A new modeling study reveals that a large pulse of meltwater flowing north from North America into the Arctic Ocean is likely responsible for the major climate shift that occurred 12,900 years ago, and suggests the need for enhanced scrutiny of current melting of Arctic land and sea ice. The last major cold episode on Earth, the Younger Dryas, was 12,900 years ago and is considered to have been triggered by a large meltwater flood from lakes along the edge of the Laurentide Ice Sheet that covered much of North America. This influx of freshwater into the Arctic Ocean is thought to have weakened the ocean "conveyer belt" of currents known as the Atlantic Meridional Overturning Circulation. The weakened conveyor belt in turn may have diminished the flow of warm water to high latitudes, and led to the cold Younger Dryas period. Climate scientists have debated whether this flood of ice-sheet meltwater first flowed northwest into the Arctic or directly into the western North Atlantic via the St. Lawrence River. To see which flood route best explained the abrupt drop in temperature at the onset of the Younger Dryas, a sophisticated, high-resolution, ocean sea-ice model was developed and used to study the impact of meltwater from the two outlets on the Atlantic Meridional Overturning Circulation. Simulation results showed that meltwater from the St. Lawrence Valley would have weakened this circulation by approximately 15% whereas freshwater from the Mackenzie Valley would have weakened this conveyer belt by >30%, suggesting that the Mackenzie Valley was the likely route for meltwater that triggered the Younger Dryas. This work highlights the Arctic as a primary driver for abrupt climate change, and is especially relevant considering the rapid changes in sea-ice and Greenland ice sheet melting in this region over the last 10 years.
Reference: Condron, A. and P. Winsor. 2012. “Meltwater Routing and the Younger Dryas,” Proceedings of the National Academy of Sciences USA, DOI: 10.1073/pnas.1207381109. (Reference link).
Contact: Renu Joseph, SC-23.1, (301) 903-9237, Dorothy Koch, SC-23.1, (301) 903-0105
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