Misinterpreting proxy data for paleoclimate signals: A comment on Shukla et al. 2020

Abstract

Shukla et al. explored paleoclimatic signals from a ~8 m thick profile of a moraine-dammed lake in the central Himalaya exposed due to lake burst from a flash flood in 2013. The main objective of their research work is to understand the complex glacial-climate system during late-Holocene. They attempted a novel multi proxy approach for paleoclimate reconstruction but their work suffers from misinterpretation of various proxies and erroneous/misleading discussion. We therefore report following major points in this comment article. (1) Misinterpretation of magnetic parameters: Magnetic susceptibility (χlf) has been used to interpret changes in magnetic mineralogy rather than concentration of magnetic minerals. Susceptibility of anhysteretic remanence (χARM) has been used at several places to indicate presence of superparamagnetic (SP) and multi domain (MD) ferrimagnetic particles rather than single domain (SD) ferrimagnetic (magnetite) particles. Interpreting erroneous negative values of percentage of frequency dependent susceptibility (χfd%) for climate change. (2) Poor chronology: Overlaps in ages of glacial-lake sediments. (3) References: Several statements in paper have not been referenced and some of them have out of place citations. (4) Carefree writing: Authors have shown typical example of carefree writing of a research article, for example, giving units to dimensionless parameter S-ratio, and χfd%, differences in units of χlf in text and figure, different depths for the same age in text and figure. (5) Over interpretation: Authors at places have interpreted climatic variations based on only one sample. (6) Poor justifications: Authors did not provide any detailed justification for proxy data while interpreting climatic variations. (7) No data (results) on mineralogy and trace elements were given. Overall it is not only a problem of presentation and misinterpretation of proxy data but the study also fails to deliver the final message of climate change and glacier dynamics in the central Himalaya.