Holocene marine¹⁴C reservoir age variability: Evidence from²³⁰Th-dated corals in the South China Sea

Abstract

[1] The South China Sea (SCS) is well connected with the western Pacific and influenced by the East Asian monsoon. We have examined temporal variations in radiocarbon marine reservoir ages (R) and regional marine reservoir corrections (DR) of the SCS during the Holocene using paired measurements of AMS 14 C and TIMS 230Th on 20 pristine corals. The results show large fluctuations in both R and DR values over the past 7500 years (yrs) with two distinct plateaus during 7.5-5.6 and 3.5-2.5 thousand calendar years before present (cal ka BP). The respective weighted mean DR values of these plateaus are 151 ± 85 and 89 ± 59 yrs, which are significantly higher than its modern value of −23 ± 52 yrs. This suggests that using a constant modern DR value to calibrate 14 C dates of the SCS marine samples will introduce additional errors to the calibrated ages. Our results provide the first database for the Holocene R and DR values of the SCS for improved radiocarbon calibration of marine samples. We interpret the two DR plateaus as being related to two intervals with weakened El Niño -Southern Oscillation (ENSO) and intensified East Asian summer monsoon (EASM). This is because the 14 C content of the SCS surface water is controlled by both the 14 C concentration of the Pacific North Equatorial Current (NEC) which is in turn influenced by ENSO-induced upwelling along the Pacific equator and vertical upwelling within the SCS as a result of moisture transportation to midlatitude region to supply the EASM rainfall.

A Marine Reservoir Correction for the Houtman-Abrolhos Archipelago, East Indian Ocean, Western Australia

“…This apparent stability occurs during the rise in frequency of El Niño versus La Niña patterns up to the present time in the trend towards modern conditions seen in the western Pacific with more protracted and higher amplitude El Niño events (e.g. McGregor et al 2008;Yu et al 2010). Factors responsible for the stability of the R signal at the Abrolhos over the last 3000 yr also include minimal tectonic activity, oceanographic simplicity, and a smooth, mostly linear sea-level decline after the Holocene highstand (Collins et al 2006;Ulm 2006;Burr et al 2009;Petchey et al 2009).…”

Asian Monsoon Variability Recorded in Other Archives

“…Over the past four decades, a series of coral proxies have been developed and used to reconstruct paleorecords. Based on these coral proxy records, scientists commonly reconstruct SST (Charles et al 1997;Saenger et al 2009), sea surface salinity (SSS) and (or) precipitation (LeBec et al 2000;Iijima et al 2005; Mertz-Kraus 2009), ocean acidification (Pelejero et al 2005;Wei et al 2009;), sea level (Rohling et al 2008;Yu et al 2009;Liu et al 2011a), ocean mixing and upwelling and Suess effect (Druffel 1997;Yu et al 2010b), and river discharge histories (Isdale 1984;Peng et al 2002). These paleoclimatic records are important for the assessment of perturbations to natural climate variability by anthropogenic forcing, for climate predictability and for a better understanding of the dominant modes of the global climate system, e.g., the El Niño-Southern Oscillation (ENSO) phenomenon of tropical Pacific origin, the Asian and African monsoon, the Arctic Oscillation (AO)/North Atlantic Oscillation (NAO), the Pacific Decadal Oscillation (PDO), and the mechanisms of decadal climate variability.…”

Holocene sea level and climate variability on the Great Barrier Reef, Australia

“…Gagan et al, 1994, Switzer et al, 2010, fixed biological indicators (e.g. Gill, 1972, Lewis et al, 2008), and fossil coral reefs and microatolls (Chappell, 1983b, Chappell, 1983a, McLean and Woodroffe, 1990 generally support a mid-Holocene RSL highstand, although the exact magnitude and timing varies considerably with estimates ranging between +0.7m to +3.0m between ~7500 and 5500 yBP (Chappell, 1983b, Chappell, 1983a, Fleming et al, 1998, Yu and Zhao, 2010). Yet the most contentious issue is whether RSL regressed smoothly or oscillated to present levels since the mid-Holocene highstand (Chappell, 1983a.…”

“…Initial investigations of fossil microatolls relied on radiocarbon dating ( 14 C) to determine the age of these samples however, these were sometimes either uncalibrated, or inappropriately corrected for 14 C marine reservoir effects, or calibrated with the IntCal04 dataset using the Marine04 "global" marine calibration database (Hughen et al, 2004) that does not take into consideration the temporal variability of local/regional ΔR values which may fluctuate by 2008, Yu et al, 2010). More recently uranium-thorium (or U-series) dating has been adopted as a method for determining coral ages, with age errors significantly reduced compared to earlier 14 C techniques Th (Cheng et al, 2000, McCulloch and , Cobb et al, 2003.…”

“…Additionally, directly comparing or combining data from separate studies is problematic as: a) the reference datum and the absolute elevation of the indicators being used may differ; b) inconsistent methods between studies are used to establish elevation and age; c) large age errors may be associated with dating techniques [e.g. for 14 C dating, substantial age errors up to ± 500 years may be introduced if temporal changes in atmospheric production rates as well as global and regional marine 14 C reservoir effects are taken into consideration , Yu et al, 2010]; and d) the environmental context of the indicators is critically important but is often difficult to interpret and commonly not reported.…”