Marino, Maria; Rodrigues, Teresa; Quivelli, Ornella; Girone, Angela; Maiorano, Patrizia; Bassinot, Franck (2025): Paleoproductivity proxies and alkenone precursors in the Western Mediterranean during the Early-Middle Pleistocene transition [dataset bundled publication]. PANGAEA, https://doi.org/10.1594/PANGAEA.982519

Multidisciplinary analyses (taxonomic analysis of coccolithophore assemblages, stable oxygen isotopes, marine and terrestrial biomarkers) have been carried out on sediments from Ocean Drilling Program Site 975 in the Algero-Balearic basin (38°53.8′ N, 4°30.6′ E), through late marine isotope stage (MIS) 20-19 (from 800 to 756 thousand years ago). The aim of the study was to compare coccolithophore paleoproductivity proxies, such as C37 alkenone concentration (ng/g) and nannofossil accumulation rate (NAR=coccoliths * cm- 2 * kyr-1), and understand their relationship with paleoceanographic condition and paleoenvironmental changes, alkenone-producing precursors and unsaturated C37 alkenone compounds (C37:2, C37:3, C37:4).

Measurements of stable oxygen isotope analysis were performed on four to fifteen specimens of Globigerina bulloides (250–315 μm). These analyses were performed on an Isoprime 100 (Elementar) dual-inlet Isotope Ratio Mass Spectrometer (Elementar) at the Laboratoire des Sciences du Climat et de l'Environnement (LSCE, France). The results are expressed as δ18O vs V-PDB (in ‰) through calibration to international NBS standards. Quantitative analyses on coccolithophores were performed at the Dipartimento di Scienze della Terra e Geoambientali, Bari University (Italy), using a polarized light microscope at 1000 X magnification, and abundances were determined by counting at least 500 coccoliths of all sizes. Nannofossil dissolution index (DI) has been calculated as follows: small gephyrocapsids/(small gephyrocapsids + Calcidiscus leptoporus). Marine and terrestrial biomarkers have been processed at the Instituto Português do Mar e da Atmosfera (Portugal). The patterns of C37 alkenone concentration and NAR provided reliable information on past paleoproductivity changes. The Alkanol Preservation Index (API) obtained by the relative proportion of n-hexacosan-1-ol (C26OH) to the sum of C26OH plus n-nonacosane (C29) [API = C26OH/(C26OH + C29)], was used as a proxy of sea bottom ventilation in the basin. Sea surface temperature (SST) was estimated calculating the alkenone Uk'37 index that is based on the di- and tri-unsaturated alkenone ratio [(C37:2)/(C37:2 + C37:3)] and converted into temperature values using the global core top calibration of annual SST [Uk'37 = (0.033*SST) + 0.044], with a methodology uncertainty of ±0.5 ◦C. Tetra-unsaturated compound (C37:4) was considered as an indicator of lower temperature and low salinity waters and linked to polar and subpolar water influx into the Western Mediterranean.

This dataset was funded by a Geoscience PhD scholarship from University of Bari, Italy.