Thermocline oceanic

The oceans are subdivided into surface (100—1000-m) ocean and deep ocean. The zone separating the warmer, surface water from the lower, cooler layer (oceanic thermocline) is characterized by a density gradient that prevents mixing. 

In this section we briefly review what controls the density of seawater and the vertical density stratification of the ocean. Surface currents, abyssal circulation, and thermocline circulation are considered individually. 

Fig. 10-8 The pathways followed by the water ventilating the main oceanic thermocline. (Reproduced with permission from W. S. Broecker and T.-H. Peng (1982). Tracers in the Sea," p. 440, Eldigio Press, Palisades, NY.)... 

The transition region between the surface and deep ocean is referred to as the thermocline. This... 

The horizontal isopycnal thermocline model is important for the problem of determining the fate of the excess atmospheric CO2. The increase of CO2 in the atmosphere is modulated by transport of excess CO2 from the atmosphere into the interior of the ocean. The direct ventilation of the thermocline in its outcropping regions at high latitudes plays an important... 

Fig. 14-6 Profiles of potential temperature and phosphate at 21 29 N, 122 15 W in the Pacific Ocean and a schematic representation of the oceanic processes controlling the P distribution. The dominant processes shown are (1) upwelling of nutrient-rich waters, (2) biological productivity and the sinking of biogenic particles, (3) regeneration of P by the decomposition of organic matter within the water column and surface sediments, (4) decomposition of particles below the main thermocline, (5) slow exchange between surface and deep waters, and (6) incorporation of P into the bottom sediments.

Quite a bit of DOC is also injected into the subsurface ocean via isopycnal mixing in which water is transported down to the top of the thermocline. This subduction is associated with the seasonal formation of mode water, which occurs mostly on the... 

The density of seawater varies from a maximum of c = 29, observed in deep antarctic waters, to a minimum of c = 25 in subtropical oceanic thermoclinal waters. The high density of polar waters causes them to sink beneath subtropical waters and constitutes the driving force of deep oceanic circulation. 

The mean residence time of carbon in the mixed layer of the sea before transfer into the deep sea is of considerable interest, for as has already been pointed out, the rate of this transfer will eventually govern the levels of excess 14C in the atmosphere. There have been several estimates of this residence time. Craig (29) concluded that it was most probably not more than 10 years, and in one of his calculations he deduced a value of 4 years. Broecker et al. (14) concluded it was 5 years in the Atlantic Ocean and 8 years in the Pacific Ocean. Nydal (45) found that for the North Atlantic it was around 3 years or less. The profiles of Figure 6, and a few others which are not shown, all show a significant penetration of excess 14C below the mixed surface layer, pointing to a short residence time, of the order of 2 years, in the mixed layer of the sea before transfer below the thermocline into the deep sea. Considering the size of the oceans these data are very meager, and no firm conclusions can be drawn from them. However, continued measurements of 14C in the sea should help to establish a firmer estimate of this quantity. 

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