Quantifying bioturbation of a simulated ash fall event

<p>Tephrochronology allows the establishment of ‘isochrons’ between marine, lacustrine, terrestrial and ice cores, typically based on the geochemical fingerprint of the tephra. The development of cryptotephrochronology has revealed a vast inventory of isochrons which hold the potential to improve stratigraphic correlation and identify systemic leads and lags in periods of rapid climate change. Unfortunately, bioturbation acts to blur these isochrons, reducing the temporal resolution in marine and lacustrine records. In order to better resolve these event horizons, we require a better understanding of bioturbative processes, and the depth and time over which they operate. To this end, an ash fall event was simulated on the intertidal zone of the Eden Estuary, Fife, Scotland and sediment cores were collected over 10 days. A novel approach to tephra quantification was developed, using the imaging software ImageJ. Our results showed limited bioturbation (mixed depth=18 mm), most likely owing to the fine grain size, low-energy environment and the resulting faunal composition of the sediments. These results imply a strong ecological control on bioturbation, and suggest that inferences may be made about palaeoenvironments from the observed bioturbation profiles. </p

Iceberg-rafted tephra as a potential tool for the reconstruction of ice-sheet processes and ocean surface circulation in the glacial North Atlantic

<p>Ice-rafted tephra deposits, of Marine Isotope Stage 6 (MIS 6) age, from Site U 1304 on the Gardar Drift, North Atlantic were examined for their shard size distribution and major element composition. The heterogeneous composition, large shard sizes and association with ice-rafted debris (IRD) indicate that these late MIS 6 deposits were transported by iceberg-rafting from Iceland to Site U 1304. Comparison of individual shard geochemistry with the geochemistry of Holocene volcanic systems from Iceland allows the identification of different potential volcanic source regions. This detailed geochemical analysis, when combined with Icelandic Ice Sheet (IIS) flow models for the Last Glacial Maximum (LGM), suggests that the IIS had calving margins to both the north and south during the late MIS 6 and that icebergs could have been transported to the Site U 1304 by following surface ocean circulation patterns similar to those that prevailed during the LGM. We demonstrate that the descriptive concept of Icelandic glass in the characterization of tephra components within North Atlantic IRD can be significantly improved through quantitative characterization and that such data hold the potential to help constrain surface ocean circulation models, while also potentially yielding new information about the IIS during earlier glacial periods. </p