Salinity

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Figure 7

Salinity

The oceanographer does have one tool to help understand the poorly sampled water cycle over the ocean: the oceanic salt content or salinity. Evaporation leaves salt behind, thereby increasing salinity; precipitation dilutes the salt content and freshens surface waters. Salinity can be thought of as analogous to humidity in the atmosphere. The general patterns of surface salinity reflect the workings of the global water cycle, the mid-latitude evaporation zones have high salinity, while precipitation zones at high and low latitudes have low salinity (Figure 7). Salinity is much harder to measure than temperature, so there is not nearly so much historical data to examine for climatological trends. However, we have reason to be optimistic about the future; the ARGO program of profiling floats is rapidly expanding the number of salinity profiles available around the globe ( http://www.argo.ucsd.edu/ ), a new salinity-sensing satellite (AQUARIUS  http://aquarius.nasa.gov/ ) is due to be launched in 2010, and here at WHOI we have been developing new foul-proof salinity sensors for deployment on surface drifters and moorings ( See  http://www.whoi.edu/science/po/people/rschmitt/  ).  One of the most striking features of the surface salinity pattern is the higher salinity of the Atlantic Ocean.  This may be largely due to loss of water vapor to the Pacific across Central America, and the lack of  water supply from the Sahara.  These higher salinities mean higher seawater densities, so  that the North Atlantic hosts a main sinking site of the meridional overturning circulation.  There surface waters flow north to become cooled by the atmosphere to become dense water which sinks to depth and flows southward.  A great deal of heat transport is associated with this overturning circulation, which is believed to have been disrupted by glacial meltwater in the past ( http://www.whoi.edu/page.do?pid=12073&tid=282&cid=10149 ).  Thus, salinity is intimately tied to the general circulation of the ocean and the climate of Earth. 

We acknowledge the National Science Foundation for generous support of this research.

 

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Last updated August 15, 2008
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