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The diversity, co-occurrence patterns, and assembly processes of microeukaryotes in Antarctic freshwater lakes are not well understood, despite its wide distribution and ecological importance. This study used Illumina high-throughput sequencing to explore five freshwater lakes' microeukaryotic communities on the Fildes Peninsula during three summer seasons. A total of 33 phyla were detected, with the phytoplankton occupying the highest percentage of sequences (accounting for up to 98 %). Meanwhile, the main dominant taxa were Chrysophyta, Chlorophyta, and Cryptophyta. Alpha diversity varied among lakes, with Changhu (CH), Kitec (KT) lake having higher values, and Yue Ya (YY) lake having the lowest value. There were significant differences in microeukaryotic communities between lakes, with spatial and temporal variation in the relative abundance of dominant taxa (P

High-resolution palaeo-climate records documenting sea ice extent over the Industrial Era is an important source of information to fully understand the emergence and magnitude of on-going changes and better predict future climate evolution of the Arctic Ocean. In this study, source-specific highly branched isoprenoids (HBIs) and phytosterols were measured in multicores retrieved from the Chukchi shelf region to document the history of seasonal sea ice in this area since the beginning of the Industrial Era. HBIs at the end of the 19th century (AD 1865-1875) point to a retreat of the sea ice edge and rapid return to colder conditions. After 1920-1930 AD, proxy records indicate a steady sea ice retreat reaching a maximum in the 1990s. Sympagic biomarker IP25 and HBI II were generally low during negative Arctic Oscillation (AO) (i.e., before 1920s) while higher values were found during positive AO, in particular in the 1990s. Our data also suggest a role of remote ocean circulation features.Among existing indices for semi-quantitative of sea ice concentration, the H-Print % sea ice index seems to generally perform less than so-called phytoplankton marker-IP25 (PIP25) index to estimate spring sea ice concentration (SpSIC). However, PBIP25-derived SpSIC better reproduce decadal scale variability and the long-term sea ice decline since the mid-20th century. Our results also highlight the lack of data for improving the PIP25 and their relationship to sea ice.