The formation and evolution of the Antarctic Ice Sheet : a combined model-data approach – Alan Kennedy, University of Bristol

The Antarctic ice sheet formed approximately 34 million years ago at the Eocene-Oligocene Transition (EOT): a period of large-scale shifts in climate.  The role that plate tectonics had during this period of global cooling in influencing global climate and, in particular, the formation of the Antarctic ice sheet remains uncertain.

(a) The relative position of landmasses during the Eocene (56-33.9 Million years before the present) (b) The relative position of landmasses during the Oligocene (33.9 - 23 million years before the present) (c) the imposed Antarctic ice sheet used in the analysis (figure from Getech PLC)

Fig.1 – Palaeogeographic reconstructions showing the relative position of the Earth’s landmassess during the (a) Eocene (56-33.9 Million years before the present) (b) Oligocene (33.9 – 23 million years before the present) and (c) the imposed Antarctic ice sheet used in the analysis (figure from Getech PLC)

 

In my research, I have looked at the relative positions of the continents during the Eocene and Oligocene (Fig. 1) and modelled global climate during those periods as the Antarctic ice sheet was forming. Antarctic ice growth is known to affect atmospheric circulation in the Southern Hemisphere, driving stronger westerly winds over the Southern Ocean. The position of landmasses relative to Antarctica can cause these winds to significantly alter ocean circulation patterns and deep-water formation, leading to unexpected responses of sea surface temperature in the Southern Oceans during those periods (Fig. 2).

Modelled sea surface temperature response to Antarctic ice growth for the Eocene (a) and Oligocene (b) palaeogeographies. Note the major differences in the South Pacific and Southern Ocean.

Fig. 2 – Modelled sea surface temperature response to Antarctic ice growth for the Eocene (a) and Oligocene (b) palaeogeographies. Note how the movement of landmasses during those periods and those interactions with formation of the Antarctic ice sheet have affected the sea surface temperature both positively and negatively in the South Pacific and Southern Ocean.

 

The work highlights not only the important role that the Antarctic ice sheet plays in influencing global climate, but also that sensitivity to plate tectonics should be taken into account when using climate models to support geochemical data to infer past climates.  Further work will involve modelling the growth of the Antarctic ice sheet and subsequent variations in its size with colleagues from the Bristol Glaciology Centre. This will help inform our understanding of how the ice sheet has responded to natural forcings in the past.

This research, carried out by Alan KennedyDr Alex Farnsworth and Prof Dan Lunt (University of Bristol), Dr. Carrie Lear (Cardiff University)  and Dr. Paul Markwick (CASE partner Getech PLC), is featured in a special issue of the Philosophical Transactions of the Royal Society A.  Kennedy A.T., Farnsworth A., Lunt D.J., Lear C.H., & Markwick P.J. (2015) Atmospheric and oceanic impacts of Antarctic glaciation across the Eocene–Oligocene transition. Phil. Trans. R. Soc. A, 373, 20140419, doi:10.1098/rsta.2014.0419.

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