SST) And Salinity Research Articles

Climate Variability, Coastal Livelihoods, and the Influence of Ocean Change on Fish Catch in the Coastal Savannah Zone of Ghana

Coastal zones, despite their contribution to global economies, continue to suffer the negative impacts of climate variability, which limit the livelihoods of people, particularly small-scale fishermen. This study examined climate variability, coastal livelihoods, and the influence of ocean change on the total annual fish catch in Ghana’s Coastal Savannah zone. The mixed-methods approach was used to analyze primary data (semi-structured questionnaires and interviews), secondary data (sea surface temperature (SST) and salinity (SSS), and fish catch), and statistical tests (chi-square, binary logistic regression, and multiple regression). Findings revealed a significant increase in climate variability awareness among fishermen, attributed to the influence of broadcast media. However, they lack sufficient information regarding the transformation of cities, the urbanization process, and its impact on the global climate. Increasing temperatures and sea level rise emerged as the most prevalent impacts of climate variability over the past two decades in the zone. Although the fishermen lack awareness regarding the changes in SSS and their effects on fish, the findings of the multiple regression analysis established that changes in SSS exert a more pronounced effect on the decreasing fishing catch in the zone compared to those in SST. Empirical fish catch records supported the fishermen’s claim of a substantial decrease in total fish catch in the zone over the past 20 years. Aside from climate variability impacts, the involvement of many people and light fishing emerged as additional factors contributing to the decreasing fish catch in the zone. High premix fuel prices or shortages and “saiko” activities were the main obstacles that hindered the fishermen’s activities. “Saiko” is an unlawful activity in which foreign industrial trawlers sell fish directly to Ghanaian canoes or small-scale fishermen at sea. The fishermen lack sufficient means of supporting their livelihoods, as there is a lack of viable alternative livelihood options. Additionally, the majority of the fishermen experience symptoms of fever and headaches. The binary logistic regression analysis showed that the fishermen’s income insufficiency could be substantially reduced if they were to have their own houses, canoes, or fish all year. This situation highlights the need for heightened support from policymakers for improved sustainable livelihood prospects as well as health and well-being.

Holocene sea surface temperature and salinity variations in the central South China Sea

The South China Sea (SCS) is sensitive to the East Asian monsoon (EAM) and changes in the Western Pacific. However, because of the difficulty of sampling and lack of data in the central SCS, many uncertainties remain the primary driving force of paleoclimatic variations. Here, a sediment core JL136, from the central SCS, was used to evaluate variations of sea surface temperature (SST) and salinity (SSS) during the Holocene, and then the corresponding influencing factors were analyzed, based on measured Mg/Ca ratio and stable isotopic compositions (δ18O and δ13C) of planktonic foraminifera Globigerinoides ruber sensu stricto (s.s.). The results show that the Mg/Ca-SST change is consistent with the speleothem δ18O records across most Asian monsoon regions on the Holocene long-term trend, revealing that the central SCS record is a response to the East Asian Summer Monsoon (EASM) intensity changes induced by Northern Hemisphere summer insolation (NHSI) variation. During the early Holocene (11.6–8.8 ka), SSS was low with an average of 32.7 psu, which may be related to palaeogeographic variations with sea level changes and the increased coastal water due to the opening of the Taiwan Strait. During the mid-late Holocene, high salinity ocean water was fully exchanged with the SCS due to the influence of high sea level, with an overall higher salinity in the SCS compared with the early Holocene (average 33.8 psu). In addition, the SSS broadly showed an increasing trend, which may be mainly controlled by the weakening EASM intensity and the decreasing precipitation during the low NHSI.

A 334-year coral record of surface temperature and salinity variability in the greater Agulhas Current region

Abstract. The Agulhas Current (AC) off the southern tip of Africa is one of the strongest western boundary currents and a crucial choke point of inter-ocean heat and salt exchange between the Indian Ocean and the southern Atlantic Ocean. However, large uncertainties remain concerning the sea surface temperature (SST) and salinity (SSS) variability in the AC region and their driving mechanisms over longer timescales, due to only short observational datasets being available and the highly dynamic nature of the region. Here, we present an annual coral skeletal Sr/Ca composite record paired with an established composite oxygen isotope record from Ifaty and Tulear reefs in southwestern Madagascar to obtain a 334-year (1661–1995) reconstruction of δ18Oseawater changes related to surface salinity variability in the wider Agulhas Current region. Our new annual δ18Oseawater composite record from Ifaty traces surface salinity of the southern Mozambique Channel and AC core region from the SODA reanalysis between 1958 and 1995. δ18Oseawater appears to be mainly driven by large-scale wind forcing in the southern Indian Ocean on interannual to decadal timescales. The δ18Oseawater and SST at Ifaty show characteristic interannual variability of between 2 and 4 years and interdecadal variability of 8 to 16 years, coherent with El Niño–Southern Oscillation (ENSO) records. Lagged correlations with the multivariate ENSO index reveals a 1–2-year lag of δ18Oseawater and salinity at Ifaty and the AC region, suggesting that propagation of anomalies by ocean Rossby waves may contribute to salinity changes in the wider southwestern Indian Ocean. The δ18Oseawater and SST reconstructions at Ifaty reveal the highest interannual variability during the Little Ice Age, especially around 1700 CE, which is in agreement with other Indo-Pacific coral studies. Our study demonstrates the huge potential to unlock past interannual and decadal changes in surface ocean hydrology and ocean transport dynamics from coral δ18Oseawater beyond the short instrumental record.

The Role of Freshwater Forcing on Surface Predictability in the Gulf of Mexico

AbstractThe potential predictability of fields at the ocean surface in the northern Gulf of Mexico (GoM) is investigated through five ensembles of regional ocean simulations between 2014 and 2016. The ensembles explore two horizontal resolutions and different representations of the riverine inflow, and focus on the interactions between the Loop Current system (LCS) and the riverine system. The potential predictability of the surface fields is high when simulated by an ocean‐only model forced by appropriate atmospheric forcing and boundary conditions, and the ensembles simulate similar LCS behavior up to 5 months. The ensemble spread provides a mean to quantify the potential predictability. The ensembles confirm that LCS‐riverine interactions are modulated by the LC mesoscale variability. The relationship is two‐ways, with the LCS being influenced by—And not only influencing—The freshwater plume. Whenever the freshwater flux is strong, the northward extension of the LCS is constrained by the intensified salinity fronts. This influence is slightly stronger if the riverine inflow is simulated in an active fashion with a meridional velocity component proportional to the flux. Sea surface temperature (SST) and salinity (SSS) predictability have opposite seasonality in their signal, with the SST (SSS) being more predictable in summer (winter). Partially resolving submesoscale instabilities and improving the realism of the riverine fluxes’ representation causes the spread to increase, especially in SST. When increasing resolution, the spread increases also for surface vorticity due to feedbacks between the mesoscale and submesoscale circulations. The intraseasonal and interannual signal in vorticity is however similar among ensembles.

Planktic foraminiferal δ18O values indicate precipitation variability in the southeastern South China Sea over the last 175 ka BP

The South China Sea (SCS) is an important research area of the tropical water cycle and an important pathway by which the Asian monsoon transports water vapor and heat from the tropical ocean to the Asian continent, yet its response to low-latitude tropical processes is poorly resolved. Here, we report high-resolution records of the oxygen isotopes (δ18O) of planktic Globigerinoides ruber and Globorotalia menardii at different depths and Mg/Ca ratios from a core in the southeastern SCS over the last 175 ka BP to discuss the variability of sea surface temperature (SST) and salinity (SSS) patterns, which can provide insights into understanding SCS hydroclimate dynamics. The records show that SST was characterized by glacial-interglacial cycles largely controlled by ice volume and orbital insolation-driven changes in monsoon circulation. Several short high-frequency intervals of high SST in the glacial periods and low SST in the stadial periods corresponded to variations involving enhanced winter or summer monsoons. The variation in δ18O is obviously influenced by monsoon-driven SSS. Although the δ18O values in different areas of the SCS were similar, the comparison shows that the δ18O values in the study area were lower than those in the northern SCS but higher than those in the southern SCS, appearing to reveal the tropical water cycle process of evaporation, transmission and rainfall in the SCS. The negative deviation in δ18O peaks indicated heavy precipitation in the southeastern SCS caused by an enhanced convection intensity and strengthened summer monsoons. A valuable set of surface and subsurface Δδ18OG.r-G.m (Δδ18OG. ruber - Δδ18OG. menardii) records proved that more negative δ18O shifts must be closely related to the surface seawater environment. However, negative shifts in δ18O were controlled by different mechanisms during the glacial and interglacial periods. In the interglacial periods, the northward shift of the intertropical convergence zone (ITCZ) and summer solar insolation played a key role in precipitation, whereas in the glacial periods, El Niño events and differences in the thermal properties between the sea and land dominated.

High-resolution sea surface temperature and salinity dynamics in the northern Okinawa Trough over the last 24 kyr

Based on the high-resolution Mg/Ca and oxygen isotope ratio (δ18O) of planktonic foraminifera Globigerinoides ruber, sea surface temperature (SST) and salinity (SSS) were reconstructed in Core PC-1 from the northern Okinawa Trough during the last 24 kyr. From the last glacial maximum to Holocene, SST varied from 20.2°C to 24.6°C. Millennial-scale climatic events of the SST during the last glacial, such as the Heinrich events, Bølling-Allerød warming, and Younger Dryas, have been identified, which are synchronous with the climate changes in the North Atlantic, suggesting a teleconnection between the northwestern Pacific and the North Atlantic. During the last 24 kyr, the SSS variation can be divided into three parts: (1) during 21–15.5 ka, there was a significantly low SSS; (2) during 15.5–11.7 ka, the SSS increased obviously; (3) since 11.7 ka, the SSS is relatively stable. In order to discuss the main factors influencing the SSS in the northern Okinawa Trough, the relative abundance of Pulleniatina obliquiloculata and the oxygen isotope difference between the northern and middle Okinawa Trough (Δδ18Osw) have been used to indicate the intensity of the Kuroshio Current and Changjiang freshwater discharge, respectively. The Δδ18Osw result shows that there is a large amount of Changjiang freshwater emptied into the northern Okinawa Trough during 18–15.5 ka, which is caused by the subtropical monsoon rain band lingering in the lower reaches of the Changjiang River drainage, supporting the Jet Transition Hypothesis. As the Kuroshio Current strengthened since 15.5 ka as indicated by the increased relative abundance of P. obliquiloculata, the variation of Kuroshio Current became the more important contribution to the SSS in the study region. The results of our study indicate that the key factor influencing the SSS in the northern Okinawa Trough is variable during the last 24 kyr.

Hydrodynamic variability in the Southern Bight of the North Sea in response to typical atmospheric and tidal regimes. Benefit of using a high resolution model

In this paper, the hydrodynamics of the Southern Bight of the North Sea (SBNS) and in particular, the Belgian Coastal Zone (BCZ) is investigated on daily to seasonal time scales using a high resolution hydrodynamical model. The Regional Ocean Modeling System (ROMS) is implemented over the SBNS with 5 km resolution and downscaled at 1 km resolution over the BCZ in a two-way nesting configuration run over a three years period (i.e. 2006–2008). The benefit of using a high resolution model over the BCZ is assessed through an extensive comparison of model results with data from satellite and in-situ fixed platforms as well as reference products available for the region. The validation exercise and the results analysis are conducted with a particular focus on hydrodynamic features that are expected to impact the sediment transport. We find that despite the validation procedure does not allow to clearly demonstrate better performance of the high resolution model compared to the coarse resolution model in terms of overtidal circulation, sea surface temperature (SST) and salinity (SSS), the high resolution model resolves additional details in the variability of residual circulation and Scheldt salinity plume dynamics. The analysis of the response of the simulated hydrodynamics to atmospheric regimes for neap and spring tide highlights the major role played by the wind direction on the averaged currents and plume extension. The strongest currents and minimum plume extension are obtained under southwestern winds and neap tide while when northeastern winds prevail, the plume extension is at its maximum and the circulation is the weakest. We show that while neap tides allow the establishment of streamlined circulation, the spring tides induce more turbulent circulation which can favor the retention of transported elements. This latter property could not be resolved with the 5 km resolution model.

Estimating spatial and temporal variation in ocean surface pCO2 in the Gulf of Mexico using remote sensing and machine learning techniques

Research on the carbon cycle of coastal marine systems has been of wide concern recently. Accurate knowledge of the temporal and spatial distributions of sea-surface partial pressure (pCO2) can reflect the seasonal and spatial heterogeneity of CO2 flux and is, therefore, essential for quantifying the ocean's role in carbon cycling. However, it is difficult to use one model to estimate pCO2 and determine its controlling variables for an entire region due to the prominent spatiotemporal heterogeneity of pCO2 in coastal areas. Cubist is a commonly-used model for zoning; thus, it can be applied to the estimation and regional analysis of pCO2 in the Gulf of Mexico (GOM). A cubist model integrated with satellite images was used here to estimate pCO2 in the GOM, a river-dominated coastal area, using satellite products, including chlorophyll-a concentration (Chl-a), sea-surface temperature (SST) and salinity (SSS), and the diffuse attenuation coefficient at 490 nm (Kd-490). The model was based on a semi-mechanistic model and integrated the high-accuracy advantages of machine learning methods. The overall performance showed a root mean square error (RMSE) of 8.42 μatm with a coefficient of determination (R2) of 0.87. Based on the heterogeneity of environmental factors, the GOM area was divided into 6 sub-regions, consisting estuaries, near-shores, and open seas, reflecting a gradient distribution of pCO2. Factor importance and correlation analyses showed that salinity, chlorophyll-a, and temperature are the main controlling environmental variables of pCO2, corresponding to both biological and physical effects. Seasonal changes in the GOM region were also analyzed and explained by changes in the environmental variables. Therefore, considering both high accuracy and interpretability, the cubist-based model was an ideal method for pCO2 estimation and spatiotemporal heterogeneity analysis.

Unique Post-telemetry Recapture Enables Development of Multi-Element Isoscapes From Barnacle Shell for Retracing Host Movement

Many ecological investigations rely on understanding the movement of animals through marine environments. Most available tracking techniques are invasive (e.g., tissue sampling) and require extensive effort and/or cost (e.g., capture-mark-recapture or satellite telemetry). The isotopic compositions of barnacle shells (delta C-13 and delta O-18) are known to record the ambient water temperature and salinity conditions in which they grew. Thus, isotopic analysis of barnacles on animals or objects has the potential to yield information about their movement between water bodies of varying isotopic properties. We present, for the first time, isotopic data for barnacle shell samples that grew on a satellite-tracked sea turtle host. The satellite telemetry record, together with documented barnacle growth rates, allowed for sequential samples from individual barnacle shells to be assigned a specific time and location for direct comparison of isotope values to environmental conditions. We developed models that allow barnacle shell delta C-13 and delta O-18 to be linked, with a high degree of predictability, to sea surface temperature (SST) and salinity (SSS). Our sea turtle case study demonstrated how these models can be used to create isoscapes, allowing hosts to be tracked in space and time at higher resolution than most attempts to use soft-tissue isotopes for a similar purpose, and at considerably lower cost than satellite telemetry. The conceptual advance presented here could be applied widely to understand the movement of any animal or object that carries hitchhiking barnacles.

South Brazilian Bight mid- to late Holocene hydrographic fluctuations

Here, we present two high temporal resolution Holocene sea surface temperature (SST) and salinity (SSS) reconstructions for the SW Atlantic. Mg/Ca data together with the oxygen isotopic composition (δ18O) of a shallow dwelling planktonic foraminifera species (Globigerinoides ruber (pink)). Two marine sediment cores collected at ~ 25°S are used to assess mid- to late Holocene sea surface hydrographic conditions in the continental shelf of the South Brazilian Bight. Our results show multi-centennial-scale changes of up to 2.7 °C in SST and 0.8‰ in ice volume corrected seawater δ18O (a proxy for SSS, indicating changes of up to 2 salinity units). In phase, multicentennial-scale negative SST and SSS incursions were interpreted to indicate shelf-break upwelling events and the northward intrusion of the Plata Plume Water (PPW) under a strengthened Brazil Current (BC) flow. The latitudinal SST gradient between our two records (ΔSST7616–7610), applied here as a proxy for the BC strength, supports the existing hypothesis of antiphase between the BC and the North Brazil Current strength during the last 7 ka. Positive ΔSST7616–7610 values suggest the presence of the PPW at latitudes of up to 25.5°S, while negative ΔSST7616–7610 values (centred at around 5.4, 4.3, 2.2 and 1.3 cal ka BP) occurring synchronously with cold events in the Northern Hemisphere suggests that the Atlantic Meridional Overturning Circulation played a central role in the SW Atlantic mid- to late Holocene surface hydrographic conditions.

High-Resolution Sea Surface Temperature and Salinity in Coastal Areas Worldwide from Raw Satellite Data

The aim of this work is to obtain high-resolution values of sea surface salinity (SSS) and temperature (SST) in the global ocean by using raw satellite data (i.e., without any band data pre-processing or atmospheric correction). Sentinel-2 Level 1-C Top of Atmosphere (TOA) reflectance data is used to obtain accurate SSS and SST information. A deep neural network is built to link the band information with in situ data from different buoys, vessels, drifters, and other platforms around the world. The neural network used in this paper includes shortcuts, providing an improved performance compared with the equivalent feed-forward architecture. The in situ information used as input for the network has been obtained from the Copernicus Marine In situ Service. Sentinel-2 platform-centred band data has been processed using Google Earth Engine in areas of 100 m × 100 m. Accurate salinity values are estimated for the first time independently of temperature. Salinity results rely only on direct satellite observations, although it presented a clear dependency on temperature ranges. Results show the neural network has good interpolation and extrapolation capabilities. Test results present correlation coefficients of 82% and 84% for salinity and temperature, respectively. The most common error for both SST and SSS is 0.4 °C and 0.4 PSU. The sensitivity analysis shows that outliers are present in areas where the number of observations is very low. The network is finally applied over a complete Sentinel-2 tile, presenting sensible patterns for river-sea interaction, as well as seasonal variations. The methodology presented here is relevant for detailed coastal and oceanographic applications, reducing the time for data pre-processing, and it is applicable to a wide range of satellites, as the information is directly obtained from TOA data.

Reconstruction of Large-Scale Sea Surface Temperature and Salinity Fields Using Sub-Regional EOF Patterns From Models

A method for reconstruction of gridded fields of sea surface variables from time-dependent observations, using sub-regional EOF (Empirical Orthogonal Functions) patterns from models, is presented and tested. Covariance fields, calculated from the model results over long enough time span, are used to find EOF modes. The gravest “observational” amplitudes and their first temporal derivatives are determined from the least-square minimization of fitting errors in relation to the observed values. The field is reconstructed by superposition of continuous model-based mode patterns multiplied by observational amplitudes that meet adopted statistical limits. If the observational amplitude exceeds the limits, gridded fields for this and higher modes are not produced. We applied the method in the northeastern Baltic over the model time series 2010-2015. Daily averages of sea surface temperature (SST) and salinity (SSS) from the high-resolution (grid step 0.5 nautical miles) sub-regional HBM model were spatially averaged over bins of 5x5 nautical miles. Three first modes cover 99% of variance of temperature and 61.4% of salinity. As shown by experiments with pseudo-observations (model values at these points reconstructed to the model grid and then compared with the original model data), reconstruction performance depends on the configuration of the observation points in the model domain. Still, a few first modes usually produce acceptable results. When removing the SST seasonal cycle prior to EOF analysis, spatial patterns of leading modes remained practically unchanged, share of variance of the three first modes was reduced to 88,6% and reconstruction errors were reduced by about 25%. Sufficient spatial data coverage of the larger basin with ship-born observations usually takes quite long time – of the order of month; therefore, time correction of the amplitudes using the found temporal derivatives improves the accuracy of reconstruction. The method is compared with the Optimal Interpolation (OI) by using the pseudo-observations. Results show that, for SST reconstruction, the OI method is significantly worse than the EOF method. For SSS, OI is slightly better than EOF. The superiority of EOF is that the remote correlation patterns can be used in the reconstruction, which is important when the observations are sparse.

Decoding sea surface and paleoclimate conditions in the eastern Mediterranean over the Tortonian-Messinian Transition

New sedimentological, micropaleontological and geochemical data from the Upper Miocene pre-evaporitic sedimentary sequence of the Faneromeni section (Crete Island, eastern Mediterranean) revealed a stepwise restriction of the Mediterranean Sea preceding the Messinian Salinity Crisis (MSC), which was modulated by a sedimentary cyclicity responding to orbital parameters. This cyclicity is manifested by lithological alternations from laminated to indurated homogeneous marls and clayey limestones, and covers the Tortonian-Messinian Transition (TMT; 7.6–6.7 Ma). This time window covers the successive closure of the marine Mediterranean-Atlantic gateways, which culminated in the onset of the MSC. In the present study, we present the first evidence for changes in the upper water column reflected by sea surface temperature (SST) and salinity (SSS) variations that correlate with pronounced paleoclimatic fluctuations. Planktonic foraminiferal isotopes, in combination with paired mixed layer Sr/Ca-derived SST data, reveal that the very warm late Tortonian interval has been followed by a strong long-term cooling (~10 °C) and desalination (~10‰) trend during the earliest Messinian, attributed to the paroxysmal phase of the so-called “siphon” event. In particular, the climate shift that occurred at the end of a global carbon isotope (δ13C) decrease suggests that changes in the carbon cycle were instrumental in driving late Miocene climate dynamics (cooling and aridity) in the progressively isolated eastern Mediterranean Sea. The observed salinity variability during this time interval also provides further insights about seasonal freshwater inputs and gives new support to the much-debated hydrologic regime (linear salinity increase vs step-function evolution with strong salinity fluctuations) preceding the deposition of evaporites. The novel methodology of foraminiferal Sr/Ca paleothermometry and results of this study could have numerous potential applications to other regions and relevant extreme geological events. Therefore, in the near future we expect this approach to add important new information to our understanding of Neogene climates.

Long-term trends and regional variability in extreme temperature and salinity conditions experienced by coastal marine organisms on Vancouver Island, Canada

Studies of ocean temperature and salinity typically focus on global or large-scale trends that may not accurately reflect the conditions experienced locally by marine organisms. When assessing impacts of climate change, it is important to document local conditions, and also to focus on the most physiologically stressful time of year. Our goals were therefore to (1) characterize long-term trends in sea surface temperature (SST) and salinity (SSS) experienced by coastal marine organisms during the most stressful time of year around Vancouver Island; and (2) document variation between east and west coasts of Vancouver Island in terms of SST, SSS, and daytime rock surface temperatures in the intertidal zone. Over an 82-yr period, from 1935 to 2016, summertime SST on both coasts increased by 0.67–0.78 °C (i.e., 0.82–0.97 °C per century). Trends in salinity differed between coasts: east coast salinity increased by 3.9 while west coast salinity decreased by 0.64. Although long-term SST trends are the same on both coasts, during the most stressful time of year, east coast waters are on average 4.3 °C warmer and salinity is 7.8 lower than on the west coast. Rock temperature in the mid and upper intertidal zone during daytime low tides is 3.9–4.2 °C warmer on the east coast. Populations of marine organisms inhabiting the coasts of Vancouver Island have therefore been experiencing long-term changes in abiotic stress, as well as persistent spatial variation in climate-related conditions during the most stressful months of the year.

Significant seasonal contrast in the Arabian Sea during deglaciation: Evidence from oxygen isotopic analyses of individual planktic foraminifera

The variation of stable isotopes between individual shells of planktic foraminifera of a given species and size may provide short-term seasonal insight into past sea surface temperature (SST) and salinity (SSS). In this context, oxygen isotope analyses of individual Globigerinoides sacculifer were carried out from the Ocean Drilling Program Site 723A in the western Arabian Sea to unravel seasonal changes over the last 22 kyr. δ18O values of single shells of G. sacculifer range from of 0.54–2.09‰ at various discrete depths in the core which spans the last 22 kyr. Maximum inter-shell δ18O variability and relatively higher standard deviation is noticed from 20 to 10 kyr (deglaciation), whereas from 10 kyr onwards (Holocene) inter-shell δ18O variability decreases. Based on statistical inferences, we interpret this result as greater seasonal SST and SSS contrasts during the deglaciation compared to the Holocene. These winter-to-summer contrasts during the deglaciation can likely be explained by a net reduction in summer upwelling linked to changes in wind forcing and net evaporation-minus-precipitation that might, along with local causes, be related to deglacial shifts in the intertropical convergence zone (ITCZ). We note that a common winter-dominated SST signal in the Arabian Sea and in Greenland was pervasive during the last glacial period, strengthening evidence of a North Atlantic link with Indian Ocean SST. Thus, the present study has wider implications in understanding whether the forcing mechanism of tropical monsoon climate lies in high latitudes or in the tropics.

Sea surface salinity and temperature in the southern Atlantic Ocean from South African icebreakers, 2010–2017

Abstract. We present here sea surface salinity (SSS) and temperature (SST) data collected on board the S.A. Agulhas-I and S.A. Agulhas-II research vessels, in the framework of the South African National Antarctic Programme (SANAP). Onboard Sea-Bird thermosalinographs were regularly calibrated and continuously monitored in-between cruises, and no appreciable sensor drift emerged. Water samples were taken on a daily basis and later analyzed with a Portasal salinometer; some CTD measurements collected along the cruises were used to validate the data. No systematic differences appeared after a rigorous quality control on continuous data. Results show that salinity measurement error was a few hundredths of a unit on the practical salinity scale. Quality control included several steps, among which an automatic detection of unreliable values through selected threshold criteria and an attribution of quality flags based on multiple criteria, i.e., analysis of information included in the cruise reports, detection of insufficient flow and/or presence of air bubbles and ice crystals in the seawater pipe, visual inspection of individual campaigns, and ex post check of sea ice maps for confirming ice field locations. This data processing led us to discard about 36 % of acquired observations, while reliable data showed an excellent agreement with several independent SSS products. Nevertheless, a sea ice flag has been included for identifying valid data which could have been affected by scattered sea ice contamination. In our opinion, this dataset, available through an unrestricted repository at https://doi.org/10.7289/V56M3545, contributes to improving the knowledge of surface water features in one of the most important regions for global climate. The dataset will be highly valuable for studies focusing on climate variability in the Atlantic sector of the Southern Ocean, especially across the Antarctic Circumpolar Current and its fronts. Furthermore, we expect that the collected SSS data will represent a valuable tool for the calibration and validation of recent satellite observations provided by SMOS and Aquarius missions.

Inconsistent sea surface temperature and salinity changing trend in the northern South China Sea since 7.0 ka BP

The South China Sea (SCS) is an important moisture and heat source in the Asian monsoon system, and its environmental changes influence economic and social stability in Southeast Asia and East Asian. Previous records on sea surface temperature (SST) and salinity (SSS) were mostly from one sediment core, and/or only showed fragmentary information. It is hard to provide insights into the mechanisms of the overall paleoceanographical environmental variability in the northern SCS. In this study, paired δ18O and Mg/Ca records of planktonic foraminifer Globigerinoides ruber from Core S0204B nearby the Luzon Strait (21°13.818′N, 118°3.077′, water depth 1822 m), and Core GHE 27L (19.85°N, 115.34°E, water depth of 1533 m) in the central northern SCS, were analyzed, so as to better understand the physical process of the SST and SSS changes in the northern SCS and its relationship with the tropical Pacific. The results demonstrate that the SST is relatively stable and seawater δ18O (δ18Osw) values, a salinity proxy, shows a decrease trend since 7.0 ka BP in Core S0204B. By contrast, SST and δ18Osw in Core GHE 27L exhibit an overall increasing trend at the same time, indicating apparent regional discrepancy on the changing trend of the SST and SSS in the northern SCS. We suggest that the thermal and hydrographic conditions in Core S0204B were primarily influenced by the outer western Pacific water. However, the thermal and hydrographic conditions in Core GHE 27L may be predominantly controlled by the weakened Asian monsoon during the mid-late Holocene, which was induced by the southern migration of Intertropical Convergence Zone (ITCZ) and stronger EI Niño Southern Oscillation.

Comparison of Remotely-Sensed Sea Surface Temperature and Salinity Products With in Situ Measurements From British Columbia, Canada

Sea surface temperature (SST) and salinity (SSS) are essential variables at the ocean and atmosphere interface when considering risk factors for disease in farmed and wild fish stocks. Ecological research has witnessed a recent trend in use of digital and satellite technologies, including remote-sensing tools. We explored spatial coverage of remotely-sensed SST and SSS data and compared them with in situ measurements of water temperatures and salinity, which led to suggested adjustments to the remotely-sensed data for its use in aquaculture research. The in situ data were from farms and wild surveillance sites in coastal British Columbia, Canada, from 2003 to 2016. Concurrent SST and SSS values were extracted from remotely-sensed products and compared with 20,513 and 20,038 in situ records for water temperature and salinity, respectively, from 232 different sites. Among nine SST products evaluated, the UKMO OSTIA SST (UK Meteorological Office) had the highest retrieval, and highest concordance correlation coefficient (0.86), highest index of agreement (0.93), fewest missing values, and smallest mean and SD values for bias, when compared to in situ measurements. A mixed linear regression model with UKMO OSTIA SST as the predictor for in situ measurements estimated an adjustment coefficient of 0.89 °C for UKMO OSTIA SST. None of the three SSS products evaluated provided appropriate corresponding values for in situ sites, suggesting that spatial coverage for the study area is currently lacking. This study demonstrates that, among SST products, UKMO OSTIA SST is currently best suited for aquaculture studies in coastal BC. The near real-time availability of these data with the estimated adjustment would allow their use in forecast models, surveillance of pathogens, and the creation of risk maps.

Changes to Yucat\xe1n Peninsula precipitation associated with salinity and temperature extremes of the Caribbean Sea during the Maya civilization collapse

Explanations of the Classic Maya civilization demise on the Yucatán Peninsula during the Terminal Classic Period (TCP; ~CE 750–1050) are controversial. Multiyear droughts are one likely cause, but the role of the Caribbean Sea, the dominant moisture source for Mesoamerica, remains largely unknown. Here we present bimonthly-resolved snapshots of reconstructed sea surface temperature (SST) and salinity (SSS) variability in the southern Caribbean from precisely dated fossil corals. The results indicate pronounced interannual to decadal SST and SSS variability during the TCP, which may be temporally coherent to precipitation anomalies on the Yucatán. Our results are best explained by changed Caribbean SST gradients affecting the Caribbean low-level atmospheric jet with consequences for Mesoamerican precipitation, which are possibly linked to changes in Atlantic Meridional Overturning Circulation strength. Our findings provide a new perspective on the anomalous hydrological changes during the TCP that complement the oft-suggested southward displacement of the Intertropical Convergence Zone. We advocate for a strong role of Caribbean SST and SSS condition changes and related ocean-atmosphere interactions that notably influenced the propagation and transport of precipitation to the Yucatán Peninsula during the TCP.

On the persistence and coherence of subpolar sea surface temperature and salinity anomalies associated with the Atlantic multidecadal variability

AbstractThis study identifies key features associated with the Atlantic multidecadal variability (AMV) in both observations and a fully coupled climate model, e.g., decadal persistence of monthly mean subpolar North Atlantic (NA) sea surface temperature (SST) and salinity (SSS) anomalies, and high coherence at low frequency among subpolar NA SST/SSS, upper ocean heat/salt content, and the Atlantic Meridional Overturning Circulation (AMOC) fingerprint. These key AMV features, which can be used to distinguish the AMV mechanism, cannot be explained by the slab ocean model results or the red noise process but are consistent with the ocean dynamics mechanism. This study also shows that at low frequency, the correlation and regression between net surface heat flux and SST anomalies are key indicators of the relative roles of oceanic versus atmospheric forcing in SST anomalies. The oceanic forcing plays a dominant role in the subpolar NA SST anomalies associated with the AMV.