsoon regions both to the central and eastern Pacific (the eastern Walker cell), and to the central and western Indian Ocean (the western Walker cell). Analyses of upper-ocean data confirm previous results and show that ENSO El Niño and La Niña events as well as Indian Ocean SST dipole (or zonal mode) events are often large-amplitude excursions of the TBO in the tropical Pacific and Indian Oceans, respectively, associated with anomalous eastern and western Walker cell circulations, coupled ocean dynamics, and upper-ocean temperature and heat content anomalies. Other years with similar but lower-amplitude signals in the tropical Pacific and Indian Oceans also contribute to the TBO. Observed upper-ocean data for the Indian Ocean show that slowly eastward-propagating equatorial ocean heat content anomalies, westward-propagating ocean Rossby waves south of the equator, and anomalous cross-equatorial ocean heat transports contribute to the heat content anomalies in the Indian Ocean and thus to the ocean memory and consequent SST anomalies, which are an essential part of the TBO.

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14

Pasquier, Benoît, Mark Holzer, Matthew A. Chamberlain, Richard J. Matear, Nathaniel L. Bindoff e François W. Primeau. "Optimal parameters for the ocean's nutrient, carbon, and oxygen cycles compensate for circulation biases but replumb the biological pump". Biogeosciences 20, n. 14 (26 luglio 2023): 2985–3009. http://dx.doi.org/10.5194/bg-20-2985-2023.

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Abstract. Accurate predictive modeling of the ocean's global carbon and oxygen cycles is challenging because of uncertainties in both biogeochemistry and ocean circulation. Advances over the last decade have made parameter optimization feasible, allowing models to better match observed biogeochemical fields. However, does fitting a biogeochemical model to observed tracers using a circulation with known biases robustly capture the inner workings of the biological pump? Here we embed a mechanistic model of the ocean's coupled nutrient, carbon, and oxygen cycles into two circulations for the current climate. To assess the effects of biases, one circulation (ACCESS-M) is derived from a climate model and the other from data assimilation of observations (OCIM2). We find that parameter optimization compensates for circulation biases at the expense of altering how the biological pump operates. Tracer observations constrain pump strength and regenerated inventories for both circulations, but ACCESS-M export production optimizes to twice that of OCIM2 to compensate for ACCESS-M having lower sequestration efficiencies driven by less efficient particle transfer and shorter residence times. Idealized simulations forcing complete Southern Ocean nutrient utilization show that the response of the optimized system is sensitive to the embedding circulation. In ACCESS-M, Southern Ocean nutrient and dissolved inorganic carbon (DIC) trapping is partially short circuited by unrealistically deep mixed layers. For both circulations, intense Southern Ocean production deoxygenates Southern-Ocean-sourced deep waters, muting the imprint of circulation biases on oxygen. Our findings highlight that the biological pump's plumbing needs careful assessment to predict the biogeochemical response to ecological changes, even when optimally matching observations.

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15

Döös, Kristofer, Joakim Kjellsson, Jan Zika, Frédéric Laliberté, Laurent Brodeau e Aitor Aldama Campino. "The Coupled Ocean–Atmosphere Hydrothermohaline Circulation". Journal of Climate 30, n. 2 (gennaio 2017): 631–47. http://dx.doi.org/10.1175/jcli-d-15-0759.1.

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The thermohaline circulation of the ocean is compared to the hydrothermal circulation of the atmosphere. The oceanic thermohaline circulation is expressed in potential temperature–absolute salinity space and comprises a tropical cell, a conveyor belt cell, and a polar cell, whereas the atmospheric hydrothermal circulation is expressed in potential temperature–specific humidity space and unifies the tropical Hadley and Walker cells as well as the midlatitude eddies into a single, global circulation. The oceanic thermohaline streamfunction makes it possible to analyze and quantify the entire World Ocean conversion rate between cold–warm and fresh–saline waters in one single representation. Its atmospheric analog, the hydrothermal streamfunction, instead captures the conversion rate between cold–warm and dry–humid air in one single representation. It is shown that the ocean thermohaline and the atmospheric hydrothermal cells are connected by the exchange of heat and freshwater through the sea surface. The two circulations are compared on the same diagram by scaling the axes such that the latent heat energy required to move an air parcel on the moisture axis is equivalent to that needed to move a water parcel on the salinity axis. Such a comparison leads the authors to propose that the Clausius–Clapeyron relationship guides both the moist branch of the atmospheric hydrothermal circulation and the warming branches of the tropical and conveyor belt cells of the oceanic thermohaline circulation.

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Misumi, K., K. Lindsay, J. K. Moore, S. C. Doney, F. O. Bryan, D. Tsumune e Y. Yoshida. "The iron budget in ocean surface waters in the 20th and 21st centuries: projections by the Community Earth System Model version 1". Biogeosciences Discussions 10, n. 5 (22 maggio 2013): 8505–59. http://dx.doi.org/10.5194/bgd-10-8505-2013.

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Abstract. We investigated the simulated iron budget in ocean surface waters in the 1990s and 2090s using the Community Earth System Model version 1 and the Representative Concentration Pathway 8.5 future CO2 emission scenario. We assumed that exogenous iron inputs did not change during the whole simulation period; thus, iron budget changes were attributed solely to changes in ocean circulation and mixing in response to projected global warming. The model simulated the major features of ocean circulation and dissolved iron distribution for the present climate reasonably well. Detailed iron budget analysis revealed that roughly 70% of the iron supplied to surface waters in high-nutrient, low-chlorophyll (HNLC) regions is contributed by ocean circulation and mixing processes, but the dominant supply mechanism differed in each HNLC region: vertical mixing in the Southern Ocean, upwelling in the eastern equatorial Pacific, and deposition of iron-bearing dust in the subarctic North Pacific. In the 2090s, our model projected an increased iron supply to HNLC surface waters, even though enhanced stratification was predicted to reduce iron entrainment from deeper waters. This unexpected result could be attributed largely to changes in the meridional overturning and gyre-scale circulations that intensified the advective supply of iron to surface waters, especially in the eastern equatorial Pacific. The simulated primary and export productions in the 2090s decreased globally by 6% and 13%, respectively, whereas in the HNLC regions, they increased by 11% and 6%, respectively. Roughly half of the elevated production could be attributed to the intensified iron supply. The projected ocean circulation and mixing changes are consistent with recent observations of responses to the warming climate and with other Coupled Model Intercomparison Project model projections. We conclude that future ocean circulation and mixing changes will likely elevate the iron supply to HNLC surface waters and will potentially buffer future reductions in ocean productivity. External inputs of iron to the oceans are likely to be modified with climate change. Future work must incorporate robust estimates of these processes affecting the marine iron cycle.

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17

Gačić, Miroslav, e Manuel Bensi. "Ocean Exchange and Circulation". Water 12, n. 3 (20 marzo 2020): 882. http://dx.doi.org/10.3390/w12030882.

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The great spatial and temporal variability, which characterizes the marine environment, requires a huge effort to be observed and studied properly since changes in circulation and mixing processes directly influence the variability of the physical and biogeochemical properties. A multi-platform approach and a collaborative effort, in addition to optimizing both data collection and quality, is needed to bring the scientific community to more efficient monitoring and predicting of the world ocean processes. This Special Issue consists of nine original scientific articles that address oceanic circulation and water mass exchange. Most of them deal with mean circulation, basin and sub-basin-scale flows, mesoscale eddies, and internal processes (e.g., mixing and internal waves) that contribute to the redistribution of oceanic properties and energy within the ocean. One paper deals with numerical modelling application finalized to evaluate the capacity of coastal vegetated areas to mitigate the impact of a tsunami. The study areas in which these topics are developed include both oceanic areas and semi-enclosed seas such as the Mediterranean Sea, the Norwegian Sea and the Fram Strait, the South China Sea, and the Northwest Pacific. Scientific findings presented in this Special Issue highlight how a combination of various modern observation techniques can improve our understanding of the complex physical and biogeochemical processes in the ocean.

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18

Zahn, Rainer. "Deep ocean circulation puzzle". Nature 356, n. 6372 (aprile 1992): 744–45. http://dx.doi.org/10.1038/356744a0.

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19

Wells, Neil C. "Ocean circulation and climate". Continental Shelf Research 22, n. 10 (giugno 2002): 1559–60. http://dx.doi.org/10.1016/s0278-4343(02)00005-5.

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20

McCreary, J. P. "Modeling Equatorial Ocean Circulation". Annual Review of Fluid Mechanics 17, n. 1 (gennaio 1985): 359–409. http://dx.doi.org/10.1146/annurev.fl.17.010185.002043.

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21

Blanckenburg, F. v. "PALEOCEANOGRAPHY:Tracing Past Ocean Circulation?" Science 286, n. 5446 (3 dicembre 1999): 1862b—1863. http://dx.doi.org/10.1126/science.286.5446.1862b.

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Latif, Mojib. "Tropical Ocean Circulation Experiments". Journal of Physical Oceanography 17, n. 2 (febbraio 1987): 246–63. http://dx.doi.org/10.1175/1520-0485(1987)017<0246:toce>2.0.co;2.

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Frajka-Williams, E. "Sustaining observations of the unsteady ocean circulation". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 372, n. 2025 (28 settembre 2014): 20130335. http://dx.doi.org/10.1098/rsta.2013.0335.

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Sustained observations of ocean properties reveal a global warming trend and rising sea levels. These changes have been documented by traditional ship-based measurements of ocean properties, whereas more recent Argo profiling floats and satellite records permit estimates of ocean changes on a near real-time basis. Through these and newer methods of observing the oceans, scientists are moving from quantifying the ‘state of the ocean’ to monitoring its variability, and distinguishing the physical processes bringing signals of change. In this paper, I give a brief overview of the UK contributions to the physical oceanographic observations, and the role they have played in the wider global observing systems. While temperature and salinity are the primary measurements of physical oceanography, new transbasin mooring arrays also resolve changes in ocean circulation on daily timescales. Emerging technologies permit routine observations at higher-than-ever spatial resolutions. Following this, I then give a personal perspective on the future of sustained observations. New measurement techniques promise exciting discoveries concerning the role of smaller scales and boundary processes in setting the large-scale ocean circulation and the ocean's role in climate. The challenges now facing the scientific community include sustaining critical observations in the case of funding system changes or shifts in government priorities. These long records will enable a determination of the role and response of the ocean to climate change.

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Wu, Yang, Xiaoming Zhai e Zhaomin Wang. "Decadal-Mean Impact of Including Ocean Surface Currents in Bulk Formulas on Surface Air–Sea Fluxes and Ocean General Circulation". Journal of Climate 30, n. 23 (dicembre 2017): 9511–25. http://dx.doi.org/10.1175/jcli-d-17-0001.1.

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The decadal-mean impact of including ocean surface currents in the bulk formulas on surface air–sea fluxes and the ocean general circulation is investigated for the first time using a global eddy-permitting coupled ocean–sea ice model. Although including ocean surface currents in air–sea flux calculations only weakens the surface wind stress by a few percent, it significantly reduces wind power input to both geostrophic and ageostrophic motions, and damps the eddy and mean kinetic energy throughout the water column. Furthermore, the strength of the horizontal gyre circulations and the Atlantic meridional overturning circulation are found to decrease considerably (by 10%–15% and ~13%, respectively). As a result of the weakened ocean general circulation, the maximum northward global ocean heat transport decreases by about 0.2 PW, resulting in a lower sea surface temperature and reduced surface heat loss in the northern North Atlantic. Additional sensitivity model experiments further demonstrate that it is including ocean surface currents in the wind stress calculation that dominates this decadal impact, with including ocean surface currents in the turbulent heat flux calculations making only a minor contribution. These results highlight the importance of properly accounting for ocean surface currents in surface air–sea fluxes in modeling the ocean circulation and climate.

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Hu, Shineng, Shang-Ping Xie e Wei Liu. "Global Pattern Formation of Net Ocean Surface Heat Flux Response to Greenhouse Warming". Journal of Climate 33, n. 17 (1 settembre 2020): 7503–22. http://dx.doi.org/10.1175/jcli-d-19-0642.1.

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AbstractThis study examines global patterns of net ocean surface heat flux changes (ΔQnet) under greenhouse warming in an ocean–atmosphere coupled model based on a heat budget decomposition. The regional structure of ΔQnet is primarily shaped by ocean heat divergence changes (ΔOHD): excessive heat is absorbed by higher-latitude oceans (mainly over the North Atlantic and the Southern Ocean), transported equatorward, and stored in lower-latitude oceans with the rest being released to the tropical atmosphere. The overall global pattern of ΔOHD is primarily due to the circulation change and partially compensated by the passive advection effect, except for the Southern Ocean, which requires further investigations for a more definitive attribution. The mechanisms of North Atlantic surface heat uptake are further explored. In another set of global warming simulations, a perturbation of freshwater removal is imposed over the subpolar North Atlantic to largely offset the CO2-induced changes in the local ocean vertical stratification, barotropic gyre, and the Atlantic meridional overturning circulation (AMOC). Results from the freshwater perturbation experiments suggest that a significant portion of the positive ΔQnet over the North Atlantic under greenhouse warming is caused by the Atlantic circulation changes, perhaps mainly by the slowdown of AMOC, while the passive advection effect can contribute to the regional variations of ΔQnet. Our results imply that ocean circulation changes are critical for shaping global warming pattern and thus hydrological cycle changes.

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Hu, Shijian, Janet Sprintall, Cong Guan, Michael J. McPhaden, Fan Wang, Dunxin Hu e Wenju Cai. "Deep-reaching acceleration of global mean ocean circulation over the past two decades". Science Advances 6, n. 6 (febbraio 2020): eaax7727. http://dx.doi.org/10.1126/sciadv.aax7727.

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Ocean circulation redistributes Earth’s energy and water masses and influences global climate. Under historical greenhouse warming, regional ocean currents show diverse tendencies, but whether there is an emerging trend of the global mean ocean circulation system is not yet clear. Here, we show a statistically significant increasing trend in the globally integrated oceanic kinetic energy since the early 1990s, indicating a substantial acceleration of global mean ocean circulation. The increasing trend in kinetic energy is particularly prominent in the global tropical oceans, reaching depths of thousands of meters. The deep-reaching acceleration of the ocean circulation is mainly induced by a planetary intensification of surface winds since the early 1990s. Although possibly influenced by wind changes associated with the onset of a negative Pacific decadal oscillation since the late 1990s, the recent acceleration is far larger than that associated with natural variability, suggesting that it is principally part of a long-term trend.

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Proshutinsky, Andrey, Dmitry Dukhovskoy, Mary-Louise Timmermans, Richard Krishfield e Jonathan L. Bamber. "Arctic circulation regimes". Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences 373, n. 2052 (13 ottobre 2015): 20140160. http://dx.doi.org/10.1098/rsta.2014.0160.

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Between 1948 and 1996, mean annual environmental parameters in the Arctic experienced a well-pronounced decadal variability with two basic circulation patterns: cyclonic and anticyclonic alternating at 5 to 7 year intervals. During cyclonic regimes, low sea-level atmospheric pressure (SLP) dominated over the Arctic Ocean driving sea ice and the upper ocean counterclockwise; the Arctic atmosphere was relatively warm and humid, and freshwater flux from the Arctic Ocean towards the subarctic seas was intensified. By contrast, during anticylonic circulation regimes, high SLP dominated driving sea ice and the upper ocean clockwise. Meanwhile, the atmosphere was cold and dry and the freshwater flux from the Arctic to the subarctic seas was reduced. Since 1997, however, the Arctic system has been under the influence of an anticyclonic circulation regime (17 years) with a set of environmental parameters that are atypical for this regime. We discuss a hypothesis explaining the causes and mechanisms regulating the intensity and duration of Arctic circulation regimes, and speculate how changes in freshwater fluxes from the Arctic Ocean and Greenland impact environmental conditions and interrupt their decadal variability.

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Kanzow, Torsten, e Martin Visbeck. "Ocean circulation - Does large-scale ocean overturning circulation vary with climate change? [Present]". PAGES news 20, n. 1 (febbraio 2012): 14. http://dx.doi.org/10.22498/pages.20.1.14.

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Skinner, Luke. "Ocean circulation - Does large-scale ocean overturning circulation vary with climate change? [Past]". PAGES news 20, n. 1 (febbraio 2012): 15. http://dx.doi.org/10.22498/pages.20.1.15.

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Smith, Robin S., Clotilde Dubois e Jochem Marotzke. "Global Climate and Ocean Circulation on an Aquaplanet Ocean–Atmosphere General Circulation Model". Journal of Climate 19, n. 18 (15 settembre 2006): 4719–37. http://dx.doi.org/10.1175/jcli3874.1.

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Abstract A low-resolution coupled ocean–atmosphere general circulation model (OAGCM) is used to study the characteristics of the large-scale ocean circulation and its climatic impacts in a series of global coupled aquaplanet experiments. Three configurations, designed to produce fundamentally different ocean circulation regimes, are considered. The first has no obstruction to zonal flow, the second contains a low barrier that blocks zonal flow in the ocean at all latitudes, creating a single enclosed basin, while the third contains a gap in the barrier to allow circumglobal flow at high southern latitudes. Warm greenhouse climates with a global average air surface temperature of around 27°C result in all cases. Equator-to-pole temperature gradients are shallower than that of a current climate simulation. While changes in the land configuration cause regional changes in temperature, winds, and rainfall, heat transports within the system are little affected. Inhibition of all ocean transport on the aquaplanet leads to a reduction in global mean surface temperature of 8°C, along with a sharpening of the meridional temperature gradient. This results from a reduction in global atmospheric water vapor content and an increase in tropical albedo, both of which act to reduce global surface temperatures. Fitting a simple radiative model to the atmospheric characteristics of the OAGCM solutions suggests that a simpler atmosphere model, with radiative parameters chosen a priori based on the changing surface configuration, would have produced qualitatively different results. This implies that studies with reduced complexity atmospheres need to be guided by more complex OAGCM results on a case-by-case basis.

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31

Zhao, Mengnan, Rui M. Ponte, Ou Wang e Rick Lumpkin. "Using Drifter Velocity Measurements to Assess and Constrain Coarse-Resolution Ocean Models". Journal of Atmospheric and Oceanic Technology 38, n. 4 (aprile 2021): 909–19. http://dx.doi.org/10.1175/jtech-d-20-0159.1.

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AbstractProperly fitting ocean models to observations is crucial for improving model performance and understanding ocean dynamics. Near-surface velocity measurements from the Global Drifter Program (GDP) contain valuable information about upper-ocean circulation and air–sea fluxes on various space and time scales. This study explores whether GDP measurements can be used for usefully constraining the surface circulation from coarse-resolution ocean models, using global solutions produced by the consortium for Estimating the Circulation and Climate of the Ocean (ECCO) as an example. To address this problem, a careful examination of velocity data errors is required. Comparisons between an ECCO model simulation, performed without any data constraints, and GDP and Ocean Surface Current Analyses Real-Time (OSCAR) velocity data, over the period 1992–2017, reveal considerable differences in magnitude and pattern. These comparisons are used to estimate GDP data errors in the context of the time-mean and time-variable surface circulations. Both instrumental errors and errors associated with limitations in model physics and resolution (representation errors) are considered. Given the estimated model–data differences, errors, and signal-to-noise ratios, our results indicate that constraining ocean-state estimates to GDP can have a substantial impact on the ECCO large-scale time-mean surface circulation over extensive areas. Impact of GDP data constraints on the ECCO time-variable circulation would be weaker and mainly limited to low latitudes. Representation errors contribute substantially to degrading the data impacts.

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32

Meccia, Virna L., Doroteaciro Iovino e Alessio Bellucci. "North Atlantic gyre circulation in PRIMAVERA models". Climate Dynamics 56, n. 11-12 (14 febbraio 2021): 4075–90. http://dx.doi.org/10.1007/s00382-021-05686-z.

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Abstract (sommario):

AbstractWe study the impact of horizontal resolution in setting the North Atlantic gyre circulation and representing the ocean–atmosphere interactions that modulate the low-frequency variability in the region. Simulations from five state-of-the-art climate models performed at standard and high-resolution as part of the High-Resolution Model Inter-comparison Project (HighResMIP) were analysed. In some models, the resolution is enhanced in the atmospheric and oceanic components whereas, in some other models, the resolution is increased only in the atmosphere. Enhancing the horizontal resolution from non-eddy to eddy-permitting ocean produces stronger barotropic mass transports inside the subpolar and subtropical gyres. The first mode of inter-annual variability is associated with the North Atlantic Oscillation (NAO) in all the cases. The rapid ocean response to it consists of a shift in the position of the inter-gyre zone and it is better captured by the non-eddy models. The delayed ocean response consists of an intensification of the subpolar gyre (SPG) after around 3 years of a positive phase of NAO and it is better represented by the eddy-permitting oceans. A lagged relationship between the intensity of the SPG and the Atlantic Meridional Overturning Circulation (AMOC) is stronger in the cases of the non-eddy ocean. Then, the SPG is more tightly coupled to the AMOC in low-resolution models.

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33

Phillips, Helen E., Amit Tandon, Ryo Furue, Raleigh Hood, Caroline C. Ummenhofer, Jessica A. Benthuysen, Viviane Menezes et al. "Progress in understanding of Indian Ocean circulation, variability, air–sea exchange, and impacts on biogeochemistry". Ocean Science 17, n. 6 (26 novembre 2021): 1677–751. http://dx.doi.org/10.5194/os-17-1677-2021.

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Abstract (sommario):

Abstract. Over the past decade, our understanding of the Indian Ocean has advanced through concerted efforts toward measuring the ocean circulation and air–sea exchanges, detecting changes in water masses, and linking physical processes to ecologically important variables. New circulation pathways and mechanisms have been discovered that control atmospheric and oceanic mean state and variability. This review brings together new understanding of the ocean–atmosphere system in the Indian Ocean since the last comprehensive review, describing the Indian Ocean circulation patterns, air–sea interactions, and climate variability. Coordinated international focus on the Indian Ocean has motivated the application of new technologies to deliver higher-resolution observations and models of Indian Ocean processes. As a result we are discovering the importance of small-scale processes in setting the large-scale gradients and circulation, interactions between physical and biogeochemical processes, interactions between boundary currents and the interior, and interactions between the surface and the deep ocean. A newly discovered regional climate mode in the southeast Indian Ocean, the Ningaloo Niño, has instigated more regional air–sea coupling and marine heatwave research in the global oceans. In the last decade, we have seen rapid warming of the Indian Ocean overlaid with extremes in the form of marine heatwaves. These events have motivated studies that have delivered new insight into the variability in ocean heat content and exchanges in the Indian Ocean and have highlighted the critical role of the Indian Ocean as a clearing house for anthropogenic heat. This synthesis paper reviews the advances in these areas in the last decade.

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34

Divakaran, Prasanth, e Gary B. Brassington. "Arterial ocean circulation of the southeast Indian Ocean". Geophysical Research Letters 38, n. 1 (5 gennaio 2011): n/a. http://dx.doi.org/10.1029/2010gl045574.

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35

Schultz, Colin. "How ocean ridges affect large-scale ocean circulation". Eos, Transactions American Geophysical Union 92, n. 42 (18 ottobre 2011): 372. http://dx.doi.org/10.1029/2011eo420009.

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36

Schmittner, Andreas, Tiago A. M. Silva, Klaus Fraedrich, Edilbert Kirk e Frank Lunkeit. "Effects of Mountains and Ice Sheets on Global Ocean Circulation*". Journal of Climate 24, n. 11 (1 giugno 2011): 2814–29. http://dx.doi.org/10.1175/2010jcli3982.1.

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Abstract (sommario):

Abstract The impact of mountains and ice sheets on the large-scale circulation of the world’s oceans is investigated in a series of simulations with a new coupled ocean–atmosphere model [Oregon State University–University of Victoria model (OSUVic)], in which the height of orography is scaled from 1.5 times the actual height (at T42 resolution) to 0 (no mountains). The results suggest that the effects of mountains and ice sheets on the buoyancy and momentum transfer from the atmosphere to the surface ocean determine the present pattern of deep ocean circulation. Higher mountains reduce water vapor transport from the Pacific and Indian Oceans into the Atlantic Ocean and contribute to increased (decreased) salinities and enhanced (reduced) deep-water formation and meridional overturning circulation in the Atlantic (Pacific). Orographic effects also lead to the observed interhemispheric asymmetry of midlatitude zonal wind stress. The presence of the Antarctic ice sheet cools winter air temperatures by more than 20°C directly above the ice sheet and sets up a polar meridional overturning cell in the atmosphere. The resulting increased meridional temperature gradient strengthens midlatitude westerlies by ~25% and shifts them poleward by ~10°. This leads to enhanced and poleward-shifted upwelling of deep waters in the Southern Ocean, a stronger Antarctic Circumpolar Current, increased poleward atmospheric moisture transport, and more advection of high-salinity Indian Ocean water into the South Atlantic. Thus, it is the current configuration of mountains and ice sheets on earth that determines the difference in deep-water formation between the Atlantic and the Pacific.

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37

Kriest, Iris, Paul Kähler, Wolfgang Koeve, Karin Kvale, Volkmar Sauerland e Andreas Oschlies. "One size fits all? Calibrating an ocean biogeochemistry model for different circulations". Biogeosciences 17, n. 12 (18 giugno 2020): 3057–82. http://dx.doi.org/10.5194/bg-17-3057-2020.

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Abstract (sommario):

Abstract. Global biogeochemical ocean models are often tuned to match the observed distributions and fluxes of inorganic and organic quantities. This tuning is typically carried out “by hand”. However, this rather subjective approach might not yield the best fit to observations, is closely linked to the circulation employed and is thus influenced by its specific features and even its faults. We here investigate the effect of model tuning, via objective optimisation, of one biogeochemical model of intermediate complexity when simulated in five different offline circulations. For each circulation, three of six model parameters have been adjusted to characteristic features of the respective circulation. The values of these three parameters – namely, the oxygen utilisation of remineralisation, the particle flux parameter and potential nitrogen fixation rate – correlate significantly with deep mixing and ideal age of North Atlantic Deep Water (NADW) and the outcrop area of Antarctic Intermediate Waters (AAIW) and Subantarctic Mode Water (SAMW) in the Southern Ocean. The clear relationship between these parameters and circulation characteristics, which can be easily diagnosed from global models, can provide guidance when tuning global biogeochemistry within any new circulation model. The results from 20 global cross-validation experiments show that parameter sets optimised for a specific circulation can be transferred between similar circulations without losing too much of the model's fit to observed quantities. When compared to model intercomparisons of subjectively tuned, global coupled biogeochemistry–circulation models, each with different circulation and/or biogeochemistry, our results show a much lower range of oxygen inventory, oxygen minimum zone (OMZ) volume and global biogeochemical fluxes. Export production depends to a large extent on the circulation applied, while deep particle flux is mostly determined by the particle flux parameter. Oxygen inventory, OMZ volume, primary production and fixed-nitrogen turnover depend more or less equally on both factors, with OMZ volume showing the highest sensitivity, and residual variability. These results show a beneficial effect of optimisation, even when a biogeochemical model is first optimised in a relatively coarse circulation and then transferred to a different finer-resolution circulation model.

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38

Vecchi, Gabriel A., e Brian J. Soden. "Global Warming and the Weakening of the Tropical Circulation". Journal of Climate 20, n. 17 (1 settembre 2007): 4316–40. http://dx.doi.org/10.1175/jcli4258.1.

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Abstract (sommario):

Abstract This study examines the response of the tropical atmospheric and oceanic circulation to increasing greenhouse gases using a coordinated set of twenty-first-century climate model experiments performed for the Intergovernmental Panel on Climate Change (IPCC) Fourth Assessment Report (AR4). The strength of the atmospheric overturning circulation decreases as the climate warms in all IPCC AR4 models, in a manner consistent with the thermodynamic scaling arguments of Held and Soden. The weakening occurs preferentially in the zonally asymmetric (i.e., Walker) rather than zonal-mean (i.e., Hadley) component of the tropical circulation and is shown to induce substantial changes to the thermal structure and circulation of the tropical oceans. Evidence suggests that the overall circulation weakens by decreasing the frequency of strong updrafts and increasing the frequency of weak updrafts, although the robustness of this behavior across all models cannot be confirmed because of the lack of data. As the climate warms, changes in both the atmospheric and ocean circulation over the tropical Pacific Ocean resemble “El Niño–like” conditions; however, the mechanisms are shown to be distinct from those of El Niño and are reproduced in both mixed layer and full ocean dynamics coupled climate models. The character of the Indian Ocean response to global warming resembles that of Indian Ocean dipole mode events. The consensus of model results presented here is also consistent with recently detected changes in sea level pressure since the mid–nineteenth century.

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39

Brown, J., C. A. Clayson, L. Kantha e T. Rojsiraphisal. "North Indian Ocean variability during the Indian Ocean dipole". Ocean Science Discussions 5, n. 2 (9 giugno 2008): 213–53. http://dx.doi.org/10.5194/osd-5-213-2008.

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Abstract (sommario):

Abstract. The circulation in the North Indian Ocean (NIO henceforth) is highly seasonally variable. Periodically reversing monsoon winds (southwesterly during summer and northeasterly during winter) give rise to seasonally reversing current systems off the coast of Somalia and India. In addition to this annual monsoon cycle, the NIO circulation varies semiannually because of equatorial currents reversing four times each year. These descriptions are typical, but how does the NIO circulation behave during anomalous years, during an Indian Ocean dipole (IOD) for instance? Unfortunately, in situ observational data are rather sparse and reliance has to be placed on numerical models to understand this variability. In this paper, we estimate the surface current variability from a 12-year hindcast of the NIO for 1993–2004 using a 1/2° resolution circulation model that assimilates both altimetric sea surface height anomalies and sea surface temperature. Presented in this paper is an examination of surface currents in the NIO basin during the IOD. During the non-IOD period of 2000–2004, the typical equatorial circulation of the NIO reverses four times each year and transports water across the basin preventing a large sea surface temperature difference between the western and eastern NIO. Conversely, IOD years are noted for strong easterly and westerly wind outbursts along the equator. The impact of these outbursts on the NIO circulation is to reverse the direction of the currents – when compared to non-IOD years – during the summer for negative IOD events (1996 and 1998) and during the fall for positive IOD events (1994 and 1997). This reversal of current direction leads to large temperature differences between the western and eastern NIO.

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40

Jones, E. Peter. "Circulation in the Arctic Ocean". Polar Research 20, n. 2 (12 gennaio 2001): 139–46. http://dx.doi.org/10.3402/polar.v20i2.6510.

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41

Schiermeier, Quirin. "Ocean circulation noisy, not stalling". Nature 448, n. 7156 (agosto 2007): 844–45. http://dx.doi.org/10.1038/448844b.

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42

Gille, Sarah, Joseph Metzger e Robin Tokmakian. "Seafloor Topography and Ocean Circulation". Oceanography 17, n. 1 (1 marzo 2004): 47–54. http://dx.doi.org/10.5670/oceanog.2004.66.

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43

Hasselmann, Klaus. "Ocean circulation and climate change". Tellus B: Chemical and Physical Meteorology 43, n. 4 (gennaio 1991): 82–103. http://dx.doi.org/10.3402/tellusb.v43i4.15399.

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44

Jones, E. Peter. "Circulation in the Arctic Ocean". Polar Research 20, n. 2 (dicembre 2001): 139–46. http://dx.doi.org/10.1111/j.1751-8369.2001.tb00049.x.

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45

Manoj, C., A. Kuvshinov, S. Maus e H. Lühr. "Ocean circulation generated magnetic signals". Earth, Planets and Space 58, n. 4 (aprile 2006): 429–37. http://dx.doi.org/10.1186/bf03351939.

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46

Klinck, John M. "General Circulation of the Ocean". Eos, Transactions American Geophysical Union 68, n. 27 (1987): 621. http://dx.doi.org/10.1029/eo068i027p00621-02.

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47

Woods, J. D. "The World Ocean Circulation Experiment". Nature 314, n. 6011 (aprile 1985): 501–11. http://dx.doi.org/10.1038/314501a0.

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48

Anonymous. "The World Ocean Circulation Experiment". Eos, Transactions American Geophysical Union 73, n. 3 (1992): 34. http://dx.doi.org/10.1029/91eo10034.

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49

Smith, H. J. "Spinning up ocean circulation discretely". Science 345, n. 6194 (17 luglio 2014): 280. http://dx.doi.org/10.1126/science.345.6194.280-p.

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50

McWilliams, James C., e Juan M. Restrepo. "The Wave-Driven Ocean Circulation". Journal of Physical Oceanography 29, n. 10 (ottobre 1999): 2523–40. http://dx.doi.org/10.1175/1520-0485(1999)029<2523:twdoc>2.0.co;2.

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