An international scientific expedition set sail recently for the Sub-Antarctic Front -- an area known for the stormiest sea and wind conditions on the planet -- to study how water mixes across the boundary and supplies essential nutrients to the ocean food chain.
The Sub-Antarctic Front is a 30-nautical-mile wide oceanic boundary, with cold water formed near the Antarctic to its south and salty, warm water to its north. The boundary stretches 12,400 miles around the globe.
The front is part of the Antarctic Circumpolar Current, the biggest current system in the world's oceans. Far from a clear straight line, it is identified from satellite by swirling ocean eddies and meanders up to 120 miles across.
"The front is both a strong current which reaches from the sea surface to the sea floor and a boundary between distinct marine environments," says Dr. Steve Rintoul, an oceanographer with CSIRO, Australia's federal science agency. "Different biological communities dominate on either side of the front. One aim of this expedition is to identify what factors control the productivity and carbon cycle in the different environments."
Rintoul and Dr. Tom Trull are leading the two-ship expedition that includes more than 30 scientists from Australia, France, Belgium, New Zealand and the United States.
"The front itself is a region of enhanced algae levels, but the reasons for this are unclear," said Trull. "One possibility is that upward motions caused by the meandering of the front bring iron into the surface waters, where it can be used by phytoplankton at the base of the food chain."
The expedition will study these vertical motions. The role of iron and other nutrients will also be studied by monitoring the uptake of radioactive tracers in shipboard phytoplankton growth experiments.
Moored particle traps, which will collect weekly samples throughout the year, will measure how much organic material sinks from the sea surface to the deep sea.
"One of the big questions with regard to the marine carbon cycle is how much carbon dioxide is removed from the atmosphere by the southern ocean, and what happens to the carbon once in the ocean. The particle traps and studies carried out on Aurora Australis will allow us to address this question for the Sub-Antarctic Front," said Trull.
The eddies and meanders of the front also carry heat from north to south across the front, balancing the heat lost to the cold atmosphere near Antarctica.
"By understanding the dynamics of the eddies, we can get a better handle on the role of the eddies in the global heat balance," said Rintoul.
The Sub-Antarctic Zone expedition is one of a number of research initiatives taking place during the International Year of the Ocean.