Seasonal thermocline

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]...

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).

Technically the thermocline is the depth zone over which the vertical temperature gradient reaches maximal values. This depth zone varies with season, latitude and longitude, and local environmental conditions. The top of the thermocline is defined by... 

Another type of seasonally driven export event is associated with larger diatoms (>50pm) that grow vmder nutrient- and light-limited conditions at the base of the euphotic zone. These diatoms seem to imdergo a mass settling event, called a fall dump, in response to destratification of the summer thermocline due to seasonal cooling and early winter storms. These diatoms sink rapidly and are relatively well preserved in the 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... 

However, salinity values are easily obtained with a salinometer (which measures electrical conductivity and is appropriately calibrated with standard solutions and adjusted to account for T effects). The salinity of seawater increases if the loss of H2O (evaporation, formation of ice) exceeds the atmospheric input (rain plus rivers), and diminishes near deltas and lagoons. Salinity and temperature concur antithetically to define the density of seawater. The surface temperature of the sea reflects primarily the latitude and season of sampling. The vertical thermal profile defines three zones surface (10-100 m), where T is practically constant thermoclinal (100-1000 m), where T diminishes regularly with depth and abyssal... 

Fig. 3 Vertical profiles of the water potential temperature (T , degrees Celsius), water salinity (S, practical salinity unit), and water specific potential density (or , kgm-3) a in upper layer of the Black Sea central area in August 1995 and b in deep layer (mean values based on high vertical resolution CTD measurements). 1 Upper mixed layer, 2 seasonal pycnocline (thermocline), 3 cool intermediate layer, 4 main pycnocline (halocline), 5 deep pycnocline, 6 bottom mixed layer...

The T,S structure of the Black Sea waters consists of a few characteristic layers with different thicknesses top-down the upper mixed layer, the seasonal pycnocline (thermocline) the cold intermediate layer, the main pycnocline (halocline) the isothermal intermediate layer the thickest deep layer with a slow temperature and salinity increase with depth and the near-bottom mixed layer. 

Surface water temperatures are extremely variable, obviously influenced by location and season. The minimum temperature found in polar latitudes approaches the freezing point of nearly —2 °C. Equatorial oceanic waters can reach 30 °C. Temperature variations with depth are far from consistent. In a region where mixing prevails, as observed especially in the surface waters, a layer forms with a relatively uniform temperature. The zone immediately beneath normally exhibits a sharp change in temperature, known as the thermocline. The thermocline in the ocean extends down to about 1000 m within equatorial and temperate latitudes. It acts as an important boundary in the ocean, separating the surface and deep layers and limiting mixing between these two reservoirs. 

The distribution of oxygen in ocean waters contains information about primary production. For example, the amount of excess oxygen present in the seasonal thermocline in the Pacific was long ago used to suggest that " C-based estimates of primary production were severely underestimating levels of primary production in the ocean (Shulenberger and Reid, 1981). Oxygen deficiencies in deeper waters have been used to estimate levels of export production (Jenkins, 1982). 

Bentaleb 1., Grimalt J. O., Vidussi F., Marty J.-C., Martin V., Denis M., Hatte C., and Fontugne M. (1999) The C37 alkenone record of seawater temperatures during seasonal thermocline stratification. Mar. Chem. 64, 301-313. 

With a shallow, surface-mixed layer and broad thermocline (early season case), a broad, deep phytoplankton maximum in the thermocline is produced. 

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