Analytical phytoplankton carbon measurements spanning diverse ecosystems

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Journal Article
Deep-Sea Research Part I: Oceanographic Research Papers, 2015, 102 pp. 16 - 25
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© 2015 The Authors. The measurement of phytoplankton carbon (C < inf > phyto < /inf > ) in the field has been a long-sought but elusive goal in oceanography. Proxy measurements of C < inf > phyto < /inf > have been employed in the past, but are subject to many confounding influences that undermine their accuracy. Here we report the first directly measured C < inf > phyto < /inf > values from the open ocean. The C < inf > phyto < /inf > samples were collected from a diversity of environments, ranging from Pacific and Atlantic oligotrophic gyres to equatorial upwelling systems to temperate spring conditions. When compared to earlier proxies, direct measurements of C < inf > phyto < /inf > exhibit the strongest relationship with particulate backscattering coefficients (b < inf > bp < /inf > ) (R < sup > 2 < /sup > =0.69). Chlorophyll concentration and total particulate organic carbon (POC) concentration accounted for ~20% less variability in C < inf > phyto < /inf > than b < inf > bp < /inf > . Ratios of C < inf > phyto < /inf > to Chl a span an order of magnitude moving across and within distinct ecosystems. Similarly, C < inf > phyto < /inf > :POC ratios were variable with the lowest values coming from productive temperate waters and the highest from oligotrophic gyres. A strong relationship between C < inf > phyto < /inf > and b < inf > bp < /inf > is particularly significant because b < inf > bp < /inf > is a property retrievable from satellite ocean color measurements. Our results, therefore, are highly encouraging for the global monitoring of phytoplankton biomass from space. The continued application of our C < inf > phyto < /inf > measurement approach will enable validation of satellite retrievals and contribute to an improved understanding of environmental controls on phytoplankton biomass and physiology.
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