Marine20—The Marine Radiocarbon Age Calibration Curve (0–55,000 cal BP)

Abstract

The concentration of radiocarbon (14C) differs between ocean and atmosphere. Radiocarbon determinations from samples which obtained their 14C in the marine environment therefore need a marine-specific calibration curve and cannot be calibrated directly against the atmospheric-based IntCal20 curve. This paper presents Marine20, an update to the internationally agreed marine radiocarbon age calibration curve that provides a non-polar global-average marine record of radiocarbon from 0–55 cal kBP and serves as a baseline for regional oceanic variation. Marine20 is intended for calibration of marine radiocarbon samples from non-polar regions; it is not suitable for calibration in polar regions where variability in sea ice extent, ocean upwelling and air-sea gas exchange may have caused larger changes to concentrations of marine radiocarbon. The Marine20 curve is based upon 500 simulations with an ocean/atmosphere/biosphere box-model of the global carbon cycle that has been forced by posterior realizations of our Northern Hemispheric atmospheric IntCal20 14C curve and reconstructed changes in CO2 obtained from ice core data. These forcings enable us to incorporate carbon cycle dynamics and temporal changes in the atmospheric 14C level. The box-model simulations of the global-average marine radiocarbon reservoir age are similar to those of a more complex three-dimensional ocean general circulation model. However, simplicity and speed of the box model allow us to use a Monte Carlo approach to rigorously propagate the uncertainty in both the historic concentration of atmospheric 14C and other key parameters of the carbon cycle through to our final Marine20 calibration curve. This robust propagation of uncertainty is fundamental to providing reliable precision for the radiocarbon age calibration of marine based samples. We make a first step towards deconvolving the contributions of different processes to the total uncertainty; discuss the main differences of Marine20 from the previous age calibration curve Marine13; and identify the limitations of our approach together with key areas for further work. The updated values for ΔR, the regional marine radiocarbon reservoir age corrections required to calibrate against Marine20, can be found at the data base http://calib.org/marine/.

Holocene sea level and environmental change at the southern Cape – an 8.5 kyr multi-proxy paleoclimate record from lake Voёlvlei, South Africa

“…2). The distinct overlap of a bulk and the macro-particle age and bulk and charcoal ages confirm the reservoir correction and application of the Marine20 calibration curve (Heaton et al, 2020) for bulk samples in Unit A. The only exception are the bulk 14 C-ages at 11.19 and 5.66 m sediment depth, which are too young for their stratigraphic position.…”

“…For the final age-depth modelling, all aforementioned results were used. Bulk organic and n-alkane 14 C-ages from the terrestrial part of the sediment core were calibrated with the SHcal20 data calibration curve (Hogg et al, 2020), whereas 14 C-ages from the marine part of the record were calibrated with the Marine20 calibration curve (Heaton et al, 2020) and additionally corrected for a marine reservoir effect using a ΔR of 134 ± 38 14 C yrs as previously reported by Wündsch et al (2016b) ( Table 1). For the compound-class n-alkane samples, the SHCal20 calibration curve (Hogg et al, 2020) was applied due to a predominance of terrestrial synthesized long-chain n-alkanes (C29, C31, C33) in the samples (cf., section 4.3; Table 1).…”

Cosmogenic isotope measurements from recently deglaciated bedrock as a new tool to decipher changes in Greenland Ice Sheet size

“…Hard-water effects on the 14 C ages, which could make age determinations erroneously old, are unlikely in our study area because lake catchments are dominated by Archean gneiss, and the study lakes are all well above local marine limits. All new radiocarbon ages are calibrated using CALIB 8.2 and the INTCAL20 dataset, and previously reported radiocarbon ages are re-calibrated in the same manner using the INTCAL20 and MARINE20 datasets (Stuiver et al, 2020;Heaton et al, 2020; Table S1; Table S7).…”

The IntCal20 Approach to Radiocarbon Calibration Curve Construction: A New Methodology Using Bayesian Splines and Errors-in-Variables

“…Including such covariance is likely to require modifications to current calibration software. These realizations, with their covariance information, have however already been used in the creation of Marine20 (Heaton et al 2020 in this issue) to rigorously propagate our atmospheric uncertainties through to the marine calibration curve.…”

“…Finally, we discuss potential future work in Section 6 along with areas we have identified for further improvement for the next IntCal iteration. Note that the statistical approaches to the creation of SHCal20 (Hogg et al 2020 in this issue) and Marine20 (Heaton et al 2020 in this issue) are presented within those papers and not discussed in detail here.…”