ABSTRACT
This interpretation is strongly supported by the sediment trap data presented in Fig. 2. The sampling depth of 200 m below the surface was choosen since it has been suggested that vertical fluxes of organic matter passing that depth should be equivalent to new production (21,22). Temporal variations of about one order of magnitude are observed for both the total mass flux and the particulate Th-234 flux. The range of mass fluxes which we observe, 50-350 mg/m2/d is within the range of results obtained for open ocean waters (22). It can be seen that the pattern of the temporal variation of the Th-234 flux is similar to that of the total mass flux. In other words, the specific activity of Th-234 in the trap samples is fairly constant within approximately a factor of 2. Moreover, the mean specific activity, 1500 dpm/g of dry material is close to that found in other open ocean areas (12,13) and to that predicted in biogenic debris (23) due to passive uptake by phytoplancton cells.
