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Seasonal ITCZ migration dynamically controls the location of the (sub)tropical Atlantic biogeochemical divide

Seasonal ITCZ migration dynamically controls the location of the (sub)tropical Atlantic biogeochemical divide
Seasonal ITCZ migration dynamically controls the location of the (sub)tropical Atlantic biogeochemical divide
Inorganic nitrogen depletion restricts productivity in much of the low-latitude oceans, generating a selective advantage for diazotrophic organisms capable of fixing atmospheric dinitrogen (N2). However, the abundance and activity of diazotrophs can in turn be controlled by the availability of other potentially limiting nutrients, including phosphorus (P) and iron (Fe). Here we present high-resolution data (?0.3°) for dissolved iron, aluminum, and inorganic phosphorus that confirm the existence of a sharp north–south biogeochemical boundary in the surface nutrient concentrations of the (sub)tropical Atlantic Ocean. Combining satellite-based precipitation data with results from a previous study, we here demonstrate that wet deposition in the region of the intertropical convergence zone acts as the major dissolved iron source to surface waters. Moreover, corresponding observations of N2 fixation and the distribution of diazotrophic Trichodesmium spp. indicate that movement in the region of elevated dissolved iron as a result of the seasonal migration of the intertropical convergence zone drives a shift in the latitudinal distribution of diazotrophy and corresponding dissolved inorganic phosphorus depletion. These conclusions are consistent with the results of an idealized numerical model of the system. The boundary between the distinct biogeochemical systems of the (sub)tropical Atlantic thus appears to be defined by the diazotrophic response to spatial–temporal variability in external Fe inputs. Consequently, in addition to demonstrating a unique seasonal cycle forced by atmospheric nutrient inputs, we suggest that the underlying biogeochemical mechanisms would likely characterize the response of oligotrophic systems to altered environmental forcing over longer timescales.
0027-8424
1438-1442
Schlosser, C.
7990a0cc-cfe9-4dd5-9c45-899c03186207
Klar, J.K.
9205d127-a1cf-4a2e-b4e2-d01210c4f88d
Wake, B.D.
f9ab6e3f-6d4d-4c2b-8c8f-2b5c0b8edabe
Snow, J.T.
74cb4d5c-2d12-4707-920f-95f230f42cfc
Honey, D.J.
e1eff6d8-6bd8-411b-a3d1-521ef9e20f37
Woodward, E.M.S.
3ac3b98f-78c7-4b43-acf9-bba3253752b5
Lohan, M.C.
6ca10597-2d0f-40e8-8e4f-7619dfac5088
Achterberg, E.P.
685ce961-8c45-4503-9f03-50f6561202b9
Moore, C.M.
7ec80b7b-bedc-4dd5-8924-0f5d01927b12
Schlosser, C.
7990a0cc-cfe9-4dd5-9c45-899c03186207
Klar, J.K.
9205d127-a1cf-4a2e-b4e2-d01210c4f88d
Wake, B.D.
f9ab6e3f-6d4d-4c2b-8c8f-2b5c0b8edabe
Snow, J.T.
74cb4d5c-2d12-4707-920f-95f230f42cfc
Honey, D.J.
e1eff6d8-6bd8-411b-a3d1-521ef9e20f37
Woodward, E.M.S.
3ac3b98f-78c7-4b43-acf9-bba3253752b5
Lohan, M.C.
6ca10597-2d0f-40e8-8e4f-7619dfac5088
Achterberg, E.P.
685ce961-8c45-4503-9f03-50f6561202b9
Moore, C.M.
7ec80b7b-bedc-4dd5-8924-0f5d01927b12

Schlosser, C., Klar, J.K., Wake, B.D., Snow, J.T., Honey, D.J., Woodward, E.M.S., Lohan, M.C., Achterberg, E.P. and Moore, C.M. (2014) Seasonal ITCZ migration dynamically controls the location of the (sub)tropical Atlantic biogeochemical divide. Proceedings of the National Academy of Sciences, 111 (4), 1438-1442. (doi:10.1073/pnas.1318670111).

Record type: Article

Abstract

Inorganic nitrogen depletion restricts productivity in much of the low-latitude oceans, generating a selective advantage for diazotrophic organisms capable of fixing atmospheric dinitrogen (N2). However, the abundance and activity of diazotrophs can in turn be controlled by the availability of other potentially limiting nutrients, including phosphorus (P) and iron (Fe). Here we present high-resolution data (?0.3°) for dissolved iron, aluminum, and inorganic phosphorus that confirm the existence of a sharp north–south biogeochemical boundary in the surface nutrient concentrations of the (sub)tropical Atlantic Ocean. Combining satellite-based precipitation data with results from a previous study, we here demonstrate that wet deposition in the region of the intertropical convergence zone acts as the major dissolved iron source to surface waters. Moreover, corresponding observations of N2 fixation and the distribution of diazotrophic Trichodesmium spp. indicate that movement in the region of elevated dissolved iron as a result of the seasonal migration of the intertropical convergence zone drives a shift in the latitudinal distribution of diazotrophy and corresponding dissolved inorganic phosphorus depletion. These conclusions are consistent with the results of an idealized numerical model of the system. The boundary between the distinct biogeochemical systems of the (sub)tropical Atlantic thus appears to be defined by the diazotrophic response to spatial–temporal variability in external Fe inputs. Consequently, in addition to demonstrating a unique seasonal cycle forced by atmospheric nutrient inputs, we suggest that the underlying biogeochemical mechanisms would likely characterize the response of oligotrophic systems to altered environmental forcing over longer timescales.

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More information

e-pub ahead of print date: 23 December 2013
Published date: 28 January 2014
Organisations: Ocean and Earth Science, Geochemistry, Marine Biogeochemistry

Identifiers

Local EPrints ID: 361478
URI: http://eprints.soton.ac.uk/id/eprint/361478
ISSN: 0027-8424
PURE UUID: 03d40f7a-5810-4eab-887f-5996f1fbbf9c
ORCID for M.C. Lohan: ORCID iD orcid.org/0000-0002-5340-3108

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Date deposited: 22 Jan 2014 11:58
Last modified: 16 May 2020 00:41

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Contributors

Author: C. Schlosser
Author: J.K. Klar
Author: B.D. Wake
Author: J.T. Snow
Author: D.J. Honey
Author: E.M.S. Woodward
Author: M.C. Lohan ORCID iD
Author: E.P. Achterberg
Author: C.M. Moore

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