Abstract
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.
Highlights
Different groups of experts have developed several state-of-the-art eddy-permitting general ocean circulation models with long simulations and elegant and efficient assimilation methods
We first describe the average sea ice patterns in the Southern Ocean sectors, its spatial signature and evidence that this property is related to the Antarctic Bottom Water (AABW) formation in the reanalysis products investigated (Sect. 3.1)
In ECCO2, the mechanism of AABW formation resulted in erroneous representations of the Southern Ocean, such as high AABW volumes and lower sea ice concentrations and thicknesses, emphasizing that open ocean deep convection inserts errors into the simulation (e.g., Azaneu et al, 2014; this study)
Summary
Different groups of experts have developed several state-of-the-art eddy-permitting general ocean circulation models with long simulations and elegant and efficient assimilation methods. Based on those models, ocean reanalysis products, which reconstruct oceanic features using governing ocean equations and observed data, have been coupled with global climate models (GCMs) to produce detailed climate estimates (Lee et al, 2009). One of the features receiving special attention in ocean reanalysis products is the representation of the lower limb of the Atlantic Meridional Overturning Circulation (AMOC) In this sense, recent assessments have revealed several model inconsistencies related to the Southern Ocean dense water formation and export, which is a key process in the AMOC lower limb dynamics (e.g., Azaneu et al, 2014). The deep water changes properties and along the way forms Circumpolar Deep Water (CDW) as it enters the Southern Ocean (e.g., Talley, 2013)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
