Rewriting history: Ion exchange & the fidelity of barium isotope records in Equatorial Pacific sediments

Julien Middleton
Thursday, February 8, 2024 · 1:00 pm to · 2:00 pm
ESB 5104 & Zoom

Barite (BaSO4) in ocean sediments has long been used to reconstruct seawater isotope compositions of sulfur, oxygen, strontium, and calcium, and the mineral’s accumulation rate offers a record of climatically relevant marine carbon export over centennial to millennial timescales. Recent advances in barium (Ba) stable isotope geochemistry offer a new dimension for understanding Ba cycling, including: tracking oceanic Ba sources, tracing deep water mass mixing, characterizing sediment recycling in the mantle, and reconstructing marine Ba cycling through the rock record. The latter application assumes the preservation of the primary Ba isotope composition set during barite formation in the surface ocean. However, this assumption has yet to be fully investigated during early diagenesis, that is, during chemical changes that may occur after deposition of the mineral on the seafloor, under oxic conditions.

To this end, we will discuss the Ba isotope composition of porewaters and co-located barites in Equatorial Pacific sediments and unpack a series of laboratory experiments revealing Ba isotope fractionation during ion exchange. Ion exchange of this type occurs between the mineral and a surrounding fluid while at chemical equilibrium and does not affect the morphology of the mineral. This work provides the first evidence for barite ion exchange in the marine environment and identifies a previously uncharacterized mode of Ba isotope fractionation associated with the process. More broadly, it provides an example of how isotopic fractionation during ion exchange may impact climatically relevant isotope records and suggests a need to investigate the impact of this process on metals and minerals beyond Ba and barite.

Zoom link: 

Meeting ID: 612 2790 8464

Passcode: 009405

Please note that after the seminar, the candidate will give a chalk-talk regarding their research plan over the next five years at ESB 5104 @2:30 pm, you are welcome to join as well!