Response of calcareous nannoplankton to climatic events in Mediterranean and Arctic climate hot-spots during the last 30,000 years

This thesis presents paleoclimatic and paleoceanographic reconstructions from selected sites of Mediterranean and Arctic areas, based on the analyses of coccolithophore fossil assemblage oscillations during the last 30,000 years. Coccolithophores are marine unicellular algae that produce calcium carbonate plates (coccoliths) which can be preserved within marine sediments in the fossil record as calcareous nannofossils at the end of their life cycle. Coccolithophores distribute within the photic zone of the water column, being highly sensitive to variations in environmental condition features (i.e. insolation rates, temperature, nutrient concentration). Therefore, their fossil record can provide relevant information regarding past climate conditions. Within this work, the calcareous nannofossil content was studied from five sediment cores. Three gravity cores were sampled in the Mediterranean Sea namely, the ND14Mbis core collected in the North Ionian Sea during the NEXTDATA 2014 research cruise, the NDT_09 core from the South Tyrrhenian Sea (Marsili Basin) and the NDT_22 from the Ligurian Sea both sampled during the NEXTDATA 2016 research cruise. Two cores from the Arctic area were collected from the western Spitsbergen margin on the Bellsund Drift crest. The dataset available includes the GS191-02BC box core, collected during the EUROFLEETS2 PREPARED research cruise in 2014, and the IRIDYA-02PC piston core sampled during the PRA-IRIDYA Arctic Expedition in 2021. This work takes advantage of some multidisciplinary projects, including the AMUSED (A Multidisciplinary Study of past global climatE changes from continental and marine archives in the MeDiterranean region), ERC-TIMED (REP-683237) and INGV project 2019 (Paleoclimate variability during Late Holocene in the Central Mediterranean and Balkans: terrestrial and marine archive comparison) as far as the Mediterranean cores and the IRIDYA (Integrated reconstruction of ice sheet dynamics during Late Quaternary Arctic climatic transitions) project which involved the Arctic sites. The high-resolution results obtained from calcareous nannofossil analyses were integrated with other proxies including Accelerated Mass Spectrometer radiocarbon datings, stable isotope data (18O, 13C) and bulk sediment composition obtained through X-Ray Fluorescence analysis. The multiproxy approach enabled a detailed reconstruction of the oceanographic and climatic variability in the study regions since the last Late Glacial period. In the Mediterranean sites, the oscillations of the calcareous nannofossil assemblages recorded the tripartition of the Heinrich Stadials 2 and 1, the development of the Meltwater pulse 1A – timing event during the Bølling-Allerød warm inter-stadial, and the transition towards stratified and oligotrophic conditions of the water column at the onset of the Holocene. In the Ionian Sea, lithological and ecological indications evidenced the deposition of the Sapropel 1 between 10 and 6.5 kiloannum Before Present (ka BP). In the Ligurian Sea, the dataset suggested the development of Organic Rich Layer 1-like conditions from the onset of the Bølling-Allerød interval (14.3 ka BP) until 8.8 ka BP. At the top of both records, higher indications of continental runoff highlighted the onset of cooler and wetter conditions linked to the development of the Little Ice Age. In the Arctic sites, low diversity of the calcareous nannofossil assemblage was generally observed. During the Late Pleistocene, the onset of the Hein-rich-like (2 and 1), Younger Dryas and Meltwater pulses (1A0 and 1A) abrupt events strongly influenced the overall assemblages of calcareous nannofossils. Despite the discontinuous trends, a coccolithophore-based logarithmic ratio developed through Principal Component Analysis highlighted oscillations of the Polar Front over the study area during the past c.a. 24 kiloyears (ky). Notably, during the Holocene a millennial-scale southward position of the Polar Front occurred between 9 and 6 ka BP. From 2 ka BP, the overall coccolithophore ecological reconstruction suggested conditions increasingly influenced by a strengthened Atlantic water advection, though cooler conditions were recorded between 1980 and 2000 Current Era. Overall, the paleoclimatic reconstructions carried out in the local frameworks were placed into a broader global context. Lastly, a comparative analysis of the timing of the climatic events recorded among lower and higher latitudes was also conducted, highlighting potential coincidences and delays of the recorded events.