X-ray fluorescence core scanning records of chemical weathering and monsoon evolution over the past 5 Myr in the southern South China Sea

Abstract

We present ultrahigh resolution K/Al and Ti/Al records at ODP Site 1143 for the past 5 Myr, which were obtained by nondestructive X-ray fluorescence (XRF) core scanning on the sediment surface of the archive half cores of this site at a step of 1 cm. The K/Al and Ti/Al records and their amplitudes of the variability on glacial/interglacial cycles show a markedly increasing trend since ∼2.5 Ma, indicating a gradual strengthening of the chemical weathering and the East Asian summer monsoon under the influences from the Northern Hemisphere glaciation (NHG). Evolutive cross spectral analyses of K/Al with benthic foraminiferal δ 18 O reveal that phases of the East Asian summer monsoon abruptly changed by more than 90 at 4.0 Ma, 2.75 Ma, 1.0 Ma and 0.6 Ma relative to global ice volume at the obliquity and the precession bands over the past 5 Myr. Strong 400 kyr and 100 kyr cycles in the K/Al and Ti/Al records consistently exist over the past 5 Myr. Particularly, these cycles are highly coherent with the long and short eccentricity cycles in the truncated insolation at 65N, indicating an eccentricity forcing of the East Asian summer monsoon. The chemical weathering recorded in the elemental records of ODP Site 1143 also shows highly coherent relationship with the ocean carbon reservoir at the eccentricity, the obliquity and the precession bands over the late Pliocene and Pleistocene. Copyright 2011 by the American Geophysical Union.