Studies of 26Al and 10Be as Potential Constraints on Paleoproductivity and Extraterrestrial Influx

University Of Southern California, Los Angeles CA

Investigators

Abstract

ABSTRACT OCE-0117895 The source functions and geochemical pathways of 26Al (half-life 0.72 My) and 10Be (1.5 My) in the sea are closely linked. These radioisotopes, produced mainly by the interaction of cosmic rays with the atmospheric constituents, enter the ocean via wet and dry fallout with a nearly constant ratio and deposit to the seafloor through particle scavenging. The scavenging time of 10Be is comparable to the ocean mixing time of ~103 years,but that of 26Al is about 30 times shorter. As a consequence, 10Be is more readily transported to areas of high particle flux or high productivity such as ocean margins, where the deposition ratio of 10Be/26Al becomes much higher than their production ratio. These features -relatively stable source function, constant production ratio,and high particle reactivity with differential removal -render the two nuclides as a pair suitable for tracing geochemical and geophysical processes. In this project, researchers at the University of Southern California will evaluate the utility of the 10Be/26Al ratio in sediments as a proxy for paleo-particle flux or paleoproductivity, and the use of the 3He/26Al ratio in sediment cores to probe the factors affecting the flux of earth-bound interplanetary dust particles (IDP) and its variation with time. Measurements of 10Be and 26Al will be carried out on samples of seawater, sediment-trap material, and sediment, and of 3He in sediment cores. Measurements of U-Th isotopes, 27Al, 9Be, opal, carbonates and other chemical components will also be made on sediment trap and sediment samples. Data so obtained will be used to study the spatial and temporal variations in the distribution and flux of 10Be and 26Al and the mechanisms causing the variations. The influence of particle composition and remineralization on the sedimentary 10Be/26Al signals will be investigated to constrain better the 10Be/26Al proxy which will be applied to sediment cores from the equatorial Pacific and the Antarctic to provide an understanding of the productivity changes in areas characterized by high-nutrients and low-chlorophyll of the surface water. Past variations in IDP will be examined by the coupled measurements of 3He/26Al and 3He/230Th in sediment cores.