318: Wilkes Land Glacial History

While the South Pole is covered by a glacier today, the South Pole was not always a frozen wasteland. Glaciation only started about 34 million years ago. As global temperatures changed throughout geologic history,  the amount of ice covering Antarctica changed with it.  As carbon dioxide (a greenhouse gas) amounts have increased and decreased in the atmosphere throughout history, the amount of ice has also fluctuated, so understanding ice flow through geologic time provides a picture of the impact of changing temperatures. It is particularly important to understand how anthropogenic warming has affected rapid ice melting in polar regions. Global carbon dioxide levels are increasing today in amounts not seen in the geologic past . The most recent time interval that had comparable atmospheric carbon dioxide levels occurred 17–15 million years ago, when the earth last warmed. Thus to best understand the future, it is imperative to understand the past and how Earth systems behaved or responded to increased greenhouse gasses in the atmosphere.

A map of the different locations drilled during Expedition 318 off the coast of Antarctica. Drill locations are denoted by the red dots. Obtained from  Integrated Ocean Drilling Program Expedition 318 Summary

Integrated Ocean Drilling Program Expedition 318 focused on the Wilkes Land Ice Shelf, located on the eastern half of the Antarctic continent. The purpose of the expedition was to drill into the ice sheet to understand how much ice melt occurred, and the rate at which it occurred throughout the past 34 million years. In understanding the rate of ice melt it becomes possible to correlate carbon dioxide levels and accompanying temperature increases in the recent past with ice melt and growth. Additionally, another objective of  the mission was to understand how phytoplankton (marine photosynthesizers) have changed through the Holocene (~117 thousand years ago to today). Understanding these changes can provide some insight into how biologic life has changed throughout recent geologic history, particularly in response to changes in the glacial ice.

The change in global temperature in the past 80 million years in relation to ice sheet activity. Time in millions of years is on the left side, and change in global temperatures (in degrees Celsius) is on the bottom axis. The left panel indicates the amount of temperature change through time with major biotic (e.g., extinction of the dinosaurs) and abiotic (e.g., first Antarctic ice sheet) denoted. Right panel indicates how warm the Earth was. Greenhouse world indicates an Earth that had very little to no ice sheets at either of the poles; Transitional world indicates a time when the Earth began to cool down and ice sheets began to appear; Icehouse world was a time when persistent ice sheets were at the South and then the North poles. Obtained from Integrated Ocean Drilling Program Expedition 318 Summary

Results from this expedition were found to be quite alarming. Scientists found that global ice amounts increase and decrease with global carbon dioxide concentrations respectively. This conclusion supported the hypothesis made by scientists that the amount of carbon dioxide in the atmosphere is tightly correlated with the amount of ice melt that is occurring into ocean waters. However, most alarmingly the rate of ice melt exceeded predictions, showing that global sea level rise may occur faster than previously expected. 

References

Gulick, S., Shevenell, A., Montelli, A. et al. Initiation and long-term instability of the East Antarctic Ice Sheet. Nature 552, 225–229 (2017). https://doi.org/10.1038/nature25026

Expedition 318 Scientists, 2011. Expedition 318 summary. In Escutia, C., Brinkhuis, H., Klaus, A., and the Expedition 318 Scientists, Proc. IODP, 318: Tokyo (Integrated Ocean Drilling Program Management International, Inc.). doi:10.2204/iodp.proc.318.101.2011

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