Species-specific reservoir effect estimates: A case study of archaeological marine samples from the Bering Strait

Due to the marine reservoir effect, radiocarbon dates of marine samples require a correction. Marine reservoir effects, however, may vary among different marine species within a given body of water. Factors such as diet, feeding depth and migratory behaviour all affect the 14C date of a marine organism. Moreover, there is often significant variation within single marine species. Whilst the careful consideration of the Δ R values of a single marine species in a given location is important, so too is the full range of Δ R values within an ecosystem. This paper illustrates this point, using a sample pairing method to estimate the reservoir effects in 17 marine samples, of eight different species, from the archaeological site of Ekven (Eastern Chukotka, Siberia). An OxCal model is used to assess the strength of these estimates. The marine reservoir effects of samples passing the model range from Δ R (Marine20) = 136 ± 41–Δ R = 460 ± 40. Marine reservoir effect estimates of these samples and other published samples are used to explore variability in the wider Bering Strait region. The archaeological implications of this variability are also discussed. The calibrating of 14C dates from human bone collagen, for example, could be improved by applying a dietary relevant marine reservoir effect correction. For humans from the site of Ekven, a Δ R (Marine20) correction of 289 ± 124 years or reservoir age correction of 842 ± 123 years is suggested.

NEW MARINE RESERVOIR CORRECTION VALUES (ΔR) APPLICABLE TO DATES ON NEOLITHIC SHELLS FROM THE SOUTH COAST OF KOREA

ABSTRACT Shells from Neolithic shell midden sites have been routinely dated in Korea, but they have not been calibrated based on the correction values (ΔR) for the marine reservoir effect (MRE). A lack of proper calibration has left dates on shells incomparable to those on terrestrial samples, and thus unusable in building the chronological sequence of shell middens. Here, we report the two new ΔR values of a pre-bomb (pre-1950) blue mussel from the south coast. We applied the two new and the two previously reported ΔR values to the three dates on marine shells from the Bibongri shell midden in southeastern Korea. Our ΔR adjusted calibration and the comparison to dates on charcoal and bone remains clarify an ambiguity in the stratigraphy and the Early Neolithic chronology at Bibongri. Our contribution is to provide the ΔR values that can be further applied to other Neolithic shell middens along the south coast.

THE NEKSELØ FISH WEIR AND MARINE RESERVOIR EFFECT IN NEOLITHIZATION PERIOD DENMARK

ABSTRACT The Nekselø Wickerwork provides an unusually solid estimate on the marine reservoir age in the Holocene. The basis for this result is a 5200-year-old fish weir, built of hazel wood with a brief biological age of its own. Oysters settled on this construction. They had lived only for a short number of years when the fence capsized and was covered in mud and the mollusks suffocated. Based on the difference in radiocarbon (14C) age between accelerator mass spectrometry (AMS) samples of oyster shells and wood, respectively, the marine reservoir age for this site is estimated to 273 ± 18 14C years. Re-evaluations of previously produced data from geological and archaeological sites of Holocene date in the Danish archipelago indicate marine reservoir ages in the same order as that of the Wickerwork. Consequently, we recommend the use of the new value, rather than the ca. 400 14C years hitherto favored, when correcting for the dietary induced reservoir effect in radiocarbon dates of humans and animals from the Late Mesolithic and Early Neolithic periods of this region.

Quantifying marine reservoir effect variability along the Northwest Coast of North America

Recognition of marine reservoir effect (MRE) spatial and temporal variability must be accounted for in any radiocarbon-based paleoclimate, geomorphological, or archaeological reconstruction in a coastal setting. ΔR values from 37 shell-wood pairs across southern Southeast Alaska provide a robust local evaluation of the MRE, reporting a local Early Holocene weighted ΔR average of 265 ± 205, with a significantly higher ΔR average of 410 ± 60 for samples near limestone karst. Integration with our synthesis of extant MRE calibrations for the Northwest Coast of North America suggests that despite local variability, regional ΔR averages echo proxies for coastal upwelling: regional weighted averages were at their highest in the Bølling-Allerød interstade (575 ± 165) and their lowest in the Younger Dryas stade (−55 ± 110). Weighted ΔR averages across the Northwest Coast rose to a Holocene high during the Early Holocene warm period (245 ± 200) before settling into a stable Holocene average ΔR of 145 ± 165, which persisted until the late Holocene. Our quantification of local and regional shifts in the MRE shines a light on present methodological issues involved in MRE corrections in mixed-feeder, diet-based calibrations of archaeological and paleontological specimens.

Investigation of reservoir age variations in Lake Druksiai caused by anthropogenic factors

<p>The reservoir effect (RE) is defined as the difference between the radiocarbon isotope ratio (<sup>14</sup>C/<sup>12</sup>C) in the terrestrial and aquatic samples. Both natural processes and anthropogenic activities affecting carbon cycle in the water ecosystem can lead to changes in the RE. Therefore, reservoir effect studies can help to assess the impact of external factors on a hydrological system [1].</p><p>The aim of this research was to evaluate the impact of anthropogenic <sup>14</sup>C contamination from Ignalina nuclear power plant (Ignalina NPP, INPP) on the Lake Drūkšiai system. The lake water was used to cool the reactors of the INPP. The lake sediment and fish (both benthic and pelagic) scale samples were collected from the Drūkšiai lake. ABA (acid-base-acid) chemical pretreatment procedure was used to extract humin (HM) and humic acid (HA) fractions from the sediments. Radiocarbon measurements in these samples were performed using the accelerator mass spectrometer (AMS).</p><p>In 1963, increased concentrations of radiocarbon due to the testing of nuclear weapons showed that atmosphere-lake CO<sub>2</sub> exchange accounted for about 22% carbon in bottom sediments. During the first 15 years of operation of the Ignalina Nuclear Power Plant, <sup>14</sup>C-enriched dissolved inorganic carbon (DIC) was continuously released into Lake Druksiai. During that period, an average of about 0.24 GBq of radiocarbon was released per year. Measurements of radiocarbon concentrations in fish confirm that the <sup>14</sup>C contamination was in dissolved inorganic form.</p><p>Around 2000, <sup>14</sup>C-enriched DIC (2.3 GBq radiocarbon) was released into Lake Druksiai from Ignalina NPP. In addition, organic compounds were additionally released in the same year. These compounds were not <sup>14</sup>C-enriched but affected the interaction between humic and humic acids. Almost a decade after the end of operation of the Ignalina NPP, there is still some <sup>14</sup>C pollution (from INPP) remaining in Lake Druksiai. The concentration of radiocarbon in the bottom sediments is still higher than in the atmosphere. </p><p> </p><p>[1] R. Barisevičiūtė et al., Tracing Carbon Isotope Variations in Lake Sediments Caused by Environmental Factors During the Past Century: A Case Study of Lake Tapeliai, Lithuania, Radiocarbon 61(4), 885–903, (2019).</p>