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ABSTRACT

Suspended coccoliths are abundantly distributed throughout the water column down to 5 km along a meridional aphotic water profile of the central North Pacific Ocean. Their state of preservation varies from unaltered to slightly etched at all depths. This observation contradicts the expectation that coccoliths falling from the photic layer should dissolve and disappear in the calcite-undersaturated part of the water column. The species composition of coccolithophore assemblages in the overlying productive layer was reflected throughout the aphotic water column with no significant change. Electron microscopic study of fecal pellets from grazers collected at depth by a sediment trap as well as laboratory experiments feeding cultured coccolithophores to small zooplankton suggest that fecal transport is an efficient process removing the coccoliths produced in surface waters directly to the deep-sea floor. The suspended coccoliths can be classified into two categories; the free-falling coccoliths from the surface productive layer which are the result of shedding from host coccolithophores while they are living, and the suspended coccoliths replenished at any depth by spilling out from the host fecal pellets while they descend. The type 1 coccoliths probably will be dissolved as soon as they pass the calcite saturation depth. The majority of the type 2 coccoliths may eventually dissolve at under-saturated depths before descending very far, but are widely distributed throughout the deep-sea column at least temporarily. Thus the suspended coccoliths may play a very small role but the direct and rapid transport of coccoliths via fecal pellets appears to be the main channel in carbonate ooze sedimentation on the deep sea floor.

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