Holocene environmental change recorded in shallow coastal lakes of the Coorong region, southeastern Australia

Abstract

Elemental (TOC, C/N), isotopic (d13Corg) and molecular (13C-NMR) analysis of sapropels within the Holocene carbonate mudstone successions of three coastal lakes of the Coorong region, South Australia, indicates that they are composed primarily of aquatic organic matter derived from algae and other photoautotrophs that utilised HCO3 - as their dissolved inorganic carbon source. Isotopic analysis of sedimentary carbonate (d13 Cinorg, d18O) suggests that this lacustrine organic matter was subject to post-depositional methanogenesis, that lake water salinity has increased during the late Holocene and that sapropel deposition in the southernmost two of these lakes was not restricted to times of wetter environmental conditions.