Oceanographic changes

Broad-scale water movements in the ocean are driven by wind generated surface currents, which not only affect surface layers, but also drive upwelling and downwelling in certain areas, and by the thermohaline circulation.

The thermohaline circulation results from cold, hypersaline and, therefore, dense water in Polar regions (notably the Arctic Ocean) sinking and moving (mostly from the North Atlantic) to the equator across the ocean floor. This drives a conveyor-belt, with further cool water being added from the Southern Ocean there is a deep water current which flows into both the Indian and Pacific Oceans and this drives an upwelling of nutrient and oxygen rich water which then flows back towards the Atlantic in the surface layers. This continuous circulation oxygenates the deep oceans and redistributes heat from equator to the poles. Increases in temperature are already leading to melting sea ice. It has been speculated that the reduction in salinity and, therefore, density of polar waters could, in turn, reduce the strength of thermohaline circulation. Not only would this limit transport of oceanic heat to various regions of the world but warmer waters in the tropics would hold less dissolved carbon dioxide further enhancing its build up in the atmosphere.

Sea surface temperatures affect the patterns in atmospheric pressure, which in turn are responsible for wind generation. Accelerated warming of the oceans may produce stronger winds in certain areas, and could increase the frequency of extreme events such as storms and hurricanes. Changes in wind generated surface currents would not only modify the weather conditions for many continents but an alteration of the upwelling process could have serious effects on the marine ecosystem. Upwelling is the result of water being pulled away from an area by surface currents and replaced by water from greater depths. This nutrient-rich deeper water is vital for primary production and if reduced in certain areas could seriously affect species distribution and abundance.