unclear, but essential to quantify. The majority of the world’s population lives
within 50 miles of the coastal ocean and relies on its services for its support. These
services have been estimated to the equivalent of $21 trillion per year (coasts and
oceans). It is therefore important to estimate the additional pressures that global
change may exert over the oceans and coastal zones in order to preserve their
services.
Table 2 introduces some general principles on the expected biological
adaptations to global change. Moving beyond these principles requires a major
step from observing and correlating trends to identifying cause—effect processes.
We have to recognize that every effect on individual species and processes
involves a cascade of responses that is likely to affect the structure and dynamics
of whole communities and ecosystems. In elucidating these causal processes we
need to separate long-term global trends from decadal and multidecadal natural
cycles. In this contribution this will be achieved through detailed analysis of the
links between atmospheric climate, which is largely globally driven, and
oceanographic climate, which is regionally or locally controlled, as well as the
subsequent biological adaptations, in a number of selected case studies. A section
on the constraints that the exploitation of marine biological resources may exert
on the adaptations of marine ecosystems to global change will follow.
The Thermohaline Circulation
Marine communities live in a three-dimensional environment where the depth
axis may determine diametrically opposite conditions and control mechanisms.
The conventional ocean circulation is characterized by a wind-driven upper
circulation that gives rise to massive, near-surface flows such as the Gulf Stream
and the Kuroshio and Antarctic Circumpolar currents. Superimposed upon this
circulation is the so-called thermohaline circulation (THC). This is driven by
surface-ocean density contrasts arising from temperature and salt variations
produced by strong atmospheric cooling and wind-induced evaporation. The
THC transports huge amounts of heat from the equator to the poles. It has
enormous consequences for the weather of Western Europe, warming parts of the
continent by up to 10 °C in mean temperature. To balance this transport, water
sinks 2—3 km after cooling, and flows back towards the equator along the ocean
bottom, eventually returning to the surface, primarily near the ocean boundaries.
Through this process oxygen is pumped into the deep sea, sustaining life at depth.
Concerns over the potential consequences of global warming on the THC
were initially ignored, but evidence that the THC has closed down in the past
has changed this perception. — The THC is very sensitive to the amount of
R. Costanza, R. d’Arge, R. de Groot, S. Farber, M. Grasso, B. Hannon, K. Limburg, S. Naeem, R. V.
O’Neill, J. Paruelo, R. G. Raskin, P, Sutton and M. van den Belt, Nature, 1997, 387, 253—260.
L. Hughes, Tree, 2000, 15, 56—61.
S. Manabe and R. J. Stouffer, J. Clim., 1988, 1, 841—866.
G. D. Egbert and R. D. Ray, Nature, 2000, 405, 775—778.
W. S. Broecker, Nature, 1987, 328, 123—126.
J. T. Houghton, L. G. Meira Filho, B. A. Callander, N. Harris, A. Kattenberg and K. Maskell,
Climate Change, Cambridge University Press, 1995.
D. Seidov and M. Maslin, Geology, 1999, 27, 23—26.
M. Barange
60
within 50 miles of the coastal ocean and relies on its services for its support. These
services have been estimated to the equivalent of $21 trillion per year (coasts and
oceans). It is therefore important to estimate the additional pressures that global
change may exert over the oceans and coastal zones in order to preserve their
services.
Table 2 introduces some general principles on the expected biological
adaptations to global change. Moving beyond these principles requires a major
step from observing and correlating trends to identifying cause—effect processes.
We have to recognize that every effect on individual species and processes
involves a cascade of responses that is likely to affect the structure and dynamics
of whole communities and ecosystems. In elucidating these causal processes we
need to separate long-term global trends from decadal and multidecadal natural
cycles. In this contribution this will be achieved through detailed analysis of the
links between atmospheric climate, which is largely globally driven, and
oceanographic climate, which is regionally or locally controlled, as well as the
subsequent biological adaptations, in a number of selected case studies. A section
on the constraints that the exploitation of marine biological resources may exert
on the adaptations of marine ecosystems to global change will follow.
The Thermohaline Circulation
Marine communities live in a three-dimensional environment where the depth
axis may determine diametrically opposite conditions and control mechanisms.
The conventional ocean circulation is characterized by a wind-driven upper
circulation that gives rise to massive, near-surface flows such as the Gulf Stream
and the Kuroshio and Antarctic Circumpolar currents. Superimposed upon this
circulation is the so-called thermohaline circulation (THC). This is driven by
surface-ocean density contrasts arising from temperature and salt variations
produced by strong atmospheric cooling and wind-induced evaporation. The
THC transports huge amounts of heat from the equator to the poles. It has
enormous consequences for the weather of Western Europe, warming parts of the
continent by up to 10 °C in mean temperature. To balance this transport, water
sinks 2—3 km after cooling, and flows back towards the equator along the ocean
bottom, eventually returning to the surface, primarily near the ocean boundaries.
Through this process oxygen is pumped into the deep sea, sustaining life at depth.
Concerns over the potential consequences of global warming on the THC
were initially ignored, but evidence that the THC has closed down in the past
has changed this perception. — The THC is very sensitive to the amount of
R. Costanza, R. d’Arge, R. de Groot, S. Farber, M. Grasso, B. Hannon, K. Limburg, S. Naeem, R. V.
O’Neill, J. Paruelo, R. G. Raskin, P, Sutton and M. van den Belt, Nature, 1997, 387, 253—260.
L. Hughes, Tree, 2000, 15, 56—61.
S. Manabe and R. J. Stouffer, J. Clim., 1988, 1, 841—866.
G. D. Egbert and R. D. Ray, Nature, 2000, 405, 775—778.
W. S. Broecker, Nature, 1987, 328, 123—126.
J. T. Houghton, L. G. Meira Filho, B. A. Callander, N. Harris, A. Kattenberg and K. Maskell,
Climate Change, Cambridge University Press, 1995.
D. Seidov and M. Maslin, Geology, 1999, 27, 23—26.
M. Barange
60