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Particle export from the euphotic zone: estimates using a novel drifting sediment trap, 234Th and new production

Particle export from the euphotic zone: estimates using a novel drifting sediment trap, 234Th and new production
Particle export from the euphotic zone: estimates using a novel drifting sediment trap, 234Th and new production
We describe the first results obtained using a novel free-drifting neutrally buoyant sediment trap called PELAGRA (Particle Export measurement using a LAGRAngian trap). The trap uses an APEX float (Autonomous Profiling EXplorer) to maintain its location at a predetermined depth or density horizon and is designed to be deployed in the depth range 100–600 m for periods of up to a week. PELAGRA was deployed into a well characterised region of the Northeast (NE) Atlantic over the Porcupine Abyssal Plain (PAP) during the summers of 2003, 2004, 2005 and 2006 in post-bloom conditions. In parallel, measurements were made of total and new primary production and estimates of particle export based on 234Th deficits in the upper water column. Samples of sinking material from PELAGRA were recovered almost uncontaminated by “swimmers”. The material collected differed from that obtained using water bottles and an in situ filtration system and this indicated selective export of centric diatoms. Fluxes of 234Th into the traps were less than that calculated from the deficit of this isotope in the upper water column. It is concluded that this reflects export events that had occurred prior to these deployments. Fluxes of organic carbon into the PELAGRA traps were similar to those expected from measurements of new production in the upper mixed layer. During 2006, simultaneous PELAGRA deployments at depths of 150 and 250 m provided a direct measurement of the decrease in flux with depth. This decrease was substantially more than that predicted by the often-used “Martin equation” and yielded a “b value” of 1.7. Using this value in the NE Atlantic about 14% of the total production reaches a depth of 150 m during the post-bloom period under nutrient limitation.

particle flux, thorium-234, carbon export, biogeochemistry, sediment trap, northeast atlantic
0967-0637
1484-1502
Lampitt, R.S.
dfc3785c-fc7d-41fa-89ee-d0c6e27503ad
Boorman, B.
f884fa25-f60c-4b35-bea8-85697732e9f4
Brown, L.
71ebbeab-98c3-45f3-b3f2-200387870709
Lucas, M.
48aafe1b-184a-4925-9e5a-028699026b0b
Salter, I.
805cba99-e754-417b-aac1-cee3a259aced
Sanders, R.
02c163c1-8f5e-49ad-857c-d28f7da66c65
Saw, K.
aba28de9-80bc-426f-8b96-22d637550649
Seeyave, S.
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Thomalla, S.J.
f2a33709-cab9-42b1-9cbd-a1f4c50be7b4
Turnewitsch, R.
7d9e29ea-1a91-4968-903e-ca32f525b0c6
Lampitt, R.S.
dfc3785c-fc7d-41fa-89ee-d0c6e27503ad
Boorman, B.
f884fa25-f60c-4b35-bea8-85697732e9f4
Brown, L.
71ebbeab-98c3-45f3-b3f2-200387870709
Lucas, M.
48aafe1b-184a-4925-9e5a-028699026b0b
Salter, I.
805cba99-e754-417b-aac1-cee3a259aced
Sanders, R.
02c163c1-8f5e-49ad-857c-d28f7da66c65
Saw, K.
aba28de9-80bc-426f-8b96-22d637550649
Seeyave, S.
8099548d-0140-44b7-9a54-2c5ef473c821
Thomalla, S.J.
f2a33709-cab9-42b1-9cbd-a1f4c50be7b4
Turnewitsch, R.
7d9e29ea-1a91-4968-903e-ca32f525b0c6

Lampitt, R.S., Boorman, B., Brown, L., Lucas, M., Salter, I., Sanders, R., Saw, K., Seeyave, S., Thomalla, S.J. and Turnewitsch, R. (2008) Particle export from the euphotic zone: estimates using a novel drifting sediment trap, 234Th and new production. Deep Sea Research Part I: Oceanographic Research Papers, 55 (11), 1484-1502. (doi:10.1016/j.dsr.2008.07.002).

Record type: Article

Abstract

We describe the first results obtained using a novel free-drifting neutrally buoyant sediment trap called PELAGRA (Particle Export measurement using a LAGRAngian trap). The trap uses an APEX float (Autonomous Profiling EXplorer) to maintain its location at a predetermined depth or density horizon and is designed to be deployed in the depth range 100–600 m for periods of up to a week. PELAGRA was deployed into a well characterised region of the Northeast (NE) Atlantic over the Porcupine Abyssal Plain (PAP) during the summers of 2003, 2004, 2005 and 2006 in post-bloom conditions. In parallel, measurements were made of total and new primary production and estimates of particle export based on 234Th deficits in the upper water column. Samples of sinking material from PELAGRA were recovered almost uncontaminated by “swimmers”. The material collected differed from that obtained using water bottles and an in situ filtration system and this indicated selective export of centric diatoms. Fluxes of 234Th into the traps were less than that calculated from the deficit of this isotope in the upper water column. It is concluded that this reflects export events that had occurred prior to these deployments. Fluxes of organic carbon into the PELAGRA traps were similar to those expected from measurements of new production in the upper mixed layer. During 2006, simultaneous PELAGRA deployments at depths of 150 and 250 m provided a direct measurement of the decrease in flux with depth. This decrease was substantially more than that predicted by the often-used “Martin equation” and yielded a “b value” of 1.7. Using this value in the NE Atlantic about 14% of the total production reaches a depth of 150 m during the post-bloom period under nutrient limitation.

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More information

e-pub ahead of print date: 12 July 2008
Published date: November 2008
Keywords: particle flux, thorium-234, carbon export, biogeochemistry, sediment trap, northeast atlantic

Identifiers

Local EPrints ID: 63721
URI: http://eprints.soton.ac.uk/id/eprint/63721
ISSN: 0967-0637
PURE UUID: 186b07d7-293d-4931-920c-08ff338090a6

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Date deposited: 24 Oct 2008
Last modified: 15 Mar 2024 11:42

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Contributors

Author: R.S. Lampitt
Author: B. Boorman
Author: L. Brown
Author: M. Lucas
Author: I. Salter
Author: R. Sanders
Author: K. Saw
Author: S. Seeyave
Author: S.J. Thomalla
Author: R. Turnewitsch

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