Chronological interpretation of characteristics of the Late Pleistocene-Holocene Lake sediments by the example of the Upper Boguty Lake, South-Eastern Altai

When studying the late Pleistocene–Holocene lacustrine sedimentary records from lake cores, the chronological interpretation of the analyzed characteristics is made applying a depth-age model (DAM). Usually, DAM is based on the results of radiocarbon dating. As a rule, the measured value is correlated with the average or median value of the calibrated 14C age of the corresponding centimeter of the core. This approach ensures the transfer of data from the depth scale of the sedimentary section to the calendar time scale “point to point”, i. e., seemingly, without loss of accuracy. However, in reality it ignores the probabilistic nature of determining calendar age and can thus lead to erroneous chronological reconstructions or an overestimation of their accuracy. We propose an alternative approach that takes into account the probability density function of the calendar age calculated applying the DAM and allows to avoid these problems. By the example of the late Pleistocene–Holocene bottom sediments of the Upper Boguty Lake located in the high-mountain Boguty Depression, South-Eastern Altai, the difference in the application of both approaches to the chronological interpretation of the results of anthracological and spore-pollen analyses is demonstrated. The analyzed sediment characteristics – the charcoal accumulation rate (CHAR) and the content of pollen of woody vegetation in pollen-spore spectra – refer to fundamentally different types of data. Two sample sets represent discrete / relatively continuous measured numerical values and the presence/absence of zero values. It is shown that the chronological reconstruction of both types of data should be carried out taking into account the probability density of the calendar age calculated applying the DAM. Another important issue for correct reconstructions is the appropriate interpretation of zero values of measured characteristics, which is especially important in case of discrete sample. Zero values can be either true, reflecting real changes in the natural paleoenvironmental conditions, or be a result of missing or impossible to determine a specific parameter in a small volume of sediment sample. In each case, the researcher must make an appropriate choice using additional information. In general, the accuracy of the chronological interpretation of the analyzed characteristics of lake sediments and the reliability of the further paleogeographic reconstruction are determined primarily by the quality of the DAM. In this context the presented approach allows us to understand the limitations and accuracy of this reconstruction.

1. Butvilovsky V.V., 1993. Paleogeography of the Latest Glaciation

2. and Holocene of Altai: A Catastrophic Model. Tomsk: Tomsk

3. State Univ., 253 p (in Russian)

4. Bronnikova M.A., Agatova A.R., Lebedeva M.P., Nepop R.K., Konoplianikova Y.V., Turova I.V., 201). Record of Holocene changes in high-mountain landscapes of southeastern Altai in the soil–sedimentary sequence of the Boguty river valley. Eurasian Soil Science, 51, 1381-1396.

5. Agatova, A.R., Khazina, I.V., Bronnikova, M.A., Uspenskaya, O.N., Nepop, R.K., 2018. Reconstruction of postglacial landscape evolution within the eastern periphery of Chuya depression on the basis of multidisciplinary analysis of peats in Boguty river basin, SE Altai, Russia. IOP Conference Series: Earth and Environmental Science. 138(1), 012001.

6. Agatova, A., Nepop, R., Nazarov, A., Ovchinnikov, I., Moska, P., 2021. Climatically driven Holocene glacier advances in the Russian Altai based on radiocarbon and OSL dating and tree ring analysis. Climate, 9(11), 162.

7. Agatova, A.R., Nepop, R.K., Shchetnikov, A.A., Krainov, M.A., Ivanov, E.V., Filinov, I.A., P. Ding, Xu Yi-G., 2023. Sedimentary Records of High-Mountain Lakes in Arid Russian Altai: First Results of Studies (Last Glacial Maximum-Holocene). Doklady Earth Sciences. https://doi.org/10.1134/S1028334X23602626.

8. Faegri K., Iversen J., Krzywinski K., Kaland P.E., 1989 Textbook of pollen analysis. Chichester-New York-Toronto-Sinapore: John Willey & sons, p. 328.

9. Feurdean A., Veski S., Florescu G., Vannière B., Pfeiffer M., O'Hara R.B., Stivrins N., Amon L., Heinsalu A., Vassiljev J., Hickler T., 2017. Broadleaf deciduous forest counterbalanced the direct effect of climate on Holocene fire regime in hemiboreal/boreal region (NE Europe). Quaternary Science Reviews, 169, 378-390.

10. Kelly R.F., Higuera P.E., Barrett C.M., Hu F.S., 2011. A signal-to-noise index to quantify the potential for peak detection in sediment-charcoal records. Quaternary Researches, 75, 11-17.

11. Mustaphi, C.J.C., Pisaric, M.F., 2014. A classification for macroscopic charcoal morphologies found in Holocene lacustrine sediments. Progress in Physical Geography, 38(6), 734-754.

12. Nepop R.K., Agatova A.R., Uspenskaya O.N., 2020. Climatically driven late Pleistocene–Holocene hydrological system transformation and landscape evolution in the eastern periphery of Chuya basin, SE Altai, Russia. Quaternary International, 538, 63-79.

13. Whitlock C., Larsen C. Charcoal as a fire proxy. Tracking Environmental Change Using Lake Sediments. Developments in Paleoenvironmental Research. 2002. V. 3. Springer, Dordrecht, the Netherlands. pp. 75–97.