Sediment accumulation rates and particle mixing at northwestern Pacific seamounts

Abstract

Cobalt-rich ferromanganese crusts are present on seamount summits throughout the northwestern Pacific at water depths of approximately 1000 to 2500 m, where they are often associated with unconsolidated sediments. Sedimentation rates at the summits of seamounts calculated from ages 14 C were 0.61 to 2.05 cm kyr −1 , higher than those of the surrounding abyssal plain. Sediments at seamount summits consist almost entirely of carbonate, which may contribute to higher sedimentation rates at summits than at seamount feet, which are below the carbonate compensation depth. The shallowest mixing layer depth and the smallest particle mixing coefficient (estimated from 210 Pb data) at the summit areas than at the foot of seamounts; suggest a weak bioturbation activity in the peaks. The difference in bottom-water dissolved oxygen and particulate organic matter concentrations between the summits and feet of the seamounts in the northwestern Pacific may contribute to this difference in bioturbation activity. • Sediment cores were collected from three guyots in the northwestern Pacific • Sediment accumulation rates on seamount summits were 0.61–2.05 cm kyr −1 • Mixing layer depth/particle mixing coefficients imply weak bioturbation on summits • Dissolved oxygen and particulate organic matter may markedly influence bioturbation