Composition of diatom communities and their contribution to plankton biomass in the naturally iron-fertilized region of Kerguelen in the Southern Ocean
2016
In the naturally iron-fertilized surface waters of the northern Kerguelen Plateau region, the early spring diatom community
composition and contribution to plankton carbon biomass were investigated and compared with the high nutrient, low
chlorophyll (HNLC) surrounding waters. The large iron-induced blooms were dominated by small diatom species belonging
to the genera Chaetoceros (Hyalochaete) and Thalassiosira, which rapidly responded to the onset of favorable light-conditions
in the meander of the Polar Front. In comparison, the iron-limited HNLC area was typically characterized by autotrophic
nanoeukaryote-dominated communities and by larger and more heavily silicified diatom species (e.g. Fragilariopsis spp.).
Our results support the hypothesis that diatoms are valuable vectors of carbon export to depth in naturally iron-fertilized
systems of the Southern Ocean. Furthermore, our results corroborate observations of the exported diatom assemblage
from a sediment trap deployed in the iron-fertilized area, whereby the dominant Chaetoceros (Hyalochaete) cells were less
efficiently exported than the less abundant, yet heavily silicified, cells of Thalassionema nitzschioides and Fragilariopsis
kerguelensis. Our observations emphasize the strong influence of species-specific diatom cell properties combined with
trophic interactions on matter export efficiency, and illustrate the tight link between the specific composition of
phytoplankton communities and the biogeochemical properties characterizing the study area.
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