Thermocline

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. 

South America to about the date line (180 ). These trade winds also drive near-equatorial surface flow westward as the South Equatorial Current (SEC). This piles up warm surface water in the western Pacific to create a deep warm pool and results in depression of the depth of the thermocline from east to west. The westward flow in the surface SEC is partly compensated by a return flow to the east in the thermocline ( 150m) called the Equatorial Undercurrent (EUC). 

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... 

Nuclear bomb produced " 002 and (as HTO) have been used to describe and model this rapid thermocline ventilation (Ostlund et ah, 1974 Sarmiento et ah, 1982 Fine et al., 1983). For example, changes in the distributions of tritium (Rooth and Ostlund, 1972) in the western Atlantic between 1972 (GEOSECS) and 1981 (TTO) are shown in Fig. 10-10 (Ostlund and Fine, 1979 Baes and Mulholland, 1985). In the 10 years following the atmospheric bomb tests of the early 1960s, a massive penetration of F1 (tritium) into the thermocline has occurred at all depths. Comparison of the GEOSECS and TTO data, which have a 9 year time difference, clearly shows the rapid ventilation of the North Atlantic and the value of such transient" tracers. A similar transient effect can be seen in the penetrative distribution of manmade chlorofluorocarbons, which have been released over a longer period (40 years) (Gammon et al., 1982). 

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.

Fig. 3 The annual development of the seasonal thermocline (expressed as temperature gradients) (a) for a selected set of years when hypolimnetic withdrawal resulted in a deep thermocline and an extensive metalimnion, and (b) for a selected set of years when epilimnetic water flowed through the intermediate outlet inducing the development of a shallower thermocline. The solid black line shows the daily development of the withdrawal depth and the gray areas the bottom of the reservoir. Modified from Moreno-Ostos et al. [37]...

The reason for this decoupling between climate and water temperature in the reservoir is explained in Fig. 3. Moreno-Ostos et al. [37] demonstrated that the degree of stratification and the location of the thermocline both depended on... 

The thermocline is located at about 14—25 m deep [38, 39]. In the hypolimnion, the stratification can produce oxygen depletion and anoxic water with H2S [36, 38, 39]. In winter the minimum water temperature can be around 5-9°C [38, 43]. The surface water temperature of the reservoir can be estimated as [28, 43]... 

The reservoir of Riba-roja presents a weak stratification in summer, so that surface water temperatures are 24—27°C and 18-21°C at the bottom [36, 39], The thermocline is situated between 14 and 21 m deep [38, 39], During this time of the year, the water entering the reservoir of Riba-roja from the reservoir of Mequinensa is colder than the water coming from the Segre River. In consequence, the denser Ebro River water sinks and flows along the bottom of the reservoir while the Segre River water floats and flows along the surface [40, 41], The deep water can be anoxic [36, 38, 39], In winter, the water temperature is uniform in the water column and the minimum values are around 11°C [38],... 

Pit lake at the former El Mine is a meromictic lake with a thermocline and a chemocline coinciding at the depth 20 m, where former open pit was connected to the shaft. 

Figure 6. Fluctuations of the carbonate 6 Zn values down the core ODP 849 (Central Pacific) compared with the SPECMAP scale of The Zn isotope fluctuations are modulated by two significant periods of 35.2 and 21.2 ka, the latter being ascribed to precession. Pichat et al. (2003) assigned this modulation to changes in the stability of the thermocline.

Figure 7. Map of 6 Zn (%o) in the surface layer of FeMn-nodules. High-latitude samples have isotopically heavier Zn than low-latitude samples. This feature was interpreted by Marechal et al. (2000) as reflecting the presence of a Zn-depleted seasonal thermocline at high latitude. Map drawn using the GMT software package (Wessel and Smith 1991).

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