Ocean Water Vertically Mixes As It Rushes Over Undersea Mountains
September 19, 2013

Ocean Water Vertically Mixes As It Rushes Over Undersea Mountains

April Flowers for redOrbit.com - Your Universe Online

In the ocean near Antarctica, an international research team has solved the mystery of how deep and mid-depth ocean waters are mixed.

The study, published in the journal Nature, reveals that sea water mixes dramatically as it rushes over undersea mountains in Drake Passage - the channel between the southern tip of South America and the Antarctic continent. This mixing of oceanic water layers is vital in the regulation of the Earth's climate and ocean currents.

Until now, climate models have lacked the detailed information on ocean mixing necessary for accurate long-term climate projections. This study, carried out by the University of Exeter, the University of East Anglia, the University of Southampton, the Woods Hole Oceanographic Institution, the British Antarctic Survey and the Scottish Association for Marine Science, is providing that insight.

The research team worked in some of the wildest waters on the planet to measure mixing in the Southern Ocean. They released tiny quantities of an inert chemical tracer into the Southeast Pacific, and then tracked it for several years as it went through Drake Passage. This allowed them to observe how quickly the ocean mixed.

In the Pacific, the tracer revealed almost no vertical mixing. However, once the waters passed over the mountainous ocean floor in the relatively narrow continental gap that forms the Drake Passage, dramatic vertical mixing was discovered.

The Drake Passage is a deep waterway nearly 600 miles wide with an average depth of 11,000 feet that connects the Atlantic and Pacific oceans. The passage runs between Cape Horn at the southernmost tip of South America and the South Shetland Islands, which are approximately 100 miles north of the Atlantic Peninsula. The Drake Passage delineates the transition zone between the cool, humid subpolar climate conditions of Tierra del Fuego and the frigid, polar regions of Antartica.

Professor Andrew Watson from the University of Exeter's College of Life and Environmental Sciences said, "A thorough understanding of the process of ocean mixing is crucial to our understanding of the overall climate system. Our study indicates that virtually all the mixing in the Southern Ocean occurs in Drake Passage and at a few other undersea mountain locations. Our study will provide climate scientists with the detailed information about the oceans that they currently lack."

Carbon dioxide (CO2) from the atmosphere is transferred to the deep sea by ocean mixing. This ultimately controls the rate at which the ocean takes up CO2. The process will remove much of the CO2 that we release into the atmosphere, over several hundred years, ultimately storing it in the deep ocean.

Climate is also affected by ocean mixing. An increase in the rate of deep sea mixing, for example, would enable the ocean to transfer more heat towards the poles.

Slower ocean mixing between the surface and the deep sea might be the cause of lower concentrations of atmospheric carbon dioxide present during the ice ages, scientists have hypothesized. The underlying mechanisms for this are unclear at this point, but it further emphasizes the need to understand the link between ocean mixing and climate.