2470 million-year-old banded iron formation reveals a climatic oscillation consistent with the Gleissberg solar cycle

Abstract

Modern-day solar cycles due to the solar magnetic field oscillation are well recognized. Owing to the response of Earth’s climate to solar activity fluctuation, solar cycles in the Phanerozoic Eon have been recorded by laminites and fossil tree rings. However, the existence of magnetic cycles within the Sun younger than 3100 million-year-old is still unknown. The deposition of Precambrian banded iron formations (BIFs) reflects the primary productivity of the early ferruginous oceans and is coupled to climatic fluctuations. Here we apply synchrotron-radiation-based µ-XRF with a 20 µm interval on a 60 mm long, 2470 million-year-old BIF from the Kuruman Formation, South Africa. Our spectral analyses of multiple elemental concentration series reveal prominent and consistent 80-year cyclicity, which is best explained by the Gleissberg solar cycle. We hypothesize that solar cycles have already modulated the early Paleoproterozoic climate mainly through high energy irradiance coupled solar radiative forcing oscillation and the solar magnetic field controlled galactic cosmic ray fluctuation. Our result provides the record of solar magnetic field oscillations with stable and close-to-present cycle durations at least since the beginning of the Paleoproterozoic Era.