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

Abstract

[1] 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 d18 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 65°N, 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.Citation: Tian, J., X. Xie, W. Ma, H. Jin, and P. Wang (2011), X-ray fluorescence core scanning records of chemical weathering and monsoon evolution over the past 5

Persistent 400,000-year variability of Antarctic ice volume and the carbon cycle is revealed throughout the Plio-Pleistocene

“…For long-term changes, our analysis shows that surface-air temperatures rise in coherence with a reduction in AIS volume and lower d 13 C. A possible mechanism for this relation is weathering, which could be ascribed to changes in the sea level and the waxing and waning of the AIS 1 . For the past 5 Myr, a coherent relationship has been identified between chemical weathering proxies and benthic d 13 C data at orbital time scales, indicating that an increase in chemical weathering may result in lower d 13 C and a pCO2 increase 34 . During the Pleistocene, however, sea-level changes are largely controlled by NH ice volume.…”

The global monsoon across timescales: coherent variability of regional monsoons

“…By using techniques such as magnetic measurements and X-ray fluorescence core scanning, a broad spectrum of periodicities has been found in Neogene records of African summer (e); note the seasonal reversal of the wind direction. The gray bar shows the poleward limit of summer monsoon over land and the intertropical convergence zone over the ocean ; modified from Kutzbach and Gallimore, 1989). and Asian monsoons, ranging from semi-precession to longeccentricity timescales (Larrasoaña et al, 2003;Tian et al, 2011). Most promising are records from deep seas where sedimentation rates are high, such as around large river estuaries.…”

“…Nevertheless, long eccentricity of 400 ka is the most stable orbital parameter throughout the geological his- tory (Berger et al, 1992;Matthews and Froelich, 2002), and recognition of its influence has increased remarkably over the last decade. Now, these long-eccentricity cycles have been extensively documented in δ 13 C records of various time intervals of the Cenozoic, including the transition from the Paleocene to the Eocene (Cramer et al, 2003), the early Oligocene (30.5-34.0 Ma) (Salamy and Zachos, 1999;Zachos et al, 2005), the middle Oligocene (Wade and Pälike, 2004), the late Oligocene to the early Miocene (20.5-25.5 Ma;Paul et al, 2000;Zachos et al, 2001;Pä-like et al, 2006b), the early to middle Miocene (13-24 Ma) (Billups et al, 2002;Holbourn et al, 2007), and up to the Pliocene (Ziegler et al, 2010b;Tian et al, 2011). These studies document a fundamental forced mode in the Cenozoic hydrological and oceanic carbon cycles.…”

“…For example, high-resolution records of chemical weathering rates in marine sediments ascribed to monsoon precipitation have been used extensively. With the introduction of the new techniques of nondestructive analyses such as X-ray fluorescence, some element ratios such as Ti / Al and K / Si have been used to explore variability in monsoon precipitation with a much higher time resolution than previously available chemical analyses (e.g., Tian et al, 2011). River runoff is another index used in paleo-monsoon assessment, with the best example perhaps being the sapropel layers deposited in the Mediterranean produced by the extreme Nile flooding in response to the intensified African summer monsoon (e.g., Ziegler et al, 2010b).…”

“…The ODP Leg 160 to the eastern Mediterranean in 1995 (Emeis et al, 1996) and Leg 184 to the South China Sea in 1999 (P. Wang et al, 2000) recovered monsoon records back to the Neogene based on the rain-related proxies of chemical weathering rate, sapropel occurrence, and types of land vegetation. With the application of new techniques like X-ray fluorescence core scanning, the time resolutions of these reconstructions approach two-to three-hundred years for the last 5 Ma (e.g., Tian et al, 2011).…”