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

Dr Ruza Ivanovic (SEE), Dr Lauren Gregoire

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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 new ones to understand the cause and consequences of rapid climate change in the high latitudes.


At 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 Bølling 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 Bølling 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 ( for more information and before applying.

Project Aim

The 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 (Bølling Warming).

Research Questions

It is expected that the project will evolve in line with the best research on the topic. The student will be fully supported to follow their interests and make the project their own. Here is an example of the direction the PhD could take:

Chapter/paper 1: Establishing the trigger for Heinrich Stadial 1

• Is it possible to improve simulations of the Last Glacial Maximum oceans, e.g. by retuning the model?

• What is the best scenario of ice sheet evolution during the early last deglaciation?

• Did rapid deglaciation of the Barents-Kara Sea region drive a slowdown in Atlantic Ocean circulation 19-18 thousand years ago?

• Does the initial condition of the climate and ocean control their response to meltwater?

Chapter/paper 2: Understanding the cause of enhanced iceberg calving

• Did Atlantic Ocean subsurface warming enhance rates of iceberg calving?

• What was the relationship between Eurasian and North American iceberg calving?

• How did freshwater from melting icebergs influence ocean circulation?

• Was there also a role for the thermal heat flux from icebergs?

Chapter/paper 3: A better knowledge of abrupt warming

• Was the Bølling Warming a forced event or a product of internal climate instability?

International Network

The candidate will have the opportunity to benefit from and feed directly into:

- The Paleoclimate Model Intercomparison Project (PMIP), for which the lead-supervisor and co-supervisor are working group leaders []

- CLIVAR (a World Climate Research Programme initiative) Atlantic Regional Panel, for which the lead-supervisor is a panel member []

Click here for a full project description.

Related undergraduate subjects:

  • Applied mathematics
  • Atmospheric science
  • Chemistry
  • Computer science
  • Computing
  • Earth science
  • Earth system science
  • Engineering
  • Environmental science
  • Geochemistry
  • Geography
  • Geological science
  • Geology
  • Geophysical science
  • Geophysics
  • Geoscience
  • Hydrology
  • Mathematics
  • Mechanical engineering
  • Meteorology
  • Natural sciences
  • Oceanography
  • Physical geography
  • Physical science
  • Physics