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7 Ocean Currents
the far Western Pacific. This change generated a deepening of the equatorial
warm-water layer and caused the layer to spread eastward to South America,
where it arrived by March 1997. The combination of deepening warm water and
weakening Trade Winds resulted in a warming of the far eastern tropical Pacific,
which was first noticeable in May, and by the year's end the warming episode
had spread westward with temperatures of several degrees Celsius above normal
in the central and eastern tropical Pacific. This caused an unusual drought with
incidents of prolonged forest fires in the far Western Pacific.
El Nino has been a key player in the earth's climatic variability for a very
long time, and has only recently become appreciated in scientific, economic,
and social terms. Because this is a book on fluid mechanics and its ecological
implications, I am limiting the discussion of the El Nino consequences to the
biological ones only. This discussion is given in Chap. 15.
7.7 Continental Shelf Flow
7.7.1 Overview of Continental Shelf Waters
A continental shelf is an almost flat plain or terrace that borders a continent
and slopes gently towards the ocean basin. The offshore boundary of the continental shelf is the shelf break, usually at a water depth of about 130-200 m.
Continental shelf widths range from a few kilometres, along the Pacific coast
of the North and South America, to more than 1000 km in the Arctic Ocean.
Seaward of the continental shelf break is a steeper continental slope of
about 4°, continuing to a water depth of 2-3 km. At the toe of the continental
slope, the ocean floor flattens with average gradient of 1 0. This broad underwater plain of sediment is known as the continental rise. Some of the continental
rises extend seaward more than 500 km to water depths approaching 4000 m.
As the continental shelves are situated between land and open ocean, they
are influenced by both. Rivers transport freshwater and dissolved chemical
components, including nutrients and mud, into shelf waters. These land-origin
substances are subsequently mixed, dispersed by winds, waves, currents and
tides. In general, there is a large variety of currents with time scales ranging
from seconds (turbulence, wind-generated waves), to months and years (climatic variations).
Due to intensive mixing induced by waves and currents, there is efficient
recycling of nutrients derived from microbiological decomposition of organic
matter near the ocean floor. This nutrient regeneration is essential for plant
growth and to provide abundant organic matter to support large fish stocks.
In addition, cold nutrient-rich oceanic waters and associated materials intrude
onto the shelf, promoting conditions favourable for higher productivity on the
continental shelf than in the open ocean. Although the waters of the continental
shelves compose only 10 per cent of the ocean area, they provide 90 per cent
of the world's annual fish catch (Pinet, 1992).
7 Ocean Currents
the far Western Pacific. This change generated a deepening of the equatorial
warm-water layer and caused the layer to spread eastward to South America,
where it arrived by March 1997. The combination of deepening warm water and
weakening Trade Winds resulted in a warming of the far eastern tropical Pacific,
which was first noticeable in May, and by the year's end the warming episode
had spread westward with temperatures of several degrees Celsius above normal
in the central and eastern tropical Pacific. This caused an unusual drought with
incidents of prolonged forest fires in the far Western Pacific.
El Nino has been a key player in the earth's climatic variability for a very
long time, and has only recently become appreciated in scientific, economic,
and social terms. Because this is a book on fluid mechanics and its ecological
implications, I am limiting the discussion of the El Nino consequences to the
biological ones only. This discussion is given in Chap. 15.
7.7 Continental Shelf Flow
7.7.1 Overview of Continental Shelf Waters
A continental shelf is an almost flat plain or terrace that borders a continent
and slopes gently towards the ocean basin. The offshore boundary of the continental shelf is the shelf break, usually at a water depth of about 130-200 m.
Continental shelf widths range from a few kilometres, along the Pacific coast
of the North and South America, to more than 1000 km in the Arctic Ocean.
Seaward of the continental shelf break is a steeper continental slope of
about 4°, continuing to a water depth of 2-3 km. At the toe of the continental
slope, the ocean floor flattens with average gradient of 1 0. This broad underwater plain of sediment is known as the continental rise. Some of the continental
rises extend seaward more than 500 km to water depths approaching 4000 m.
As the continental shelves are situated between land and open ocean, they
are influenced by both. Rivers transport freshwater and dissolved chemical
components, including nutrients and mud, into shelf waters. These land-origin
substances are subsequently mixed, dispersed by winds, waves, currents and
tides. In general, there is a large variety of currents with time scales ranging
from seconds (turbulence, wind-generated waves), to months and years (climatic variations).
Due to intensive mixing induced by waves and currents, there is efficient
recycling of nutrients derived from microbiological decomposition of organic
matter near the ocean floor. This nutrient regeneration is essential for plant
growth and to provide abundant organic matter to support large fish stocks.
In addition, cold nutrient-rich oceanic waters and associated materials intrude
onto the shelf, promoting conditions favourable for higher productivity on the
continental shelf than in the open ocean. Although the waters of the continental
shelves compose only 10 per cent of the ocean area, they provide 90 per cent
of the world's annual fish catch (Pinet, 1992).