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. Coccolithophores are globally distributed microscopic marine algae thatexert a major influence on the global carbon cycle through calcification andprimary productivity. There is recent interest in coccolithophore polarcommunities; however field observations regarding their biogeographicdistribution are scarce for the Southern Ocean (SO). This study documents thelatitudinal, as well as in depth, variability in the coccolithophoreassemblage composition and the coccolith mass variation in the ecologicallydominant Emiliania huxleyi across the Drake Passage. Ninety-six water samples were takenbetween 10 and 150 m water depth from 18 stations during POLARSTERNExpedition PS97 (February–April 2016). A minimum of 200 coccospheres persample were identified in the scanning electron microscope, and coccolith masswas estimated with light microscopy. We find that coccolithophore abundance,diversity and maximum depth habitat decrease southwards, marking differentoceanographic fronts as ecological boundaries. We characterize three zones:(1) the Chilean margin, where E. huxleyi type A (normal and overcalcified) and type Rare present; (2) the Subantarctic Zone (SAZ), where E. huxleyi reaches maximum valuesof 212.5×103  cells L −1 and types B/C, C and O are dominant; and (3) the PolarFront Zone (PFZ), where E. huxleyi types B/C and C dominate. We link the decreasingtrend in E. huxleyi coccolith mass to the poleward latitudinal succession from the type Ato the type B group. Remarkably, we find that coccolith mass is stronglyanticorrelated to total alkalinity, total CO2 , the bicarbonate ion and pH.We speculate that low temperatures are a greater limiting factor thancarbonate chemistry in the Southern Ocean. However, further in situoceanographic data are needed to verify the proposed relationships. Wehypothesize that assemblage composition and calcification modes of E. huxleyi in theDrake Passage will be strongly influenced by the ongoing climate change.

Calcification and latitudinal distribution of extant coccolithophores across the Drake Passage during late austral summer 2016