Effects of Current
125
Sea and the Persian Gulf. Here the saline waters sink to intennediate depths below
the thennocline, and affect the development of the oxygen minimum in the Arabian
Sea. Basins with anti-estuarine circulation tend to collect carbonate on the sea floor,
and tend to discriminate against organic carbon, opaline silica, and phosphatic deposits.
The influx of Atlantic surface waters into the Mediterranean is a strong current
and a huge river: 50 times the Mississippi at flood stage. It is said that the Battle of
Trafalgar (1805) owed its outcome to the Gibraltar Current. The reason given is that
the French and Spanish fleet had to wait for favorable winds to buck the Current,
while Nelson was able to assemble his fleet and poise it for strike. In modem times,
the submarines invading the Mediterranean had to struggle against the deep outflow.
Already in 1820, the British Admiral W. H. Smyth observed the in- and outflow
through the Gibraltar Straits, and gave the correct explanation. It was not, however,
generally accepted for another 50 years of discussion.
The inverse situation - shallow current out of, deep current into the basin - is
typical for estuaries and fjords, and occurs on a large scale in the Black Sea and the
Baltic Sea. Excess precipitation over evaporation is necessary to develop this circulation. At the Bosporus, the connection between the Black Sea and the Mediterranean,
fishennen have known since time immemorial that their nets would pull toward the
Mediterranean at the surface and toward the Black Sea at the bottom. L. F. Marsili
(1681), pioneer in marine geology, confirmed the effect by measurement and correctly explained the currents as being due to density differences. The light excess
water flows out of the Black Sea at the top; the heavy saline water from the Mediterranean falls toward the bottom of the Black Sea, displacing the less saline water
above. Ultimately, anaerobic conditions result from this circulation, called estuarine,
and organic-rich deposits accumulate on the sea floor. The hows and whys are discussed in Section 7.6.
4.3.6 Turbidity Currents. We have already discussed the activity of mud-laden,
gravity-driven currents in connection with the origin of continental slopes, submarine
canyons and deep-sea fans (Chap. 2.10). These currents differ from the others here
listed in several important ways: (1) they are strictly episodic; (2) they derive their
power from excess density due to suspended sediment, and (3) they run downhill,
transporting large amounts of material.
Further Reading
McCave IN (ed) (1976) The benthic boundary layer. Plenum, New York
Komar PD (1976) Beach processes and sedimentation. Prentice-Hall, Englewood Cliffs NJ
Allen JRL (1982) Sedimentary structures, their character and physical basis. Elsevier, Amsterdam
Pickard L, Emery WJ (1982) Descriptive physical oceanography - an introduction, 4th ed. Pergamon Press, Oxford
Hollister CD, Nowell ARM (eds) (1985) Deep ocean sediment transport, vol I. Elsevier, Amsterdam
Hollister CD, McCave IN, Nowell ARM (eds) (1988) Deep ocean sediment transport, vol 2. Elsevier, Amsterdam
125
Sea and the Persian Gulf. Here the saline waters sink to intennediate depths below
the thennocline, and affect the development of the oxygen minimum in the Arabian
Sea. Basins with anti-estuarine circulation tend to collect carbonate on the sea floor,
and tend to discriminate against organic carbon, opaline silica, and phosphatic deposits.
The influx of Atlantic surface waters into the Mediterranean is a strong current
and a huge river: 50 times the Mississippi at flood stage. It is said that the Battle of
Trafalgar (1805) owed its outcome to the Gibraltar Current. The reason given is that
the French and Spanish fleet had to wait for favorable winds to buck the Current,
while Nelson was able to assemble his fleet and poise it for strike. In modem times,
the submarines invading the Mediterranean had to struggle against the deep outflow.
Already in 1820, the British Admiral W. H. Smyth observed the in- and outflow
through the Gibraltar Straits, and gave the correct explanation. It was not, however,
generally accepted for another 50 years of discussion.
The inverse situation - shallow current out of, deep current into the basin - is
typical for estuaries and fjords, and occurs on a large scale in the Black Sea and the
Baltic Sea. Excess precipitation over evaporation is necessary to develop this circulation. At the Bosporus, the connection between the Black Sea and the Mediterranean,
fishennen have known since time immemorial that their nets would pull toward the
Mediterranean at the surface and toward the Black Sea at the bottom. L. F. Marsili
(1681), pioneer in marine geology, confirmed the effect by measurement and correctly explained the currents as being due to density differences. The light excess
water flows out of the Black Sea at the top; the heavy saline water from the Mediterranean falls toward the bottom of the Black Sea, displacing the less saline water
above. Ultimately, anaerobic conditions result from this circulation, called estuarine,
and organic-rich deposits accumulate on the sea floor. The hows and whys are discussed in Section 7.6.
4.3.6 Turbidity Currents. We have already discussed the activity of mud-laden,
gravity-driven currents in connection with the origin of continental slopes, submarine
canyons and deep-sea fans (Chap. 2.10). These currents differ from the others here
listed in several important ways: (1) they are strictly episodic; (2) they derive their
power from excess density due to suspended sediment, and (3) they run downhill,
transporting large amounts of material.
Further Reading
McCave IN (ed) (1976) The benthic boundary layer. Plenum, New York
Komar PD (1976) Beach processes and sedimentation. Prentice-Hall, Englewood Cliffs NJ
Allen JRL (1982) Sedimentary structures, their character and physical basis. Elsevier, Amsterdam
Pickard L, Emery WJ (1982) Descriptive physical oceanography - an introduction, 4th ed. Pergamon Press, Oxford
Hollister CD, Nowell ARM (eds) (1985) Deep ocean sediment transport, vol I. Elsevier, Amsterdam
Hollister CD, McCave IN, Nowell ARM (eds) (1988) Deep ocean sediment transport, vol 2. Elsevier, Amsterdam