MIT2_500s09_read02

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Unformatted text preview: MIT OpenCourseWare http://ocw.mit.edu 2.500 Desalination and Water Purification Spring 2009 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms . Introduction To Physical Oceanography Robert H. Stewart Department of Oceanography Texas A & M University Copyright 2007 September 2007 Edition Chapter 6 Temperature, Salinity, and Density Heat uxes, evaporation, rain, river inow, and freezing and melting of sea ice all inuence the distribution of temperature and salinity at the oceans surface. Changes in temperature and salinity can increase or decrease the density of wa- ter at the surface, which can lead to convection. If water from the surface sinks into the deeper ocean, it retains a distinctive relationship between temperature and salinity which helps oceanographers track the movement of deep water. In addition, temperature, salinity, and pressure are used to calculate density. The distribution of density inside the ocean is directly related to the distribution of horizontal pressure gradients and ocean currents. For all these reasons, we need to know the distribution of temperature, salinity, and density in the ocean. Before discussing the distribution of temperature and salinity, lets first de- fine what we mean by the terms, especially salinity. 6.1 Definition of Salinity At the simplest level, salinity is the total amount of dissolved material in grams in one kilogram of sea water. Thus salinity is a dimensionless quantity. It has no units. The variability of dissolved salt is very small, and we must be very careful to define salinity in ways that are accurate and practical. To better understand the need for accuracy, look at figure 6.1. Notice that the range of salinity for most of the oceans water is from 34.60 to 34.80 parts per thousand, which is 200 parts per million. The variability in the deep North Pacific is even smaller, about 20 parts per million. If we want to classify water with different salinity, we need definitions and instruments accurate to about one part per million. Notice that the range of temperature is much larger, about 1 C, and temperature is easier to measure....
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MIT2_500s09_read02 - MIT OpenCourseWare http://ocw.mit.edu...

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