The Fate of the Southern Weddell Sea Continental Shelf in a Warming Climate

• Published in: Journal of climate Vol. 30; no. 12; pp. 4337 - 4350
• Main Authors: Hellmer, Hartmut H., Kauker, Frank, Timmermann, Ralph, Hattermann, Tore
• Format: Journal Article
• Language: English
• Published: Boston American Meteorological Society 01.06.2017
• Subjects: 20th century; Antarctic ice; Antarctic ice sheet; Antarctic ice shelves; Atmosphere; Atmospheric forcing; Atmospheric models; Carbon dioxide; Carbon dioxide concentration; Circulation; Climate; Climate change; Computer simulation; Continental shelf circulation; Continental shelves; Deep water; Dynamics; Feedback; Glaciation; Global warming; Heat; Ice; Ice sheet dynamics; Ice shelves; Land ice; Loads (forces); Mass flux; Melting; Meltwater; Ocean models; Ocean-atmosphere interaction; Sea level; Shelf dynamics; Simulation; Stability; Warm water; Weddell Sea; Southern Ocean
• ISSN: 0894-8755; 1520-0442
• DOI: 10.1175/jcli-d-16-0420.1

Warm water of open ocean origin on the continental shelf of the Amundsen and Bellingshausen Seas causes the highest basal melt rates reported for Antarctic ice shelves with severe consequences for the ice shelf/ice sheet dynamics. Ice shelves fringing the broad continental shelf in theWeddell and Ross Seas melt at rates orders ofmagnitude smaller. However, simulations using coupled ice–ocean models forced with the atmospheric output of the HadCM3 SRES-A1B scenario run (CO₂ concentration in the atmosphere reaches 700 ppmv by the year 2100 and stays at that level for an additional 100 years) show that the circulation in the southern Weddell Sea changes during the twenty-first century. Derivatives of Circumpolar Deep Water are directed southward underneath the Filchner–Ronne Ice Shelf, warming the cavity and dramatically increasing basal melting. To find out whether the open ocean will always continue to power the melting, the authors extend their simulations, applying twentieth-century atmospheric forcing, both alone and together with prescribed basal mass flux at the end of (or during) the SRES-A1B scenario run. The results identify a tipping point in the southern Weddell Sea: once warm water flushes the ice shelf cavity a positive meltwater feedback enhances the shelf circulation and the onshore transport of open ocean heat. The process is irreversible with a recurrence to twentieth-century atmospheric forcing and can only be halted through prescribing a return to twentieth-century basal melt rates. This finding might have strong implications for the stability of the Antarctic ice sheet.