Mo isotopes as redox indicators for the Southern Tethys during the PETM

Abstract:

As several ocean and climate models predict a decline in dissolved ocean oxygen concentrations associated with future global warming [1], recent research is increasingly focusing on past episodes of low ocean oxygen levels. Trace metals are generally enriched in organic‐rich sediments deposited under such low oxygen conditions, and the concentration and isotopic signatures of several of these elements (e.g. Mo, U, Cr) may be applied as proxies to reconstruct the processes involved in these redox changes [2,3]. This project investigates the use of the molybdenum isotope system as a proxy for redox changes during an interval of abrupt environmental change spanning the Paleocene/Eocene boundary (the Paleocene/Eocene Thermal Maximum, PETM, ~56 Ma). The PETM is characterized by global warming and environmental and ecological changes including decreased ocean oxygen levels [4]. Study of the PETM can therefore offer us a valuable insight into how marine ecosystems and biogeochemical cycles may respond to future climate changes, and the predicted decrease of oxygen concentrations in seawater. The molybdenum concentrations and isotope compositions of organic-rich sediments spanning the PETM have been obtained from a Jordan oil shale drill core (OS-28). The obtained δ^98/95Mo isotopic ratios range between -0.12‰ and 1.59‰ and coincide with significant fluctuations in trace metal abundances. The data together demonstrate that the global environmental changes associated with the PETM were manifest in the Jordanian basin as significant changes in basin hydrography and dissolved oxygen levels.