Articles | Volume 13, issue 6
Ocean Sci., 13, 851–872, 2017
Ocean Sci., 13, 851–872, 2017

Research article 07 Nov 2017

Research article | 07 Nov 2017

On deep convection events and Antarctic Bottom Water formation in ocean reanalysis products

Wilton Aguiar, Mauricio M. Mata, and Rodrigo Kerr Wilton Aguiar et al.
  • Laboratório de Estudos dos Oceanos e Clima, Instituto de Oceanografia, Universidade Federal do Rio Grande – FURG. Rio Grande, RS, 96203-900, Brazil

Abstract. Open ocean deep convection is a common source of error in the representation of Antarctic Bottom Water (AABW) formation in ocean general circulation models. Although those events are well described in non-assimilatory ocean simulations, the recent appearance of a massive open ocean polynya in the Estimating the Circulation and Climate of the Ocean Phase II reanalysis product (ECCO2) raises questions on which mechanisms are responsible for those spurious events and whether they are also present in other state-of-the-art assimilatory reanalysis products. To investigate this issue, we evaluate how three recently released high-resolution ocean reanalysis products form AABW in their simulations. We found that two of the products create AABW by open ocean deep convection events in the Weddell Sea that are triggered by the interaction of sea ice with the Warm Deep Water, which shows that the assimilation of sea ice is not enough to avoid the appearance of open ocean polynyas. The third reanalysis, My Ocean University Reading UR025.4, creates AABW using a rather dynamically accurate mechanism. The UR025.4 product depicts both continental shelf convection and the export of Dense Shelf Water to the open ocean. Although the accuracy of the AABW formation in this reanalysis product represents an advancement in the representation of the Southern Ocean dynamics, the differences between the real and simulated processes suggest that substantial improvements in the ocean reanalysis products are still needed to accurately represent AABW formation.

Short summary
In ocean models, Antarctic Bottom Water (AABW) formation is frequently misrepresented. Hence, assessing the causes of spurious formation is important to ensure accurate future simulations. Only one of the state-of-art reanalyses investigated showed AABW formation accurately. Spurious formation in the other two products resulted from opening of open ocean polynyas. The relatively accurate AABW formation in one of the products is an important advance in the simulation of deep ocean circulation.