Counterintuitive carbon-to-nutrient coupling in an Arctic pelagic ecosystem

Counterintuitive carbon-to-nutrient coupling in an Arctic pelagic ecosystem
Publication Type
Journal Article
Year of Publication

Thingstad TF, Bellerby RGJ, Bratbak G, Borsheim KY, Egge JK, Heldal M, Larsen A, Neill C, Nejstgaard J, Norland S, Sandaa RA, Skjoldal EF, Tanaka T, Thyrhaug R, Topper B

ISBN Number

DOC, Dissolved Organic Carbon, Carbon to nutrient coupling, microbial food web, Arctic, mesocosm, Svalbard, Norway, 1 m3


Predicting the ocean’s role in the global carbon cycle requires anunderstanding of the stoichiometric coupling between carbon andgrowth-limiting elements in biogeochemical processes. A recentaddition to such knowledge is that the carbon/nitrogen ratio ofinorganic consumption and release of dissolved organic mattermay increase in a high-CO2 world1. This will, however, yield anegative feedback on atmospheric CO2 only if the extra organicmaterial escapes mineralization within the photic zone. Here weshow, in the context of an Arctic pelagic ecosystem, how the fateand effects of added degradable organic carbon depend criticallyon the state of the microbial food web. When bacterial growth ratewas limited by mineral nutrients, extra organic carbon accumulatedin the system. When bacteria were limited by organic carbon,however, addition of labile dissolved organic carbon reducedphytoplankton biomass and activity and also the rate at whichtotal organic carbon accumulated, explained as the result of stimulatedbacterial competition for mineral nutrients. This counterintuitive‘more organic carbon gives less organic carbon’ effectwas particularly pronounced in diatom-dominated systems wherethe carbon/mineral nutrient ratio in phytoplankton productionwas high. Our results highlight how descriptions of present andfuture states of the oceanic carbon cycle require detailed understandingof the stoichiometric coupling between carbon andgrowth-limiting mineral nutrients in both autotrophic and heterotrophicprocesses.

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