Abstract
High-precision analysis using accelerator mass spectrometry (AMS) was performed upon known-age Holocene and modern, pre-bomb coral samples to generate a marine reservoir age correction value (ΔR) for the Houtman-Abrolhos Archipelago (28.7°S, 113.8°E) off the Western Australian coast. The mean ΔR value calculated for the Abrolhos Islands, 54 ± 30 yr (1 σ) agrees well with regional ΔR values for Leeuwin Current source waters (N-NW Australia-Java) of 60 ± 38 yr. The Abrolhos Islands show little variation with ΔR values of the northwestern and north Australian coast, underlining the dominance of the more equilibrated western Pacific-derived waters of the Leeuwin Current over local upwelling. The Abrolhos Islands ΔR values have remained stable over the last 2896 cal yr BP, being also attributed to the Leeuwin Current and the El Niño Southern Oscillation (ENSO) signal during this period. Expected future trends will be a strengthening of the teleconnection of the Abrolhos Islands to the climatic patterns of the equatorial Pacific via enhanced ENSO and global warming activity strengthening the Leeuwin Current. The possible effect upon the trend of future ΔR values may be to maintain similar values and an increase in stability. However, warming trends of global climate change may cause increasing dissimilarity of ΔR values due to the effects of increasing heat stress upon lower-latitude coral communities.
Highlights
Surface ocean radiocarbon levels are largely representative of the proportionate contributions of atmospheric CO2 and 14C-depleted subsurface water dissolved inorganic carbon (DIC), making them lower than atmospheric and terrestrial 14C
This paper presents a local marine reservoir correction for the southernmost coral reef complex in the Indian Ocean and evaluates this in context with R values calculated for the source waters of influential currents including local values in the broader region
Low 13C values present in these results may indicate exposure of sample material to freshwater (Southon et al 2002) and subsequent diagenetic effects and/or geological alteration—a common occurrence in emergent pavements and coral rubble ridges exposed above sea level (Nothdurft et al 2007; Nothdurft and Webb 2009)
Summary
Surface ocean radiocarbon levels are largely representative of the proportionate contributions of atmospheric CO2 and 14C-depleted subsurface water DIC, making them lower than atmospheric and terrestrial 14C. The marine reservoir age has regional variation referred to as the marine reservoir correction or R value and represents the local influence of ocean and atmospheric mixing due to currents, gyres, upwelling and climatic variations, which vary on seasonal to multidecadal scales (Stuiver and Reimer 1986; Stuiver et al 1986; Stuiver and Braziunas 1993; Reimer and Reimer 2001). To avoid potential errors when selecting R values (or material to sample) for calculating site or regional averages, one must consider beforehand criteria such as: the trophic level and particular feeding habits of sampled organisms; the physicochemical nature of the aquatic environment and habitat of collection; the possibility of diagenetic alteration; and the dating/calibration methods, calculations, and corrections used (Reimer and Reimer 2001; Scholz et al 2004; Ulm 2006; Nothdurft et al 2007; Nothdurft and Webb 2009)
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