Coccolithophore assemblage data from sediment core M35003-4 from the western subtropical North Atlantic Ocean spanning the past 55 ka. The assemblage data were used to assess changes in biodiversity and assemblage composition during the past 24 ka, i.e., from the Last Glacial Maximum to the current warm period covering the last deglaciation.Samples were analysed at 5 cm intervals and were prepared using a combined dilution/filtering technique as described by Andruleit (1996, doi:10.2307/1485964). Between 50 and 100 mg of dry bulk sediment was brought into suspension using demineralized water buffered with ammonia (pH ~ 8.5-9). The suspension was ultrasonicated for 15 to 30 s, split (split factor = 100) using a rotary splitter and filtered onto polycarbonate membrane filters (0.4 µm pore size) using a vacuum pump. Samples were dried at 40°C for 24 h before ~1x1 cm filter aliquots were mounted on an aluminium stub that was prepared with electroconductive, self-adhesive, carbon-based discs (PLANO Leit tabs). The mounted samples were sputtered with gold/palladium in a Polaron SC7640 Sputter Coater.Coccolith counts (N) were made manually using a Zeiss DSM 940A scanning electron microscope at 3,000x magnification. Two samples were counted on SEM images at 2,000x magnification. A minimum of 288 coccoliths were counted. Sample mass (m), magnification, split factor (k) and the area of the scanned transect (A) and the filter (F) are given for all samples to allow calculation of the concentration of coccoliths per gram of dry bulk sediment, which was calculated using: (FN)/(kA*m).Coccolithophore taxonomy follows Young et al. (2003, doi:10.58998/jnr2297). Species not reported in the data are assumed to be absent (that is, zero abundance). Two subspecies of Calcidiscus leptoporus were distinguished: Calcidiscus leptoporus subsp. quadriperforatus and Calcidiscus leptoporus subsp. leptoporus. The ladder was further subdivided into small (= 5 µm) coccoliths. The variety Rhabdosphaera clavigera var. stylifera was distinguished from Rhabdosphaera clavigera. Counts of unidentified and reworked specimens are given. The chronology of the time series presented here is the revised age model included in the PALMOD 130k marine palaeoclimate data synthesis V1.1 (Jonkers et al., 2020, doi:10.5194/essd-12-1053-2020) and is based on radiocarbon ages measured on planktonic foraminifera.
