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The oceans
The oceans

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4.5 Surface water masses

The surface circulation patterns (Figure 15) and the resulting Ekman drift can be compared with the SST (Figure 9) and the sea-surface salinity (Figure 10b). There are large volumes of water in the mixed layers where both the temperature and salinity are relatively constant. Such a water volume with relatively constant temperature and salinity is called a water mass. Section 3 noted that the surface temperature and salinity are determined by the regional climate and so water masses are regionally named (Figure 20).

Described image
Figure 20 The global distribution of the most common upper ocean water masses. The boundaries between the different water masses are diffuse as properties gradually change.
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Figure 20

This is a global map, presented in the Goode homolosine projection (resembling an orange peel) that shows the location of upper ocean water masses.

Lines of latitude are presented at 10° intervals and numbered throughout the projection at 20° intervals from 80° S through 0° and to 80° N.

Lines of longitude are shown at 10° intervals with numbered markers found along 10° S (latitude line) and only for longitude 120° E, 180°, 120° W and 60° W.

The borders of the identified ocean masses are shown by solid blue lines.

The labelled ocean masses and approximate locations are listed below:

Pacific Subarctic Upper Water: North Pacific between North America and Russia, down to approximately 40° N

West North Pacific Central Water: Northwest Pacific from 40° N to 5° N and from the East Asian coast to 160° W.

East North Pacific Transition Water: a narrow band along the mid and west North American coast.

East North Pacific Central Water: Northeast Pacific between the West North Pacific Central Water and East North Pacific Transition Water

Pacific Equatorial Water: a narrow band across the Pacific straddling the Equator, approximately 5° N to 5° S.

Arabian Sea Water: confined to the Arabian Sea.

Indian Equatorial Water: Indian Ocean as far south as Madagascar and Northern Australia.

Indonesian Upper Water: including waters around Indonesia and Northern Australian coast.

Atlantic Subarctic Upper Water: Northwestern Atlantic, including waters to the east of Iceland, Baffin Bay and the northeast Atlantic as far south as the Canadian/American border.

West North Atlantic Central Water: the Western Atlantic from the Canadian/American border to the north coast of South America and as far east as approximately 35° W.

East North Atlantic Central Water: the northeast Atlantic from approximately 35° W to the coast of Europe and North Africa. As far south as 10° N and reaching as far north as Iceland.

South Atlantic Central Water: the entire south Atlantic between South America and Africa from 10° N to 40° S.

East South Pacific Transition Water: a narrow band along the South American coast from Peru to approximately 45° S.

East South Pacific Central Water: from South America and the boundary with the East South Pacific Transition Water to approximately 170° W from approximately 5° S and 40° S.

West South Pacific Central Water: in the same latitudinal band as the East South Pacific Central Water and extending to the east coast of Australia.

South Indian Central Water: a band in the Indian Ocean from Australia to Africa from 20° S to approximately 35° S.

Subantarctic Surface Water: an undulating circumpolar band from approximately 40° S to 55° S.

Antarctic Surface Water: an undulating circumpolar band from approximately 55° S to the Antarctic coast.

Figure 20 The global distribution of the most common upper ocean water masses. The boundaries between the different water masses are ...

  • Would all of the surface water masses shown in Figure 20 have the same density anomaly? Hint - you may have to look at Figures 9, 10b and 12.

  • No, they would not. The density of water is a function of temperature and salinity, and each water mass has a different temperature and salinity value. You can see from Figure 12 that different temperatures and salinities lead to different densities.