CIESM - the Mediterranean Marine Research Network

Dynamics of Mediterranean straits and channels

F. Briand, editor

CIESM Science Series 2, Bulletin de l'Institut océanographique, Monaco, n° sp. 17.

Summary

The role of the Strait of Gibraltar in the evolution of Mediterranean water, properties and circulation
C. Garrett
Recent contributions of remote sensing to the study of internal waves in the straits of Gibraltar and Messina
W. Alpers, P. Brandt, A. Rubino and J.O. Backhaus
Water exchanges in the Balearic channels
J.L. Lopez-Jurado, J. Garcia Lafuente, J.-M. Pinot and A. Alvarez
Plankton dynamics in relation to physical structures around the Ibiza Channel
M.-L. Fernandez de Puelles
Les détroits dans la perspective de protection de l'environnement méditerranéen : les exemples de Bonifacio et de Messine
M. Dubost, B. Massa et C. Loussouarn
The characteristics of the water masses and the water transport in the Sicily Strait at long time scales
M. Astraldi, G.P. Gasparini, S. Sparnocchia, M. Moretti and E. Sansone
Thermohaline properties and circulation in the Otranto Strait
M. Gacic, V. Kovacevic, B. Manca, E. Papageorgiou, P.M. Poulain, P. Scarazzato and A. Vetrano
Influence of the water exchange through the Dardanelles on the thermohaline structure of the Aegean Sea
V.I. Vlasenko, N.M. Stashchuk, V.A. Ivanov, E.G. Nikolaenko, O. Uslu and H. Benli
Chemical exchange between the Mediterranean and the Black Sea via the Turkish straits
Ç. Polat and S. Tügrul
A review of the exchange flow regime and mixing in the Bosphorus Strait
E. Özsoy, M.A. Latif, H.I. Sur and Y. Goryachkin
On the biology of the Turkish straits system
B. Özsoy and A.A. Öztürk.

Preface
by Prof. F. Briand

Interest in Mediterranean straits has been driven since antique times by geopolitical considerations far more than by science. For the past 2500 years, these areas have been recognized as major strategic assets, yielding enormous political and economic advantages. As a result, the history of straits has been one of wars, more than peace, as regional powers kept confronting each other for their military control. The Trojan War was waged for this precise reason: it was to gain free access to the Black Sea that the ancient Greeks attacked Troy which then controlled the Dardanelles. Centuries later the Persian Xerxes and his 150,000 men managed to cross a bridge of 300 ships on the Hellespont to invade Greece. In the Western Mediterranean, Carthage was already a major maritime power at the time, through its control of what we know as the Strait of Sicily and the Strait of Gibraltar. In more recent times the latter proved to be the strategic lock for naval power in the Napoleonic wars.

The earliest "scientific" investigations of Mediterranean straits were conducted by sea-faring peoples and explorers like the Phoenicians, Minoans, Egyptians and the Greeks who, at the very least, must have taken water soundings to ensure safe navigation. Navigation the straits required much courage, since they were a gateway to unexplored worlds charged with plenty of myths, mystery, and also real dangers. For a long time the columns of Hercules marked the dividing line between the known and the unknown seas. Thousands of sailors lost their life in their vicinity, crushed by the powerful tidal currents which are a permanent feature of straits. It is out of such feats that heroes of legend are made, and his narrow escape from Carrybde and Scilla - the dreaded and treacherous whirlpools of the Strait of Messina - did much to contribute to the universal fame of Ulysses.

Gradually the ancient fascination for the gateways to new worlds turned into genuine scientific curiosity. Nearly 500 years ago, these extraordinary lines were written by Leonardo da Vinci: "Thus you make a model of the Mediterranean sea ... In this model you let the rivers be commensurate with the size and outlines of the sea ... Then you let the waters of the Nile, Don, Po and other rivers of that size flow into the sea, which will have its outlet through the Strait of Gibraltar... In this way you will soon see whence the water currents take objects and where they deposit them".

Many years were to pass before this astonishing foresight of modern dynamic marine modelling techniques would be backed up by hard scientific evidence. The concept of a subsurface Mediterranean outflow through the Strait of Gibraltar was established by the ingenious laboratory experiments of Marsigli in the late 17th century. It was confirmed ... Some 200 years later by the filed observations of salinity and temperature of Carpenter and Jeffreys which led them to conclude that Mediterranean waters are constantly being renewed through the Strait of Gibraltar by an exchange of overflowing Atlantic water and deeper, denser, Mediterranean water. For the next 100 years, improving the quantitative estimates of the inflow and outflow transports through the Strait absorbed, at one time or another, some of the best physical oceanographers of the world, such as Nielsen and Lacombe.

This volume reflects the remarkable contribution of straits to recent advances in theoretical and applied oceanography. In March 1995, CIESM organised a special symposium in Malta, which focused upon the critical exchange of water masses, biological species, chemical elements and pollutants through the various Mediterranean straits. The success met by the symposium encouraged us to explore the matter further and to gather in a single volume some of the most recent findings and hypotheses on the question.

The Mediterranean sea is rich in straits and narrows, providing varied and numerous angles for study. Today most of the scientific interest in straits focuses on the dynamics and mixing of water masses, on the interference with meso- and small-scale structures, on the determination of maximal versus submaximal exchange, and on a host of issues related to flow with multiple density layers. As the reader will discover, advances on these questions have been rapid and substantial in recent years and this volume offers many fresh insights on the hydrological processes taking place in the straits of Gibraltar, Messina, Sicily, Otranto, in the Balearic channels and in the Turkish straits. Undoubtedly the coming decade will see further breakthroughs in our knowledge of the subject, as new technologies such as satellite radar images, to which we owe the clear signatures of internal wave patterns in the straits of Gibraltar and Messina presented here, become increasingly available.

Physical oceanography is not the only domain covered. Looking at straits from an ecological perspective, one is struck by their vulnerability to traffic and by their critical role in allowing the transfer of marine species between adjacent seas. Genetic flux through Mediterranean straits is an emerging domain of research, offering at this time only few, sketchy, pieces of evidence. It will take time before researchers manage to fully grasp the qualitative and quantitative trends involved in this complex biogeographical puzzle. In the meanwhile, environmental planners would do well to apply the "precautionary principle" to straits, recognizing them as unique and fragile biological corridors which must form an explicit part of integrated conservation strategies for both the marine and avian faunas in the region.

I am grateful to Christine Poupon and to Anne Toulemont for the great care they took in overseeing the successive phases involved in the physical transformation of the manuscripts. The assistance of Dr Claude Millot, who critically reviewed several chapters of the volume, is also warmly acknowledged.

	CIESM PUBLICATIONS - Miscellaneous __________________________________________
	Dynamics of Mediterranean straits and channels F. Briand, editor CIESM Science Series 2, Bulletin de l'Institut océanographique, Monaco, n° sp. 17. Summary The role of the Strait of Gibraltar in the evolution of Mediterranean water, properties and circulation C. Garrett Recent contributions of remote sensing to the study of internal waves in the straits of Gibraltar and Messina W. Alpers, P. Brandt, A. Rubino and J.O. Backhaus Water exchanges in the Balearic channels J.L. Lopez-Jurado, J. Garcia Lafuente, J.-M. Pinot and A. Alvarez Plankton dynamics in relation to physical structures around the Ibiza Channel M.-L. Fernandez de Puelles Les détroits dans la perspective de protection de l'environnement méditerranéen : les exemples de Bonifacio et de Messine M. Dubost, B. Massa et C. Loussouarn The characteristics of the water masses and the water transport in the Sicily Strait at long time scales M. Astraldi, G.P. Gasparini, S. Sparnocchia, M. Moretti and E. Sansone Thermohaline properties and circulation in the Otranto Strait M. Gacic, V. Kovacevic, B. Manca, E. Papageorgiou, P.M. Poulain, P. Scarazzato and A. Vetrano Influence of the water exchange through the Dardanelles on the thermohaline structure of the Aegean Sea V.I. Vlasenko, N.M. Stashchuk, V.A. Ivanov, E.G. Nikolaenko, O. Uslu and H. Benli Chemical exchange between the Mediterranean and the Black Sea via the Turkish straits Ç. Polat and S. Tügrul A review of the exchange flow regime and mixing in the Bosphorus Strait E. Özsoy, M.A. Latif, H.I. Sur and Y. Goryachkin On the biology of the Turkish straits system B. Özsoy and A.A. Öztürk. Preface by Prof. F. Briand Interest in Mediterranean straits has been driven since antique times by geopolitical considerations far more than by science. For the past 2500 years, these areas have been recognized as major strategic assets, yielding enormous political and economic advantages. As a result, the history of straits has been one of wars, more than peace, as regional powers kept confronting each other for their military control. The Trojan War was waged for this precise reason: it was to gain free access to the Black Sea that the ancient Greeks attacked Troy which then controlled the Dardanelles. Centuries later the Persian Xerxes and his 150,000 men managed to cross a bridge of 300 ships on the Hellespont to invade Greece. In the Western Mediterranean, Carthage was already a major maritime power at the time, through its control of what we know as the Strait of Sicily and the Strait of Gibraltar. In more recent times the latter proved to be the strategic lock for naval power in the Napoleonic wars. The earliest "scientific" investigations of Mediterranean straits were conducted by sea-faring peoples and explorers like the Phoenicians, Minoans, Egyptians and the Greeks who, at the very least, must have taken water soundings to ensure safe navigation. Navigation the straits required much courage, since they were a gateway to unexplored worlds charged with plenty of myths, mystery, and also real dangers. For a long time the columns of Hercules marked the dividing line between the known and the unknown seas. Thousands of sailors lost their life in their vicinity, crushed by the powerful tidal currents which are a permanent feature of straits. It is out of such feats that heroes of legend are made, and his narrow escape from Carrybde and Scilla - the dreaded and treacherous whirlpools of the Strait of Messina - did much to contribute to the universal fame of Ulysses. Gradually the ancient fascination for the gateways to new worlds turned into genuine scientific curiosity. Nearly 500 years ago, these extraordinary lines were written by Leonardo da Vinci: "Thus you make a model of the Mediterranean sea ... In this model you let the rivers be commensurate with the size and outlines of the sea ... Then you let the waters of the Nile, Don, Po and other rivers of that size flow into the sea, which will have its outlet through the Strait of Gibraltar... In this way you will soon see whence the water currents take objects and where they deposit them". Many years were to pass before this astonishing foresight of modern dynamic marine modelling techniques would be backed up by hard scientific evidence. The concept of a subsurface Mediterranean outflow through the Strait of Gibraltar was established by the ingenious laboratory experiments of Marsigli in the late 17th century. It was confirmed ... Some 200 years later by the filed observations of salinity and temperature of Carpenter and Jeffreys which led them to conclude that Mediterranean waters are constantly being renewed through the Strait of Gibraltar by an exchange of overflowing Atlantic water and deeper, denser, Mediterranean water. For the next 100 years, improving the quantitative estimates of the inflow and outflow transports through the Strait absorbed, at one time or another, some of the best physical oceanographers of the world, such as Nielsen and Lacombe. This volume reflects the remarkable contribution of straits to recent advances in theoretical and applied oceanography. In March 1995, CIESM organised a special symposium in Malta, which focused upon the critical exchange of water masses, biological species, chemical elements and pollutants through the various Mediterranean straits. The success met by the symposium encouraged us to explore the matter further and to gather in a single volume some of the most recent findings and hypotheses on the question. The Mediterranean sea is rich in straits and narrows, providing varied and numerous angles for study. Today most of the scientific interest in straits focuses on the dynamics and mixing of water masses, on the interference with meso- and small-scale structures, on the determination of maximal versus submaximal exchange, and on a host of issues related to flow with multiple density layers. As the reader will discover, advances on these questions have been rapid and substantial in recent years and this volume offers many fresh insights on the hydrological processes taking place in the straits of Gibraltar, Messina, Sicily, Otranto, in the Balearic channels and in the Turkish straits. Undoubtedly the coming decade will see further breakthroughs in our knowledge of the subject, as new technologies such as satellite radar images, to which we owe the clear signatures of internal wave patterns in the straits of Gibraltar and Messina presented here, become increasingly available. Physical oceanography is not the only domain covered. Looking at straits from an ecological perspective, one is struck by their vulnerability to traffic and by their critical role in allowing the transfer of marine species between adjacent seas. Genetic flux through Mediterranean straits is an emerging domain of research, offering at this time only few, sketchy, pieces of evidence. It will take time before researchers manage to fully grasp the qualitative and quantitative trends involved in this complex biogeographical puzzle. In the meanwhile, environmental planners would do well to apply the "precautionary principle" to straits, recognizing them as unique and fragile biological corridors which must form an explicit part of integrated conservation strategies for both the marine and avian faunas in the region. I am grateful to Christine Poupon and to Anne Toulemont for the great care they took in overseeing the successive phases involved in the physical transformation of the manuscripts. The assistance of Dr Claude Millot, who critically reviewed several chapters of the volume, is also warmly acknowledged.
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