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Thick-shelled, grazer-protected diatoms decouple ocean carbon and silicon cycles in the iron-limited Antarctic Circumpolar Current

Thick-shelled, grazer-protected diatoms decouple ocean carbon and silicon cycles in the iron-limited Antarctic Circumpolar Current
Thick-shelled, grazer-protected diatoms decouple ocean carbon and silicon cycles in the iron-limited Antarctic Circumpolar Current
Diatoms of the iron-replete continental margins and North Atlantic are key exporters of organic carbon. In contrast, diatoms of the iron-limited Antarctic Circumpolar Current sequester silicon, but comparatively little carbon, in the underlying deep ocean and sediments. Because the Southern Ocean is the major hub of oceanic nutrient distribution, selective silicon sequestration there limits diatom blooms elsewhere and consequently the biotic carbon sequestration potential of the entire ocean. We investigated this paradox in an in situ iron fertilization experiment by comparing accumulation and sinking of diatom populations inside and outside the iron-fertilized patch over 5 wk. A bloom comprising various thin- and thick-shelled diatom species developed inside the patch despite the presence of large grazer populations. After the third week, most of the thinner-shelled diatom species underwent mass mortality, formed large, mucous aggregates, and sank out en masse (carbon sinkers). In contrast, thicker-shelled species, in particular Fragilariopsis kerguelensis, persisted in the surface layers, sank mainly empty shells continuously, and reduced silicate concentrations to similar levels both inside and outside the patch (silica sinkers). These patterns imply that thick-shelled, hence grazer-protected, diatom species evolved in response to heavy copepod grazing pressure in the presence of an abundant silicate supply. The ecology of these silica-sinking species decouples silicon and carbon cycles in the iron-limited Southern Ocean, whereas carbon-sinking species, when stimulated by iron fertilization, export more carbon per silicon. Our results suggest that large-scale iron fertilization of the silicate-rich Southern Ocean will not change silicon sequestration but will add carbon to the sinking silica flux.
evolutionary arms race top-down control geo-engineering
0027-8424
20633-20638
Assmy, P.
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Smetacek, V.
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Montresor, M.
bd79a96b-a673-41ad-aa40-8c97c4db82e7
Klaas, C.
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Henjes, J.
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Strass, V.H.
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Arrieta, J.M.
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Bathmann, U.
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Berg, G.M.
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Breitbarth, E.
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Cisewski, B.
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Friedrichs, L.
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Fuchs, N.
32429b3e-c930-4a00-b484-47892cd85a76
Herndl, G.J.
161e0a0f-36cd-4e81-92c6-b7fb5a163227
Jansen, S.
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Kragefsky, S.
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Latasa, M.
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Peeken, I.
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Rottgers, R.
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Scharek, R.
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Schuller, S.E.
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Steigenberger, S.
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Webb, A.
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Wolf-Gladrow, D.
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Assmy, P.
2ac59097-1e82-4644-a864-09a387269488
Smetacek, V.
4b4e1972-8b55-40ee-a69d-63ad4442480b
Montresor, M.
bd79a96b-a673-41ad-aa40-8c97c4db82e7
Klaas, C.
58c3cb88-7f55-496b-95d6-cf2445bab9ee
Henjes, J.
bae206e8-1b36-497a-bc0d-1b454e7774b5
Strass, V.H.
ffd244f4-43d0-4916-a063-7008231cdf5e
Arrieta, J.M.
bbbd29e5-51f5-4cc0-8d71-331f8c444e94
Bathmann, U.
d1690b0e-5f83-49e2-b884-c4ca12b20387
Berg, G.M.
abe7f47b-a691-4f22-a669-58238c9e9c4c
Breitbarth, E.
6dbfea7a-f1a4-4e49-a605-56a684723efa
Cisewski, B.
04eebca5-773b-4d78-9372-2fcbab869bf6
Friedrichs, L.
6d3533ee-e88a-4fe0-bd9f-e47bdcb5eeb5
Fuchs, N.
32429b3e-c930-4a00-b484-47892cd85a76
Herndl, G.J.
161e0a0f-36cd-4e81-92c6-b7fb5a163227
Jansen, S.
08f39fcb-b5c9-41c9-8bb7-81b9f1ed8f74
Kragefsky, S.
240fef8f-1c60-4b34-ba6e-69762f53f168
Latasa, M.
ea83c152-ddfe-4fd7-8682-d74c86d0b20d
Peeken, I.
91855863-da37-4431-8087-3d5f4ba47520
Rottgers, R.
fd35f0e5-e151-4eee-bf20-bb03de64c296
Scharek, R.
21551e5a-c369-489b-8e98-55bd52f389cf
Schuller, S.E.
b861a43e-7938-43b7-9089-ac13205a8bae
Steigenberger, S.
15c989b8-dd0d-454c-b3cc-08d4290eaff0
Webb, A.
dfbf7223-9771-4465-9770-2e535e9f11d0
Wolf-Gladrow, D.
23fc194b-d2ea-4dfa-b965-686f6438bd32

Assmy, P., Smetacek, V., Montresor, M., Klaas, C., Henjes, J., Strass, V.H., Arrieta, J.M., Bathmann, U., Berg, G.M., Breitbarth, E., Cisewski, B., Friedrichs, L., Fuchs, N., Herndl, G.J., Jansen, S., Kragefsky, S., Latasa, M., Peeken, I., Rottgers, R., Scharek, R., Schuller, S.E., Steigenberger, S., Webb, A. and Wolf-Gladrow, D. (2013) Thick-shelled, grazer-protected diatoms decouple ocean carbon and silicon cycles in the iron-limited Antarctic Circumpolar Current. Proceedings of the National Academy of Sciences, 110 (51), 20633-20638. (doi:10.1073/pnas.1309345110).

Record type: Article

Abstract

Diatoms of the iron-replete continental margins and North Atlantic are key exporters of organic carbon. In contrast, diatoms of the iron-limited Antarctic Circumpolar Current sequester silicon, but comparatively little carbon, in the underlying deep ocean and sediments. Because the Southern Ocean is the major hub of oceanic nutrient distribution, selective silicon sequestration there limits diatom blooms elsewhere and consequently the biotic carbon sequestration potential of the entire ocean. We investigated this paradox in an in situ iron fertilization experiment by comparing accumulation and sinking of diatom populations inside and outside the iron-fertilized patch over 5 wk. A bloom comprising various thin- and thick-shelled diatom species developed inside the patch despite the presence of large grazer populations. After the third week, most of the thinner-shelled diatom species underwent mass mortality, formed large, mucous aggregates, and sank out en masse (carbon sinkers). In contrast, thicker-shelled species, in particular Fragilariopsis kerguelensis, persisted in the surface layers, sank mainly empty shells continuously, and reduced silicate concentrations to similar levels both inside and outside the patch (silica sinkers). These patterns imply that thick-shelled, hence grazer-protected, diatom species evolved in response to heavy copepod grazing pressure in the presence of an abundant silicate supply. The ecology of these silica-sinking species decouples silicon and carbon cycles in the iron-limited Southern Ocean, whereas carbon-sinking species, when stimulated by iron fertilization, export more carbon per silicon. Our results suggest that large-scale iron fertilization of the silicate-rich Southern Ocean will not change silicon sequestration but will add carbon to the sinking silica flux.

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Published date: 17 December 2013
Keywords: evolutionary arms race top-down control geo-engineering
Organisations: Ocean and Earth Science

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Local EPrints ID: 361120
URI: https://eprints.soton.ac.uk/id/eprint/361120
ISSN: 0027-8424
PURE UUID: e2128f63-e9fe-46a6-9193-2255b7034460

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Date deposited: 13 Jan 2014 16:13
Last modified: 18 Jul 2017 03:07

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Contributors

Author: P. Assmy
Author: V. Smetacek
Author: M. Montresor
Author: C. Klaas
Author: J. Henjes
Author: V.H. Strass
Author: J.M. Arrieta
Author: U. Bathmann
Author: G.M. Berg
Author: E. Breitbarth
Author: B. Cisewski
Author: L. Friedrichs
Author: N. Fuchs
Author: G.J. Herndl
Author: S. Jansen
Author: S. Kragefsky
Author: M. Latasa
Author: I. Peeken
Author: R. Rottgers
Author: R. Scharek
Author: S.E. Schuller
Author: S. Steigenberger
Author: A. Webb
Author: D. Wolf-Gladrow

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