Stratification density

As described in Chap. 5, the density difference which can lead to rollover is as small as 0.5 %. This small size of the requisite for rollover has been seen experimentally on many rollover events. Indeed, the first reported event, the La Spezia rollover, was initiated by a density difference of only 0.7 %. 

This small difference is difficult to detect directly with available in-tank instrumentation of multiple temperature measurements, densitometers or BOR monitoring. Furthermore, the success of any mixing operation to remove stratification is difficult to judge. So, how do we go forward  

The first step is to prevent stratification in the first place [ 1 ], while the second step is to have effective mixing capability in each tank as the simple answer for avoiding a rollover. The third step is to have adequate in-tank instmmentation. Failing these steps, then eventually you may be faced with handling an uncontrolled rollover. 

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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. 

All surface seawater is presently supersaturated with respect to biogenic calcite and aragonite with Cl ranging from 2.5 at high latitudes and 6.0 at low latitudes. The elevated supersaturations at low latitude reflect higher [COj ] due to (1) the effect of temperature on CO2 solubility and the for HCO3, and (2) density stratification. At low latitudes, enhanced stratification prevents the upwelling of C02-rich deep waters. 

The depth of the mixed layer is important for two reasons. First, phytoplankton can be carried out of the photic zone and, hence, halt net primary production if the mixed layer is deeper than the photic zone. Second, the bottom of the mixed layer marks the upper limit to which density stratification in the thermocline inhibits upward vertical transport of nutrients. If the photic zone extends into the thermocline, phytoplankton... 

Seasonal shifts at mid-latitudes in the standing stocks of nutrients, phytoplankton, and the heterotrophic consumer community of bacteria, protozoa, and zooplankton. Also shown are seasonal changes in density stratification of the mixed layer. Source From Black, J. A. (1986). Oceans and Coasts, Wm. C. Brown Publishers, p. 143. 

The interplay of physical controls is less complicated in the Polar and Trade (tropical) domains. As shown in Figure 24.11a, only one phytoplankton bloom occurs in the Polar domain, but is larger in amplitude than at mid-latitudes (Westerlies). Phytoplankton growth in the subpolar region is prolific because uniformly cold atmospheric temperatures suppress density stratification of the water column. Abundant winds ensure that... 

These data suggest that biogeochemical domains undergo a systems switch on time scales required for return of exported nutrients to the sea surfece. In oligotrophic waters, this return requires decades to centuries as the strong density stratification at these sites forces the return to proceed through the meridional overturning circulation. 

Density stratification in coastal waters can result from increased freshwater flows from land due to heavy rainfall, and from seasonal surfece warming. Changes in winds and currents alter upwelling conditions that can also affect stratification, while concurrently affecting nutrient resupply to the surface waters. These changing environmental... 

Density stratification Gradients in the density of seawater caused by the presence of different water masses. In a stable density configuration, density increases with increasing depth. 

Turbulent mixing coefficient Constant of porportionality used in Pick s First and Second Laws to predict changes in solute concentration over time or fluxes from solute gradients that arise from turbulent mixing. The constant is a function of length scales and the degree of density stratification and hence is termed a coefficient . 

Vertical segregation The vertical gradient in biogenic materials, such as nutrients and O2, that is established by the interaction between the biogeochemical cycling of particulate organic matter and the vertical density stratification of the water column. Strongest at mid and low latitudes. 

Mira variables form an important subgroup of the red giant stars which are typical representatives of stars showing burnt material at their surfaces. Since the photospheres of Miras are not in hydrostatic equilibrium but are characterized by spherically very extended density stratifications, their properties and emitted spectra differ substantially from those of non-Miras, and any attempts to analyse Mira spectra by means of conventional techniques must fail. Non-hydrostatic models are needed for analysis work. 

Land (1987) has reviewed and discussed theories for the formation of saline brines in sedimentary basins. We will summarize his major relevant conclusions here. He points out that theories for deriving most brines from connate seawater, by processes such as shale membrane filtration, or connate evaporitic brines are usually inadequate to explain their composition, volume and distribution, and that most brines must be related, at least in part, to the interaction of subsurface waters with evaporite beds (primarily halite). The commonly observed increase in dissolved solids with depth is probably largely the result of simple "thermo-haline" circulation and density stratification. Also many basins have basal sequences of evaporites in them. Cation concentrations are largely controlled by mineral solubilities, with carbonate and feldspar minerals dominating so that Ca2+ must exceed Mg2+, and Na+ must exceed K+ (Figures 8.8 and 8.9). Land (1987) hypothesizes that in deep basins devolatilization reactions associated with basement metamorphism may also provide an important source of dissolved components. 

Because mixing in the vertical direction is suppressed by a stable density stratification, a slowly diluting vapor cloud that hugs the ground is generated. 

Increase in the input of the organic matter and nutrients into the Black Sea causes increase of total phytoplankton biomass. In summer due to formation of the temperature, salinity and density stratification and algal blooms, decay of dead phytoplankton leads, in turn, to the oxygen lack and near-bottom hypoxia [9]. These processes have to consider as the consequence of anthropogenic eutrophication of the sea [9]. 

In [48], it was shown that, in order to simulate the cold intermediate layer of the Black Sea (see [3]), one should take into account the dependence of the vertical turbulent mixing coefficient on the density stratification of the waters. In this case, the optimal coefficients in the well-known formula by Munk-Anderson for the Black Sea occurred to be an order of magnitude lower than those for the World Ocean. 

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