Antarctic sea ice

Targeted observation and process-informed modelling of Antarctic sea ice (TOPIMASI)

Antarctic sea ice plays a major role in the global climate system. Its presence maintains cold conditions that help sustain Antarctica’s ice sheets, and it affects the rate of global warming by changing heat uptake in the Southern Ocean. Antarctic sea ice has a significant influence on both the ocean and atmospheric components of the climate system, and sea ice extent is closely linked with weather systems over New Zealand.

While the rapid retreat of Arctic sea ice is alarming researchers worldwide, satellite observations show that sea ice extent has actually been increasing in the Antarctic over the past 37 years. This behaviour is seemingly at odds with global warming. The truth is that current earth system models can’t faithfully reproduce the trends in sea ice coverage, and a lack of observations has meant that the drivers of these trends are poorly understood.

(In late 2016–early 2017, total Antarctic sea ice extent actually reduced. We still don’t know if this is a reversal of the pattern or just natural variability. Regardless, it’s important we understand what is going on.)

Antarctic sea ice grows and recedes fastest at the margins. The movement of the ocean surface waves break up ice on the outer edges, while extremely cold water causes sea ice to grow closer to the continent. This project involves field experiments on sea ice around Antarctica, and modelling work, to better understand the drivers of sea ice growth and decay. Our goal was to understand these processes well enough to ensure the NZ Earth System Model (NZESM) accurately reproduces the behaviour we’re seeing in Antarctic sea ice.

Key Findings:

The first phase of this project involved field experiments on the inner and outer margins of Antarctic sea ice, including the first, fixed-wing aircraft, sea ice thickness survey in Antarctica. This showed surprisingly thick, freely moving, pack ice (more than 4m thick) in the SW Ross Sea. Waves in sea ice also behave in an unexpected way, forcing a revision of ice-ocean modelling.

This is a joint project with the ESMP programme.

This project in the media:

• University of Otago professor gets $1.9m for Antarctica research, Stuff.co.nz
• Polar research should include Indigenous perspectives Nature
• Beneath the Ross Ice Shelf, RadioNZ
• Science on ice, Otago Daily Times
• What lies beneath: Why NZ’s slice of Antarctica is at the centre of an eco-mystery, Stuff.co.nz
• New Zealand’s Next Top Model, New Zealand Geographic
• Breaking the ice, NIWA