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High export via small particles before the onset of the North Atlantic spring bloom

High export via small particles before the onset of the North Atlantic spring bloom
High export via small particles before the onset of the North Atlantic spring bloom
Sinking organic matter in the North Atlantic Ocean transfers 1-3 Gt carbon year?1 from the surface ocean to the interior. The majority of this exported material is thought to be in form of large, rapidly sinking particles that aggregate during or after the spring phytoplankton bloom. However, recent work has suggested that intermittent water column stratification resulting in the termination of deep convection can isolate phytoplankton from the euphotic zone, leading to export of small particles. We present depth profiles of large (>0.1mm equivalent spherical diameter, ESD) and small (<0.1mm ESD) sinking particle concentrations and fluxes prior to the spring bloom at two contrasting sites in the North Atlantic (61°30N, 11°00W and 62°50N, 02°30W) derived from the Marine Snow Catcher and the Video Plankton Recorder. The downward flux of organic carbon via small particles ranged from 23-186 mg C m?2 d?1, often constituting the bulk of the total particulate organic carbon flux. We propose that these rates were driven by two different mechanisms: In the Norwegian Basin, small sinking particles likely reached the upper mesopelagic by disaggregation of larger, faster sinking particles. In the Iceland Basin, a storm deepened the mixed layer to >300m depth, leading to deep mixing of particles as deep as 600m. Subsequent re-stratification could trap these particles at depth and lead to high particle fluxes at depth without the need for aggregation (‘mixed layer pump'). Overall we suggest that pre-bloom fluxes to the mesopelagic are significant, and the role of small sinking particles requires careful consideration.
small sinking particles, prebloom export flux, mixed layer pump, detrainment, Marine Snow Catcher, Video Plankton Recorder
6929-6945
Giering, S.L.C.
0188d764-1647-4694-8e28-099e970d5e84
Sanders, R.
02c163c1-8f5e-49ad-857c-d28f7da66c65
Martin, A.P.
9d0d480d-9b3c-44c2-aafe-bb980ed98a6d
Lindemann, C.
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Möller, K.O.
f1e6cb60-9929-4f4e-afe4-38b59bcb7002
Daniels, C.J.
e4a51f9d-efe6-413a-8d3f-3f1eda5ce79f
Mayor, D.J.
461ddc80-a25d-45b5-873f-9cbf4aa93828
St John, M.A.
0d48b75e-1c57-4902-ae37-411ddf3cdeee
Giering, S.L.C.
0188d764-1647-4694-8e28-099e970d5e84
Sanders, R.
02c163c1-8f5e-49ad-857c-d28f7da66c65
Martin, A.P.
9d0d480d-9b3c-44c2-aafe-bb980ed98a6d
Lindemann, C.
856787fb-f794-459c-bafe-9fda9ba016b8
Möller, K.O.
f1e6cb60-9929-4f4e-afe4-38b59bcb7002
Daniels, C.J.
e4a51f9d-efe6-413a-8d3f-3f1eda5ce79f
Mayor, D.J.
461ddc80-a25d-45b5-873f-9cbf4aa93828
St John, M.A.
0d48b75e-1c57-4902-ae37-411ddf3cdeee

Giering, S.L.C., Sanders, R., Martin, A.P., Lindemann, C., Möller, K.O., Daniels, C.J., Mayor, D.J. and St John, M.A. (2016) High export via small particles before the onset of the North Atlantic spring bloom. Journal of Geophysical Research: Oceans, 121 (9), 6929-6945. (doi:10.1002/2016JC012048).

Record type: Article

Abstract

Sinking organic matter in the North Atlantic Ocean transfers 1-3 Gt carbon year?1 from the surface ocean to the interior. The majority of this exported material is thought to be in form of large, rapidly sinking particles that aggregate during or after the spring phytoplankton bloom. However, recent work has suggested that intermittent water column stratification resulting in the termination of deep convection can isolate phytoplankton from the euphotic zone, leading to export of small particles. We present depth profiles of large (>0.1mm equivalent spherical diameter, ESD) and small (<0.1mm ESD) sinking particle concentrations and fluxes prior to the spring bloom at two contrasting sites in the North Atlantic (61°30N, 11°00W and 62°50N, 02°30W) derived from the Marine Snow Catcher and the Video Plankton Recorder. The downward flux of organic carbon via small particles ranged from 23-186 mg C m?2 d?1, often constituting the bulk of the total particulate organic carbon flux. We propose that these rates were driven by two different mechanisms: In the Norwegian Basin, small sinking particles likely reached the upper mesopelagic by disaggregation of larger, faster sinking particles. In the Iceland Basin, a storm deepened the mixed layer to >300m depth, leading to deep mixing of particles as deep as 600m. Subsequent re-stratification could trap these particles at depth and lead to high particle fluxes at depth without the need for aggregation (‘mixed layer pump'). Overall we suggest that pre-bloom fluxes to the mesopelagic are significant, and the role of small sinking particles requires careful consideration.

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Accepted/In Press date: 17 August 2016
e-pub ahead of print date: 22 September 2016
Keywords: small sinking particles, prebloom export flux, mixed layer pump, detrainment, Marine Snow Catcher, Video Plankton Recorder
Organisations: Ocean and Earth Science, Marine Biogeochemistry

Identifiers

Local EPrints ID: 399813
URI: http://eprints.soton.ac.uk/id/eprint/399813
PURE UUID: a305a3b1-d5d0-4f84-96aa-9c0f5729f60c

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Date deposited: 30 Aug 2016 13:17
Last modified: 07 Jan 2022 21:50

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Contributors

Author: S.L.C. Giering
Author: R. Sanders
Author: A.P. Martin
Author: C. Lindemann
Author: K.O. Möller
Author: C.J. Daniels
Author: D.J. Mayor
Author: M.A. St John

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