Miniature radiocarbon measurements ( <  150 µg C) from sediments of Lake Żabińskie, Poland: effect of precision and dating density on age–depth models

Abstract

Abstract. The recent development of the MIni CArbon DAting System (MICADAS) allows researchers to obtain radiocarbon (14C) ages from a variety of samples with miniature amounts of carbon (<150 µg C) by using a gas ion source input that bypasses the graphitization step used for conventional 14C dating with accelerator mass spectrometry (AMS). The ability to measure smaller samples, at reduced cost compared with graphitized samples, allows for greater dating density of sediments with low macrofossil concentrations. In this study, we use a section of varved sediments from Lake Żabińskie, NE Poland, as a case study to assess the usefulness of miniature samples from terrestrial plant macrofossils for dating lake sediments. Radiocarbon samples analyzed using gas-source techniques were measured from the same depths as larger graphitized samples to compare the reliability and precision of the two techniques directly. We find that the analytical precision of gas-source measurements decreases as sample mass decreases but is comparable with graphitized samples of a similar size (approximately 150 µg C). For samples larger than 40 µg C and younger than 6000 BP, the uncalibrated 1σ age uncertainty is consistently less than 150 years (±0.010 F14C). The reliability of 14C ages from both techniques is assessed via comparison with a best-age estimate for the sediment sequence, which is the result of an OxCal V sequence that integrates varve counts with 14C ages. No bias is evident in the ages produced by either gas-source input or graphitization. None of the 14C ages in our dataset are clear outliers; the 95 % confidence intervals of all 48 calibrated 14C ages overlap with the median best-age estimate. The effects of sample mass (which defines the expected analytical age uncertainty) and dating density on age–depth models are evaluated via simulated sets of 14C ages that are used as inputs for OxCal P-sequence age–depth models. Nine different sampling scenarios were simulated in which the mass of 14C samples and the number of samples were manipulated. The simulated age–depth models suggest that the lower analytical precision associated with miniature samples can be compensated for by increased dating density. The data presented in this paper can improve sampling strategies and can inform expectations of age uncertainty from miniature radiocarbon samples as well as age–depth model outcomes for lacustrine sediments.

Holocene phototrophic community and anoxia dynamics in meromictic Lake Jaczno (NE Poland) using high-resolution hyperspectral imaging and HPLC data

“…The chronology is based on 18 radiocarbon accelerator mass spectrometry (AMS) dates on taxonomically identified terrestrial plant macrofossils (Table 1) measured at the Laboratory for the Analysis of Radiocarbon at the University of Bern. Samples with <300 µg C were measured using the gassource input of the Mini Carbon Dating System (MICADAS) (Szidat et al, 2014;Zander et al, 2020). The age-depth model was calculated using bacon (rbacon v. 2.4.2) (Blaauw and Christen, 2011;Blaauw et al, 2020) and the IntCal13 calibration curve (Reimer et al, 2013).…”

Holocene phototrophic community and anoxia dynamics in meromictic Lake Jaczno (NE Poland) using high-resolution hyperspectral imaging and HPLC data

“…The chronology is based on 18 radiocarbon AMS dates on taxonomically identified terrestrial plant macrofossils (Table 1) measured at the Laboratory for Radiocarbon Analysis at the University of Bern. Samples with < 300 μg C were measured using the gas-source input of the MIni CArbon DAting System (Szidat et al, 2014;Zander et al, 2020). The age-depth model was calculated using Bacon (rbacon v. 2.4.2;Blaauw et al, 2020;Blaauw and Christeny, 2011) and the IntCal13 calibration curve (Reimer et al, 2013).…”

New approaches to dating intermittently varved sediment, Columbine lake, Colorado, USA

“…To gather enough material for a standard graphite-based AMS measurement, the radiocarbon samples in this study were composed of a mixture of aquatic and terrestrial material (Table 3). Samples of mixed composition have been shown to yield ages that are generally too old (Zander et al, 2019). Both aquatic and terrestrial macrofossils are associated with processes that can increase their apparent age.…”

“…These systematic biases are typically assessed by comparing the varve chronology to radiometric methods ( 137 Cs, 210 Pb, and 14 C) and can sometimes be corrected. For example, the agreement between varve and radiometric chronologies can be evaluated objectively through OxCal's V_sequence, for example (Bronk Ramsey, 1995;Tian et al, 2005;Zander et al, 2019). The 14 C ages can reveal missing sediment intervals where missing varves can be inserted (Tian et al, 2005).…”