Abstract
Free and "bound" long-chain alkenones (C (sub 37:2) and C (sub 37:3) ) in oxidized and unoxidized sections of four organic matter-rich Pliocene and Miocene Madeira Abyssal Plain turbidites (one from Ocean Drilling Program site 951B and three from site 952A) were analyzed to determine the effect of severe post depositional oxidation on the value of U (sub 37) (super k') . The profiles of both alkenones across the redox boundary show a preferential degradation of the C (sub 37:3) compared to the C (sub 37:2) compound. Because of the high initial U (sub 37) (super k') values and the way of calculating the U (sub 37) (super k') this degradation hardly influences the U (sub 37) (super k') profiles. However, for lower U (sub 37) (super k') values, measured selective degradation would increase U (sub 37) (super k') up to 0.17 units, equivalent to 5 degrees C. For most of the U (sub 37) (super k') band-width, much smaller degradation already increases U (sub 37) (super k') beyond the analytical error (0.017 units). Consequently, for interpreting the U (sub 37) (super k') record in terms of past sea surface temperatures, selective degradation needs serious consideration. Copyright 1998 by the American Geophysical Union.