5: Water and Seawater
- Page ID
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CC1 Density and Layering in Fluids: Water in the oceans is arranged in layers according to the water density. Many movements of water masses in the oceans are driven by differences in water density.
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CC3 Convection and Convection Cells: Fluids, including ocean water, that are cooled from above or heated from below, sink or rise because their density is increased or reduced respectively. This establishes convection processes that are a primary cause of vertical movements and the mixing of ocean waters.
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CC5 Transfer and Storage of Heat by Water: Water’s high heat capacity allows large amounts of heat to be stored in the oceans and released to the atmosphere without much change of ocean water temperature. Water’s high latent heat of vaporization allows large amounts of heat to be transferred to the atmosphere in water vapor and then transported elsewhere. Water’s high latent heat of fusion allows ice to act as a heat buffer reducing climate extremes in high latitude regions.
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CC6 Salinity, Temperature, Pressure, and Water Density: Seawater density is controlled by temperature, salinity, and to a lesser extent pressure. Density is higher at lower temperatures, higher salinities, and higher pressures. Movements of water below the ocean surface layer are driven primarily by density differences.
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CC7 Radioactivity and Age Dating: Seawater contains naturally occurring and man-made radioisotopes of many elements at very low concentrations. These are useful for tracing movements of the elements through biogeochemical cycles.
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CC8 Residence Time: The residence time of an element in seawater is the average length of time atoms of the element spend in the oceans and it depends, to a large extent, on the rate of processes that remove them from solution. Residence time is a major factor in determining the concentration of elements in seawater.
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CC9 The Global Greenhouse Effect: The oceans play a major part in studies of the greenhouse effect because the oceans store large amounts of carbon dioxide and are a source of other greenhouse gases including methane.
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CC14 Phototrophy, Light, and Nutrients: Phototrophy, that includes photosynthesis, the major processes in the production of living matter, depend on the availability of light. Thus, the transmission of light through ocean water limits the depth to which phototrophy may occur.
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CC18 Toxicity: Many dissolved constituents of seawater become toxic to marine life at concentrations above their natural levels in seawater. A number of these constituents are nutrients that can limit primary production if their concentrations are too low. Thus, life depends on the relatively invariable concentrations of dissolved chemicals in the oceans.
Although most of us are aware that water is essential to life as we know it, the range of unique properties of water that make life possible is less well known. For example, the properties of water:
- Help to create and control climate and weather
- Influence the formation and modification of the land and seafloor topography
- Enable essential chemicals to be transported to and within living organisms
- Control many features of our physical environment, such as rain, snow, and the waves on oceans and lakes
- Underlie the functioning of many aspects of modern society, ranging from cooling systems for automobile engines and power plants, to ice cubes that keep drinks cold in summer
The dissolving power of water, the composition of seawater, and the processes that add or remove dissolved substances in ocean water are important to the studies of sediments (Chap. 6), life in the oceans (Chaps. 12, 14, 15), and pollution (Chap. 16).
Water’s unique physical properties are critically important to processes discussed in many chapters in this text, especially ocean–atmosphere interactions (Chap. 7) and the circulation of water in the oceans (Chap. 10). The behavior of sound and of electromagnetic radiation, including visible light, as they pass through seawater is important to ocean life (Chap. 12) and contributes to the difficulties faced by oceanographers in studying the oceans (Chaps. 2, 3). Light and sound transmission also influence the survival and reproduction strategies of marine species (Chap. 14).
In this chapter, we will investigate the extraordinary properties of water that permit it to support life on our planet, we will discuss how water’s dissolving ability affects the chemical composition of ocean water, and we will examine the most important physical properties of water and some of the ways that they influence the Earth and our environment.