Marine thorium and protactinium distributions

Adsorption to sinking particulate matter, known as scavenging, is an important yet elusive term in the budgets of many bioactive and contaminant trace metals in the ocean. Scavenging is also involved in the cycling of other trace metals used in ocean sediments to learn about ocean processes, such as circulation rates or biological productivity, of the geologic past. This dissertation is an oceanographic exploration of the naturally-occurring radionuclides 230Th, 232Th and 231Pa aimed to better understand how their scavenging behavior can be utilized to trace chemical flux in the modern and the past ocean. While 230Th and 231Pa are produced by the radioactive decay of uranium dissolved in seawater, 232Th is added to the ocean via the input of continental material. Removal of Th by scavenging should be equivalent for both Th isotopes based on chemical principles. I use measured 232Th inventories from the North Pacific water column and apply a removal rate based on 234U:230Th disequilibria to estimate the flux of dissolved trace elements, such as the micro-nutrient Fe, to the ocean through the deposition of mineral dust (Chapter 2). Results from this study also raise the possibility o