Ukpabi, Ndubuisi; Seidenkrantz, Marit-Solveig (2026): Coccolith abundance, assemblage structure, and sedimentological properties along core DA12‑11/2‑ST1‑GC01 [dataset]. PANGAEA, https://doi.pangaea.de/10.1594/PANGAEA.996239 (DOI registration in progress),

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In: Ukpabi, N; Seidenkrantz, M-S (2026): High resolution Holocene coccolithophore assemblages, absolute abundances, and hydrographic index (CHI) calculations from sediment core DA12 11/2 ST1 GC01, Iceland Basin [dataset bundled publication]. PANGAEA, https://doi.org/10.1594/PANGAEA.996263

This dataset presents a high resolution sequence of coccolithophore assemblages and absolute abundances from 0–419 cm in core DA12 11/2 ST1 GC01, capturing fine scale ecological variability across predominantly dark grey calcareous ooze interspersed with discrete ash layers. Coccolith counts range from extremely low values in ash dominated horizons to >900 specimens in more stable intervals, with absolute abundances varying by over two orders of magnitude. Assemblages are consistently dominated by Coccolithus pelagicus, Gephyrocapsa spp., and Emiliania huxleyi, whose shifting proportions delineate transitions between cool, stratified, and nutrient rich surface water states. Upper Holocene samples show strong C. pelagicus dominance with intermittent increases in E. huxleyi, reflecting oscillations between Atlantic influenced and Polar modified waters. Mid core intervals exhibit pronounced rises in Gephyrocapsa spp., marking episodes of enhanced small form productivity and possible changes in mixing intensity. Occasional occurrences of Helicosphaera carteri, Syracosphaera pulchra, Umbilicosphaera spp., and rare Pontosphaera taxa indicate intermittent incursions of warmer or more oligotrophic conditions. Ash layers consistently show reduced counts, simplified assemblages, and strong dominance by a single taxon, reflecting ecological suppression during volcanic deposition. Across the full sequence, the interplay between dominant and accessory taxa reveals coherent patterns of hydrographic restructuring, including shifts in thermal regimes, salinity gradients, nutrient supply, and stratification intensity. These assemblage variations provide a detailed ecological fingerprint of Holocene surface water dynamics in the Iceland Basin and form the basis for subsequent derivation of ecological contrasts and hydrographic indices.