Modelling the impact of ocean warming on melting and water masses of ice shelves in the Eastern Weddell Sea

Abstract

The Eastern Weddell Ice Shelves (EWIS) are believed to modify the water masses of the coastal current and thus preconditions the water mass formation in the southern and western Weddell Sea. We apply various ocean warming scenarios to investigate the impact on the temperature-salinity distribution and the sub-ice shelf melting in the Eastern Weddell Sea. In our numerical experiments the warming is imposed homogeneously along the open inflow boundaries of the model domain, leading to a warming of the Warm Deep Water (WDW) further downstream. Our modelling results indicate a weak quadratic dependence of the melt rate at the ice shelf base on the imposed amount of warming, which is consistent with earlier studies. The total melt rate has a strong dependence on the applied ocean warming depth. If the warming is restricted to the upper ocean (above 1000 m), the water column (aside from the mixed surface layer) in the vicinity of the ice shelves stabilises. Hence, reduced vertical mixing will reduce the potential of Antarctic Bottom Water formation further downstream with consequences on the global thermohaline circulation. If the warming extends to the abyss, the WDW core moves significantly closer to the continental shelf break. This sharpens the Antarctic Slope Front and leads to a reduced density stratification. In contrast to the narrow shelf bathymetry in the EWIS region, a wider continental shelf (like in the southern Weddell Sea) partly protects ice shelves from remote ocean warming. Hence, the freshwater production rate of, e.g., the Filchner Ronne Ice Shelf increases much less compared to the EWIS for identical warming scenarios. Our study therefore indicates that the iceocean interaction has a significant impact on the temperature-salinity distribution and the water column stability in the vicinity of ice shelves located along a narrow continental shelf. The effects of ocean warming and the impact of increased freshwater fluxes on the circulation are of the same order of magnitude and superimposed. Therefore, a consideration of this interaction in large-scale climate studies is essential.

Connecting Antarctic Cross-Slope Exchange with Southern Ocean Overturning

“…Thus the net heat flux varies more rapidly with t ASF , 0 than with t ASF $ 0. This is consistent with the hypothesis that warm CDW inflow to the Ross and Amundsen Seas is controlled by seasonal changes in the offshore easterlies (Thoma et al 2010;Dinniman et al 2011), but seems to contradict the idea that changes in offshore westerly wind stress control CDW intrusions into the Amundsen Sea (Thoma et al 2008).…”

“…In particular, the contribution of mesoscale eddies to the cross-shelf transport remains unclear, though recent high-resolution modeling studies suggest that eddies may dominate the shoreward transport of Circumpolar Deep Water (CDW) beneath Antarctic ice shelves (Thoma et al 2008;Dinniman et al 2011;Nøst et al 2011). We will focus on the sensitivity of the MOC to changes in the easterlies that drive the ASF.…”

Modeling Antarctic ice shelf responses to future climate changes and impacts on the ocean

“…[43] A similar mechanism, i.e., effect of upstream melt waters on downstream regions, may also happen in other sectors [Thoma et al, 2010]. It is found that increased melt waters of ice shelves in the Eastern Weddell Sea play a role in freshening coastal waters over the continental shelf in the Weddell Sea and the signal spreads to the Scotia Sea (Figures 10 and 12).…”

“…[6] In ocean general circulation models, an ice front between ice shelf and ocean had been often treated as a solid continental boundary. Over the past decade, threedimensional ocean models which include an elaborate ice shelf component have been developed, and the ice shelfocean interaction and their impact on sea ice and ocean have been investigated [Assmann et al, 2003;Assmann and Timmermann, 2005;Beckmann et al, 1999;Holland et al, 2010;Jenkins and Holland, 2002;Losch, 2008;Makinson et al, 2011, Reddy et al, 2010Thoma et al, 2006Thoma et al, , 2008Thoma et al, , 2010Timmermann et al, 2002aTimmermann et al, , 2002bWilliams et al, 1998Williams et al, , 2002Galton-Fenzi et al, 2012]. However, most of the previous ice shelf-ocean modeling studies use regional models in which a few ice shelves are represented in the model domain.…”

Understanding and Modelling Rapid Dynamic Changes of Tidewater Outlet Glaciers: Issues and Implications

“…Although such ocean models are becoming available now (Thoma et al 2010; review; Holland et al 2010;Payne et al 2007) their application is still limited and importantly they lack a direct coupling with dynamic ice flow models. Examples of such limitations are (1) the poorly known fjord bathymetry and vertical stratification of waters which are crucial for mixing the waters at the ice interface (Straneo et al 2011), (2) lack of information of the ambient fjord water temperature and salinity, and, importantly, (3) the lack of understanding of the replacement of fjordwater with coastal ocean water.…”