ADAPTation von COCCOlithophoriden-Gemeinschaften auf Umweltveränderungen im Südozean (ADAPT-COCCO)
Zusammenfassung der Projektergebnisse
This project provided new insight into the latitudinal, as well as in depth, variability in the coccolithophore assemblage composition and the coccolith mass variation in the ecologically dominant Emiliania huxleyi across the Drake Passage. Plankton samples and recent surface sediment samples were used to better constrain the overlapping influences of environmental factors, such as temperature, and carbonate chemistry on the dynamic occurrences of the calcareous nannoplankton. Coccolithophore abundance, diversity, and maximum depth habitat decrease southwards, portraying the oceanographic fronts as ecological boundaries. Marked shifts in cell numbers, community composition, and diversity occurred at the Subantarctic Front and Polar Front characterizing three three zones: (1) the Chilean margin, where E. huxleyi type A (normal and over-calcified) and type R were present; (2) the Subantarctic Zone, where E. huxleyi reached maximum numbers and types B/C, C and O were dominant; and (3) the Polar Front Zone, where E. huxleyi types B/C and C dominate. The general decreasing trend in E. huxleyi coccolith mass can be linked to the poleward latitudinal succession from the type A group to the type B group. Remarkably, we found that coccolith mass was strongly anticorrelated to total alkalinity, total CO2, the bi-carbonate ion and pH. We speculate that low temperatures are a greater limiting factor than carbonate chemistry in the Southern Ocean. However, further in situ oceanographic data are needed to verify the proposed relationships. We hypothesized that assemblage composition and calcification modes of E. huxleyi in the Drake Passage will be strongly influenced by the ongoing climate change. Furthermore, coccolith assemblages preserved in surface sediments of southernmost Chile and across the Drake Passage were studied, to identify the coccolith response to steep environmental gradients across the frontal system of the Antarctic Circumpolar Current in comparison with hydrodynamic and post-depositional processes occurring in this region. We used statistical analyses to explore which environmental parameters influenced the coccolith assemblages by means of cluster and redundancy analyses. High coccolith abundances and species diversity occurred in the sediments compared to studies in the same area and in other sectors of the Southern Ocean. A surprisingly high species richness south of the Polar Front was observed where factors such as temporary thriving coccolithophore communities in the surface waters, transport of settling coccoliths via surface and bottom currents or eddies influence the (sub-)fossil coccolith assemblages. We also assessed the morphological diversity of the dominant taxa E. huxleyi, and were able to distinguish five morphotypes in the surface sediments for the first time. These E. huxleyi morphologies reflect diverging biogeographical distributions, trending towards smaller and lighter coccoliths to the south as observed in the plankton, although selective dissolution of less calcified species and morphotypes clearly alter the assemblage south of the Polar Front and at depths > 3.1 km. However, this study also emphasized the importance of documenting those morphologies in relation to changing environmental conditions to assess their response to projected environmental change in the Southern Ocean.
Projektbezogene Publikationen (Auswahl)
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(2019). Calcification and latitudinal distribution of extant coccolithophores across the Drake Passage during late austral summer 2016. Biogeosciences, 16, 3679–3702
Saavedra-Pellitero, M., Baumann, K.-H., Fuertes, M.A., Schulz, H., Marcon, Y., Vollmar, N.M., Flores, J.-A., Lamy, F.
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(2022). Distribution of coccoliths in surface sediments across the Drake Passage and calcification of Emiliania huxleyi morphotypes. Biogeosciences, 19, 585–612
Vollmar, N.M., Baumann, K.-H., Saavedra-Pellitero, M., Hernández-Almeida, I.
