Elements of Physical Oceanography 2.2 Ocean Structure 17
Part A | 2.2
2.2 Ocean Structure
The global atmosphere and the ocean interact in ways
that structure the ocean into fairly distinct upper ocean
layer, which extends down to about 1000 m (3284 ft),
and deep ocean layer, which extends to the bottom. On
one hand, air–sea interactions create vast amounts of
sinking cold, dense water in the polar oceans north and
south of 40
ı latitude. On the other hand, in the subtropical and tropical regions between 40
ı S and 40
ı N,
air–sea interactions warms a buoyant upper layer of
the ocean that overlies a deep layer of cold, dense
water throughout the world’s oceans. The contoureddensity section the Atlantic Ocean in Fig. 2.2 highlights the 2 layers. In particular, the region of closely
packed of the isopycnals – the pycnocline – in the
upper few 100 m represents a dynamical barrier to
80° S
N
60°
40°
20°
26
25
27
27.5
27.8
27.85
27.9
0°
20°
40°
60°
Latitude
Depth (m)
σ t
0
1000
2000
3000
4000
5000
6000
Fig. 2.2 A south–north section of contours of density
anomaly ( t D water density 1000) in the western Atlantic; showing how the upper and lower layers of the
ocean between 50
ı S and 50
ı N are defined by closely
packed isopycnals – a strong pycnocline or density stratification – at a depth of about 800 m (after [2.2])
Equator
Tropics
High latitude
23
24
25
26
27
28
Density σ t
Depth (m)
0
1000
2000
3000
4000
Fig. 2.3 Typical density anomaly versus depth profiles at
low and high latitudes (after [2.2])
vertical mixing between upper and deep layer of the
ocean.
The trio of oceanic water column density profiles
in Fig. 2.3 demonstrates how the strength of the pynocline in the equatorial/tropical water column is much
stronger than that in the high latitude polar regions.
Density or specific weight of sea water is a function
of temperature, salinity, and pressure. Variations in sea
water temperature and salinity (which determine density) vary substantially in the upper layer water column
forming their respective thermoclines and haloclines.
These variations, in general, are due to the influences of
heat exchange and precipitation/evaporation across the
air–sea interface at a particular latitude and season. In
the deep ocean layer, below 1000 m, these characteristics tend to be relatively constant. The upper ocean layer
may be subdivided further into regions of seasonal and
main pycnocline (and corresponding thermoclines and
haloclines); particularly in the subtropics between 20
ı
and 40
ı latitudes where density/temperature/salinity
gradients are largest extending, respectively, from the
surface to about 60 m and from this depth to about
1000 m (Fig. 2.4).
5
1 0
1 5
2 0
Temperature (°C)
Shallow
wind-mixed
layer
Shallow
thermocline
Winter
deepest
wind-mixed
layer
Fall
wind-mixed
layer deepening
Deep permanent
thermocline
Spring
Summer
Depth (m)
0
20
40
60
80
100
120
Fig. 2.4 The seasonal variability of a typical subtropical
temperature profile (after [2.3])
Part A | 2.2
2.2 Ocean Structure
The global atmosphere and the ocean interact in ways
that structure the ocean into fairly distinct upper ocean
layer, which extends down to about 1000 m (3284 ft),
and deep ocean layer, which extends to the bottom. On
one hand, air–sea interactions create vast amounts of
sinking cold, dense water in the polar oceans north and
south of 40
ı latitude. On the other hand, in the subtropical and tropical regions between 40
ı S and 40
ı N,
air–sea interactions warms a buoyant upper layer of
the ocean that overlies a deep layer of cold, dense
water throughout the world’s oceans. The contoureddensity section the Atlantic Ocean in Fig. 2.2 highlights the 2 layers. In particular, the region of closely
packed of the isopycnals – the pycnocline – in the
upper few 100 m represents a dynamical barrier to
80° S
N
60°
40°
20°
26
25
27
27.5
27.8
27.85
27.9
0°
20°
40°
60°
Latitude
Depth (m)
σ t
0
1000
2000
3000
4000
5000
6000
Fig. 2.2 A south–north section of contours of density
anomaly ( t D water density 1000) in the western Atlantic; showing how the upper and lower layers of the
ocean between 50
ı S and 50
ı N are defined by closely
packed isopycnals – a strong pycnocline or density stratification – at a depth of about 800 m (after [2.2])
Equator
Tropics
High latitude
23
24
25
26
27
28
Density σ t
Depth (m)
0
1000
2000
3000
4000
Fig. 2.3 Typical density anomaly versus depth profiles at
low and high latitudes (after [2.2])
vertical mixing between upper and deep layer of the
ocean.
The trio of oceanic water column density profiles
in Fig. 2.3 demonstrates how the strength of the pynocline in the equatorial/tropical water column is much
stronger than that in the high latitude polar regions.
Density or specific weight of sea water is a function
of temperature, salinity, and pressure. Variations in sea
water temperature and salinity (which determine density) vary substantially in the upper layer water column
forming their respective thermoclines and haloclines.
These variations, in general, are due to the influences of
heat exchange and precipitation/evaporation across the
air–sea interface at a particular latitude and season. In
the deep ocean layer, below 1000 m, these characteristics tend to be relatively constant. The upper ocean layer
may be subdivided further into regions of seasonal and
main pycnocline (and corresponding thermoclines and
haloclines); particularly in the subtropics between 20
ı
and 40
ı latitudes where density/temperature/salinity
gradients are largest extending, respectively, from the
surface to about 60 m and from this depth to about
1000 m (Fig. 2.4).
5
1 0
1 5
2 0
Temperature (°C)
Shallow
wind-mixed
layer
Shallow
thermocline
Winter
deepest
wind-mixed
layer
Fall
wind-mixed
layer deepening
Deep permanent
thermocline
Spring
Summer
Depth (m)
0
20
40
60
80
100
120
Fig. 2.4 The seasonal variability of a typical subtropical
temperature profile (after [2.3])