Salinity |
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SalinityThe 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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The Global Water Cycle
