Evidence for Sun-Climate Connections on Multi-Centennial to Millennial Timescales

 

Author:Gerard C. Bond
Affiliation: Lamont-Doherty Earth Observatory

 

New evidence from deep sea cores in the North Atlantic suggests that recurring southward shifts of drift ice were influenced by variations in solar output through the entire Holocene. Five high-resolution records of petrologic tracers of drift ice from three widely separated sites reveal a series of rapid, multi-centennial timescale oscillations (300-500 years) that are bundled into the millennial duration events.The cold phases of the multi-centennial oscillations closely match prominent, similarly-paced decreases in production rates of the cosmogenic nuclides carbon 14 and beryllium 10.The close association of those long-term variations in nuclides with distinct bundles of 4 to 6 Maunder-type solar cycles is evidence that the nuclide variations reflect solar activity and not climate. The most likely cause of each recurring southward penetration of drift ice is a shift to persistent N-NE surface winds, resembling somewhat atmospheric circulation during reduced AO/NAO. Correlatives of the solar-linked drift ice events of the North Atlantic have now been found in SW Alaska, in the Arctic Ocean, in Greenland ice cores, and in proxy records of the Asian monsoon from the Arabian Sea. At most of these sites the proxy evidence can also be explained by shifts in atmospheric circulation. The implication of these findings is that changes in solar activity altered the N. Hemisphere planetary circulation. Proxy evidence for deep ocean circulation from the North Atlantic suggests that additional amplification of the solar-forced variations there may have come from perturbations to the North Atlanticís thermohaline circulation.