A new flow cytometry method enabling rapid purification of fossil pollen from terrestrial sediments for AMS radiocarbon dating

Abstract

Radiocarbon (14C) accelerator mass spectrometry (AMS) dating has played a significant role towards improving our understanding of the timing of events and rates of change in archaeological and environmental records over the last 50 000 years. Although it is not always possible to find suitable macrofossils for 14C dating, microfossils, notably plant pollen, are a viable alternative. Obtaining preserved pollen samples of known provenance and of sufficient quantity for dating by 14C AMS is, however, challenging because of time‐consuming methods of extraction and purification and possible contamination from other organic material. Here we report a new, rapid and straightforward method using flow cytometry (FCM) to distinguish, sort and collect sufficient quantities of fossil pollen with minimal contamination from lake sediments for radiocarbon dating. Using this approach, we demonstrate 14C AMS ages that date back to at least 40 ka BP. While future work may be required to refine purification methodologies for different sample types and to precisely quantify the dating limit of this approach, FCM dating of microfossils shows considerable promise in generating robust geochronological frameworks for sequences that have previously proved problematic. Copyright © 2013 John Wiley & Sons, Ltd.

Palaeoclimate records 60–8 ka in the Austrian and Swiss Alps and their forelands

“…compound or fossil-specific radiocarbon dating (e.g. Tennant et al, 2013) or microtephra analyses (e.g. Pollard et al, 2006;Huber et al, 2010), may significantly reduce dating uncertainties for the time interval 50e15 ka.…”

Recent methodological advances in Quaternary palaeoecological proxies

“…Any opportunity to improve both accuracy and efficiency of pollen analysis, thereby lowering the cost, is surely to be welcomed and the novel technique of isolating pollen from sediments more quickly and effectively is therefore an exciting development (Tennant et al, 2013). 3 About time: improved radiocarbon calibration Vita-Finzi (1973: 47) once noted that 'since geological time is not salami, slicing it up has no particular virtue but if it is to be sliced there is no need to botch the job'. This somewhat tongue-in-cheek comment hides what is in reality an imperative to accurately fix events in geological time, for without robust age models palaeocological reconstructions are purely narratives -a series of more or less interesting stories.…”

The Encyclopedia of Archaeological Sciences

“…Dense media separation may either be undertaken at a single target density (e.g., 1.5 times the density of water, or 1.5 SG) in which pollen grains, which have a typical density of slightly less than 1.5 SG (Régnell and Everitt 1992), float, or at a series of decreasing densities (e.g., from 1.6-1.15 SG), allowing selection of the purest residue(s) for dating (Vandergoes and Prior 2003). Alternatives to density separations include manual selection of individual grains using a micromanipulator (e.g., Long, Davis, and De Lanois 1992), and isolation of pollen grains using flow cytometry (Tennant et al 2013). However, the former technique is generally too time-consuming to be practical unless very large pollen grains such as Picea are abundant, and the latter has yet to be routinely applied for radiocarbon dating.…”