A 10ka Holocene record of cyclic precipitation in a closed catchment in SE Australia, associated with episodes of solar Grand Minima and variations in galactic cosmic ray flux

Lake George is a closed basin located 50 km north-east of Canberra, in southeastern Australia.  Historical records indicate that lake levels directly reflect precipitation; eight cycles of high water levels (up to 7m depth), interspersed with dry lake conditions, have occurred since 1820 CE. Over longer time scales, shoreline sediments also record phases of high water up to 14m depth in Lake George during the past 15000 years. Optically stimulated luminescence (OSL) chronologies show multiple high lake phases extending through the Holocene, with a dominant cyclic pattern of c. 2300 y.

Here we compare the Holocene lake-level data with astronomical and solar phenomena over the same time period. In particular, we calculate a cyclicity in the Grand Alignments (GAs) of the four Jovian planets of 4628 y and near GAs occurring at 2314 y intervals, the timing of which is coeval with the Lake George filling events. GAs have been observed to align with Grand Minima (GMs) (eg Maunder and Spoerer Minima) in solar activity (sunspots) which produce phases of high galactic cosmic ray flux on Earth. The timing of GMs is obtained by reconstruction of ¹⁰Be and ¹⁴C fluxes as recorded in terrestrial sediments.  These high fluxes also appear to show a temporal relationship with occurrence of the lake level highs. 

The recognition of cosmic ray flux episodes, rather than individual GMs, strongly indicates an association between observed solar activity and the high lake levels as preserved in the Lake George sediment archive. The time span 0-9.4ka contains four GM episodes and 13 OSL dated lake levels.  Of the latter, 69% date within the episodes of GM. The evidence suggests that precipitation in the Lake George basin has been associated with Jovian planet grand alignments and near GAs for at least the past 15000 years, and with phases of reduced solar and interplanetary magnetic field  strength and increased GCR flux in the vicinity of the Earth. 

The study supports the hypothesis that solar activity exhibits the well -known Hallstatt cycle periodicity (2300 yr).  Mechanisms for cause and effect remain subjects for further study.