Trace elements as proxies for seasonality in a modern speleothem from northeast India

Abstract

In monsoonal regions, speleothem proxy records focus on the wet season and are typically interpreted as records of “monsoon strength.” More often than not, the question about the relative importance of changes of rainfall amount versus seasonality and/or moisture source remains unclear. Here we combine a sub-seasonally resolved speleothem trace element record from Mawmluh Cave in NE India with I-STAL forward modeling experiments to show that dry season effective infiltration is the main driver of proxy variability in this Indian Summer Monsoon dominated region. Winter temperature driven ventilation of Mawmluh Cave further biases proxy records towards the dry season through enhanced CO2 degassing and increased stalagmite growth rates. During the 1976-1998 warm phase of the Pacific Decadal Oscillation, winter rainfall above Mawmluh Cave increased, which is reflected in higher δ18O values and reduced seasonal amplitudes in trace elements.