Investigating the fractionation behaviour and mass balance of cadmium isotopes during continental weathering and marine burial.

Organic carbon burial plays an important role in the global carbon cycle, and changes in the magnitude of such carbon burial have the potential to impact the global climate. Recent studies have shown that stable cadmium isotopes (δ114/110Cd) have potential as a tracer for marine organic carbon burial. However, the input and output fluxes and isotopic fractionation behaviour of Cd in the marine system are currently insufficiently constrained for robust application as a paleo-proxy. For example, while the main input flux of Cd to the oceans is from rivers, the isotopic behaviour of Cd during its passage through estuarine mixing zones is poorly understood. In this study we will present Cd concentration and isotopic measurements of waters spanning a salinity gradient of 34–1 PSU and bedload sediments collected from the Milford Haven estuary in Pembrokeshire, western Wales, The aim is to test the conservative behaviour of Cd in the estuarine mixing zone, to constrain the composition of Cd from weathering in a shale and sandstone dominated catchment, and to investigate the fractionation of Cd during catchment weathering. These data will help in better understanding the riverine input flux of cadmium into the oceans, and the marine cadmium budget.