Colloquium: Jeremy Owens

Approaching a more holistic view of ocean redox conditions using thallium isotopes

Jeremy Owens, Woods Hole Oceanographic Institution

Abstract:  Global ocean reduction-oxidation (redox) conditions are closely coupled with biological, chemical and climatic evolution throughout Earth history. To date, geochemical proxies can reliably fingerprint redox end-members; however, intermediate conditions remain ambiguous due to a lack of proxy development. Therefore, quantifying the entire range of redox conditions in the ancient oceans using geochemical tracers has been futile. I will present a new proxy, thallium isotopes, to understand Mn-oxide burial which can lead to quantifying the extent of bottom water oxygenation. Here, I will present data from the modern ocean calibrating the proxy and two ancient applications of the proxy. Thallium isotopes show a significant excursion during one of our best known and studied climate events, oceanic anoxic event at the Cenomanian-Turonian boundary event, suggesting a reduction of global Mn-oxide burial. Preliminary data from Archean samples advocate for global Mn-oxide burial meaning the ocean contained oxygenated waters at the sediment water interface.