An experimental field study to test the stability of lipids used for the TEX86 and U37K′ palaeothermometers

We report a one year field experiment to Study sedimentary degradation of isoprenoid glycerol dialkyl glycerol tetraethers (GDGTs) and long-chain alkenones. lipids used for the TEX86 and U-37(K') sea surface temperature (SST) proxies, respectively. Homogenised surface sediments from the Namibian upwelling region were set out oil moorings in oxic (Oder Bay and Arkona Bay, Baltic Sea) and sub-oxic to anoxic (Gottland Basin; Baltic Sea) waters and in oxic Atlantic waters off Cape Blanc for one year to assess the influence of oxygen exposure oil GDGTs and alkenones. No selective degradation effect oil both TEX86 and U-37(K') proxies was evident under anoxic and sub-oxic conditions. Under oxic conditions, GDGT concentrations and the TEX86 did not significantly change as well. However, selective degradation of alkenones occurred at all oxic sites resulting in a small but significant increase of the U-37(K') index by Lip to 0.06 units, corresponding to a temperature increase of up to 1.8 degrees C. Our results demonstrate that selective alkenone degradation is a relatively Fast process and complement earlier evidence for selective degradation of alkenones in the laboratory, water column and sediments. In contrast, our results suggest that the TEX86 is relatively resistant to selective oxic degradation at least oil relatively short (years) time scales. (C) 2009 Elsevier Ltd. All rights reserved.