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Depth-resolved particle associated microbial respiration in the northeast Atlantic

Depth-resolved particle associated microbial respiration in the northeast Atlantic
Depth-resolved particle associated microbial respiration in the northeast Atlantic
Atmospheric levels of carbon dioxide are tightly linked to the depth at which sinking particulate organic carbon (POC) is remineralised in the ocean. Rapid attenuation of downward POC flux typically occurs in the upper mesopelagic (top few hundred metres of the water column), with much slower loss rates deeper in the ocean. Currently, we lack understanding of the processes that drive POC attenuation, resulting in large uncertainties in the mesopelagic carbon budget. Attempts to balance the POC supply to the mesopelagic with respiration by zooplankton and microbes rarely succeed. Where a balance has been found, depth-resolved estimates reveal large compensating imbalances in the upper and lower mesopelagic. In particular, it has been suggested that respiration by free-living microbes and zooplankton in the upper mesopelagic are too low to explain the observed flux attenuation of POC within this layer. We test the hypothesis that particle-associated microbes contribute significantly to community respiration in the mesopelagic, measuring particle-associated microbial respiration of POC in the northeast Atlantic through shipboard measurements on individual marine snow aggregates collected at depth (36–500?m). We find very low rates of both absolute and carbon-specific particle-associated microbial respiration (<?3?%?d?1), suggesting that this term cannot solve imbalances in the upper mesopelagic POC budget. The relative importance of particle-associated microbial respiration increases with depth, accounting for up to 33?% of POC loss in the mid-mesopelagic (128–500?m). We suggest that POC attenuation in the upper mesopelagic (36–128?m) is driven by the transformation of large, fast-sinking particles to smaller, slow-sinking and suspended particles via processes such as zooplankton fragmentation and solubilisation, and that this shift to non-sinking POC may help to explain imbalances in the mesopelagic carbon budget.
1726-4170
4927-4943
Belcher, Anna
604905f0-adc0-4503-b8b3-d5b5f9960771
Iverson, Morten
f390eddb-4806-4b32-914e-0f1e64e9a568
Giering, Sari
559cd7b3-38c7-479e-bea0-9b87e810ae5c
Riou, Virginie
a46ff574-b638-4ad0-a21e-ba4c799dd636
Henson, Stephanie A.
d6532e17-a65b-4d7b-9ee3-755ecb565c19
Berline, Leo
cc44ad89-4a6c-4214-ac26-c752bd73f1d4
Guilloux, Loic
ea02e81e-dfbe-4e39-a7d8-815743107ff0
Sanders, Richard
02c163c1-8f5e-49ad-857c-d28f7da66c65
Belcher, Anna
604905f0-adc0-4503-b8b3-d5b5f9960771
Iverson, Morten
f390eddb-4806-4b32-914e-0f1e64e9a568
Giering, Sari
559cd7b3-38c7-479e-bea0-9b87e810ae5c
Riou, Virginie
a46ff574-b638-4ad0-a21e-ba4c799dd636
Henson, Stephanie A.
d6532e17-a65b-4d7b-9ee3-755ecb565c19
Berline, Leo
cc44ad89-4a6c-4214-ac26-c752bd73f1d4
Guilloux, Loic
ea02e81e-dfbe-4e39-a7d8-815743107ff0
Sanders, Richard
02c163c1-8f5e-49ad-857c-d28f7da66c65

Belcher, Anna, Iverson, Morten, Giering, Sari, Riou, Virginie, Henson, Stephanie A., Berline, Leo, Guilloux, Loic and Sanders, Richard (2016) Depth-resolved particle associated microbial respiration in the northeast Atlantic. Biogeosciences, 13 (17), 4927-4943. (doi:10.5194/bg-2016-130).

Record type: Article

Abstract

Atmospheric levels of carbon dioxide are tightly linked to the depth at which sinking particulate organic carbon (POC) is remineralised in the ocean. Rapid attenuation of downward POC flux typically occurs in the upper mesopelagic (top few hundred metres of the water column), with much slower loss rates deeper in the ocean. Currently, we lack understanding of the processes that drive POC attenuation, resulting in large uncertainties in the mesopelagic carbon budget. Attempts to balance the POC supply to the mesopelagic with respiration by zooplankton and microbes rarely succeed. Where a balance has been found, depth-resolved estimates reveal large compensating imbalances in the upper and lower mesopelagic. In particular, it has been suggested that respiration by free-living microbes and zooplankton in the upper mesopelagic are too low to explain the observed flux attenuation of POC within this layer. We test the hypothesis that particle-associated microbes contribute significantly to community respiration in the mesopelagic, measuring particle-associated microbial respiration of POC in the northeast Atlantic through shipboard measurements on individual marine snow aggregates collected at depth (36–500?m). We find very low rates of both absolute and carbon-specific particle-associated microbial respiration (<?3?%?d?1), suggesting that this term cannot solve imbalances in the upper mesopelagic POC budget. The relative importance of particle-associated microbial respiration increases with depth, accounting for up to 33?% of POC loss in the mid-mesopelagic (128–500?m). We suggest that POC attenuation in the upper mesopelagic (36–128?m) is driven by the transformation of large, fast-sinking particles to smaller, slow-sinking and suspended particles via processes such as zooplankton fragmentation and solubilisation, and that this shift to non-sinking POC may help to explain imbalances in the mesopelagic carbon budget.

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Accepted/In Press date: 14 April 2016
e-pub ahead of print date: 15 April 2016
Published date: 7 September 2016
Organisations: Ocean and Earth Science, Marine Biogeochemistry

Identifiers

Local EPrints ID: 396640
URI: https://eprints.soton.ac.uk/id/eprint/396640
ISSN: 1726-4170
PURE UUID: 43a040c7-313c-4f23-a2fb-dc2affa26616

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Date deposited: 09 Jun 2016 13:18
Last modified: 09 Jan 2018 18:04

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Contributors

Author: Anna Belcher
Author: Morten Iverson
Author: Sari Giering
Author: Virginie Riou
Author: Leo Berline
Author: Loic Guilloux
Author: Richard Sanders

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