# Comment on “14C plateau tuning – A misleading approach or trendsetting tool for marine paleoclimate studies?” by Michael Sarnthein and Pieter M. Grootes

Edouard Bard, Timothy J. Heaton

► To cite this version:

Edouard Bard, Timothy J. Heaton. Comment on “14C plateau tuning – A misleading approach or trendsetting tool for marine paleoclimate studies?” by Michael Sarnthein and Pieter M. Grootes. Climate of the Past, 2022, 10.5194/cp-2021-173-CC1. hal-04924693

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¹⁴C plateau tuning – A misleading approach or trendsetting tool for
marine paleoclimate studies?

Michael Sarnthein¹ and Pieter M. Grootes²)

1) Institute of Geosciences, University of Kiel, Olshausenstr. 40, 24098 Kiel, Germany,
*michael.sarnthein@ifg.uni-kiel.de*

2) Institute of Ecosystem Research, University of Kiel, Olshausenstr. 40, 24098 Kiel,
Germany, *pgrootes@ecology.uni-kiel.de*

11 *Corresponding author*:

Michael Sarnthein, *michael.sarnthein@ifg.uni-kiel.de*,

15 ABSTRACT

16 On the basis of minor time scale adjustments including the synchronization on IntCal20 the
17 Suigetsu-based atmospheric ¹⁴C plateau structures are shown to be authentic. Their global
18 significance is demonstrated by the coherence with the tree ring record 10 to 15 cal. ka and by
19 coherent features in the ¹⁴C record of Hulu Cave back to 35 cal. ka. The suite of atmospheric
20 structures can be recognized in high-resolution ocean sediment records independent of various
21 processes leading to partial distortion of a sediment record. This provides a unique tool for
22 global stratigraphic correlation and paleoceanographic studies as shown by supplementary
23 figures and tables from 19 cores obtained from key locations in the world ocean.
24
25

24

25
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26 INTRODUCTION

27 Sarnthein et al. (2020) gave a synthesis of the growing evidence of the value of ¹⁴C plateau

28 tuning (PT) for the chronostratigraphic correlation of last glacial-to-deglacial paleoclimate events

29 in marine proxy records to each other, to climate events recorded in ice cores, and to

30 speleothems, moreover, to well-dated terrestrial climate records. Bard and Heaton (2021) (B&H)

31 published a follow-up paper that fundamentally denunciates concept and techniques of PT. The

32 concerns of B&H were based on perceived problems with the atmospheric plateau structures we

33 observe for the (Suigetsu-based) radiocarbon record and came from various paleoclimatic,

34 paleoceanographic, sedimentological, and statistical perspectives. Their critique provided a rare

35 opportunity to discuss and clarify the (perceived) flaws and weaknesses and strengths of PT. In

36 CP Discussions (Grootes and Sarnthein, 2021; Sarnthein and Grootes, 2021) we rejected the

37 critique as it was largely based on:

38 1) A fundamental misunderstanding of plateau identification: This is not based on the

39 identification of any single plateau but rather on the best pattern match of a complete suite of

40 plateaus; much like correlating ice or sediment core-based δ¹⁸O records.

41 2) B&H's focus on the physics of surface ocean ¹⁴C fluctuations, using a 1998 box-model, instead

42 of those of the ¹⁴C difference between atmosphere and surface ocean (MRA).

43 The B&H response in CP Discussions and their paper, largely ignore this reasoning as well as our

44 detailed answers to their 17 points of critique, stick to an incorrect perception of the basic

45 assumptions used for PT and avoid a real discussion.

46

47 We here present evidence for the authenticity of Suigetsu ¹⁴C plateaus as atmospheric ¹⁴C

48 structures that can be observed worldwide. Also, we show that analogous ¹⁴C structures in

49 ocean planktic sediment records are not merely a result of various sedimentation processes such
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<figure><img src="image_6.png" /></figure>

50 as bioturbational mixing. Finally, to foster future use and discussion of PT, we add as

51 supplementary material a comprehensive set of tables and figures for all 19 ocean sediment

52 records published so far on the new IntCal20 time scale.

53

54 **Atmospheric <sup>14</sup>C plateaus and jumps are reproduced by diverse statistical approaches**

55 We here present our Suigetsu-based plateau and jump structures, plotted in the Δ¹⁴C domain,

56 together with the atmospheric Δ¹⁴C wiggles 14–30 cal. ka as defined by a Bayesian spline over

57 the total of Suigetsu ¹⁴C ages (shown with 1σ by B&H 2021, Fig. 3a), now all plotted vs. IntCal20

58 ages (Bronk Ramsey et al., 2020) (Fig. 1 and Table 1). Moreover, after a careful check of the

59 position of plateau boundaries, we slightly revised three of them, (i) a slight upward shift of the

60 base of plateau 7, (ii) omission of the boundary between plateaus 6b and 6a, and (iii) a minimal

61 backward shift of the 5a-b plateau boundary by a single age date. To our surprise and

62 satisfaction, the unification of time scales used plus these minimal changes resulted in a basic

63 upgrade and substantial overlap of the atmospheric ¹⁴C structures revealed by the two

64 independent methods, the Bayesian spline and the visual inspection of ¹⁴C plateaus and jumps

65 back to 27 cal. ka. This agreement on authentic structures of atmospheric ¹⁴C may be regarded

66 as a corner stone crucial to justify PT as legitimate tool for stratigraphic correlation.

67

68 Prior to 27 cal ka, however, the raw Suigetsu ¹⁴C ages for plateaus 10b and 11, generated by

69 different laboratories, are diverging by up to 1000 yr at analytical 1σ uncertainties of ~150 to

70 <400 years (Bronk Ramsey et al., 2012), a discrepancy that our plateau definitions tried to bridge

71 by weighted average values, the Bayesian spline, however, has valued differently.

72
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73 The plateau structures of the Suigetsu atmospheric ¹⁴C record are clearly paired with IntCal20 tree ring- and floating tree ring-based ¹⁴C structures for the interval 10 - ~15 cal. ka (Fig. 2; suppl.

74 by Adolphi et al., 2017). Thus Fig. 2 can positively answer the question, raised by B&H (2021), whether the ¹⁴C plateau structures defined by Sarnthein et al. (2020) in the Lake Suigetsu record present a suite of authentic features of atmospheric ¹⁴C, that indeed can be globally reproduced.

75
76
77 For comparison, the smoothed character of the IntCal20 curve beyond 14 ka is due to a change in the available calibration data rather than to a fundamental change in the atmosphere (Reimer et al., 2020; B&H, 2021). This is supported by a comparison of Bayesian spline compilations of the Suigetsu (green) and the Hulu speleothem (magenta) datasets over the period 20-30 cal. ka, with Hulu deconvoluted using a MatLab algorithm (Fig. 3 from Bronk Ramsey et al., 2020).

83
84
85
86
87
88
89
90
91 Consequently, we regard it legitimate to extrapolate our interpretation of fine structures in the Suigetsu ¹⁴C record further back, at least up to 27 cal. ka (Fig. 4). That is, we may assume that prior to 15 cal. ka the continuing ¹⁴C fine structures of the admittedly somewhat noisy Suigetsu record of atmospheric ¹⁴C jumps and plateaus come close to reality per analogy with the match with the tree ring record 10 to ~15 cal. ka. Our reasoning is supported independently by various Suigetsu plateaus between 15 and 30 cal. ka and structures further back (e.g., parts of plateaus number 2b, 4, 6, 8, 9; Fig. 4) that are largely reproduced also by a Bayesian spline of analogous ¹⁴C plateau structures in the deconvoluted U/Th-dated ¹⁴C record based on Hulu Cave data (Fig.

92 3; from Bronk Ramsey et al., 2020). Altogether, the Suigetsu record of atmospheric ¹⁴C wiggles provides over its full length a suitable target for global correlation. This is more authentic than the better defined ¹⁴C trend of the Hulu speleothem and the IntCal20 records that, admittedly, have been smoothed.

96
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97 Objections against the use of this Suigetsu ¹⁴C record instead of IntCal20 ¹⁴C ages as basis for the definition of atmospheric ¹⁴C plateaus and jumps, as formulated by B&H 2021, ignore a crucial difference between PT and ¹⁴C calibration. *Calibration* aims to provide the best possible estimate for the ‘calendar’ age corresponding to a ¹⁴C age. This estimate is provided by IntCal20, the collection of pointwise averages of 2500 Bayesian spline realizations of the ¹⁴C calibration curve, based on all sorts of available ¹⁴C ages prior to 14 cal. ka. Statistically integrating Suigetsu and floating tree ring ages, as purely atmospheric record, with a number of carbonate-based coral-, marine sediment-, and speleothem-based records, results in a statistically secure but smoothed IntCal20 record (B&H Fig. 4b).

106
107 *PT* is a research tool that employs a suite of medium well age-calibrated structures in the Suigetsu atmospheric ¹⁴C record as global reference to explore the ¹⁴C fine structure of noisy, local ocean plankton records (Suppl. Materials Fig. S1-S19). This is a new but trendsetting approximation to obtain a new order of age tie points for centennial-to-millennial-scale global stratigraphic correlation and a major addition to the role of radiocarbon as key tracer (Heaton et al., 2021).

113
114 Both on the basis of visual inspection and the 1st derivative of a ¹⁴C record (see Figs. S1–S19) the robustness and uncertainty of the age tie points are best calibrated at the marked ¹⁴C-age jumps that separate two subsequent ¹⁴C plateaus each, the range of which is marked by enveloping 'boxes' in Fig. 4. Accordingly, the uncertainty in the cal. age of the beginning and end of a ¹⁴C jump/plateau hardly exceeds ±50 to ±100 years, when employing the age estimates listed by Bronk Ramsey et al. (2020).

120
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121 Uncertainty levels of the exploratory PT chronology are, inevitably, somewhat higher than those acceptable for a ¹⁴C calibration. This concerns the identification of plateaus as well as the definition of plateau boundaries in some less densely sampled planktic ¹⁴C records (c.f. Figs. S1-S19). In view of the identification Sarnthein et al. (2020) again emphasized that the validity of certain atmospheric ¹⁴C plateaus assigned to structures in a single sediment ¹⁴C record must be verified by detailed comparison with coarser-spaced 'conventional' stratigraphic tie points in an ocean sediment record such as those provided by planktic δ¹⁸O records (e.g., DO event 1), turning points in sea surface temperature, tephra layers (e.g., Fig. S16).

129

130 Correlation of atmospheric and planktic ¹⁴C records

131 With the reproducibility of Suigetsu atmospheric ¹⁴C concentration patterns and their value as a tool for PT global correlation studies established, the question remains whether high-resolution planktic sediment ¹⁴C records indeed reflect primarily the atmospheric ¹⁴C structures defined in the Suigetsu record. B&H (2021) explored this question in their modeling of hypothetical ‘Suigetsu’ and ‘Cariaco’ records derived by adding appropriate noise to a section of the IntCal20 tree ring record. Their calculations indicated that no statistically robust signal could be extracted which, as explained above, does not preclude the use of PT as an exploratory tool for age correlation. B&H failed to consider the full period 10~15 cal ka where tree ring-based ¹⁴C structures overlap with Suigetsu data and restricted their tree-ring comparison to the less informative section 12.0-13.9 ka. Yet, even for this section their modeled ‘Cariaco’ curves indicate the underlying IntCal20 tree-ring ¹⁴C fluctuations that could be used by PT to explore the age correlation of such a record.

143
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144 Two important questions raised by B&H (2021) were (i) Can ¹⁴C structures observed in planktic
¹⁴C records result ‘accidentally’ from various processes characteristic of sediment deposition and
bioturbation? and (ii) Can a reliable correlation between atmospheric and planktic ¹⁴C plateaus
be made?

148

149 B&H's repeated objection to plateau identification in marine sediment cores was based on
150 disturbance by bioturbational mixing. This objection is invalid for three reasons:
151 -- At high latitudes and water depths >3000 m (with reduced flux of Corg) the bioturbational
152 homogenic mixing depth amounts to 2-3 cm (Trauth et al., 1997). This won't affect ¹⁴C signals at
153 average sedimentation rates of 10 - 50 cm/ky. At these high rates mixing depths even reaching
154 7-10 cm in low latitudes are little relevant, also shown by paired trends of quasi-continuous, e.g.,
155 XRF-based proxy records.

156 -- Wide sediment sections in five out of 19 cores in Sarnthein et al. (2020; cores MD3180,
157 MD2503, ODP1002D, ODP893A, PS97-137; Suppl. Figs. S3, S4, S11, S10, S15; Table S20) are
158 laminated, thus largely free of bioturbational mixing.

159 -- Planktic species counts in two high-resolution, non-laminated cores (GIK23074, SHAK06-5K)
160 refute any age offsets of the ¹⁴C plateau signal due to differential bioturbation.

161

162 Results of the earlier use of PT on planktic sediment ¹⁴C records, now converted to the Bronk-
163 Ramsey et al, (2020) time scale, are presented for comparison as supplemental material (Suppl.
164 Materials Fig. and Tables S1-S19). Though sediment deposition and bioturbational processes
165 occasionally locally affect the sediment ¹⁴C records, the full pattern of sequential ¹⁴C fluctuations
generally allows a reliable correlation.

167
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168 The age tie points provided by ¹⁴C PT bring more age control to the sediment records and, in doing so, reveal fluctuations in sediment deposition that were hitherto undefined as well as coeval variations in marine reservoir ages (MRA). Such short-term and local small-scale changes in sedimentation rate and MRA critically depend on the potential plateau numbers assigned to a plateau suite by alternative models of PT. The choice of tuning model, finally, is carefully based on and constrained by conventional sediment properties and stratigraphic tie points (e.g., Fig. S16a). In case of persisting alternative age models, we prefer the model where sedimentation rates and MRA's show the lowest fluctuations over a suite of subsequent plateaus (e.g., Fig. S5) (Sarnthein et al., 2007).

177
178 Most of the gaps and lows in sediment deposition defined by PT are already indicated by major age jumps that mark the record of raw ¹⁴C ages, independent of any PT (Suppl. Materials, Figs. S2, S6, S10, S13 to S19). Short-term major changes of sedimentation rate have been established independently by 230Th-based high-resolution age control for North Atlantic sediment cores (Missiaen et al. 2019), which supports the reality of the sediment fluctuations revealed by PT.
179
180
181
182 Most sedimentation spikes, moreover, make sense in terms of paleoceanography and paleoclimate. Pertinent changes in sedimentation rate may thus be derived by PT, but may also serve as corrective to obtain a best possible tuning of atmospheric and marine sediment-based plateau suites.

187
188 CONCLUSION

189 On the basis of coherence with tree ring records 10 to 15 cal. ka we can conclude that the pattern of ¹⁴C fluctuations in the atmospheric Suigetsu record represents an atmospheric ¹⁴C signal that can be used for global correlation with a precision better than ±50 to ±100 years. The
<figure><img src="image_14.png" /></figure>

192 PT technique explores the detailed dating of planktic $^{14}$C records by correlation to the Suigetsu signal, requiring it to be consistent with the available conventional evidence of stratigraphic correlation. The results of PT provide new insights into local marine reservoir ages (MRA), thus to local oceanography by revealing short-term changes in sedimentation rate and regional ocean mixing. These are important tracers for studies of paleoceanography and paleoclimatic events on a global atmospheric time scale. Such changes are often missed by the widely employed wide-spaced set of conventional age tie points and related average sedimentation of ocean sediment records.

200

201 ACKNOWLEDGMENTS

202 We are grateful to S. Beil, Kiel, for generous computer assistance.

203

204 Data availability

205

206 All primary radiocarbon data and cal. ages assigned are stored at PANGAEA.de® under , , ,

207

208 REFERENCES

209 Adolphi, F., Raimund Muscheler, Michael Friedrich, Dominik Güttler, Lukas Wacker, Sahra

210 Talamo, Bernd Kromer: Radiocarbon calibration uncertainties during the last deglaciation:

211 Insights from new floating tree-ring chronologies, Quaternary Science Reviews, 170, 98-108,

212 2017.

213 Bard, E. and Heaton, T.J.: On the tuning of plateaus in atmospheric and oceanic $^{14}$C records

214 to derive calendar chronologies of deep-sea cores and records of $^{14}$C marine reservoir age

215 changes. Climate of the Past, 17, 1701–1725. https://doi.org/10.5194/cp-17-1701-2021

216 Bronk Ramsey, C., Staff, R. A., Bryant, C. L., Brock, F., Kitagawa, H., van der Plicht, J.,

217 Schlolaut, G., Marshall, M. H., Brauer, A., Lamb, H. F., Payne, R. L., Tarasov, P. E., Haraguchi, T.,

218 Gotanda, K., Yonenobu, H., Yokoyama, Y., Tada, R., and Nakagawa, T.: A complete terrestrial

219 radiocarbon record for 11.2 to 52.8 kyr B.P., Science, 338, 370–374, 2012.
<figure><img src="image_15.png" /></figure>

220 Bronk Ramsey, C., Heaton, T.J., Schlolaut, G., Staff, R.A., Bryant, C.L., Lamb, H.F., Marshall,

221 M.H., Nakagawa, T.: Reanalysis of the atmospheric radiocarbon calibration record from Lake

222 Suigetsu, Japan. Radiocarbon, https://doi.org/10.1017/RDC.2020.18, 2020

223 Grootes, P.M. and Sarnthein, M.: Community comment on “On the tuning of plateaus in atmospheric and oceanic C records to derive calendar chronologies of deep-sea cores and records of C marine reservoir age changes” by Edouard Bard and Timothy J. Heaton, Clim. Past Discuss., https://doi.org/10.5194/cp-2020-164-CC2, 2021.

227 Heaton, T.J., Bard, E., Bronk Ramsey, C., Butzin, M., Köhler, P., Muscheler, R., Reimer, P.J., Sun. Wacker, L.: Radiocarbon: A key tracer for studying Earth's dynamo, climate system, carbon cycle, and Sun. Science, 374, 707-718, 2021.

230 Missiaen, L., Waelbroeck, C., Pichat, S., Jaccard, S.L., Eynaud, F., Greenop, R., Burke, A.: Improving North Atlantic Marine Core Chronologies using 230Th normalization. Paleooceanography and Paleoclimate, 34, 1057-1073, 2019.

233 Reimer P.J., Austin W.E.N., Bard E., Bayliss A., Blackwell P.G., Bronk Ramsey C., Butzin M., Cheng H., Edwards R.L., Friedrich M., Grootes P.M., Guilderson T.P., Hajdas I., Heaton T.J., Hogg A.G., Hughen K.A., Kromer B., Manning S.W., Muscheler R., Palmer J.G., Pearson C., van der Plicht H., Reimer R.W., Richards D., Scott E.M., Southon J.R., Turney C.S.M., Wacker L., Adophi F., Büntgen U., Capano M., Fahrni S., Fogtmann-Schulz A., Friedrich R., Kudsk S., Miyake F., Olsen J., Reinig F., Minoru Sakamoto M., Sookdeo A., Talamo S. The IntCal20 Northern Hemisphere radiocarbon calibration curve (0-55 kcal BP). Radiocarbon 62, 725-757, doi: 10.1017/RDC.2020.41, 2020.

241 Sarnthein, M., Grootes, P.M., Kennett, J.P., and Nadeau, M.: ¹⁴C Reservoir ages show deglacial changes in ocean currents and carbon cycle, Geophys. Monograph – Am. Geophys. Union, 173, 175–196, 2007.

244 Sarnthein, M., Küssner, K., Grootes, P.M., Ausin, B., Eglinton, T., Muglia, J., Muscheler, R., Schlolaut, G. Plateaus and jumps in the atmospheric radiocarbon record – Potential origin and value as global age markers for glacial-to-deglacial paleoceanography, a synthesis. Climate of the Past, 16, 2547–2571, doi: 10.5194/cp-16-2547-2020, 2020.

248 Sarnthein, M. and Grootes, P. M.: Community comment on “On the tuning of plateaus in atmospheric and oceanic C records to derive calendar chronologies of deep-sea cores and records of C marine reservoir age changes” by Edouard Bard and Timothy J. Heaton, Clim. Past Discuss., https://doi.org/10.5194/cp-2020-164-CC1, 2021.

252 Trauth, M.H., Sarnthein, M. and M. Arnold, M.: Bioturbational mixing depth and carbon flux at the seafloor. - Paleooceanography, 12, 517-526., 1997.
<figure><img src="image_16.png" /></figure>

255 TABLES and FIGURES

256 Table 1 a and b. Summary of recently revised U/Th model-based age estimates (Bronk Ramsey et al., 2020) for ~30 plateau (pl.) boundaries in the atmospheric ¹⁴C record identified in Lake

258 Suigetsu Core SG06 by means of visual inspection over the interval 10.5–27 cal. ka (Sarnthein et al., 2015, suppl. and modified). At the right-hand side, three columns give the average (Ø) and uncertainty range of ¹⁴C ages for each ¹⁴C plateau.

261

<table><thead><tr><th>SUIGETSU Plateau Top<br>SG06_2012<br>Plateau no.</th><th>IntCal20<br>U/Th-based<br>age (yr BP)</th><th>Depth<br>(cm c.d.)</th><th>Plateau Base<br>IntCal20<br>U/Th-based<br>age (yr BP)</th><th>Depth<br>(cm c.d.)</th><th>Ø 14C Age<br>of 14C Plateau<br>(14C yr)</th><th>±Uncertainty<br>(14C yr)</th><th>14C age BP<br>min/max.<br>(1.6 σ range)</th></tr></thead><tbody><tr><td>'Preboreal'</td><td>10560</td><td>1325</td><td>11108</td><td>1383</td><td>9525</td><td>-170/+110</td><td>9356/<br>9635</td></tr><tr><td>'Top YD'</td><td>11281</td><td>1402</td><td>11755</td><td>1453</td><td>10060</td><td>-100/+35</td><td>9963/<br>10095</td></tr><tr><td>'YD'</td><td>11895</td><td>1467</td><td>12475</td><td>1525</td><td>10380</td><td>-170/<br>124</td><td>10211/<br>10504</td></tr><tr><td>'no name'</td><td>12780</td><td>1555</td><td>13080</td><td>1582</td><td>11000</td><td>-85/<br>114</td><td>10915/<br>11114</td></tr><tr><td>1a</td><td>13656</td><td>1626</td><td>14065</td><td>1657</td><td>12006</td><td>100</td><td>11857/<br>12050</td></tr><tr><td>1</td><td>14187</td><td>1666</td><td>15044</td><td>1740</td><td>12471</td><td>185</td><td>12315/<br>12683</td></tr><tr><td>2a</td><td>15415</td><td>1754</td><td>16531</td><td>1802</td><td>13406</td><td>245</td><td>13174/<br>13665</td></tr><tr><td>2b</td><td>16531</td><td>1802</td><td>16940</td><td>1820</td><td>13850</td><td>40</td><td>13808/<br>13885</td></tr><tr><td>3</td><td>17579</td><td>1847</td><td>18189</td><td>1888</td><td>14671</td><td>105</td><td>14582/<br>14792</td></tr><tr><td>4</td><td>18790</td><td>1913</td><td>19793</td><td>1971</td><td>15851</td><td>190</td><td>15661/<br>16044</td></tr></tbody></table>

262
<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /></figure>

<table><tr><td>5a</td><td>19922</td><td>1978</td><td>20240</td><td>2003</td><td>16670</td><td>90</td><td>16570/<br/>16750</td></tr><tr><td>5b</td><td>20240</td><td>2003</td><td>20919</td><td>2032</td><td>17007</td><td>190</td><td>16830/<br/>17247</td></tr><tr><td>6</td><td>21173</td><td>2105</td><td>22300</td><td>2132</td><td>17766</td><td>404</td><td>17433/<br/>18240</td></tr><tr><td>7</td><td>22604</td><td>2140</td><td>22940</td><td>2171</td><td>18844</td><td>117</td><td>18741/<br/>18975</td></tr><tr><td>8</td><td>23237</td><td>2175</td><td>24300</td><td>2257</td><td>19715</td><td>-290<br/>325</td><td>19425/<br/>20041</td></tr><tr><td>9</td><td>24300</td><td>2257</td><td>25250</td><td>2312</td><td>20465</td><td>-227<br/>263</td><td>20238/<br/>20728</td></tr><tr><td>10a</td><td>25656</td><td>2358</td><td>26960</td><td>2400</td><td>22328</td><td>-380<br/>270</td><td>21946/<br/>22600</td></tr><tr><td>10b</td><td>26960</td><td>2400</td><td>27612</td><td>2426</td><td>22708</td><td>-475<br/>440</td><td>22233/<br/>23147</td></tr><tr><td>11</td><td>27900</td><td>2443</td><td>28898</td><td>2525</td><td>24088</td><td>-360<br/>505</td><td>23727/<br/>24595</td></tr></table>

263

264
<figure><img src="image_19.png" /></figure>

265 Figure 1. Raw ¹⁴C data of Lake Suigetsu (blue dots), converted into ‰ Δ¹⁴C units, plotted vs. cal.

266 ages of Bronk Ramsey et al. (2020). A Bayesian spline named "Suigetsu only curve" (pink band,

267 B&H 2021, Fig. 3a modified) shows periods of gradually decreasing atmospheric Δ¹⁴C values,

268 reflecting 15 atmospheric ¹⁴C age plateaus and their uncertainty range as defined by Sarnthein

269 et al. (2020; numbers listed in Table 1). In between, rapidly increasing atmospheric Δ¹⁴C values

270 reflect short gaps or ¹⁴C age 'jumps' between plateaus. Superimposed are straight lines that

271 display the atmospheric Δ¹⁴C structures as originally defined by visual inspection of raw ¹⁴C ages

272 and 1st derivative technique (Sarnthein et al., 2020; and Suppl. Figs. 1-19), with green lines using

273 the initial chronology of Bronk Ramsey et al. (2012; B&H 2021) and dark pink lines using the

274 recently revised ages of Bronk Ramsey et al. (2020).

275

<figure><img src="image_20.png" /><figcaption>Figure 1</figcaption></figure>

276

277

278 Figure 2. High-resolution record of atmospheric ¹⁴C jumps and plateaus (= suite of labeled

279 horizontal boxes that envelop scatter bands of largely constant ¹⁴C ages extending over

280 >300 cal. yr) in a sediment section of Lake Suigetsu (Fig. 2 of Sarnthein et al., 2020) vs.

281 tree ring-based ¹⁴C jumps and plateaus 10–14.5 cal. ka (Reimer et al., 2013; 14.0-14.4

282 cal. ka: suppl. by data of Adolphi et al., 2017). Blue line averages paired double and
<figure><img src="image_21.png" /></figure>

triple ¹⁴C ages of Suigetsu plant macrofossils. Age control points (cal. ka) follow varve counts (Schlolaut et al., 2018) and U/Th model-based ages of Bronk Ramsey et al. (2012 and 2020). YD = Younger Dryas, B/A = Bølling-Allerød.

<figure><img src="image_22.png" /></figure>

Figure 3. (Courtesy of Bronk Ramsey et al., 2020). A comparison of Bayesian spline compilations of datasets of Suigetsu (green) and Hulu speleothem (magenta) over the period 20-35 cal. ka, transformed using a MatLab deconvolution algorithm (linear ramp with mean of 420 years). Gradually decreasing atmospheric Δ¹⁴C values reflect atmospheric ¹⁴C age plateaus and their uncertainty range (black numbers in brackets). Rising Δ¹⁴C values reflect atmospheric ¹⁴C age jumps.
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294

295

296 Figure 4. Atmospheric <sup>14</sup>C ages and error bars of Lake Suigetsu plant macrofossils vs. U/Th-based

297 model age of 15–21 (bottom) and 21–27 (top) cal. ka (blue dots; Sarnthein et al., 2020, modified,

298 using age data of Bronk Ramsey et al., 2020). <sup>14</sup>C plateaus longer than 250 yr are outlined by a

299 suite of labeled horizontal boxes that envelop scatter bands of largely constant or slightly rising

300 <sup>14</sup>C ages, separated by "<sup>14</sup>C jumps". Red boxes outline contemporary <sup>14</sup>C plateaus found in the

301 Hulu <sup>14</sup>C record. 1:1 line reflects a gradient of one <sup>14</sup>C yr per cal. yr.
<figure><img src="image_26.png" /></figure>

<figure><img src="image_27.png" /></figure>

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304 **¹⁴C PLATEAU TUNING – A MISLEADING APPROACH OR TRENDSETTING TOOL FOR MARINE**

305 **PALEOCLIMATE STUDIES?**

306

307 Michael Sarnthein¹) and Pieter M. Grootes²)

308

309 **SUPPLEMENTARY MATERIALS** (i.e., just an overview for a fast-reading reviewer)

310

311 **SUPPLEMENTARY FIGURES AND TABLES**

312 Figures S1 - S19.

313 Planktic ¹⁴C records of sediment cores plotted vs. core depth. Core location and references to

314 data source are given in Table S20. Planktic ¹⁴C plateaus (horizontal boxes) are compared to

315 atmospheric (atm) ¹⁴C plateau suite of Lake Suigetsu (Bronk Ramsey et al., 2020), where

316 calendar ages of plateau boundaries (and average atmospheric ¹⁴C ages; Fig. S12) are given

317 below. Local planktic reservoir ages (in blue) result from the difference between the average raw

318 ¹⁴C age of planktic ¹⁴C plateaus measured in the core and the ¹⁴C age of equivalent atmospheric

319 ¹⁴C plateaus numbered 1 – 10 (numbers in brackets). Top panel shows units of the 1st derivative

320 (¹⁴C yr per m core depth) and 1-σ uncertainty range, with high values indicating ¹⁴C jumps and

321 ¹⁴C plateaus (numbered in red) constrained at 'half-height' by asterisks (as defined in Sarnthein

322 et al. 2015). B/A = Bølling-Allerød; HS-1, HS-2 = Heinrich Stadial 1 and Heinrich Stadial 2; LGM =

323 Last Glacial Maximum. Sedimentation rates are based on ages of ¹⁴C plateau boundaries. Red

324 double slash indicates sedimentation gap.

325

326 Suppl. Tables S1 - S19.

327 Planktic and benthic ¹⁴C ages measured in 19 ocean sediment cores. All cal. ages (yr BP) were

328 deduced by means of ¹⁴C plateau tuning and adjusted to the IntCal20 U/Th-based model time
<figure><img src="image_31.png" /></figure>

<figure><img src="image_32.png" /></figure>

329 scale of Bronk Ramsey et al. (2020). Core locations and data sources are listed in Table S20.

330 Tables S1 - S19 are being deposited at Pangaea.de.

331

332 Suppl. Table S 20. Core locations and data sources (and references) for 19 core sites from key

333 positions in the world ocean, used for generating a PT-based time scale for planktic and benthic

334 ¹⁴C ages displayed in Tables S1 - S19.

335