Plumbing the Southern Ocean
The Southern Ocean contains only about 10 percent of the world's ocean water, but scientists are discovering that it has a vital role in regulating the earth's climate and the temperature of the world's oceans
HOBART, AUSTRALIA — CAPT. Ewald Brune knows the moods of the Southern Ocean."It can be as flat as a millpond or as stormy as a hurricane," says the veteran of 12 years of Southern Ocean voyaging. And, when it's in a rage, he admits, "It's the worst weather in the world." Fisherman Malcolm Hart of the village of Strahan, on Tasmania's west coast, says an oil rig exploring off Tasmania's west coast had barrels swept off its deck by high seas. The deck was 90 feet above the surface of the ocean. Mr. Hart says a research buoy off the coast has recorded swells of up to 108 feet. "Oh, you have to watch the weather," says Mr. Hart, who has fished the Southern Ocean for 30 years. During the winter, about a third of the Southern Ocean is covered by sea ice as Antarctica's extent doubles from its summer size. The ice can pose even more dangers than the waves. This year, South African sailor John Martin had to abandon his $1 million sailboat after hitting a "growler," a broken-up iceberg, in the Southern Ocean. The Southern Ocean, containing about 10 percent of the world's ocean water, covers less area than the Indian, Atlantic, or Pacific Oceans, each of which it joins. But scientists are now discovering that the Southern Ocean is an integral part of the earth's circulation and climate system. "It is like an oceanic conveyor belt where you have cold and saline antarctic waters sinking to the bottom. This cold water then flows north well into the northern hemisphere where it 'upwells' and you have warmer water flowing south," says Harvey Marchant, a principal research scientist at the Australian Antarctic Division, based in Hobart. This, in effect, regulates the temperature of the world's oceans. "So even though it is only 10 percent of the world's oceans, it has a much larger effect," says Dr. Marchant. Unlike the Arctic Ocean, which is not very deep and virtually surrounded by land, the Southern Ocean is deep, surrounding a continent the size of Australia. The Arctic is less saline since it is fed by large rivers in North America and Asia. In addition, the Southern Ocean has the world's largest currents. Even though they only move at one to two knots, they are massive, says John Church, a scientist at the Commonwealth Scientific and Industrial Research Organization's (CSIRO) Division of Oceanography. He estimates the Southern Ocean currents move about 130 million cubic feet of water per second. By way of comparison, all of the world's rivers combined carry 1 million cubic feet of water per second. This September scientists from the Antarctic Division and CSIRO will board the 18-month-old research vessel Aurora Australis to try to better understand how these currents transport heat and salt and fresh water. The vessel will measure the entire water column every 30 miles from Tasmania to the ice encompassing Antarctica. Some instruments are designed to be left behind for future monitoring. Scientists will focus their measurements on the amount of carbon in the water. This will allow them to calculate the amount of carbon dioxide absorbed into the Southern Ocean. Researchers believe the Southern Ocean absorbs more carbon dioxide than it releases. In scientific terms, the ocean is a "sink" for carbon dioxide. "There is a certain concentration of CO2 [carbon dioxide] in the atmosphere and a certain amount in the surface of the water. You get a flux from the ocean to the atmosphere or back depending on the concentration," explains Garth Paltridge, director of the Institute of Antarctic and Southern Ocean Studies at the University of Tasmania. Since the rest of the world produces more carbon dioxide than it consumes, the Southern Ocean may help to slow down this worldwide increase. Major consumers of carbon dioxide are found in a narrow band of water that extends out from the sea ice. This 20- to 30-foot-deep zone tends to have a low salinity and, says Marchant, "It is the zone of greatest biological activity in the Southern Ocean." Researchers believe that organisms within this zone such as diatoms act like biological pumps, using sunlight to help convert dissolved carbon dioxide into carbon, carbohydrates, and fats, the stuff of which living organisms are made. But these carbon-dioxide absorbers may be in danger. Since most live near the surface of the water, they may be susceptible to increases in ultraviolet light caused by the hole in the ozone layer that occurs in the summer. "We have found some organisms which appear to be under stress," says Marchant. Marchant and other research groups have found that some of the organisms develop their own sunscreens and other protective mechanisms. Unfortunately, these organisms are poor food for grazing animals such as the Antarctic krill. (See story, below left.) "The upshot of all this is that if [ultraviolet] conditions further increase, the Southern Ocean may not be as good a sink," says Marchant. "We need the Southern Ocean to be a sink," he adds. "Ideally, we need all the world's oceans to be a sink. If 2 percent of the carbon in the [world's oceans] were released, the concentration of atmospheric CO2 [carbon dioxide] ... would double." At this point, Dr. Church says, the CSIRO effort "won't address the issue of temperature changes but will try to understand the magnitude so we can improve the climate models so we can predict future climate changes." Adds Paltridge, "If you want to forecast the concentration of carbon dioxide in the future, you need to know what is put in by man and what is taken out by nature." Even the fierce wind and waves need to be studied. The wild sea conditions create froth and bubbles. These bubbles release material into the atmosphere and back into the water. So even the storms in the Southern Ocean serve a purpose. Along with the new research ship, scientists will be helped by a new generation of satellites designed to take extremely accurate measurements of water surface temperature, color, and wind speed. The first of the satellites, ERS-1, was launched on July 17 from French Guiana. "It will provide an accuracy of a quarter of a degree Celsius," says Ian Barton, a research scientist with CSIRO's Division of Atmospheric Research in Melbourne.