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NERSC Initiative for Scientific Exploration (NISE) 2011 Awards

High resolution modeling to identify the location of the meltwater flood responsible for the Younger Dryas cold episode

Alan Condron, Pennsylvania State University

Associated NERSC Project: Abrupt Climate Change and the Atlantic Meridional Overturning Circulation (m1068)
Principal Investigator: Peter Winsor, University of Alaska Fairbanks

NISE Award: 1,000,000 Hours
Award Date: June 2011

As the rate of melt from the Greenland and Antarctic ice sheets increases in the future, the additional meltwater entering the ocean could threaten the continuation of our present-day warm climate by causing us to suddenly plunge into a very cold, glacial period. Our research aims to understand where this stability threshold lies, and how close our modern day climate is to crossing it.

Using the state-of-the-art, high resolution, Massachusetts Institute of Technology general circulation model (MITgcm), our previous research results have begun to allow us to develop a more complete understanding of the role glacial meltwater floods played in modulating the earth’s climate in the past. By modeling the discharge of meltwater from a number of different regions of the North American continent at a numerical resolution many times higher than achievable if we had not had access to the NERSC supercomputing center, we have been able to show that the delivery of meltwater to the ocean in the past was very different from the conceptual ‘textbook’ idea that meltwater created a large homogeneous fresh layer over the sub-polar North Atlantic. These results have been met with considerable enthusiasm by the scientific community and have now been published in the journal of Geophysical Research Letters

We request additional computer hours to try and resolve the on-going debate in the scientific community as to the geographic location, magnitude, and duration, of the meltwater pulse(s) responsible for triggering a ~1300 year cold episode around 13,000 cal years ago, known as the Younger Dryas. The main contenders for this title are meltwater discharged to the ocean from either via the Mackenzie River (i.e into the western Arctic) or the Gulf of St. Lawrence (western North Atlantic). A number of other sources have also been hypothesized, including the discharge of thick sea-ice from the Arctic, and meltwater from the Eurasian Ice sheet.

We will release meltwater into our model at each location, at a range of magnitudes, and differing durations (years to decades), in order to quantify which meltwater sources have the largest impact on the climate system, and therefore which had the most potential to trigger a Younger Dryas like cold episode. We will also undertake a series of integrations looking at the impact of freshwater at different states of the climate system, including full glacial and relative warm (modern) conditions. Computer hours are also requested to extend the length of several existing integrations to more fully understand the impact of freshwater on the climate system.

The research we are undertaking has a direct bearing on understanding our future climate by quantifying the impact of freshwater from accelerated melting of glaciers around Greenland and Antarctica. Due to the computationally demanding nature of these experiments – integrations typically utilize 1800 processors - access to the supercomputing center at NERSC is required to carry out our proposed experiments. Our integrations have typically been run on Franklin, but we have recently had considerable success integrating our configuration on NERSCs new Hopper II machine.