During the Last Glacial Maximum 20,000 years ago, northern North Atlantic surface waters were sinking to depth and flowing south along the seafloor at comparable rates to today. According to a new study published online this week in Nature Geoscience, episodic reductions in the strength of this overturning circulation were associated with abrupt climate change events.
Summer Praetorius and colleagues analysed sediment grain sizes and carbon isotopes in bottom-dwelling microorganisms to assess changes in flow strength of North Atlantic deep and intermediate waters for the past 25,000 years. They found periodic reductions in the flow strength, particularly during the transition from glacial to interglacial conditions. These reductions were associated with Northern Hemisphere cooling events, such as the Younger Dryas cold reversal. The team also found a reduction in flow that may be linked to the final glacial outburst flood 8,200 years ago.
The authors suggest that episodic reductions in the strength of bottom water currents were associated with a decrease in North Atlantic overturning circulation and abrupt climate change events.