Research Briefs

Ice sheets and climate change during the late Pleistocene

An iceberg floating in the ocean.

An iceberg in Wolstenholm Fjord, just north of Thule, Greenland. (Photo by James Hannigan.)

New research that involves NCAR scientist Bette Otto-Bliesner questions conventional wisdom with regard to massive iceberg discharges in the North Atlantic Ocean during the last glacial period, pointing toward climate rather than ice sheet instability as a cause.

The study, published in Proceedings of the National Academy of Sciences, focuses on Heinrich events—episodic discharges of icebergs from the Hudson Strait Ice Stream and Laurentide Ice Sheet into the North Atlantic that occurred during glacial intervals. During these events, armadas of icebergs broke off from the ice sheet and traversed the North Atlantic over hundreds of years, influencing regional climate and ocean circulation.

Scientists have traditionally thought that Heinrich events resulted from instabilities within the ice sheets once they grew to large sizes. In recent years, they’ve begun looking more at the impact of climate on Heinrich events.

For the study, the research team combined climate simulations from the NCAR-based Community Climate System Model (CCSM) with data from the fossil benthic foraminifera, whose ratio of magnesium to calcium provides a record of ocean temperatures.

Results suggest that subsurface warming in the North Atlantic basin occurred at the same time as large reductions in deep circulation, with subsurface ocean temperatures increasing by about 2°C in the intervals just prior to Heinrich events. Simulations show that this temperature rise could increase melt rate beneath ice shelves and ultimately cause a Heinrich event. The findings could be important for understanding how ice sheets may behave in the future as Earth’s climate warms.

Shaun A. Marcott, Peter U. Clark, Laurie Padman, Gary P. Klinkhammer, Scott R. Springer, Zhengyu Liu, Bette L. Otto-Bliesner, Anders E. Carlson, Andy Ungerer, June Padman, Feng He, Jun Cheng, and Andreas Schmittner, "Ice-shelf collapse from subsurface warming as a trigger for Heinrich events," Proceedings of the National Academy of Sciences, 10.1073/pnas.1104772108