C05_08

Semi-millennial structure of the Suigetsu atmospheric ¹⁴C record

Sarnthein M¹, Grootes P¹

¹University of Kiel, Kiel, Germany

Centennial-to-millennial-scale fluctuations in atmospheric ¹⁴C concentration on time-scales from years to millennia have been documented by tree-rings for the last 15 kyr. Further back, terrestrial macrofossils from sediment cores of Lake Suigetsu extend this ¹⁴C record from ~10 ka to 50 ka. The significance of these features is under debate since the signal-to-noise ratio of the record is low. Yet, coherent semi-millennial-scale structures were identified by three different techniques, namely visual inspection, a first derivative of the ¹⁴C-age vs calendar age, and Bayesian spline inflections of ¹⁴C concentration vs calendar age. Accordingly, the semi-millennial features of the noisy Suigetsu ¹⁴C record may be objectively real. Being corroborated by the tree ring-based ¹⁴C master record ~10 to ~15 cal. ka, the features attain global significance and extend the fine-scale variability back to ~35 cal. ka. Carbonate-based ¹⁴C records from ocean sediments and speleothems appear far smoother. Together with data from Suigetsu and floating tree ring sections, these records form the backbone of the IntCal20 record that beyond 15 ka largely misses the Suigetsu fine structure. ¹⁴C decay reduces ¹⁴C-signal amplitudes over time, so Holocene ¹⁴C signals of solar modulation disappear below noise level during earlier times. Accordingly, most ¹⁴C structures visible >15 ka originally had larger signals, most likely, connected to climate, ocean-atmosphere CO₂ exchange, and carbon cycle. During this time, the Suigetsu ¹⁴C fine structure may thus give valuable information about these forcings. Also, it may serve for valuable global stratigraphic correlation of pertinent ¹⁴C records of oceanic plankton sediments.