Extreme conditions ahead for ocean researchers

By Environmental News Network staff

The Aurora Australis

(ENN) -- In search of answers about the vast oceans of the world, scientists from the Cooperative Research Center for Antarctica and the Southern Ocean are heading into the icy Southern Ocean during the Antarctic winter to investigate why vast sections of ocean adjoining the Antarctic coast remain ice-free during the winter months.

This major midwinter scientific expedition will begin to endure the extreme conditions Wednesday, when it leaves from Hobart, Australia.

"Unfortunately, the only way to fully understand this phenomenon is to be there in winter," says scientific cruise leader Dr Ian Allison.

The 54 expedition members aboard the Aurora Australis, including oceanographers, glaciologists, meteorologists and biologists, can expect average temperatures around -19 degrees C and persistent, gale force winds. They will journey across approximately 400 kilometers of ice pack to spend six weeks near the Antarctic coast.

The voyage is a significant Australian research initiative in the International Year of the Ocean.

Allison said that scientists have known for some time that open water and thin ice regions called "polynyas" occur near the Antarctic coast in areas otherwise covered by pack ice. This is the first time that a research program has been undertaken during the difficult winter months to study the conditions firsthand.

"Understanding all the processes occurring within the polynyas is important in understanding other global climate issues" said Senator Ian Macdonald, parliamentary secretary for the Antarctic.

"This voyage is an opportunity to investigate for the first time oceanic conditions in and around the Mertz Polynya, together with key sea-ice, meteorological and biological observations. The research undertaken on the midwinter voyage will help scientists more clearly define the influences of the Antarctic region on global climate", said Senator Macdonald.

"Exchanges of energy, water and gases between the ocean and atmosphere around Antarctica help determine conditions around the rest of the world. This is another example of Australia's contribution to understanding global climate change".

The research group will target the 'Mertz Polynya' near the coast of Adelie Land, almost directly south of Tasmania, in one of the windiest places on Earth. In fact, the researchers believe that it is these strong and persistent katabatic winds blowing down the Mertz Glacier which maintain the relatively ice-free conditions in the region.

According to Southern Ocean specialists at the Antarctic CRC, the Australian Antarctic Division and CSIRO Marine Research, coastal polynyas are regions of rapid ice production where heat is continually lost from the ocean to the cold polar atmosphere above.

Salt is removed from the ice as it forms, increasing the density of the underlying water. This cold, dense water is known as Antarctic Bottom Water and sinks deep into the ocean carrying with it oxygen and other gases. Antarctic Bottom Water spreads its way through the depths of the world's oceans and plays a major role in the global ocean circulation. Water formed in this way is estimated to occupy about one quarter of the volume of the oceans.

During an earlier voyage on the Aurora Australis in April of this year seven oceanographic moorings were successfully laid in both open water and midwinter pack ice regions adjoining the Mertz Glacier. The moorings, in depths from 500 meters to 3,000 meters, contain 34 instruments which measure water temperature from near the surface to the ocean floor, as well as record salinity, fluctuations in ocean current, sea-ice thickness and pressure.

The research team will use the information from these instruments to answer key questions about the way the deep waters of the ocean are formed. Other instruments, including buoys, automatic weather stations, meteorological balloons and helicopter-borne probes will complete the picture of how the atmosphere, ocean and sea-ice interact.

Biologists will also be fully occupied during the voyage investigating whether the polynya acts as an "oasis" where krill and other forms of life congregate. Studies will be carried out to assess the importance of the polynya to birds, seals and whales during the harsh Antarctic winter.

The Southern Ocean voyage leaves Hobart on Wednesday. The Aurora Australis is scheduled to return to Hobart early in September.

For more information, contact Craig Macaulay, CSIRO, email: craig.macaulay@marine.csiro.au.

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