Analysis of magnitude, drivers, and mechanisms of salinity variability in the tropical Atlantic

J. Karstensen, P. Brandt and Y. Fu

Workpackage 1.3 will analyze spatial and temporal scales and magnitude of salinity anomalies in the tropical Atlantic Ocean using observational data collected by ships and other observing platforms.

In general, the work can be separated by the spatial and temporal scales under investigation:

Basin scale
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Observational data acquired along zonal sections in the tropical Atlantic will be analyzed to quantify the meridional freshwater transport associated with the so called "Meridional Overturning Circulation".
In combining recent data with historical data, and by analyzing the output from assimilation models (TP 3.1), the long term variability of the meridional freshwater transport will be quantified.

Figure 1: The analysis of the large scale meridional transport of freshwater is based on full water depth observations (surface to more than 6000 m), collected during dedicated research cruises from coast to coast (Trinidad/Tobago to Senegal). Upper: Research cruise Meteor M96 (May 2013), Lower: Research cruise Meteor M09 (February 1989).

Local scale
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Observational data acquired by ships, autonomous platforms (Glider, moorings) and satellites will be combined with non-oceanic freshwater fluxes (evaporation, precipitation, and river run-off) to calculate freshwater flux variability in the upper ocean.

Figure 2: Observational data in very high temporal and spatial resolution is collected with autonomous observing systems such as underwater gliders (http://www.geomar.de/en/research/fb1/fb1-po/observing-systems/floats-glider-auv/).

Specific research questions to be answered:

  • How much freshwater is transported equatorward/poleward by the meridional overturning circulation and what can be said about the variability of the meridional freshwater transport?

  • Do observed and modeled meridional freshwater transports agree?

  • How sensitive is the meridional freshwater transport to variability in the upper layer (Ekman contribution)?