Collaborative Research: The Ocean-Atmosphere Carbon Cycle and Climate Change: Constraints from Radiocarbon and Climate History

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The PIs will obtain and interpret cave speleothem 14C/12C records and high-resolution climate records from the same samples from Crevice Cave, Missouri and Hulu Cave, Nanjing, China. The records will be dated independently and precisely with high precision 230Th and 231Pa techniques enabling determination of initial 14C/12C values and establishment of an absolute chronology. The PIs will use the records to (1) reconstruct atmospheric 14C/12C for the whole radiocarbon timescale (the last 45 ky) and (2) compare those records directly to the climate records from the same samples. The former will place constraints on the operation of the ocean-atmosphere carbon cycle since glacial times. The latter will characterize the interplay between changes in the carbon cycle and climate change. Both have implications for the understanding of the current and future carbon cycle. Recent work indicates extremely high and variable atmospheric 14C/12C for much of the interval between 44 and 34 Ka. The radiocarbon values are generally well above values that can be achieved with the modern carbon cycle, even if terrestrial and solar magnetic fields were negligible. These data therefore require significant differences between the modern and glacial carbon cycles, as well as large temporal changes in the glacial carbon cycle. The far-reaching implications of this work require replication, ideally at sites other than the Bahamas, the site where this evidence was collected.