New results from an investigation into Antarctica’s potential contribution to sea level rise are reported this week (Sunday 20 June) by scientists from the British Antarctic Survey (BAS), Lamont-Doherty Earth Observatory (LDEO) and the National Oceanography Centre in the journal Nature Geoscience.
Thinning ice in West Antarctica is currently contributing nearly 10 per cent of global sea level rise and scientists have identified Pine Island Glacier (PIG) as a major source. As part of a series of investigations to better understand the impact of melting ice on sea level an exciting new discovery has been made. Using Autosub (an autonomous underwater vehicle) to dive deep and travel far beneath the pine Island Glacier’s floating ice shelf, scientists captured ocean and sea-floor measurements, which revealed a 300m high ridge (mountain) on the sea floor.
Pine Island Glacier was once grounded on (sitting on top of) this underwater ridge, which slowed its flow into the sea. However, in recent decades it has thinned and disconnected from the ridge, allowing the glacier to move ice more rapidly from the land into the sea. This also permitted deep warm ocean water to flow over the ridge and into a widening cavity that now extends to an area of 1000 km2 under the ice shelf. The warm water, trapped under the ice, is causing the bottom of the ice shelf to melt, resulting in continuous thinning and acceleration of the glacier.
Lead author Dr Adrian Jenkins of British Antarctic Survey said, “The discovery of the ridge has raised new questions about whether the current loss of ice from Pine Island Glacier is caused by recent climate change or is a continuation of a longer-term process that began when the glacier disconnected from the ridge.
“We do not know what kick-started the initial retreat from the ridge, but we do know that it started some time prior to 1970. Since detailed observations of Pine Island Glacier only began in the 1990s, we now need to use other techniques such as ice core analysis and computer modelling to look much further into the glacier’s history in order to understand if what we see now is part of a long term trend of ice sheet contraction. This work is vital for evaluating the risk of potential wide-spread collapse of West Antarctic glaciers.”
Steven Mosher has graciously allowed me to add my two cents worth here. As you know, I love data, it beats theories every time.
First, data on the location of the Pine Island Glacier:
Figure W1. Pine Island Glacier, Antarctica. The West Antarctic Peninsula is at the top right. Pine Island Glacier is shown by the snowflake. The white box outlines the area for which I show sea surface temperature (SST) below.
Next, data on the ocean surface temperatures. There are a couple of SST datasets that cover this area. Both are available at KNMI, that amazing resource. One is the Hadley HADISST Ice and Sea Surface Dataset. The other is the Reynolds satellite based dataset. Here’s what they say about the sea surface temperatures in the area outlined by the white box:
Figure W2. Change in sea surface temperature (SST) in the ocean off of Pine Island Glacier.
Conclusions? Well, it seems clear that the change in the sea surface temperature is not the reason for the melting of the Pine Island Glacier, SSTs have been dropping there for the last thirty years …
Regards to all,