Abstract
Abstract. A large array of proxy records suggests that the “4.2 ka event” marks an approximately 300-year long period (∼3.9 to 4.2 ka) of major climate change across the globe. However, the climatic manifestation of this event, including its onset, duration, and termination, remains less clear in the Indian summer monsoon (ISM) domain. Here, we present new oxygen isotope (δ18O) data from a pair of speleothems (ML.1 and ML.2) from Mawmluh Cave, Meghalaya, India, that provide a high-resolution record of ISM variability during a period (∼3.78 and 4.44 ka) that fully encompasses the 4.2 ka event. The sub-annually to annually resolved ML.1 δ18O record is constrained by 18 230Th dates with an average dating error of ±13 years (2σ) and a resolution of ∼40 years, which allows us to characterize the ISM variability with unprecedented detail. The inferred pattern of ISM variability during the period contemporaneous with the 4.2 ka event shares broad similarities and key differences with the previous reconstructions of ISM from the Mawmluh Cave and other proxy records from the region. Our data suggest that the ISM intensity, in the context of the length of our record, abruptly decreased at ∼4.0 ka (∼±13 years), marking the onset of a multi-centennial period of relatively reduced ISM, which was punctuated by at least two multi-decadal droughts between ∼3.9 and 4.0 ka. The latter stands out in contrast with some previous proxy reconstructions of the ISM, in which the 4.2 ka event has been depicted as a singular multi-centennial drought.
Highlights
In South Asia, the 4.2 ka event has been linked to a weakening of the Indian summer monsoon (ISM) and the ensuing de-urbanization
A number of proxy records from the Indian subcontinent suggest that a major weakening of the ISM occurred around the 4.2 ka event (Staubwasser et al, 2003; Berkelhammer et al, 2012; Dixit et al, 2014; Nakamura et al, 2016; Kathayat et al, 2017; Figs. 1 and 2)
Our new records are sub-annually to annually (ML.1) and sub-decadally resolved (ML.2) and have unprecedented chronologic constraints, which allow us to characterize the nature of ISM variability during the 4.2 ka event more precisely than previously possible
Summary
The time interval between 4.2 and 3.9 ka (thousand of years before present, where present is 1950 CE) constitutes an important period from both climatological and archeological perspectives (e.g., Weiss et al, 1993; Cullen et al, 2000; Staubwasser et al, 2003; Berkelhammer et al, 2012; Weiss, 2016). A number of archeological studies suggest that the 4.2 ka event was associated with a series of cultural and societal changes in the Mediterranean, Middle East, Africa, and South and East Asia (e.g., Weiss et al, 1993; Enzel et al, 1999; Cullen et al, 2000; Staubwasser et al, 2003; Marshall et al, 2011; Liu and Feng, 2012; Dixit et al, 2014; Weiss, 2016). A number of proxy records from the Indian subcontinent suggest that a major weakening of the ISM occurred around the 4.2 ka event Our new records are sub-annually to annually (ML.1) and sub-decadally resolved (ML.2) and have unprecedented chronologic constraints, which allow us to characterize the nature of ISM variability during the 4.2 ka event more precisely than previously possible
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