Disentangling Geomagnetic and Precipitation Signals in an 80-kyr Chinese Loess Record of¹⁰Be

Abstract

The cosmogenic radionuclide 10 Be is produced by cosmic-ray spallation in Earth's atmosphere. Its production rate is regulated by the geomagnetic field intensity, so that its accumulation rate in aeolian sediments can, in principle, be used to derive high-resolution records of geomagnetic field changes. However, 10 Be atmospheric fallout rate also varies locally depending on rainfall rate. The accumulation rate of 10 Be in sediments is further complicated by overprinting of the geomagnetic and precipitation signals by 10 Be attached to remobilized dust, which fell from the atmosphere at some time in the past.Here, we demonstrate that these signals can be deconvoluted to derive both geomagnetic field intensity and paleoprecipitation records of Asian Monsoon intensity in an 80,000-yr-long 10 Be record from Chinese loess. The strong similarity between our derived paleomagnetic intensity record and the SINT 200 (Guyodo andValet 1996) and NAPIS 75 (Laj et al. 2002) stackedmarine records suggests that this method might be used to produce multimillion-yr-long records of paleomagnetic intensity from loess. This technique also reveals a new method for extracting quantitative paleoprecipitation records from continental interior regions. Our derived precipitation record is broadly similar to the speleothem δ 18 O-based records of paleo-Asian Monsoon intensity from Dongge (Yuan et al. 2004) and Hulu (Wang et al. 2001) caves, and suggests that the paleo-Asian Monsoon intensity may be responding to a combination of both Northern and Southern Hemisphere insolation forcing.

Measurement of 10Be Concentration of Modern Falling Dust in Northern China

“…The 10 dust BeO samples compare well with previous measurements on Luochuan loess measured at the VERA AMS laboratory in Vienna and NSF-AMS in Tucson (Zhou et al 2007a). Therefore, the obtained modern falling dust 10 Be signals can be considered a robust value for 10 Be concentration in the recycled dust component of Chinese loess.…”

“…Figure 2a shows the average mass-corrected 10 Be concentrations of modern falling dust samples from Ansai station during 2008 and 2009. The mean value is 1.21 × 10 8 atoms/g, which is similar to that found in loess especially during the glacial stages (Shen et al 2000;Zhou et al 2007a), and the adjacent Dingbian falling dust 10 Be concentration (1.25 ± 0.06 × 10 8 atoms/g) reported by Shen et al (2009). The calculated relative standard deviation (RSD), which is the ratio of the standard deviation (SD) with its mean value, is ~13%, suggesting that the dust 10 Be signal is relatively uniform on seasonal scales.…”

Meteoric cosmogenic Beryllium-10 adsorbed to river sediment and soil: Applications for Earth-surface dynamics

“…After production, the particle-reactive 10 BeO or 10 Be(OH) 2 diffuses through the atmosphere until it attaches to an atmospheric aerosol. Precipitation cleanses the atmosphere of 10 Be attached to aerosols to a degree that is not currently known (Field et al, 2006;Zhou et al, 2007). When delivered to an aqueous environment, 10 Be is ultimately scavenged from non-acidic water on settling particles and deposited in marine and lacustrine bottom sediments where it decays with a half-life of 1.39 million yr (Nishiizumi, 2007;Chmeleff et al, 2009;Korschinek et al, 2009).…”

Evolution of the Indian summer monsoon during the interval 32.7–11.4cal. ka BP: Evidence from the Baoxiu peat, Yunnan, southwest China

“…An increase in monsoon rainfall during this period is also recorded in sediments of the Yuanbao Loess on the western edge of the Chinese Loess Plateau . A 10 Be record from a Luochuan Loess profile in central China gives further evidence for a strong summer monsoon from 23 to 19 ka BP (Zhou et al, 2007). However, various proxy climate indicators from both terrestrial and marine sediments suggest a weakening of the ISM during this time.…”