| MadSci Network: Earth Sciences |
Dr. Edwards,
The short answer is salinity has the greatest effect on density. As
you can see below, a change in salinity of 0.5ppt will change
sigma-t by about 0.4 units at any temperature or salinity while the effect
of a change of 1oC varies in salty and fresh water from decreasing
salinity by approximately 0.3 sigma-t units to increasing density
slightly. However, the effect of both temperature and salinity on density
varies with changes in temperature and salinity. For example, the change in
sigma-t for water at 0 ppt salinity and 20oC will change by -0.3 sigma-t
units for every 10C increase in temperature. The same water (0ppt,20oC)
will change by 0.4 sigma-t units for every 0.5ppt increase in salinity.
But, as mentioned the response to changes in salinity and temperature
varies so that a salty warm water parcel (30oC, 40ppt) is less sensitive to
changes in salinity than a cold, fresh water parcel, but more sensitive to
changes in temperature. The following table shoud help. It is drawn from
"DESCRIPTIVE PHYSICAL OCEANOGRAPHY,An introduction" by Pickard and Emery.
Figure 3.1: Variation in sigma-t with variations in temperature and
salinity as functions of temperature and salinity
CHANGE IN SIGMA-T AS A FUNCTION OF:
1oC increase in temp 0.5ppt increase in salinity
Salinity 0 20 40 0 20 40
Temp (oC)
30 -0.30 -0.33 -0.34 0.39 0.38 0.38
20 -0.21 -0.24 -0.27 0.40 0.38 0.38
10 -0.09 -0.14 -0.18 0.41 0.39 0.39
0 +0.07 -0.01 -0.17 0.43 0.40 0.40
I hope this answers your question and I also hope the table looks like
a table. I checked a few intro Ocenography texts and they did not contain
adequate information on this subject, so I urge you to consult an
introductory physical oceanography text for more detailed information.
Good Luck!
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