Gyres subpolar

Oligotrophic denotes waters of the central parts of the subtropical gyres. Transitional denotes waters that lie between the subtropical and subpolar zones and also includes the extremities of the equatorial divergence zones. Source. After Eppley R. N. and B. J. Peterson (1979). Nature 282, 677-680. 

In the subpolar gyre and in the northern sector of the subtropical gyre, the nutrient stream encounters the deep winter mixed-layers and outcrops (Fig. 13.9A), thus sustaining the annual convective supply of nitrate to the surface (WUhams and... 

Figure 13-9 Schematic views of (A) meridional and vertical transport of nitrate in the upper Atlantic basin and (B) associated horizontal transport pathways. Nitrate-rich Circumpolar Deep Water (CDW) upwells in the Southern Hemisphere and the residual mean flow transports some of this upwelled water across the polar front into the regions of intermediate and mode water formation. Nitrate-rich Sub-Antarctic Mode Water (SAMW) and Antarctic Intermediate Water move northward in the thermocline, ultimately outcropping in the subpolar North Atlantic. Ekman transfer provides a source of nitrate to the subtropical gyre along with lateral and vertical eddy transport processes.

Quantification of subduction and formation rates for subtropical underwaters and in the North Atlantic its interannual variability that is negatively correlated with intermediate waters of the eastern subpolar gyre. 

Figure 11.1 Recent global circulation of the surface water and the regions enriched with warm-water brachiopod species. ST - subtropical gyres SP - subpolar gyres enriched regions are hatched global upwellings are shown schematically as thick blacklines (I - Californian, 2 - Peru-Chilean, 3 - Canarian, 4 - Benguelan, 5 - Arabian). Tectonic plates in recent position after Scotese (1992). Global circulation in the Pacific after Burkov (1968), in the Indian Ocean after Neyman (1970), in the Atlantic after Bulatov (1971).

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