Study focusses on history of climate change, rainfall pattern

Visualise a landscape with dense evergreen forests stretching from the Western Ghats up to the coastline. Kerala would have looked something like that about 10,000 to 5,000 years ago in time, according to the findings of a study conducted by a team of scientists from the Agharkar Research Institute, Pune; Centre for Earth Science Studies, Thiruvananthapuram; and Birbal Sahni Institute of Palaeobotany, Lucknow.

Peat deposits unearthed from wetlands and riverbanks in Kerala are helping scientists unravel the history of climate change and geological evolution along the southwest coast of India.

Scientific analysis of buried sub-fossil logs and partially carbonized wood remains dug up from the Kollam - Kodungalloor stretch suggests that the coastal plains and adjoining midlands west of the Western Ghats were once covered with thick tropical evergreen forests lashed by heavy monsoon rain.

The study funded by the Council of Scientific and Industrial Research (CSIR) and the Kerala State Council for Science, Technology, and Environment (KSCSTE) indicates that the high rainfall and low-sea level, in the period between 9,000 and 6,000 years ago, had a significant impact on the development and sustenance of dense wet evergreen forests covering the entire terrain from the Western Ghats to the coast.

A pointer

In a paper published in PLOS One, an international open access online journal brought out by the Public Library of Science, the scientists conclude that the intensification of the monsoon during the period from 8,500 to 5,500 years ago, coupled with sea-level rise, had led to almost catastrophic floods, causing the destruction of the forests and their burial under clay, silt, and sand.

Climate data

According to the paper authored by K.P.N. Kumaran, Palynologist, Agharkar Institute; D. Padmalal, CESS; and others; the peat deposits provide a valuable source of climate data, alleviating the lack of meteorological records dating back to the Holocene period, 10,000 to 5,000 years back in time. These sub-fossil logs of tropical evergreen forests represent a unique paleoenvironmental database and contribute to a better understanding of the intensified Asian summer monsoon, it says. Peat represents the first stage in the carbonisation of wood, the subsequent ones being lignite and coal.

During their investigations, the scientists came across a large number of tree trunks embedded in carbonaceous and silty clays at different locations along the Kollam- Ernakulam coast, the banks of the Kayankulam and Vembanad lagoons, and paddy fields and swamps in the midland region. As many as 25 species of wood were identified by the team.

The paper concludes that the intensified and prolonged monsoon, estimated to be two to three times more than the present, was responsible for the destruction of the dense forests stretching from the Western Ghats to the coast. The drastic increase in river flow and sediment transport could have abruptly flooded the forest and buried the trees even before the formation of the major backwater systems including the Vembanad lagoon.

The paper published on April 11 observes that the abundance of wood fossils along with dissolved carbon makes the wetlands of Southwest India one of the best carbon sinks in the country. The authors add that the wetlands hold immense potential for palaeoecological reconstruction of long-term landscape and vegetation changes.