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Sustained upwelling of subsurface iron supplies seasonally persistent phytoplankton blooms around the Southern Kerguelen Plateau, Southern Ocean
journal contribution
posted on 2023-05-19, 21:26 authored by Christina SchallenbergChristina Schallenberg, Sophie BestleySophie Bestley, Andreas KlockerAndreas Klocker, Trull, TW, Diana Davies, Melanie EastMelanie East, Eriksen, R, Roden, NP, Sander, SG, Sumner, M, Ashley TownsendAshley Townsend, Pier van der MerwePier van der Merwe, Karen WestwoodKaren Westwood, Kathrin WuttigKathrin Wuttig, Andrew BowieAndrew BowieAlthough 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.
History
Publication title
Journal of Geophysical Research: OceansVolume
123Issue
8Pagination
5986-6003ISSN
2169-9275Department/School
Institute for Marine and Antarctic StudiesPublisher
Wiley-Blackwell Publishing, Inc.Place of publication
United StatesRights statement
©2018. American Geophysical Union. All Rights Reserved.Repository Status
- Restricted