Tropical semi-arid grasslands are a widespread and ecologically and economically important terrestrial biome. Here, we use paleoecology to understand woodland-grassland transitions across the mid-to-late Holocene period in the Banni grassland, western India. Multi proxy analyses involving palynology, phytoliths and elemental geochemistry were carried out on two sediment cores retrieved from wetlands (Chachi and Luna), to understand temporal fluctuations in vegetation, moisture availability and other environmental parameters. Based on the results, the Chachi core was divided in to two major climatic phases. Phase 1 (4600-2500 cal yr BP) was characterized by high precipitation and abundance of pollen types and phytolith morphotypes that indicate the presence of woody savanna, and mesic herbaceous taxa. Phase 2 (2500 cal yr BP to the present) was characterized by lower precipitation, lower abundance of mesic taxa and an increase in grass phytolith abundance. However, the period from ~1000 cal yr BP to the present was characterised by the increased abundance of leguminous taxa, dryland herbs/shrubs and a decline in grass phytolith abundance. The Luna core (~1000 cal yr BP to the present) also showed results matching with the Chachi core for this latter period. Overall, moisture availability in the ecosystem appears to have declined since 4600 cal yr BP, and the vegetation has responded to this. Although the balance between tree, shrub and grass elements has fluctuated, overall, the region has remained as an open 'grass and shrub savanna' with sparse woody vegetation throughout this period. Our study 3 provides insights into the vegetation dynamics and environmental settings in a poorly understood tropical arid-grassland ecosystem from Asia during the mid-late Holocene.
Ice rafted debris (IRD) records were studied in two sediment cores (SK200/22a and SK200/27) from the sub-Antarctic and Polar frontal regime of the Indian sector of Southern Ocean for their distribution and provenance during the last 22,000 years. The IRD fraction consists of quartz and lithic grains, with the lithic grains dominated by volcaniclastic materials. IRD content was high at marine isotope stage 2 but decreased dramatically to near absence at the Termination 1 and the Holocene. The concentration of IRD at glacial section of the core SK200/27 was nearly twice that of SK200/22a. Moreover, IRD were more abundant at the last glacial maxima (LGM) in SK200/27 with its peak abundance proceeding by nearly two millennia than at SK200/22a. It appears that an intensification of Antarctic glaciation combined with a northward migration of the Polar Front during LGM promoted high IRD flux at SK200/27 and subsequent deglacial warming have influenced the IRD supply at SK200/22a. Quartz and lithic grains may have derived from two different sources, the former transported from the Antarctic mainland, while the latter from the islands of volcanic origin from Southern Ocean. Sea-ice, influenced by the Antarctic Circumpolar Current is suggested to be a dominant mechanism for the distribution of lithic IRD in the region.
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