GEOTRACES - Intercalibration Studies of Short-lived U/Th Series Isotopes and Marine Particles

点击翻译按钮获取中文摘要

During the next ten to twelve years, scientists from oceanographic laboratories around the world will participate in GEOTRACES -- a benchmark effort to investigate the distribution and behavior of chemicals in the sea that can give insight into the way the ocean works as a geophysical system. With funding from this grant, scientists at the Woods Hole Oceanographic Institution will participate in a pair of GEOTRACES intercalibration cruises in 2008 and 2009. They will focus their efforts on understanding the physical and chemical principles governing the spatial and temporal distributions of radioisotopes in the natural Uranium-Thorium decay series. U-Th tracers are likely to be vital to the interpretation of key GEOTRACES trace elements that are particle- reactive and bioactive. Essentially, thorium isotopes will provide direct information on the vertical fluxes and remineralization rates on time scales of days/weeks (234Th t ½ = 24.1 d) up to several years (228Th t ½ = 1.91 yr), while 228Ra (t ½ = 5.75 y) is a tracer of horizontal transport from basin margins to the interior on time scales of months to years. The investigators contend that these effects, i.e. surface scavenging and remineralization as well as horizontal transport of suspended particles far from ocean boundaries, are important in setting the distributions of many trace elements that will be measured in GEOTRACES, and important for understanding oceanic processes in their own right. Specifically, the Woods Hole group will: 1) participate with other GEOTRACES scientists in the general particulate trace element intercalibration efforts comparing in-situ vs. bottle vs. deck based sampling methods and making basic filter and operational comparisons appropriate for a wider suite of particle reactive trace elements for distribution to the scientific community; 2) organize and lead distribution of particulate 234Th and 238Th for intercalibration among that community; and 3) work on a novel set of sampling and analytical methods to improve accuracy and reduce water requirements for this suite of Th and Ra isotopes. In terms of broader impacts, it is clear that this effort will benefit oceanographic research activites well beyond GEOTRACES inasmuch as new practical and theoretical knowledge about sampling and analytical methodologies will be obtained. The project will also involve significant inter-institutional collaboration, both within the US and internationally, as marine radiochemists around the world will have the opportunity to participate in analytical intercalibration activities.