The age calibration program, CALIB (Stuiver & Reimer 1986), first made available in 1986 and subsequently modified in 1987 (revision 2.0 and 2.1), has been amended anew. The 1993 program (revision 3.0) incorporates further refinements and a new calibration data set covering nearly 22,000 cal yr (≈18,400 14C yr). The new data, and corrections to the previously used data set, derive from a 6-yr (1986–1992) time-scale calibration effort of several laboratories.

/pdf/extended-14c-data-base-and-revised-calib-3-0-14c-age-4x1nxe8awy.pdf

Extended 14C Data Base and Revised Calib 3.0 14C Age Calibration Program

A new calibration curve for the conversion of radiocarbon ages to calibrated (cal) ages has been constructed and internationally ratified to replace IntCal98, which extended from 0-24 cal kyr BP (Before Present, 0 cal BP = AD 1950). The new calibration data set for terrestrial samples extends from 0-26 cal kyr BP, but with much higher resolution beyond 11.4 cal kyr BP than IntCal98. Dendrochronologically-dated tree-ring samples cover the period from 0-12.4 cal kyr BP. Beyond the end of the tree rings, data from marine records (corals and foraminifera) are converted to the atmospheric equivalent with a site-specific marine reservoir correction to provide terrestrial calibration from 12.4-26.0 cal kyr BP. A substantial enhancement relative to IntCal98 is the introduction of a coherent statistical approach based on a random walk model, which takes into account the uncertainty in both the calendar age and the 14C age to calculate the underlying calibration curve (Buck and Blackwell, this issue). The tree-ring data sets, sources of uncertainty, and regional offsets are discussed here. The marine data sets and calibration curve for marine samples from the surface mixed layer (Marine04) are discussed in brief, but details are presented in Hughen et al. (this issue a). We do not make a recommendation for calibration beyond 26 cal kyr BP at this time; however, potential calibration data sets are compared in another paper (van der Plicht et al., this issue).

/pdf/intcal04-terrestrial-radiocarbon-age-calibration-0-26-cal-4fi3x62yke.pdf

IntCal04 terrestrial radiocarbon age calibration, 0-26 cal kyr BP

From a societal, weather, and climate perspective, precipitation intensity, duration, frequency, and phase are as much of concern as total amounts, as these factors determine the disposition of precipitation once it hits the ground and how much runs off. At the extremes of precipitation incidence are the events that give rise to floods and droughts, whose changes in occurrence and severity have an enormous impact on the environment and society. Hence, advancing understanding and the ability to model and predict the character of precipitation is vital but requires new approaches to examining data and models. Various mechanisms, storms and so forth, exist to bring about precipitation. Because the rate of precipitation, conditional on when it falls, greatly exceeds the rate of replenishment of moisture by surface evaporation, most precipitation comes from moisture already in the atmosphere at the time the storm begins, and transport of moisture by the storm-scale circulation into the storm is vital....

/pdf/the-changing-character-of-precipitation-5gto4ulnge.pdf

The Changing Character of Precipitation

Organic geochemical proxies of paleoceanographic, paleolimnologic, and paleoclimatic processes

zero. In contrast, in the years around a sunspot maximum there is seldom a day when a number of spots cannot be seen, and often hundreds are present. Past counts of sunspot number are readily available from the year 1700 (3), [m and workers in solar and terrestrial studies often use the record as though it were of of uniform quality. In fact, it is not. Thus it is advisable, from time to time, to

https://science.sciencemag.org/content/sci/192/4245/1189.full.pdf

The Maunder Minimum

The recent increased interest in aqueous geochemistry courses is likely driven by our need to understand, as quantitatively as possible, processes controlling chemical compositions in polluted waters that require remediation. However, to understand anthropogenic influences, one must understand natural processes and environmental conditions.

Most Earth science departments now offer courses that address the area described as low-temperature geochemistry or aquatic chemistry or environmental geochemistry. Drever's book is prominent among several texts available as resources for this type of course. The third edition of Drever's text is ideal for a first class in low-temperature geochemistry.

https://agupubs.onlinelibrary.wiley.com/doi/pdf/10.1029/97EO00305

The Geochemistry of Natural Waters

Previously known natural variations in the stable isotope ratio of chlorine, 37Cl/35Cl, have been within the experimental error of ±1.0‰. [All our measurements are reported in terms of δ37 in units of ‰; δ37Cl = |(Rx/Rs)−1|×1,000, where R = 37Cl/35Cl.] Using methyl chloride gas in a ratio mass spectrometer, we have increased the precision of measurement to ±0.24%, and report here significant isotope variation in natural chlorides. In general, salt deposits and saline hydrothermal springs tend to be enriched in 37Cl with respect to seawater. Groundwater shows both enrichment and depletion with respect to seawater. Saline groundwater becomes more enriched in 37Cl with increasing depth.

Natural chlorine isotope variations

Stable carbon isotope measurements in tree rings have been explored as potential indicators of past climate1,2, and as proxy data for reconstructions of the history of 13C/12C variations of atmospheric carbon dioxide as related to the global carbon cycle3–6. Results of these studies are often conflicting, perhaps partly due to the limited style of sampling natural systems with large inherent spatial variability. We have examined stable carbon isotopic trends in tree rings among several radii of the same tree (Pinus edulis Engelm.) and among several trees from the same site, to determine the extent of this variability. The circumferential range in δ13C values of cellulose is ∼1–1.5‰, whereas among individuals it is ∼2–3‰. Tests to determine how well various combinations of cores fit the trend of an individual tree or of the site as a whole indicate that pooling four cores from four trees accurately represent site δ13C trends and absolute values.

Sampling strategy for stable carbon isotope analysis of tree rings in pine

An isotopic fractionation step between carbon fixed in the leaves and that assimilated into wood cellulose has not previously been included in atmosphere–plant fractionation models. Data presented here, however, show that the magnitude of such a fractionation step may be significant. In an experiment which involved 10 juniper trees from around Arizona, cellulose of leaves was found to be isotopically lighter than that of the corresponding tree rings in all trees by an average of 2‰. In a second experiment, the δ13C of leaf material from a juniper tree sampled at monthly intervals was compared with the δ13C of the corresponding ring. For cellulose, δ13C of the wood varied with changes in δ13C of the leaves and was persistently isotopically heavier by 3–4‰. Furthermore, the observed change in δ13C through the growing season suggests a temperature coefficient of about −0.27‰ °C−1. The direction of this leaf–wood fractionation precludes diffusion processes as the primary cause.

Evidence for 13 C/ 12 C fractionation between tree leaves and wood

High-precision measurement of chlorine stable isotope ratios

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