Mid-late Holocene evolutionary history and climate reconstruction of Vellayani lake, south India

Upasana S. Banerji1*, Jithu Shaji1,4, Arulbalaji P.1, Maya K.1, Vishnu Mohan S.3, Ankur J. Dabhi2, A. Shivam2, Ravi Bhushan2 and D. Padmalal1

1 National Centre for Earth Science Studies, Thiruvananthapuram-695011, Kerala, India

2 Physical Research Laboratory, Ahmedabad-380009, Gujarat, India

3 University of Kerala, Kariavattom Campus, Thiruvananthapuram-695 581, Kerala, India

4 Department of marine geology and geophysics, Cochin University of Science and Technology, Kochi-682022Kerala

The lake sediments received wide attention for archiving paleoclimate and paleo sea-level variability during the late Quaternary period. It has also been extensively used to disentangle the interrelationships existing among the regional and the global climate systems. In the present study, the applicability of lake sediments has been the major impetus to delineate the mid-late Holocene climate and sea level variability using a ~10 m sediment core retrieved from a protected freshwater lake- the Vellayani lake, southern Kerala, southwest India. The sediment core was investigated using multiproxy approach and was chronologically supported by AMS radiocarbon dates. The results show monsoon intensification and a high sea level during 6430-4390 cal yr BP led to the formation of a coastal lagoon system in the area. Climatically, a marginal reduction in monsoon during 4390-2600 cal yr BP interspersed by an intensified phase during 3800-2600 cal yr BP was observed while concurrently, a sea regression during 4390-2600 cal yr BP restricted sea water influence in the study area. Proxies indicated a significant monsoon reduction during 2600-1000 cal yr BP followed by monsoon intensification post-1000 cal yr BP. After 2600 cal yr BP, a thick pile of alluvial sediments were deposited by the Karamana River which might have hindered the tidal influence and later the basin was transformed into a freshwater lake. The present lake configuration was attained after 440 cal yr BP. Further, comparison of paleoclimate reconstructed from the present study with the global records revealed a teleconnection of Indian monsoon with the global climate system.

[A] Gradual sea regression during last 6400 cal year; [B] Comparison of terrestrial proxies with other records

Banerji, U.S., Shaji J., Arulbalaji, P., Maya, K., Vishnu Mohan S., Dabhi, A. J., Shivam, A., Bhushan, R. and Padmalal, D. Mid-late Holocene evolutionary history and climate reconstruction of Vellayani lake, south India. Quaternary International. https://doi.org/10.1016/j.quaint.2021.03. 018.

21. Banerji et al., 2021_QI

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Hydroclimate variability during the last two millennia from the mudflats of Diu Island,Western India

Upasana S. Banerji*1,2, Ravi Bhushan1, Kumar Batuk Joshi2, Jithu Shaji2 and A.J.T. Jull 3

1 Physical Research Laboratory, Department of Space, Ahmedabad-380 009, Gujarat

2 National Centre for Earth Science Studies, Ministry of Earth ScienceThiruvananthpuram-695011, Kerala

3 NSF Arizona AMS Laboratory, University of Arizona, Tucson, AZ 85721, USA

Email: upasana.s.banerji@gmail.com*

The climate variability over the western India has been significantly influenced by the perturbations in the Indian summer monsoon (ISM) and thus, provides a crucial platform to investigate the past climatic variations, weathering intensity and sediment source. The mudflats of southern Saurashtra, western India are deprived of perennial rivers but the region receives terrestrial contribution exclusively due to activation of seasonal rivers during monsoon. In the present study, an attempt has been made to investigate the past monsoon and paleo-weathering using various geochemical proxies (detrital, productivity, redox and weathering) on the mudflat sediment core of Southern Saurashtra, western Gujarat. The core is chronologically constrained by 14C, 210Pb and 137Cs dating techniques.

The study suggests ISM strengthening during Roman warm period (2000-1800 cal yr BP) with intermittent marginal ISM weakening during 1950-1970 cal yr BP and 1930-1890 cal yr BP associated with the reduced solar irradiance. Further, ISM weakening has been invoked during Dark Age Cold period (1800-1300 cal yr BP) and Little Ice Age (800-200 cal yr BP) interrupted by a marginal ISM strengthening during Medieval Warm period and the last two centuries witness climate warming. Based on historical rainfall data and Al2O3, an intermittent strengthening of ISM during 90-30 cal yr BP. A gradual increase in the weathering intensity synchronous with the rise in Sea Surface Temperature (SST) has been observed during the last 200 cal yr BP suggesting the role of temperature on the intensity of chemical weathering in the study area.

In spite of changes in the geochemical proxies as a function of ISM fluctuations, the paleoweathering intensities has remained nearly consistent wherein the chemical weathering was less operative and accompanied by the deposition of texturally immature sediments. The sediments of Diu mudflat indicate mafic signatures thereby underscoring major contribution of the Deccan basalts along with other variable sources.

(a) Study area from where the sediment core DM was retrieved; (b) downcore variation of geochemical parameters; (c) A-CN-K ternary plot for the DM sediments

Banerji U.S., Bhushan R., Joshi K.B., Shaji J. and Jull A.J.T. Hydroclimate variability during the last two millennia from the mudflats of Diu Island, Western India. Geological Journal, 2021, 10.1002/GJ.4116.

19. Banerji et al., 2021_GJ

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