¹⁰Be profiles in seawater

Abstract

A knowledge of the marine geochemical cycle of ¹⁰Be is basic to the use of this long-lived cosmogenic radioisotope (half life 1.5 Myr) in geochronological and geophysical studies^1–3. The first attempts at measuring ¹⁰Be in seawater were made only recently using nuclear accelerator spectrometry, and six concentration values from four locations have been reported^4–6. This data base must be expanded to include detailed water column profiles, so that the behaviour of ¹⁰Be in the ocean can be more fully described. A parallel case in point is the recent measurement⁷ of a detailed oceanic profile for the stable ⁹Be. We report here two water column profiles of ¹⁰Be: one in the Drake Passage near Antarctica and the other in the San Nicolas Basin about 100 km off the coast of Southern California. The San Nicolas Basin profile clearly demonstrates the regulation of ¹⁰Be distribution by particulate cycling. The data confirm the earlier suggestion⁴ of particle uptake of ¹⁰Be in the surface ocean. They also furnish evidence for regeneration of ¹⁰Be across the thermocline and near the sea floor, and for mid-water scavenging.