Australian marine reservoir effects: a guide to ∆R values
Ulm, Sean (2006) Australian marine reservoir effects: a guide to ∆R values. Australian Archaeology, 63. pp. 57-60.
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[Extract] Radiocarbon ages obtained on contemporaneous terrestrial and marine samples are not directly comparable. Samples grown in marine environments exhibit older apparent radiocarbon ages caused by the uptake of carbon which has already undergone radioactive decay through long residence times in the deep ocean. Variation in 14C activity in marine environments, although related to changes in atmospheric activity, depends greatly on local and regional factors, such as hinterland geology, tidal flushing and terrestrial water input. Such factors are highly variable and can introduce uncertainties of up to several hundred years into dates obtained on marine samples in some parts of the world.
These issues have received much attention in Pacific archaeology where determinations on marine samples are routinely scrutinised (e.g. Anderson 1991; Spriggs and Anderson 1993) and major resources have been devoted to resolving regional marine reservoir correction factors (e.g. Dye 1994; Petchey et al. 2004; Phelan 1999). In Australia, however, only very limited investigations have been conducted despite routine dating of marine and estuarine shell (e.g. Bowman 1985; Bowman and Harvey 1983). For nearby areas regional offsets of up to 400 years have been documented (Petchey et al. 2004), highlighting a key problem in a country where marine shell from open coastal sites is routinely dated.
As a first approximation it is common practice in Australia to correct marine dates for marine reservoir effect by simply subtracting a generalised factor of 450±35 years to make them comparable to coeval terrestrial (e.g. charcoal) samples. This correction value was calculated by Gillespie in the 1970s (see Gillespie 1975; Gillespie and Polach 1979; Gillespie and Temple 1977). Since that time several studies have suggested the possibility of significant deviations in regional marine reservoir signature from this generalised value (e.g. Hughes and Djohadze 1980; Murray-Wallace 1996; Ulm et al. 1999; Woodroffe et al. 1986:75, 77; Woodroffe and Mulrennan 1993).
In the last two decades researchers have gained a much more sophisticated appreciation of the complexity of global marine carbon reservoirs. One of the most significant innovations was the development of a global model of surface marine 14C activity that enabled the calibration of radiocarbon dates obtained on marine samples, including the ability to account for regional differences from the global model with the input of a regional offset value, expressed as a ΔR value (Stuiver et al. 1986). Reimer and Reimer (2001, 2006) subsequently summarised all of the available global ΔR values in a world wide web database. In this paper, I briefly discuss the principles of marine reservoir correction before presenting a guide to regional and subregional Australian ΔR values extracted from the Reimer and Reimer (2006) database and Ulm (2002).
|Item Type:||Article (Refereed Research - C1)|
|Date Deposited:||14 Jul 2011 01:55|
|FoR Codes:||21 HISTORY AND ARCHAEOLOGY > 2101 Archaeology > 210102 Archaeological Science @ 100%|
|SEO Codes:||95 CULTURAL UNDERSTANDING > 9505 Understanding Past Societies > 950503 Understanding Australias Past @ 50%
96 ENVIRONMENT > 9611 Physical and Chemical Conditions of Water > 961104 Physical and Chemical Conditions of Water in Marine Environments @ 50%