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Insights into the biogeochemical cycling of iron, nitrate, and phosphate across a 5,300km South Pacific Zonal Section (153E-150W)

Citation

Ellwood, MJ and Bowie, AR and Baker, A and Gault-Ringold, M and Hassler, C and Law, CS and Maher, WA and Marriner, A and Nodder, S and Sander, S and Stevens, C and Townsend, A and Van Der Merwe, P and Woodward, EMS and Wuttig, K and Boyd, PW, 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) pp. 187-207. ISSN 0886-6236 (2018) [Refereed Article]

Copyright Statement

Copyright 2018 American Geophysical Union

DOI: doi:10.1002/2017GB005736

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; 3033S, 153E150W) extending eastward from Australia to the oligotrophic South Pacific Ocean gyre outlining the concentrations of these key nutrients. Surface dissolved iron concentrations are elevated at >0.4nmolL−1 near continental Australia (west of 165E) and decreased eastward to ≤0.2nmolL−1 (170W150W). The supply of dissolved iron into the upper ocean (<100m) from the atmosphere and vertical diffusivity averaged 1110nmolm−2d−1. In the remote South Pacific Ocean (170W150W), atmospherically sourced iron is a significant contributor to the surface dissolved iron pool with average supply contribution of 2317% (range 3% to 55%). Surface water nitrate concentrations averaged 54nmolL−1 between 170W and 150W, while surface water phosphate concentrations averaged 5830nmolL−1. The supply of nitrogen into the upper ocean is primarily from deeper waters (241647μmolm−2d−1) with atmospheric deposition and nitrogen fixation contributing <1% to the overall flux along the eastern part of the transect. The deep water N:P ratio averaged 14.50.5 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 Details

Item Type:Refereed Article
Keywords:iron, nitrate, phosphate, South Pacific, phytoplankton, atmospheric deposition
Research Division:Earth Sciences
Research Group:Oceanography
Research Field:Chemical Oceanography
Objective Division:Environment
Objective Group:Other Environment
Objective Field:Marine Oceanic Processes (excl. climate related)
UTAS Author:Bowie, AR (Associate Professor Andrew Bowie)
UTAS Author:Gault-Ringold, M (Dr Melanie East)
UTAS Author:Townsend, A (Associate Professor Ashley Townsend)
UTAS Author:Van Der Merwe, P (Dr Pier van der Merwe)
UTAS Author:Wuttig, K (Dr Kathrin Wuttig)
UTAS Author:Boyd, PW (Professor Philip Boyd)
ID Code:125151
Year Published:2018
Funding Support:Australian Research Council (FT130100037)
Web of Science® Times Cited:4
Deposited By:CRC-Antarctic Climate & Ecosystems
Deposited On:2018-04-03
Last Modified:2019-02-15
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