On the tuning of plateaus in atmospheric and oceanic <sup>14</sup>C records to derive calendar chronologies of deep-sea cores and records of <sup>14</sup>C marine reservoir age changes

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