How deep water surfaces around Antarctica

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There’s no signpost to mark it, but about 3,000 meters underwater off the southeast coast of South America, a stream of deep water from the Atlantic Ocean spills into the Southern Ocean. Now new maps reveal in 3-D how the path of that water, called the North Atlantic Deep Water, spirals southeastward and up toward the surface around Antarctica.

The incoming water, part of the global conveyor belt of currents circulating throughout the oceans, is relatively warm and salty compared with the rest of the Southern Ocean. Researchers marshaled ocean temperature and salinity data to broadly map the deep water’s path (see map, below left). The data show that some of the water upwells close to the continental shelf along the western Antarctic Peninsula. Such intrusions have been linked to the melting of ice shelves.

For a detailed look at what controls the upwelling, the researchers turned to high-resolution climate and ocean simulations to track virtual particles traveling in the deep water (see map, below right). For example, two particles (dark blue dots) enter in water from the Atlantic and spiral clockwise toward the surface (red dots).

This and other simulations show that five key spots at large ridges and plateaus drive most of the upwelling. Deep water passing these features spawns whirlpools that in turn push the water southward and upward, the researchers report August 2 in Nature Communications. Deep water entering the Southern Ocean from the Indian and Pacific oceans follows a similar pattern.

“Until now, we mostly thought about upwelling as this really broad thing that’s just happening everywhere” in the Southern Ocean, says study coauthor Veronica Tamsitt of the Scripps Institution of Oceanography in La Jolla, Calif.

Understanding this upwelling matters because the deep water carries a lot of heat and carbon. As the climate changes, Southern Ocean upwelling may increase, which could accelerate ice shelf melting, release more carbon into the atmosphere and limit the ocean’s ability to absorb heat and carbon dioxide from the atmosphere. Today, the Southern Ocean accounts for almost half of the anthropogenic CO₂ and 75 percent of the heat that the world’s oceans soak up from the atmosphere.