Co-variation systematics of uranium and molybdenum isotopes reveal pathways for descent into euxinia in Mediterranean sapropels
OPEN ACCESS
Loading...
Author / Producer
Date
2022-05-01
Publication Type
Journal Article
ETH Bibliography
yes
Citations
Altmetric
OPEN ACCESS
Data
Abstract
The elemental concentrations and isotope compositions of molybdenum (Mo) and uranium (U) are commonly used for the reconstruction of past global and local redox conditions, and recent studies using both elements have revealed the potential of their paired application. However, such studies have generally focused either on modern marine sediments or on relatively low-resolution reconstructions of deep-time paleo-redox conditions. Here, we present high-resolution profiles (every 0.2-0.3 kyr) of Mo and U elemental and isotope compositions for anoxic organic-rich sediments of Eastern Mediterranean sapropels S5 and S7. The new Mo-U data reveal the processes leading to descent into basinal euxinia in more precise and systematic detail than lower resolution datasets focused on either Mo or U only. During the intensification from anoxic non-sulfidic to persistently euxinic conditions, δ98Mo and δ238U covariation systematics exhibit two stages. We identify the Mo-U isotope signature of the early transition from anoxic non-sulfidic to mildly euxinic conditions in the first stage, characterized by a rise in U isotope ratios (from −0.3‰ to +0.2‰ ±0.05‰) controlled by the depth within the sediment of the uranium reduction-accumulation front. As the water column turns persistently euxinic, δ98Mo values approach the seawater value for both sapropels, but δ238U evolves to different final values in the two sapropels. We interpret these differences as reflecting different redox potentials and/or different degrees of restriction of these two sapropel events, and the more gradual response of U sequestration to redox variation in comparison with threshold behavior of Mo. The findings presented here show temporal patterns in δ98Mo and δ238U on relatively short timescales that suggest the combined use of these proxies at high resolution allows detailed reconstruction of local redox and hydrographic conditions.
Permanent link
Publication status
published
External links
Editor
Book title
Journal / series
Volume
585
Pages / Article No.
117527
Publisher
Elsevier
Event
Edition / version
Methods
Software
Geographic location
Date collected
Date created
Subject
redox; molybdenum isotopes; uranium isotopes; sapropels; Eastern Mediterranean
Organisational unit
03956 - Vance, Derek / Vance, Derek
Notes
Funding
834236 - Nutrients in anoxic oceans – Trace metals in modern and ancient environments (EC)
184873 - Using trace metal isotopes to understand ocean biogeochemistry: ancient and modern (SNF)
184873 - Using trace metal isotopes to understand ocean biogeochemistry: ancient and modern (SNF)