The pteropod species Heliconoides inflatus as an archive of late Pleistocene to Holocene environmental conditions on the Northwest Shelf of Australia

Abstract

There is growing interest in the use of pteropods as potential archives of past changes in ocean chemistry. However, pteropods have rarely been used in studies of millennial-scale sedimentary records, especially in shallow-marine environments. This study obtained core data for the last 16 kyr from the Northwest Shelf of Australia (NWS). Changes in the carbonate saturation state were assessed based on the carbon isotope ratios (δ13C) of shells and the Limacina dissolution index (LDX) measured on the planktonic pteropod species Heliconoides inflatus. In addition, the calcification depth of the pteropods was estimated based on oxygen isotope values (δ18O) of pteropod shells and seawater. Our findings indicate that H. inflatus calcifies at a depth of 95–140 m. This confirms that H. inflatus records a shallow-marine signal on the NWS. The δ13C values of the pteropods record a notable decrease in carbonate ion concentrations after 8.5 ka. This decrease is associated with the post-glacial onset of humid conditions on the NWS. The studied pteropod shells are pristine throughout the 16 kyr section and have low LDX values. Therefore, the LDX proxy appears to lack the sensitivity to be applicable in this highly supersaturated, shallow-marine environment. Until this study, proxies derived from H. inflatus have been exclusively utilized in open-marine settings. Our results indicate that the δ13C values of H. inflatus also represent a useful proxy for carbonate ion concentrations in shallow-marine environments.