|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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