Multiple Be-10 records revealing the history of cosmic-ray variations across the Iceland Basin excursion

作者：Horiuchi Kazuho^*; Kamata Kanae; Maejima Shun; Sasaki Sho; Sasaki Nobuyoshi; Yamazaki Toshitsugu; Fujita Shuji; Motoyama Hideaki; Matsuzaki Hiroyuki

来源：Earth and Planetary Science Letters, 2016, 440: 105-114.

DOI：10.1016/j.epsl.2016.01.034

• beryllium isotopes
• cosmic-ray variation
• geomagnetic excursion
• solar variability
• paleomagnetism
• global synchronization

Cosmogenic Be-10 is a proxy of cosmic-ray flux, and its natural records provide vital information about the past intensity variability of the geomagnetic field and solar activity. Be-10 records also serve as powerful tools for global synchronization among a variety of paleoarchives and for elucidating sedimentary processes on natural remanent magnetization acquisition. However, high-resolution (multi-decadal to multi-centennial) records of Be-10 are scarce, especially those older than several tens of thousands of years. Here we present multiple high-resolution Be-10 records of the Iceland Basin geomagnetic excursion interval (ca. 170-200 kyr ago) obtained from sediment cores (authigenic Be-10/Be-9 ratio) and an ice core (atmospheric Be-10 flux). Comparing sedimentary Be-10 records with relative paleointensity from the same cores, we found differences in the magnetic lock-in depth, even between adjacent cores. The Be-10-proxy records from the sediment and ice cores exhibit common characteristics: an asymmetric large-scale variation, a similar to 7-kyr quasi-plateau around the maximum with a characteristic mid-term depression, and multi-millennial fluctuations in cosmic-ray flux during this interval. Minimal-synchronized and stacked Be-10 records show that maximum cosmic-ray flux occurred 188.5-190.0 kyr ago and was double the present flux. A wavelet analysis of the stacked curve reveals dominant 4-kyr and secondary 8-kyr periodicities, both of which can be interpreted as intrinsic geomagnetic cycles. The wavelet spectrum of the high-resolution ice-core record shows a periodicity of 1.7 kyr and somewhat intermingled multi centennial cycles around the maxima of Be-10, which likely represent solar cycles in this period. High resolution Be-10 records from multiple paleoarchives provide both a robust proxy record of cosmic-ray flux and a valuable tool for detailed global synchronization based on cosmic-ray variations.

• 出版日期2016-4-15
• 单位中国极地研究中心