c5 the chemistryof seawater- mc graw hill education（c 5 the chemistryof seawater - mc graw hill education）.doc

CHAPTER 5 THE CHEMISTRY OF SEAWATER Objectives 1. To acquaint you with the dissolved, particulate and gaseous components in seawater. 2. To illustrate the complex physical, chemical, and biological feedback systems that have regulated the concentrations, and interactions of these components in the world’s oceans over the last 4 billion years. Key Concepts Major Concept (I) The average waters of the world’s oceans contain 3.5% dissolved salts and 96.5% water. The content of dissolved salts in grams of salt per kilogram of seawater is called salinity. The average ocean salinity is about 35 g/kg. Related or supporting concepts: - Seawater salinity is typically reported in one of three different (but equivalent) ways: 1) grams of salt per kilogram of water (g/kg), 2) parts per thousand (ppt, or o/oo), or in 3) Practical Salinity Units (PSU). - The PSU scale is defined as the ratio of the conductivity of a seawater sample and a standard potassium chloride solution. The PSU scale and o/oo are numerically equal but the PSU scale doesn’t have any units because it is a ratio. - Sea surface salinity is controlled largely by variations in precipitation and evaporation patterns which are generally a function of latitude. Salinity is also influenced by proximity to land and variations in freshwater runoff from the continents as well as seasonal freezing and thawing at middle and high latitudes. - By examining figures 5.1 and 5.2 in your text you can see that there are two first-order patterns to sea surface salinity: a. salinity maxima occur approximately 20? to 30? north and south of the equator, and b. salinity minima occur about 5? north of the equator and about 45? north and south of the equator. - Salinity maxima occur approximately 20? to 30? north and south of the equator because of relatively dry climatic conditions that cause more evaporation than precipitation, thus concentrating the salts in the water. - The salinity minima at about 5? north of the eq