INTERFACE DISSOLUTION CONTROL OF THE C-14 PROFILE IN MARINE SEDIMENT

The process of carbonate dissolution at the sediment-water interface h as two possible end-member boundary conditions. Either the carbonate p articles dissolve mostly before they are incorporated into the sedimen t by bioturbation (interface dissolution), or the vertical mixing is r apid relative to their extermination rate (homogeneous dissolution). I n this study, a detailed radiocarbon profile was determined in deep eq uatorial Pacific sediment that receives a high rate of carbonate suppl y. In addition, a box model of sediment mixing was used to simulate ra diocarbon, carbonate content, and excess thorium profiles that result from either boundary process following a dissolution increase. Results from homogeneous dissolution imply a strong, very recent erosional ev ent, while interface dissolution suggests that moderately increased di ssolution began about 10,000 years ago. In order to achieve the observ ed mixed layer radio-carbon age, increased homogeneous dissolution wou ld concentrate a greater amount of clay and Th-230 than is observed, w hile for interface dissolution the predicted concentrations are too sm all. These results together with small discontinuities beneath the mix ed layer in Th-230 profiles suggest a two-stage increase in interface dissolution in the deep Pacific, the first occurring near the beginnin g of the Holocene and the second more recently, roughly 5000 years ago .