Previously described models and a new model were compared to determine the initial 14C content of groundwater in a partially-confined and unconfined sandstone aquifer (Fränkisches Albvorland, Germany). Isotope and chemical data were derived from samples of water, soil-CO2, and solid carbonates. The various 14C models lead to important differences in resulting groundwater ages.

From the relationship between 14C and 2H or 18O concentrations of groundwater, it must be assumed that chemical and/or physical carbon isotope exchange between the DIC and the solid carbonate has occurred provided the groundwater with lower 18O and 2H concentrations was generated during the Pleistocene. Groundwater ages deduced from 14C and 39Ar concentrations showed discrepancies which can be explained if carbon isotope exchange between DIC and solid carbonate as well as mixing of recent and fossil waters is considered.

The Meade thrust, in southeastern Idaho, is a major element of the Western Overthrust Belt. The allochthon is of geo-economic importance both as a potential hydrothermal area and as the principal mining area within the Western Phosphate Field. To assist in the development of these two resources, an understanding of the regional ground-water circulation was sought. Geologic and hydrologic data from boreholes in this area are virtually nonexistent. Waterwell development in the area has not occurred because of the abundance of springs and only a few hydrocarbon exploration boreholes have been drilled. Thus, the problem lends itself to evaluation by isotope hydrologic and geochemical methods. Ten springs from within the thrust block and around its periphery were sampled for major ions, 2H/18O, and 14C/13C analysis. Data from these analyses and from field geologic evidence have identified two distinct flow regimes within the Meade thrust allochthon. Shallow flow systems lie above the impermeable Phosphoria Formation, usually within a few hundred meters of the surface. Most of the spring waters from this system are recent and cool. In all cases, they have mean subsurface residence times of less than a few hundred years. The deeper flow systems which lie below the Phosphoria formation are hydraulically isolated from the shallow system. Warm waters from these springs have 14C contents suggesting mean ground-water residence times on the order of 15,000 years. Although these waters could have circulated to as deep as 1900m, 2H/18O results show that high temperatures were never reached. There is no evidence to suggest that water from beneath the Meade thrust has contributed to the circulation in the allochthon.

The Xi-Sha Islands comprise 35 coral reefs, cays, and islets lying to the northwest of the South China Sea. Since Miocene time, > 1200m of bioherms developed on slowly subsiding granite-gneiss bed rock. These sediments provide evidence for sea-level changes and crustal movements in the South China Sea.

From 1966 to 1979, the University of Missouri, the University of Arizona, and the Illinois State Museum conducted extensive interdisciplinary investigations of Late Pleistocene peat deposits associated with springs, some extinct, in the Pomme de Terre River Valley of the Ozark Highland, Missouri (fig 1). Most of the sites are now beneath the waters of the Harry S Truman reservoir. Archaeologic investigations in the area produced a remarkably long sequence of cultural change and development during the Holocene but produced no evidence of human presence in the area prior to 11,000 years ago despite diligent excavation of favorable bone-bearing deposits.

The Landnám of Iceland is usually dated too early by the 14C dating method, at least to judge from the tradition according to the Landnámabók. Various sources of error are considered. One, the use of driftwood, can be excluded in many cases, since birch is often selected for dating purposes. Second, the settlers may have brought wood with them. A third obvious source of uncertainty is the age of a tree before felling. It is difficult to explain the seemingly too early results by secular global variations of 14C content. A regional low level of 14C may result from volcanic activity or the small size of the land areas in the Arctic region.

Our studies on 14C chronology and palynology of Holocene sediments in southern Fujian along the western coast of the Taiwan Straits show that the natural environment has undergone three stages of development during the Holocene. From Early Holocene (ca 10,000–8000 yr ago) to Middle Holocene (8000–2500 yr ago) and then to Late Holocene (2500 yr ago), sediments varied from land-sea transitional to marine and then to terrigenous; vegetation altered from mixed forest to evergreen broad-leaf forest and then steppe; climate fluctuated from temperate to hot and then to warm. The sea-level maximum in the post-glacial period occurred at 5000–6000 yr ago, at 5 to 10m elevation. During the subsequent regression, two stable stages of sea-level dated at >3000 and ca 2000 yr ago. The climatic drying and eolian sand deposit began at 700 yr ago. The results agree with our previous studies in southern Liaoning.

A test for the reliability of 14C dating of soil was made at two sites with buried, autochthonous, and in parts, allochthonous sandy podzols, dated either litho- and pedostratigraphically or palynologically. The differences between the age ranges obtained and the apparent mean residence times (AMRT) calculated from the 14C content of alkaline extracts from fossil soil layers and horizons lean in organic matter exceed 10,000 years, corresponding to a maximum contamination with recent carbon of up to 50 %. The use of correction factors for the apparent mean residence times of podzols is not valid, not even for climate zones, because these values have a broad scatter for the same profile.

14C activities of decadal samples from beech trees growing under extreme calcareous conditions were compared to 14C activities of decadal samples of the same age from a beech tree growing in a normal mold soil in order to see whether part of the carbon assimilated during photosynthesis might originate from 14C-deficient carbonates in the soil. The calcareous soils contained from 18 to 52% calcium carbonate, and this carbonate had a mean 14C age of 10,200 to 17,600 years BP. A comparison was also made with the 14C activity of contemporaneous samples from Douglas Fir from the US North Pacific (Stuiver, 1982).

No significant depletion in 14C activity in beech trees growing in the highly calcareous soils was detected. The measured mean difference in 14C activity in beech trees from calcareous and non-calcareous sites corresponds to an uptake of 0.12 ± 0.3% carbon from soil carbonates in the calcareous sites.

Calcareous deposits known as tufa or travertine contain biogenic carbon and are a potential source of geochronologic information. Many dated samples from Karstic regions in Yugoslavia proved that 14C analyses of tufa can provide reliable data reflecting climatic conditions in the past. Systematic dating of tufa samples revealed two distinct groups of deposits: recent tufa deposits, with a sharp age limit of ∼6000 ± 500 years BP, and old tufa deposits with 14C age ranges from 25,000 ± 2300 years BP to the lowest limit of our 14C dating system (∼37,000 years). A histogram based on the initial activity AO = 0.85 shows the age distribution of randomly sampled tufas vs sample frequency. A time gap between ∼6000 BP and ∼23,000 BP is evident, reflecting cooler climatic conditions. The start of peat deposition is coincident with that of tufa growth in the Holocene.

Paleoclimatic implications of tufa growth periods obtained by 14C dating are as follows: climatic conditions that favor tufa formation at least in karstic regions, are very stringent. Therefore, climatic conditions, such as mean annual temperature and humidity, as well as hydrologic and vegetational conditions, must have been very similar in periods of tufa growth. While recent tufa deposits are coincident with the warm Holocene period, old tufa can be associated with warm interstadials in the Würm.

The effects of environmental factors such as water stress, elevated CO2, or temperature on carbon assimilation and allocation in plants have been studied extensively (Gifford and Evans, 1981; Loomis, Rabbinge, and Ng, 1979; Neales and Incoll, 1968). However, the interactions of these processes are not well understood and cannot be predicted with any degree of confidence. Continuous and simultaneous measurements of photosynthesis, transport, and sink activity have never been made during the short- and long-term responses of live, intact plants to step changes in environmental factors. Thus, direct environmental effects and adaptive responses of plants are generally not distinguished. This results in part from limitation in experimental techniques and protocol used in past studies and the lack of experimental validation of hypotheses and models (eg, Goeschl et al, 1976; Magnuson et al, 1979; Smith et al, 1970) dealing with these problems. This paper describes in detail the components of an integrated technique for studying carbon assimilation, transportation and allocation in intact live plants under any set of environmental conditions, using continuously produced 11CO2.

The real-time measurement of net photosynthesis and dark respiration of plants has been possible since the development of the infra-red analyzer and its application in the 1940's. This technique has allowed intensive investigations of the mechanisms and dynamics of carbon dioxide assimilation by green plants (Sestak, Catsky, and Jarvis, 1971). As a result, physiologic and ecologic aspects of net carbon dioxide exchange are the subject of much research (eg, Osmond, Bjorkman and Anderson, 1980).

Variability in temperature and 14C levels are recorded in coralline aragonite that grew in the Gulf Stream during the past four centuries. In particular, 18O/16O ratios reflect a decrease of ca 1°C in surface water temperature during the latter part of the Little Ice age. 14C levels also rose in the surface waters of the Gulf Stream and in atmospheric CO2 during the Maunder minimum. These observations indicate that ocean circulation may have been significantly different in the North Atlantic around the beginning of the 18th century.

Marine transport of inorganic and organic carbon is simulated by means of a computer model in which the oceans are divided into a high and low latitude region. Water transport (and with it carbon transport) is reproduced 1) as downwelling of surface waters at low latitudes, and 2) in general, as different depth-dependent turbulent diffusion in both deep-sea regions. The model is calibrated with pre-bomb 14C and validated against perturbations of total carbon, 13C/C- and 14C/C-ratios; it is compatible with carbon release from fossil fuels and from biogenic sources.

In early 1982 we attempted to compile information on 14C counting equipment from all laboratories listed in RADIOCARBON. A gratifying number of laboratories cooperated in communicating their data: more than 65% of those in which proportional counters are in operation. Our compilation covers more than 80% of all gas counters used for 14C dating. Unfortunately, the number of parameters determining counter quality as well as the spread in these factors is so large that their separate influence cannot be established beyond statistical doubt. Nevertheless qualitative and semi-quantitative trends are clearly observed. Laboratories are not identified in the data but the calculations and standardization procedures allow the laboratories to identify their own counter data in the graphs. Each plot does not contain a complete compilation of all counters. This is either because of lack of or internally inconsistent information.

As an alternative to the accelerator technique, a simple, compact, small counter system has been developed and tested for routine 14C dating. Our small counter is an all-metal design made of the OFHC copper with quartz supports for the anode (25μm stainless steel). Careful selection of materials for the counter construction was made based on the measurements of the alpha contamination. Methane as the counter filling gave better resolution and gas gain stability, whereas CO2 gave lower background counting rate and it was easier to prepare and to handle. The long term run using CH4 showed that the gas gain remained stable within 1–2% for months after the initial drop which followed the counter filling. A 7-day counting period was sufficient to achieve a 3% relative standard deviation which was considered acceptable for routine dating of younger samples.

A conventional 14C system with either a 15cm3 or a 100cm3 methane gas proportional counting tube, each constructed from high purity copper, has been used at the Washington State University 14C laboratory for three years (Sheppard, Hopper, Westberg, 1981). The electronic components of this system included highly stable (John Fluke) power supplies, modified pre-amplifiers (Canberra), and NIM amplifiers, single channel analyzers, scalers, timers, etc, (ORTEC). Modules were selected for a highly stable low-noise system. The system was designed to minimize problems generated by ground-loops, electromagnetic noise pick-up, and line noise. It operates in a copper-lined basement room of a four-story brick and concrete building along with a second and older gas proportional system which has three 500cm3 copper counting tubes operated at 2 or 3 atmospheres of methane. Analysis of the older system's background data indicates that the background counting rate of 0.8 counts per minute is virtually independent of atmospheric pressure. It has not been possible to determine the pressure dependence of the small counting tubes.

Due to traces of radium and uranium in most 14C samples, radon appears as a radioactive contamination in the CO2 prepared by combustion. This contamination must be removed by an active purification prodecure or by storing the CO2 prior to measurement. No effective electronic discrimination against radon and its daughter elements can be performed. The necessary storage time until radon has decayed varies widely, especially for marine shells. The latter material, collected from Norway and Svalbard, has been a main object for the present investigation. In a few cases, a measureable amount of radon may be left even after eight weeks. The behavior of radon and its daughter elements in a CO2 proportional counter has been studied.

The extraction of dissolved carbonate species for age dating from a 100L water sample by the direct-precipitation method (DPM) and by the gas-evolution method (GEM) has been investigated. Stable carbon-isotope fractionation between initial and final carbon dioxide evolved was ca 11‰ by GEM and 1‰ by DPM. GEM will produce isotopically lighter carbon dioxide compared with DPM if carbonate recovery is low. Extraction efficiency of > 95% can be achieved by GEM in 3 hours using nitrogen gas at a sweeping rate of 2000cc per minute. DPM requires precipitates to settle overnight to assure > 95% recovery. GEM is little affected by a high concentration of sulfate ions, whereas DPM is greatly affected by sulfate resulting in less yield.

In August 1980, the National Bureau of Standards (NBS) issued, in the form of oxalic acid, a new International Reference Material of contemporary 14C for use in radiocarbon dating laboratories. This reference material was to replace the 1975 oxalic-acid standard, supplies of which had been practically exhausted in 1978. The preparation of the new oxalic-acid standard was described in a preliminary report, as were, also, the results then available for the activity-concentration ratio of the new to the old standard obtained by a number of leading international laboratories.

With the recent completion of the analysis of all results submitted by the participating laboratories, NBS plans to issue these recently calibrated samples of oxalic acid as an NBS Standard Reference Material. There is, however, no significant difference in the reported value of its activity concentration, relative to that of the 1957 standard, from that given provisionally in 1980.

Subsequent to our report (Cavallo and Mann, 1980) a further measurement of relative activity concentration was reported by the Radiocarbon Laboratory of Peking University. Their value, and that also for δ13C, is insignificantly different from the average value of the results submitted by the eleven laboratories that participated in the international comparison organized by NBS.

13C isotope analyses of different stages of benzene synthesis have been made to study partial isotope fractionation. More than 60 analyses of carbonates, charcoal, carbon dioxide, and benzene were made in a double collector mass spectrometer. In the first stage of the synthesis (conversion to carbon dioxide) little or no fractionation was observed, beyond the analytical error of the method. Later stages of the process, show a greater and systematic fractionation. The experimental techniques are described.