Late-Holocene hydrological cycling in the maritime Ross Sea in response to the El Niño-Southern Oscillation

Abstract

Hydrological dynamics in Antarctic coastal ice-free regions are an important part of climate variability that is crucial for terrestrial ecosystems in Antarctica. However, there is no geological record of hydrological changes in lakes in the Ross Sea region. Here we used analyses of surface lake sediment and living microbial mats to show that photoautotrophic organism-derived lipid hydrogen isotopes reflected the δ²H values of lake water (δ²H_water). We present a new record of δ²H_lipids from two lacustrine sediment cores collected from Inexpressible Island in the western Ross Sea to reconstruct δ²H_water values over the past 3000 years. The reconstructed δ²H_water values range from −103 to −35 ‰, and are significantly higher than δ²H_water values of precipitation (snow). On the basis of our modern observations, the slope of the linear regression between δ²H and δ¹⁸O in lake water is lower than both global and Antarctic meteoric water lines, suggesting strong lake evaporation at our study region. Our sensitivity modeling experiment showed that the strength of evaporation is closely linked with summer air temperature. Furthermore, δ²H_lipids showed similar patterns in variations with regional air temperature recorded by ice cores in the western Ross Sea, indicating that lake surface evaporation is mainly driven by air temperature. Generalized Additive Models (GAMs) and Locally Weighted Scatterplot Smoothing (LOESS) on δ²H_lipids and published climate records in the western Ross Sea indicate that higher δ²H_C16 values are corresponding to a relatively warmer climate at 2550-1350 cal yr BP (Phase 2) while lower values (corresponding to a relatively colder climate) are found at 3000-2550 cal yr BP (Phase 1) and 1350-0 cal yr BP (Phase 3). Higher lake evaporation was caused by the incursion of warm and moist air into the western Ross Sea as mediated by anomalous high-pressure over the Amundsen Sea that often occurs during the El Niño-dominant events. Our study supports the notion that large-scale atmospheric variability controlled by the tropical Pacific plays a major role in hydrological changes in the high latitude regions of Antarctica.