Foraminifera on the deep-sea floor - lysocline and dissolution rate

Abstract

The state of preservation of foraminiferal assemblages in a region of the western equatorial Pacifie, combined with data on carbonate and 14C sedimentation rates, suggest_ the following: 1) dissolution effects are noticeable but minor above 3 000 rn depth; 2) the lysocline is near 3 400 rn and straddles a marked increase in the rate of carbonate dissolution; 3) the Joss of carbonate here is 15 to 200Jo; 4) only residual assemblages occur below 4 km depth, and these are not very sensitive to additional dissolution. A linear mode! of calcite dissolution with a defined zero Joss near 3 km and 100% Joss at the CCD provides a reasonably good approximation to the lysocline mode! which fits the data. The most sensitive preservation indices are fragmentation in the fine sand fraction, and changes in faunal composition of the fraction greater than 150 p,m.