Blue Carbon

Thermohaline circulation

Deep water formation

Deep water formation

Pacific Ocean

Surface current

Deep current

Indian Ocean

Pacific Ocean

Atlantic Ocean

Deep water formation

31 34 Practical salinity unit 36 39

Source : NASA, 2009.

(1 psu = 1 gram of salt per kilogram of water)

Figure 8: Thermohaline circulation is a 3-dimensional flow involving surface and deep ocean waters, which is driven by differences in water temperature and salinity. ( Image source: NOAA/NCDC ).

pands causing the ocean surface to rise (UNEP, 2008b). Over time, this heat will descend to greater ocean depths, increasing expansion and triggering further changes in sea level. Melting of sea ice in the Arctic, inland glaciers and continen- tal ice sheets of Greenland and Antarctica is changing the sa- linity of sea water and in some cases also contributing to sea level rise (UNEP, 2008b). So, melting and warming will have further consequences on ocean circulation, as ocean currents are driven by the interactions between water masses through a balance with temperature and salinity, which controls the den- sity. Changes in oceanic currents could expose local climates to abrupt changes in temperature. Higher water temperatures also lead to increased evaporation, making more energy avail- able for the atmosphere. This has direct consequences on

extreme weather events, as warming sea temperatures boost the destructive energy of hurricanes, typhoons, etc. Tropical sea-surface temperatures have warmed by only half a degree Celsius, while a 40% increase in the energy of hurricanes has been observed (Saunders and Lea, 2008). Warmer, low salinity surface waters together with the annual sea- sonal heating are extending and strengthening the seasonal lay- ers in the water-column (stratification), limiting the vertical move- ment of water masses. This phenomenon together with changes in wind regimes has implications for some of the most produc- tive parts of earth’s oceans (Le Quéré et al. , 2007), where upwell- ing of deep waters and nutrients enhances primary production, supporting massively abundant surface ecosystems. If reduction of upwelling occurs to any degree, marine ecosystems, fisheries


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