2016-06-30. Crippled Atlantic currents triggered ice age climate change.

posted Jul 4, 2016, 2:06 PM by Alan Gould
By Eric Hand, Science. For GSS Life and Climate chapter 10 and Climate Change chapter 7. Excerpt: The last ice age wasn’t one long big chill. Dozens of times temperatures abruptly rose or fell, causing all manner of ecological change. Mysteriously, ice cores from Greenland and Antarctica show that these sudden shifts—which occurred every 1500 years or so—were out of sync in the two hemispheres: When it got cold in the north, it grew warm in the south, and vice versa. Now, scientists have implicated the culprit behind those seesaws—changes to a conveyor belt of ocean currents known as the Atlantic Meridional Overturning Circulation (AMOC). ...Still unclear is what triggered the AMOC’s sudden slowdowns. Many of the drops correspond to so-called Heinrich events: rapid releases of icebergs from Canada’s ice sheet. These iceberg armadas often chugged through the Hudson Strait of Canada and may have discharged more ice into the Atlantic Ocean than contained in the entire ice cap of Greenland, raising ancient sea levels by 10 meters. The meltwater brought incredible amounts of freshwater to the North Atlantic, precisely where ocean currents cool off and sink. Because freshwater is less dense than saltwater, it can plug up the AMOC, preventing the overturning and deep water formation the fuels the circulation’s engine. ...Another question is whether the AMOC—currently known to be in decline—could drop off suddenly today, as depicted in the 2004 movie The Day After Tomorrow, causing temperatures to plummet across northwestern Europe....  http://www.sciencemag.org/news/2016/06/crippled-atlantic-conveyor-triggered-ice-age-climate-change