158-6 Rhenium geochemistry at the sediment-water interface of the Middle Island Sinkhole, Lake Huron

Session: Redox-Driven Nutrient and Contaminant Dynamics in Terrestrial Systems

Presenting Author:

Authors:

Abstract:

Rhenium (Re) is one of the rarest trace elements on Earth. For geochemists, Re has been used as a proxy to monitor the radioactive nuclide Technetium in nuclear burial sites, as a tracer of low-oxygen conditions in the oceans and carbon emissions from rock weathering, and to constrain groundwater chemistry. The concentration of Re in the Earth’s upper crust at just ~0.2 ng/g. Empirically, it does not react in oxic environments with Al/Fe/Mn oxyhydroxides or clay materials and operates conservatively in sea water within oxic environments. However, its behavior changes in low-oxygen environments, where it becomes rapidly removed from the dissolved phase and becomes highly enriched above crustal concentrations in sediments accumulating under sulfidic environments. The burial pathways of Re in low-oxygen settings remain highly contentious especially when concerning Re undergoing the processes of burial and diagenesis.

In this study, we explore Re geochemistry at the sediment-water interface (SWI) of the Middle Island Sinkhole (MIS), a 23 m deep karst feature with low-oxygen bottom waters within Lake Huron. MIS is considered to be a Proterozoic analogue due to its water chemistry and microbial assemblage. The low oxygen and high sulfate content of the sinkhole waters (Fig. 1) allow microbial mat communities to flourish at the SWI. Additionally, there is a unique feature of the MIS takes place on the floor of the sinkhole, where groundwater seeps up from the ground, creating a thin layer of groundwater from the Detroit River Group on the bottom of the sinkhole creating an anoxic and sulfate rich environment. In 2024, a short core sediment and porewater samples were collected. All sediments were analysis for major, minor and trace element concentrations via ICP-MS. We will present the sedimentary and porewater profiles for the MIS and discuss potential reactions involved during Re fixation. Our new insights will contribute to refine the use of Re as a paleo-redox proxy.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8274

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