CLIMATIC INFLUENCES ON THE GROWTH-RATES OF MN CRUSTS DURING THE LATE QUATERNARY

The concentration of Th-230 in Mn crust VA13-2 (146-degrees-W, 9-degrees-25'S, 4830 m) from the Pacific Ocean was measured with high depth resolution (0.02 mm) to a depth of 1.4 mm corresponding to an age of approximately 226 ka B.P. The mean growth rate estimated from these results is 6.2 +/- 0.4 mm/Ma. However, the exponential curve obtained shows two drastic events in the Th-230 concentration record with durations of 41 +/- 4 ka and 37 +/- 6 ka which are interpreted as growth standstills. The decay-corrected Th-230 concentration is inversely correlated with those of Mn, Fe and Co indicating that the Th-230 flux into the crust has been constant throughout time and that the observed fluctuations in Th-230 are due to dilution by the main components. By applying a constant Th-230 flux model, high-resolution growth rates were derived from every sample investigated. A detailed comparison of the growth pattern with the SPECMAP time table reveals that the VA13-2 growth rates tend to be higher during interglacial than during glacial periods. In particular, the observed growth standstill are associated with glacial stages 6 and 8. Further investigation of Mn crust 72 DK 9 taken from shallower water (170-degrees-35'W, 20-degrees-13'N, 1550 m) tend to confirm that there is a link between the growth rates of hydrogenetic crusts and the climate of the Late Quaternary.