Work

Sclerochronology and oxygen isotope variations in modern Conomurex luhuanus shells: An archive for reconstructing palaeotemperature and shellfish gathering on the Great Barrier Reef, Australia

Year: 2024

Type: article

Abstract: The marine gastropod Conomurex luhuanus is a common component of Holocene archaeological shell deposits in the Western Indo-Pacific region. Oxygen isotope ratios recorded in shells of C. luhuanus from the Great Barrier Reef potentially provide high-resolution data on palaeoclimatic conditions and the exploitation of coastal marine resources. However, the application of this species as a palaeoclimate and seasonal foraging archive has yet to be investigated. We employ sclerochronology techniques to analyse oxygen isotope variations in modern, live-collected shells to evaluate the efficacy of this species in recording modern environmental factors, such as sea-surface temperature (SST). We collected live C. luhuanus during the cold season (August and September), in two separate years (2019 and 2023), from reef-flat intertidal zones. Shell growth increments were studied in section and high-resolution carbonate samples were collected from the lip portion and along the body whorl to test whether shell carbonate is deposited in oxygen isotopic equilibrium with seawater and to decipher the shell growth pattern of this species. Measured δ 18 O shell ranges between −0.2 and −1.8 ‰ (VPDB) in modern samples. Despite showing variability in growth rates, including a remarkable growth stop/slowdown during the cool season that is punctuated by a red zone with closely spaced growth increments, our findings reveal that C. luhuanus deposits its aragonite shells at (or close to) equilibrium with its surrounding environment. When sampled at high resolution (sub-seasonally), oxygen isotopes can be used to reconstruct the full annual SST range. The estimated SSTs closely match the range of instrumental SSTs measured in the study area, whilst the last deposited (edge) shell-calculated SST can be used to determine the season of animal death. This study shows that well-preserved shells of C. luhuanus can serve as excellent high-resolution palaeotemperature archives for the tropical reef-flat zone. This research underpins the use of this species in future research to determine human-environment interactions and reconstruction of palaeoclimate from archaeological and fossil samples in the Western Pacific Ocean. • Oxygen isotope values of Conomurex luhuanus record the full annual range of sea-surface temperatures. • Oxygen isotope edge values can be used to determine the season of shell collection. • A unique red zone at the shell edges showed shells collected during the cold seasons. • Oxygen isotope sclerochronology shows morphology cannot reliably indicate the age.

Source: Palaeogeography Palaeoclimatology Palaeoecology

DOI: 10.1016/j.palaeo.2024.112633