Identification of the Younger Dryas Onset Was Confused by the Laacher

LETTER

Identification of the Younger Dryas onset was confused by the Laacher See volcanic eruption LETTER Evzen Stuchl´ıka,1, Daniel Vondr ´akb, Zuzana Horick ´aa, Jolana Hrub ´ac, Ana Mijovilovichd, and Günther Kletetschkac

Cheng et al. (1) provide data on oxygen-isotope δ18O sedimentary archive in the Central European paleolake in nine speleothems of Younger Dryas (YD) age from StaraJ ´ ´ımka (3) suggest that the first drop in δ18O caves situated in several continents between 42°27′ N found by Cheng et al. (cave Seso, North Greenland Ice and 21°05′ S and dated by the U-Th method. They Core Project; figure 4 of ref. 1) originated from a previ- compare this data with δ18O records in several ice ous warmer climate in combination with a long-term cli- cores from Greenland and Antarctica that were origi- mate repercussion following the LSVE (7). Then, the nally dated by the radiocarbon method. While the subsequent major continuous decrease of δ18Oindi- presented YD records of δ18O and their bowl- cates the actual YD onset, as a reaction to an extrater- shaped pattern (e.g., in speleothems and ice cores restrial impact event (ETIE) revealed by the Pt anomaly from the Northern Hemisphere) are similar to earlier along with the occurrence of microspherules and nano- published YD structures [e.g., lake sediment-based diamonds (8, 9). In addition, their data based on the pollen and Cladocera inferred temperature (2) and identification of annual bends in speleothems (Cherra- lake sediment Th/K ratio (3)], the interpretation of this punji and Rige cave samples Chy-1, Rige 3; figure S3 of data merits some criticism. Although the authors refer ref. 1) support this interpretation. Furthermore, the lag to several papers dealing with the Laacher See volca- estimated by Cheng et al. (1) of ∼50 y between their nic eruption (LSVE), they ignore any of its potential proposed YD onset and the Pt anomaly is within our effects on climate. Unfortunately, this hampers the in- error range of a ∼70-y lag (based on radiocarbon dates) terpretation of their own data and confounds the role found in the sediment of the StaraJ ´ ´ımka paleolake be- of the widespread Pt anomaly (4) and thus the actual tween the accumulation of LSVE tephra and magnetic onset of the YD, which they mistakenly associate with impact microspherules that indicate an ETIE (3). Thus, the first drop in δ18O. The LSVE tephra is one of the while the data provided by Cheng et al. (1) are improp- most important chronological markers in European la- erly interpreted, they support the validity of the YD im- custrine varved sedimentary archives that resides pact hypothesis (10). close to the onset of the YD (5). The timing of this at least Europe-wide event, based on carbonatite U-Th Acknowledgments zircon isochron age (12,900 cal. B.P.) (6) and lake varve This work was supported by grants from Czech Science Founda- tion (20-08294S) and Ministry of Education, Youth and Sports of age (12,880 cal. B.P.) (5), is within the error range of the Czech Republic with co-financing from the European Union the YD onset provided by Cheng et al. (12,870 ± 30 (grant “KOROLID,” CZ.02.1.01/0.0/0.0/15_003/0000336). We cal. B.P.) (1). Results of our recent multiproxy study of a thank David Hardekopf for language corrections.

1 H. Cheng et al., Timing and structure of the Younger Dryas event and its underlying climate dynamics. Proc. Natl. Acad. Sci. U.S.A. 117, 23408–23417 (2020). 2 A. F. Lotter et al., Younger Dryas and Allerød summer temperatures at Gerzensee (Switzerland) inferred from fossil pollen and cladoceran assemblages. Palaeogeogr. Palaeoclimatol. Palaeoecol. 159, 349–361 (2000). 3 G. Kletetschka et al., Cosmic-impact event in lake sediments from Central Europe postdates the Laacher See eruption and marks onset of the Younger Dryas. J. Geol. 126, 561–575 (2018). 4 C. R. Moore et al., Widespread platinum anomaly documented at the Younger Dryas onset in North American sedimentary sequences. Sci. Rep. 7, 44031 (2017). 5 C. S. Lane et al., The Late Quaternary tephrostratigraphy of annually laminated sediments from Meerfelder Maar, Germany. Quat. Sci. Rev. 122, 192–206 (2015).

a ˇ b Institute of Hydrobiology, Biology Centre, Czech Academy of Sciences, CZ-370 05 Cesk ´eBudejovice, Czech Republic; Institute of Environmental Studies, Faculty of Science, Charles University, CZ-128 01 Prague 2, Czech Republic; cInstitute of Hydrogeology, Engineering Geology and Applied Geophysics, Faculty of Science, Charles University, CZ-128 43 Prague 2, Czech Republic; and dInstitute of Plant Molecular Biology, Biology Centre, ˇ Czech Academy of Sciences, CZ-370 05 Cesk ´eBudejovice, Czech Republic Author contributions: E.S., D.V., Z.H., J.H., A.M., and G.K. wrote the paper. The authors declare no competing interest. Published under the PNAS license. 1To whom correspondence may be addressed. Email: [email protected]. Published January 18, 2021.

PNAS 2021 Vol. 118 No. 4 e2022485118 https://doi.org/10.1073/pnas.2022485118 | 1of2 Downloaded by guest on September 26, 2021 6 A. K. Schmitt, F. Wetzel, K. M. Cooper, H. Zou, G. Wörner, Magmatic longevity of Laacher See volcano (Eifel, Germany) indicated by U–Th dating of intrusive carbonatites. J. Petrol. 51, 1053–1085 (2010). 7 J. U. L. Baldini, R. J. Brown, N. Mawdsley, Evaluating the link between the sulfur-rich Laacher See volcanic eruption and the Younger Dryas climate anomaly. Clim. Past 14, 969–990 (2018). 8 W. S. Wolbach et al., Extraordinary biomass-burning episode and impact winter triggered by the Younger Dryas cosmic impact ∼12,800 years ago. 1. Ice cores and glaciers. J. Geol. 126, 165–184 (2018a). 9 W. S. Wolbach et al., Extraordinary biomass-burning episode and impact winter triggered by the Younger Dryas cosmic impact ∼12,800 years ago. 2. Lake, marine, and terrestrial sediments. J. Geol. 126, 185–205 (2018b). 10 R. B. Firestone et al., Evidence for an extraterrestrial impact 12,900 years ago that contributed to the megafaunal extinctions and the Younger Dryas cooling. Proc. Natl. Acad. Sci. U.S.A. 104, 16016–16021 (2007).

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