Geochemistry on manganese deposit from the Median Valley of the Mid-Atlantic Ridge

The accumulation rate is 100 mm to 200 mm/10 million year, or 2 orders of magnitude faster than the typical rate for deep-sea ferromanganese deposits.

The rapid growth rate and unusual chemistry are consistent with a hydrothermal origin or with a diagenetic origin by manganese remobilized from reduced sediments. Because of the association with an active ridge, geophysical evidence indicative of hydrothermal activity, and a scarcity of sediment in the sampling area, we suggest that a submarine hot spring has created the deposit.