Earth Science

Getting a Fix on Fixation

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Science  04 Feb 2005:
Vol. 307, Issue 5710, pp. 647
DOI: 10.1126/science.307.5710.647a

Marine net primary production (NPP) is a measure of how much atmospheric carbon is fixed via photosynthesis by organisms in the ocean. Until now, only direct field sampling has yielded accurate estimates of NPP, which has severely limited attempts to obtain detailed global estimates of its distribution and magnitude. Measuring NPP from space has failed to provide convincing values, because two essential parameters, phytoplankton carbon biomass and a term related to the physiological status of the organisms, are not directly quantifiable remotely.

Behrenfeld et al. start with satellite measurements of the chlorophyll content of upper ocean waters and the backscattering of certain wavelengths of light (which they use to estimate phytoplankton carbon biomass) and then estimate phytoplankton growth rates and calculate NPP. They can do this by taking advantage of laboratory studies that have shown that the ratio of chlorophyll to carbon biomass is a calculable function of changes in light, nutrients, and temperature. This work brings nearer the prospect of producing a more accurate picture of global marine NPP over space and time. — HJS

Global Biogeochem. Cycles 19,

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