Abstract
Abstract. The expansion of C4 vegetation during the Neogene was one of the largest reorganizations of Earth's terrestrial biome. Once thought to be globally synchronous in the late Miocene, site-specific studies have revealed differences in the timing of the expansion and suggest that local conditions play a substantial role. Here, we examine the expansion of C4 vegetation on the Indian Peninsula since the late Miocene by constructing a ∼6-million-year paleorecord with marine sediment from the Bay of Bengal at Site U1445, drilled during International Ocean Discovery Program Expedition 353. Analyses of element concentrations indicate that the marine sediment originates from the Mahanadi River in the Core Monsoon Zone (CMZ) of the Indian Peninsula. Hydrogen isotopes of the fatty acids of leaf waxes reveal an overall decrease in the CMZ precipitation since the late Miocene. Carbon isotopes of the leaf wax fatty acids suggest C4 vegetation on the Indian Peninsula existed before the end of the Miocene but expanded to even higher abundances during the mid-Pliocene to mid-Pleistocene (∼3.5 to 1.5 million years ago). Similar to the CMZ on the Indian Peninsula, a Pliocene expansion or re-expansion has previously been observed in northwest Australia and in East Africa, suggesting that these tropical ecosystems surrounding the Indian Ocean remained highly sensitive to changes in hydroclimate after the initial spread of C4 plants in late Miocene.
Highlights
The expansion of plants using the C4 photosynthetic pathway is one of the most dramatic reorganizations of the global biome during the Neogene
Marine sediment deposits in other parts of the Bay of Bengal closer to the Krishna and Godavari rivers or the Ganges and Brahmaputra rivers have a more mafic or highly variable composition that is not observed at Site U1445 (e.g., Tripathy et al, 2014; Fig. B1)
Our study provides a piece of the puzzle in unraveling the complexities of C4 vegetation expansion
Summary
The expansion of plants using the C4 photosynthetic pathway is one of the most dramatic reorganizations of the global biome during the Neogene. An increasing number of studies have shown that the timing, regional patterns, rate, and drivers of C4 grassland expansion were much more diverse and complex (An et al, 2005; Behrensmeyer et al, 2007; Huang et al, 2007; Edwards et al, 2010; Zhou et al, 2014). Along with low pCO2, a C4 photosynthetic pathway is better adapted to higher temperature, aridity, seasonality, and during disturbances such as flood, droughts, and fires (e.g., Edwards et al, 2010, and references therein). The interplay of these parameters varies amongst regions. Resolving the precise timing and factors leading to major changes in vegetation demands site-specific studies (Strömberg, 2011; Zhou et al, 2014)
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