Formation and variability of the South Pacific Sea Surface Salinity maximum in recent decades

Abstract

International audienceThis study investigates causes for the formation and variability of the Sea Surface Salinity maximum (SSS > 36) centered near 18°S-124°W in the South Pacific Ocean over the 1990-2011 period at the seasonal time scale and above. We use two monthly gridded products of SSS based on in situ measurements, high-resolution along-track Voluntary Observing Ships thermo-salinograph data, new SMOS satellite data, and a validated ocean general circulation model with no direct SSS relaxation. All products reveal a seasonal cycle of the location of the 36-isohaline barycenter of about ±400 km in longitude in response to changes in the South Pacific Convergence Zone location and Easterly winds intensity. They also show a low frequency westward shift of the barycenter of 1400 km from the mid 1990s to the early 2010s that could not be linked to the El Nino Southern Oscillation phenomena. In the model, the processes maintaining the 22 year equilibrium of the high salinity in the mixed layer are the surface forcing (˜+0.73 pss/yr), the horizontal salinity advection (˜-0.37 pss/yr), and processes occurring at the mixed layer base (˜-0.35 pss/yr)

Variations of the tropical Atlantic and Pacific SSS minimum zones and their relations to the ITCZ and SPCZ rain bands (1979-2009)

“…This finding is in agreement with Hasson et al . 's [] results which show a low‐frequency westward displacement of the high‐salinity tongue of the south‐eastern tropical Pacific.…”

“…[] have shown an eastward migration and expansion of the low‐SSS water surface located in the western Pacific warm pool, and Hasson et al . [] a westward migration of the high‐SSS water surface located in the south‐eastern tropical Pacific in the last decades. The mechanisms responsible for these observed migrations and their possible connections to low‐frequency changes in E‐P are not clearly established.…”

Sea surface salinity under rain cells: SMOS satellite and in situ drifters observations

“…Large scale seasonal biases, likely due to flaws of the thermal antenna model [Kainulainen et al, 2012] are still present in this version. In the southern tropical Pacific Ocean, they are corrected by the application of the Ocean Target Transformation so that the rms error of monthly -100 3 100 km 2 SMOS S 1cm with respect to ship S bulk has been found equal to 0.20 in the south east Pacific between 0 and 30 S, a region with very few rain events [Hasson et al, 2013]. On another hand, Hernandez et al [2014] have shown large biases (several tenths of pss) in the northern subtropical Atlantic region (15 N-35 N), largest in boreal winter.…”

Multi-dimensional interpolation of SMOS sea surface salinity with surface temperature and in situ salinity data

“…The thermohaline component of the ocean circulation is modulated by temperature and salinity changes affecting sea water density (e.g. Bingham et al, 2012;Dong et al, 2014;Hasson et al, 2013;Johnson et al, 2012;Kolodziejczyk et al, 2015;Mignot et al, 2012;Reverdin et al, 2007;Stommel, 1993). Moreover, salinity changes may affect the marine carbonate chemistry, contributing to regulate both carbon dioxide uptake/release to the atmosphere and ocean acidification (e.g.…”