Environmental Engineering Reference
In-Depth Information
Scandinavia. However, the economic and political management of industrial, agricultural,
tourism and other implications of these changes need to be cautious. The ocean may
neutralize the warming or, in the worst case, convert it to rapid regional cooling.
CONCLUSION
Earth's ocean basins are its largest individual surface feature and also collectively its
youngest, at less than 200 Ma old, owing to the repetitive growth and consumption of
dense oceanic crust through the supercontinental cycle. In that time a former super-ocean
has shrunk considerably (surviving mainly in the Pacific), the Atlantic and southern
oceans have formed and the Arctic Ocean has become encircled by continents. Oceans
play an important but hidden role in most stages of the rock cycle, since their products
are concealed until uplift or sea-level fall exposes them. Modern oceanic research reveals
the extent to which environmental history is both influenced by, and recorded in, our
oceans. Observed changes in ocean-atmosphere coupled systems and more sophisticated
AOGCMs justify much greater interest in our oceans and ocean basins.
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 hot-spot
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.
