Holocene climate and catchment change inferred from the geochemistry of Lashmars Lagoon, Kangaroo Island (Karti/Karta), southern Australia

• Published in: Palaeogeography, palaeoclimatology, palaeoecology Vol. 634; p. 111928
• Main Authors: Duxbury, Lucinda Cameron, Johns-Mead, Lluka Yohanni, Cadd, Haidee, Francke, Alexander, Löhr, Stefan C., Law, Wallace Boone, Armbrecht, Linda, Hall, Philip Anthony, Zawadzki, Atun, Jacobsen, Geraldine E., Gadd, Patricia S., Child, David P., Maxson, Charles, Thomas, Zoë Amber, Tyler, Jonathan James
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 15.01.2024
• Subjects: Hydroclimate; Itrax; Lake sediment; Weathering; X-Ray Diffraction (XRD); X-Ray Fluorescence (XRF); Weathering; Lake sediment; X-Ray Diffraction (XRD); Itrax; X-Ray Fluorescence (XRF); Hydroclimate
• ISSN: 0031-0182; 1872-616X
• DOI: 10.1016/j.palaeo.2023.111928

We present a continuous ∼7000-year sedimentary record from Lashmars Lagoon, Kangaroo Island (Karti/Karta), southern Australia, a region heavily impacted by drought and bushfires in recent decades. Records such as this are vital to contextualise current climatic and environmental shifts, particularly regarding the interplay between hydroclimate and fire-related disturbances in this ecologically sensitive area. We use high-resolution μX-ray fluorescence core scanning, complemented by bulk organic geochemistry and X-ray diffraction mineralogy of catchment soil and lake sediments to reconstruct past climate and catchment processes. Phases of elevated sediment organic matter content (inferred from high Br and total organic carbon) suggest increased lake freshening and productivity, and coincide with increased chemical weathering (inferred from high Al/K and kaolinite/illite and feldspars), likely reflecting the influence of wetter climates. Conversely, periods of high Ca correlate with biogenic carbonate inputs typical of brackish conditions, which we attribute to drier climates or a marine influence. From 7.0 ka, at the mid-Holocene sea level highstand, until 5.7 ka, we suspect Lashmars Lagoon was under virtually continuous influence from the sea. At 5.7 ka, we interpret the abrupt increase in sediment total organic carbon to reflect the severance of the connection to the sea, allowing organic material to accumulate. This, coupled with evidence of high inferred chemical weathering, suggests the climate was relatively wet at the time. After 5.4 ka, our data point to the establishment of drier conditions until the commencement of wetter climates again at 4.5 ka. From 2.5 ka, however, drier climates prevailed again until present. Notably, the climate changes recorded in the sedimentary sequence at Lashmars Lagoon seem to be linked to the strength of the Leeuwin Current, a current that brings warm tropical waters to southern Australia and demonstrates a teleconnection with the El Niño Southern Oscillation, and may well have been an important driver of rainfall on Kangaroo Island (Karti/Karta) over the past ∼7000 years. •Our record archives ∼7000 years of climate and catchment change in South Australia•Geochemical analyses are used to infer past hydroclimate and marine influence•We infer a distinctive wet period on Kangaroo Island (Karti) from 4.5 to 2.5 ka•We find evidence for a late Holocene dry period commencing at ∼2.5 ka•The strength of the Leeuwin Current may explain patterns of rainfall at our site