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

Abstract

<p><strong>Abstract.</strong> Coccolithophores are globally distributed microscopic marine algae that exert a major influence on the global carbon cycle through calcification and primary productivity. There is recent interest in coccolithophore polar communities, however field observations regarding their biogeographic distribution are scarce for the Southern Ocean. This study documents the latitudinal variability in the coccolithophore assemblage composition and the coccolith mass variation of the ecologically dominant <i>Emiliania huxleyi</i> across the Drake Passage. Ninety-six water samples were taken between 10 and 150 m water depth from 18 stations during POLARSTERN Expedition PS97 (February–April, 2016). A minimum of 200 coccospheres per sample were classified in scanning electron microscope and coccolith mass was estimated with light microscopy, using the C-Calcita software. We find that coccolithophore abundance and diversity decrease southwards marking different oceanographic fronts as ecological boundaries. We characterize three zones: (1) the Chilean margin, where <i>E. huxleyi</i> type A (normal and overcalcified) and type R are present; (2) the Subantarctic Zone (SAZ), where <i>E. huxleyi</i> reaches maximum values of 212.5×10<sup>3</sup>cells/L and types B/C, C, O are dominant. (3) The Polar Front Zone (PFZ), where <i>E. huxleyi</i> types B/C and C dominate. We link the decreasing trend in <i>E. huxleyi</i> coccolith mass to the poleward latitudinal succesion from type A to type B group. Remarkably, we find that coccolith mass is strongly anticorrelated to total alkalinity, total CO<sub>2</sub>, bicarbonate ion and pH. We speculate that low temperatures are a greater limiting factor than carbonate chemistry in the Southern Ocean. However, further in situ oceanographical data is needed to verify the proposed relationships. We hypothesize that assemblage composition and calcification modes of <i>E. huxleyi </i> in the Drake Passage will be strongly influenced by the ongoing climate change.</p>