CENTENNIAL TO MILLENNIAL-SCALE FLUCTUATIONS OF THE LAKE SUIGETSU ATMOSPHERIC 14 C RECORD REPRESENT AUTHENTIC 14 C FEATURES OVER LAST GLACIAL-TO-DEGLACIAL TIMES

• Published in: Radiocarbon 2023-07, p.1-12
• Main Authors: Sarnthein, Michael, Grootes, Pieter M, Mudelsee, Manfred
• Format: Article
• Language: English
• ISSN: 0033-8222; 1945-5755
• DOI: 10.1017/RDC.2023.47

Short-term fluctuations in atmospheric radiocarbon ( 14 C) concentration mark the tree-ring record for the last ∼15 kyr. Terrestrial macrofossils from sediment cores of Lake Suigetsu, Japan, extend this record of fluctuations back to >35 cal ka BP. Their significance, however, is under debate since the signal-to-noise ratio of the Suigetsu record is low and progressively decreases with increasing age. Coherent semi-millennial-scale structures of the Suigetsu 14 C record have nevertheless been identified by three different techniques, namely visual inspection, analyses of the first derivative of 14 C vs. calendar age, and Bayesian spline inflections of 14 C concentration vs. calendar age, and hence appear objectively real. These 14 C fluctuations correlate closely with those of the tree-ring-based 14 C master record ∼10–14 cal ka. Thus, Suigetsu fine structures attain global significance and may properly reflect atmospheric 14 C variability back to ∼35 cal ka. Carbonate-based 14 C records from speleothems and ocean sediments are far smoother and form, together with Suigetsu and other data, the backbone of the IntCal20 record >14 cal ka that largely lacks the Suigetsu fine structure. 14 C decay reduces 14 C-signal amplitudes over time, so Holocene-style 14 C signals of solar modulation disappear in the noise beyond ∼10 cal ka. The remaining older 14 C fine structures had larger forcings, most likely linked to climate and carbon cycle, especially ocean-atmosphere CO 2 exchange, and thus contain valuable information about these factors. They may also provide global stratigraphic tie points to correlate 14 C records of oceanic plankton sediments and climate signals independent of problems with local 14 C reservoir effects.