Climate Research News

Two new studies summarised in a news article in Science magazine point to wind-induced circulation changes in the ocean as the dominant cause of the recent ice losses through the glaciers draining both the Greenland and West Antarctic ice sheets, not ‘global warming.’

The two stuides referred to are:

‘Acceleration of Jakobshavn Isbræ triggered by warm subsurface ocean waters’ by Holland et al, published in Nature Geoscience.

The Abstract states:

Observations over the past decades show a rapid acceleration of several outlet glaciers in Greenland and Antarctica¹. One of the largest changes is a sudden switch of Jakobshavn Isbræ, a large outlet glacier feeding a deep-ocean fjord on Greenland’s west coast, from slow thickening to rapid thinning² in 1997, associated with a doubling in glacier velocity³. Suggested explanations for the speed-up of Jakobshavn Isbræ include increased lubrication of the ice–bedrock interface as more meltwater has drained to the glacier bed during recent warmer summers⁴ and weakening and break-up of the floating ice tongue that buttressed the glacier⁵. Here we present hydrographic data that show a sudden increase in subsurface ocean temperature in 1997 along the entire west coast of Greenland, suggesting that the changes in Jakobshavn Isbræ were instead triggered by the arrival of relatively warm water originating from the Irminger Sea near Iceland. We trace these oceanic changes back to changes in the atmospheric circulation in the North Atlantic region. We conclude that the prediction of future rapid dynamic responses of other outlet glaciers to climate change will require an improved understanding of the effect of changes in regional ocean and atmosphere circulation on the delivery of warm subsurface waters to the periphery of the ice sheets.

And:

‘Modelling Circumpolar Deep Water intrusions on the Amundsen Sea continental shelf, Antarctica’ by Thoma et al, published in GRL.

The Abstract states:

Results are presented from an isopycnic coordinate model of ocean circulation in the Amundsen Sea, focusing on the delivery of Circumpolar Deep Water (CDW) to the inner continental shelf around Pine Island Bay. The warmest waters to reach this region are channeled through a submarine trough, accessed via bathymetric irregularities along the shelf break. Temporal variability in the influx of CDW is related to regional wind forcing. Easterly winds over the shelf edge change to westerlies when the Amundsen Sea Low migrates west and south in winter/spring. This drives seasonal on-shelf flow, while inter-annual changes in the wind forcing lead to inflow variability on a decadal timescale. A modelled period of warming following low CDW influx in the late 1980’s and early 1990’s coincides with a period of observed thinning and acceleration of Pine Island Glacier.

October 3rd, 2008 | Tags: Climate Change | Category: News | Subscribe to comments | Leave a comment | Trackback URL