New sedimentary evidence reveals a unique history of C(4) 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 ~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 ~1 Ma and particularly from ~0.4 Ma is later than other parts of the world.