As the debate on climate change progresses, the focus on the poles has increased. The ice covered poles can be seen as a sort of thermometer for Earth since they respond almost immediately to changes in the climate. With technology as advanced as it is, videos showing geomorphological changes at the poles are a dime a dozen (I felt obligated to put in an amateur video because there are really cute penguins running from the waves here even though there are other videos showing part of the ice sheet collapsing clearer)
It is not unusual to see parts of the ice sheets break off, every summer the glaciers retreat and advance during winter. However, over the last 50 years, it has been observed that glaciers at both poles have been in retreat and despite re-growth during the winter months, there are an increasing number of glaciers that have not regained their original mass. While global warming does cause the loss of ice mass at the poles, the loss of ice mass at the poles is also contributed by ‘increasing precipitation, changing ocean temperatures’ (Cook et al, 2005). Most of the ice loss has been observed on the marginal parts of the ice sheet since they are the most susceptible to such environmental changes.
Below is map of Antarctica and the Antarctic Peninsula is indicated by the red box.
The Antarctic Peninsula is a Northwest extension of the main continent and observations have shown that it is showing much higher vulnerability to climate changes compared to the continent itself. Since the 1950s, the climate has warmed by 2 degrees (Cook et al, 2005). This regional warming of the Peninsula has led to a 10 fold increase in glacier flow and rapid ice sheet retreat (Rignort, 2006). In the paper 'Retreating Glacier Fronts on the Antarctic Peninsula Over the Past Half-Century' by Cook et al in 2005, there are satellite images of the glacier retreat of Sheldon Glacier, Adelaide Island showing its retreat in 2001 compared to 1986. The break-up of the ice shelf is observed with the smaller ice extent and the broken, drifting ice shelf. From the earliest known position of ice shelves in 1953, 87% of glaciers in the Peninsula have shown overall retreat. The image below shows how much the Sheldon Glacier has retreated from 1947 to 2001.
(BBC, 2005)
One of the reasons for the observed overall retreat of ice shelves is due to climate. The Antarctic Peninsula is warming at a rate of 3.4 degrees Celsius (give or take 1 degree Celsius) per century (Shevenell et al, 2011). This warming coincides with the positive rates of glacier retreat as shown by the figure below.
However, in the figure above, while the general trend throughout the whole of the Antarctic Peninsula is a glacier retreat corresponding with a general increase in temperature there were advances in glaciers from 1945 to 1964. This suggests that there are other factors that influence the extent of the ice shelves in the Peninsula.
The reason for this discrepancy is due to the ocean-atmosphere heat exchange over the Antarctic Peninsula. It was found that from the 1950s, the Southern Hemisphere Westerlies that bring warmer air from the lower latitudes to the higher latitudes have experienced either a southerly migration (thus bring warmer air to higher latitudes) or has intensified (Shevenell et al, 2011). This then affects the Antarctic Circumpolar Current (ACC), which is an ocean current that circles the Antarctic, causing it to migrate southwards and/or intensify as well. This allows warm Circumpolar Deep Water to upwell along the Peninsula partly due to the ocean bathymetry and the ACC’s proximity and to mix with surface waters.
As a result, the advancement of glaciers prior to 1950 were due to the Westerlies being nearer to the Equator and not having that significant of an effect on the ACC, allowing for cooling of the climate. However, after that warming occurred due to the above described process and in combination with the anthropogenic global warming, this is resulted in the Antarctic Peninsula (and the rest of the Antarctic) to warm and thus experience a lesser extent of ice cover.
Journals:
Cook, A.J., Fox, A.J., Vaughan, D.C., Ferrigno, J.G. (2005) 'Retreating Glacier Fronts on the Antarctic Peninsula over the Past Half-Century', Science, 308, 5721, 541-544.
Rignot, E. (2006) 'Changes in ice dynamics and mass balance of the Antarctic ice sheet', Philosophical Transactions: Mathematical, Physical and Engineering Sciences, 364, 1844, 1637-1655.
Shevenell, A.E., Ingalls, A.E., Domack, E.W and Kelly, C. (2011) ' Holocene Southern Ocean surface temperature variability west of the Antarctic Peninsula', Nature, 470, 250-255.
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