The Antarctic Deep Sea Gets Colder [Alfred Wegener Institute]

The Antarctic deep sea gets colder, which might stimulate the circulation of the oceanic water masses. This is the first result of the Polarstern expedition of the Alfred Wegener Institute for Polar and Marine Research in the Helmholtz Association that has just ended in Punta Arenas/Chile. At the same time satellite images from the Antarctic summer have shown the largest sea-ice extent on record. In the coming years autonomous measuring buoys will be used to find out whether the cold Antarctic summer induces a new trend or was only a "slip".

The Polarstern expedition ANT-XXIV/3 was dedicated to examining the oceanic circulation and the oceanic cycles of materials that depend on it. Core themes were the projects CASO (Climate of Antarctica and the Southern Ocean) and GEOTRACES, two of the main projects in the Antarctic in the International Polar Year 2007/08. Under the direction of Dr. Eberhard Fahrbach, Oceanographer at the Alfred Wegener Institute, 58 scientists from ten countries were on board the research vessel Polarstern in the Southern Ocean from 6 February until 16 April, 2008. They studied ocean currents as well as the distribution of temperature, salt content and trace substances in Antarctic sea water. "We want to investigate the role of the Southern Ocean for past, present and future climate," chief scientist Fahrbach said. The sinking water masses in the Southern Ocean are part of the overturning in this region and thus play a major role in global climate. "While the last Arctic summer was the warmest on record, we had a cold summer with a sea-ice maximum in the Antarctic. The expedition shall form the basis for understanding the opposing developments in the Arctic and in the Antarctic," Fahrbach said. In the frame of the GEOTRACES project the scientists found the smallest iron concentrations ever measured in the ocean. As iron is an essential trace element for algal growth, and algae assimilate CO2 from the air, the concentration of iron is an important parameter against the background of the discussion to what extent the oceans may act as a carbon sink.

As the oceanic changes only become visible after several years and also differ spatially, the data achieved during the Polarstern expeditions are not sufficient to discern long-term developments. The data gap can only be closed with the aid of autonomous observing systems, moored at the seafloor or drifting freely, that provide oceanic data for several years. "As a contribution to the Southern Ocean Observation System we deployed, in international cooperation, 18 moored observing stations, and we recovered 20. With a total of 65 floating systems that can also collect data under the sea ice and are active for up to five years we constructed a unique and extensive measuring network," Fahrbach said. In order to get the public, and especially the young generation, interested in science and research and to sensitise them for environmental processes, two teachers were on board Polarstern. Both took an active part in research work and communicated their experiences to pupils, colleagues and the media via internet and telephone. "We will bring home many impressions from this expedition, and we will be able to provide a lively picture of the polar regions and their impact on the whole earth to the pupils," Charlotte Lohse, teacher at the Heisenberg-Gymnasium in Hamburg, and Stefan Theisen from the Free Waldorf School in Kiel said.

http://www.terradaily.com/reports/Ozone_Hole_Recovery_May_Reshape_Southern_Hemisphere_Climate_Change_999.html

Ozone Hole Recovery May Reshape Southern Hemisphere Climate Change

Boulder CO (SPX) Apr 29, 2008

A full recovery of the stratospheric ozone hole could modify climate change in the Southern Hemisphere and even amplify Antarctic warming, according to scientists from the University of Colorado at Boulder, the National Oceanic and Atmospheric Administration and NASA.

While Earth’s average surface temperatures have been increasing, the interior of Antarctica has exhibited a unique cooling trend during the austral summer and fall caused by ozone depletion, said Judith Perlwitz of the Cooperative Institute for Research in Environmental Sciences, a joint institute of CU-Boulder and NOAA. “If the successful control of ozone-depleting substances allows for a full recovery of the ozone hole over Antarctica, we may finally see the interior of Antarctica begin to warm with the rest of the world,” Perlwitz said.

Perlwitz is lead author of a new study on the subject to be published April 26 in Geophysical Research Letters. Co-authors include Steven Pawson and Eric Nielson of NASA’s Goddard Space Flight Center in Greenbelt, Md., and Ryan Fogt and William Neff of NOAA’s Earth System Research Laboratory in Boulder. The study was supported by NASA’s Modeling and Analysis Program.

The authors used a NASA supercomputer model that included interactions between the climate and stratospheric ozone chemistry to examine how changes in the ozone hole influence climate and weather near Earth’s surface, said Perlwitz.

The study authors calculated that when stratospheric ozone levels return to near pre-1969 levels by the end of the 21st century, large-scale atmospheric circulation patterns now shielding the Antarctic interior from warmer air masses to the north will begin to break down during the austral summer. The circulation patterns are collectively known as a positive phase of the Southern Annular Mode, or SAM.

The scientists found that as ozone levels recover, the lower stratosphere over the polar region will absorb more harmful ultraviolet radiation from the sun. This could cause air temperatures roughly 6 to 12 miles above Earth’s surface to rise by as much as 16 degrees Fahrenheit, reducing the strong north-south temperature gradient that currently favors the positive phase of SAM, said the research team.

The supercomputer modeling effort also indicated that ozone hole recovery would weaken the intense westerly winds that currently whip around Antarctica and block air masses from crossing into the continent’s interior. As a result, Antarctica would no longer be isolated from the warming patterns affecting the rest of the world.

NASA’s Pawson said ozone recovery over Antarctica would essentially reverse summertime climate and atmospheric circulation changes that have been caused by the presence of the ozone hole. “It appears that ozone-induced climate change occurred quickly, over 20 to 30 years, in response to the rapid onset of the ozone hole,” he said. “These seasonal changes will decay more slowly than they built up, since it takes longer to cleanse the stratosphere of ozone-depleting gases than it took for them to build up.”

The seasonal shift in large-scale circulation patterns could have repercussions for Australia and South America as well. Other studies have shown that the positive phase of SAM is associated with cooler temperatures over much of Australia and increased rainfall over Australia’s southeast coastline.

During late spring and early summer, the positive phase of SAM also is associated with drier conditions in South America’s productive agricultural areas like Argentina, Brazil, Uruguay and Paraguay, said Perlwitz. If ozone recovery induces a shift away from a positive SAM, Australia could experience warmer and drier conditions while South America could get wetter, she said.

But just how influential a full stratospheric ozone recovery will be on Southern Hemisphere climate largely depends on the future rate of greenhouse gas emissions, according to the GRL authors. Projected increases in human-emitted greenhouse gases like carbon dioxide will be the main driver for strengthening the positive phase of SAM.

“In running our model simulations, we assumed that greenhouse gases like carbon dioxide would double over the next 40 years and then slowly level off,” said Perlwitz. “If human activities cause more rapid increases in greenhouse gases, or if we continue to produce these gases for a longer period of time, then the positive SAM may dominate year-round and dwarf any climatic effects caused by ozone recovery.”

Computer simulations are inherently Aristotelian, that is, they discover nothing that wasn’t already in the premise; purely deduction. Repeal the Law of the Excluded Middle and dump Aristotle.

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