Mississippi River - Gulf of Mexico thallium boundary exchange and benthic fluxes Cruise 2

The thallium (Tl) isotope system has been drawing increasing attention as a promising tracer for global ocean oxygen content changes on millennial to million-year timescales. Despite considerable research on marine Tl mass balance and increasing applications of Tl isotopes as a paleo-redox proxy, there is a notable gap in our understanding of Tl source/sink fluxes at the land–ocean boundary. Additional research on the Tl transfer at the land-ocean boundary (e.g., boundary exchange due to particle reactivity changes along the salinity gradient) and Tl diagenesis in various sedimentary environments (e.g., various lithology and redox environments) are thus critical to narrow down uncertainties of the marine Tl mass balance, with important implications of marine Tl geochemistry and interpretations of paleo-redox reconstructions from Tl isotopes. The proposed cruises aim to investigate the magnitude of Tl benthic fluxes under dynamic continental margin environments (e.g., redox and clay mineralogy) via field sampling of water columns, porewaters, in-situ incubation and sequential extraction of sediment cores from the Gulf of America and end members from the Mississippi River.