Abstract
Abstract. Ocean–sea-ice coupled models constrained by various observations provide different ice thickness estimates in the Antarctic. We evaluate contemporary monthly ice thickness from four reanalyses in the Weddell Sea: the German contribution of the project Estimating the Circulation and Climate of the Ocean Version 2 (GECCO2), the Southern Ocean State Estimate (SOSE), the Ensemble Kalman Filter system based on the Nucleus for European Modelling of the Ocean (NEMO-EnKF) and the Global Ice–Ocean Modeling and Assimilation System (GIOMAS). The evaluation is performed against reference satellite and in situ observations from ICESat-1, Envisat, upward-looking sonars and visual ship-based sea-ice observations. Compared with ICESat-1, NEMO-EnKF has the highest correlation coefficient (CC) of 0.54 and lowest root mean square error (RMSE) of 0.44 m. Compared with in situ observations, SOSE has the highest CC of 0.77 and lowest RMSE of 0.72 m. All reanalyses underestimate ice thickness near the coast of the western Weddell Sea with respect to ICESat-1 and in situ observations even though these observational estimates may be biased low. GECCO2 and NEMO-EnKF reproduce the seasonal variation in first-year ice thickness reasonably well in the eastern Weddell Sea. In contrast, GIOMAS ice thickness performs best in the central Weddell Sea, while SOSE ice thickness agrees most with the observations from the southern coast of the Weddell Sea. In addition, only NEMO-EnKF can reproduce the seasonal evolution of the large-scale spatial distribution of ice thickness, characterized by the thick ice shifting from the southwestern and western Weddell Sea in summer to the western and northwestern Weddell Sea in spring. We infer that the thick ice distribution is correlated with its better simulation of northward ice motion in the western Weddell Sea. These results demonstrate the possibilities and limitations of using current sea-ice reanalysis for understanding the recent variability of sea-ice volume in the Antarctic.
Highlights
Antarctic sea ice is a crucial component of the climate system
Reanalyses tend to overestimate sea-ice thickness in contrast to ASPeCt, which is consistent with the results reported in Timmermann et al (2005)
We find that accurate northward ice motion in the western Weddell Sea is related to thick ice accumulation in the southwestern Weddell Sea and that sea-ice thickness distribution is consistent with observations
Summary
Antarctic sea ice is a crucial component of the climate system. In contrast to the rapid sea-ice decline in the Arctic, the sea-ice extent of the Antarctic has exhibited an overall positive trend during the past 4 decades (Simmonds, 2015; Comiso et al, 2017) even when taking into consideration the relatively fast decrease observed from 2014 to 2017 (Turner and Comiso, 2017; Parkinson, 2019). Several investigations have been made to estimate long-term Antarctic sea-ice thickness changes using ice–ocean coupled models with data assimilation (e.g., Zhang and Rothrock, 2003; Massonnet et al, 2013; Köhl, 2015; Mazloff et al, 2010), resulting in openly available sea-ice thickness products. These sea-ice thickness products have been used for various studies.
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