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. We assess the methodology of the so-called 14C plateau tuning (PT) technique used to date marine sediment records and determine 14C marine reservoir ages (MRAs) as recently reviewed by Sarnthein et al. (2020). The main identified problems are linked to the assumption of constant MRAduring 14C age plateaus; the lack of consideration of foraminiferaabundance changes coupled to bioturbation that can create spurious plateausin marine sediments; the assumption that plateaus have the same shapes anddurations in atmospheric and oceanic records; the implication thatatmospheric 14C / 12C peaked instantaneously from one plateau to the next; that the 14C plateaus represent 82 % of the total time spent between 14 000 and 29 000 cal yr BP, whereas during the remaining 18 % ofthe time, the radiocarbon clock was running almost 5 times faster than theradioactive decay; that the sparsity, combined with the level of analyticaluncertainties and additional noise, in both atmospheric and marine data donot currently allow one to reliably or robustly identify plateaus (shouldthey exist) beyond 15 000 cal yr BP; and that the determination andidentification of plateaus in the deep-sea cores is reliant upon significantchanges in sedimentation rate within those marine sediments which are, apriori, unknown and are not verified with an independent method. The concerns we raise are supported and strengthened with carbon cyclebox model experiments and statistical simulations of pseudo-atmospheric andpseudo-marine records, allowing us to question the ability to identify andtune 14C age plateaus in the context of noisy and sparse data.

climate of the past

On the tuning of plateaus in atmospheric and oceanic &amp;lt;sup&amp;gt;14&amp;lt;/sup&amp;gt;C records to derive calendar chronologies of deep-sea cores and records of &amp;lt;sup&amp;gt;14&amp;lt;/sup&amp;gt;C marine reservoir age changes