Analytical phytoplankton carbon measurements spanning diverse ecosystems

The measurement of phytoplankton carbon (C-phyto) in the field has been a long-sought but elusive goal in oceanography. Proxy measurements of Cot,. 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-phyto values from the open ocean. The C-phyto. 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-phyto exhibit the strongest relationship with particulate backscattering coefficients (b(bp)) (R-2=0.69). Chlorophyll concentration and total particulate organic carbon (POC) concentration accounted for similar to 20% less variability in C-phyto than b(bp) Ratios of C-phyto to Chl a span an order of magnitude moving across and within distinct ecosystems. Similarly, C-phyto:POC ratios were variable with the lowest values coming from productive temperate waters and the highest from oligotrophic gyres. A strong relationship between C-phyto and b(bp) is particularly significant because bhp is a property retrievable from satellite ocean color measurements. Our results, therefore, are highly encouraging for the global monitoring of phytoplanIcton biomass from space. The continued application of our Coy. measurement approach will enable validation of satellite retrievals and contribute to an improved understanding of environmental controls on phytoplankton biomass and physiology. (C) 2015 The Authors. Published by Elsevier Ltd.