POLLEN IN MARINE-SEDIMENTS AS AN INDICATOR OF OXIDATION OF ORGANIC-MATTER

Organic carbon burial in marine sediments generates virtually all atmo spheric oxygen, and provides a long-term sink for about 20% of all car bon(1,2); it is therefore important to understand the mechanisms contr olling organic carbon preservation. There is a fraction of organic mat ter that is preserved under reducing conditions but which can be rapid ly oxidized if exposed to molecular oxygen(3-6). It is not clear, howe ver, how much of the total organic matter preserved in marine sediment s is oxygen-sensitive. Here we present results from a relict turbidite in the Madeira abyssal plain which suggest that pollen grains can be used as a sensitive tracer of oxygen-sensitive organic carbon. We find that pollen grains were completely degraded within 10 kyr in the pres ence of diffusively introduced oxygen, but were well preserved for at least 100 kyr under anoxic conditions. We also present pollen data fro m the Pacific Northwest continental shelf, which suggest that oxic deg radation can explain the decrease in organic carbon with depth commonl y observed in coastal sediments.