The d13C-record of benthic forams from the N. Atlantic shows minima during glacials along with a shallowing of the
lysocline and a stronger inflow of AABW. Together they suggest minima of deep water ventilation during glacials. However, the level of O2-content is difficult to asses from these proxies because we do not know the initial level of ventilation glacial deep water. Lower than present-day oxygen levels are also suggested by higher than average Corg-contents and by the presence of authigenic U in glacial sediments. Incorporation of authigenic uranium from sea water into sediments occurs when dissolved
U(VI) is reduced to immobile U(IV) in a suboxic environment.
We have developped a model which relates the authigenic U-content of sediments to their Corg-content, to the accumulation rate and to the O2-content of deep water. Thus, from the knowledge of U, Corg and the accumulation rate, the oxygen level during authigenic U-incorporation in the sediments may be evaluated. The model was developped an tested on eastern Mediterranean sapropels, which display a variety of different U- and Corg-contents.
The same model applied to sediment cores from the N. Atlantic, where data on the U, Corg and accumulation rates are available, suggests glacial deep water O2-contents in the range between 10 and 30 µmol /Liter.