Millennial-scale vegetation and climatic changes from an Early to Mid-Holocene lacustrine archive in Central Ganga Plains using multiple biotic proxies

Abstract The Indo-Gangetic floodplains have many abandoned meander cut-offs and oxbow lakes that can serve as potential archives for high-resolution paleoclimatic reconstruction. Previously, a few of these lakes have been investigated for understanding the regional Holocene climatic history, but these studies are generally limited by a lack of high chrono-stratigraphic resolution. To develop an understanding of the role of local and/or regional climate forcings, an oxbow lake (Baraila Tal) in the Central Ganga Plains has been studied using multiple biotic proxies such as pollen, phytoliths, diatoms, and sponge spicules. Millennial-scale climatic fluctuations and vegetation history for the Early to Mid-Holocene period have been reconstructed using 17 AMS radiocarbon dates from two trenches, 3–4 m deep. Five major biotic zones have been delineated between 13.2 and 4.8 kyr BP. Zone I (∼13–12 kyr BP) shows small patches of dry tropical woody flora along with tall C4 grass indicating a moderately dry climate. The presence of low-temperature herbs indicates an active NE monsoon but the paucity of arboreals indicates a weakened Indian Summer Monsoon (ISM). The high percentages of Phacotus lenticularis cysts in Zone II (12–9 kyr BP) indicate the presence of stagnant, lime-rich inland waters under relatively colder climatic conditions. The appearance of evergreen forest groves around 11.5 kyr BP indicates an increase in humidity, and lake deepening was inferred between 10.9 and 10.3 kyr BP. Sediment accumulation rate shows a sudden drop at ∼10.3 kyr BP indicating a complete cut-off of the oxbow lake from the fluvial channel. Zone III (9–8 kyr BP) records millennial-scale drying with a complete absence of aquatic pollen between 8.9 and 7.7 kyr BP. The expansion of short C4 grass in Zone IV (8–7 kyr BP) further indicates drier conditions. Zone V (7 –∼5 kyr BP) shows very high percentages of sponge spicules that flourish in clear waters, and represents a strengthened ISM and a subsequent lake expansion.