RESPONSE OF MANGANESE IN THE OCEAN TO THE CLIMATIC CYCLES IN THE QUATERNARY

Profiles of the Th-230 concentration in Mn crusts from the central Pacific Ocean measured at extremely high depth resolution reveal that the growth rates of Mn crusts are influenced by climate. Based on a "constant flux model" the sections of maximum Th-230 concentration correspond to periods of slow growth during glacial stages. Fast growth occurred during interglacial stages 1, 5, and 7, probably due to a larger supply of Mn oxides from the water column. High-resolution profiles of Th-230 and Be-10 in sediment cores from high biological productivity areas display radioisotope maxima in the interglacial stages and minima during glacial periods, the ratio of the fluxes of Be-10/Th-230 being >= 4. The only exceptions are observed at 135 and 270 kyr B.P., where the ratio of the fluxes is as low as 0.1 to 0.3. We presume that this "Th-230 anomaly" reflects short periods of time at the end of glacials when precipitation of MnO2 occurred. This hypothesis is confirmed by peaks of Mn observed in sediment cores mainly at the transitions from glacial to inter-glacial stages. The standing crops of Mn in these layers suggest release of Mn2+ from the sediments during glacial stages and buildup of Mn in the water column to concentrations of up to 10 mu mol/L.