Previous rapid thinning of Pine Island Glacier sheds light on future Antarctic ice loss.
New research, published this week in Science, suggests that the largest single contributor to global sea level rise, a glacier of the West Antarctic Ice Sheet, may continue thinning for decades to come. Geologists from the UK, USA and Germany found that Pine Island Glacier (PIG), which is rapidly accelerating, thinning and retreating, has thinned rapidly before. The team say their findings demonstrate the potential for current ice loss to continue for several decades yet.
Their findings reveal that 8000 years ago the glacier thinned as fast as it has in recent decades, providing an important model for its future behaviour. The glacier is currently experiencing significant acceleration, thinning and retreat that is thought to be caused by ‘ocean-driven’ melting; an increase in warm ocean water finding its way under the ice shelf.
After two decades of rapid ice loss, concerns are arising over how much more ice will be lost to the ocean in the future. Model projections of the future of PIG contain large uncertainties, leaving questions about the rate, timing and persistence of future sea level rise. Rocks exposed by retreating or thinning glaciers provide evidence of past ice sheet change, which helps scientists to predict possible future change. The geologists used highly sensitive dating techniques, pioneered by one of the team, to track the thinning of PIG through time, and to show that the past thinning lasted for several decades.
Lead author Joanne Johnson from the British Antarctic Survey (BAS) said: "Our geological data show us the history of Pine Island Glacier in greater detail than ever before. The fact that it thinned so rapidly in the past demonstrates how sensitive it is to environmental change; small changes can produce dramatic and long-lasting results. Based on what we know, we can expect the rapid ice loss to continue for a long time yet, especially if ocean-driven melting of the ice shelf in front of Pine Island Glacier continues at current rates,"
Professor Mike Bentley, a co-leader of the project based at Durham University said: “This paper is part of a wide range of international scientific efforts to understand the behaviour of this important glacier. The results we’re publishing are the product of long days spent sampling rocks from mountains in Antarctica, coupled to some exceptionally precise and time-consuming laboratory analyses. The results are clear in showing a remarkably abrupt thinning of the glacier 8000 years ago”.
Dr Dylan Rood, of the University of Glasgow and the Scottish Universities Environmental Research Centre, first worked on the project as part of a post-doctoral position at the Lawrence Livermore National Laboratory in the United States.
Dr Rood said: “We reconstructed the history of the thinning of the ice stream by dating the exposure of glacially-transported rocks as they emerged from the ice at different elevations. This involved using an accelerator mass spectrometer to measure the isotope beryllium-10 in the samples produced by bombardment of cosmic radiation at the Earth’s surface, which allowed us to date the samples with tremendous accuracy, underpinning the findings of the whole project.”
This work was funded by the Natural Environment Research Council and Lamont-Doherty Earth Observatory, USA (through a Marie Tharp fellowship awarded to Joanne Johnson). Logistic support was provided by the Alfred Wegener Institute.
The paper: Rapid Thinning of Pine Island Glacier in the Early Holocene by J S Johnson, M J Bentley, J A Smith, R C Finkel, D H Rood, K Gohl, G Balco, R D Larter, J M Schaefer is published in Science on Thursday 20 February 2014. doi:10.1126/science.1247385
First published: 21 February 2014