Chemometric perspectives on plankton community responses to natural iron fertilisation over and downstream of the Kerguelen Plateau in the Southern Ocean

Type Article
Date 2015
Language English
Author(s) Trull Thomas1, 2, Davies Diana M.1, 2, Dehairs Frank3, Cavagna Anne-Julie4, Lasbleiz Marine5, 6, Laurenceau Cornec Emmanuel C.1, 2, 3, D'Ovidio Francesco7, Planchon Frederic8, Leblanc Karine5, 6, Queguiner Bernard5, 6, Blain Stephane9, 10
Affiliation(s) 1 : CSIRO Marine and Atmospheric Research, Hobart, Tasmania, Australia
2 : Antarctic Climate and Ecosystems Cooperative Research Centre, Hobart, Tasmania, Australia
3 : Institute for Marine and Antarctic Studies, University of Tasmania, Hobart, Tasmania, Australia
4 : Analytical, Environmental and Geochemistry; Earth Sciences Research Group, Vrije Universiteit Brussel, Belgium
5 : Aix-Marseille Université, Marseille, France
6 : Université de Toulon, France
7 : LOCEAN–IPSL, Université Pierre et Marie Curie, Paris, France
8 : Laboratoire des Sciences de l’Environnement Marin (LEMAR), Université de Brest, IUEM, Plouzané, France
9 : Sorbonne Universités, UPMC Univ Paris 06, UMR7621, Laboratoire d’Océanographie Microbienne, Observatoire Océanologique, 66650 Banyuls/mer, France
10 : CNRS, Laboratoire d’Océanographie Microbienne, Observatoire Océanologique, 66650 Banyuls/mer, France
Source Biogeosciences (1726-4170) (European Geosciences Union (EGU)), 2015 , Vol. 12 , N. 4 , P. 1029-1056
DOI 10.5194/bg-12-1029-2015
WOS© Times Cited 25
Abstract We examined phytoplankton community responses to natural iron fertilisation at 32 sites over and downstream from the Kerguelen Plateau in the Southern Ocean during the austral spring bloom in October-November 2011. The community structure was estimated from chemical and isotopic measurements (particulate organic carbon - POC; C-13-POC; particulate nitrogen -PN; N-15-PN; and biogenic silica - BSi) on size-fractionated samples from surface waters (300, 210, 50, 20, 5, and 1 mu m fractions). Higher values of C-13-POC (vs. co-located C-13 values for dissolved inorganic carbon -DIC) were taken as indicative of faster growth rates and higher values of N-15-PN (vs. co-located N-15-NO3 source values) as indicative of greater nitrate use (rather than ammonium use, i.e. higher f ratios). Community responses varied in relation to both regional circulation and the advance of the bloom. Iron-fertilised waters over the plateau developed dominance by very large diatoms (50-210 mu m) with high BSi / POC ratios, high growth rates, and significant ammonium recycling (lower f ratios) as biomass built up. In contrast, downstream polar frontal waters with a similar or higher iron supply were dominated by smaller diatoms (20-50 mu m) and exhibited greater ammonium recycling. Stations in a deep-water bathymetrically trapped recirculation south of the polar front with lower iron levels showed the large-cell dominance observed on the plateau but much less biomass. Comparison of these communities to surface water nitrate (and silicate) depletions as a proxy for export shows that the low-biomass recirculation feature had exported similar amounts of nitrogen to the high-biomass blooms over the plateau and north of the polar front. This suggests that early spring trophodynamic and export responses differed between regions with persistent low levels vs. intermittent high levels of iron fertilisation.
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Trull Thomas, Davies Diana M., Dehairs Frank, Cavagna Anne-Julie, Lasbleiz Marine, Laurenceau Cornec Emmanuel C., D'Ovidio Francesco, Planchon Frederic, Leblanc Karine, Queguiner Bernard, Blain Stephane (2015). Chemometric perspectives on plankton community responses to natural iron fertilisation over and downstream of the Kerguelen Plateau in the Southern Ocean. Biogeosciences, 12(4), 1029-1056. Publisher's official version : https://doi.org/10.5194/bg-12-1029-2015 , Open Access version : https://archimer.ifremer.fr/doc/00255/36642/