The ocean's coldest, saltiest waters are disappearing -- thanks to Antarctic currents shutting down.
Researchers have been scratching their heads at the disappearance of the coldest, saltiest seawater over last couple of decades. Historically, this “Antarctic Bottom Water” originates in the Weddell and Ross Seas when it cools in polynya — areas of open water in which sea ice does not form — and then sinks down into the deep. After, it roams the Earth on a sort of “ocean conveyor belt,” taking almost 1,000 years to return from where it came, distributing yummy nutrients (at least I imagine they taste good if you’re plankton) and helping to keep the Earth’s climate in check along the way. But scientific sleuths think they’ve now solved the mystery of the vanishing waters: Climate change is causing more precipitation over the southern ocean, shutting down the normal mixing process.
Why? Because of density. Normally, the Weddell Sea’s surface waters are denser (because they’re colder, thanks to cooling off in the polynya) than what’s below, causing them to sink down and form Antarctic Bottom Water. But now, the increased renewal of super-fresh stuff keeps the Weddell Sea’s surface water density low, so it just stays on top instead of replenishing the Antarctic Bottom Water stores below. “I like to say it’s like a bottle of Italian salad dressing — so it separates between the dense stuff underneath and the less dense stuff on top,” says Eric Galbraith, assistant professor of Earth System Dynamics at McGill and coauthor of the new paper.