engleski

Phytoplankton species composition contributing to carbon export - Sea to Space particle investigation

Phytoplankton fuels the biological pump: the phyto- carbon can be naturally sequestered in the deep ocean through complex ecological and physical processes. When it comes to phytoplankton, it is not just the quantity, but also the carbon quality that matters, therefore it is crucial to identify the species community composition. During Sea2Space cruise with R/V Falkor in January/February 2017, we investigated three stations in the North Pacific, ranging from the oligotrophic subtropical gyre to the upwelling-influenced coast of California. We collected seawater sampled with a CTD rosette in the mixed layer above the sediment trap platforms. Microscopical analyses revealed three distinct communities at stations congruent with their trophical status. At Station 1 microphytoplankton and nanophytoplankton reached abundances up to 4.8 x 103 cells L-1 and 1.8 x 104 cells L-1, respectively. The community was composed of 31 diatoms, 15 dinoflagellates, 11 coccolithophores and 5 crypto/silicoflagellate morphotypes. Dominant species were single-celled Chaetoceros sp., Leptocylindrus mediterraneus, N. bicapitata, N. braarudii, Gymnodinium spp., Gyrodinium spp., Calciosolenia murrayi, Discosphaera tubifera and Michelsarsia elegans. At Station 2 micro- and nanophytoplankton reached counts up to 4.1 x 103 and 2.2 x 104 cells L-1, respectively. The community was composed of 26 diatoms, 10 dinoflagellates, 10 coccolithophores and 4 hapto/crypto/silicoflagellate morphotypes. Dominant species were single-celled Chaetoceros sp., L. mediterraneus, Nitzschia sp., Gyrodinium spp., Calciosolenia murrayi, C. brasiliensis, Discosphaera tubifera and Ophiaster sp. At the coastal Station 3 phytoplankton was the most diverse and the cell counts were one magnitude higher than at the other stations, with micro- and nanophytoplankton reaching up to 4.4 x 104 cells L-1 and 1.1 x 105 cells L-1. The community was composed of 57 diatoms, 15 dinoflagellates, 4 coccolithophores and 9 crypto/green flagellate morphotypes. Dominant species were Chaetoceros convolutus, N. longissima, Pseudo-nitzschia pseudodelicatissima, Rhizosolenia hebetata var. hemispina, Rhizosolenia sp., Thalassiosira sp., Gyrodinium spp.

phytoplankton, carbon export

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