Seasonal oxygen cycling and primary production in the Sargasso Sea

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Abstract
The hydrographic record at Station S in the Sargasso Sea showed the development of a subsurface O2 maximum within the euphothic zone which must be of photosynthetic origin. Consideration of insolation, heat budgets and available 3He/3H data yielded an estimate of 5 M m-2 yr-1 for the vertically integrated O2 production rate. Gas exchange calculations revealed a similar O2 flux leaving the surface, and examination of respiration cycles below the euphotic zone yielded consistent results. Such results point to new production of the order of 50 g C m-2 yr-1. By using a more realistic mixed layer-thermocline model (Klein and Coste, 1984) it appeared that the flux of nutrients into the euphotic zone is sufficient to support such a production. The pulse-like nature of nutrient injection implied by this model raises the possibility of a spatially variable efficiency of recycling which may account for the disparity between the above observations and the level of new production inferred from 14C and 15N incubation techniques.