Sea Ice Edge

Loss of sea ice cover affects the amount of light and CO2 entering the ocean. Photo: Rebecca MacNeil

Highlights from sea ice and carbon cycle feedback research 2021/22

1 August 2022

In winter, sea ice grows from the edge of the Ross Ice Shelf and out over the Southern Ocean, and in summer it melts. But its extent varies from year to year, influenced by changes in atmospheric and open-ocean conditions. Understanding the difference between seasonal variability and long-term change, is key to predicting the future of Antarctic sea ice and its role in the global climate system. Understanding atmospheric circulation and sea ice variability is also critical to the exchange of carbon dioxide (CO2) and other gases between the atmosphere and ocean. The Southern Ocean plays a vital role in the removal of CO2 from the atmosphere, but the future of this globally important sink is uncertain.

The Antarctic Science Platform’s Project 4 – Sea Ice and Carbon Cycle Feedbacks has a team of researchers exploring:

  • What are the drivers of variability in the cycles of sea ice growth and decay in the Ross Sea?
  • What are the drivers of change in Southern Ocean CO2 uptake and release?
  • Are they related, and what are the consequences for oceans, ice shelves, ecosystems, and carbon budgets?

The project focusses on the Ross Sea region, with particular attention to the Ross Sea and Terra Nova Bay polynyas (these ice production factories are areas of open ocean surrounded by sea ice). Analysis of variability in sea ice and the carbon cycle on larger scales, and connections to atmospheric circulation, will involve climate processes across the whole of the Southern Ocean and much of the Southern Hemisphere.

Past, present and future change are being investigated using a combination of paleoclimate proxies, modern observations, remote sensing, and empirical and process modelling. New knowledge will improve future projections of sea ice change, and improved understanding of linkages between sea ice, ice sheets, the carbon cycle and ocean biology.

Air flask collecting

Collecting an air sample aboard a Heritage Expeditions cruise, 2017 Photo: Sherry Ott

The 2021/22 year highlights include the development of new modelling and measurement techniques, and significant fieldwork was undertaken.

Two objective techniques were developed for categorising sea ice imagery and for defining the location and size of polynyas in the Ross Sea region.

Air samples have continued to be collected by several “vessels of opportunity” to add to the existing database and to support models of ocean-air interactions and carbon cycle dynamics for the Southern Ocean and Ross Sea. Under separate funding, we are collecting and measuring samples from Baring Head and Macquarie Island, sites which are essential for the interpretation of the ASP results.

The snow radar was integrated into the EM-bird and tested in Antarctica. Though our collaborators Christian Haas (EM-bird operation) and Sarah Thompson (Australian Antarctic Program Partnership; support of ground validation for on ice measurements) were unable to join the field work, they supported this work remotely, along with the Scott Base team. Four EM-bird flights were conducted over sea ice and across the transition to the ice shelf, where we found deep snow. Maximum penetration depth of the snow radar in this area was about 2 meters. Preliminary analysis shows it is possible to simultaneously measure snow depth and sea ice thickness, as well as detecting the thickness of the sub-ice platelet layer.

EM Bird flying

Four EM-bird flights were conducted over sea ice and across the transition to the ice shelf. Photo: Anthony Powell

In a collaboration with Project 3, a new technology designed to sample the sub-ice platelet layer was tested for the first time in McMurdo Sound. The sub-ice platelet layer consists of an accumulation of disc-shaped ice crystals on the underside of sea ice, originating from supercooled water generated by basal melting of ice shelves. The layer is a significant component of Antarctic marine ecosystems, providing habitat for sea ice algae and a protective environment for the egg and larval stages of fish species, including Antarctic silverfish.

The custom-made drilling and sampling system successfully retrieved intact cores, promising to allow researchers to investigate the physical properties of the sub-ice platelet layer and its associated biology.

Sympagic community sampler in action

The first sample of platelet ice is drawn up the Sympagic Sampler into the Perspex tube using the Venturi system. Photo: Brett Grant/NIWA

Platelet ice measurements were also supported through an Opportunity Fund project in collaboration with the Korean Antarctic Programme at Terra Nova Bay. Drill hole and ground-based single- and multi-frequency electromagnetic (EM) measurements were undertaken of the thickness distributions of Ice Shelf Water (ISW) influenced fast ice and sub-ice platelet layer (SIPL). The data are being used to investigate how the distributions of ISW-influenced fast ice and SIPL relate to polynya dynamics and ocean circulation in Terra Nova Bay.

The Sea Ice Mass Balance station was recovered, and a year-round seafloor-mounted oceanographic mooring was deployed (the latter in collaboration with NIWA). Full-depth profiles of water column properties were collected at neap and spring tides, and these will serve as critical reference data for the timeseries data from the moored instruments.

Sea ice mass balance station 2021 22 season Photo by Greg Leonard

In 2021/22 the sea ice mass balance station was located on first year sea ice, about 900m north of the McMurdo Ice Shelf edge. Mt Discovery and Brown Peninsula can be seen in the background. Photo: Greg Leonard