Séminaire
Projections of climate change indicate increased precipitation in the equatorial region and at high latitudes and decreased precipitation in the subtropics, and a general increase in ocean stratification. We use the available oceanographic and IPCC AR4 simulations temperature, salinity and oxygen profile data for the period 1970 to 2005 and satellite altimetry to examine the evidence for such Southern Ocean changes on a range of time scales including eddy time scales. Globally we find increased salinities near the upper-ocean salinity maximum and decreased salinities in the Southern Ocean surface waters and intermediate salinity minimum (~700m deep). These salinity changes imply about a 1% decrease in the precipitation-minus-evaporation over the mid-latitudes oceans and about a 5% increase in the precipitation-minus-evaporation in the Southern Ocean since 1970. These new and independent ocean derived estimates of changes in precipitation-minus-evaporation extend the growing evidence for an acceleration of the Earth’s water cycle.
An analysis of oxygen changes through out the Southern Ocean shows a coherent decrease in zonal averages at almost all latitudes above 1500m. Sub-ducting mode and salinity minimum waters in Southern Ocean have reduced oxygen concentration, and the upwelling circumpolar-deep water is also reduced (up to 10%). These changes are most simply explained by increased biological consumption resulting from reduced renewal rates. The inventories of oxygen, heat and sea-level show that these Southern Ocean outcropping density surfaces are driving these decreases in oxygen and increases in heat and sea-level. We compare these changes with projections of future climates for the Southern Ocean, largely driven by the amosphere.
galod@locean-ipsl.upmc.fr