Impact of Climate Change on Past Indian Monsoon and Circulation: A Perspective Based on Radiogenic and Trace Metal Geochemistry

Harunur Rashid,Yang Wang,Alexandra T Gourlan

doi:10.3390/atmos12030330

Abstract

The Indian summer monsoon (ISM), one of the dramatic illustrations of seasonal hydrological variability in the climate system, affects billions of lives. The ISM dominantly controls the northern Indian Ocean sea-surface salinity, mostly in the Bay of Bengal and the Andaman Sea, by the Ganga-Brahmaputra-Meghna and Irrawaddy-Salween rivers outflow and direct rainfall. In the past decade, numerous studies have used radiogenic neodymium (εNd) isotopes of seawater to link Indian subcontinent erosion and the ensuing increase in discharge that results in changes in the north Indian Ocean sea surface. Here we synthesized the state of the ISM and ocean circulation using the neodymium and hafnium isotopes from north Indian Ocean deep-sea sediments. Our data suggest that the Bay of Bengal and north Indian Ocean sea-surface conditions were most likely modulated by changes in the ISM strength during the last glacial-interglacial cycle. These findings contrast to the hypothesis that suggests that the bottom water neodymium isotopes of the northern Indian Ocean were modulated by switching between two distant sources, namely North Atlantic Deep Water and Antarctic bottom water. Furthermore, the consistency between the neodymium and hafnium isotopes during the last glacial maximum and Holocene suggests a weak and dry ISM and strong and wet conditions, respectively. These data also indicate that the primary source of these isotopes was the Himalayas. Our results support the previously published paleo-proxy records, indicating weak and strong monsoons for the same periods. Moreover, our data further support the hypothesis that the northern Indian Ocean neodymium isotopes were decoupled from the global ocean neodymium budget due to the greater regional influence by the great Ganga-Brahmaputra-Meghna and Irrawaddy-Salween discharge draining the Indian subcontinent to the Bay of Bengal and the Andaman Sea.

Highlights

Monsoons represent one of the Earth’s most dynamic interactions between the atmosphere, ocean, and continent [1,2,3]
We present combined seawater and detrital εNd and εHf data from one of the tropical northern Indian Ocean sites—758 of the Ocean Drilling Program (ODP)—to reconstruct the past strength of the Indian summer monsoon (ISM)
Gourlan et al [23] considered the primary sources of Nd contributing to εNd values in the northern Indian Ocean: (i) the Himalayan rivers, (ii) the Indonesian Throughflow, and (iii) the North Atlantic Deep Water

Summary

Introduction

Monsoons represent one of the Earth’s most dynamic interactions between the atmosphere, ocean, and continent [1,2,3]. If the 2019 Intergovernmental Panel for Climate Change predictions of global temperature rise are correct, the freshwater availability resulting from the melting of these glaciers and monsoonal rainfall becomes a significant concern for sustaining the livelihood of a billion people. In this context, past climate studies that refer to the present issues of global warming and glacial melt could shed light on the monsoon’s future aspects for the Indian subcontinent

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Conclusion