Alkenone temperature and carbon isotope records: Temporal resolution, offsets, and regionality



[1] Over the last decade the number of paleoceanographic studies presenting and discussing alkenone-derived sea surface temperature (SST) records and carbon isotope ratios of alkenones (δ13Calkenones) has increased rapidly. This short review paper summarizes the state of knowledge about SST variability determined by alkenone paleothermometry in sediment trap studies and investigations of marine sediments for timescales of single to millions of years. In particular from the evaluation of Quaternary records, characteristic temperature pattern have emerged that mismatch with SST curves estimated by other methods, e.g., foraminiferal stable oxygen isotopes and transfer functions. In future studies the spatial distribution of such variance patterns typically observed in alkenone SST curves should be checked in order to better understand their meaning for ocean circulation changes and a possible relationship to global climate change. On the other hand, certain physical and biological processes have the potential to put the reliability of alkenone SST curves into question. Accordingly, examples for possible effects of bioturbational mixing, lateral transport of remote alkenones, diagnetic alteration and degradation of alkenone composition, biogeographic and temporal diversity changes in alkenone-producing algae, as well as the influence of changes in salinity and nutrient conditions on the alkenone paleotemperature signal, are briefly mentioned, highlighting the need for more detailed future studies on these issues. Finally, a short summary on the status of the use of the δ13Calkenones signal as a proxy for past variations in the carbon dioxide pressure (PCO2) in ocean surface waters and related problems is given.