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

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Up to recent years, the study of salinity and freshwater distribution changes was hampered by the lack of temporal and spatial resolution of the observations, so that salinity anomalies could only be studied by averaging over 5 years. With the onset of the Argo programme, the number of salinity profiles dramatically increased, and 1.9 million Argo profiles were collected in the global ocean between the onset of the program in 1999 and April 2014. The full Argo array was in place in the North Atlantic around 2005 - 2007. Despite this effort, the spatial and temporal coverage is not sufficient to identify salinity variations in detail in the subpolar North Atlantic. We used the Argo profiles to exploit the relation between the salinity profiles and dynamic height. Dynamic height is also measured by altimetry, and high quality data are available since 1992. A combination of Argo floats and altimeter data thus allowed us to extend the time period with high sampling (starting about 2005-2007) into the past till 1992, the onset of the altimeter measurements. In the first phase, high spatial (0.25 x 0.25 grid) and temporal (daily) resolution salinity time series (1992-2012) in the upper 700m were constructed using Argo data and altimetry. To calculate the influence of local freshwater fluxes on the salinity changes, the updated HOAPS 3 climatology HOAPS 3.3 became available in May 2015 and was applied. The objectives of the continuation proposal are based on the results of the first phase, and are (i) Analyse the monthly to multiannual variability in the regional salinity contents, together with freshwater fluxes and involved processes using observations (Argo, CTD, altimeter), a high resolution (1/24) model, results from the GECCO2 synthesis (TP 3.1) and from the updated HOAPS climatology (TP 2.1). Calculate content changes and influence of surface freshwater fluxes for upper 700m and separately for the mixed layer. (ii) Study the evolution and variability of surface and subsurface structures of fronts, meanders, and eddies, calculate salinity content anomalies in eddies, follow salinity anomalies along their pathways and assess the role of the involved processes (iii) Calculate time series of eddy salinity transports in the upper 700m, especially into the subpolar western Atlantic and across the MAR into the eastern Atlantic, and (iv) check whether the salinity reconstructions are valid in regions shallower than 1900m depth in the Northeast Atlantic, and test whether the quality of the reconstructions of the salinity profile improve by adding satellite observations of surface salinity.