"When Arctic climate changes, waters in the Arctic can go from storing large quantities of freshwater to exporting that freshwater to the North Atlantic in large pulses, referred to as great salinity anomalies," Greene explains. "These GSAs flow southward, disrupting the ocean's circulation patterns and altering the temperature stratification observed in marine ecosystems."
In the continental shelf waters of the Northwest Atlantic, the arrival of a GSA during the early 1990s led to a major ecosystem reorganization, or regime shift. Some ocean ecosystems in the Northwest Atlantic saw major drops in salinity, increased stratification, an explosion of some marine invertebrate populations and a collapse of cod stocks.
"The changes in shelf ecosystems between the 1980s and 1990s were remarkable," says Greene. "Now we have a much better idea about the role climate had in this regime shift."
The changes observed in recent decades are only the tip of the iceberg. Previous interglacial periods have ended when the global ocean's deep circulation slowed in response to reductions in the formation of North Atlantic Deep Water, or NADW, a large, deep mass of highly saline water in the North Atlantic.
At these tipping points in the Earth's history, NADW formation was disrupted by pulses of freshwater entering the North Atlantic. The slowing of the global ocean's deep circulation results in less heat being transported to higher latitudes, accelerating ice formation and advancing the Earth into glacial conditions.
Recent modeling studies show that NADW formation will likely be resilient to freshwater pulses from the Arctic during the 21st century, according to the authors.
|Contact: Cheryl Dybas|
National Science Foundation