A 2000-year record of hydroclimate variability inferred from oxygen isotopes in lake sediments on Kangaroo Island (Karti/Karta), South Australia

Understanding past hydroclimate variability through high-resolution records is key to assessing the recurrence of extreme climatic events, including prolonged droughts and floods and for sustainable environmental and economic planning. This study presents a sub-decadal-scale hydroclimate reconstruction based on oxygen isotope analysis of ostracod valves, extracted from the sediments of Lashmars Lagoon, Kangaroo Island, South Australia. Sediment dating was based on 19 accelerator mass spectrometry (AMS) radiocarbon ( 14 C) dates from pollen and plant macrofossils, alongside lead-210 and plutonium concentration analyses. Spanning the last ∼2000 years, the oxygen isotopes record a series of multi-decadal wet and dry periods, manifest in the relative precipitation-evaporation balance of the lake. Of note, the record implies periods of prolonged declines in water balance, tentatively interpreted as droughts, from ∼525 to 575 CE, ∼770–790 CE, ∼825–850 CE, and ∼980–1020 CE. By contrast, the periods from ∼150 to 450 CE and ∼600–750 CE were relatively wet. Unfortunately, ostracods were absent within the sediments deposited between ∼1250 and 1590 CE and as a result, no hydroclimatic pattern could be determined for this time period. The period from ∼1590 to 1800 CE appears to have been notably dry, prior to an increase in effective moisture during the last 200 years. The Lashmars Lagoon record exhibits similar trends to a record from Blue Lake, Mt. Gambier, approx. 500 km to the southeast. However, these records contrast with other hydroclimate records from further east, implying a complex relationship with regional climate drivers. Comparison with instrumental period rainfall data, and reconstructed indices for major ocean–atmosphere interactions suggests that periods of increased moisture balance on Kangaroo Island were influenced by a combination of Southern Ocean and Indian Ocean derived climate drivers. • Lashmars Lagoon δ 18 O ostracod record reflects changes in the precipitation-evaporation balance. • Prolonged declines in water balance, from ∼525 to 575 CE, ∼770–790 CE, ∼825–850 CE, and ∼980–1020 CE. • By contrast, the periods from ∼150 to 450 CE and ∼600–750 CE were relatively wet. • Dry climate between ∼1590 and 1800 CE contrasts with other studies (wetter conditions) in SE Australia. • Dry periods align with southward shifts in the westerly winds inferred from S. American pollen records.