Water masses oscillations west off Svalbard during the past 150 years: micropaleontological evidences.

Micropalaeontological proxies are highly sensitive to environmental changes and are useful tools to investigate the paleo-features (i.e., temperature, sea ice coverage, nutrient supply, etc.) of Arctic environments. The box core GS191-02BC was collected at 1650 m of water depth on the Bellsund Drift crest, on the western slope of Svalbard (Lucchi et al., 2014). It consists of 25 cm of bioturbated sediments, which were analysed for calcareous nannofossils, benthic and planktic foraminifera and diatoms associations. The record covers the last 150 years, from 1866 CE to 2014 CE (210Pb ages). The H/P ratio (Emiliania huxleyi/Coccolithus pelagicus) of calcareous nannofossil was used to investigate the fluctuations between the warm, salty Atlantic Waters (AWs) and the cool, fresher Arctic Waters (ArWs; Carbonara et al., 2016). A ratio >1 was related to predominant AWs influence, while the <1 ratio was referred to the ArWs influence (Andruleit and Baumann, 1998). This proxy was coupled with distributional variations of total nannofossil and diatom abundances using “Sea Ice Margin” (Actinocyclus curvatulus and Fragilariopsis oceanica) and “Cold Water Group” (Thalassiosira antarctica, Rhizosolenia hebetata and Bacterosira bathyomphala) diatom species and variations in planktic and benthic foraminifera associations. The ratio of the benthic foraminifera Epistomenella exigua/Oridorsalis tener was used as a food availability index. Three principal water masses fluctuations were identified: i) from 1905 CE to 1980 CE there is a shift from Arctic to Atlantic waters affinity, ii) from1980 CE to 2005 CE, the AWs dominated conditions shift to a cooler environment (ArWs dominated), in which diatoms bloom while calcareous nannofossil abundance decreases, iii) from 2005 to 2014, there is a return to warmer waters conditions. These micropalaeontological evidences highlight that over the last 150 years, the investigated area went through intense and fast changes. In this framework, sedimentological and geochemical considerations will be furtherly made to have a complete overview of the reported events.