Australia: The Land Where Time Began

A biography of the Australian continent 

Amundsen Sea Shelf Break – Oceanographic Observations

The environment of the continental shelf of the Amundsen Sea and Bellingshausen Sea are markedly different from that of other circumpolar seas in which the water temperatures are close to the surface freezing point throughout. Near-freezing temperatures are encountered only in the upper most few hundred metres of the water column in the Amundsen/Bellingshausen sector. A broad thermocline below the surface layer tends towards upper Circumpolar Deep Water (uCDW), which is present in a form that is almost unmodified from its off-shelf manifestation (Giulivi & Jacobs, 1996). The ice shelves of the Amundsen Sea and the Bellingshausen Sea are indicated by this to experience ocean temperatures that are some 3^oC warmer than those experienced by other Antarctic ice shelves, and the rates of basal melting are correspondingly higher (Jacobs et al., 1996).

According to Walker et al. Pine Island Bay, in the eastern Amundsen Sea, has had attention focused on it in recent years. Pine Island Glacier and Thwaites Glacier, which are 2 of the largest glaciers that drain the West Antarctic Ice Sheet, discharge into Pine Island Bay.

The melt rate of the Pine Island Glacier is more than 10 m per year (Jenkins et al., 1997; Hellmer et al., 2002; Sheppard et al., 2002). It has been found that the Pine Island glacier appears to be retreating (Rignot, 1998). It has also been observed that a similar thinning signature has also been observed near the grounding line of the Smith Glacier (Sheppard et al., 2002).

The synchronous response of all 3 floating glacier tongues is said by Walker et al. to be more suggestive of a response to external forcing than of an internal change of dynamics in the glaciers, though the cause of these changes is far from certain. The ocean is the most likely driver of change. The sensitivity of the Pine Island Glacier melt rates to minor changes in water temperature has been demonstrated (Hellmer et al., 1998). Change in the rate of supply or the temperature of the upper Cold Deep Water in Pine Island Bay could have a major impact on the ice shelves in that sector.

Sources & Further reading

1. Walker, D. P., A. Jenkins, K. M. Assmann, D. R. Shoosmith and M. A. Brandon (2013). "Oceanographic observations at the shelf break of the Amundsen Sea, Antarctica." Journal of Geophysical Research: Oceans 118(6): 2906-2918.