Filling in Munk’s ‘orbital gap’ in climate and sea-level variability

Abstract

Abstract This study explores the linkage between lunar precessions, solar activity, plus their interactions, and the interannual variability of climate indices and Australian sea level. The focus is on variability longer than the lunar nodal cycle (18.6 years), but shorter than millennia, also known as orbital gap. Climate indices include the Pacific Decadal Oscillation, El Niño-Southern Oscillation, the Southern Oscillation Index, the Indian Ocean Dipole, and the Southern Annular Mode. Long-term (> 100 years) sea-level data were examined at Fremantle (Western Australia) and Fort Denison (Sydney, Eastern Australia). Periodicities associated with gravitational and radiational forces were fitted to 3-yr- and 5-yr-filtered records of each climate index and of sea-level records. All fits, 10 for climate indices and 12 for sea level, explained the variance of all filtered records remarkably well (>60%). Findings suggest that lunar precessions and their interactions with solar activity may be connected to interannual variations in oceanic mixing. Mixing leads to climate variability through transport of heat, mass and solutes in the atmosphere and ocean, and ultimately relates to interannual sea-level variability. This study represents the possibility of astronomic effects on Earth’s environmental variables, beyond the internal variability of the ocean-atmosphere system.