Massive ancient Ice Age dam failure impacted local climate, Pacific Ocean

The complete and total failure of an Ice Age dam at a South American lake roughly one-third as big as Wales released fresh water into the Pacific Ocean on several occasions and was significant enough to change the circulation of this portion of the hydrosphere, new research claims.

Published Friday in the journal Nature journal Scientific Reports, the new study explained that the freshwater lake, which previously occupied a basin that now contains Lago General Carrera in Chile and Lago Buenos Aires in Argentina, had been drained multiple times between 13,000 and 8,000 years ago – and that the results were borderline catastrophic.

At its highest point, this lake extended more than 7,400km2 and held more than of 1,500 km3 worth of water, Professor Neil Glasser of Aberystwyth University and his colleagues explained. That water was kept in place by a natural dam made from a large ice sheet, but as that ice sheet began to shrink, the lake started to drain rapidly into the nearby oceans.

“This was a massive lake,” Glasser, lead author on the paper, explained in a statement. “When it drained, it released around 1150km3 of fresh water from the melting glaciers into the Atlantic and Pacific oceans – equivalent to around 600 million Olympic-sized swimming pools. This had a considerable impact on the Pacific Ocean circulation and regional climate at the time.”

Effects felt as far east as the Falkland Islands

As the lake drained, a considerable amount of the freshwater it contained drained into the sea near Golfo Peñas, south of the Chilean capital Santiago, the researchers said. That freshwater would have rested on top of the saltwater as it spread out and affected regional ocean currents throughout southern South America.

The draining of the lake had a significant impact on the entire region, they explained. It would have led to decreased rainfall amounts in the winter, as well as cooler air and ocean temperatures around Cape Horn. The effects would have even been felt as far east as the Falkland Islands, the team discovered by analyzing sediment samples and conducting simulations.

Glasser and scientists from Exeter, Stockholm and Reading Universities and the British Antarctic Survey, used a laboratory technique called single-grain optically stimulated luminescence dating to analyze sediments deposited by the former lake to find out when each of the draining events took place, and used Digital Elevation Models (DEMs) to identify the lake shorelines, altitudes and drainage routes, as well as to calculate the volume of water released by each event.

Finally, they used an ocean-atmosphere climate model to determine the impact of dumping this amount of freshwater into the Pacific Ocean – something that Glaser said is important in light of the fact that researchers “are currently concerned about the volumes of fresh water entering the oceans from the melting ice sheets in Greenland and Antarctica and this gives us an indication of the likely effects.”

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