There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Radiocarbon (14C) ages cannot provide absolutely dated chronologies for archaeological or paleoenvironmental studies directly but must be converted to calendar age equivalents using a calibration curve compensating for fluctuations in atmospheric 14C concentration. Although calibration curves are constructed from independently dated archives, they invariably require revision as new data become available and our understanding of the Earth system improves. In this volume the international 14C calibration curves for both the Northern and Southern Hemispheres, as well as for the ocean surface layer, have been updated to include a wealth of new data and extended to 55,000 cal BP. Based on tree rings, IntCal20 now extends as a fully atmospheric record to ca. 13,900 cal BP. For the older part of the timescale, IntCal20 comprises statistically integrated evidence from floating tree-ring chronologies, lacustrine and marine sediments, speleothems, and corals. We utilized improved evaluation of the timescales and location variable 14C offsets from the atmosphere (reservoir age, dead carbon fraction) for each dataset. New statistical methods have refined the structure of the calibration curves while maintaining a robust treatment of uncertainties in the 14C ages, the calendar ages and other corrections. The inclusion of modeled marine reservoir ages derived from a three-dimensional ocean circulation model has allowed us to apply more appropriate reservoir corrections to the marine 14C data rather than the previous use of constant regional offsets from the atmosphere. Here we provide an overview of the new and revised datasets and the associated methods used for the construction of the IntCal20 curve and explore potential regional offsets for tree-ring data. We discuss the main differences with respect to the previous calibration curve, IntCal13, and some of the implications for archaeology and geosciences ranging from the recent past to the time of the extinction of the Neanderthals.

https://dspace.stir.ac.uk/bitstream/1893/30981/1/intcal20_northern_hemisphere_radiocarbon_age_calibration_curve_055_cal_kbp.pdf

The IntCal20 Northern Hemisphere Radiocarbon Age Calibration Curve (0-55 cal kBP)

Time is divided by geologists according to marked shifts in Earth's state. Recent global environmental changes suggest that Earth may have entered a new human-dominated geological epoch, the Anthropocene. Here we review the historical genesis of the idea and assess anthropogenic signatures in the geological record against the formal requirements for the recognition of a new epoch. The evidence suggests that of the various proposed dates two do appear to conform to the criteria to mark the beginning of the Anthropocene: 1610 and 1964. The formal establishment of an Anthropocene Epoch would mark a fundamental change in the relationship between humans and the Earth system.

https://bertaux.files.wordpress.com/2015/04/3-12-15-lewis-maslin-defining-the-anthropocene-nature14258.pdf

Defining the Anthropocene

Human activity is leaving a pervasive and persistent signature on Earth. Vigorous debate continues about whether this warrants recognition as a new geologic time unit known as the Anthropocene. We review anthropogenic markers of functional changes in the Earth system through the stratigraphic record. The appearance of manufactured materials in sediments, including aluminum, plastics, and concrete, coincides with global spikes in fallout radionuclides and particulates from fossil fuel combustion. Carbon, nitrogen, and phosphorus cycles have been substantially modified over the past century. Rates of sea-level rise and the extent of human perturbation of the climate system exceed Late Holocene changes. Biotic changes include species invasions worldwide and accelerating rates of extinction. These combined signals render the Anthropocene stratigraphically distinct from the Holocene and earlier epochs.

http://science.sciencemag.org/content/sci/351/6269/aad2622.full.pdf

The Anthropocene is functionally and stratigraphically distinct from the Holocene

We present a compilation of tropospheric 14 CO 2 for the period 1950–2010, based on published radiocarbon data from selected records of atmospheric CO 2 sampling and tree-ring series. This compilation is a new version of the compilation by Hua and Barbetti (2004) and consists of yearly summer data sets for zonal, hemispheric, and global levels of atmospheric 14 C. In addition, compiled (and extended) monthly data sets for 5 atmospheric zones (3 in the Northern Hemisphere and 2 in the Southern Hemisphere) are reported. The annual data sets are for use in regional and global carbon model calculations, while the extended monthly data sets serve as calibration curves for 14 C dating of recent, short-lived terrestrial organic materials. DOI:  10.2458/azu_js_rc.v55i2.16177

/pdf/atmospheric-radiocarbon-for-the-period-1950-2010-389xyc3dxt.pdf

Atmospheric Radiocarbon for the Period 1950–2010

Atmospheric radiocarbon for the period 1950–2019

New records of δ13C and ∆14C values in annual rings of pine and oak from different sites around the world were obtained with a time resolution of 1 yr. The results obtained for Europe (Poland), east Asia (Japan), and South America (Peru) are presented in this paper. The δ13C and radiocarbon concentration of α-cellulose from annual tree rings of pine and of the latewood of oak were measured by both accelerator mass spectrometry (AMS) and liquid scintillation spectrometry (LSC). The values of 14S, which represent decreasing 14C concentrations caused by the emission of CO2 from fossil fuel use (Suess effect; Suess 1955), were calculated for each site. Low average 14S (about -0.4 to 0.8%) values for clean areas and high values (about 3.4-3.6%) for industrial and/or urbanized areas were noted. Records of the δ13C values obtained for pine and oak from Poland were used to reconstruct climate changes during the last 400 yr. The results clearly indicate the climate cooling during the periods of the Maunder minimum (1645-1715) and the Dalton minimum (1790-1820). The anti-correlation between the δ13C and ∆14C records during those 2 periods is clear if the 14C record is shifted toward older ages by 24 yr.

/pdf/carbon-isotopes-in-tree-rings-climate-and-the-suess-effect-4sw326ziut.pdf

Carbon isotopes in tree rings: climate and the suess effect interferences in the last 400 years

Variations of anthropogenic CO2 in urban area deduced by radiocarbon concentration in modern tree rings.

In 1994, the Gliwice Radiocarbon Laboratory began operating a liquid scintillation spectrometry system, consisting of a Quantulus 1220 (super TM) spectrometer and two vacuum rigs for benzene production. This paper describes the procedures used for the benzene synthesis from samples containing $lt;1 g of carbon and in the range 1 to 10 g of carbon. We also present the Quantulus calibration procedures used in the Gliwice Radiocarbon Laboratory and NERC Radiocarbon Laboratory, and compare the calibration parameters.

/pdf/commissioning-of-a-quantulus-1220-liquid-scintillation-beta-6mnwmswtzb.pdf

Andrzej Z. Rakowski

Papers

Atmospheric Radiocarbon for the Period 1950–2010

Atmospheric radiocarbon for the period 1950–2019

Carbon isotopes in tree rings: climate and the suess effect interferences in the last 400 years

Variations of anthropogenic CO2 in urban area deduced by radiocarbon concentration in modern tree rings.

Commissioning of a Quantulus 1220™ Liquid Scintillation Beta Spectrometer for Measuring 14C and 3H at Natural Abundance Levels