Abstract

The Ross Sea polynya is one of the most productive regions of the Southern Ocean sustaining a rich marine fauna. We analyzed total amounts of diatoms, opal, organic carbon, nitrogen and magnetic susceptibility in two cores recovered in 2021 from the Ross Sea during RV ARAON Expedition ANA11, in order to investigate past variations of marine primary productivity in the Ross Sea polynya. Two short cores – core 54 (length: 35 cm) located in the northern part of the polynya and core 59 (length: 45 cm) located at a coastal site – show sedimentation rates ranging between 0.07 and 0.08 cm yr-1, estimated by the 210Pb dating technique. Core 54 showed a good preservation of diatoms than Core 59, which was characterized by higher amounts of diatom remains below 20–35 cm with high values of magnetic susceptibility. Core 59 may infer more terrigenous inputs and fragmentation by erosion. We reconstructed sea-ice condition based on the ratios of Eucampia antarctica (terminal versus intercalary valves), Fragilariopsis curta/F. cylindrus, F. kerguelensis, where high values of these ratios are known to indicate stronger marine sea-ice condition. We speculate that core 54 was influenced by stronger seaice condition between 1600–1850 AD, possibly related to the Little Ice Age (LIA) – a regionally colder period followed by abrupt modern-era warming since 1850 AD. The observed higher diatom productivity during the cold LIA periods is the likelihood of more efficient polynya condition favoring diatom growth, tentatively associated with intensified katabatic winds and Amundsen Sea low (ASL). Comprehending such linkages requires further in-depth interpretations of physical-biological coupling processes in the Ross Sea polynya environments, as well as sufficient age control.