Potential regime shift in decreased sea ice production after Mertz Glacier calving

Sea ice production, which is critical to the formation of Antarctic Bottom Water, has declined significantly off George V Land in East Antarctica since the calving of the Mertz Glacier Tongue in February 2010. Scientists from the Antarctic Climate & Ecosystems Co-operative Research Centre (ACE CRC) used satellite data to detect a 14 – 20% decrease (relative to the mean from 2000—2009) in sea ice production off George V Land in the two winters after the glacier tongue’s calving. They suggest that 50% of this decrease in sea ice production can be attributed to the changes in the icescape post-calving. Their research has been published in the journalNature Communications. Antarctic Bottom Water is a vital component of the global climate system. In the sector of East Antarctica below Australia, Antarctic Bottom Water is produced from overflows of dense shelf water that form in association with sea ice production in the George V Land polynya system. Polynyas, sometimes called ice factories, are regions of enhanced sea ice production structured by the local icescape that form dense shelf water from the brine rejected when sea ice freezes. The paper states that this abrupt change to the regional icescape has resulted in a decrease in total sea ice production for the region, and that this decrease could be part of a regime shift to decreased dense shelf water export and Antarctic Bottom Water production from this region for the coming decades. One of the paper’s co-lead authors, ACE CRC sea-ice specialist Dr Guy Williams, said major calving events were a natural part of the interaction between Antarctica and the surrounding ocean and were increasingly relevant as a potential response and feedback to climate change. “Here, for the first time, we are closely observing an important Antarctic polynya environment before and after such an event. In that sense East Antarctic ocean climate history is unfolding before our eyes and it is a very exciting experiment to be involved in,” he said. Dr Williams said the findings highlighted the dynamic nature of the ice front around Antarctica over decadal timescales. “Our findings present an ongoing challenge to the polar climate modelling community in terms of how to include dynamic ice front changes, such as those occurring in this region, into simulations.” A similar challenge exists for observational studies attempting to assess long-term climate trends over timescales interspersed with these structural changes to the system. ‘’We will continue to monitor George V land and plan to extend our analysis to the surrounding regions to assess the impact of the calving on the regional icescape.” The paper’s co-lead authors are Takeshi Tamura (National Institute of Polar Research, Japan, ACE CRC) and Guy Williams (ACE CRC), with Alex Fraser (ACE CRC) and K.I. Ohshima (Institute of Low Temperature of Science, Japan).

Authorised by the CEO of the Antarctic Climate and Ecosystems Cooperative Research Centre October 2019.

The ACE CRC was established and supported under the Australian Government’s Cooperative Research Centres Program.

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