Iron supply and demand in the upper oceanFung I., S. Meyn, I. Tegen, S.C. Doney, J. John and J.K.B. Bishop (2000)Global Biogeochemical Cycles, 14, 281-296.
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Abstract.
Iron is hypothesized to be a limiting micronutrient for ocean primary
production. This paper presents an analysis of the iron budget in the
upper ocean. The global distribution of annual iron assimilation by
phytoplankton was estimated from distributions of satellite-derived
oceanic primary production and measured (Fe:C)cellular ratios. The
distributions of iron supply by upwelling/mixing and aeolian deposition
were obtained by applying (Fe:NO3)dissolved ratios to the nitrate supply
and by assuming the soluble fraction of mineral aerosols. A lower bound on
the rate of iron recycling in the photic zone was estimated as the
difference between iron assimilation and supply. Global iron assimilation
by phytoplankton for the open ocean was estimated to be 12x10^9 mol Fe
yr-1 . Atmospheric deposition of total Fe is estimated to be 96x10^9 mol
Fe yr-1 in the open ocean, with the soluble Fe fraction ranging between 1
and 10% (or 1 to 10x10^9 mol Fe yr-1 ). By comparison, the
upwelling/entrainment supply of dissolved Fe to the upper ocean is small,
~0.7x10^9 mol Fe yr-1 . Uncertainties in the aeolian flux and assimilation
may be as large as a factor of 5 to 10 but remain difficult to quantify,
as information is limited about the form and transformation of iron from
the soil to phytoplankton incorporation. An iron stress index, relating
the (Fe:N) demand to the (Fe:N) supply, confirms the production in the
high-nitrate low-chlorophyll regions is indeed limited by iron
availability.
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Figure: Iron Stress Index
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