The Atlantic and Pacific Climate Connection

Biggest of them all

The global ocean circulation system, often called the Ocean Conveyor, transports heat worldwide. White sections represent warm surface currents. Purple sections represent cold deep currents. Credit: Jayne Doucette, Woods Hole Oceanographic Institution

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.

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.

The Bering Straight during the last glacial maximum. Credit: Ehlers and Gibbard, 2004

“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.

Oceans away

Mauna Kea on Hawaii’s Big Island was once covered in ice.

As I reported earlier, new research is showing the intimate connections between the Atlantic and Pacific oceans during past major climate events. Just because an ocean is an ocean away, doesn’t mean it doesn’t feel the impact of, say, the collapse of the Atlantic conveyor belt, as happened as the last Ice Age ended some 17,000 years ago.

Now another study of around the same time period was published recently by researchers at Oregon State University in the journal Earth and Planetary Letters. This study examined the tallest mountain in the world. Not Mount Everest — that’s the highest. Mount Mauna Kea, on the Big Island of Hawaii rises some 30,000 feet from the Pacific Ocean floor, making it the actual tallest, even though most of it’s underwater.

Mauna Kea, if you can believe it, once had a large glacial ice cap of more than 40 miles some 21,000 years ago. Peter Clark, a geosciences professor at OSU looked at how that glacier disappeared as the Ice Age ended and the planet become warmer.

One surprising discovery, found in Helium isotope deposits within boulders, was that the glacier began readvancing back again some 15,400 years ago. Looking at the historical record, that change matched a major slowdown at the time in the Atlantic conveyor belt.

Normally you think of the Atlantic conveyor belt as controlling temperatures in Europe and the northern Atlantic. When it slows down it gets chillier. But the findings from OSC confirm suspicions that the rest of the planet changes, too. At Mauna Kea cooled down as well and precipitation jumped by quite a bit.

Maybe this was because of an uptick in storm events? When the Atlantic gets sluggish, the whole world catches a cold.