CO2 Stirred from Antarctic Depths by Wind Shifts
16.03.2009 - Atmosphere & Space, Water & Oceans, Ice & Snow, Other, Antarctic
A new paper published this week in Science by Robert Anderson,geochemist at the National Oceanic and Atmospheric Administration (NOAA), and his team of researchers shows that natural releases of carbon dioxide from the SouthernOcean due to shifting wind patterns might very well have amplifiedglobal warming at the end of the last ice age. Ice cores show that theends of other ice ages were also marked by rises in CO2.
A change in Earth's orbit, resulting in rising levels of the greenhouse gas CO2, is widely believed to have triggered the end of the last ice age. This rise in CO2, levels now has an explanation, thanks to a team of scientists at Columbia University's Lamont-Doherty Earth Observatory: the orbital shift supposedly triggered a southward displacement in westerly winds, causing heavy overturning in the Southern Ocean and pumping carbon dioxide from the water into the air. The westerly winds likely shifted south due to larger amounts of sunlight hitting the northern ice cap, causing it to melt and paradoxically create a cooling effect in the North Atlantic.
The theory, first suggested tow years ago by J.R. Toggweiler, a scientist at the NOAA, was tested for the first time by Anderson and his colleagues when they studied sediments from the bottom of the Southern Ocean to measure the rate of overturning. The rate of overturning regulates the amount of CO2 in the atmosphere.
Richard Matear, a researcher at Australia's Commonwealth Scientific and Industrial Research Organisation, describes a scenario which supports this theory, in which a southerly shift in winds increases CO2 venting in the Southern Ocean. Plants, which absorb CO2 during photosynthesis, are unable to absorb all the added nutrients, causing atmospheric CO2 to rise. However Axel Timmermann, a climate modeller at the University of Hawaii, believes the westerly winds do not simply shift north-south. He argues that upwelling in the Southern Ocean could not have raised CO2 levels in the air and an intensification of the westerly winds would, along with upwelling, also have increased plant growth in the South-eastern Pacific, which would have absorbed enough atmospheric CO2 to compensate for the added upwelling in the Southern Ocean.
Nonetheless, Anderson argues that further research is necessary. If the theory he and Toggweier are backing is correct, the amount of CO2 produced could be "large enough to offset some of the mitigation strategies that are being proposed to counteract rising CO2." In past 40 years, the winds have shifted south as much as they did 17,000 years ago at the end of the last ice age, so any CO2 added to the atmosphere could exacerbate anthropogenic induced warming already underway.
