Mechanisms driving formation and preservation of the laminated sediments of Edisto Inlet, western Ross Sea (Antarctica): the sub-seasonal variability of particle composition and fluxes.

Laminated diatomaceous deposits have been documented in the Edisto Inlet (western Ross Sea). The sediments show alternating dark, rich in IPSO25 biomarker, indicative of fast ice, and light laminae, dominated by Corethron pennatum diatoms. Based on these observations, the dynamics of fast ice was reconstructed over the last 2.6 ka for the western Ross Sea. However, the lack of direct observations introduces uncertainty into the paleoclimatic and paleoceanographic interpretation of these laminated sediments. The project LASAGNE (Laminated Sediments in the Magnificent Edisto Inlet, Victoria Land: What processes control their deposition and preservation?), funded by the Italian Program of Antarctic Research (PNRA), proposed a multidisciplinary study that integrates the characteristics of fast ice, water column, and surface sediment, aiming to obtain information on the factors influencing formation and preservation of laminated sediment in Edisto Inlet. The project integrates also biological data (phytoplankton, microzooplankton and foraminifera) collected in situ, and time series of satellite images of sea ice. The main goal was to provide new insights into the sub-seasonal formation of laminated sediments, offering a backbone for the interpretation of paleoclimatic sedimentary archives. An oceanographic mooring was deployed between March 2022 and February 2023, to investigate the mechanisms driving the formation of sediment laminations. The purpose was to test whether the deposition of dark sediments (rich in sympagic diatoms such as Berkeleya adeliensis) occurs in late spring-early summer, while light sediment (mainly composed of Corethron pennatum) represents sedimentation in late summer early autumn. The mooring data reveals that sediment lamination arises from the significant seasonal variability of particle fluxes and composition. Additionally, the thermohaline properties and dynamics of water masses in Edisto Inlet exhibit pronounced seasonal changes. Similarly, diatom assemblages and sea ice cover also undergo significant seasonal variations. Taken together, these environmental factors contribute to the formation of a pair of laminae (dark in late spring, light in late summer) during years characterized by the retreat of sea ice and the presence of open water conditions in late summer. The preservation of lamination is subsequently guaranteed by a high sedimentation rate, limited oxygen penetration, and reduced biological mixing.