Continuous surface dwelling of manganese nodules on a hill on the Madeira Abyssal Plain during abrupt sedimentation changes

The accretion rate of manganese nodules and the sedimentation rate of the underlying sediment has been studied with 10 Be and 14 C on a nodule covered hill in the Madeira Abyssal Plain. The accretion rate of (3.2±0.6) mm/Ma for the nodules is considerably smaller than the average sedimentation rate of 12 mm/ka for the last 50–100 ka. The mechanism that kept the nodules at the surface in this specific environment during the last 40 ka is likely to be flotation. The discovery of a large manganese-covered concretion in a piston core points to a long period of sediment winnowing. The 14 C analyses also seem to point to an increase in the sedimentation rate round 6500 yrs B.P.