New Zealand scientists who have endured months of polar darkness over winter in Antarctica say they have shown for the first time that cold water melted from ice shelves enhances the growth of sea ice over winter.
"This mechanism potentially explains why Antarctic sea ice has not seen the same dramatic decline as Arctic sea ice," National Institute of Water and Atmospheric research scientist Dr Mike Williams said.
Sea ice is a buffer between the ocean and the atmosphere and plays a key role in the global environment.It also plays an important role in a process that transports oxygen and carbon dioxide to the ocean bottom so that life can be supported even at great depths.
During the winter, up to 18 million sq km of ocean is covered by sea ice, but by the end of summer, only about 3 million sq km remains.The New Zealand scientists who watched open ocean transformed into 2m thick ice in just a few months said today that for the first time, one of the driving forces in this transformation has been clearly observed and understood.
"It is the water from under the ice shelf that drives the dramatic sea ice growth," said the team known on the internet as "the sea ice crew". Led in Antarctica by Dr Andy Mahoney of Otago University, they wintered at Scott Base from February to October, conducting surveys at two locations in McMurdo Sound, and have just returned with huge amounts of scientific data.Their sea level observations have provided information about the thickness and volume of the sea ice not available from satellites, and details of the complex relationship between ice shelves and sea ice.
The scientists used three measuring techniques.They recorded water temperature and salinity from the surface down to the sea floor, made acoustic measurements of the currents and ice content of the water at different depths, and drilled ice cores drilled to measure sea ice thickness.
For one set of measurements they spent 28 hours raising and lowering a device at regular intervals down to 575m depth to measure the salinity and temperature of the water.They now believe that cold water melted from the floating part of Antarctica's ice sheet -- the ice shelves -- is causing more sea ice to grow, especially in winter.
"This may explain why Antarctic sea ice has not declined as quickly as Arctic sea ice in response to global warming," said Dr Williams."In effect, the melting ice shelves may be buffering the sea ice."
