Pavón-Carrasco F J, Gómez-Paccard M, Campuzano S A, González-Rouco J F, Osete M L
Universidad Complutense de Madrid, 28040, Madrid, Spain.
Instituto de Geociencias IGEO (UCM-CSIC), 28040, Madrid, Spain.
Sci Rep. 2018 Jun 29;8(1):9820. doi: 10.1038/s41598-018-28115-4.
The production of cosmogenic isotopes offers a unique way to reconstruct solar activity during the Holocene. It is influenced by both the solar and Earth magnetic fields and thus their combined effect needs to be disentangled to infer past solar irradiance. Nowadays, it is assumed that the long-term variations of cosmogenic production are modulated by the geomagnetic field and that the solar field dominates over shorter wavelengths. In this process, the effects of the non-dipolar terms of the geomagnetic field are considered negligible. Here we analyse these assumptions and demonstrate that, for a constant solar modulation potential, the geomagnetic field exerts a strong modulation of multi-centennial to millennial wavelengths (periods of 800 and 2200 yr). Moreover, we demonstrate that the non-dipole terms derived from the harmonic degree 3 and above produce maximum differences of 7% in the global average radiocarbon production rate. The results are supported by the identification, for the first time, of a robust coherence between the production rates independently estimated from geomagnetic reconstructions and that inferred from natural archives. This implies the need to review past solar forcing reconstructions, with important implications both for the assessment of solar-climate relationships as well as for the present and future generation of paleoclimate models.
宇宙成因同位素的产生为重建全新世期间的太阳活动提供了一种独特的方法。它受到太阳磁场和地球磁场的共同影响，因此需要厘清它们的综合效应，以便推断过去的太阳辐照度。如今，人们认为宇宙成因产生的长期变化受地磁场调制，而太阳磁场在较短波长上起主导作用。在此过程中，地磁场非偶极项的影响被认为可以忽略不计。本文分析了这些假设，并证明，对于恒定的太阳调制势，地磁场对多世纪至千年时间尺度（800年和2200年周期）的波长有强烈调制作用。此外，我们还证明，从3阶及以上球谐项导出的非偶极项在全球平均放射性碳产生率上产生的最大差异为7%。首次从地磁重建独立估算的产生率与从自然档案推断的产生率之间发现了稳健的一致性，这支持了上述结果。这意味着有必要重新审视过去的太阳强迫重建，这对评估太阳与气候的关系以及古气候模型的当前和未来发展都具有重要意义。
