Insights into the biogeochemical cycling of iron, nitrate, and phosphate across a 5,300 km South Pacific zonal section (153°E–150°W)

Ellwood, Michael J., Bowie, Andrew R., Baker, Alex ORCID: https://orcid.org/0000-0002-8365-8953, Gault-Ringold, Melanie, Hassler, Christel, Law, Cliff S., Maher, William, Marriner, Andrew, Nodder, Scott, Sander, Sylvia, Stevens, Craig, Townsend, Ashley, van der Merwe, Pier, Woodward, E. Malcolm S., Wuttig, Kathrin and Boyd, Philip W. (2018) Insights into the biogeochemical cycling of iron, nitrate, and phosphate across a 5,300 km South Pacific zonal section (153°E–150°W). Global Biogeochemical Cycles, 32 (2). 187–207. ISSN 0886-6236

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Abstract

Iron, phosphate and nitrate are essential nutrients for phytoplankton growth and hence their supply into the surface ocean controls oceanic primary production. Here, we present a GEOTRACES zonal section (GP13; 30-33oS, 153oE-150oW) extending eastwards from Australia to the oligotrophic South Pacific Ocean gyre outlining the concentrations of these key nutrients. Surface dissolved iron concentrations are elevated at >0.4 nmol L-1 near continental Australia (west of 165°E) and decreased eastward to ≤0.2 nmol L-1 (170oW-150oW). The supply of dissolved iron into the upper ocean (<100m) from the atmosphere and vertical diffusivity averaged 11 ±10 nmol m-2 d-1. In the remote South Pacific Ocean (170oW-150oW) atmospherically sourced iron is a significant contributor to the surface dissolved iron pool with average supply contribution of 23 ± 17% (range 3% to 55%). Surface-water nitrate concentrations averaged 5 ±4 nmol L-1 between 170oW and 150oW whilst surface-water phosphate concentrations averaged 58 ±30 nmol L-1. The supply of nitrogen into the upper ocean is primarily from deeper waters (24-1647 μmol m-2 d-1) with atmospheric deposition and nitrogen fixation contributing <1% to the overall flux, in remote South Pacific waters. The deep water N:P ratio averaged 16 ±3 but declined to <1 above the deep chlorophyll maximum (DCM) indicating a high N:P assimilation ratio by phytoplankton leading to almost quantitative removal of nitrate. The supply stoichiometry for iron and nitrogen relative to phosphate at and above the DCM declines eastward leading to two biogeographical provinces: one with diazotroph production and the other without diazotroph production.

Item Type:	Article
Uncontrolled Keywords:	iron,nitrate,phosphate,sw pacific ocean,phytoplankton
Faculty \ School:	Faculty of Science > School of Environmental Sciences Faculty of Science > School of Natural Sciences
UEA Research Groups:	Faculty of Science > Research Groups > Centre for Ocean and Atmospheric Sciences
Depositing User:	Pure Connector
Date Deposited:	23 Jan 2018 14:30
Last Modified:	21 Oct 2022 17:34
URI:	https://ueaeprints.uea.ac.uk/id/eprint/66045
DOI:	10.1002/2017GB005736

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