Going with the flow
Researchers brave Drake Passage to map world's largest ocean current
Posted November 21, 2008
Most people who cross Drake Passage by ship are eager for the two-day journey to be over as quickly as possible. The ocean passage splitting the tips of South America and the Antarctic Peninsula is infamously rough, turning even hardened seafarers green around the gills.
But a team of oceanographers will spend more than three weeks in the Drake in November and December to learn more about the world’s largest ocean current, the Antarctic Circumpolar Current (ACC) . Drake Passage, the chokepoint where the current narrows, is the ideal place to study the ACC, according to Teresa Chereskin , a principal investigator for the project and chief scientist for the cruise aboard the RVIB Nathaniel B. Palmer .
“We’re there long enough so that we see all kinds of weather,” said Chereskin, a researcher with Scripps Institution of Oceanography at the University of California in San Diego . “Last year, we were really blessed in the first few days because it was ‘Drake Lake,’ and you don’t get that very much.”
A year ago at about the same time, Chereskin and her team, including principal investigators Kathleen Donohue and Randolph Watts , both with the Graduate School of Oceanography at the University of Rhode Island (URI) , deployed an array of instruments in the passage to take data on a number of ocean properties — from acoustic travel times in the water column, which can be related to density and temperature, to ocean current and pressure. This year they will collect their first data via telemetry from the instruments.
“Our observations will help us understand why the current is there, what forces it, and what controls its variability,” explained Donohue, URI associate research professor.
The ACC is a set of sharp density fronts and their associated currents that spirals around Antarctica from west to east, linking the world’s three major bodies of water — the Atlantic, Pacific and Indian oceans. “In that sense, you can think of it as a major conduit between the [ocean] basins. That’s one important reason to study it,” Donohue noted.
The ACC formed about 41 million years ago when Drake Passage between South America and Antarctica opened. Some scientists believe the birth of the ACC eventually led to the formation of major ice sheets on the world’s southernmost continent, though the theory is still widely debated. [See related story: Open case]
However, oceans and climate are indisputably linked. For example, the ocean current that brushes across Western Europe helps keep temperatures more temperate there than its high latitude would otherwise suggest. Similarly, the ACC helps insulate Antarctica.
But climate change has come to Antarctica, particularly West Antarctica, where glaciers are moving faster and discharging more ice into the ocean and ice shelves are collapsing. The changes are also whipping up the west winds that drive the ACC around the continent.
“We anticipate that the Antarctic Circumpolar Current may be highly sensitive to climate change,” Donohue said. “It is driven by winds, and since the winds appear to be changing as a result of climate change, the current may change as well.”