[A-CC21] Ice cores and past environmental changes

[ACC21-08] Long-term periodicities in solar activity between 170 and 200 kyr ago reconstructed from ¹⁰Be in ice-core and sediment archives

★Invited papers

*Kazuho Horiuchi¹, Kanae Kamata¹, Shun Maejima¹, Sho Sasaki¹, Nobuyoshi Sasaki¹, Toshitsugu Yamazaki², Shuji Fujita³, Hideaki Motoyama³, Hiroyuki Matsuzaki⁴ (1.Graduate School of Science and Technology, Hirosaki University, 2.The Atmosphere and Ocean Research Institute, The University of Tokyo, 3.National Institute of Polar Research, 4.The University Museum, The University of Tokyo)

Centennial to millennial periodicities of past solar activity in the Holocene epoch have been well investigated by using cosmogenic-nuclides records from tree-ring (¹⁴C) and ice-core (¹⁰Be) archives. However, those of the older ages are quite unclear because high-resolution records of cosmogenic nuclides are scarce. We obtained multiple high-resolution ¹⁰Be records (atmospheric ¹⁰Be flux and authigenic ¹⁰Be/⁹Be ratio) of 170–200 kyr ago, the period that includes the Iceland Basin geomagnetic excursion interval (Horiuchi et al., in press). Strong consistency among the records enables us to construct a robust ¹⁰Be stack of this interval. A wavelet analysis of the stacked record reveals 4-kyr and 8-kyr periodicities, both of which can be interpreted as intrinsic geomagnetic cycles. We also found a cycle of 1.7 kyr in the ¹⁰Be stack record, but it is significant only near the ¹⁰Be maximum (the minimum of the geomagnetic paleointensity). A relative enhancement of solar modulation in ¹⁰Be production is predicted with reduced paleointensity (Masarik and Beer, 1999; Beer et al., 2012). Therefore, it is possible to attribute this cosmogenic 1.7-kyr cycle to the long-term solar cycle that is identified in this period. The wavelet spectrum of the highest-resolution ¹⁰Be record (obtained from the Dome Fuji ice core) shows more a detailed structure than the stacked record. The 4- and 1.7-kyr cycles show similar tendencies to, and are clearer than, those of the stack. The spectrum also shows somewhat intermingled multi-centennial (0.3, 0.5 and 0.7 kyr) cycles around the maxima of ¹⁰Be, which likely represent solar cycles in this period (note: 200-yr Suess/de Vries cycle is under the detection limit of our record). On the other hand, the 2.2–2.4-kyr Hallstatt cycle and 1-kyr Eddy cycle, which are frequently documented in Holocene cosmogenic records, are not dominant in our records.