Last 20,000 years of climatic change

Authors

  • D.P. Agarwal Physical Research Laboratory, Navrangpura, Ahmedabad 380009, India

DOI:

https://doi.org/10.54991/jop.1991.1788

Keywords:

Palaeoecology, Palaeoclimate, Vegetation

Abstract

Recent evidence, especially from continental Asia, shows that there are marked latitudinal differences in global climatic changes. From India, we now have new evidence from Kashmir, Rajasthan and the Arabian Sea which shows that in the north (35°- 40° N latitude) warming had started c. 20,000 yrs BP in Kashmir, Ladakh and Nepal when in higher latitudes it was still the Last Glacial Maximum (LGM). At c. 18 Kyr, Butapathri (Kashmir) bogs show emergence of thermophilous plants like Alnus, Juglans, Carpinus at the cost of conifers. A palaeosol on the loess profile of Kashmir is datable to c. 18 Kyr which again shows climatic amelioration. Organic matter from this palaeosol gives δ 13C values of about -24‰ indicating that it was derived from C3 type of vegetation. Presence of an Upper Palaeolithic culture at this time, in Kashmir, again confirms a period of climatic amelioration.

From Ladakh, Bhattacharya has inferred climatic amelioration from the higher percentage of Juniper during 20- 20 Kyr period. Similarly in Nepal, a climatic amelioration is indicated. In Rajasthan, c. 18 Kyr is a period of aridity. Maximum sand building activity is TL dated by Singhvi to c. 14 Kyr and just preceeds the strengthening of the monsoon in c. 13 Kyr. Upwelling at c. 13 Kyr in the Arabian Sea has been reported by Anderson et at. (1990) and the French group has shown a similar evidence of monsoon strengthening at c. 13 Kyr based on pollen evidence fom African lakes. Unfortunately, we have only one 14C date from Butapathri which shows that at c. 10 Kyr the cooler oscillation was on its way out and warming had gradually started. We need more closely spaced 14C dates for such profiles. In the Arabian Sea cores the spike at c. 18 Kyr of freshwater (low salinity, low δ 18O, high δ 13C) has been interpreted variously as due to the strengthening of NE monsoon or due to Tibetan ice melt. The role of Tibet in climate forcing is being emphasized by multiple new data. It will be relevant to know what was happening in peninsular India during this period.

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Published

1991-12-31

How to Cite

Agarwal, D. (1991). Last 20,000 years of climatic change. Journal of Palaeosciences, 40, 393. https://doi.org/10.54991/jop.1991.1788

Issue

Section

Short Articles