Research project: Resolving past changes in ocean oxygenation
Currently Active:
Yes
The record of changes in the dissolved oxygen concentration of seawater is crucial for understanding Earths climate in the past, and for predicting future climate scenarios. Changes in ocean oxygenation are commonly determined from sedimentary records of metals that have multiple valence states at Earth surface conditions. However, the interpretation of such records is not straightforward because metal concentrations are influenced by many different variables that vary independently of oxygen.
Project Overview
Ocean Biogeochemical Cycle of Cr
Project Aims
This project aims to validate the utility of Chromium (Cr) isotopes as a tracer of dissolved oxygen in the oceans, through study of natural and experimental systems. These results will ultimately lead to an improved understanding of the mechanisms and feedback processes that regulate ocean oxygenation, including the operation of the carbon cycle, ocean circulation and climate.
Core sites investigates
Objectives
To determine the isotopic fractionation and mechanisms of Cr uptake and use by:
Characterising the chemical and Cr isotopic signature of marine sediments deposited in a range of redox conditions.
Assessing the potential for post-depositional mobility of Cr and Cr isotopes by analysis of turbidites, sapropels and a carbonate diagenetic sequence.
Quantifying the effects of weathering processes and hydrothermal exchange, through measurement of continental and hydrothermal sources in a range of continental rock types, rivers and hydrothermal fluids.
Assessing the effects of biogeochemical processes on Cr stable isotopes by measurement of seawater profiles, in open ocean and shelf sea environments.
Current Progress: Sapropels
Sapropels are sharply-defined organic-rich units deposited in the Mediterranean. Although their formation is still under debate, it is generally thought that they represent intervals of enhanced palaeoproductivity in surface waters combined with improved organic matter preservation under decreased oxygen conditions.
Recent work by Hélène Planquette has shown that the upper part of Sapropel unit S1 (deposited between 6 and 9 kyr B.P.) is associated with positive δ53/52Cr ratios, suggesting that post-depositional processes remobilized and oxidised Cr in this layer. Further work is currently being performed to assess the extent to which the Cr isotopic composition of other sedimentary records may be affected by reventilation processes.
Funding
This project is funded by NERC and will run from 2010 to 2014
