Freshwater budget and salinity variability in the subpolar and subtropical gyres of the North Atlantic

M. Rhein and I. Stendardo

Salinity distribution in the North Atlantic can be affected by several factors. On longer time scale global warming can affect salinity by changes in the hydrological cycle affecting the sea surface salinity. These changes are then introduced into the interior by vertical migration of density surfaces caused by changes in the ocean ventilation. Global warming could also lead to a poleward migration of isopycnals due to increased surface temperature, which also modifies salinity. In the North Atlantic, long-term trends are overlaid by vigorous decadal and multidecadal oscillations related to the Atlantic Multidecadal Oscillation (AMO) that can cause either a strengthening or a weakening of the Atlantic Meridional Overturning Circulation (AMOC). It has been shown that both salinity and temperature changes are linked to these decadal and multidecadal oscillations. Finally, changes in the wind driven circulation with a consequence shift of the subpolar front, that separates the Subpolar from the Subtropical gyre, can affect salinity by changing its distribution between the two gyres.

Up to recent years, salinity changes and fresh water distributions could only be studied by averaging data over 5 years due to the lack of temporal and spatial resolution of salinity observations. Thanks to the Argo program, the temporal and spatial resolution of salinity profiles have significantly improved, allowing to determine seasonal changes since the start of the program in the early 2000s. Distributed evenly throughout the year, Argo profiles, however, can also be utilized to apply the GEM (Gravest Empirical Mode) parameterization. This relates sea surface height (SSH) measured from the altimeter with T/S profiles derived from the Argo program. SSH time series are available with high temporal and spatial resolution since 1992. We will use this GEM technique to calculate the changes in the salinity distributions since 1992 with high temporal and spatial resolution.

Figure: Argo profiles in 2011 in the North Atlantic (red dots).