A US study published in Nature provides further evidence that climate change may have a direct and rapid impact on ocean salinity, which in turn, may affect deep ocean circulation and climate. The researchers reconstructed a 45,000 to 60,000 year-old record of ocean temperature and salinity from the chemical traces in fossil shells of tiny planktonic animals recovered from deep sea sediment cores and compared their results to the record of abrupt climate change recorded in ice cores from Greenland. The results show that sudden shifts in temperature over Greenland and tropical rainfall patterns during the last ice age were linked to rapid changes in the salinity of the North Atlantic Ocean. In particular, the ice records show that cycles of sudden warming, when temperatures in Greenland rose by five to ten degrees Celsius over a few decades, matched rapid changes in surface-water salinity in the north Atlantic subtropical gyre. This deep-ocean circulation cell is very sensitive to changes in the density of north Atlantic surface waters and could slow down if the upper water masses become less salty or too warm. Consequently, a warmer climate and higher rainfall in the North Atlantic could potentially alter this deep-circulation cell, which in turn could result in a much colder climate in Europe.
Source: Matthew W. Schmidt, Maryline J. Vautravers and Howard J. Spero (2006) « Rapid subtropical North Atlantic salinity oscillations across Dansgaard–Oeschger cycles », Nature 443: 561-564.
Image source, NASA: Link
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