Geoscience Reference
In-Depth Information
KEY POINTS
1
Large-scale ocean basin topography reflects its formative tectonic processes. Deep subduction zone
trenches contrast with shallow continental shelves, which are broader on passive margins. Abyssal plains
are interrupted by mid-ocean ridges and hotspot submarine volcanoes. All are draped in varying thicknesses
of terrigenous or marine sediments, thinning seaward of the continental slope, down which they also slump
and flow.
2
Oceans contain almost all planetary water and therefore act as the principal source and sink of the
atmospheric and terrestrial hydrological cycles. Sea water is a weak saline solution of eleven principal
elements derived largely from terrigenous sources and lithified in due course as deep-sea chemical
precipitates or ocean-margin evaporite rocks.
3
Sea water is stirred superficially by Earth's wind belts. A thermohaline circulation exists at depth, driven
by buoyancy differences influenced by water density and temperature. In addition, gravitational attraction
by sun and moon pull tidal waves and currents around the oceans. They have a low magnitude in mid-
ocean but rise as they encounter coastlines.
4
Sea level fluctuates over geological time scales, determined by a combination of eustatic controls on water
volume and isostatic controls on ocean basin geometry. Regular Quaternary iso-eustatic fluctuations of
3-5 per cent of average ocean depth (3ยท73 km) have significantly altered coastlines and climates.
5
Oceans have a moderating influence on global climate. Surface waters act as a major heat store, having
a high thermal capacity which mitigates seasonal temperature fluctuations in maritime climates and reduces
meridional temperature extremes. Ocean-atmosphere-ice sheet coupling regulates Earth's energy and
moisture balances and may impose both positive and negative feedbacks to global atmospheric warming.
FURTHER READING
Bigg, G. R. (1996) The Oceans and Climate, Cambridge: Cambridge University Press. A concise and very readable account
of ocean processes as biogeochemical systems. It sets out the nature of ocean interactions with adjacent environments
and provides a good basis for understanding current developments in related aspects of global environmental change.
Kershaw, S. (2000) Oceanography: an Earth Science perspective, Cheltenham: Thornes. Starting with a conventional view
of the nature of ocean basins, sea water, ocean circulation and sedimentation, this text explores the dynamic evolution
of all components over long geological time scales before concluding with a review of contemporary human impacts.
Redfern, R. (2000) Origins: the evolution of continents, oceans and life, London: Cassell. Far more than covering the oceans
alone, this superbly illustrated book supports Part Three on the geosphere and the following Part Four on the biosphere.
Its evolutionary Earth approach proceeds, in essence, through the oceans as the largest single planetary surface.
WEB RESOURCES
http://www.ocean.com A
commercial new-media channel website in partnership with organizations and academic
institutions, which provides access to many areas of scientific and human interest in Earth's oceans, including direct
free access to current news stories in published media, interactive, imaging, video, DVD and other services around
the world. It also provides film-sharing opportunities with amateur, as well as professional, interests in Earth's oceans.
http://www.sea-search.net/mdic/welcome.html Th
e International Oceanographic Commission operates under UNESCO
and provides a wide range of data, information and current news on ocean monitoring, environmental protection,
fisheries and ecosystems, climate change implications and management issues relating to Earth's oceans.
