Radiocarbon surface ocean reservoir ages over the past 6,000 years from Porites microatolls, Christmas (Kiritimati) Island, central Pacific Ocean

Fink, D; Carilli, JE; McGregor, HV; Woodroffe, CD; Zhao, JX; Fallon, SJ

Radiocarbon surface ocean reservoir ages over the past 6,000 years from Porites microatolls, Christmas (Kiritimati) Island, central Pacific Ocean

Date

2012-08-05

Authors

Publisher

Australian Geosciences Council

Abstract

We present radiocarbon reservoir (ΔR) values over the past 5,000 years based on high-precision paired U-series and AMS 14C in modern and fossil Porites coral micro-atolls from Christmas Island (2N, 157W). The data set (n∼25) allows temporal reconstruction of ΔR with ∼250 year spacing. Christmas Island lies within the Equatorial Counter Current and the NINO3.4 region with a climate frequently punctuated by higher precipitation and warmer SSTs during El-Nino. Along its coastal perimeter, and throughout the internal network of tidal flats and lagoons, which in the late Holocene were flourishing reefal environments, fossil and modern microatolls abound. Microatolls are large discoid colonies with horizontal radial growth axes constrained in upwards vertical growth by spring tide low-water level. Consequently, a single microatoll can extend to ∼9 m in diameter representing an exceptional ∼300 years of continuous growth. Sr/Ca and δ18O in modern microatolls faithfully replicate instrumental climate records (SSTs, rainfall). Results from numerous fossil cores (1500–5500 years BP) shows distinct variability in ENSO variance both in frequency and amplitude domains compared to modern microatolls. These fossil populations are used to generate a temporal pattern of ΔR variability. Strict criteria were followed with respect to secondary calcite (via quantitative XRD), unaltered microstructure (via thin sections) and ensuring splits of identical coral chips for dual U-series and AMS 14C. Preliminary results show a ΔR decrease at about 2000 BP. Further analyses of correlations of ΔR deviations from the long term average with changes in regional ocean surface currents and in paleo-ENSO variance are in progress.

Keywords

Carbon 14, Seas, Islands, Pacific Ocean, Fossils, Corals, Data, Coastal waters, Climates, Environment, Microstructure, Southern Oscillation

Citation

Fink, D., Carilli, J., McGregor, H, V., Woodroffe, C., Zhao, J.-x. & Fallon, S. (2012). Radiocarbon surface ocean reservoir ages over the past 6,000 years from Porites microatolls, Christmas (Kiritimati) Island, central Pacific Ocean. Paper presented to the 34th International Geological Congress 2012, "Unearthing our Past and Future - Resourcing Tomorrow", Brisbane, Australia, 5-10 August 2012. (pp. 3497).