¹⁴ C Activity and Global Carbon Cycle Changes over the Past 50,000 Years

Abstract

A series of 14C measurements in Ocean Drilling Program cores from the tropical Cariaco Basin, which have been correlated to the annual-layer counted chronology for the Greenland Ice Sheet Project 2 (GISP2) ice core, provides a high-resolution calibration of the radiocarbon time scale back to 50,000 years before the present. Independent radiometric dating of events correlated to GISP2 suggests that the calibration is accurate. Reconstructed 14C activities varied substantially during the last glacial period, including sharp peaks synchronous with the Laschamp and Mono Lake geomagnetic field intensity minimal and cosmogenic nuclide peaks in ice cores and marine sediments. Simulations with a geochemical box model suggest that much of the variability can be explained by geomagnetically modulated changes in 14C production rate together with plausible changes in deep-ocean ventilation and the global carbon cycle during glaciation.

Antarctic link to deep flow speed variation during Marine Isotope Stage 3 in the western North Atlantic

“…This is supported by the simultaneous shifts off North Venezuela with those at Greenland argued by Hughen et al [36] on ultra-high resolution records. However the time scale for the ice core used here is not the current glaciological age scale, 'ss09sea' of Johnsen et al [37] but the newly proposed age scale for the Greenland ice cores (the SFCP04 timescale of Shackleton et al [38]) because this is better in the lower part of MIS 3 [39].…”

Feedback between deglaciation, volcanism, and atmospheric CO2

“…The average rate of decline in atmospheric Δ 14 C over the last 40 ka is − 15‰/ka, as indicated by the estimates of Hughen et al (2004). This rate of decrease appears more than twice as fast (− 33‰/ka) during the last deglaciation, 18-7 ka, and Broecker and Barker (2007) have called particular attention to the rapid decline between 17.5 and 14.5 ka (−70‰/ka), the source of which remains unknown.…”

The chronology of abrupt climate change and Late Upper Palaeolithic human adaptation in Europe

“…The Lateglacial part of both of these calibration datasets is, however, based largely on radiocarbon-dated marine samples from paired U-Th/ 14 C dated corals (Bard et al, 2004Burr et al, 2004) and laminated sediments from the Cariaco Basin (tropical Atlantic; Hughen et al, 2004), because dendrochronology records do not yet extend as a continuous series to much before the start of the Holocene. The Cariaco laminated marine sediment calibration extends through the period 14 700 to 12 400 cal.…”