Ukpabi Ndubuisi edgar2005ng@gmail.com 0000-0002-8535-9041 Aarhus University AU http://www.au.dk/en/ https://ror.org/01aj84f44 Seidenkrantz Marit-Solveig mss@geo.au.dk 0000-0002-1973-5969 Aarhus University AU http://www.au.dk/en/ https://ror.org/01aj84f44 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 https://doi.org/10.1594/PANGAEA.996263 2026-07-31T08:36:04 This dataset provides high resolution coccolithophore assemblage counts, absolute abundances, ecological contrast indices, and derived hydrographic metrics from marine sediment core DA12 11/2 ST1 GC01, retrieved from the Iceland Basin at 2120 m water depth. The record spans the entire Holocene and consists predominantly of dark grey, fine grained calcareous ooze with occasional ash layers. Coccolithophore assemblages were analysed at 5 cm intervals, corresponding to an average temporal resolution of ~70–80 years in the upper Holocene. Each sample was freeze dried, homogenized, deflocculated, and mounted for light microscopy and scanning electron microscopy. A minimum of 300 coccoliths were identified to species level per sample, following established taxonomic criteria. Absolute abundances were calculated from the total number of coccoliths in 0.01 g of sediment using field of view geometry and subsample mass. As stated in the dataset, "C = N g−1 FOV = Field of Vision (fields counted)". Species included Calcidiscus leptoporus, Coccolithus pelagicus, Gephyrocapsa spp., Emiliania huxleyi, Helicosphaera carteri, Syracosphaera pulchra, Umbilicosphaera spp., Pontosphaera discopora, Pontosphaera japonica, and Braarudosphaera bigelowii. Ecological preferences of taxa were used to construct four Ecological Contrast Indices (thermal, salinity, nutrient, and stratification/mixing). These contrasts were combined to produce the Coccolithophore Hydrographic Index (CHI), a dimensionless proxy summarizing warm–cold, saline–fresh, oligotrophic–nutrient rich, and stratified–mixed ecological states. CHI values were log transformed, z scored, and tanh scaled to generate standardized hydrographic anomalies and percentile based state classifications. The dataset includes raw CHI, log₁₀(CHI), CHI_zscore, CHI_sx, percentile thresholds (Q10, Q90), and trend classifications derived from rolling slope analysis. This dataset provides a continuous, quantitative record of coccolithophore community structure and hydrographic variability in the Iceland Basin throughout the Holocene. It is intended for paleoceanographic reconstructions, proxy comparison studies, and multiproxy analyses of North Atlantic surface water dynamics. Ukpabi Ndubuisi edgar2005ng@gmail.com 0000-0002-8535-9041 Seidenkrantz Marit-Solveig mss@geo.au.dk 0000-0002-1973-5969 in press Holocene hydrography of the Iceland Basin from coccolith ecological contrasts: A multi‑axis index for salinity and stratification journal article Marine Micropaleontology -20.702729999999995 -20.702729999999995 61.608929999999994 61.608929999999994 -20.702729999999995 61.608929999999994 2025-09-12T14:20:00 2025-09-12T14:20:00 DA12-11/2-GC01 G1 61.60893 -20.70273 Iceland Basin -2120.0 2025-09-12T14:20:00 Dana12-11 Dana12-11 Reykjavik, Iceland 2012-09-24T00:00:00 2012-09-24 Hirtshals, Denmark 2012-09-30T00:00:00 2012-09-30 Dana (1981) https://dana.dtu.dk/en/historien-om-dana Røy, Hans Røy, Hans https://geo.au.dk/fileadmin/ingen_mappe_valgt/Paleoceanography_group/Benthic_Marine_Research_Course_Final_Report_2013_v3.pdf Dana (1981) https://dana.dtu.dk/en/historien-om-dana Gravity corer GC 3 CC-BY-4.0 Creative Commons Attribution 4.0 International https://creativecommons.org/licenses/by/4.0/ Depth, top/min | Depth top | Depth, bottom/max | Depth bot | Sediment colour | Color description | Color descr | Description | Sediment type | Sediment | Coccoliths, total | Cocco | Counting, coccoliths | Number of fields of view | Fields | Petri dish radius | Radius | Optical field radius | Subsample weight | Subsample, dry mass | Subsamp dm | Initial sample weight | Sample, dry mass | Samp dm | Absolute coccolith number | Coccoliths | Absolute coccolith abundance | Calcidiscus leptoporus | C. leptoporus | Coccolithus pelagicus | C. pelagicus | Helicosphaera carteri | H. carteri | Gephyrocapsa spp. | Emiliania huxleyi | E. huxleyi | Syracosphaera pulchra | S. pulchra | Umbilicosphaera spp. | Pontosphaera discopora | P. discopora | Pontosphaera japonica | P. japonica | Braarudosphaera bigelowii | B. bigelowii | Coccolithophore hydrographic index | CHI | log10(CHI) | Logarithm | log | CHI z-score | Z-score | Warm sum | Ecological sum index | Sum index | Cold sum | HighSal sum | LowSal sum | Oligo sum | Nutrient sum | Stratified sum | Mixing sum | Thermal contrast | Hydrographic contrast index | Hydrographic contrast | Salinity contrast | Nutrient contrast | StratMix contrast | tanh scaled state index CHI_sx | Hyperbolic tangent | tanh | Hydrographic state class | Class | Percentile flags (Low, Normal, High) | Percentile threshold, description | Percentile threshold descr | Warming, Cooling, Alternating | Trend class | Trend arrow | State–trend combination | Zones 1–5 | Ecozone citable absolute abundance Atlantic Water CHI index coccolith assemblages Coccolithophores ecological contrasts ecological polarity Holocene hydrographic reconstruction Iceland Basin Micropaleontology Paleoceanography Polar Water quantitative microscopy Salinity sediment core DA12 11/2 ST1 GC01 SEM Stratification method4786 param1052 param105760 param112130 param113739 param1140 param1265 param137479 param1404 param14619 param14926 param156427 param20889 param20891 param20894 param20896 param20907 param21383 param25420 param3 param4 param433 param50868 param514590 param541011 param551909 param567700 param567701 param567702 param567703 param567717 param567718 param567720 param567721 param567722 param567723 param6141 param6157 param628 param7637 param84878 param88037 param89367 param906 pi118597 author118597 author28069 basis4446 campaign3423278 event2970337 geocode1599 geocode1600 geocode1601 geocode8128 inst20913 journal10825 license21 method11107 ref140894 term21355 term37651 term390 term47129 term48664 term50476 term54576 term60911 term61002 term77707 term78404 term78405 term78406 term78407 term78408 term78409 term78410 term78411 term78412 term78413 term78414