The ice age, oceans and climate: triggers of iceberg calving and rapid temperature change

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This PhD project will use numerical modelling in order to establish the complex chain of events that took place early in the last deglaciation, linking catastrophic ice sheet collapse, iceberg armadas, rapid cooling, abrupt warming and the complete reorganisation of largescale Atlantic Ocean circulation. The candidate will explore possible mechanisms that link these different parts of the earth system, undertaking high profile research to examine existing hypotheses and create news ones to understand the cause and consequences of rapid climate change in the high latitudes.BACKGROUNDAt the Last Glacial Maximum (21,000 years ago), vast ice sheets stretched across much of the Northern Hemisphere, covering large expanses of North America, Greenland and Eurasia. As climate warmed, and the ice sheets began retreating, an intriguing chain of events was triggered in the North Atlantic. Largescale ocean circulation slowed, climate cooled, armadas of icebergs were released, ocean circulation rapidly strengthened and temperatures abruptly rose. Although well documented individually (Heinrich Stadial 1, Heinrich Event 1, the Bolling Warming), it remains unknown precisely how and even if these events were linked. Two recent studies put forward the tentative hypothesis that melting of the Eurasian ice sheet caused ocean circulation to slow-down, cooling the North Atlantic region and triggering enhanced iceberg calving from the Eurasian ice sheet. This amplified the initial change, increasing iceberg production from North America and sustaining the cooling. But, this chain of events has never been tested. Furthermore, it remains unclear what caused the last of these events; the abrupt Bolling Warming. Was it a rapid reduction in the amount of meltwater reaching the ocean? Was a critical threshold in atmospheric CO2 crossed? Or was it simply the result of an inherently unstable climate regime? The last deglaciation is the best documented period of abrupt climate change, yet we do not understand how and why the recorded events took place. This exciting project tackles this challenge, testing ice-ocean-atmosphere interactions to produce seminal new knowledge of our climate.Please contact the lead supervisor (r.ivanovic@leeds.ac.uk) for more information and before applying.PROJECT AIMThe candidate will run complex numerical climate and ice sheet models to examine the interplay between climate, icebergs and ocean circulation in the early period of the last deglaciation (21-14.5 thousand years ago). The overall aim is to establish the chain of events surrounding Heinrich Stadial 1, involving ice sheet melting, a rapid slowdown of the largescale Atlantic Ocean circulation (Atlantic Meridional Overturning Circulation, AMOC), North Atlantic cooling, enhanced iceberg discharge from the Eurasian and North American ice sheets (Heinrich Event 1), a resumption of the AMOC and abrupt warming (Bolling Warming).