Oceans surface mixed layer

K.E. Brainerd, M.C. Gregg (1993). Diurnal restratification and turbulence in the oceanic surface mixed layer. 2. Modeling. J. Geophys. Res., 98,22657-22664. 

Dissolved CO exhibits diurnal variability in the surface ocean in response to its photolytic source, although this is also indicative of a strong sink term. The decline in the surface mixed-layer CO concentration in the dark results from a combination of CO oxidation, vertical mixing, and air-sea exchange. As the equilibration time between atmosphere and oceanic surface mixed layer is on the order of a month, this suggests that the former two processes dominate. Superimposed upon the diurnal cycle of CO in the surface ocean are spatial and seasonal gradients that result from the interaction of photoproduction and the sink processes. Below the euphotic zone CO is uniformly low throughout the intermediate water column. 

Once pollutants enter the oceanic surface mixed layer they sorb to phytoplankton and a fraction will sink associated to phytoplankton cells, fecal pellets, and other aggregates (Figure 17.2). Fluxes of chemicals between water and plankton (Fwp>... 

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... 

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 ... 

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 ...

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... 

Warming of the surface ocean by solar heating and turbulence induced by wind stress compete to create a surface mixed layer over most of the ocean that is 10-100 m deep except in some high-latitude areas, where the ocean is mixed more deeply. In the subtropical and... 

In the centre of the north Pacific subtropical gyre, Bruland et al., on the basis of a vertical profile, emphasized a significant aeolian contribution to the dissolved Fe concentration in the surface mixed layer (surface concentration of 0.35 nM compared with the minimum of 0.02 nM at 70-100 m) (159). Taking into account the study of Hutchins et al. demonstrating that Fe assimilated by plankton in sueh oceanic waters is recycled on a timescale of days, they concluded that a substantial part of Fe entering through the atmospheric input is recycled and is retained in the oligotrophic mixed layer (160). 

The lower euphotic zone (depths of 70-100 m), which is isolated from direct atmospheric inputs, is subjected to intensified processes of Fe scavenging that determine the extremely low concentration of 0.02 nM. At depths below 100 m, dissolved Fe exhibits the characteristic nutrient-type distribution observed in other zones of the Pacific Ocean (10, 161). The same authors emphasized that in regions where new production is high and intensified scavenging occurs within the surface mixed layer, the dissolved Fe concentration assumes concentrations similar to those they observed in the central gyre at depths of 70-100 m (159). 

The preceding discussion of trace elements in seawater has assumed that the oceans have a uniform, warm, nutrient-depleted surface mixed layer and a static deep zone. In fact, at high latitudes surface seawater is cold enough to destroy any density stratification, mixing the oceans to depths of up to 1000 m. This dense surface water sinks and flows slowly into the centre of the oceans as a layer of... 

Rudels, B., Anderson, L.G. and Jones, E.P. (1996) Formation and evolution of the surface mixed layer and halocline of the Arctic Ocean. Journal of Geophysical Research, 101, 8807-8821. 

The vertical structure of the ocean features a decrease of temperature with increasing depth and a correspondingly stable stratification. A shallow surface layer of 50-100 m thickness is vertically well mixed due to agitation by wind force. This portion represents only a small subvolume, but it is of crucial importance to the exchange of C02 with the atmosphere. Compared with the bulk of the ocean, the mixed layer responds quickly to changes in the atmosphere and it must be treated as a separate reservoir. The depth of the mixed layer is variable. We adopt the recommendation of Bolin et al. (1981) and use a value of 75 m. This is a seasonal average obtained by Bathen (1972) from measurements in the Pacific Ocean. 

Representative values of particulate organic carbon in the surface mixed layer of different areas of the ocean (Pocklington and MacKinnon, in press)... 

Ni fixation is the major input of fixed N to the ocean (Figure 2). N2 fixation is carried out by Ni fixers, cyanobacteria and other microorganisms able to convert N2 into biomass N. Subsequent remineralization of this biomass supplies new N to the dissolved fixed N pools in the surface and subsurface ocean. Field collections of Trichodesmium colonies, the best-known genus of open ocean N2 fixer, have yielded a of c. — 2%o to - -0.5%o. Taking into account the of dissolved N2 (0.6%o in the surface mixed layer), this range in is consistent... 

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