enhanced general phytoplankton growth. Tyrrell et al. suggest that Trichodesmium
fixes N 2 and releases DON that may enhance growth of other phytoplankton.
(^) Menkes et al. (2002) examined the distribution of nutrients, plankton, and nekton in
the crest of a tropical instability wave in the Atlantic Ocean (Plate 11.6). Maxima
within the wave crests were relatively high: chlorophyll 0.8–1 mg m−3, net primary
production 1500 g C m−2 d−1, zooplankton stocks 40 mg dry wt. m−3, and abundant
micronekton consisting of small pelagic fishes (predominantly the deep-migrating
Vinciguerria nimbaria). The data indicate successively higher trophic levels extending
northward downstream away from the equator (Menkes et al. 2002). Such mesoscale
features appear to be important, in enhancing production at multiple levels, and may
support the tuna fishery in the equatorial Atlantic (Lebourges-Dhaussy et al. 2000).
Coastal Biomes and Coastal Upwelling
Ecosystems
(^) Coastal waters generally are more nutrient-rich and more productive than oceanic
ecosystems. Inshore over shelves, mixing by tidal currents (of velocity us m s−1) stirs
the water column to the bottom over depths as great as h m, calculated from h/us^3 >
∼80. Maps of that criterion around the British Isles and along the shelf of the
northeastern USA correlate with the inshore limit of spring–summer stratification in
waters to seaward. The phytoplankton inside that boundary are usually diatom
dominated, although silicate can become limiting in summer. Beyond that boundary,
diatoms are less important, except during spring blooms. Coastal seas are less
frequently, but sometimes, iron-limited, especially where h/us^3 > 80, but major
nutrients can be removed to very low concentrations both in the tropics and seasonally
in high latitudes.
Eastern Boundary Current Systems (EBCS)
(^) Coasts with an equatorward component in the prevailing alongshore winds are located
adjacent to eastern boundary currents, and coastal upwelling is generated next to these
coasts by seaward acceleration of the surface layer due to the Coriolis effect. After
modest reduction in sea-level height, the offshore flow is balanced by shoreward and
rising flow in deeper layers. This carries nutrient-laden, relatively cold water into the
euphotic zone. After an initial period of incubation, phytoplankton blooms develop
and consume the nutrients. Depletion occurs at various distances offshore. The four
major EBCS are the California, Peru/Humboldt, Canary, and Benguela Currents (Fig.
11.37). They differ in levels of primary production (as estimated from ocean color)