Surface mixed layer

The ocean system is separated into three major reservoirs that best represent the dominant pools and pathways of P transport within the ocean. The surface ocean reservoir (5) is defined as the upper 300 m of the oceanic water column. As discussed in an earlier section and displayed in Fig. 14-6, the surface layer roughly corresponds to the surface mixed layer where all... 

This perturbation comes only from the carbonate in the approximately 100 meters thick surface mixed layer it contains about 0.15 g carbon/cm2, approximately equal to that in the atmosphere and to the organic carbon dissolved in the total depth of the sea. In the case of organic carbon, the total depth of the sea is involved because bacterial decomposition occurs at all depths, producing methane and carbon monoxide with both of which the sea is saturated, so that these gases are bubbling up from all depths. In comparison the sea is not saturated with C02 at any depth. 

As a result of an accident a cloud of hexachlorobenzene (HCB) of approximatively circular shape floats in the surface-mixed layer of the ocean. At time t0 when the patch is first detected, it has approximately the shape of a two-dimensional normal distribution ... 

Until May 1985, the PCE content of Greifensee was relatively small (between about 40 and 80 moles, see Fig. 23.7). On June 3, 1985, a PCE content of more than 200 moles was found in the lake. The PCE was mainly detected in the surface mixed layer (about 4 m deep) and in the thermocline. On July 1, 1985, the PCE content was still around 200 moles, but the concentration maximum had moved from the surface to the thermocline. This concentration peak remained visible throughout the summer and fall until the PCE content had returned to its normal level. 

As shown in Figure 23.7, the continuous lake model nicely describes the concentration maximum, which slowly moved to greater depth due to the deepening of the surface mixed layer. From the model calculation we can conclude that the processes involved in producing this maximum were the combination of riverine PCE input into the surface mixed layer and loss to the atmosphere by gas transfer. The extra input of PCE into the lake between May 6 and July 1, 1985 had to be about 360 moles. The model calculations suggest that the input had dropped to virtually zero after July 1. Part of the compound was quickly and continuously lost to the atmosphere so that the PCE content of the lake never increased much beyond 200 moles. 

Figure 7.4 Down-core profiles of 234Th and 210Pb for Fourleague Bay (USA) Shortterm deposition rates and accumulation rates are calculated using these profiles. The inflection of 210Pb at the base of the surface mixed layer (dashed line) reflects the logarithmic decrease in excess activities associated with decay, from which an accumulation rate can be calculated. (Modified from Day et al., 1995.)...

Figure 13.20 Temporal variation in CO2 fluxes at three stations in the Hudson River estuary. Positive values represent production of CC and negative values are consumption. CO2 consumption represents the sum of net primary production (NPP) integrated over the photic zone and dark assimilation integrated over the surface mixed layer. Error bars represent 1 standard deviation. (Modified from Taylor et al., 2003.)...

Table 1 lists DMS and DMSPt variations as averages in the surface mixed layer. In the coastal... 

Table 1 Averages and ranges (in parenthesis) of DMS and DMSPt in the surface mixed layer (defined by 0.125 kg m 3 density difference) in different seasons and in different regions of the Indian Ocean ...

Aeolian iron and stratification of the surface mixed layer in the future 1551... 

Figure 12 The net scavenging rate constant, (d ), of from the surface mixed layer of the Pacific...

If the vertical distribution of particulate thorium is uniform, as would be the case in the surface mixed layer of the ocean for example, and if the system is at steady state, then Equation (3) reduces to... 

Depth profiles of cell densities in the photic zone generally show E. huxleyi to live within the mixed layer. Cortes et al. (2001) studied the seasonal depth distribution of coccohthophorid species off Hawaii. Sampling showed that the main production occurred in the middle photic zone (50-100 m), which lay within the mixed layer for most of the year. While the depth of maximum E. huxleyi density varied during the annual cycle, it generally lay between the shallowest sampling level (10 m) and 100 m. Depth profiles off Bermuda (Haidar and Thierstein, 2001) found that maximum densities of E. huxleyi were nearly always shallower than 100 m, and more commonly within the upper 50 m. The highest cell densities for E. huxleyi recorded were at 1 m depth in March, after the seasonal advection of nitrate into the mixed layer. Seven years of water-column particulate data off Bermuda confirm that alkenone concentrations in the surface mixed layer are 2-4 times higher than in the deep fluorescence maximum at 75-110 m (Conte et al., 2001). 

Figure 1 Particle cycling in the surface mixed layer of marine sediments. The processing of the rain of particles to the seafloor results in exchanges of solutes across the sediment-water interface and alteration of the particulate reactants, so that the composition of accumulating sediment is signiflcantly different from that of the particulate rain...

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