Sustained upwelling of subsurface iron supplies seasonally persistent phytoplankton blooms around the Southern Kerguelen Plateau, Southern Ocean

Although the supply of iron generally limits phytoplankton productivity in the Southern Ocean, substantial seasonal blooms are observed over and downstream of the Kerguelen plateau in the Indian sector of the Southern Ocean. Surprisingly, of the oceanic blooms, those associated with the deeper south...

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Bibliographic Details
Published in:Journal of Geophysical Research: Oceans
Main Authors: Schallenberg, C, Bestley, S, Klocker, A, Trull, TW, Davies, DM, Gault-Ringold, M, Eriksen, R, Roden, NP, Sander, SG, Sumner, M, Townsend, AT, van der Merwe, P, Westwood, K, Wuttig, K, Bowie, A
Format: Article in Journal/Newspaper
Language:English
Published: Wiley-Blackwell Publishing, Inc. 2018
Subjects:
upwelling
phytoplankton bloom
Southern Ocean
iron
Antarctic
The Antarctic
Austral
Kerguelen
Indian
Antarc*
Online Access:https://eprints.utas.edu.au/45142/
https://eprints.utas.edu.au/45142/2/128431.pdf
Description
Summary:Although the supply of iron generally limits phytoplankton productivity in the Southern Ocean, substantial seasonal blooms are observed over and downstream of the Kerguelen plateau in the Indian sector of the Southern Ocean. Surprisingly, of the oceanic blooms, those associated with the deeper southern plateau last much longer (∼3 months) than the northern bloom (∼1‐month downstream of northern plateau). In this study, iron supply mechanisms around the southern plateau were investigated, obtaining profiles of dissolved iron (<0.2 μm, dFe) to 2,000‐m deep at 25 stations during austral summer 2016. The dFe concentrations in surface waters (≤100‐m depth) ranged from below the detection limit (DL, median of 0.026 nmol/kg) to 0.34 nmol/kg near the Antarctic shelf, with almost half the data points below detection. These low and—with few exceptions—largely spatially invariant concentrations, presumably driven by seasonal drawdown of this essential micronutrient by phytoplankton, could not explain observed patterns in chlorophyll a. In contrast, dFe concentrations (0.05–1.27 nmol/kg) in subsurface waters (100–800 m) showed strong spatial variations that can explain bloom patterns around the southern Kerguelen plateau when considered in the context of frontal locations and associated frontal processes, including upwelling, that may increase the upward supply of dFe in the region. This sustained vertical dFe supply distinguishes the southern blooms from the bloom downstream of the northern Kerguelen plateau and explains their persistence through the season.

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