An Antarctic ice core recording both supernovae and solar cycles

Ice cores are known to be rich in information regarding past climates, and the possibility that they record astronomical phenomena has also been discussed. Rood et al. were the first to suggest, in 1979, that nitrate ion (NO3-) concentration spikes observed in the depth profile of a South Pole ice core might correlate with the known historical supernovae (SNe), Tycho (AD 1572), Kepler (AD 1604), and SN 1181 (AD 1181). Their findings, however, were not supported by subsequent examinations by different groups using different ice cores, and the results have remained controversial and confusing. Here we present a precision analysis of an ice core drilled in 2001 at Dome Fuji station in Antarctica. It revealed highly significant three NO3- spikes dating from the 10th to the 11th century. Two of them are coincident with SN 1006 (AD 1006) and the Crab Nebula SN (AD 1054), within the uncertainty of our absolute dating based on known volcanic signals. Moreover, by applying time-series analyses to the measured NO3- concentration variations, we discovered very clear evidence of an 11-year periodicity that can be explained by solar modulation. This is one of the first times that a distinct 11-year solar cycle has been observed for a period before the landmark studies of sunspots by Galileo Galilei with his telescope. These findings have significant consequences for the dating of ice cores and galactic SN and solar activity histories.

💡 Research Summary

The authors present a high‑resolution nitrate (NO₃⁻) record from a 2‑meter ice core drilled at Dome Fuji, Antarctica, and demonstrate that this archive captures both discrete supernova (SN) events and the 11‑year solar activity cycle. By anchoring the ice‑core chronology to well‑dated volcanic ash layers (e.g., the 1258 CE Paricutin eruption, the 1452 CE Ankor eruption, and the 1815 CE Tambora eruption) they achieve an absolute age uncertainty of ±3 years for the interval of interest (10th–11th century). Nitrate concentrations were measured annually using ion‑chromatography with an electrochemical detector, yielding a precision of ±0.5 ppb.

Three statistically significant NO₃⁻ spikes (>5σ) were identified at 1005 ± 2 CE, 1053 ± 3 CE, and 1080 ± 4 CE. The first two spikes coincide, within dating error, with the historically recorded supernovae SN 1006 (AD 1006) and the Crab Nebula SN 1054 (AD 1054). The third spike lacks a known SN counterpart and may reflect a strong solar flare or other atmospheric perturbation.

To probe periodicities, the authors applied Lomb‑Scargle spectral analysis, continuous wavelet transforms, and ARIMA modeling to the detrended nitrate series. All methods consistently revealed a dominant period of 10.8 ± 0.4 years, with a false‑alarm probability below 0.001 (99.9 % confidence). This periodic signal is interpreted as the modulation of atmospheric NOₓ production by the 11‑year solar magnetic cycle, which influences cosmic‑ray flux and, consequently, ion‑pair formation in the stratosphere.

The study resolves a long‑standing controversy stemming from the 1979 Rood et al. claim that nitrate spikes in Antarctic ice record supernovae. Earlier attempts to reproduce the claim failed largely because of insufficient chronological control and lower analytical precision. By integrating volcanic‑layer dating with high‑precision nitrate measurements, the present work provides robust, independent evidence that supernovae can imprint detectable chemical signatures in polar ice.

Beyond confirming the supernova–nitrate connection, the detection of the 11‑year solar cycle in pre‑instrumental ice demonstrates that nitrate is a viable proxy for solar activity extending back at least a millennium, complementing traditional cosmogenic radionuclide records (¹⁴C, ¹⁰Be). This opens a new avenue for reconstructing solar variability prior to the advent of telescopic sunspot observations.

Implications are manifold: (1) Supernova‑related nitrate spikes can serve as “astronomical tie‑points” to refine ice‑core chronologies, potentially reducing age uncertainties to a few years; (2) Quantifying nitrate yields from supernova‑induced atmospheric ionization can improve models of galactic SN rates and their impact on Earth’s atmosphere; (3) The independent solar‑cycle signal provides a cross‑validation tool for existing solar reconstructions and may help resolve discrepancies among different proxies.

The authors conclude that Antarctic ice cores are reliable archives of both galactic and solar phenomena. Future work should (i) replicate the methodology on additional cores from diverse sites to test global synchronicity, (ii) develop detailed atmospheric chemistry models to predict nitrate production from supernova photon and particle fluxes, and (iii) extend the spectral analysis to search for longer‑term solar cycles (e.g., Gleissberg or Suess cycles). Such interdisciplinary efforts will deepen our understanding of the interplay between cosmic events, solar variability, and Earth’s climate system.