Redating the earliest evidence of the mid-Holocene relative sea-level highstand in Australia and implications for global sea-level rise

PLoS One. 2019 Jul 17;14(7):e0218430. doi: 10.1371/journal.pone.0218430. eCollection 2019.

Abstract

Reconstructing past sea levels can help constrain uncertainties surrounding the rate of change, magnitude, and impacts of the projected increase through the 21st century. Of significance is the mid-Holocene relative sea-level highstand in tectonically stable and remote (far-field) locations from major ice sheets. The east coast of Australia provides an excellent arena in which to investigate changes in relative sea level during the Holocene. Considerable debate surrounds both the peak level and timing of the east coast highstand. The southeast Australian site of Bulli Beach provides the earliest evidence for the establishment of a highstand in the Southern Hemisphere, although questions have been raised about the pretreatment and type of material that was radiocarbon dated for the development of the regional sea-level curve. Here we undertake a detailed morpho- and chronostratigraphic study at Bulli Beach to better constrain the timing of the Holocene highstand in eastern Australia. In contrast to wood and charcoal samples that may provide anomalously old ages, probably due to inbuilt age, we find that short-lived terrestrial plant macrofossils provide a robust chronological framework. Bayesian modelling of the ages provide improved dating of the earliest evidence for a highstand at 6,880±50 cal BP, approximately a millennium later than previously reported. Our results from Bulli now closely align with other sea-level reconstructions along the east coast of Australia, and provide evidence for a synchronous relative sea-level highstand that extends from the Gulf of Carpentaria to Tasmania. Our refined age appears to be coincident with major ice mass loss from Northern Hemisphere and Antarctic ice sheets, supporting previous studies that suggest these may have played a role in the relative sea-level highstand. Further work is now needed to investigate the environmental impacts of regional sea levels, and refine the timing of the subsequent sea-level fall in the Holocene and its influence on coastal evolution.

Publication types

  • Historical Article
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antarctic Regions
  • Australia
  • Carbon Isotopes / analysis
  • Fossils*
  • History, Ancient
  • Ice Cover*
  • Sea Level Rise / history*

Substances

  • Carbon Isotopes

Grants and funding

This work was supported by grants from the Australian Research Council (project numbers FL100100195, CE170100015, and FT120100656). Alan Williams is employed by Extent Heritage Pty Ltd (AHMS), as Associate Director, Aboriginal Heritage Team Leader. However, the works submitted to PLOS One are the product of Alan’s academic research, and have no relationship to, or influence from, AHMS. Alan undertakes this research in his own time, and has received no financial, or other, support in the development of this works from AHMS. They similarly have had no involvement in the development, submission or review of the manuscript. Extent Heritage Pty Ltd (AHMS) provided support in the form of salary for author AW, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific role of this author is articulated in the ‘author contributions’ section.