Journal articles on the topic 'Variability of the surface salinity'
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Drushka, Kyla, William E. Asher, Janet Sprintall, Sarah T. Gille, and Clifford Hoang. "Global Patterns of Submesoscale Surface Salinity Variability." Journal of Physical Oceanography 49, no. 7 (July 2019): 1669–85. http://dx.doi.org/10.1175/jpo-d-19-0018.1.
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AbstractSurface salinity variability on O(1–10) km lateral scales (the submesoscale) generates density variability and thus has implications for submesoscale dynamics. Satellite salinity measurements represent a spatial average over horizontal scales of approximately 40–100 km but are compared to point measurements for validation, so submesoscale salinity variability also complicates validation of satellite salinities. Here, we combine several databases of historical thermosalinograph (TSG) measurements made from ships to globally characterize surface submesoscale salinity, temperature, and density variability. In river plumes; regions affected by ice melt or upwelling; and the Gulf Stream, South Atlantic, and Agulhas Currents, submesoscale surface salinity variability is large. In these regions, horizontal salinity variability appears to explain some of the differences between surface salinities from the Aquarius and SMOS satellites and salinities measured with Argo floats. In other words, apparent satellite errors in highly variable regions in fact arise because Argo point measurements do not represent spatially averaged satellite data. Salinity dominates over temperature in generating submesoscale surface density variability throughout the tropical rainbands, in river plumes, and in polar regions. Horizontal density fronts on 10-km scales tend to be compensated (salinity and temperature have opposing effects on density) throughout most of the global oceans, with the exception of the south Indian and southwest Pacific Oceans between 20° and 30°S, where fronts tend to be anticompensated.
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Boutin, J., Y. Chao, W. E. Asher, T. Delcroix, R. Drucker, K. Drushka, N. Kolodziejczyk, et al. "Satellite and In Situ Salinity: Understanding Near-Surface Stratification and Subfootprint Variability." Bulletin of the American Meteorological Society 97, no. 8 (August 1, 2016): 1391–407. http://dx.doi.org/10.1175/bams-d-15-00032.1.
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Abstract Remote sensing of salinity using satellite-mounted microwave radiometers provides new perspectives for studying ocean dynamics and the global hydrological cycle. Calibration and validation of these measurements is challenging because satellite and in situ methods measure salinity differently. Microwave radiometers measure the salinity in the top few centimeters of the ocean, whereas most in situ observations are reported below a depth of a few meters. Additionally, satellites measure salinity as a spatial average over an area of about 100 × 100 km2. In contrast, in situ sensors provide pointwise measurements at the location of the sensor. Thus, the presence of vertical gradients in, and horizontal variability of, sea surface salinity complicates comparison of satellite and in situ measurements. This paper synthesizes present knowledge of the magnitude and the processes that contribute to the formation and evolution of vertical and horizontal variability in near-surface salinity. Rainfall, freshwater plumes, and evaporation can generate vertical gradients of salinity, and in some cases these gradients can be large enough to affect validation of satellite measurements. Similarly, mesoscale to submesoscale processes can lead to horizontal variability that can also affect comparisons of satellite data to in situ data. Comparisons between satellite and in situ salinity measurements must take into account both vertical stratification and horizontal variability.
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Forget, Gaël, and Carl Wunsch. "Estimated Global Hydrographic Variability." Journal of Physical Oceanography 37, no. 8 (August 1, 2007): 1997–2008. http://dx.doi.org/10.1175/jpo3072.1.
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Abstract An estimate is made of the three-dimensional global oceanic temperature and salinity variability, omitting the seasonal cycle, both as a major descriptive element of the ocean circulation and for use in the error estimates of state estimation. Historical hydrography, recent data from the World Ocean Circulation Experiment, and Argo profile data are all used. Root-mean-square vertical displacements in the upper 300 m of the ocean are generally smaller than 50 m, except in energetic boundary currents and in the North Atlantic subpolar gyre. Variability in temperature and salinity is strongly correlated below the top 100 m. Salinity contributions to sea surface height variability appear more significant at low latitudes than expected, possibly resulting from advective and diffusive processes. Results are generally consistent with altimetric variability under two simple kinematic hypotheses, and much of the observed structure coincides with known dynamical features. A large fraction of the sea surface height variability is consistent with the hypothesis of dominance of the first baroclinic mode.
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Reverdin, G. "North Atlantic Subpolar Gyre Surface Variability (1895–2009)." Journal of Climate 23, no. 17 (September 1, 2010): 4571–84. http://dx.doi.org/10.1175/2010jcli3493.1.
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Abstract Surface temperature, salinity, and density are examined in the northeastern part of the North Atlantic subpolar gyre over the last 115 years of measurements. This region presents coherent variability in space but also between different seasons, with relatively small trends and large multidecadal variability. The most significant trend is a lowering in surface density. Multidecadal variability in T and S is large and is usually similar, with the largest difference between the two in the 1920s and a tendency of T to lead S. Multidecadal T and S are correlated with the winter North Atlantic Oscillation (NAO) index at 0 or 1-yr lag for T and 0 to 3-yr lag for S. This suggests a strong contribution of advection. The lag between T and S is also suggestive of a contribution of air–sea fluxes of heat or freshwater, but probably more so at high frequencies than at the multidecadal time scales. Salinity higher frequency is correlated with NAO at a 2–3-yr lag, whereas T higher frequency variability presents no correlation with NAO at any lag. This suggests different relations between seasonal NAO indices and air–sea heat fluxes patterns in this region before and after 1960; also the advective signal is more clearly identified in salinity in this region.
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Sharma, Rashmi, Neeraj Agarwal, Imran M. Momin, Sujit Basu, and Vijay K. Agarwal. "Simulated Sea Surface Salinity Variability in the Tropical Indian Ocean." Journal of Climate 23, no. 24 (December 15, 2010): 6542–54. http://dx.doi.org/10.1175/2010jcli3721.1.
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Abstract A long-period (15 yr) simulation of sea surface salinity (SSS) obtained from a hindcast run of an ocean general circulation model (OGCM) forced by the NCEP–NCAR daily reanalysis product is analyzed in the tropical Indian Ocean (TIO). The objective of the study is twofold: assess the capability of the model to provide realistic simulations of SSS and characterize the SSS variability in view of upcoming satellite salinity missions. Model fields are evaluated in terms of mean, standard deviation, and characteristic temporal scales of SSS variability. Results show that the standard deviations range from 0.2 to 1.5 psu, with larger values in regions with strong seasonal transitions of surface currents (south of India) and along the coast in the Bay of Bengal (strong Kelvin-wave-induced currents). Comparison of simulated SSS with collocated SSS measurements from the National Oceanographic Data Center and Argo floats resulted in a high correlation of 0.85 and a root-mean-square error (RMSE) of 0.4 psu. The correlations are quite high (>0.75) up to a depth of 300 m. Daily simulations of SSS compare well with a Research Moored Array for African–Asian–Australian Monsoon Analysis and Prediction (RAMA) buoy in the eastern equatorial Indian Ocean (1.5°S, 90°E) with an RMSE of 0.3 psu and a correlation better than 0.6. Model SSS compares well with observations at all time scales (intraseasonal, seasonal, and interannual). The decorrelation scales computed from model and buoy SSS suggest that the proposed 10-day sampling of future salinity sensors would be able to resolve much of the salinity variability at time scales longer than intraseasonal. This inference is significant in view of satellite salinity sensors, such as Soil Moisture and Ocean Salinity (SMOS) and Aquarius.
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Subrahmanyam, Bulusu, V. S. N. Murty, and David M. Heffner. "Sea surface salinity variability in the tropical Indian Ocean." Remote Sensing of Environment 115, no. 3 (March 2011): 944–56. http://dx.doi.org/10.1016/j.rse.2010.12.004.
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Bingham, Frederick M., Julius J. M. Busecke, and Arnold L. Gordon. "Variability of the South Pacific Subtropical Surface Salinity Maximum." Journal of Geophysical Research: Oceans 124, no. 8 (August 2019): 6050–66. http://dx.doi.org/10.1029/2018jc014598.
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Spall, Michael A. "Variability of sea surface salinity in stochastically forced systems." Climate Dynamics 8, no. 3 (January 1993): 151–60. http://dx.doi.org/10.1007/bf00208094.
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Cherniavskaia, Ekaterina A., Ivan Sudakov, Kenneth M. Golden, Courtenay Strong, and Leonid A. Timokhov. "Observed winter salinity fields in the surface layer of the Arctic Ocean and statistical approaches to predicting large-scale anomalies and patterns." Annals of Glaciology 59, no. 76pt2 (April 23, 2018): 83–100. http://dx.doi.org/10.1017/aog.2018.10.
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AbstractSignificant salinity anomalies have been observed in the Arctic Ocean surface layer during the last decade. Our study is based on an extensive gridded dataset of winter salinity in the upper 50 m layer of the Arctic Ocean for the periods 1950–1993 and 2007–2012, obtained from ~20 000 profiles. We investigate the interannual variability of the salinity fields, identify predominant patterns of anomalous behavior and leading modes of variability, and develop a statistical model for the prediction of surface-layer salinity. The statistical model is based on linear regression equations linking the principal components of surface-layer salinity obtained through empirical orthogonal function decomposition with environmental factors, such as atmospheric circulation, river runoff, ice processes and water exchange with neighboring oceans. Using this model, we obtain prognostic fields of the surface-layer salinity for the winter period 2013–2014. The prognostic fields generated by the model show tendencies of surface-layer salinification, which were also observed in previous years. Although the used data are proprietary and have gaps, they provide the most spatiotemporally detailed observational resource for studying multidecadal variations in basin-wide Arctic salinity. Thus, there is community value in the identification, dissemination and modeling of the principal modes of variability in this salinity record.
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Reverdin, G., S. Morisset, J. Boutin, N. Martin, M. Sena-Martins, F. Gaillard, P. Blouch, et al. "Validation of Salinity Data from Surface Drifters." Journal of Atmospheric and Oceanic Technology 31, no. 4 (April 1, 2014): 967–83. http://dx.doi.org/10.1175/jtech-d-13-00158.1.
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Abstract Salinity measurements from 119 surface drifters in 2007–12 were assessed; 80% [Surface Velocity Program with a barometer with a salinity sensor (SVP-BS)] and 75% [SVP with salinity (SVP-S)] of the salinity data were found to be usable, after editing out some spikes. Sudden salinity jumps are found in drifter salinity records that are not always associated with temperature jumps, in particular in the wet tropics. A method is proposed to decide whether and how to correct those jumps, and the uncertainty in the correction applied. Northeast of South America, in a region influenced by the Amazon plume and fresh coastal water, drifter salinity is very variable, but a comparison with data from the Soil Moisture and Ocean Salinity satellite suggests that this variability is usually reasonable. The drifter salinity accuracy is then explored based on comparisons with data from Argo floats and from thermosalinographs (TSGs) of ships of opportunity. SVP-S/SVP-BS drifter records do not usually present significant biases within the first 6 months, but afterward biases sometimes need to be corrected (altogether, 16% of the SVP-BS records). Biases start earlier after 3 months for drifters not protected by antifouling paint. For the few drifters for which large corrections were applied to portions of the record, the accuracy cannot be proven to be better than 0.1 psu, and it cannot be proven to be better than 0.5 psu for data in the largest variability area off northeast South America. Elsewhere, after excluding portions of the records with suspicious salinity jumps or when large corrections were applied, the comparisons rule out average biases in individual drifter salinity record larger than 0.02 psu (midlatitudes) and 0.05 psu (tropics).
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Shoup, Casey G., Bulusu Subrahmanyam, and Heather L. Roman‐Stork. "Madden‐Julian Oscillation‐Induced Sea Surface Salinity Variability as Detected in Satellite‐Derived Salinity." Geophysical Research Letters 46, no. 16 (August 19, 2019): 9748–56. http://dx.doi.org/10.1029/2019gl083694.
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Zanna, Laure, and Eli Tziperman. "Optimal Surface Excitation of the Thermohaline Circulation." Journal of Physical Oceanography 38, no. 8 (August 1, 2008): 1820–30. http://dx.doi.org/10.1175/2008jpo3752.1.
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Abstract The amplification of thermohaline circulation (THC) anomalies resulting from heat and freshwater forcing at the ocean surface is investigated in a zonally averaged coupled ocean–atmosphere model. Optimal initial conditions of surface temperature and salinity leading to the largest THC growth are computed, and so are the structures of stochastic surface temperature and salinity forcing that excite maximum THC variance (stochastic optimals). When the THC amplitude is defined as its sum of squares (equivalent to using the standard L2 norm), the nonnormal linearized dynamics lead to an amplification with a time scale on the order of 100 yr. The optimal initial conditions have a vanishing THC anomaly, and the complex amplification mechanism involves the advection of both temperature and salinity anomalies by the mean flow and of the mean temperature and salinity by the anomaly flow. The L2 characterization of THC anomalies leads to physically interesting results, yet to a mathematically singular problem. A novel alternative characterizing the THC amplitude by its maximum value, as often done in general circulation model studies, is therefore introduced. This complementary method is shown to be equivalent to using the L-infinity norm, and the needed mathematical approach is developed and applied to the THC problem. Under this norm, an amplification occurs within 10 yr explained by the classic salinity advective feedback mechanism. The analysis of the stochastic optimals shows that the character of the THC variability may be very sensitive to the spatial pattern of the surface forcing. In particular, a maximum THC variance and long-time-scale variability are excited by a basin-scale surface forcing pattern, while a significantly higher frequency and to some extent a weaker variability are induced by a smooth and large-scale, yet mostly concentrated in polar areas, surface forcing pattern. Overall, the results suggest that a large THC variability can be efficiently excited by atmospheric surface forcing, and the simple model used here makes several predictions that would be interesting to test using more complex models.
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Mignot, J., and C. Frankignoul. "On the interannual variability of surface salinity in the Atlantic." Climate Dynamics 20, no. 6 (January 14, 2003): 555–65. http://dx.doi.org/10.1007/s00382-002-0294-0.
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Benallal, M. A., H. Moussa, F. Touratier, C. Goyet, and A. Poisson. "Ocean salinity from satellite-derived temperature in the Antarctic Ocean." Antarctic Science 28, no. 2 (December 1, 2015): 127–34. http://dx.doi.org/10.1017/s0954102015000516.
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AbstractThe aim of the MINERVE project (Mesures à l’INterface Eau-aiR de la Variabilité des Échanges de CO2) is to observe and understand the seasonal and interannual variability of the partial pressure of CO2(pCO2) in surface waters using hydrological and biogeochemical data in the Southern Ocean south of Australia. Logistics routes of the RVAstrolabeprovide access to scarcely studied areas, thus allowing us to understand the different processes acting in this area of the Antarctic Ocean. The surface area covered by these cruises, however, is tiny compared with the total surface area of the Antarctic Ocean. Correlations betweenin situsurface temperature and salinity data were applied to satellite images of sea surface temperature to map ocean surface salinity over a much wider area than under the cruise tracks. Comparisons with salinity data from satellites which provide ~100 km resolution and 0.1 accuracy indicate that we are able to map salinity at 4 km resolution and almost the same accuracy of ± 0.1.
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Laurian, Audine, Alban Lazar, and Gilles Reverdin. "Generation Mechanism of Spiciness Anomalies: An OGCM Analysis in the North Atlantic Subtropical Gyre." Journal of Physical Oceanography 39, no. 4 (April 1, 2009): 1003–18. http://dx.doi.org/10.1175/2008jpo3896.1.
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Abstract Oceanic teleconnections between the low and midlatitudes are a key mechanism to understanding the climate variability. Spiciness anomalies (density-compensated anomalies) have been shown to transport temperature and salinity signals when propagating along current streamlines in the subtropical gyres of the Atlantic and Pacific Oceans. The generation mechanism of spiciness anomalies in the North Atlantic subtropical gyre is investigated using an analytical model based on the late-winter subduction of salinity and temperature anomalies along isopycnal surfaces. The keystone of this approach is the change of the coordinates frame from isobaric to isopycnic surfaces, suited for subduction problems. The isopycnal nature of spiciness anomalies and the use of a linear density equation allows for the analytical model to depend only upon surface temperature and salinity anomalies, the mean thermocline currents, and the surface density ratio. This model clarifies and above all quantifies the mechanism by which surface temperature and salinity anomalies are modulated by density ratios to produce fully different isopycnal temperature and salinity anomalies. A global run from the ocean GCM (OGCM) Océan Parallélisé (OPA) over the period 1948–2002 provides the reference data in which the North Atlantic subtropical thermocline spiciness variability is analyzed. Two EOF modes are sufficient to explain half of the low-frequency variability in the OGCM: one is maximum over the northeastern subtropics, and the other is in the central basin. The analytical model reproduces well the spatial pattern, amplitude, and sign of these two main modes. It confirms that the two centers of action of the anomalies are conditioned by the surface density ratio, the first corresponding to null salinity gradients and the second to near-density-compensated temperature gradients. Considering that the analytical model has good skills at reproducing the decadal variability of the OGCM spiciness anomalies in the permanent thermocline, it is believed that this is an interesting tool to understand and forecast the ventilation of the North Atlantic subtropical gyre at this time scale.
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Zhi, Hai, Rong-Hua Zhang, Pengfei Lin, and Shiwei Shi. "Effects of Salinity Variability on Recent El Niño Events." Atmosphere 10, no. 8 (August 19, 2019): 475. http://dx.doi.org/10.3390/atmos10080475.
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Ocean salinity variability provides a new way to study the evolution of the the El Niño-Southern Oscillation (ENSO). Comparisons between the salinity variation and related processes responsible for sea surface temperature anomaly (SSTA) were extensively examined for the two strong El Niño (EN) events in 1997/1998 and 2015/2016, and a special EN event in 2014/2015. The results show that the development of EN is significantly correlated with a sea surface salinity anomaly (SSSA) in the tropical western-central Pacific. In the spring of 1997 and 2015 with strong EN events, the western-central equatorial Pacific exhibited significant negative SSSA that propagated eastward to the west of the dateline. The negative SSSA induced increased barrier layer thickness (BLT) which enhanced sea surface temperature (SST) warming in the tropical central Pacific. In contrast, although a negative SSSA occurred during April of the 2014/2015 weak EN event in the western-central equatorial Pacific, this SSSA was mainly confined to between 160° E and 180° E without significant eastward movement, resulting in a weakened BLT thickening process and a weak modulation effect on SST. We also confirm that the surface forcing associated with fresh water flux (FWF: evaporation (E) minus precipitation (P)) plays a prominent role in the surface salinity tendency in the tropical Pacific during EN events. Moreover, the negative FWF anomaly leads a strong negative SSSA by two months. Compared with the two strong ENs, the early negative FWF anomaly in the weak 2014/2015 EN did not present distinct development and eastward propagation and weakened rapidly in the summer of 2015. We demonstrate that change in salinity can modulate the ENSO, and the variation of SSSA and associated physical processes in the tropical western-central Pacific and could be used as an indicator for predicting the development of ENSO.
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Bryan, Frank, and Scott Bachman. "Isohaline Salinity Budget of the North Atlantic Salinity Maximum." Journal of Physical Oceanography 45, no. 3 (March 2015): 724–36. http://dx.doi.org/10.1175/jpo-d-14-0172.1.
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AbstractIn this study, the salinity budget of the North Atlantic subtropical salinity maximum region for control volumes bounded by isohaline surfaces is analyzed. The authors provide closed budgets based on output from a high-resolution numerical simulation and partial budgets based on analyses of observational climatologies of hydrography and surface fluxes. With this choice of control volume, advection is eliminated from the instantaneous volume-integrated salt budget, and time-mean advection is eliminated from the budget evaluated from time-averaged data. In this way, the role of irreversible mixing processes in the maintenance and variability of the salinity maximum are more readily revealed. By carrying out the analysis with both near-instantaneous and time-averaged model output, the role of mesoscale eddies in stirring and mixing for this water mass is determined. This study finds that the small-scale mixing acting on enhanced gradients generated by the mesoscale eddies is approximately equal to that acting on the large-scale gradients estimated from climatological-mean conditions. The isohaline salinity budget can be related to water mass transformation rates associated with surface forcing and mixing processes in a straightforward manner. The authors find that the surface net evaporation in the North Atlantic salinity maximum region accounts for a transformation of 7 Sverdrups (Sv; 1 Sv ≡ 106 m3 s−1) of water across the 37-psu isohaline outcrop into the salinity maximum in the simulation, whereas the estimate based on climatological observations is 9 to 10 Sv.
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D’Addezio, Joseph M., Bulusu Subrahmanyam, Ebenezer S. Nyadjro, and V. S. N. Murty. "Seasonal Variability of Salinity and Salt Transport in the Northern Indian Ocean." Journal of Physical Oceanography 45, no. 7 (July 2015): 1947–66. http://dx.doi.org/10.1175/jpo-d-14-0210.1.
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AbstractAnalyses using a suite of observational datasets (Aquarius and Argo) and model simulations are carried out to examine the seasonal variability of salinity in the northern Indian Ocean (NIO). The model simulations include Estimating the Circulation and Climate of the Ocean, Phase II (ECCO2), the European Centre for Medium-Range Weather Forecasts–Ocean Reanalysis System 4 (ECMWF–ORAS4), Simple Ocean Data Assimilation (SODA) reanalysis, and the Hybrid Coordinate Ocean Model (HYCOM). The analyses of salinity at the surface and at depths up to 200 m, surface salt transport in the top 5-m layer, and depth-integrated salt transports revealed different salinity processes in the NIO that are dominantly related to the semiannual monsoons. Aquarius proves a useful tool for observing this dynamic region and reveals some aspects of sea surface salinity (SSS) variability that Argo cannot resolve. The study revealed large disagreement between surface salt transports derived from observed- and analysis-derived salinity fields. Although differences in SSS between the observations and the model solutions are small, model simulations provide much greater spatial variability of surface salt transports due to finer detailed current structure. Meridional depth-integrated salt transports along 6°N revealed dominant advective processes from the surface toward near-bottom depths. In the Arabian Sea (Bay of Bengal), the net monthly mean maximum northward (southward) salt transport of ~50 × 106 kg s −1 occurs in July, and annual-mean salt transports across this section are about −2.5 × 106 kg s −1 (3 × 106 kg s −1).
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Terray, Laurent, Lola Corre, Sophie Cravatte, Thierry Delcroix, Gilles Reverdin, and Aurélien Ribes. "Near-Surface Salinity as Nature’s Rain Gauge to Detect Human Influence on the Tropical Water Cycle." Journal of Climate 25, no. 3 (February 1, 2012): 958–77. http://dx.doi.org/10.1175/jcli-d-10-05025.1.
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Abstract Changes in the global water cycle are expected as a result of anthropogenic climate change, but large uncertainties exist in how these changes will be manifest regionally. This is especially the case over the tropical oceans, where observed estimates of precipitation and evaporation disagree considerably. An alternative approach is to examine changes in near-surface salinity. Datasets of observed tropical Pacific and Atlantic near-surface salinity combined with climate model simulations are used to assess the possible causes and significance of salinity changes over the late twentieth century. Two different detection methodologies are then applied to evaluate the extent to which observed large-scale changes in near-surface salinity can be attributed to anthropogenic climate change. Basin-averaged observed changes are shown to enhance salinity geographical contrasts between the two basins: the Pacific is getting fresher and the Atlantic saltier. While the observed Pacific and interbasin-averaged salinity changes exceed the range of internal variability provided from control climate simulations, Atlantic changes are within the model estimates. Spatial patterns of salinity change, including a fresher western Pacific warm pool and a saltier subtropical North Atlantic, are not consistent with internal climate variability. They are similar to anthropogenic response patterns obtained from transient twentieth- and twenty-first-century integrations, therefore suggesting a discernible human influence on the late twentieth-century evolution of the tropical marine water cycle. Changes in the tropical and midlatitudes Atlantic salinity levels are not found to be significant compared to internal variability. Implications of the results for understanding of the recent and future marine tropical water cycle changes are discussed.
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Busecke, Julius, Ryan P. Abernathey, and Arnold L. Gordon. "Lateral Eddy Mixing in the Subtropical Salinity Maxima of the Global Ocean." Journal of Physical Oceanography 47, no. 4 (April 2017): 737–54. http://dx.doi.org/10.1175/jpo-d-16-0215.1.
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AbstractA suite of observationally driven model experiments is used to investigate the contribution of near-surface lateral eddy mixing to the subtropical surface salinity maxima in the global ocean. Surface fields of salinity are treated as a passive tracer and stirred by surface velocities derived from altimetry, leading to irreversible water-mass transformation. In the absence of surface forcing and vertical processes, the transformation rate can be directly related to the integrated diffusion across tracer contours, which is determined by the observed velocities. The destruction rates of the salinity maxima by lateral mixing can be compared to the production rates by surface forcing, which act to strengthen the maxima. The ratio of destruction by eddy mixing in the surface layer versus the surface forcing exhibits regional differences in the mean—from 10% in the South Pacific to up to 25% in the south Indian. Furthermore, the regional basins show seasonal and interannual variability in eddy mixing. The dominant mechanism for this temporal variability varies regionally. Most notably, the North Pacific shows a large sensitivity to the background salinity fields and a weak sensitivity to the velocity fields, while the North Atlantic exhibits the opposite behavior. The different mechanism for temporal variability could have impacts on the manifestation of a changing hydrological cycle in the sea surface salinity (SSS) field specifically in the North Pacific. The authors find evidence for large-scale interannual changes of eddy diffusivity and transformation rate in several ocean basins that could be related to large-scale climate forcing.
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Kido, Shoichiro, and Tomoki Tozuka. "Salinity Variability Associated with the Positive Indian Ocean Dipole and Its Impact on the Upper Ocean Temperature." Journal of Climate 30, no. 19 (September 1, 2017): 7885–907. http://dx.doi.org/10.1175/jcli-d-17-0133.1.
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Abstract Both surface and subsurface salinity variability associated with positive Indian Ocean dipole (pIOD) events and its impacts on the sea surface temperature (SST) evolution are investigated through analysis of observational/reanalysis data and sensitivity experiments with a one-dimensional mixed layer model. During the pIOD, negative (positive) sea surface salinity (SSS) anomalies appear in the central-eastern equatorial Indian Ocean (southeastern tropical Indian Ocean). In addition to these SSS anomalies, positive (negative) salinity anomalies are found near the pycnocline in the eastern equatorial Indian Ocean (southern tropical Indian Ocean). A salinity balance analysis shows that these subsurface salinity anomalies are mainly generated by zonal and vertical salt advection anomalies induced by anomalous currents associated with the pIOD. These salinity anomalies stabilize (destabilize) the upper ocean stratification in the central-eastern equatorial (southeastern tropical) Indian Ocean. By decomposing observed densities into contribution from temperature and salinity anomalies, it is shown that the contribution from anomalous salinity stratification is comparable to that from anomalous thermal stratification. Furthermore, impacts of these salinity anomalies on the SST evolution are quantified for the first time using a one-dimensional mixed layer model. Since enhanced salinity stratification in the central-eastern equatorial Indian Ocean suppresses vertical mixing, significant warming of about 0.3°–0.5°C occurs. On the other hand, stronger vertical mixing associated with reduced salinity stratification results in significant SST cooling of about 0.2°–0.5°C in the southeastern tropical Indian Ocean. These results suggest that variations in salinity may potentially play a crucial role in the evolution of the pIOD.
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Lund, David C., and William Curry. "Florida Current surface temperature and salinity variability during the last millennium." Paleoceanography 21, no. 2 (May 5, 2006): n/a. http://dx.doi.org/10.1029/2005pa001218.
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Häkkinen, Sirpa. "Surface salinity variability in the northern North Atlantic during recent decades." Journal of Geophysical Research: Oceans 107, no. C12 (September 18, 2002): SRF 4–1—SRF 4–12. http://dx.doi.org/10.1029/2001jc000812.
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Chao, Yi, John D. Farrara, Guy Schumann, Konstantinos M. Andreadis, and Delwyn Moller. "Sea surface salinity variability in response to the Congo river discharge." Continental Shelf Research 99 (May 2015): 35–45. http://dx.doi.org/10.1016/j.csr.2015.03.005.
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Świątek, Małgorzata. "Long-term variability of water temperature and salinity at the Polish coast." Bulletin of Geography. Physical Geography Series 16, no. 1 (June 18, 2019): 115–30. http://dx.doi.org/10.2478/bgeo-2019-0008.
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Abstract The variability of surface water temperature and water salinity at the south coast of the Baltic in the years 1950–2015 was studied in the article. To that aim, monthly surface water temperature values in Świnoujście, Międzyzdroje, Kołobrzeg (from 1957), Władysławowo, Hel and Gdynia were used, as well as monthly water salinity values in Międzyzdroje, Władysławowo, Hel and Gdynia, all obtained from IMGW-PIB (Institute of Meteorology and Water Management – National Research Institute). Linear regression and Pearson’s simple correlation coefficient of individual monthly, seasonal and annual series of temperature and salinity values over time (in subsequent years) were used to analyse the temporal changes of the examined parameters. In the analysed period a rise in the annual water temperature was recorded in Międzyzdroje, Władysławowo, Hel and Gdynia, while the extent of the changes increased towards the east. There were also positive trends in temperature values in individual months. At the same time, there was a decrease in water salinity, which was also found to be most distinct in the eastern part of the coast. In Władysławowo, Hel and Gdynia, statistically significant drops occurred in nearly all months. During the months featuring statistically insignificant trends, the observed change trends were also negative. Concurrent water temperature increases and water salinity decreases consequently caused a decline in sea water surface density at the Polish Baltic coast.
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Reverdin, Gilles, Hedinn Valdimarsson, Gael Alory, Denis Diverres, Francis Bringas, Gustavo Goni, Lars Heilmann, Leon Chafik, Tanguy Szekely, and Andrew R. Friedman. "North Atlantic subpolar gyre along predetermined ship tracks since 1993: a monthly data set of surface temperature, salinity, and density." Earth System Science Data 10, no. 3 (August 1, 2018): 1403–15. http://dx.doi.org/10.5194/essd-10-1403-2018.
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Abstract. We present a binned product of sea surface temperature, sea surface salinity, and sea surface density data in the North Atlantic subpolar gyre from 1993 to 2017 that resolves seasonal variability along specific ship routes (https://doi.org/10.6096/SSS-BIN-NASG). The characteristics of this product are described and validated through comparisons to other monthly products. Data presented in this work were collected in regions crossed by two predetermined ship transects, between Denmark and western Greenland (AX01) and between Iceland, Newfoundland, and the northeastern USA (AX02). The data were binned along a selected usable transect. The analysis and the strong correlation between successive seasons indicate that in large parts of the subpolar gyre, the binning approach is robust and resolves the seasonal timescales, in particular after 1997 and in regions away from the continental shelf. Prior to 2002, there was no winter sampling over the West Greenland Shelf. Variability in sea surface salinity increases towards Newfoundland south of 54∘ N, as well as in the western Iceland Basin along 59∘ N. Variability in sea surface temperature presents less spatial structure with an increase westward and towards Newfoundland. The contribution of temperature variability to density dominates in the eastern part of the gyre, whereas the contribution of salinity variability dominates in the southwestern part along AX02.
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Mannshardt, Elizabeth, Katarina Sucic, Montserrat Fuentes, and Frederick M. Bingham. "Comparison of Distributional Statistics of Aquarius and Argo Sea Surface Salinity Measurements." Journal of Atmospheric and Oceanic Technology 33, no. 1 (January 2016): 103–18. http://dx.doi.org/10.1175/jtech-d-15-0068.1.
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AbstractSalinity is an indicator of the interaction between ocean circulation and the global water cycle, which in turn affects the regulation of the earth’s climate. To thoroughly understand sea surface salinity’s connection to processes that define the hydrological cycle, such as surface forcing and ocean mixing, there is need for proper validation of remotely sensed salinity products with independent measurements, beyond central tendencies, across the entire distribution of salinity. Because of its fine spatial and temporal coverage, Aquarius presents an ideal measurement system for fully characterizing the distribution and properties of sea surface salinity. Using the first 33 months of Aquarius, version 3.0, level 2 sea surface salinity data, both central tendencies and distributional quantile characteristics across time and space are investigated, and a statistical validation of Aquarius measurements with Argo in situ observations is conducted. Several aspects are considered, including regional characteristics and temporal agreement, as well as seasonal differences by ocean basin and hemisphere. Regional studies examine the time and space scales of variability through time series comparisons and an analysis of quantile properties. Results indicate that there are significant differences between the tails of their respective distributions, especially the lower tail. The Aquarius data show longer, fatter lower tails, indicating higher probability to sample low-salinity events. There is also evidence of differences in measurement variation between Aquarius and Argo. These results are seen across seasons, ocean basins, hemispheres, and regions.
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Thadathil, Pankajakshan, Prasad Thoppil, R. R. Rao, P. M. Muraleedharan, Y. K. Somayajulu, V. V. Gopalakrishna, Raghu Murtugudde, G. V. Reddy, and C. Revichandran. "Seasonal Variability of the Observed Barrier Layer in the Arabian Sea*." Journal of Physical Oceanography 38, no. 3 (March 1, 2008): 624–38. http://dx.doi.org/10.1175/2007jpo3798.1.
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Abstract The formation mechanisms of the barrier layer (BL) and its seasonal variability in the Arabian Sea (AS) are studied using a comprehensive dataset of temperature and salinity profiles from Argo and other archives for the AS. Relatively thick BL of 20–60 m with large spatial extent is found in the central-southwestern AS (CSWAS), the convergence zone of the monsoon wind, during the peak summer monsoon (July–August) and in the southeastern AS (SEAS) and northeastern AS (NEAS) during the winter (January–February). Although the BL in the SEAS has been reported before, the observed thick BL in the central-southwestern AS during the peak summer monsoon and in the northeastern AS during late winter are the new findings of this study. The seasonal variability of BL thickness (BLT) is closely related to the processes that occur during summer and winter monsoons. During both seasons, the Ekman processes and the distribution of low-salinity waters in the surface layer show a dominant influence on the observed BLT distributions. In addition, Kelvin and Rossby waves also modulate the observed BL thickness in the AS. The relatively low salinity surface water overlying the Arabian Sea high-salinity water (ASHSW) provides an ideal ground for strong haline stratification in the CSWAS (during summer monsoon) and in NEAS (during winter monsoon). During summer, northward advection of equatorial low-salinity water by the Somali Current and the offshore advection of low-salinity water from the upwelling region facilitate the salinity stratification that is necessary to develop the observed BL in the CSWAS. In the SEAS, during winter, the winter monsoon current (WMC) carries less saline water over relatively high salinity ambient water to form the observed BL there. The winter West India Coastal Current (WICC) transports the low-salinity water from the SEAS to the NEAS, where it lies over the subducted ASHSW leading to strong haline stratification. Ekman pumping together with the downwelling Kelvin wave in the NEAS deepen the thermocline to cause the observed thick BL in the NEAS.
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Schneider, Niklas, Emanuele Di Lorenzo, and Pearn P. Niiler. "Salinity Variations in the Southern California Current*." Journal of Physical Oceanography 35, no. 8 (August 1, 2005): 1421–36. http://dx.doi.org/10.1175/jpo2759.1.
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Abstract Hydrographic observations southwestward of the Southern California Bight in the period 1937–99 show that temperature and salinity variations have very different interannual variability. Temperature varies within and above the thermocline and is correlated with climate indices of El Niño, the Pacific decadal oscillation, and local upwelling. Salinity variability is largest in the surface layers of the offshore salinity minimum and is characterized by decadal-time-scale changes. The salinity anomalies are independent of temperature, of heave of the pycnocline, and of the climate indices. Calculations demonstrate that long-shore anomalous geostrophic advection of the mean salinity gradient accumulates along the mean southward trajectory along the California Current and produces the observed salinity variations. The flow anomalies for this advective process are independent of large-scale climate indices. It is hypothesized that low-frequency variability of the California Current system results from unresolved, small-scale atmospheric forcing or from the ocean mesoscale upstream of the Southern California Bight.
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Trott, Corinne B., Bulusu Subrahmanyam, Heather L. Roman-Stork, V. S. N. Murty, and C. Gnanaseelan. "Variability of Intraseasonal Oscillations and Synoptic Signals in Sea Surface Salinity in the Bay of Bengal." Journal of Climate 32, no. 20 (September 11, 2019): 6703–28. http://dx.doi.org/10.1175/jcli-d-19-0178.1.
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Abstract Intraseasonal oscillations (ISOs) significantly impact southwest monsoon precipitation and Bay of Bengal (BoB) variability. The response of ISOs in sea surface salinity (SSS) to those in the atmosphere is investigated in the BoB from 2005 to 2017. The three intraseasonal processes examined in this study are the 30–90-day and 10–20-day ISOs and 3–7-day synoptic weather signals. A variety of salinity data from NASA’s Soil Moisture Active Passive (SMAP) and the European Space Agency’s (ESA’s) Soil Moisture and Ocean Salinity (SMOS) satellite missions and from reanalysis using the Hybrid Coordinate Ocean Model (HYCOM) and operational analysis of Climate Forecast System version 2 (CFSv2) were utilized for the study. It is found that the 30–90-day ISO salinity signal propagates northward following the northward propagation of convection and precipitation ISOs. The 10–20-day ISO in SSS and precipitation deviate largely in the northern BoB wherein the river runoff largely impacts the SSS. The weather systems strongly impact the 3–7-day signal in SSS prior to and after the southwest monsoon. Overall, we find that satellite salinity products captured better the SSS signal of ISO due to inherent inclusion of river runoff and mixed layer processes. CFSv2, in particular, underestimates the SSS signal due to the misrepresentation of river runoff in the model. This study highlights the need to include realistic riverine freshwater influx for better model simulations, as accurate salinity simulation is mandatory for the representation of air–sea coupling in models.
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Henocq, Claire, Jacqueline Boutin, Gilles Reverdin, François Petitcolin, Sabine Arnault, and Philippe Lattes. "Vertical Variability of Near-Surface Salinity in the Tropics: Consequences for L-Band Radiometer Calibration and Validation." Journal of Atmospheric and Oceanic Technology 27, no. 1 (January 1, 2010): 192–209. http://dx.doi.org/10.1175/2009jtecho670.1.
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Abstract Two satellite missions are planned to be launched in the next two years; the European Space Agency (ESA) Soil Moisture and Ocean Salinity (SMOS) and the National Aeronautics and Space Administration (NASA) Aquarius missions aim at detecting sea surface salinity (SSS) using L-band radiometry (1.4 GHz). At that frequency, the skin depth is on the order of 1 cm. However, the calibration and validation of L-band-retrieved SSS will be done with in situ measurements, mainly taken at 5-m depth. To anticipate and understand vertical salinity differences in the first 10 m of the ocean surface layer, in situ vertical profiles are analyzed. The influence of rain events is studied. Tropical Atmosphere Ocean (TAO) moorings, the most comprehensive dataset, provide measurements of salinity taken simultaneously at 1, 5, and 10 m and measurements of rain rate. Then, observations of vertical salinity differences, sorted according to their vertical levels, are expanded through the tropical band (30°S–30°N) using thermosalinographs (TSG), floats, expendable conductivity–temperature–depth (XCTD), and CTD data. Vertical salinity differences higher than 0.1 pss are observed in the Pacific, Atlantic, and Indian Oceans, mainly between 0° and 15°N, which coincides with the average position of the intertropical convergence zone (ITCZ). Some differences exceed 0.5 pss locally and persist for more than 10 days. A statistical approach is developed for the detection of large vertical salinity differences, knowing the history of rain events and the simultaneous wind intensity, as estimated from satellite measurements.
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Sosnin, Valery A., and Natalia I. Rudykh. "Salinity minimum in the subsurface layers of the Japan Sea." Izvestiya TINRO 180, no. 1 (March 30, 2015): 236–47. http://dx.doi.org/10.26428/1606-9919-2015-180-236-247.
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Seasonal variability of vertical salinity distribution in the Japan Sea is considered. On the base of high accuracy data from the databases WODC-2013 (USA), JODC (Japan), and the databases of Far-Eastern State Hydrometeorological Institute and Pacific Oceanological Institute (Russia), several cases of salinity minimums are analyzed and interpreted taking into account seasonal variability of salinity profiles. High vertical homogeneity by salinity is noted for the Japan Sea waters, and the subsurface salinity minimum can be considered as a result of continuous changes of freshwater balance. It could be formed in the layers from the sea surface to 150-250 m as a temporary local extreme caused by prevalence of evaporation over precipitation on the sea surface in some seasons - that’s why it is observed seasonally. There is concluded that such conservative patterns as water masses are absent in the sea, at least in its active upper layers, but vertical salinity profiles are changing permanently under influence of changing freshwater fluxes, and their extremes appear or disappear in compliance with the dialectic laws.
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Bingham, F. M., G. R. Foltz, and M. J. McPhaden. "Seasonal cycles of surface layer salinity in the Pacific Ocean." Ocean Science 6, no. 3 (August 24, 2010): 775–87. http://dx.doi.org/10.5194/os-6-775-2010.
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Abstract. The seasonal variability of surface layer salinity (SLS) is examined in the Pacific Ocean between 40° S and 60° N using a variety of data sources. Significant seasonal cycles were found in 5 regions: 1) The western North Pacific, 2) The northeastern North Pacific and Alaska gyre, 3) the intertropical convergence zone (ITCZ), 4) an area of the central North Pacific north of the Hawaiian Islands, 5) the central South Pacific along 10–20° S. Amplitudes range from 0.1 to > 0.5. The largest amplitudes are in the tropical band and the western North Pacific. Maximum salinity is obtained in late (northern) winter in the western North Pacific, late winter and early spring in the northeastern North Pacific, early summer in the ITCZ area, late summer and early fall in the central North Pacific area and (austral) winter in the central South Pacific. Large areas of the Pacific have no significant seasonal variation in SLS. Seasonal variability of evaporation rate, precipitation rate and the difference between them (E-P) were calculated from the OAFlux and Global Precipitation Climatology Project datasets. Typical amplitudes of E-P are 0.1–1 × 10−4 kg m−2 s−1. The seasonal variability of E-P is largely dominated by variability in evaporation in the western North Pacific and precipitation elsewhere. The largest amplitudes are in areas along the edge of the western North Pacific and in the far eastern tropical Pacific around 10° N. Phases in these areas indicate maximum E-P in mid- to late winter in these areas of large amplitude. The closest correspondence between E-P and SLS is in the ITCZ. E-P was combined with seasonal variation of the mixed-layer depth to calculate the freshwater flux forcing term of the SLS balance equation. The term was found to be similar in magnitude and distribution to E-P. Some other terms of the SLS balance were calculated. Horizontal advection was found to have seasonal cycles in a region near the equator. Entrainment was found to be mostly not significant except for a small region along 2.5–7.5° N in the eastern Pacific. Averaged spatially over large areas in the western North Pacific, ITCZ, South Pacific and northern North Pacific, the seasonal cycle is mostly a balance between changes in SLS and E-P, with entrainment and advection playing relatively minor roles. This work highlights the potentially significant role of surface salinity in the hydrologic cycle and in subtropical mode water formation. It can also help to interpret measurements that will soon be available from the Aquarius and SMOS (Soil Moisture and Ocean Salinity) satellite missions.
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Jury, Mark R. "Long-Term Variability and Trends in the Caribbean Sea." International Journal of Oceanography 2011 (March 2, 2011): 1–9. http://dx.doi.org/10.1155/2011/465810.
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Upper ocean conditions in the Caribbean Sea are studied for long-term variability and trends using filtered surface observations and ocean model reanalysis fields. A principal component analysis is made, and trends in the leading mode are extracted. Sea surface temperature shows an accelerating upward trend while air pressure exhibits quasidecadal fluctuations. Sea surface height and subsurface temperature rise linearly while subsurface salinity exhibits fresher upper and saltier lower layers. The amplitude of warming is highest in the southern Caribbean east of 75°W near 150 m and lowest near the surface, indicating little role for a top-down process such as air-sea exchange. The freshening surface layer does not appear connected to river discharge or regional rainfall, so changes in ocean advection and sources are the likely drivers. Westward currents exhibit a reduction of throughflow and an influx from the Windward Passage. The Caribbean Current has slowed ~0.06 m/s in the reanalysis era. Crop yields show little sensitivity to ocean conditions but tend to follow rainfall. Marine catch per capita in the Caribbean follows subsurface currents and vertical motion but is less affected by temperature and salinity.
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Katsura, Shota, Eitarou Oka, Bo Qiu, and Niklas Schneider. "Formation and Subduction of North Pacific Tropical Water and Their Interannual Variability." Journal of Physical Oceanography 43, no. 11 (November 1, 2013): 2400–2415. http://dx.doi.org/10.1175/jpo-d-13-031.1.
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Abstract Formation and subduction of the North Pacific Tropical Water (NPTW), its interannual variability, and its associated mechanisms were investigated by using gridded Argo-profiling float data and various surface flux data in 2003–11. The NPTW has two formation sites in the center of the North Pacific subtropical gyre, corresponding to two regional sea surface salinity maxima. Mixed layer salinity variations in these two NPTW formation sites were found to be significantly different. While seasonal variation was prominent in the eastern formation site, interannual variation was dominant in the western site. The mixed layer salinity variation in the eastern site was controlled mainly by evaporation, precipitation, and entrainment of fresher water below the mixed layer and was closely related to the seasonal variation of the mixed layer depth. In the western site, the effect of entrainment is small due to a small vertical difference in salinity across the mixed layer base, and excess evaporation over precipitation that tended to be balanced by eddy diffusion, whose strength varied interannually in association with the Pacific decadal oscillation. After subduction, denser NPTW that formed in the eastern site dissipated quickly, while the lighter one that formed in the western site was advected westward as far as the Philippine Sea, transmitting the interannual variation of salinity away from its formation region.
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Bingham, Frederick M., and Zhijin Li. "Spatial Scales of Sea Surface Salinity Subfootprint Variability in the SPURS Regions." Remote Sensing 12, no. 23 (December 6, 2020): 3996. http://dx.doi.org/10.3390/rs12233996.
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Subfootprint variability (SFV), or representativeness error, is variability within the footprint of a satellite that can impact validation by comparison of in situ and remote sensing data. This study seeks to determine the size of the sea surface salinity (SSS) SFV as a function of footprint size in two regions that were heavily sampled with in situ data. The Salinity Processes in the Upper-ocean Regional Studies-1 (SPURS-1) experiment was conducted in the subtropical North Atlantic in the period 2012–2013, whereas the SPURS-2 study was conducted in the tropical eastern North Pacific in the period 2016–2017. SSS SFV was also computed using a high-resolution regional model based on the Regional Ocean Modeling System (ROMS). We computed SFV at footprint sizes ranging from 20 to 100 km for both regions. SFV is strongly seasonal, but for different reasons in the two regions. In the SPURS-1 region, the meso- and submesoscale variability seemed to control the size of the SFV. In the SPURS-2 region, the SFV is much larger than SPURS-1 and controlled by patchy rainfall.
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Zhang, Rong, and Geoffrey K. Vallis. "Impact of Great Salinity Anomalies on the Low-Frequency Variability of the North Atlantic Climate." Journal of Climate 19, no. 3 (February 1, 2006): 470–82. http://dx.doi.org/10.1175/jcli3623.1.
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Abstract In this paper, it is shown that coherent large-scale low-frequency variabilities in the North Atlantic Ocean—that is, the variations of thermohaline circulation, deep western boundary current, northern recirculation gyre, and Gulf Stream path—are associated with high-latitude oceanic Great Salinity Anomaly events. In particular, a dipolar sea surface temperature anomaly (warming off the U.S. east coast and cooling south of Greenland) can be triggered by the Great Salinity Anomaly events several years in advance, thus providing a degree of long-term predictability to the system. Diagnosed phase relationships among an observed proxy for Great Salinity Anomaly events, the Labrador Sea sea surface temperature anomaly, and the North Atlantic Oscillation are also discussed.
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Boutin, J., J. L. Vergely, S. Marchand, F. D'Amico, A. Hasson, N. Kolodziejczyk, N. Reul, G. Reverdin, and J. Vialard. "New SMOS Sea Surface Salinity with reduced systematic errors and improved variability." Remote Sensing of Environment 214 (September 2018): 115–34. http://dx.doi.org/10.1016/j.rse.2018.05.022.
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D'Addezio, Joseph M., Frederick M. Bingham, and Gregg A. Jacobs. "Sea surface salinity subfootprint variability estimates from regional high-resolution model simulations." Remote Sensing of Environment 233 (November 2019): 111365. http://dx.doi.org/10.1016/j.rse.2019.111365.
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Tomczak, Matthias. "Salinity variability in the surface layer of the tropical western Pacific Ocean." Journal of Geophysical Research 100, no. C10 (1995): 20499. http://dx.doi.org/10.1029/95jc01544.
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Pant, Vimlesh, M. S. Girishkumar, T. V. S. Udaya Bhaskar, M. Ravichandran, Fabrice Papa, and V. P. Thangaprakash. "Observed interannual variability of near-surface salinity in the Bay of Bengal." Journal of Geophysical Research: Oceans 120, no. 5 (May 2015): 3315–29. http://dx.doi.org/10.1002/2014jc010340.
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Hall, A., and S. Manabe. "Can local linear stochastic theory explain sea surface temperature and salinity variability?" Climate Dynamics 13, no. 3 (March 26, 1997): 167–80. http://dx.doi.org/10.1007/s003820050158.
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Yang, M., S. L. Liu, Z. F. Yang, T. Sun, and Robert Beazley. "Multivariate and geostatistical analysis of wetland soil salinity in nested areas of the Yellow River Delta." Soil Research 47, no. 5 (2009): 486. http://dx.doi.org/10.1071/sr08211.
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This study investigated scale dependency of certain soil salinity ions in topsoil horizons in the Yellow River Delta in north-east Shandong province, China. Factorial kriging analysis (FKA) was used to analyse spatial variability of soil salinity ions (Na+, K+, Mg2+, Ca2+, Cl–, SO42–) sampled at 3 nested areas over a geologically contrasting region. Correlation analysis and principal component analysis (PCA) were performed on the logarithmic variables, then multivariate geostatistics was used to investigate scale dependency of soil salinity spatial variability and auto- and cross-variograms exhibited by 3 spatial structures: nugget effect, short-range, and long-range structures. Statistical analysis showed that NaCl was the main salinity type over the 3 nested sample areas. In addition, the variables were random and regional, which implied that a linear model of coregionalisation was feasible for the analysis of their spatial variability. The coefficients of the coregionalisation matrix showed that the short-range structures of auto- and cross-correlation for soil salinity were dominant at the large and middle-sized sample areas, while the long-range structure dominated at the small area. The resulting structural correlation coefficients showed strong correlations between variables changing as a function of spatial scale. These relationships between soil salinity variables at different spatial structures were not acquired by the linear correlation coefficients. PCA was then performed on the coregionalisation matrices at each sample area to summarise the relationships among variables at different spatial structures. From the synthetic analysis of coregionalisation matrices, correlation matrices, and principal components, we concluded that soil genesis and parent material may act on short-range variation of soil salinity, while climate and topography may influence long-range structure at the large sample area. At the middle-sized sample area, variations were mostly affected by mineral fertilisation at the short-range structure, while human activities such as irrigation and drainage in wetland restorations influenced the soil salinity spatial variability at the long-range scale. Vegetation and groundwater table may also be important factors influencing the spatial variability of soil salinity at different spatial structures at the small sample areas.
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Weller, R. A., J. T. Farrar, Hyodae Seo, Channing Prend, Debasis Sengupta, J. Sree Lekha, M. Ravichandran, and R. Venkatesen. "Moored Observations of the Surface Meteorology and Air–Sea Fluxes in the Northern Bay of Bengal in 2015." Journal of Climate 32, no. 2 (December 28, 2018): 549–73. http://dx.doi.org/10.1175/jcli-d-18-0413.1.
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Abstract Time series of surface meteorology and air–sea fluxes from the northern Bay of Bengal are analyzed, quantifying annual and seasonal means, variability, and the potential for surface fluxes to contribute significantly to variability in surface temperature and salinity. Strong signals were associated with solar insolation and its modulation by cloud cover, and, in the 5- to 50-day range, with intraseasonal oscillations (ISOs). The northeast (NE) monsoon (DJF) was typically cloud free, with strong latent heat loss and several moderate wind events, and had the only seasonal mean ocean heat loss. The spring intermonsoon (MAM) was cloud free and had light winds and the strongest ocean heating. Strong ISOs and Tropical Cyclone Komen were seen in the southwest (SW) monsoon (JJA), when 65% of the 2.2-m total rain fell, and oceanic mean heating was small. The fall intermonsoon (SON) initially had moderate convective systems and mean ocean heating, with a transition to drier winds and mean ocean heat loss in the last month. Observed surface freshwater flux applied to a layer of the observed thickness produced drops in salinity with timing and magnitude similar to the initial drops in salinity in the summer monsoon, but did not reproduce the salinity variability of the fall intermonsoon. Observed surface heat flux has the potential to cause the temperature trends of the different seasons, but uncertainty in how shortwave radiation is absorbed in the upper ocean limits quantifying the role of surface forcing in the evolution of mixed layer temperature.
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Cheng, Lijing, Kevin E. Trenberth, Nicolas Gruber, John P. Abraham, John T. Fasullo, Guancheng Li, Michael E. Mann, Xuanming Zhao, and Jiang Zhu. "Improved Estimates of Changes in Upper Ocean Salinity and the Hydrological Cycle." Journal of Climate 33, no. 23 (December 2020): 10357–81. http://dx.doi.org/10.1175/jcli-d-20-0366.1.
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AbstractOcean salinity records the hydrological cycle and its changes, but data scarcity and the large changes in sampling make the reconstructions of long-term salinity changes challenging. Here, we present a new observational estimate of changes in ocean salinity since 1960 from the surface to 2000 m. We overcome some of the inconsistencies present in existing salinity reconstructions by using an interpolation technique that uses information on the spatiotemporal covariability of salinity taken from model simulations. The interpolation technique is comprehensively evaluated using recent Argo-dominated observations through subsample tests. The new product strengthens previous findings that ocean surface and subsurface salinity contrasts have increased (i.e., the existing salinity pattern has amplified). We quantify this contrast by assessing the difference between the salinity in regions of high and low salinity averaged over the top 2000 m, a metric we refer to as SC2000. The increase in SC2000 is highly distinguishable from the sampling error and less affected by interannual variability and sampling error than if this metric was computed just for the surface. SC2000 increased by 1.9% ± 0.6% from 1960 to 1990 and by 3.3% ± 0.4% from 1991 to 2017 (5.2% ± 0.4% for 1960–2017), indicating an acceleration of the pattern amplification in recent decades. Combining this estimate with model simulations, we show that the change in SC2000 since 1960 emerges clearly as an anthropogenic signal from the natural variability. Based on the salinity-contrast metrics and model simulations, we find a water cycle amplification of 2.6% ± 4.4% K−1 since 1960, with the larger error than salinity metric mainly being due to model uncertainty.
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Hu, Shijian, Ying Zhang, Ming Feng, Yan Du, Janet Sprintall, Fan Wang, Dunxin Hu, Qiang Xie, and Fei Chai. "Interannual to Decadal Variability of Upper-Ocean Salinity in the Southern Indian Ocean and the Role of the Indonesian Throughflow." Journal of Climate 32, no. 19 (August 29, 2019): 6403–21. http://dx.doi.org/10.1175/jcli-d-19-0056.1.
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Abstract Variability of oceanic salinity, an indicator of the global hydrological cycle, plays an important role in the basin-scale ocean circulation. In this study, interannual to decadal variability of salinity in the upper layer of the Indian Ocean is investigated using Argo observations since 2004 and data assimilating model outputs (1992–2015). The southeastern Indian Ocean shows the strongest interannual to decadal variability of upper-ocean salinity in the Indian Ocean. Westward propagation of salinity anomalies along isopycnal surfaces is detected in the southern Indian Ocean and attributed to zonal salinity advection anomalies associated with the Indonesian Throughflow and the South Equatorial Current. Composite and salinity budget analyses show that horizontal advection is a major contributor to the interannual to decadal salinity variability of the southern Indian Ocean, and the local air–sea freshwater flux plays a secondary role. The Pacific decadal oscillation (PDO) and El Niño–Southern Oscillation (ENSO) modulate the salinity variability in the southeastern Indian Ocean, with low salinity anomalies occurring during the negative phases of the PDO and ENSO and high salinity anomalies during their positive phases. The Indonesian Throughflow plays an essential role in transmitting the PDO- and ENSO-related salinity signals into the Indian Ocean. A statistical model is proposed based on the PDO index, which successfully predicts the southeastern Indian Ocean salinity variability with a lead time of 10 months.
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Yan, Youfang, Eric P. Chassignet, Yiquan Qi, and William K. Dewar. "Freshening of Subsurface Waters in the Northwest Pacific Subtropical Gyre: Observations and Dynamics." Journal of Physical Oceanography 43, no. 12 (December 1, 2013): 2733–51. http://dx.doi.org/10.1175/jpo-d-13-03.1.
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Abstract Subsurface salinity anomalies propagating between mid- and low latitudes along isopycnal surfaces have been shown to play an important role in modulating ocean and climate variability. In this study, a sustained freshening and southwestward propagation of subsurface salinity anomalies in the northwest Pacific subtropical gyre and its dynamical mechanism are investigated using observations, numerical outputs, and a predictive model. Analyses of the observations show a pronounced subsurface freshening with salinity decreasing about 0.25 PSU near the 24.5-σθ surface in the northwest Pacific subtropical gyre during 2003–11. This freshening is found to be related to the surface forcing of salinity anomalies in the outcrop zone (25°–35°N, 130°–160°E). A predictive model based on the assumption of salinity conservation along the outcrop isopycnals is derived and used to examine this surface-forcing mechanism. The resemblance between the spatial structures of the subsurface salinity derived from the predictive model and from observations and numerical outputs suggests that subsurface salinity anomalies are ventilated over the outcrop zone. A salinity anomaly with an amplitude of about 0.25 PSU generated by the surface forcing is subducted in the outcrop zone and then propagates southwestward, accompanied by potential vorticity anomalies, to the east of Luzon Strait (~15°N) in roughly one year. When the anomalies reach 15°N, they turn and move gradually eastward toward the central Pacific, associated with an eastward countercurrent on the southern subtropical gyre.
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Plourde, Stéphane, Ian H. McQuinn, Frédéric Maps, Jean-François St-Pierre, Diane Lavoie, and Pierre Joly. "Daytime depth and thermal habitat of two sympatric krill species in response to surface salinity variability in the Gulf of St Lawrence, eastern Canada." ICES Journal of Marine Science 71, no. 2 (February 18, 2013): 272–81. http://dx.doi.org/10.1093/icesjms/fst023.
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Abstract Plourde, S., McQuinn, I. H., Maps, F., St-Pierre, J-F., Lavoie, D., and Joly, P. 2014. Daytime depth and thermal habitat of two sympatric krill species in response to surface salinity variability in the Gulf of St Lawrence, eastern Canada. – ICES Journal of Marine Science, 71: 272–281. We describe the response of acoustically determined weighted mean depth (WMD) of two sympatric species of krill, Thysanoessa raschii and Meganyctiphanes norvegica, to variations in surface salinity during summer in the Gulf of St Lawrence. In this coastal system, non-living particulates and CDOM carried by the freshwater run-off of the St Lawrence River and several large rivers have a strong impact on turbidity and light attenuance in the surface layer. The WMD of T. raschii and M. norvegica were significantly and positively related to surface salinity. However, M. norvegica was found deeper and in warmer water than T. raschii, and the latter had a steeper response to surface salinity. The species-specific relationships between daytime WMD and surface salinity enabled us to estimate both species regional and interannual variations in summertime temperature habitat during a 21-year period (1991–2011). The variability in daytime WMD resulted in significant inter- and intraspecific differences in the temperature experienced by adult krill that may impact development, growth, and reproduction. Our study illustrated the importance of considering species-specific responses to environmental forcing in coupled biophysical models that aim to explore the impacts of environmental variations on krill dynamics.
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Zhang, Zheen, Thomas Pohlmann, and Xueen Chen. "Correlation between subsurface salinity anomalies in the Bay of Bengal and the Indian Ocean Dipole and governing mechanisms." Ocean Science 17, no. 1 (March 3, 2021): 393–409. http://dx.doi.org/10.5194/os-17-393-2021.
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Abstract. Lead–lag correlations between the subsurface temperature and salinity anomalies in the Bay of Bengal (BoB) and the Indian Ocean Dipole (IOD) are revealed in model results, ocean synthesis, and observations. Mechanisms for such correlations are further investigated using the Hamburg Shelf Ocean Model (HAMSOM), mainly relating to the salinity variability. It is found that the subsurface salinity anomaly of the BoB positively correlates to the IOD, with a lag of 3 months on average, while the subsurface temperature anomaly correlates negatively. The model results suggest the remote forcing from the equatorial Indian Ocean dominates the interannual subsurface salinity variability in the BoB. The coastal Kelvin waves carry signals of positive (negative) salinity anomalies from the eastern equatorial Indian Ocean and propagate counterclockwise along the coasts of the BoB during positive (negative) IOD events. Subsequently, westward Rossby waves propagate these signals to the basin at a relatively slow speed, which causes a considerable delay of the subsurface salinity anomalies in the correlation. By analyzing the salinity budget of the BoB, it is found that diffusion dominates the salinity changes near the surface, while advection dominates the subsurface; the vertical advection of salinity contributes positively to this correlation, while the horizontal advection contributes negatively. These results suggest that the IOD plays a crucial role in the interannual subsurface salinity variability in the BoB.
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Moreau, M., T. Corrège, E. P. Dassié, and F. Le Cornec. "Evidence for the non-influence of salinity variability on the coral Sr/Ca paleothermometer." Climate of the Past Discussions 10, no. 2 (April 14, 2014): 1783–98. http://dx.doi.org/10.5194/cpd-10-1783-2014.
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Abstract. The influence of salinity in the incorporation of trace elements in the skeleton of calcareous organisms is still poorly known. Studies on foraminiferal Mg/Ca thermometry have suggested a bias due to Sea Surface Salinity (SSS) variations, leading to potential erroneous estimation of Mg/Ca-based Sea Surface Temperature (SST). Culture experiments seem to indicate that in three coral species (not including the widely used Porites genus), salinity does not influence the Sr/Ca thermometer. In this study, we test the salinity effect on coral Sr/Ca-based SST reconstructions at monthly and interannual timescales in open-ocean environmental conditions, using a large spatial compilation of published coral data (mainly based on the Porites genus) originating from the Western Pacific Ocean, the Atlantic Ocean, the Indian Ocean, the China Sea and the Red Sea and adding a new Eastern Pacific coral Sr/Ca record from the Clipperton atoll. We use simple and multiple regressions between Sr/Ca on one hand and SST and SSS on the other hand at the various sites. We find no evidence for a salinity bias on the Sr/Ca SST proxy for the two studied timescales. This study reinforces the use of coral Sr/Ca as a reliable paleothermometer.