An Icelandic freshwater radiocarbon reservoir effect: Implications for lacustrine ¹⁴C chronologies

Abstract

A freshwater radiocarbon (14C) reservoir effect (FRE) is a 14C age offset between the atmospheric and freshwater carbon reservoirs. FREs can be on the order of 10 000 14C yr in extreme examples and are a crucial consideration for 14C dating of palaeoenvironmental and archaeological samples. Correction for a FRE may be possible, provided the FRE and the proportion of FRE-affected carbon within a sample can be accurately quantified. However, although such correction is desirable for affected samples, it is essential that such correction is accurate in order to produce useful chronological information. Accuracy of FRE correction can be limited by spatial variation in FRE within a freshwater system, but despite this there is currently a paucity of information to identify and quantify such variability within affected systems. Here we present results of a study that investigates the effects of spatial FRE variation upon dating accuracy within the freshwater system of Lake Mývatn, northern Iceland. A substantial FRE (>10 000 14C yr) has previously been identified in archaeological and modern samples from the region, which shows the potential for considerable spatial variability. The study also assesses the use of δ13C and δ15N in age correction of affected samples. The results show that benthic detritus and organisms at primary trophic levels from locations within the lake are affected by a FRE of at least 3500 14C yr, with clear spatial variation resulting in 14C age differences of up to 7670 14C yr between samples. There is a broad correlation between stable isotope values and FRE within the data set. However, large associated uncertainties currently preclude highly accurate and precise stable isotope-based quantification of the proportion of FRE-affected carbon within archaeological and palaeoenvironmental samples from Mývatn and the surrounding region.

Mussels with Meat: Bivalve Tissue-Shell Radiocarbon Age Differences and Archaeological Implications

“…Freshwater reservoir effects present a large local variability, and may reach much larger 14 C offsets than marine reservoirs, often of several thousands of years (Geyh et al 1998;Geyh 2000;Hall and Henderson 2001;Zhou et al 2009;Ascough et al 2010). Causes for FRE include long residence times of groundwater, dissolved carbonates originating from the geological background, oxidation of old organic matter and sediments, and glacier meltdown (Olsson 1980;Landmeyer and Stone 1995;Lanting and van der Plicht 1998;Levin and Hesshaimer 2000;Geyh 2000;Hall and Henderson 2001;Ascough et al 2010Ascough et al , 2011.…”

Stable Isotopes, Chronology, and Bayesian Models for the Viking Archaeology of North-East Iceland

“…It has been known that radiocarbon dating in the area around Lake Mývatn (Mývatnssveit) is complicated by the impact of marine and freshwater reservoir effects on both human and certain faunal remains (Ascough et al 2007(Ascough et al , 2010(Ascough et al , 2011(Ascough et al , 2012, which is due to the consumption of both marine fish transported from coastal sites and local freshwater resources (e.g., freshwater fish and waterfowl) (McGovern et al 2006. The result is a high degree of overlap in the values for δ 13 C and δ 15 N between animals from terrestrial, marine, and freshwater systems, making it difficult to use just these two isotopes for understanding from where humans derive their dietary protein.…”

Radiocarbon in ecology: Insights and perspectives from aquatic and terrestrial studies

“…NH , Northern hemisphere; POC sink , sinking particulate organic carbon; POC susp , suspended particulate organic carbon; SH , Southern hemisphere; SOC , soil or sediment organic carbon; SMR , small mountain river; TPP , total primary production. References: [1] (Komada, Druffel, & Trumbore, ); [2] (Hwang et al., ); [3] (Druffel & Williams, ); [4] (Abbott & Stafford, ); [5] (Fernandes et al., ); [6] (Druffel, Bauer, Williams, Griffin, & Wolgast, ); [7] (Ascough et al., )…”