Abstract. We present a summary of biomass data for 11 plankton functional types (PFTs) plus phytoplankton pigment data, compiled as part of the MARine Ecosystem biomass DATa (MAREDAT) initiative. The goal of the MAREDAT initiative is to provide, in due course, global gridded data products with coverage of all planktic components of the global ocean ecosystem. This special issue is the first step towards achieving this. The PFTs presented here include picophytoplankton, diazotrophs, coccolithophores, Phaeocystis, diatoms, picoheterotrophs, microzooplankton, foraminifers, mesozooplankton, pteropods and macrozooplankton. All variables have been gridded onto a World Ocean Atlas (WOA) grid (1 • × 1 • × 33 vertical levels × monthly climatologies). The results show that abundance is much better constrained than their carbon content/elemental composition, and coastal seas and other high productivity regions have much better coverage than the much larger volumes where biomass is relatively low. The data show that (1) the global total heterotrophic biomass (2.0-4.6 Pg C) is at least as high as the total autotrophic biomass (0.5-2.4 Pg C excluding nanophytoplankton and autotrophic dinoflagellates); (2) the biomass of zooplankton calcifiers (0.03-0.67 Pg C) is substantially higher than that of coccolithophores (0.001-0.03 Pg C); (3) patchiness of biomass distribution increases with organism size; and (4) although zooplankton biomass measurements below 200 m are rare, the limited measurements available suggest that Bacteria and Archaea are not the only important heterotrophs in the deep sea. More data will be needed to characterise ocean ecosystem functioning and associated biogeochemistry in the Southern Hemisphere and below 200 m. Future efforts to understand marine ecosystem composition and functioning will be helped both by further archiving of historical data and future sampling at new locations.Microzooplankton database:

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[1] Basin-scale distributions of light absorption by chromophoric dissolved organic matter (CDOM) are positively correlated (R 2 > 0.8) with apparent oxygen utilization (AOU) within the top kilometer of the Pacific and Indian Oceans. However, a much weaker correspondence is found for the Atlantic (R 2 < 0.05). Strong correlation between CDOM and AOU indicates that CDOM is created as a byproduct of the oxidation of organic matter from sinking particles. The observed meridional-depth sections of CDOM result from a balance between biogeochemical processes (autochthonous production and solar bleaching) and the meridional overturning circulation. Rapid mixing in the Atlantic dilutes CDOM in the interior and implies that the time scale for CDOM accumulation is greater than ∼50 years. CDOM emerges as a unique tracer for diagnosing changes in biogeochemistry and the overturning circulation, similar to dissolved oxygen, with the additional feature that it can be quantified from satellite observation.

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