SPP 527 Subproject: Calcium isotope fractionation during transport and recrystallisation processes in marine deep sea sediments

Basic data for this project

Description

Marine biogenic calcium carbonate shells are important archives for changes of the System Earth throughout Earth history, as their element and isotopic composition is used for many paleo-environmental proxies. The reliability of those proxies depends not only on primary factors but also on the preservation, which in turn depends on processes like partial dissolution and recrystallization. Sediments retrieved during IODP Expeditions 320/321 provide well preserved high resolution archives throughout the Cenozoic; they are hence the basis for important paleoclimate reconstructions. Nevertheless, despite the overall well preservation, pore water analyses reveal indications for carbonate recrystallization. A tool for the investigation of diagentic processes in marine sediments, including recrystallization, is the isotopic composition of Ca. One of the main aims of this study is to use Ca isotopes to determine recrystallization rates of the carbonate sediments of the deep-sea sediments drilled by IODP Exp. 320/321, and to evaluate the preservation of the proxy archives. We will determine first the Ca isotopic composition of pore water and sediments. Based on these data we will model carbonate recrystallization rates. However, the Ca isotopic composition of pore water does not exclusively depend on recrystallization. Some parameters that might influence the Ca isotope signature in sedimentary pore water are not fully investigated yet. One of the processes pending further characterisation is the Ca isotope fractionation during diffusive Ca transport. We will conduct experiments in order to quantify the mass dependent isotope fractionation during diffusion through sediments. These results will be considered in modelling the recrystallization rates in order to avoid systematic inaccuracies and they will contribute to a better understanding of processes in pore waters of marine sediments.