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Particle flux in the oceans: Challenging the steady state assumption

Particle flux in the oceans: Challenging the steady state assumption
Particle flux in the oceans: Challenging the steady state assumption
Atmospheric carbon dioxide levels are strongly controlled by the depth at which the organic matter that sinks out of the surface ocean is remineralized. This depth is generally estimated from particle flux profiles measured using sediment traps. Inherent in this analysis is a steady state assumption; that export from the surface does not significantly change in the time it takes material to reach the deepest trap. However, recent observations suggest that a significant fraction of material in the mesopelagic zone sinks slowly enough to bring this into doubt. We use data from a study in the North Atlantic during July/August 2009 to challenge the steady state assumption. An increase in biogenic silica flux with depth was observed which we interpret, based on vertical profiles of diatom taxonomy, as representing the remnants of the spring diatom bloom sinking slowly (<40?m d-1). We were able to reproduce this behaviour using a simple model using satellite-derived export rates and literature-derived remineralization rates. We further provide a simple equation to estimate ‘additional’ (or ‘excess’) POC supply to the dark ocean during non-steady state conditions, which is not captured by traditional sediment trap deployments. In seasonal systems, mesopelagic net organic carbon supply could be wrong by as much as 25% when assuming steady state. We conclude that the steady state assumption leads to misinterpretation of particle flux profiles when input fluxes from the upper ocean vary on the order of weeks, such as in temperate and polar regions with strong seasonal cycles in export.
Non-steady state, slow sinking particles, carbon export, biogenic silica, particle flux, sediment trap
0886-6236
159-171
Giering, Sarah L.C.
fa349d1b-7c28-482b-b379-824e2688bbb4
Sanders, Richard
02c163c1-8f5e-49ad-857c-d28f7da66c65
Martin, Adrian P.
9d0d480d-9b3c-44c2-aafe-bb980ed98a6d
Henson, Stephanie A.
d6532e17-a65b-4d7b-9ee3-755ecb565c19
Riley, Jennifer
4cf9f8c5-5c07-466b-83de-4088f97d498c
Marsay, Chris M.
f18098e4-e58c-4799-a7fc-5d6f8ec95677
Johns, David
6c9778aa-a490-4f69-9462-94ffa486247d
Giering, Sarah L.C.
fa349d1b-7c28-482b-b379-824e2688bbb4
Sanders, Richard
02c163c1-8f5e-49ad-857c-d28f7da66c65
Martin, Adrian P.
9d0d480d-9b3c-44c2-aafe-bb980ed98a6d
Henson, Stephanie A.
d6532e17-a65b-4d7b-9ee3-755ecb565c19
Riley, Jennifer
4cf9f8c5-5c07-466b-83de-4088f97d498c
Marsay, Chris M.
f18098e4-e58c-4799-a7fc-5d6f8ec95677
Johns, David
6c9778aa-a490-4f69-9462-94ffa486247d

Giering, Sarah L.C., Sanders, Richard, Martin, Adrian P., Henson, Stephanie A., Riley, Jennifer, Marsay, Chris M. and Johns, David (2017) Particle flux in the oceans: Challenging the steady state assumption. Global Biogeochemical Cycles, 31 (1), 159-171. (doi:10.1002/2016GB005424).

Record type: Article

Abstract

Atmospheric carbon dioxide levels are strongly controlled by the depth at which the organic matter that sinks out of the surface ocean is remineralized. This depth is generally estimated from particle flux profiles measured using sediment traps. Inherent in this analysis is a steady state assumption; that export from the surface does not significantly change in the time it takes material to reach the deepest trap. However, recent observations suggest that a significant fraction of material in the mesopelagic zone sinks slowly enough to bring this into doubt. We use data from a study in the North Atlantic during July/August 2009 to challenge the steady state assumption. An increase in biogenic silica flux with depth was observed which we interpret, based on vertical profiles of diatom taxonomy, as representing the remnants of the spring diatom bloom sinking slowly (<40?m d-1). We were able to reproduce this behaviour using a simple model using satellite-derived export rates and literature-derived remineralization rates. We further provide a simple equation to estimate ‘additional’ (or ‘excess’) POC supply to the dark ocean during non-steady state conditions, which is not captured by traditional sediment trap deployments. In seasonal systems, mesopelagic net organic carbon supply could be wrong by as much as 25% when assuming steady state. We conclude that the steady state assumption leads to misinterpretation of particle flux profiles when input fluxes from the upper ocean vary on the order of weeks, such as in temperate and polar regions with strong seasonal cycles in export.

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Accepted/In Press date: 30 December 2016
e-pub ahead of print date: 28 January 2017
Published date: 28 January 2017
Keywords: Non-steady state, slow sinking particles, carbon export, biogenic silica, particle flux, sediment trap
Organisations: Ocean and Earth Science, Marine Biogeochemistry, Ocean Biochemistry & Ecosystems, National Oceanography Centre

Identifiers

Local EPrints ID: 404499
URI: https://eprints.soton.ac.uk/id/eprint/404499
ISSN: 0886-6236
PURE UUID: 49e3c0da-23a4-4a20-b2a2-4dbea66911b6

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Date deposited: 10 Jan 2017 10:32
Last modified: 10 Dec 2019 06:16

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Contributors

Author: Sarah L.C. Giering
Author: Richard Sanders
Author: Adrian P. Martin
Author: Jennifer Riley
Author: Chris M. Marsay
Author: David Johns

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