Australia: The Land Where Time Began

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The West Antarctic Ice Shelf warming from beneath

The West Antarctic Ice Sheet, that is mostly grounded below sea level, making it sensitive to warming of the ocean, contains enough water to raise the global sea level by several metres if if melted. Over the past decades it has been suggested that glaciers discharging into the Amundsen Sea are thinning at accelerated rates, the mechanism proposed being warm water beneath the ice shelves. There are 3 deep troughs crosscutting the continental shelf beneath the Amundsen Sea, and though oceanographic data are limited it has been proposed that these trough allow the movement of warm ocean water can gain access to the ice shelves. The authors1 have carried out studies on 1 of the troughs in the continental shelf in 2010 in which they made direct measurements of temperatures, salinities and velocities from an ocean mooring and ship transect in the central Amundsen Sea. Their results indicate there is persistent inflow of relatively warm, salty water at the bottom of the trough towards the ice shelf that continues throughout the year, with cooler water outflowing above. Barotropic current fluctuations are superimposed on this background flow, though they make no significant contribution to the overall transport. These results contradict results of numerical models which indicate that there are seasonal flow changes as a a response to regional winds. According to the results of the authors1 there is no strong seasonal variability in the flow of warm water to the Central Amundsen Shelf.


Warm water is transported towards the continent, the authors1 suggesting it probably contributes to the melting of the Getz, Dotson and Crosson ice shelves from below. According to the authors1 if temperatures and velocities are correlated a net transport of warm water could also be caused by the barotropic current. The flux of heat content above that of similar water at the freezing temperature is a relevant of warm water transportation. As shown in Fig 4d, based on barotropic and baroclinic velocity components, at the location of the mooring shows the vertically-integrated heat flux per unit width. Large fluctuations around a small mean value of 0.4 ± 49 MW m-1 by the barotropic velocity fluctuations. The authors1 suggest that as the barotropic component should be included in the transect estimates as it does not contribute to the long-term warm water flow onto the shelf.

The time series data set resulting from this study is the first that can be used to validate the numerical model that has suggested the forcing by  strong westerlies in winter of the inflow of warm water onto the continental shelf of the Amundsen Sea. A baroclinic inflow that has little  if any seasonality is shown by observations. The authors1 say this data set is too short to facilitate a seasonality study that is more detailed, suggesting that new mooring observations will be invaluable in the untangling of the general circulation pattern and the mechanisms of forcing of the inflows of warm water with the resulting ice shelf decay on the Amundsen shelf.

 Sources & Further reading

  1. Arneborg, L., A. K. Wahlin, G. Bjork, B. Liljebladh, and A. H. Orsi. "Persistent Inflow of Warm Water onto the Central Amundsen Shelf." Nature Geosci 5, no. 12 (12//print 2012): 876-80.


Author: M. H. Monroe
Last updated 20/12/2012 

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