New sedimentary evidence reveals a unique history of C4 biomass in continental East Asia since the early Miocene

Pyrogenic carbon (PyC) and n-alkane data from sediments in the northern South China Sea reveal variations in material from C-4 plants in East Asia over the last similar to 19 Ma. These data indicate the likely presence of C-4 taxa during the earliest part of the record analysed, with C-4 species also prominent during the mid and late Miocene and especially the mid Quaternary. Notably the two records diverge after the mid Quaternary, when PyC data indicate a reduced contribution of C-4 taxa to biomass burning, whereas plant-derived n-alkanes indicate a greater abundance of C-4 plants. This divergence likely reflects differences in the predominant source areas of organic materials accumulating at the coring site, with PyC representing a larger source area that includes material transported in the atmosphere from more temperate (relatively cooler and drier) parts of East Asia. Variations in the relative abundances of C-3 and C-4 taxa appear to be linked to a combination of environmental factors that have varied temporally and geographically and that are unique to East Asia. A major expansion of C-4 biomass in warmer subtropical parts of eastern Asia from similar to 1 Ma and particularly from similar to 0.4 Ma is later than other parts of the world.