Surface Salinity in the North Atlantic subtropical gyre: During the STRASSE/SPURS Summer 2012 Cruise

Reverdin, Gilles ... et. al.-- Special issue on SPURS: Salinity Processes in the Upper-ocean Regional Study.-- 10 pages, 7 figuresWe investigated a 100 × 100 km high-salinity region of the North Atlantic subtropical gyre during the Sub-Tropical Atlantic Surface Salinity Experiment/Salinity Processes in the Upper-ocean Regional Study (STRASSE/SPURS) cruise from August 21, 2012, to September 9, 2012. Results showed great variability in sea surface salinity (SSS; over 0.3 psu) in the mesoscale, over 7 cm of total evaporation, and little diapycnal mixing below 36 m depth, the deepest mixed layers encountered. Strong currents in the southwestern part of the domain, and the penetration of freshwater, suggest that advection contributed greatly to salinity evolution. However, it was further observed that a smaller cyclonic structure tucked between the high SSS band and the strongest currents contributed to the transport of high SSS water along a narrow front. Cross-frontal transport by mixing is also a possible cause of summertime reduction of SSS. The observed structure was also responsible for significant southward salt transport over more than 200 km. © 2015 by The Oceanography Society. All rights reservedThis effort was supported nationally in France by CNES/TOSCA with the Gloscal and SMOS projects and by LEFE/INSU for the STRASSE/SPURS project, in Spain at ICM/CSIC by the Spanish national R+D plan (project AYA2010-22062-C05). The cruise took place on board R/V Thalassa owned by IFREMER and operated by GENAVIR. Support from the ship’s captain and crew during the STRASSE cruise is gratefully acknowledged. Some French instruments were also funded by INSU and IFREMER, and the trimaran platform Ocarina was also partially funded by IPSL. Nicolas Kolodziejczyk’s postdoctoral fellowship was awarded by CNES. Support for ASIP work is from the Office of Naval Research under Award No. N62909-12-1-7064, and Graig Sutherland’s scholarship PGSD3-410251-258 2011 was awarded by the National Research Council of Canada. SVP drifters were provided by the Global Drifter Program, NOAA grant #NA10OAR432056. LC and VH were supported by NASA grant #NNX12AI67G and NOAA grant #NA10OAR432056Peer Reviewe

Study of the potential for existing bathythermic string drifters

Evaluation report on the use of subsurface temperature buoy data and on their ability to provide suitable measurements in the ocean boundary laye

The Near Surface Equatorial Indian Ocean in 1979. Part I: Linear Dynamics

Different wind field analyses are used to force a one layer adiabatic model of the near equatorial surface circulation in the Indian Ocean in 1979. The model simulates the major features of the observations: eastward jets were present in April-May and in October-November in the central Indian Ocean in phase with the local winds; the seasonal changes of thermocline depth in the western part of the basin are related to the near equatorial currents. Significant discrepancies are also found. Some are due to the uncertainty in the wind fields. Correlation between different wind fields are only of the order of 0.75 for the low frequencies and magnitude can vary by a factor of 1.5. Others are attributed to model inadequacies especially the neglect of nonlinearity and the oversimplification of the vertical structure. There is an unrealistic energy focus in the central Indian Ocean though, in general, seasonal changes are underestimated by at least 30%. Simpler dynamics failed to produce a reasonable agreement over the whole basin. A Yoshida jet did well for the currents in the central part of the basin, but did not reproduce the mass changes in the west. Sverdrup equilibrium reproduces the model zonal slope of the thermocline, but not the currents

Recent changes in the surface salinity of the North Atlantic subpolar gyre

Sea surface salinity (SSS) was measured since 1896 along 60°N between Greenland and the North Sea and since 1993 between Iceland and Newfoundland. Along 60°N away from the shelves, and north of 53°N, the amplitude of the seasonal cycle is comparable to or less than interannual variability. In these parts of the North Atlantic subpolar gyre, large-scale deviations from the seasonal cycle correlate from one season to the next. This suggests that in these regions, summer and autumn surface data are useful for monitoring changes in upper ocean salinity best diagnosed from less common winter surface data. Further south near the subarctic front, the Labrador Current or near shelves where seasonal variability is strong, this is not the case. Along 60°N, the multiannual low-frequency variability is well correlated across the basin and exhibits fresher surface water since the mid 1970s than in the late 1920s to 1960s. SSS in the Irminger Sea along 60°N lags by 1-year SSS farther east in the Iceland Basin. Variability between Iceland and Newfoundland within the Irminger Sea north of 54°N presents similar characteristics to what is observed along 60°N. Variability near the northwest corner of the North Atlantic Current (52°N/45°W) is larger and is not correlated to what is found further north. Maps of SSS were constructed for a few recent seasons between July 1996 and June 2000, which illustrate the fresh conditions found usually during that period across the whole North Atlantic subpolar gyre, although this includes an episode of higher salinity. The SSS anomaly maps have large uncertainties but suggest that the highest SSS occurred before the spring of 1998 in the Iceland Basin, and after that, in the Irminger Sea. This is followed by fresher conditions, first in the Labrador and Iceland Basin, reaching recently the Irminger Sea

Diurnal Warming Observations with ASIP in the subtropical Northern Atlantic

European Geosciences Union General Assembly 2015 (EGU2015), 12-17 April 2015, Vienna, Austria.-- 1 pageQuantification of air-sea exchange fluxes of energy, moisture, momentum and gases require in situ-measurements of the near-surface layer of the ocean. In the framework of the Salinity Processes in the Upper Ocean Regional Study (SPURS) project, we participated in two cruises to the North Atlantic Salinity Maximum (NASM) region. Observations in the upper ocean are obtained with the Air Sea Interaction Profiler (ASIP), which is an upwardly-rising microstructure instrument designed to study processes in the mixing layer of the ocean. ASIP operates autonomously for up to two days, obtaining undisturbed profiles within the water column from depth to the immediate surface. During the SPURS experiment, ASIP was deployed on several occasions, resulting in a total of over 1000 profiles of the ocean surface boundary layer. ASIP is equipped with microstructure sensors for temperature (FP07), conductivity (SBE07), shear, accurate C-T sensors, a PAR and an oxygen sensor. The high resolution temperature profiles obtained, combined with information on local meteorological variables, allow for an accurate study of the temporal and vertical variability of diurnal warming of the upper ocean boundary layer. Characteristics of the measured diurnal warming at the ocean surface and at specific depth levels are compared to physics-based models of near-surface warming. Mixing rates in the upper ocean are determined from the turbulent dissipation rate, calculated from profiles of the turbulent shear. This information is used to quantify variability between the modeled and observed diurnal warming signalPeer Reviewe

North Atlantic extratropical and subpolar gyre variability during the last 120 years: a gridded dataset of surface temperature, salinity, and density. Part 1: dataset validation and RMS variability

We present a binned annual product (BINS) of sea surface temperature (SST), sea surface salinity (SSS), and sea surface density (SSD) observations for 1896–2015 of the subpolar North Atlantic between 40° N and 70° N, mostly excluding the shelf areas. The product of bin averages over spatial scales on the order of 200 to 500 km, reproducing most of the interannual variability in different time series covering at least the last three decades or of the along-track ship monitoring. Comparisons with other SSS and SST gridded products available since 1950 suggest that BINS captures the large decadal to multidecadal variability. Comparison with the HadSST3 SST product since 1896 also indicates that the decadal and multidecadal variability is usually well-reproduced, with small differences in long-term trends or in areas with marginal data coverage in either of the two products. Outside of the Labrador Sea and Greenland margins, interannual variability is rather similar in different seasons. Variability at periods longer than 15 years is a large part of the total interannual variability, both for SST and SSS, except possibly in the south-western part of the domain. Variability in SST and SSS increases towards the west, with the contribution of salinity variability to density dominating that of temperature in the western Atlantic, except close to the Gulf Stream and North Atlantic Current in the southwest area. Weaker variability and larger relative temperature contributions to density changes are found in the eastern part of the gyre and south of Iceland

Design a buoy fitted with a low cost salinity sensor

A number of prototypes equipped with different sensors (if more than one exists) will be tested at sea with different methods to avoid bio-fouling. CNRS will conduct evaluation of the test performed by NK