Oceanic Types and Their Controls
2
Oceans occupy some 70 % of the Earth’s surface
and extend from the North Pole to the shores of
Antarctica. There are great differences in the character of the oceans, and these differences are of
fundamental importance, both in the geography of
the oceans themselves, and to the climatic patterns
of the whole Earth. The surface of the ocean is
differentiated into regions, or zones, with different
hydrologic properties resulting from unevenness
in the action of solar radiation and other phenomena of the climate of the atmosphere.
Ocean hydrology and atmospheric climate are
both dynamic and closely interrelated. Ocean
hydrology may be defined as the seasonal variation in temperature and salinity of the water. It
controls the distribution of oceanic life. We use
ocean hydrology to differentiate regional-scale
ecosystem units and to indicate the extent of
each unit. With continental ecosystems, atmosphere is primarily responsible for ecoregions
but in the ocean, the physical properties of the
water determine ecoregions, not the atmosphere.
2.1
Factors Controlling Ocean
Hydrology
In order to establish the hydrographic zones of
the world ocean, we must determine the
boundaries of the zones. Our approach to this
task is to analyze those factors that control the
distribution of zones, and to use significant
changes in those controls as the boundary
criteria. This distribution in the character of the
oceans is related to the following controlling
factors:
2.1.1 Latitude
Heating depends predominantly on latitude. If the
Earth were covered completely with water,
thereby eliminating the deflection of currents by
land masses, there would be circumferential
zones of equal ocean temperature. The actual
distribution forms a more complicated pattern
(Fig. 2.1). Water temperatures range from well
over 27
C in the equatorial region, to below 0
C
at the poles. Areas of higher temperature promote
higher evaporation and therefore higher salinity.
At low latitudes throughout the year and in
middle latitudes in the summer, a warm surface
layer develops, which may be as much as 500 m
thick. Below the warm layer, separated by a
thermocline, is a layer of cold water extending
to the ocean floor. In Arctic and Antarctic
regions, the warm surface water layer disappears
and is replaced by cold water lying at the surface.
The boundary between water types, called the
oceanic polar front, is nearly always associated
with a convergence of surface currents, discussed
below.
2.1.2 Major Wind Systems
Prevailing surface winds set surface currents in
motion and modify the simple latitudinal
R.G. Bailey, Ecoregions, DOI 10.1007/978-1-4939-0524-9_2, # Springer Science+Media, LLC 2014
9
2
Oceans occupy some 70 % of the Earth’s surface
and extend from the North Pole to the shores of
Antarctica. There are great differences in the character of the oceans, and these differences are of
fundamental importance, both in the geography of
the oceans themselves, and to the climatic patterns
of the whole Earth. The surface of the ocean is
differentiated into regions, or zones, with different
hydrologic properties resulting from unevenness
in the action of solar radiation and other phenomena of the climate of the atmosphere.
Ocean hydrology and atmospheric climate are
both dynamic and closely interrelated. Ocean
hydrology may be defined as the seasonal variation in temperature and salinity of the water. It
controls the distribution of oceanic life. We use
ocean hydrology to differentiate regional-scale
ecosystem units and to indicate the extent of
each unit. With continental ecosystems, atmosphere is primarily responsible for ecoregions
but in the ocean, the physical properties of the
water determine ecoregions, not the atmosphere.
2.1
Factors Controlling Ocean
Hydrology
In order to establish the hydrographic zones of
the world ocean, we must determine the
boundaries of the zones. Our approach to this
task is to analyze those factors that control the
distribution of zones, and to use significant
changes in those controls as the boundary
criteria. This distribution in the character of the
oceans is related to the following controlling
factors:
2.1.1 Latitude
Heating depends predominantly on latitude. If the
Earth were covered completely with water,
thereby eliminating the deflection of currents by
land masses, there would be circumferential
zones of equal ocean temperature. The actual
distribution forms a more complicated pattern
(Fig. 2.1). Water temperatures range from well
over 27
C in the equatorial region, to below 0
C
at the poles. Areas of higher temperature promote
higher evaporation and therefore higher salinity.
At low latitudes throughout the year and in
middle latitudes in the summer, a warm surface
layer develops, which may be as much as 500 m
thick. Below the warm layer, separated by a
thermocline, is a layer of cold water extending
to the ocean floor. In Arctic and Antarctic
regions, the warm surface water layer disappears
and is replaced by cold water lying at the surface.
The boundary between water types, called the
oceanic polar front, is nearly always associated
with a convergence of surface currents, discussed
below.
2.1.2 Major Wind Systems
Prevailing surface winds set surface currents in
motion and modify the simple latitudinal
R.G. Bailey, Ecoregions, DOI 10.1007/978-1-4939-0524-9_2, # Springer Science+Media, LLC 2014
9