POSTDEPOSITIONAL OXIC DEGRADATION OF ALKENONES - IMPLICATIONS FOR THEMEASUREMENT OF PALAEO SEA-SURFACE TEMPERATURES

Free and ''bound'' long-chain alkenones (C-37:2 and C-37:3) in oxidize d and unoxidized sections of four organic matter-rich Pliocene and Mio cene Madeira Abyssal Plain turbidites (one from Ocean Drilling Program site 951B and three from site 952A) were analyzed to determine the ef fect of severe post depositional oxidation on the value of U-37(k'). T he profiles of both alkenones across the redox boundary show a prefere ntial degradation of the C-37:3 compared to the C-37:2 compound. Becau se of the high initial U-37(k') values and the way of calculating the U-37(k') this degradation hardly influences the U-37(k') profiles. How ever, for lower U-37(k') values, measured selective degradation would increase U-37(k') up to 0.17 units, equivalent to 5 degrees C. For mos t of the U-37(k') band-width, much smaller degradation already increas es U-37(k') beyond the analytical error (0.017 units). Consequently, f or interpreting the U-37(k') record in terms of past sea surface tempe ratures, selective degradation needs serious consideration.