Assessment of the structure and variability of Weddell Sea water masses in distinct ocean reanalysis products

We assessed and evaluated the performance of five ocean reanalysis in reproducing essential hydrographic properties and their associated temporal variability for the Weddell Sea, Antarctica. The products used in this assessment were ECMWF ORAS4, CFSR, MyOcean UR025.4, ECCO2 and SODA. The present study focuses on the Weddell Sea deep layer, which is composed of the following three main water masses: Warm Deep Water (WDW), Weddell Sea Deep Water (WSDW) and Weddell Sea Bottom Water (WSBW). Moreover, all the ocean reanalysis products analyzed showed limited capabilities in representing the surface water masses in the Weddell Sea. The MyOcean UR025.4 product provided the most accurate representation of the structure of the Weddell Sea water masses when compared to observations. The CFSR and ECCO2 products were not able to represent the WSBW throughout the simulation period. The expected WDW warming was only reproduced by the SODA product, while the ECCO2 product was able to represent the WSDW's hydrographic properties trends. All of these ocean reanalysis systems were able to represent the decrease in the WSBW's density. Our results also showed that a simple increase in horizontal resolution does not necessarily imply better representation of the deep layers. Rather, it is needed to observe the physics involved in each model and their parameterizations because the Southern Ocean suffers from the lack of in situ data, and it is biased by summer observations. The choice of the reanalysis product should be made carefully, taking into account the performance, the parameters of interest, and the type of physical processes to be evaluated.