Was LIA synchronous with equa-tropical climate? A multiproxy study from the southwest coast of India

Abstract

A comprehensive study of the Mundrothruthu (MT) core (70 cm) from the Asthamudi wetland in Kollam, Kerala, India reveals three climate phases during the Little Ice Age (LIA) through multi-proxy investigations. The period (1507–1518 CE) shows high agricultural activity indicated by abundant diatom diversity, significant terrestrial influx, and freshwater runoff. Elevated TOC% and δ¹³C_TOC values suggest high temperature and a warm, humid climate, likely driven by high terrestrial influx and transport of organic matter from the nearby surroundings. This may have increased the organic matter influx to the estuary leading to high TOC% and more negative δ¹³C values. The second phase (1519–1548 CE) is characterized by increased marine incursion due to enhanced tidal currents, evidenced by a rise in marine palynomorphs, mixed terrestrial and marine organic matter, less negative δ¹³C values, and increased mud content. This shift likely reflects changes in sea level or tidal dynamics. The final period (1548–1804 CE) is marked by further enhancement of marine taxa, lower TOC%, and δ¹³C_TOC values, indicating reduced atmospheric CO₂ and a temperature decrease of about 1 °C. This period is associated with reduced solar insolation and a southward shift of the Inter Tropical Convergence Zone (ITCZ). The study highlights both synchronous and asynchronous climatic behavior on the southwest coast of India relative to global changes during the LIA. Initially warm and humid with high agricultural productivity, the region gradually shifted to marine-dominated conditions due to tidal dynamics and broader climatic shifts. These findings underscore the complex interplay between local and global climatic factors during the LIA.