Late-Holocene climate response and glacial fluctuations revealed by the sediment record of the monsoon-dominated Chorabari Lake, Central Himalaya

Abstract

We studied a periglacial lake situated in the monsoon-dominated Central Himalaya where an interplay of monsoonal precipitation and glacial fluctuations during the late Holocene is well preserved. A major catastrophe occurred on 16–17 June 2013, with heavy rains causing rupturing of the moraine-dammed Chorabari Lake located in the Mandakini basin, Central Himalaya, and exposed 8-m-thick section of the lacustrine strata. We reconstructed the late-Holocene climatic variability in the region using multi-parametric approach including magnetic, mineralogical and chemical (XRF) properties of sediments, paired with grain size and optically simulated luminescence (OSL) dating. The OSL chronology suggests that the lake was formed by a lateral moraine during the deglaciation phase of Chorabari Glacier between 4.2 and 3.9 ka and thereafter the lake deposited about 8-m-thick sediment sequence in the past 2.3 ka. The climatic reconstruction of the lake broadly represents the late-Holocene glacial chronology of the Central Himalaya coupled with many short-term climatic perturbations recorded at a peri-glacial lake setting. The major climatic phases inferred from the study suggests (1) a cold period between 260 BCE and 270 CE, (2) warmer conditions between 900 and 1260 CE for glacial recession and (3) glacial conditions between ~1370 and 1720 CE when the glacier gained volume probably during the ‘Little Ice Age’ (LIA). We suggest a high glacial sensitivity to climatic variability in the monsoon-dominated region of the Himalaya.

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

“…greigite) as well as bacterial magnetite in certain cases or environment that have been well reported from various lakes globally (Kim et al, 2005;Paasche et al, 2004;Snowball, 1991Snowball, , 1994. Shukla et al (2020) wrote that 'in periods of climatic transition, the supply of minerogenic material to lakes is reduced and the sediment with a lower organic content were deposited. A slow deposition rate could also lead to magnetite dissolution, resulting in a low magnetic concentration and high S-ratio.…”

“…This does not imply that concentration of antiferromagnetic minerals have increased and should not be used for climatic interpretations (or only carefully). Shukla et al (2020) did not provide details of instrument or lab used. They also did not report the accuracy and precision of measurements for major and trace elements.…”

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Shukla et al (2020) investigated relationship between climate change and glacial system of the central Himalaya during late-Holocene using multi-proxy study of the Chorabari glaciallake sediments in the Mandakini basin. There are several shortcomings in the article, which have been described sectionwise.

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“…There are several shortcomings in the article, which have been described sectionwise. Shukla et al (2020) mentioned that they had carried out mineralogical analysis (also in abstract). However, no results and discussion on mineralogical analysis have been provided.…”

“…The IRM bf (IRM measurement in backfield after first saturating sample in forward field) at 300 mT is mostly used for calculation of S-ratio and is expressed as −IRM −300mT /SIRM (King and Channell, 1991;Liu et al, 2007). Shukla et al (2020) have also incorrectly cited reference of Stober and Thompson (1979b) 'Magnetic remanence acquisition in Finnish lake sediments. Geophysical Journal of the Royal Astronomical Society 57: 727-739' for calculation of S-ratio.…”