Edisto Inlet as a sentinel for Late Holocene environmental changes over the Ross Sea: insights from foraminifera turnover events

Abstract. Identifying marine environmental changes is important to understand the processes that govern the Earth's climate system and its interacting components. Microfossil assemblages are one of the most used palaeoenvironmental tracers, with their community composition responding to changes in the physiochemical characteristics of the environment. In this context, foraminifera have been extensively used due to their preservation potential. However, little attention has been paid to the properties of the whole foraminiferal community that, in turn, can be used to depict a comprehensive view of the environment. In this study we focused on the laminated marine sediment core TR17-08 collected in Edisto Inlet (Ross Sea, Antarctica) and the turnover events that characterized the benthic foraminiferal fauna over the last 3.6 kyr. Using rate-of-change (RoC) analysis, three distinct turnover events were recognized having a long-term effect on the fauna: at 2.7–2.5, 1.2–1.0 and 0.7 kyr BP. At 2.7–2.5 kyr BP, Miliammina arenacea disappears and are substituted by different calcareous species, such as Epistominella exigua, Nonionella iridea and Stainforthia feylingi. Aligning with the micropalaeontological interpretations, changes in X-ray fluorescence (XRF) ratios (Zr / Rb; Ca / Ti and Br / Ti) were coeval with the interpretation derived from the RoC and the microfossils assemblage composition. Over this transition, a switch from multi-year landfast sea ice (3.6–2.7 kyr BP) to a seasonal sea-ice-dominated environment (2.5–1.2 kyr BP) was driven by a change in the water mass characteristics, increasing the mCDW (modified Circumpolar Deep Water) content inside the fjord as well as increase the duration of the summer ice-free period. Higher RoC values suggested the absence of a stable benthic foraminifera community under the frequent multi-year landfast sea-ice scenario, while the lowest RoC values during the seasonal sea-ice phase are present, especially within the 2–1.5 kyr BP interval, aligning with the macrofaunal response inside the inlet. Continental archives (penguin and elephant seals remains) along the Victoria Land coast recorded such a change in the sea-ice type during the Late Holocene. This study provides further evidence of a change in the sea-ice state in the Ross Sea after 2.7–2.5 kyr BP, thus supporting that this water mass intrusion onto the continental shelf was more prominent during the 2.5–1.2 kyr BP period, in accordance with the persistent summer positive mode of the Southern Annular Mode. Lastly, this study highlights that using ecological properties of the benthic foraminifera community can be a valuable source of information for high-resolution studies and can provide additional insights into the palaeoenvironmental interpretation and palaeoclimatic reconstruction that uses benthic foraminiferal species as environmental indicators.