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A combination of Broenkow's nutrient oxygen model and Bowden's residence time evaluation of upwelled waters enabled us to calculate the "net community production" (NCP) in coastal upwelling areas (NW Africa, SW Africa, Peru) and in an open upwelling (Costa Rica Dome). Since NCP represents mainly new production in terms of phosphorus or nitrogen, and since it derives from integrated nutrient consumption over the main production area, a good picture of the average fertility of these zones is obtained. In terms of carbon, NCP averaged 0.6 g C m-2 d-l off Peru, 1.1 off SW Africa, and 2.3 off NW Africa. However, production budget per kilometer of coastline is greater for both Peru and SW Africa than it is for NW Africa. The lower activities off Peru and off SW Africa correspond to a relatively high nutrient-low chlorophyll (HNLC) situation, characterized by a slowly growing phytoplankton standing stock. Such HNLC situations are greatly pronounced in the Costa Rica Dome, with NCP values as low as 0.14 g C m-2 d-l. Herbivorous grazing in the freshly upwelled source water appears to be the most plausible explanation for the low chlorophyll. This mechanism for cropping phytoplankton and retarding nutrient uptake provides a way to spread nutrient input to the open ocean. Italso explains the prevalence of oxygen undersaturation (and CO, oversaturation) in the surface waters of the equatorial upwelling. By using the NW African data and NCP and ammonium excretion rates from the literature we could calculate an Eppley ffactor (pN0, -: pNO,-f pNH,+) of 0.64. *

Previous hydrological investigations of the Gibraltar Strait have left some questions unanswered as regards the composition of the Mediterranean outflow into the Atlantic Ocean. In the present study, nutrient, oxygen, and chlorophyll distributions are used to characterize the main water masses flowing through the Strait of Gibraltar and the Alboran Sea, with particular reference to Levantine Intermediate Water (LIW) and Western Mediterranean Deep Water (WMDW). High chlorophyll a concentrations, reaching 3 μg L−1 at the subsurface, are observed in the northern part of the anticyclonic Alboran Sea gyre. The salinity subsurface minimum (≃36), located temporarily in the strait, corresponds to high nutrient concentrations (7–8 μg at. L−1). Diagram analysis shows that in the upwelling area off the Spanish coast, nutrients are largely transported into the photic zone, and that photosynthetic nitrate consumption actually takes place. Consequently, the formation of the Alboran Sea O2 extraminimum can be related to the enhanced new production. Most of the lowest O2 values (<4.00 mL L−1) also correspond to a slight nutrient maximum (PO4 and NO3). Comparative diagram analysis of biologically affected parameters (oxygen and nutrients) versus salinity as a conservative property confirms and expands results from the classical θ‐S analysis. Oxygen and silicate exhibit the best tracer qualities for the circulation pattern, demonstrating in particular that during the period of observations, water rich in LIW feeds the Mediterranean outflow.

The supply and utilization of organic carbon in the deep western Mediterranean Sea was investigated based on measured electron transport system (ETS) activities of the nanoplankton and microplankton. The total carbon oxidation rate between 200 and 3000 m, as calculated from ETS activity, was 15.0 g C m−2 yr−1. This represents 21% of the primary production and is similar to published estimates of the annual new production. A vertical advection ‐ diffusion ‐ reaction model based on profiles of salinity, oxygen, and the carbon oxidation rate converted to oxygen consumption yielded a deepwater residence time of about 7 years, in close agreement with a published estimate based on bomb‐produced tritium profiles. This suggested that the ETS‐based rates in the deep waters were reasonably accurate. These deep rates were much greater than ETS‐based rates from the same depths in the Atlantic and equatorial Pacific Oceans. In the western Mediterranean, ETS‐based rates also greatly exceeded the rate predicted from the primary production rate and sediment trap relationships. The rapid rates observed in the deep western Mediterranean are not consistent with the supply of organic matter via rapidly sinking particulate material. Instead, rates may be supported by dissolved organic carbon (DOC) transported to depth by wintertime deepwater convection. In order to account for the portion of the ETS‐based rate which was not explained by the sediment trap flux, DOC concentrations in the surface waters entrained during deepwater formation would need to be only 11 μmol C L−1 greater than those in the deep waters exiting the basin. ETS activities from the equatorial Pacific (Packard et al., 1988) may also implicate DOC in supporting deep‐sea metabolism. There, ETS‐based carbon oxidation rates between 200 and 5000 m greatly exceeded rates calculated from sediment trap data in the same region. The source of the organic matter being respired may ultimately be the high rates of new production in the equatorial Pacific region, but the mechanism by which this material is transported to depth cannot be determined from these data. The ETS data from both the Mediterranean and the Pacific indicate much greater rates of carbon oxidation in the deep sea than expected from existing sediment trap results. Globally, transport of DOC into the deep sea possibly could rival the sinking particulate flux in importance for deep‐sea metabolism.

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