Abstract
MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 242:95-109 (2002) - doi:10.3354/meps242095 Fluxes of carbon in the upper ocean: regulation by food-web control nodes Louis Legendre1,*, Richard B. Rivkin2 1Laboratoire d¹Océanographie de Villefranche, BP 28, 06234 Villefranche-sur-Mer Cedex, France 2Ocean Sciences Centre, Memorial University of Newfoundland, St John¹s, NF A1C 5S7, Canada *E-mail: legendre@obs-vlfr.fr ABSTRACT: We present a new approach to assess the role of upper ocean pelagic food webs on the partitioning of phytoplankton production (PT) into its 3 principal component fluxes: remineralization to CO2 (i.e. respiration, R), transfer to the pelagic food web (F), and downward export (ET); ET is the sum of its particulate (POC) and dissolved (DOC) organic carbon components (ET = EDOC + EPOC). Although it is well known that there are relationships between the size and trophic structure of the planktonic community on the one hand, and the export of organic carbon (OC) from the euphotic zone and its potential sequestration below the permanent pycnocline on the other hand, the causative mechanisms for these relationships are not well understood. Here, we propose that the fluxes of OC in the upper ocean depend on the coexistence of a relatively small POC pool, which is responsible for the fluxes PT, R, F and EPOC, and a much larger DOC pool, which sustains both bacterial production and EDOC. In our model, phytoplankton, microbial heterotrophic plankton, and large zooplankton are the 3 food-web control nodes of the 5 carbon fluxes (PT, R, F, EDOC and EDOC). The phytoplankton node controls the downward flux of phytodetritus (mostly from large phytoplankton), which is often the major component of EPOC. The microbial heterotrophic plankton node is responsible for most of the remineralization of OC to CO2 and the uptake and release of DOC. This node therefore controls the size of the DOC pool that can be exported downwards. The large zooplankton node controls both the transfer of POC to large metazoans and part of the downward POC flux (EPOC; faecal pellets and vertically migrating organisms). We implemented our model by estimating export as ET = PT - R at 8 sites in different regions of the World Ocean. The functional relationship between ET and Pnew was highly significant (r2 = 0.85): In contrast to other approaches, where export is calculated as a fraction of PT, we estimate ET as the difference between 2 independent variables (i.e. PT and R); hence our approach produces some regional values ET < 0 - these regions are net heterotrophic. Overall, our approach improves our understanding of carbon cycling and export in the upper ocean. KEY WORDS: Bacteria · DOC · Export · Food web models · Heterotrophy · Microbial heterotrophic plankton · Phytoplankton · Zooplankton Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 242. Online publication date: October 25, 2002 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2002 Inter-Research.
Highlights
Quantification of the rates, patterns and mechanisms that control the photosynthetic uptake of carbon by marine phytoplankton and the fate of the resulting organic carbon (OC) has been a central objective ofMar Ecol Prog Ser 242: 95–109, 2002 tionships between the size and trophic structure of the planktonic community, and between the export of OC from the euphotic zone and its potential sequestration below the permanent pycnocline (e.g. Boyd & Newton 1995, 1999, Rivkin et al 1996, Legendre & Michaud 1998, Fasham et al 1999, Vézina & Savenkoff 1999), the causative mechanisms for these relationships are not well understood
We present a new approach to assess the role of upper ocean pelagic food webs on the partitioning of phytoplankton production (PT) into its 3 principal component fluxes: remineralization to CO2, transfer to the pelagic food web (F ), and downward export (ET); ET is the sum of its particulate (POC) and dissolved (DOC) organic carbon components (ET = exported DOC (EDOC) + EPOC)
The conceptual model developed in this paper provides an alternative approach to the analysis and estimation of food-web-controlled carbon fluxes in the upper ocean
Summary
Quantification of the rates, patterns and mechanisms that control the photosynthetic uptake of carbon by marine phytoplankton (procaryotic and eucaryotic photoautotrophic plankton) and the fate of the resulting organic carbon (OC) has been a central objective of. Living POC includes the same trophic compartments as depicted, i.e. phytoplankton (< 5 and > 5 μm-sized cells), microbial heterotrophic plankton, large zooplankton (mesozooplankton and microphagous macrozooplankton), and large metazoans. Output to MHP, Z, DOC, phytodetritus Z, DOC, CO2 M, DOC, CO2, faecal pellets CO2 CO2, DOC, disphotic zone Deep waters DOC, disphotic zone MHP Disphotic zone microbial heterotrophic plankton (and, under specific conditions, by microphagous macrozooplankton), whereas larger cells are generally eaten by large zooplankton, or if ungrazed, they sink to depth as phytodetritus The latter bifurcation is influenced by the taxonomic composition and size structure of the phytoplankton assemblage, i.e. some large or gelatinous phytoplankton taxa are not ingested by zooplankton, and others readily aggregate and sink out of the euphotic zone (Boyd & Newton 1995, 1999, DiTullio et al 2000, Armstrong et al 2001). When the microbial heterotrophic plankton (i.e. bacterial) activity is limited by inorganic nutrients or grazing, these factors influence the assimilation and the concentration of DOC and its subsequent export below the euphotic zone (2.3)
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