Showing: 1 - 1 of 1 RESULTS

Large-scale changes in Earth’s climate may originate in the Pacific

The retreat of North America’s ice sheets in the latter years of the last ice age may have begun with “catastrophic” losses of ice into the North Pacific Ocean along the coast of modern-day British Columbia and Alaska, scientists say. 

In a new study published October 1 in Science, researchers find that these pulses of rapid ice loss from what’s known as the western Cordilleran ice sheet contributed to, and perhaps triggered, the massive calving of the Laurentide ice sheet into the North Atlantic Ocean thousands of years ago. That collapse of the Laurentide ice sheet, which at one point covered large swaths of Canada and parts of the United States, ultimately led to major disturbances in the global climate (SN: 11/5/12).

The new findings cast doubt on the long-held assumption that hemispheric-scale changes in Earth’s climate originate in the North Atlantic (SN: 1/31/19). The study suggest that the melting of Alaska’s remaining glaciers into the North Pacific, though less extreme than purges of the past, could have far-ranging effects on global ocean circulation and the climate in coming centuries.

“People typically think that the Atlantic is where all the action is, and everything else follows,” says Alan Mix, a paleoclimatologist at Oregon State University in Corvallis. “We’re saying it’s the other way around.” The Cordilleran ice sheet fails earlier in the chain of reaction, “and then that signal is transmitted [from the Pacific] around the world like falling dominoes.”

In 2013, Mix and colleagues pulled sediment cores from the seafloor of the Gulf of Alaska in the hope of figuring out how exactly the Cordilleran ice sheet had changed prior to the end of the last ice age. These cores contained distinct layers of sand and silt deposited by the ice sheet’s calved icebergs during four separate occasions over the last 42,000 years. The team then used radiocarbon dating to determine the chronology of events, finding that the Cordilleran’s ice purges “surprisingly” preceded the Laurentide’s periods of abrupt ice loss, known as “Heinrich events,” by 1,000 to 1,500 years every single time.

“We’ve long known that these Heinrich events are a big deal,” says coauthor Maureen Walczak, a paleoceanographer also at Oregon State University. “They have global climate consequences associated with increases in atmospheric CO2, warming in Antarctica … and the weakening of the Asian monsoon in the Pacific. But we’ve not known why they happened.”  

Though scientists can now point the finger at the North Pacific, the exact mechanism remains unclear. Mix proposes several theories for how Cordilleran ice loss ultimately translated to mass calving of ice along North America’s east coast. It’s possible, he says, that the freshwater deposited in the North Pacific traveled northward through the Bering Strait, across the Arctic and down into the North Atlantic. There, the buoyant freshwater served as a “cap” on the ocean’s denser