Diatoms assemblage in Edisto Inlet during the last 120 years

The aim of the PNRA project HOLOFERNE was to study the Holocene sea ice variations at high-resolution. With this objective, some sediment cores and box cores were collected during the 2016/2017 Italian Antarctic Expedition in the Edisto Inlet (North-western Ross Sea, Antarctica). Here, the Holocene sediments are mainly laminated diatomaceous ooze, characterised by a high sedimentation rate; the sedimentary succession is therefore very expanded and allows recognising even temporally short environmental variations (Finocchiaro et al., 2005; Tesi et al., 2020). The study of recent sedimentary record in the Edisto Inlet offered also the possibility of coupling the micropaleontological and sedimentological data of the recent record. By means of 210Pb dating the expanded record was dated back to the last ca. 120 years indicating an average sedimentation rate of ca. 0.5 cmy-1. X-ray images and macroscopic observations highlighted the presence of two dominant facies: laminated sediments identified by the alternation of dark- and light-brown diatomaceous oozes dominated the bottom of the box core (from 58,5 to 50 cm) and from 32 cm to 6 cm. Previous studies indicate that the dark laminae are more terrigenous while the light laminae are more biogenic (Finocchiaro et al., 2005; Tesi et al., 2020). The second facies, present between 50 and 32 cm and in from 6 cm to the top, is characterised by denser, non-laminated dark brown sandy-silt sediments. Studies on diatoms show that the most important species in the laminated facies are Fragilariopsis curta and Corethronpennatum. The former, present along the entire studied sediments, indicates the constant presence of winter sea ice; the latter flourishes in stratified and ice-free surface water, indicating prolonged ice-free condition in the bay (e.g. Armand et al., 2005; Alley et al., 2018). The appearance of Proboscia spp. characterises the second facies, this diatoms species indicates the intrusion of oceanic water (e.g. Stickley et al., 2005; Campagne et al., 2016). This preliminary study indicates that the facies 1, that characterised the time period 1901-1918 and 1954- 2006, is deposited under seasonal sea ice with alternates periods during which the bay remains open for a prolonged time probably driven by global atmospheric anomalies (e.g. SAM, ENSO), whereas facies 2, that characterised the time interval 1918-1954 and 2006-2017 is probably related to oceanic water intrusion. Preliminary results based on micropaleontological and lithological analyses indicate changes in the environmental setting of the Edisto Inlet during the last 120 year. The next step of this study will be the comparison of the data with geochemical and biomarker analyses.