Sea level and climate change from geochemical analysis of corals from the Great Barrier Reef: IODP Expedition 325

点击翻译按钮获取中文摘要

One of the largest uncertainties in projections of environmental change involves the response of the Greenland and Antarctic ice sheets to 'greenhouse warming'. These ice sheets play an important role in defining climate through affecting wind patterns, through reflecting sunlight back to space and through providing sources of fresh water the can influence ocean circulation. As the planet warms, we expect these ice sheets to respond, but we are not sure in exactly what ways. The Greenland ice sheet is likely to start melting, and indeed there is already evidence to suggest that this might be happening. The Antarctic ice sheet may initially grow slightly (since it is so cold that a slight warming simply makes it easier to snow there). However, evidence from the past combined with modern observations suggests that these ice sheets are capable of extremely rapid decay through catastrophic collapse of large segments, resulting in large and rapid sea level rises. The work proposed here is focussed on the Great Barrier Reef of Australia, which, although far from the ice sheets, is well placed to reveal evidence for past ice sheet growth and collapse. We will use analysis of the chemistry of corals collected in drill cores down through the reef to reconstruct changes in water depth, and hence sea level, in the interval 11,000- 20,000 years ago. This interval coincides with the decay of the ice sheets from their maximum extent during the last ice age, to their present size. At the peak of the last ice age, global sea level was about 120m below its present level, due to the amount of water bound up as ice, so as the ice sheets melted, sea level rose. Our coral records will be used with other evidence from the types of corals and algae in the cores, to identify the rate, timing and magnitude of these sea level changes, as well as to reconstruct changes in local temperature. These data will contribute to our understanding of the triggers of ice sheet collapse and sea level rise.