Early diagenetic alteration of rare earth element and yttrium (REY) signals in marine sediments and impact on the use of REY as tracers in past and present marine environments

• Applicant: Dr. Sophie Paul
• Subject Area: Oceanography
• Term: since 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 458637508

Rare earth elements and yttrium (REY), including Nd isotopes, are frequently used as geochemical proxies for past and present environmental conditions and processes. In recent years, the use of these proxies for ancient seawater chemistry and water mass tracing has been questioned in environments where the primary signals were discovered to be overprinted during early diagenesis. Pore water-solid phase interaction can lead to fractionation and alteration of the REY patterns and Nd isotopic signatures. The underlying processes are still little understood and revealing the influence of redox zonation and lithology on pore water REY composition and processes in the sediment is the aim of this proposed project. Samples from the Pacific and Atlantic deep sea, the continental margin off Nova Scotia and the Amazon estuary will be obtained, analyzed and evaluated. REY concentrations and Nd isotopic composition in the pore water, solid phase, and overlying seawater will be compared to identify fractionation, alteration, and preservation of the proxies. The four study sites were chosen for their differences in organic matter supply and in turn variable redox zonation, as well as variable terrestrial input and therefore lithology. Such a systematic assessment of REY in pore water will fill the gap in palaeoceanographic research of understanding in which settings proxies might be reliable and in which settings they are not. Data from actual samples are urgently needed because modelling and experimental work are lacking good information of input variables and realistic environmental boundary conditions. This research will provide novel data to the so far little to non-existing dataset of REY concentrations and Nd isotopic composition in (especially oxic) pore waters.

• DFG Programme: Research Grants