Paleoproductivity modes in central Mediterranean during MIS 20 - MIS 18: calcareous plankton and alkenone variability
Description
In the present dataset we provide: Table I: In the present dataset we provide the alkenone unsaturation ratio (Uk’37) and different translations to Sea Surface Temperature (SST) according to different calibrations. Alkenone extraction was performed at Brown University, USA and followed freeze-drying ~5 g of homogenized dry sediment, using 100% Dichloromethane (DCM) and a Dionex 200 Accelerated Solvent Extractor (ASE). Prior to quantification, extracts were evaporated with nitrogen and reconstituted with 200 µL of toluene spiked with n-hexatriacontane (C36) and n-heptatriacontane (C37) internal standards. Samples were purified by silica gel flash column chromatography to further isolate the ketone fraction. Alkenone concentrations (C37:2, C37:3, C38:3 ethyl, C38:3 methyl, C38:2 2ethyl and C38:2 methyl ketones, resolved to baseline under our chromatographic conditions) were determined using an Agilent Technologies 6890 gas chromatograph–flame ionization detector (GC-FID), with Agilent Technologies DB-1 column (60 m, 0.32 mm diameter and 0.10 mm film thickness). Table II and III: Absolute (# of coccoliths per g of sediments) and relative (%) abundance of coccolithophore assemblage and of the main taxa at the Ideale section. Slides for coccolithophore analysis were prepared following Flores and Sierro (1997). Quantitative analyses were performed at University of Bari, Italy, using a polarized light microscope at 1000× magnification. Abundances were determined by counting at least 500 coccoliths of all sizes. We also provide estimate of reworked calcareous nannofossils, i.e. taxa belonging to older (Mesozoic and Paleogene-Neogene) stratigraphic intervals, estimated separately during this counting. Warm-water coccoliths include the following taxa: Umbilicosphaera sibogae s.l., Calciosolenia spp., Discosphaera tubifera, Rhabdospaera clavigera, Umbellosphaera spp., Oolithotus spp. The coccolith dissolution index (DI) was estimated according to the following ratio: DI = small Gephyrocapsa/(small Gephyrocapsa + Calcidiscus leptoporus). High values of DI indicate good preservation. Species dominance of the coccolithophore assemblage has been obtained using PAleontological STatistics Software 4.02 (Hammer et al., 2001) and is equivalent to 1-Simpson index. Table IV: Estimates of the C37 total (ng/gram dry weight sediment) and the relative proportions of C37:2/C38:2 were performed at Brown University, USA. The C37 total (ng/gram dry weight sediment) was derived by normalizing these areas to the peak areas of the internal C36 and C37 n-alkane standards and dividing by the weight of the sample extracted