Palaeovegetation and climate oscillation of western Odisha, India: A pollen data-based synthesis for the Mid-Late Holocene

Abstract

The last 6000 years are of particular interest to the understanding of the Earth System because the boundary conditions of the climate system did not change dramatically (in comparison to larger glacial–interglacial changes), and because abundant, detailed regional palaeoclimatic proxy records cover this period. Here, we present fossil pollen data and examine their climatic interpretation based on a 200-cm-deep trenched sedimentary profile from Mahanadi river side, located near the Barpahar hillock of Bargarh District, Odisha, which is influenced by the South-west and North-east monsoon. The 5840 y chronology of the sediment core is based on three 14C dates on soil samples. During 5840–4380 BP, dense tropical mixed deciduous forest consisting of Madhuca, Syzygium and Acacia flourished in the region along with Rhizophora under a warm and humid climate governed by high monsoonal activity. This phase of climate is associated with the Holocene Climatic Optimum which falls within the temporal range of 8000–5000 BP. Subsequently, an increase in humidity was discerned between 4380 and 3230 BP, as evident by increase in forest elements, under warm and relatively humid climate in response to an increased monsoon. The climate during 3230–1860 BP was mild and in general less humid than today. This climate event was inevitably influenced by a notable global cold event 4200 years ago, which is synchronous with the collapse of the world's first human empire in Mesopotamia. After this event, there was a return of more humid climate from 1860 to 1300 BP, marked by high values of Potamogeton, Myriophyllum, Nymphoides, and fungal and trilete fern spores. This is further supported by the presence of Rhizophora and Sonneratia indicating high precipitation under the influence of coastal habitation. A striking signal of the Little Ice age (LIA) was observed since 1300 BP when the climate became relatively dry, as recognized in a sudden decline in major arboreals, along with high frequency of occurrence of dry herbs. This changing pattern of humidity was also reflected in the proportions of marshy/aquatic taxa, as well as ruderal taxa which is a result of human impact. The study will be helpful to display the palaeovegetation and climate in the region between Bengal and the Ganga plain.