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Ocean Science An interactive open-access journal of the European Geosciences Union
Ocean Sci., 10, 923-946, 2014
https://doi.org/10.5194/os-10-923-2014
© Author(s) 2014. This work is distributed under
the Creative Commons Attribution 3.0 License.
Research article
21 Nov 2014
Assessment of the representation of Antarctic Bottom Water properties in the ECCO2 reanalysis
M. Azaneu, R. Kerr, and M. M. Mata Laboratório de Estudos dos Oceanos e Clima, Instituto de Oceanografia, Universidade Federal do Rio Grande (FURG), Rio Grande, RS, 96203-900, Brazil
Abstract. We analyzed the ability of the Estimating the Circulation and Climate of the Ocean – Phase II (ECCO2) reanalysis to represent the hydrographic properties and variability of Antarctic Bottom Water (AABW) in the Southern Ocean. We used a 20-year (1992–2011) observational database to perform comparisons of hydrographic properties and reanalysis output for the same time period. Four case studies based on current meter data and the AABW volume transport estimates previously reported in the literature were also evaluated. The opening and maintenance of an oceanic polynya in the Weddell Sea sector is observed after 2004 in the reanalysis product. Moreover, intense deep water production due to deep convection occurs, which leads to a scenario in which the Weddell Sea is flooded with AABW. For this reason, our analyses focused on the period that was identified as more reliable (1992–2004). The main Southern Ocean oceanographic features, as well as the characteristic shape of the regional potential temperature–salinity (θ–S) diagrams, are coincident with observations. However, the reanalysis output produces surface waters that are generally denser than observations due to the reproduction of waters that are generally saltier than expected, which probably resulted from the strong seasonality of sea ice concentrations. Bottom waters are warmer and less dense, while intermediate waters are statistically closest to the observations. The differences in bottom water properties are partially due to the inability of the reanalysis to properly reproduce the formation and export of dense waters from the shelf and the consequent absence of the densest AABW variety for most of the analyzed period. Despite differences in the absolute values, the upper AABW limit (γn ≥ 28.27 kg m−3) and AABW occupied area estimates are coincident with the observations in the World Ocean Circulation Experiment (WOCE) repeat sections SR2 and SR4. Moreover, the AABW volume export and current velocity variability are correlated with the observed time series in the most important region of dense water export (i.e., the Weddell Sea). Despite the consistency in terms of variability, the absolute volume transport and velocity estimates are underrepresented in all cases.

Citation: Azaneu, M., Kerr, R., and Mata, M. M.: Assessment of the representation of Antarctic Bottom Water properties in the ECCO2 reanalysis, Ocean Sci., 10, 923-946, https://doi.org/10.5194/os-10-923-2014, 2014.
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Short summary
We analyzed the ability of the ECCO2 reanalysis to represent the hydrographic properties and variability of Antarctic Bottom Water in the Southern Ocean. After 2004, the opening of an oceanic polynya in the Weddell Sea sector and consequent intense dense water production leads to an unrealistic scenario. Even before 2004, bottom waters are warmer and less dense than expected, while the absolute volume transport and velocity estimates are underrepresented.
We analyzed the ability of the ECCO2 reanalysis to represent the hydrographic properties and...
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