ALBERT

Description: Calcareous nannoplankton analyses on late quaternary sediments from the eastern North Atlantic ODP Site 980 (55°29'N, 14°42'W) provide detailed insight into palaeoceanographic and palaeoclimatic changes that occurred throughout the Termination II and the adjacent interglacial of the Marine Isotope Stage (MIS) 5. This study presents the development of the coccolith assemblage throughout the interglacial MIS 5 towards the beginning of the glacial MIS 4 in the vicinity of the Rockall Plateau and investigates and characterises the impact of climatic and environmental variations on the coccolith assemblage distribution between 135 and 65 ky. In general, the coccolith assemblage is dominated by Gephyrocapsa muellerae and Emiliania huxleyi, whilst significant changes in palaeoceanographic and palaeoclimatic conditions are mainly shown by variations of subordinate species. A drastic increase in coccolith accumulation rates and a change from a less to a higher diverse species assemblage indicate a rapid increase in surface water temperatures during the onset of MIS 5 from c. 127.5 ky on. Highest coccolith numbers, high numbers of taxa and a large diversity indicate highest coccolithophore primary productivity and peak interglacial conditions during MIS 5.5, which are due to the high influence of relatively warm surface water to this region. Coccolith numbers peak again around 120 ky and decline afterwards but stay above glacial levels. The two cooling events of MIS 5.4 and 5.2 interrupt the generally warm conditions and are indicated by lowered coccolith numbers, a drop of thermophile species and a reduction of the species diversity. Decreasing coccolith numbers and a slightly reduced diversity indicate that environmental conditions deteriorated towards the onset of MIS 4. The analysis of the coccolith assemblage reveals that not only the stadial events MIS 5.4 and 5.2 are characterised by colder conditions, but furthermore confirms the upcoming notion that MIS 5.5 was terminated by a slight short-term cooling of the surface water which occurred around 124 ky.

Description: Coccolithophore assemblage data from sediment core GeoB11035-1 from the NW Iberian continental margin for 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 0.5-10 cm intervals and were prepared using a combined dilution/filtering technique as described by Andruleit (1996, doi:10.2307/1485964). Between 50 and 120 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. Where possible, a minimum of 300 coccoliths were counted. In some samples fewer coccoliths were counted due to low abundances. 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: (F*N)/(k*A*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 Coccolithus pelagicus were distinguished: Coccolithus pelagicus susp. pelagicus and Coccolithus pelagicus susp. braarudii as well as two subspecies of Calcidiscus leptoporus: Calcidiscus leptoporus subsp. quadriperforatus and Calcidiscus leptoporus subsp. leptoporus. Calcidiscus leptoporus subsp. leptoporus was further subdivided into small (〈 5 µm) and larger (〉= 5 µm) specimens. Counts of unidentified and reworked specimens are given. The chronology of the time series presented here was revised using a similar approach as in the PALMOD 130k marine palaeoclimate data synthesis V1.1 (Jonkers et al., 2020, doi:10.5194/essd-12-1053-2020). It is based on radiocarbon ages measured on the planktonic foraminifera G. bulloides (〉250 µm) and tie points between the Ca/Ti record with the GISP II δ18O record (Bender et al., 2012, doi:10.1007/s00367-012-0282-2).