Characteristics of the seasonal cycle of surface layer salinity in the global ocean

Abstract

Abstract. The seasonal variability of surface layer salinity (SLS), evaporation (E), precipitation (P ), E − P , advection and vertical entrainment over the global ocean is examined using in situ salinity data, the National Centers for Environmental Prediction's Climate System Forecast Reanalysis and a number of other ancillary data. Seasonal amplitudes and phases are calculated using harmonic analysis and presented in all areas of the open ocean between 60 • S and 60 • N. Areas with large amplitude SLS seasonal variations include: the intertropical convergence zone (ITCZ) in the Atlantic, Pacific and Indian Oceans; western marginal seas of the Pacific; and the Arabian Sea. The median amplitude in areas that have statistically significant seasonal cycles of SLS is 0.19. Between about 60 • S and 60 • N, 37 % of the ocean surface has a statistically significant seasonal cycle of SLS and 75 % has a seasonal cycle of E −P . Phases of SLS have a bimodal distribution, with most areas in the Northern Hemisphere peaking in SLS in March/April and in the Southern Hemisphere in September/October.The seasonal cycle is also estimated for surface freshwater forcing using a mixed-layer depth climatology. With the exception of areas near the western boundaries of the North Atlantic and North Pacific, seasonal variability is dominated by precipitation. Surface freshwater forcing also has a bimodal distribution, with peaks in January and July, 1-2 months before the peaks of SLS. Seasonal amplitudes and phases calculated for horizontal advection show it to be important in the tropical oceans. Vertical entrainment, estimated from mixedlayer heaving, is largest in mid and high latitudes, with a seasonal cycle that peaks in late winter.The amplitudes and phases of SLS and surface fluxes compare well in a qualitative sense, suggesting that much of the variability in SLS is due to E − P . However, the amplitudes of SLS are somewhat different than would be expected and the peak of SLS comes typically about one month earlier than expected. The differences of the amplitudes of the two quantities is largest in such areas as the Amazon River plume, the Arabian Sea, the ITCZ and the eastern equatorial Pacific and Atlantic.

Impact of assimilating surface salinity from SMOS on ocean circulation estimates

“…For instance, Delcroix et al [1996] showed that in the tropics the mean and standard deviation patterns of SSS and P show good correspondence in areas of heavy rainfall. Furthermore, the global study by Bingham et al [2012] suggests that the seasonal variability of surface salinity is associated to the seasonal variability in the freshwater input through E-P. However, Vinogradova and Ponte [2013a] investigated the relationship between surface salinity and freshwater fluxes and stressed the importance of the ocean's role in evolution of SSS.…”

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.…”

Climatology and seasonality of upper ocean salinity: a three-dimensional view from argo floats

“…A later work by Chen and Tung (2014) also suggested that the slowdown of the twenty-first-century surface warming is mainly caused by heat transported to deeper layers in the Atlantic and the Southern Oceans initiated by a recurrent salinity anomaly in the subpolar North Atlantic. However, the use of salinity as a proxy for the impact of hydrological cycle encountered a mismatch of time scales between the ocean and the atmosphere (Bingham et al 2012), and efforts to detect the long-term response of "rich get richer" in sparse surface observations of rainfall and evaporation remain ambiguous (Durack et al 2012). For all these reasons, salinity in terms of both climatology and variability naturally becomes one of the most needed variables in ocean and climate sciences.…”

“…Salinity increases at the sea surface are found in evaporation-dominated regions and freshening in precipitation-dominated regions, with the spatial pattern of change strongly resembling that of the mean salinity field, consistent with an amplification of the global hydrological cycle. The seasonal variability of surface layer salinity over the global ocean was examined by Bingham et al (2012) using a variety of in situ and reanalysis data including Argo. They find that areas with large amplitude seasonal salinity variations include the Intertropical Convergence Zone (ITCZ) of the Atlantic, Pacific and Indian Oceans, western marginal seas of the Pacific, and the Arabian Sea.…”