Chemical Weathering Intensity and Terrigenous Flux in South China during the Last 90,000 Years—Evidence from Magnetic Signals in Marine Sediments

Abstract

The level of chemical weathering is strongly affected by climate. We presented magnetic properties associated with element ratios from the northern part of the South China Sea to denote links between chemical weathering intensity and monsoon changes in the previous 90,000 years. The magnetic parameter IRM AF80mT /SIRM, representing the variations of high coercivity minerals in marine sediments accompanied with the Al 2 O 3 /TiO 2 and the Chemical Index of Alteration (CIA), demonstrates strong chemical and physical weathering processes during the last 84-40 kyr when intensified Asian monsoon and warm climate occurred. High susceptibility, TiO 2 content, and relatively coarser magnetic mineral grain (relatively low ARM/SIRM ratio) also suggest more terrigenous clastic flux resulting from intensified physical erosion and river transport ability. During the 40-15 kyr period, a low IRM AF80mT /SIRM as well as chemical proxies indicate weak weathering as the climate cooled and precipitation decreased.

Influence of Sea Level Change and Centennial East Asian Monsoon Variations on Northern South China Sea Sediments Over the Past 36 kyr

“…interval in PC338. Relatively low S –300 values occurred over glacial stages at other sites because of aerosol dust inputs (Chen et al, ) or strong weathering periods (Yang et al, ). These factors caused S –300 variations within a total limit of 0.06 over the past 36 kyr B.P., so terrestrial weathering influences cannot explain the low S –300 values over the ∼32–15 kyr B.P.…”

“…; Hu et al, ), ∼0.85–0.95 for STD111 (40–0 kyr B.P. interval; Yang et al, ), >0.94 for MD12–3432 (40–0 kyr B.P. interval; Chen et al, ), >0.85 for ODP1146 (Kissel et al, ), >0.9 for Qd34 (∼14–0 kyr B.P.…”

“…The EASM is driven primarily by insolation, appearing as almost synchronous variations of EASM intensity and 308N summer insolation with interruptions by cold events (Dykoski et al, 2005). The Bølling/Allerød (B/A) and YD stages were, respectively, global warm and cold periods, while the Holocene Optimum (HO) was a warm and wet stage with inconsistent onset and duration in the EAM region (Zhang et al, 2011;Zhou et al, 2016b). It has been demonstrated that the HO occurred in the early Holocene in southern China (11.5-6 kyr B.P.…”

“…It has been demonstrated that the HO occurred in the early Holocene in southern China (11.5-6 kyr B.P. ), with an onset that was gradually later northward because of gradual northward transgression of the EASM peak Geochemistry, Geophysics, Geosystems 10.1029/2017GC007321 Zhong et al, 2010;Zhou et al, 2004Zhou et al, , 2005Zhou et al, , 2016b. v fd and v lf variations within core PC338 were coeval with regional climate, which implies that magnetic mineral supply was dominated by regional climate over the past 15 kyr.…”

“…The Qiongdongnan Basin (QB) is delineated by the black closed curve. Cores ODP1144 (Hu et al, ), STD111 (Yang et al, ), MD12–3432 (Chen et al, ), ODP1146 (Kissel et al, ), Qd34 (Yang et al, ), PC24 (Ouyang et al, ), PC83 (Yang et al, ), and PC111 (Yang et al, ) in the northern SCS have also been studied magnetically. Cores STAT22 (Cui et al, ), X2 (Xu et al, ), 337PC (Wan et al, ), and Site 38 (Liu et al, ) were used for provenance studies.…”