title: Reconciliation of the carbon budget in the ocean's twilight zone.
abstract: Photosynthesis in the surface ocean produces approximately 100 gigatonnes of organic carbon per year, of which 5 to 15 per cent is exported to the deep ocean. The rate at which the sinking carbon is converted into carbon dioxide by heterotrophic organisms at depth is important in controlling oceanic carbon storage. It remains uncertain, however, to what extent surface ocean carbon supply meets the demand of water-column biota; the discrepancy between known carbon sources and sinks is as much as two orders of magnitude. Here we present field measurements, respiration rate estimates and a steady-state model that allow us to balance carbon sources and sinks to within observational uncertainties at the Porcupine Abyssal Plain site in the eastern North Atlantic Ocean. We find that prokaryotes are responsible for 70 to 92 per cent of the estimated remineralization in the twilight zone (depths of 50 to 1,000 metres) despite the fact that much of the organic carbon is exported in the form of large, fast-sinking particles accessible to larger zooplankton. We suggest that this occurs because zooplankton fragment and ingest half of the fast-sinking particles, of which more than 30 per cent may be released as suspended and slowly sinking matter, stimulating the deep-ocean microbial loop. The synergy between microbes and zooplankton in the twilight zone is important to our understanding of the processes controlling the oceanic carbon sink.
authors.affiliation: 1] National Oceanography Centre, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK [2] Ocean and Earth Sciences, University of Southampton, European Way, Southampton SO14 3ZH, UK [3] Institute of Biological and Environmental Sciences, Oceanlab, University of Aberdeen, Newburgh AB41 6AA, UK.
authors.forename: Sarah L C
authors.initials: SL
authors.lastname: Giering
authors.affiliation: National Oceanography Centre, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK.
authors.forename: Richard
authors.initials: R
authors.lastname: Sanders
authors.affiliation: National Oceanography Centre, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK.
authors.forename: Richard S
authors.initials: RS
authors.lastname: Lampitt
authors.affiliation: National Oceanography Centre, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK.
authors.forename: Thomas R
authors.initials: TR
authors.lastname: Anderson
authors.affiliation: Aix-Marseille Université, Université de Toulon, CNRS/INSU, IRD, MIO, UM 110, 13288 Marseille Cedex 09, France.
authors.forename: Christian
authors.initials: C
authors.lastname: Tamburini
authors.affiliation: Aix-Marseille Université, Université de Toulon, CNRS/INSU, IRD, MIO, UM 110, 13288 Marseille Cedex 09, France.
authors.forename: Mehdi
authors.initials: M
authors.lastname: Boutrif
authors.affiliation: National Oceanography Centre, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK.
authors.forename: Mikhail V
authors.initials: MV
authors.lastname: Zubkov
authors.affiliation: 1] Ocean and Earth Sciences, University of Southampton, European Way, Southampton SO14 3ZH, UK [2] Department of Earth and Ocean Sciences, University of South Carolina, Columbia, South Carolina 29208, USA.
authors.forename: Chris M
authors.initials: CM
authors.lastname: Marsay
authors.affiliation: National Oceanography Centre, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK.
authors.forename: Stephanie A
authors.initials: SA
authors.lastname: Henson
authors.affiliation: National Oceanography Centre, University of Southampton, Waterfront Campus, European Way, Southampton SO14 3ZH, UK.
authors.forename: Kevin
authors.initials: K
authors.lastname: Saw
authors.affiliation: Marine Laboratory, Marine Scotland Science, Scottish Government, PO Box 101, 375 Victoria Road, Aberdeen AB11 9DB, UK.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Cook
authors.affiliation: Institute of Biological and Environmental Sciences, Oceanlab, University of Aberdeen, Newburgh AB41 6AA, UK.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Mayor
mesh_terms: D000818:Animals; D059001:Aquatic Organisms / Q000378:metabolism*; D001267:Atlantic Ocean; D058448:Biota; D002244:Carbon / Q000378:metabolism*; D057486:Carbon Cycle; D002245:Carbon Dioxide / Q000378:metabolism; D057965:Carbon Sequestration; D019069:Cell Respiration; D020387:Food Chain; D019370:Observation; D012623:Seawater / Q000737:chemistry / Q000382:microbiology; D035501:Uncertainty; D015048:Zooplankton / Q000378:metabolism
chemical_list: D002245:Carbon Dioxide; D002244:Carbon