Preprints
https://doi.org/10.5194/egusphere-2023-690
https://doi.org/10.5194/egusphere-2023-690
18 Apr 2023
 | 18 Apr 2023
Status: this preprint is open for discussion.

Southern Weddell Sea surface freshwater flux modulated by icescape and atmospheric forcing

Lukrecia Štulić, Ralph Timmermann, Stephan Paul, Rolf Zentek, Günther Heinemann, and Torsten Kanzow

Abstract. Sea-ice formation dominates surface salt forcing in the southern Weddell Sea. Brine rejected in the process of sea-ice production results in the production of High Salinity Shelf Water (HSSW) that feeds the global overturning circulation and fuels the basal melt of the adjacent ice shelf. The strongest sea-ice production rates are found in coastal polynyas, where steady offshore winds promote divergent ice movement during the freezing season. The position of fast-ice areas and the presence of grounded icebergs (icescape) can influence the formation of polynyas and therefore impact sea-ice production. We use the Finite Element Sea ice–ice shelf–Ocean Model (FESOM) forced by output from the regional atmospheric model COSMO-CLM (CCLM) with 14 km horizontal resolution to investigate the role of polynyas for the surface freshwater flux of the southern Weddell Sea (2002–2017). The representation of the icescape in our model is included by prescribing the position, shape, and temporal evolution of a largely immobile ice mélange that was forming between the Filchner-Ronne Ice Shelf (FRIS) and a major grounded iceberg, as determined from MODIS satellite data on a monthly basis. We find that 70 % of the ice produced on the continental shelf of the southern Weddell Sea is exported from the region. While coastal polynyas cover 2 % of the continental shelf area, sea-ice production within the coastal polynyas accounts for 17 % of the overall annual sea-ice production (1509 km3). The largest contributions come from the Ronne Ice Shelf and Brunt Ice Shelf polynyas, and polynyas associated with the ice mélange. Furthermore, we investigate the sensitivity of the polynya-based ice production to the i) treatment of the icescape and ii) regional atmospheric forcing. Although large-scale atmospheric fields determine the sea-ice production outside polynyas, both the treatment of the icescape and the regional atmospheric forcing are important for the regional patterns of sea-ice production in polynyas. The representation of the ice mélange is crucial for the simulation of polynyas westward/eastward of it, which are otherwise suppressed/overestimated. Compared to using ERA-Interim reanalysis as an atmospheric forcing dataset, using CCLM output reduces polynya-based ice production over the eastern continental shelf due to weaker offshore winds and yields an overall more realistic polynya representation. Our results further indicate that the location and not just the strength of the sea-ice production in polynyas is a relevant parameter in setting the properties of the HSSW produced on the continental shelf, which in turn affects the basal melting of the Filchner-Ronne Ice Shelf.

Lukrecia Štulić et al.

Status: open (until 08 Jul 2023)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Lukrecia Štulić et al.

Data sets

FESOM sea-ice production for the southern Weddell Sea, 2002-2017 Lukrecia Štulić https://doi.org/10.5281/zenodo.7761156

Lukrecia Štulić et al.

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Short summary
In the southern Weddell Sea, the strong sea-ice growth in coastal polynyas drives formation of dense shelf water. By using a sea ice-ice shelf-ocean model with representation of the changing icescape based on the satellite data, we find that polynya sea-ice growth depends on both the regional atmospheric forcing and the icescape. Location and not only strength of the sea-ice growth in polynyas affect properties of the dense shelf water and the basal melting of the Filchner-Ronne Ice Shelf.