A high-resolution record of atmospheric ¹⁴C based on Hulu Cave speleothem H82

The development of a calibration of atmospheric radiocarbon ({increment} ¹⁴C) is a significant scientific goal because it provides the means to link the numerous ¹⁴C dated paleoclimate records to a common timescale with absolutely dated records, and thereby improve our understanding the relationships between the carbon cycle and climate change. Currently, few calibration datasets that directly sample the atmospheric ¹⁴C reservoir are available beyond the end of the dendro-dated Holocene tree ring record at 12.6kyr BP (Before 1950 AD). In the absence of suitable true atmospheric records, ¹⁴C calibrations beyond this age limit are based largely on marine data, that are complicated by the marine reservoir effect, which may have varied over the glacial cycle. In this paper, we present a high-resolution record of U-Th series and ¹⁴C measurements from Hulu Cave speleothem H82, spanning 10.6-26.8kyr BP. Corrections for detrital ²³⁰Th are negligible, and the contribution of ¹⁴C-free geologic carbon to the speleothem calcite is small (5-6%) and is stable across major climate shifts. The time series provides a 16kyr record of atmospheric {increment} ¹⁴C as well as an updated age model for the existing Hulu Cave δ ¹⁸O record. The ¹⁴C data are in good overall agreement with existing marine and terrestrial ¹⁴C records, but comparisons with the Cariaco Basin marine {increment} ¹⁴C record through the deglacial interval reveal that the Cariaco reservoir age appears to have varied during parts of the Younger Dryas and Heinrich Stadial 1 cold events. This highlights the importance of developing extended high-resolution marine and terrestrial ¹⁴C records as a means of detecting changes in ocean circulation over the glacial cycle.