Hidden oceanic gateway beneath Totten Glacier

Graphic detailing the ocean floor and bedrock in the Totten Glacier ice shelf region
This graphic shows the ocean floor and bedrock in the Totten Glacier ice shelf region. The front of the ice shelf is indicated by the blue line, and the grounding line (where the ice begins to float) is delineated by the white line. Warm and deeper ocean waters require deep channels to access the grounding line. This study has identified a deep trough or gateway (red line) through which warm water (orange solid line) can access the deep parts of the grounding line and drive retreat. A secondary path (dashed orange line) is identified, but is shallower and less significant. (Photo: Jamin Greenbaum)

Ice-penetrating radar imagery has revealed a five kilometre-wide seafloor valley beneath the Totten Glacier that could allow warm water to infiltrate its base, causing potentially destabilising melting.

The discovery, published in the journal Nature Geoscience in March, is the first to identify a mechanism that could explain why the Totten is the fastest thinning glacier in East Antarctica.

It follows findings from a marine science voyage to the glacier earlier this year, which measured ocean temperatures at the front of the glacier capable of causing melt at the glacier’s grounding line (see Totten Glacier melt-down). However, oceanographers were unable to establish if or how this warm ocean water was getting under the glacier.

Australian Antarctic Division glaciologist and a contributor to the geophysical project, Dr Jason Roberts, said that the infiltration of warm water beneath the glacier, via the seafloor valley or ‘gateway’, had the long-term potential to cause 3.5 metres of sea level rise.

‘The glacier catchment reaches as deep as 1.7 kilometres below sea level and is covered by up to four kilometres of ice,’ Dr Roberts said.

‘There is enough ice in the Totten Glacier alone to raise global sea level by at least 3.5 metres, roughly equivalent to the projected contribution of the entire West Antarctic Ice Sheet if it were to completely collapse.

‘While it may take several centuries to melt, once it passes a certain point our analysis reveals it would likely be irreversible.’

Lead author of the research paper, Mr Jamin Greenbaum, a PhD student from the University of Texas at Austin, said technology played a key role in identification of the seafloor gateway.

‘Satellite analyses conducted by other teams had indicated that the ice above the seafloor was resting on solid ground,’ he said.

‘However, special analysis of ice-penetrating radar data shows the bottom of the ice over the valley is smoother and brighter than elsewhere in the area, which is a tell-tale sign that the ice is floating and being eroded by the ocean.

‘Knowing this will improve predictions of ice melt and the timing of future glacier retreat.’

The discovery comes after five field seasons of aerial surveys over more than 156 000 kilometres of the Australian Antarctic Territory. The surveys were conducted from Australia’s Casey station between 2008 and 2013 (Australian Antarctic Magazine 19: 7, 2010).

The Basler-BT67 aircraft used in the surveys was fitted out with radar, laser, gravity meter and geomagnetic sensors for determining ice thickness, bedrock topography, seafloor bathymetry, and bedrock properties.

‘The findings from this study present a strong case for using airborne geophysical surveys to look at ice-ocean interactions in other parts of Antarctica, including the virtually unknown Antarctic inner continental shelf,’ Mr Greenbaum said.

The research was conducted through the ICECAP (International Collaboration for Exploration of the Cryosphere through Aerogeophysical Profiling) project, which involved the Australian Antarctic Division, Antarctic Climate and Ecosystems Cooperative Research Centre, the University of Texas Institute for Geophysics, the US National Science Foundation, the UK’s Natural Environment Research Council, as well as NASA’s Operation IceBridge and the G. Unger Vetlesen Foundation.

Wendy Pyper and Nisha Harris
Australian Antarctic Division