Biggest of them all

Mention Arctic ice melt and the first image to come to mind is the northern Atlantic. Mostly Greenland. Sometimes the far reaches of Canada or Iceland.

Maybe it’s because the northern Atlantic is the same ocean that researchers from major institutions dip their toes in in 100-plus degree heat waves.

But way out in the Pacific, researchers at the University of Hawaii are taking a different look at the climate. In a paper published this week in the journal Science, oceanographer Axel Timmermann and colleagues explained what they found out by looking at sediment cores from the northern Pacific.

Sunrise over the Pacific Ocean

Sunrise over the Pacific Ocean

As the last major ice age ended 17,500 years ago, massive north Atlantic ice sheets melted and all the added fresh water caused the collapse of the Atlantic Ocean conveyor belt. That should have plunged the northern Hemisphere into a deep freeze.

But it didn’t quite do that. Timmermann et. al found that the northern Pacific may have been a moderating force on the climate, helping it warm a bit. It did this by creating its own conveyor belt.

“Basically the Atlantic and the Pacific swapped their roles for about 2,000 years,” said Timmermann.

The salinity that used to be in the Atlantic, shifted over to the north Pacific through new rain patterns and built up there to the point where dense, salty water sunk. The sinking water had to be resupplied by warmer water flowing poleward.

“This warm water cooled, releasing heat into the atmosphere and hence the warming effect on the climate in the Pacific realm,” Timmermann said. “So in some sense when the Atlantic shut down … the Pacific Ocean served as a kind of backup generator for the climate.”

Today’s situation is a bit different because of new topography. Because the Bering Straight is now open (during the last glacier melt it wasn’t), there’s more mixing between the northern Pacific and Atlantic Oceans. So as Greenland melts, the decrease in salinity due to the added freshwater could easily spill over into the Pacific, preventing build up of salty water there.

Still, it’s clear by this research that the Pacific is important to the climate system in ways we know little about. But of course it would be. It’s the biggest ocean of them all.

-By Alison Hawkes