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Fig. 3.23 Contribution of pressure to stratified gravitational potential energy (SGPE) (in 106 J/m2). See color plate section.

dom due to T (along 30.5°W, in kg/m3) dom due to T (along 179.5°W, in kg/m3)

dom due to T (along 30.5°W, in kg/m3) dom due to T (along 179.5°W, in kg/m3)

-80S -60S -40S -20S 0 20N 40N 60N 80N -80S -60S -40S -20S 0 20N 40N 60N 80N

-4-3.5 -3-2.5 -2-1.5 -1 -0.5 0 0.5 -4-3.5 -3-2.5 -2-1.5 -1 -0.5 0 0.5

Fig. 3.24 a, b Density anomaly due to temperature contribution for two meridional sections. See color plate section.

-80S -60S -40S -20S 0 20N 40N 60N 80N -80S -60S -40S -20S 0 20N 40N 60N 80N

-4-3.5 -3-2.5 -2-1.5 -1 -0.5 0 0.5 -4-3.5 -3-2.5 -2-1.5 -1 -0.5 0 0.5

Fig. 3.24 a, b Density anomaly due to temperature contribution for two meridional sections. See color plate section.

The contribution of temperature can be seen clearly through the meridional section of density (Fig. 3.25). In the subtropics, warm water in the upper ocean gives rise to a large difference in am0 — am < 0, while in the abyssal ocean the cold water temperature leads to a large positive am0 — am > 0 term. Therefore the contribution of this term is negative everywhere except in polar latitudes. At high latitudes, low temperature in the upper ocean gives the term am0 — am a much smaller value, which is sometimes positive in the upper ocean. Thus, this term has a small negative or positive value at high latitudes (Fig. 3.25).

The third term in Eqn. (3.142), = Ufv (am — am0) (z — z)dv, represents an integrated measure of the salinity contribution to SGPE. In the North Atlantic Ocean, especially in the subtropical basin, salinity is much higher than the mean value in the world's oceans, which is thus am — am0 > 0 for most of the Atlantic section. This leads to a domain of relatively high positive density in the upper ocean. On the other hand, in the Southern Ocean, low salinity associated with Antarctic Intermediate Water (AAIW) and Antarctic Deep Water (AADW) gives rise to negative density anomaly (Fig. 3.26a).

The situation in the North Pacific Ocean is the opposite. Owing to the relatively low salinity in this basin, the density anomaly is positive for two small areas: a shallow layer in the South Pacific subtropical gyre and a relatively salty band in the core of the Antarctic Circumpolar Water; everywhere else the density anomaly due to salinity is negative.

In the North Atlantic Ocean, especially in the subtropical basin, salinity is much higher than the mean salinity value in the world's oceans, which is thus am — am0 > 0 in the upper ocean, leading to a relatively high energy density in this basin. Another area of high value, in the Arabian Sea, is also due to the high salinity there. In comparison, salinity is low in the North Pacific Ocean, the Southern Ocean, and the Arctic Ocean; thus, the contribution to SGPE is negative in these regions (Fig. 3.27).

Stratified GPE due to temperature (106J/m2)

Stratified GPE due to temperature (106J/m2)

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