HR: 14:05h
AN: PP42C-02 INVITED     [PDF]
TI: The Dissolved Oxygen Controversy: Reconciling Oceanographic Versus Geological Perspectives
AU: * Tyson, R V
EM: r.v.tyson@ncl.ac.uk
AF: School of Civil Engineering and Geosciences, University of Newcastle, Newcastle, NE1 7RU United Kingdom
AB: Geological models for the origin of black shales have invoked a preservative effect of dysoxia-anoxia for nearly a century, yet during the last 30 years some oceanographers have used modern sediment data to question and even deny the importance of dissolved oxygen. This schism over the origin of organic-rich sediments must be addressed and healed. With regard to modern sediment observations the problem appears to be how representative the data are, how and where oxygen hypotheses are tested (and against what expectations), and how the findings may have been extrapolated and generalised. It is increasingly clear that the total organic carbon (TOC) content of sediments is a classic multivariate problem where input (productivity), preservation, and inorganic dilution must all be considered simultaneously. The most common low oxygen environments in the modern ocean are oxygen minimum zones (OMZ), but these are also characterised by high productivities, high sedimentation rates, and generally high preservation, and are thus a very poor place to isolate the role of oxygen. Furthermore, OMZ studies have used a comparative analysis of TOC above, within, and below the OMZ, where the latter is defined only by local minima, not oxygen values considered likely to have a significant effect on benthos or geochemical preservation. Sometimes hypotheses have been constructed based on data from only a narrow (suboxic-dysoxic) oxygen range, fully oxic regimes, or areas too strongly influenced by grain size. The organic-rich nature of modern deep Black Sea sediments has also been denied, but seems indisputable relative to similar oxic regimes. A critique and analysis of the available modern data (increasing all the time, but still limited) suggest that the oceanographic view that oxygen is not important is impossible to sustain as a generality, indeed a statistical non-linear effect can be identified by multiple regression analysis. In many modern settings other factors are definitely dominant, but in the slowly deposited ancient basinal facies, the role of oxygen appears to be a critical control on preservation. Important issues remain to be resolved, but the old bipolar arguments about productivity versus preservation must be cast aside in favour of more complex multivariate approaches.
DE: 4267 Paleoceanography
DE: 4802 Anoxic environments
DE: 4825 Geochemistry
DE: 4834 Hypoxic environments
SC: Paleoceanography and Paleoclimatology [PP]
MN: 2003 Fall Meeting