Environmental Engineering Reference
In-Depth Information
compensates for the slowness of thermoha-line circulation. Its unimpeded transequatorial
flow earns the alternative title Global Ocean Conveyor (Figure 11.9).
TIDES AND WAVES
TIDES
We turn, finally, to the most familiar part of ocean movement - tides and waves, which
have the greatest immediate impact at the coastline through their transmission of energy .
Tides transfer mass from one part of the global ocean to another in a regular, oscillating
manner by competition between the gravitational fields of Earth, moon and sun. Moon
and sun create tidal bulges on either side of Earth, extended in the plane of maximum
pull (Figure 11.10), but their periodicity is not identical. By rotating once in twenty-four
hours about its own axis, Earth experiences two tides (periodicity: 12·0 hr) relative to the
sun's 'fixed' position but slightly less than two (periodicity: 12·42 hr) relative to the
Moon, which also moves around Earth. Lunar tides are stronger than solar tides because
of the moon's
OCEAN - ATMOSPHERE COUPLING AND CLIMATE IN WESTERN EUROPE
new developments
Concern about the future stability of the Atlantic thermohaline circulation (THC) and
coupled ocean-atmosphere processes continues to grow, particularly with respect to
European climate. The THC is responsible for a major part of meridional heat transfer in
the North Atlantic and, therefore, the anomalous warmth which maintains western
European winter temperatures 15-20° C above the latitudinal average. Major North
Atlantic convective mixing sites are located in the Greenland and Labrador Seas. Only
the latter is connected directly with the NADW but cold water overflowing sea-bed sills
between Greenland-Iceland-Scotland is also a principal source of NADW.
Aspects of global warming may destabilize this process. The Greenland ice cap is
vulnerable to fairly rapid melting, enhancing freshwater flow into the Atlantic. Arctic
basin permafrost is melting, adding to this flux. Arctic Ocean sea ice extent in summer
has fallen by 10-15 per cent in fifty years and may be thinning by 5-10 per cent yr −1 . All
three processes reduce salinity and suppress the formation of NADW and create positive
feeedback through the reduction of ocean and land
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