Water ocean circulation

Zauker, F. and Broecker, W. S. (1992). Influence of interocean fresh water transports on ocean thermohaline circulation. /. Geophys. Res. 97, 2765-2773. 

Evaporite deposition is a much more episodic process and thus difficult to quantify. Because seawater is significantly undersaturated with respect to common evaporitic minerals, like gypsum and halite, evaporites are only formed when restricted circulation develops in an ocean basin in which evaporation exceeds precipitation. A geologically recent example is the Mediterranean Sea of 5-6 Myr ago. At this time excess evaporation exceeded the supply of ocean water through shallow inlet(s) from the Atlantic Ocean. As salinity increased, first CaS04, then NaCl precipitated. Over time, salt deposits 2-3 km thick formed. This thickness represents about 40 desiccations of the entire... 

At lower temperatures, reducing conditions are present (CH4 is stable) this is typical for the oceanic crust. Most of the hydrothermal water circulates in the oceanic crust at a temperature of around 420 K, and the reducing conditions present there are mainly controlled by the PPM mineral mixture (Alt et al., 1989). 

The actual distribution of surface sediments in the modern-day ocean is illustrated in Figure 20.2. These are somewhat different from the general model presented in Figure 20.1 due to water circulation patterns and geological features unique to each ocean basin. 

North Atlantic Deep Water (NADW), which is formed with an initial 5 C-value between 1.0 and 1.5%c, becomes gradually depleted in C as it travels southward and mixes with Antarctic bottom water, which has an average 8 C-value of 0.3%c (Kroopnick 1985). As this deep water travels to the Pacific Ocean, its C/ C ratio is further reduced by 0.5%o by the continuous flux and oxidation of organic matter in the water column. This is the basis for using 8 C-values as a tracer of paleo-oceanographic changes in deep water circulation (e.g., Curry et al. 1988). 

NADW flows southward the ongoing oxidation of organic matter results in a progressive C-depletion down to less than 0.4%c in the Southern Ocean. Reductions in observed in many cores from the North-Atlantic (Samtheim et al. 2001 Elliot et al. 2002) have been interpreted as meltwater input to the surface ocean (Heinrich events), which caused changes in deep water circulation. 

At their sampling sites in the Pacific Ocean, Santosa et al. (1997) found that MMA(V) and DMA(V) concentrations were highest at the surface with 0.012-0.016 pg L-1 and 0.048-0.185 pg L-1, respectively. The concentrations sharply declined to depths of 200 m. From depths of 200 to at least 5000 m, MMA(V) and DMA(V) concentrations stabilized at about 0.003 pg L-1 (Santosa et al., 1997). Santosa et al. (1996), 703 argue that the presence of methylarsenic in deep ocean waters is probably not due to diffusion from ocean floor sediments. Instead, the deep water methyl forms may result from the diffusion of methylarsenic-bearing surface waters, the circulation of surface waters to greater depths, and the tendency of methylarsenic not to appreciably sorb onto iron (oxy)(hydr)oxides particles. 

Marine communities are complicated biological systems of populations of individual species. As a result of their interaction, communities are in dynamic development. Their spatial structure is mostly determined by the composition of numerous biotic and abiotic factors, which depend on the totality of oceanic parameters. The latter are determined by the laws of general circulation of ocean waters, including tides and ebbs, zones of convergence and divergence, wind, and thermohaline currents. 

Begemann, F. Libby, W.F. (1957) Continental water balance, ground water inventory and storage times, surface ocean mixing rates and worldwide water circulation patterns from cosmic ray and bomb tritium. Geochemica Cosmochemica Acta, 12, 277-96. 

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