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Consistent simulations of multiple proxy responses to an abrupt climate change event.
A N LeGrande1, G A Schmidt, D T Shindell
1National Aeronautics and Space Administration, Goddard Institute for Space Studies and Center for Climate Systems Research, Columbia University, New York, NY 10025, USA. legrande@giss.nasa.gov
Summary
A massive meltwater pulse from glacial lakes caused abrupt Northern Hemisphere cooling 8.2 kiloyears ago. Climate models confirm this event diminished North Atlantic Deep Water, supporting ocean circulation
Area of Science:
- Paleoclimatology
- Climate Modeling
- Oceanography
Background:
- An abrupt cooling event occurred across the Northern Hemisphere 8.2 kiloyears before present (kyr).
- This coincided with the catastrophic drainage of glacial Lakes Agassiz and Ojibway into the Hudson Bay.
- The proposed mechanism linking this meltwater pulse to cooling involves decreased North Atlantic Deep Water formation, but direct evidence has been lacking.
Purpose of the Study:
- To investigate the role of a meltwater pulse from glacial lakes in an abrupt Northern Hemisphere cooling event.
- To test the hypothesis that this event diminished North Atlantic Deep Water formation.
- To compare model simulations with paleoclimate proxy records, including isotope, aerosol, and methane data.
Main Methods:
- Simulations using a coupled general circulation model that tracks water isotopes.
- Atmosphere-only experiments to calculate changes in atmospheric aerosol deposition (e.g., (10)Be, dust).
- Analysis of wetland methane emissions.
- Quantitative comparison of simulation results with multiple paleoclimate proxy records.
Main Results:
- Simulations showed a short period of significantly diminished North Atlantic Deep Water formation.
- Model outputs quantitatively matched paleoclimate observations, including the absence of a strong isotopic signal in the North Atlantic.
- The study successfully reconciled the meltwater pulse event with observed climate proxies.
Conclusions:
- The findings provide compelling evidence that changes in ocean circulation were a major driver of the abrupt climate change event 8.2 kyr ago.
- The study supports the proposed mechanism linking glacial lake drainage to North Atlantic Deep Water reduction and subsequent cooling.
- Direct comparison with multiple proxy records validates the model's ability to capture key aspects of this paleoclimate event.