SOLAR INFLUENCE ON THE SUBTROPICAL EASTERN PACIFIC OXYGEN MINIMUM ZONE DURING THE HOLOCENE

Recently, persistent solar influence on North Atlantic climate during the Holocene was recognized. This is based on correlation between inferred changes in production rates of the cosmogenic nuclides C-14 and Be-10 and variations at centennial to millennial time scale in proxies of drift ice measured in sediment cores. We report here close correlation of cosmogenic nuclides C-14 with sediment proxies that reflect mostly biological productivity changes during the past 10 kyr from two sites in the subtropical eastern Pacific at 23 oN off Baja California. Sediment concentrations of molybdenum and cadmium were measured at 1-cm resolution (~ 50 yr time resolution) at 400-m and 700-m sites that consist of a multicore and a gravity core at each site. The sediments were laminated throughout the Holocene and both sites are located within the present day oxygen minimum zone with bottom water oxygen < 2 µM. Sediment Cd is dominated by a particulate non-lithogenic component as in the case of modern Santa Barbara Basin thus records mostly surface water driven productivity change. Sediment Mo is enriched in reducing, sulfidic sediments as a result of low bottom water oxygen and high carbon rain rate to sea floor. The chronology of the 400-m and 700-m sites were based on 8 and 13 radiocarbon dates of benthic foraminifera for the past 10kyr, with an average sedimentation rates of ~ 20 and 30 cm/kyr, respectively. Between 2.3 kyr and 9.5kyr B.P. at 400-m site, sediment Cd and Mo after median filtering with a window length of 250 years correlated positively with cosmogenic nuclide C-14 with a correlation coefficient between 0.4 and 0.5. This correlation is significant at > 95% level and mainly reflect variations on centennial time scale. Between 2.3 kyr and 7.5 kyr B.P., proxies after median filtering with a window length of 500 years at 400-m and 700m sites are correlated with each other and with the cosmogenic C-14 with a correlation coefficient ranging from 0.6 to 0.8. This later correlation is significant at > 95% level and mostly reflect variations on millennial time scale. If indeed Ä14C in tree rings reflect changes in production rate of cosmogenic carbon-14, our records suggest that solar influence on Holocene climate extends beyond the North Atlantic and is also persistent on centennial time scale.