Selenium isotopes: A new palaeoredox proxy? Gawen R.T. Jenkin1, Andrew J.T. Shore1, Thomas M. Johnson2 1Dept. Geology, University of Leicester, U.K. 2Dept. Geology, University of Illinois at Urbana-Champaign Our hypothesis is that seawater Se-isotope variations preserved in the sedimentary record reflect changes in ocean oxygenation through geological time. To test the validity of this hypothesis, samples have been analysed from the alternating anoxic – oxic sequence of the Cariaco Basin, Venezuela. This alternating pattern has been correlated with interglacial – glacial cycles over the past 500 ka. The Se isotope ratios tend to track δ18O. Generally, relatively heavier Se ratios are characteristic of the cold, glacial isotope stages whereas lighter isotope ratios typify the warmer, interglacial isotope stages. This is the first use of Se isotopes in the field of palaeoceanography. These alternating isotope ratios could be evidence to suggest that Se isotopes do follow known ocean oxygenation patterns and so could begin their development into an oceanic oxygenation proxy. δ82/76Se and δ18O for the Cariaco Basin (ODP Leg 165). Shaded even numbers represent glacials (oxic) and odd numbers represent interglacials (anoxic).