Comment on cp-2022-39

Abstract

Multi-centennial records of past hydroclimate change are essential to understanding the resilience of aquatic ecosystems to climatic events, in addition to guiding conservation and restoration efforts. Such data are also crucial for examining the long-term controls over regional hydroclimate, and the inherent variability in extreme droughts and floods. Here, we present a 1750-year record of hydroclimate variability in The Coorong South Lagoon, South Australia, part of an internationally significant wetland system at the mouth of Australia’s largest river, the Murray River. Oxygen isotope ratios were measured in Arthritica helmsi bivalve shells preserved in sediments. The oxygen isotope record shows periods of persistent low and high moisture balance from ~500–1050 years and ~1300–1800, respectively, which is consistent with other hydroclimate reconstructions from the region. The range of oxygen isotope values in the sedimentary shells do not differ significantly from the estimated range of modern specimens from the present day lagoon. These data suggest that the restricted and highly evaporated modern day conditions are not markedly different to the pre-impacted state over the last 1750 years, although the absence of A. helmsi in the contemporary lagoon is likely a response to increased salinity, nutrient loading, and anoxia during the last century. These insights are potentially useful both in guiding management efforts in the currently degraded South Lagoon, as well as for understanding long term water resource availability in the region.