Seasonal organic matter dynamics in a temperate shelf sea

https://doi.org/10.1016/j.pocean.2018.02.021Get rights and content
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Highlights

  • Seasonal dissolved and particulate organic matter pools examined in the Celtic Sea.

  • Organic carbon (C) concentrations highest in spring and lowest in autumn.

  • Nutrient (C, N and P) dynamics decoupled with seasons and during bloom events.

  • Dissolved organic matter always carbon-rich relative to particulates.

  • DOC dominates downward C flux in summer, POC dominates downward flux in spring.

Abstract

Organic matter (OM) plays an important role in productive shelf seas and their contribution to global carbon (C) and nutrient cycles. We investigated dissolved and particulate OM (DOM and POM, respectively) dynamics over a seasonal cycle in the Celtic Sea. The quantity of OC was largest during the spring bloom and lowest in autumn. DOM was always C rich relative to the POM pool and the Redfield ratio (106C:16N:P). There was clear decoupling between C, N and P and the response of OM composition to different seasons and nutrient statuses of the microbial community. The C:P stoichiometry was much more variable than the C:N stoichiometry, which was near constant. Downward OC fluxes were dominated by POM during bloom events and DOM during the stratified summer. In terms of partitioning, 92–96% of OC was in the DOM pool throughout sampling, which given its high C:N (12.4–17) suggests it was an efficient vehicle for potential off-shelf export of C during winter mixing.

Keywords

Organic matter
Continental shelf
Carbon export

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