Acronym: OCB-031
Program: Ocean Carbon & Biogeochemistry [OCB]
Url: Project Web Site
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Organic Matter Composition, Recycling Susceptibility, and the Effectiveness of the Biological Pump – An Evaluation Using NMR Spectra of Marine Plankton

from www.us-ocb.org

Carbon (C) sequestration through fertilization of phytoplankton with micronutrients and enhancement of the absorption and retention of atmospheric C by ocean biota heavily depends on the efficiency of the “biological pump”. The long-term effectiveness of this strategy depends on a net transfer of C from the upper ocean-atmosphere system to the deep ocean where the C is removed from contact with the atmosphere for an extended period of time. This C removal can be equated to the amount of C fixation by phytoplankton minus the C cycling and regeneration in the euphotic zone. If the regeneration efficiency is increased, then despite increased C fixation, no net loss (sequestration) of C will result. A reduction in cycling efficiency in the euphotic zone, on the other hand, will increase the effectiveness of the “biological pump” and thus C sequestration.

The degree of organic matter biodegradation and recycling depends on the “reactivity” of compounds synthesized by the biota, which in turn, is controlled by the structural characteristic of these compounds. There is considerable evidence that different phytoplankton taxa differ substantially in their biogeochemical characteristics and it is likely that the relative abundance of different compounds synthesized by these distinct taxa, and even within each group at different growth conditions, will differ too. This variability in biosynthesis and thus abundance of a wide range of organic compounds in the water column would lend itself to different susceptibility for biodegradation and regeneration. Knowledge of the distribution of various organic matter structural groups synthesized by distinct taxa, the dependence of the organic matter compound classes on different growth conditions (temperature, light, nutrients) and the selective susceptibility of these compound to regeneration is crucial for estimating the potential for rapid regeneration in the euphotic zone, and thus the effectiveness of the “biological pump”.

This project uses both 13C and 31P NMR spectroscopy on various phytoplankton cultures grown under a wide range of controlled conditions and on field samples dominated by different taxa. We describe variability in the molecular composition of organic matter synthesized by different phytoplankton groups; assess the dependence of the organic matter composition synthesized on growth conditions (temperature, light, nutrient and Fe availability, and growth rate); and gain a better understanding of the susceptibility of a wide range of organic molecules (with specific functional groups) to biodegradation. Data produced in this study will help constrain and improve the parameterization of POM regeneration in C sequestration models and assess the potential success of any fertilization scenario.

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More information about project Organic Matter Composition, Recycling Susceptibility, and the Effectiveness of the Biological Pump
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Datasets associated with Organic Matter Composition, Recycling Susceptibility, and the Effectiveness of the Biological Pump
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