In this chapter, we summarize oceanic processes
and features that are important in defining the
ocean’s role in climate. We also introduce climate
phenomena in which the ocean is known to play a
significant role. The chapter is intended as an
overview of the entire subject matter of the book.
The reader is referred to the individual book chapters and to other recent literature for more detail.
1.2.1 A global perspective
The climate system is driven by energy from the sun,
with nearly half of the solar radiation absorbed at
the earth’s surface. Almost one third is reflected
back to space by the atmosphere and from the
surface and about 20% directly absorbed in the
atmosphere (Fig. 1.2.1, from Kiehl and Trenberth,
1997). Both radiative processes and ocean and
atmosphere circulations transfer this energy from
the low latitude surface where it is initially
absorbed, to higher latitudes and into the global
upper atmosphere from whence it is radiated back
to space. This is achieved through long-wave thermal radiation originating mostly from the atmosphere. To first order, the earth radiates back to
space all the energy that it receives.
The ocean’s vital role in the climate system
results from its great capacity to store and transport
heat, water and radiatively active gases around the
globe and exchange these with the atmosphere.
Many oceanic and coupled ocean–atmosphere processes, occurring on a wide range of space and time
scales, are involved.
While the annual average energy received by the
earth at the top of the atmosphere is a function
only of latitude, the distribution of climatic conditions at the bottom of the atmosphere is far from
zonal. A striking example of the oceans’ influence
is that the surface temperature of northwestern
Europe is about 10°C warmer than the zonal average (Fig. 1.1.2) because of the heat transported
northeastward in the Atlantic. Furthermore,
because of the ocean’s high heat capacity, the seasonal temperature range of maritime climates is
smaller (a few °C) than that of continental climates
(several tens of °C, see Gill, 1982, his Fig. 2.1).
Maritime climates also exhibit a delay in their summer maximum and winter minimum temperatures
compared with the cycle of solar radiation (see
Large and Nurser, Chapter 5.1).
Generally, only the surface mixed layer (typically tens to several hundreds of metres thick)
participates directly in the seasonal cycle of
heat accumulation and release. However, a smallamplitude, seasonal temperature cycle penetrates
to depths as great as 1500 m in certain highlatitude regions. On time scales of years to centuries, even the deepest ocean layers exchange
heat and other properties (e.g. salt, nutrients and
dissolved gases) with the surface layer by vertical
and horizontal advection and mixing.
The oceans contain 50 times more CO 2 than
does the atmosphere. They presently sequester
about one third of the 6 Gt of carbon released
annually through human activities. Future uptake
of CO 2 by the oceans will depend on the evolution
of ocean conditions influenced by, and influencing, a changing atmosphere. The surface ocean
exchanges CO 2 with the atmosphere seasonally in
a similar manner to the exchange of heat and thus
1.2
Ocean Processes and Climate Phenomena
Allyn Clarke, John Church and John Gould
11
OCEAN CIRCULATION AND CLIMATE
Copyright © 2001 Academic Press
ISBN 0-12-641351-7
All rights of reproduction in any form reserved
CHAPTER
and features that are important in defining the
ocean’s role in climate. We also introduce climate
phenomena in which the ocean is known to play a
significant role. The chapter is intended as an
overview of the entire subject matter of the book.
The reader is referred to the individual book chapters and to other recent literature for more detail.
1.2.1 A global perspective
The climate system is driven by energy from the sun,
with nearly half of the solar radiation absorbed at
the earth’s surface. Almost one third is reflected
back to space by the atmosphere and from the
surface and about 20% directly absorbed in the
atmosphere (Fig. 1.2.1, from Kiehl and Trenberth,
1997). Both radiative processes and ocean and
atmosphere circulations transfer this energy from
the low latitude surface where it is initially
absorbed, to higher latitudes and into the global
upper atmosphere from whence it is radiated back
to space. This is achieved through long-wave thermal radiation originating mostly from the atmosphere. To first order, the earth radiates back to
space all the energy that it receives.
The ocean’s vital role in the climate system
results from its great capacity to store and transport
heat, water and radiatively active gases around the
globe and exchange these with the atmosphere.
Many oceanic and coupled ocean–atmosphere processes, occurring on a wide range of space and time
scales, are involved.
While the annual average energy received by the
earth at the top of the atmosphere is a function
only of latitude, the distribution of climatic conditions at the bottom of the atmosphere is far from
zonal. A striking example of the oceans’ influence
is that the surface temperature of northwestern
Europe is about 10°C warmer than the zonal average (Fig. 1.1.2) because of the heat transported
northeastward in the Atlantic. Furthermore,
because of the ocean’s high heat capacity, the seasonal temperature range of maritime climates is
smaller (a few °C) than that of continental climates
(several tens of °C, see Gill, 1982, his Fig. 2.1).
Maritime climates also exhibit a delay in their summer maximum and winter minimum temperatures
compared with the cycle of solar radiation (see
Large and Nurser, Chapter 5.1).
Generally, only the surface mixed layer (typically tens to several hundreds of metres thick)
participates directly in the seasonal cycle of
heat accumulation and release. However, a smallamplitude, seasonal temperature cycle penetrates
to depths as great as 1500 m in certain highlatitude regions. On time scales of years to centuries, even the deepest ocean layers exchange
heat and other properties (e.g. salt, nutrients and
dissolved gases) with the surface layer by vertical
and horizontal advection and mixing.
The oceans contain 50 times more CO 2 than
does the atmosphere. They presently sequester
about one third of the 6 Gt of carbon released
annually through human activities. Future uptake
of CO 2 by the oceans will depend on the evolution
of ocean conditions influenced by, and influencing, a changing atmosphere. The surface ocean
exchanges CO 2 with the atmosphere seasonally in
a similar manner to the exchange of heat and thus
1.2
Ocean Processes and Climate Phenomena
Allyn Clarke, John Church and John Gould
11
OCEAN CIRCULATION AND CLIMATE
Copyright © 2001 Academic Press
ISBN 0-12-641351-7
All rights of reproduction in any form reserved
CHAPTER