ABSTRACT
Oceanography is the study of processes in oceans and seas, which, together with lakes and rivers, represent the Earth's hydrosphere; the surface marine water is irregularly distributed over the globe (Figure 1.1). Oceanography involves four interlinked aspects: physical, chemical, biological and geological, all operating within the hydrosphere. However, the hydrosphere is only one of several overlapping entities which combine to make the Earth's surface systems work; altogether these are hydrosphere, cryosphere, atmosphere, biosphere and geosphere. Oceans and seas may be thought of as lying on the geosphere and under the atmosphere, while much of the biosphere is immersed in the oceans. Of course, this view is too simple, because there is so much overlap and interchange between these components, that the Earth's surface is really an ocean-atmosphere—land linked system (Figure 1.2). To illustrate these relationships more fully, note the following points:
Water is continuously cycled through the upper layers of the solid Earth (crust and upper mantle), exchanging dissolved and particulate matter, and it has been estimated that about every 10 million years, the volume of water cycled is equivalent to the entire ocean mass. Because there is reasonable evidence that the first oceans were present by 3900 million years ago (Ma), and maybe earlier, that means a large number of water molecules have been through the crust and upper mantle 390 times. Because the hydrological cycle brings water onto land, some of those water molecules might be in your body as you read this!
Ocean basin geometry (i.e. three-dimensional shape) and circulation are greatly controlled by plate tectonics, and tectonic change over time has a profound influence on oceans and climate.
The oceans receive huge amounts of material from terrestrial erosion, and exchange gases and particles with the atmosphere.
The oceans have been substantially modified by organic activity through geological time.
The oceans store 97.2% of Earth's water, compared with the atmosphere (0.001%), ice caps and glaciers (2.15%), subsurface water (0.625%) and surface water (0.017%) (Murray, 1992). Oceans couple with the atmosphere to form a system responsible for distributing heat around the Earth, and thus play a major role in the Earth's climate system. Ocean water has about 30 times more heat capacity than the atmosphere, so small changes in ocean circulation lead to profound climatic modification, as illustrated by the ENSO events of the Pacific, and (possibly) the Younger Dryas event c.ll 000 years ago.
The oceans generate about one-third of global primary production, and are a valuable biological and food resource. Over recent decades the potential of oceans tor mineral and energy resources has become increasingly recognised.
The globe from several different viewpoints, to illustrate the large area covered by oceans, and the uneven distribution of both land and oceans. Remember that the Earth's continents and oceans are wrapped around its surface, all too easy to forget when studying features drawn using the Mercator projection used in most of the book. https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203761083/48801130-8057-4ae6-96c5-1a4abe74ca7a/content/fig00001_B.jpg" xmlns:xlink="https://www.w3.org/1999/xlink"/>