Radionuclide dating of the recent sediments of Blelham Tarn

Lake sediments of the last 1000 years provide a unique record of environmental changes. Methods of dating this record are reviewed and discussed. Sediments of the last 20 years, which are of particular biological significance because of their record of man-made changes in lakes (including enrichment and pollution) have been dated successfully by the distribution within them of the fallout product ¹³⁷Cs, present in the atmosphere since 1954 and reaching a peak of supply in 1963. The structured pattern shown by the curve for ¹³⁷Cs concentration in most sediments investigated indicates that faunal mixing of the surface muds does not destroy the vertical stratification of the sediment profile. Sediments up to 120 years old have been dated by a lead isotope technique, and the results of this proved consistent with both ¹³⁷Cs dating and with palaeomagnetic dating where this was possible. Theoretical considerations of the application of radiocarbon dating to organic material of 18th and 19th century date are reviewed. Results of application of these radionuclide techniques to the sediments of a small lake, Blelham Tarn, near Windermere, are presented. Evidence from ¹³⁷Cs and ²¹⁰Pb dating of profiles from several different positions within the lake shows that the depth of the annual increment to the sediments varies by a factor of × 2 from place to place. The concentration within the sediment of chemical and biological variables shows no significant variation from one position to another; therefore calculated values for amounts of each variable included within unit area of the annual increment depend primarily on the thickness of this at the site chosen, and so cannot be directly related to the rates of supply of, for example, pollen grains or total organic matter, and so to rates of productivity. Results from nine ¹⁴C dates on material 400–1000 years old, when correlated with analyses for pollen and sediment composition, demonstrate the profound effects of agricultural practices in the catchment (assumed to be deforestation and ploughing) in disturbing the orderly transfer to lake sediments of material eroded from the catchment.     

Sediment cores from shallow lakes preserve reliable,informative paleoenvironmental archives despite hurricane-force winds

Comparison of sediment cores collected in 1999 and 2013 from shallow Lake Harris, Florida, USA showed that the sediment maintained stratigraphic integrity despite multiple hurricanes passing through the area in 2004. Sediments less than 50 years old displayed small losses of organic matter (OM), total phosphorus (TP) and heat-extractable (HE-P) through time that are unrelated to hurricane impacts. Nevertheless, sediment that accumulated between the two core collection dates contained 4-fold more TP than was lost from the sediment over the 14-year period, indicating that sediments in Lake Harris are a net sink for water-column TP. Persistent, elevated ¹³⁷Cs activity in sediments deposited since the mid-1960s indicates protracted cesium input to the lake from this subtropical watershed. There is also evidence for downward transport of ¹³⁷Cs in the sediment profile between core collection dates. Prolonged export of ¹³⁷Cs from the watershed and downward mobility of the radionuclide in the sediment profile diminish the utility of ¹³⁷Cs as a dating tool in Lake Harris.     

Säynäjälampi and the difficulties inherent in the dating of sediments in a hard-water lake

Previous measurements of the ¹⁴C activity of lake sediments and Potamogeton plants from Säynäjälampi, collected in 1970, indicated a severe hard-water effect (Donner et al. 1971). Samples from new cores, collected in 1977, were sliced into thin sections down to 18 cm. The ¹⁴C concentration in samples down to 7 cm was similar to that obtained by the Helsinki Laboratory. The corresponding apparent ¹⁴C age is almost 2 000 years. Light-coloured layers, apparently due to catchment drainage, were used together with density diagrams to correlate the cores. The drainage history gives a time-scale showing that the lowest samples dated to correlate the cores. The drainage history gives a time-scale showing that the lowest samples dated were just old enough to be pre-bomb sediments. Three samples of submerged plants were also examined, indicating some exchange with the air and an appreciable reservoir age. The activity of the plants was significantly lower in 1978 than in 1970. One sample, well below the lowest drainage stratum, indicates a reservoir age of ca. 1 100 years. This sample yielded an apparent age of the INS fraction which was significantly different from that of the SOL fraction. The difference was determined to ca. 600 years. Total ²¹⁰Pb was determined via ²¹⁰Po using isotope dilution while ²²⁶Ra was measured with the help of radon emanation. The ²²⁶Ra was used to estimate the supported ²¹⁰Pb. The unsupported ²¹⁰Pb showed a higher sediment accumulation rate for the top nine cm of one core (the length investigated was 16.5 cm). The varying accumulation rate was explained by human activities, as could be seen from the heterogenous sediment composition of the cores. Recent vegetational change is described from direct observations since 1957. Pollen analysis does not give any reliable indication of agriculture.     

High resolution radiocarbon spike confirms tree ring dating with low sample depth

Radiocarbon (¹⁴C) has been used to date carbon-rich objects in Earth science, archeology, and history since the 1940s. New methods, using spikes in ¹⁴C caused by solar proton events, can be used to annually date wood when crossdating is not possible, such as when sample size is low, samples are floating in time, or external disturbances lead to insecure dates. Here, we use a spike in radiocarbon during a solar energetic particle (SEP) event in 774/775 CE to confirm crossdating of a poorly-replicated King Billy pine (Athrotaxis selaginoides) chronology. Low sample depth between 1498 and 1523 CE (two trees) prevented confident dating of the early period of the chronology. Three core samples with strong correlation with the master chronology that likely included the 774/775 CE Miyake SEP event were identified for radiocarbon isotope analysis. We sectioned segments centered on the estimated 774/775 CE date and then isolated the holocellulose in each sample. Samples were sent to an accelerator mass spectrometry (AMS) for radiocarbon measurements. The AMS data confirmed the crossdating accuracy of the tree ring series and reinforces the applicability of this technique to anchor poorly dated tree ring series in time. In addition, we found sample processing with a microtome proved superior for holocellulose extractions and yielded more accurate ¹⁴C measurements. We recommend sampling with a microtome, processing at least three samples per year, and including sample masses greater than 100 ug C to confirm dating using radiocarbon spikes.     

Effects of different macrophyte growth forms on sediment and P resuspension in a shallow lake

The effects of floating-leaved, submerged and emergent macrophytes on sediment resuspension and internal phosphorus loading were studied in the shallow Kirkkojärvi basin by placing sedimentation traps among different plant beds and adjacent open water and by sediment and water samples. All the three life forms considerably reduced sediment resuspension compared with non-vegetated areas. Both among submerged (Ceratophyllum demersum, Potamogeton obtusifolius, Ranunculus circinatus) and emergent (Typha angustifolia) plants, resuspension rate was on average 43% of that in the adjacent open water, while within floating-leaved plants (Nuphar lutea) the corresponding value was 87%. The effects of submerged and emergent vegetation increased in the course of the growing season together with increasing plant density. Among floating-leaved vegetation, such seasonal trend in resuspension effects was not observed. Compared with the non-vegetated area, floating-leaved, submerged and emergent plants reduced internal phosphorus loading on average by 21, 12 and 26 mg m⁻² d⁻¹, respectively. The effects of floating-leaved plants on resuspension-mediated internal phosphosrus loading were thus comparable to the effects of the other two life forms.     

Natural and anthropogenic forcing of aquatic macrophyte development in a shallow Danish lake during the last 7000 years

Aim To investigate the long‐term changes in aquatic vegetation in a lowland, shallow lake, and to assess the relationship between aquatic vegetation and natural and anthropogenic catchment changes. Location Gundsømagle Sø, Zealand, Denmark: a shallow (mean depth 1.2 m), hypereutrophic lake (mean annual total phosphorus (TP) c. 700 μg TP L^?1) located in a predominantly agricultural catchment (88% cultivated land). The lake is presently devoid of macrophytes. Methods One hundred and forty‐seven contiguous samples from a sediment core (taken in 2000) were analysed for macrofossil remains together with loss‐on‐ignition and dry weight. From an earlier sediment core (taken in 1992), 67 samples were analysed for pollen and the two cores were correlated using the ignition residue profiles. Core chronology was determined by ²¹⁰Pb and ¹³⁷Cs dating of the recent lake sediments, while older sediments were dated by pollen‐stratigraphical correlation, as ¹⁴C dating proved problematical. Aquatic macrofossil abundance was used to reconstruct past changes in the lake's plant community and water‐level. The contemporary catchment land‐use change was inferred from sedimentary pollen data, and soil erosion to the lake was deduced from the minerogenic content of the lake sediments. Results The macrofossil record covers the last 7000 years, but aquatic plant remains were scarce prior to c. 1300 bc . After this date the abundance of submerged and emergent macrophyte remains increased dramatically, paralleled by an increase in sediment minerogenic matter and non‐arboreal pollen (NAP). Aquatic plant remains were abundant for more than 3000 years until the mid 1900s. Macrofossils of Linum usitatissimum (L.) (flax) and high pollen percentages of ‘Cannabis type’ (hemp) were recorded in periods between c. 1150 bc and 1800 ad . Main conclusions Our study suggests that, between c. 5000 bc and 1300 bc , the submerged plant community was confined to the littoral zone. From 1300 bc onwards, the submerged macrophyte vegetation expanded rapidly across the lake bed, presumably as a response to lake shallowing caused by a combination of climatic‐induced water‐level lowering and enhanced erosional infilling of the lake basin due to intensified anthropogenic activities in the catchment. The lake was meso‐eutrophic and had an extensive and diverse aquatic flora for more than 3000 years, until the middle of the twentieth century. In periods between c. 1150 bc and 1800 ad , the lake experienced direct anthropogenic impact from retting of fibre plants (Linum and Cannabis). Over the last 200 years, erosional infilling of the lake basin increased drastically, probably as a result of agricultural intensification. In the twentieth century, the lake was strongly affected by nutrient enrichment from both point sources (sewage from built‐up areas) and diffuse agricultural run‐off which led to hypertrophic conditions and the collapse of the submerged vegetation c. 1950–60. The concept of ‘naturalness’ and the implications for lake conservation are discussed.     

Collagen Fingerprinting: A New Screening Technique for Radiocarbon Dating Ancient Bone

Collagen is the dominant organic component of bone and is intimately locked within the hydroxyapatite structure of this ubiquitous biomaterial that dominates archaeological and palaeontological assemblages. Radiocarbon analysis of extracted collagen is one of the most common approaches to dating bone from late Pleistocene or Holocene deposits, but dating is relatively expensive compared to other biochemical techniques. Numerous analytical methods have previously been investigated for the purpose of screening out samples that are unlikely to yield reliable dates including histological analysis, UV-stimulated fluorescence and, most commonly, the measurement of percentage nitrogen (%N) and ratio of carbon to nitrogen (C:N). Here we propose the use of collagen fingerprinting (also known as Zooarchaeology by Mass Spectrometry, or ZooMS, when applied to species identification) as an alternative screening method for radiocarbon dating, due to its ability to provide information on collagen presence and quality, alongside species identification. The method was tested on a series of sub-fossil bone specimens from cave systems on Cayman Brac (Cayman Islands), chosen due to the observable range in diagenetic alteration, and in particular, the extent of mineralisation. Six ¹⁴C dates, of 18 initial attempts, were obtained from remains of extinct hutia, Capromys sp. (Rodentia; Capromyidae), recovered from five distinct caves on Cayman Brac, and ranging from 393 ± 25 to 1588 ± 26 radiocarbon years before present (yr BP). All of the bone samples that yielded radiocarbon dates generated excellent collagen fingerprints, and conversely those that gave poor fingerprints also failed dating. Additionally, two successfully fingerprinted bone samples were screened out from a set of 81. Both subsequently generated ¹⁴C dates, demonstrating successful utilisation of ZooMS as an alternative screening mechanism to identify bone samples that are suitable for ¹⁴C analysis.     

Occupation of the Antarctic continent by petrels during the past 35 000 years: Inferences from a 14C study of stomach oil deposits

Summary The dated material was taken from organic deposits occurring in snow petrel colonies of the Untersee Oasis, central Queen Maud Land, East Antarctica. These deposits have been formed by accumulation and solidification of stomach oil regurgitated by petrels over a long time period. Within the deposits the ¹⁴C ages tend to increase with depth. Local mixing and irregular ¹⁴C profiles are of minor importance. This confirms the suitability of such material for ¹⁴C dating. According to the ¹⁴C chronology the colonies near Lake Untersee have been continuously occupied at least during the past 8 kyr. Surprisingly old ages for three samples, namely 13.8, 18.4 and 33.9 kyr BP, suggest that breeding colonies must have been in the study area during the last glacial maximum. Information about the minimum age of moraines and the timing of local ice retreat can be obtained from a correlation between the oldest ¹⁴C age of the organic material accumulated on moraines and the altitude of the sample site.     

A 14C age calibration curve for the last 60 ka: the Greenland-Hulu U/Th timescale and its impact on understanding the Middle to Upper Paleolithic transition in Western Eurasia

This paper combines the data sets available today for ¹⁴C-age calibration of the last 60 ka. By stepwise synchronization of paleoclimate signatures, each of these sets of ¹⁴C-ages is compared with the U/Th-dated Chinese Hulu Cave speleothem records, which shows global paleoclimate change in high temporal resolution. By this synchronization we have established an absolute-dated Greenland-Hulu chronological framework, against which global paleoclimate data can be referenced, extending the ¹⁴C-age calibration curve back to the limits of the radiocarbon method. Based on this new, U/Th-based Greenland_Hulu chronology, we confirm that the radiocarbon timescale underestimates calendar ages by several thousand years during most of Oxygen Isotope Stage 3. Major atmospheric ¹⁴C variations are observed for the period of the Middle to Upper Paleolithic transition, which has significant implications for dating the demise of the last Neandertals. The early part of “the transition” (with ¹⁴C ages > 35.0 ka ¹⁴C BP) coincides with the Laschamp geomagnetic excursion. This period is characterized by highly-elevated atmospheric ¹⁴C levels. The following period ca. 35.0-32.5 ka ¹⁴C BP shows a series of distinct large-scale ¹⁴C age inversions and extended plateaus. In consequence, individual archaeological ¹⁴C dates older than 35.0 ka ¹⁴C BP can be age-calibrated with relatively high precision, while individual dates in the interval 35.0-32.5 ka ¹⁴C BP are subject to large systematic age-‘distortions,’ and chronologies based on large data sets will show apparent age-overlaps of up to ca. 5,000 cal years. Nevertheless, the observed variations in past ¹⁴C levels are not as extreme as previously proposed (“Middle to Upper Paleolithic dating anomaly”), and the new chronological framework leaves ample room for application of radiocarbon dating in the age-range 45.0-25.0 ka ¹⁴C BP at high temporal resolution.     

Les derniers Homo heidelbergensis et leurs descendants les néandertaliens : datation des sites d’Orgnac 3, du Lazaret et de Zafarraya

This article presents the dating results recently obtained on three archaeological sites in Europe. At Orgnac 3 (Ardèche, France) from where the last Homo heidelbergensis fossils are associated with the first evidence of levallois technique, two speleothem formations from the 5b–6–7^th layers were U-Th dated with MC-ICPMS, giving an age range of 319–255 ka (2σ) (MIS 8–9), while the volcanic ash-bearing second layer was dated by ⁴⁰Ar/³⁹Ar, obtaining a preliminary date of 308.2 ± 6.8 ka (2σ). The combined ESR/U-Th dating of red deer enamel teeth from Lazaret cave (Alpes-Maritimes, France) attributed ages of 120–190 ka to the Acheulean and pre-Mousterian layers (MIS 6), which is in agreement with previous TIMS U-Th dates between 108 and 44 ka on calcite samples from the overlying TRA trench (MIS 5, 4, 3). At Zafarraya (Andalousie, Espagne), a number of ¹⁴C measurements on charcoal samples as well as combined ESR/U-Th dates on Capra and Equus dental enamels assigned the Mousterian artefacts and neandertalian fossils-bearing deposits an age interval between 42 and 34 ka (MIS 3).     

Dendrochronology improves understanding of the charcoal production history

Charcoal piles have become a frequent subject of research in recent years as a better understanding of past human activities in forests is sought. The age of charcoal piles is usually determined by radiocarbon dating; dendrochronology is rarely used because of the small size of preserved charcoal remains and the insufficient number of visible tree rings. This paper presents the potential for dendrochronological and ¹⁴C method in research into charcoal piles. From 14 charcoal-burning sites in the Czech Republic, 214 pieces of charcoal were anatomically identified at the genus level and dendrochronologically analysed. Our results show that fir dominated in these charcoal remains, followed by oak, beech, spruce and pine. With an overall dendrochronological dating success of 24 %, fir charcoal was dated most often (65 %) with measurable tree rings ranging from 14 to 90. The oldest charcoals were dendrochronologically dated to summer 1682 CE; conversely, the youngest had end dates in the second half of the 19th century. The relatively poor dating success of oak charcoal very likely resulted from the use of branches for charcoal production rather than tree trunks. Based on an analysis of selected charcoal samples, we confirm that radiocarbon dating provided a very wide range of dates in the post-1650 CE period and the use of the wiggle-matching method was usually challenging because of short TRW series. Based on samples with preserved waney edges, we conclude that charcoal was more commonly made from wood felled in the summer than in the winter. Despite the relatively low level of success of dendrochronological dating, it seems more effective for dating charcoal than the ¹⁴C method, especially with samples from the last 350 years.     

Radiometric dating for recent lake sediments on the Tibetan Plateau

We present radiometric data from nine lakes across the Tibetan Plateau, and compare their reliability in relation to recent research. Unsupported ²¹⁰Pb profiles show, except for one particular lake, non-exponential decline of ²¹⁰Pb activity with sediment depth. Stratigraphic dates based on global atmospheric nuclear weapons maximum fallout of ¹³⁷Cs (1963) support the use of the constant rate of ²¹⁰Pb supply (CRS) model in four of the dated cores. The discrepancy in the others is likely due to recent increased input of catchment-derived ²¹⁰Pb. ²¹⁰Pb dates in this study suggest that post depositional diffusion of ¹³⁷Cs activity has been significant. The practice of assigning early 1950s dates (start of global atmospheric thermonuclear testing) to lake sediment sequences on the Tibetan Plateau should be used with caution. ¹³⁷Cs profiles from Tibetan lake sediment cores and their geographical distribution suggest that ¹³⁷Cs derived from the 1986 Chernobyl accident or atmospheric testing in China was not sufficient to form a significant peak effective for dating.     

甘肃省徐家城旧石器遗址的年代

庄浪县徐家城遗址是甘肃省新发现的含丰富旧石器文化遗物的遗址,主要埋藏于水洛河第二级阶地上覆的马兰黄土中。AMS14C测年及气候事件对比相结合的综合年代研究显示, 遗址主要文化层时代集中在距今4.6~2.3万年间, 属于晚更新世晚期。遗址所在的陇西盆地发现近50处晚更新世旧石器遗址, 测年、黄土地层学等的综合年代学研究利于建立该地区晚更新世完整的年代学框架, 为我们进一步讨论晚更新世人类行为演化、人类行为与环境变化的互动等重要学术问题提供了基础。     

Degradation of softwood [14C lignin] lignocelluloses and its relation to the formation of humic substances in river and pond environments

The fate of lignin in water and sediment of the Garonne river (France) and of a pond in its floodplain was examined using specifically labeled [¹⁴C-lignin] lignocelluloses. No significant differences appeared in the mineralization rate of alder, poplar or willow [¹⁴C-lignin] in running water samples. Conversion of total radioactivity to ¹⁴CO₂ ranged between 18.7% and 24.4% after 120 days of incubation. Degree of ¹⁴C-labeled lignin mineralization in standing water and sediments was clearly lower, especially in submerged sediments, and was correlated with oxygen supply. After 60 days of incubation 3.3% to 7.9% of the ¹⁴C-labeled lignin was recovered in water samples as dissolved organic carbon originating from microbial metabolism. In water extracts from sediment the percentage of dissolved organic ¹⁴C was only 0.4% to 1.3% of the applied activity. In the humic fraction extracted from sediments it did not exceed 4.4% which was much lower than in soils. No significant difference appeared between river and pond conditions for humic substances formation.     

Fréquence des datations Au 14C de faunes marines post-glaciaires de l'est du Canada et variations paléoclimatiques

A statistical analysis of radiocarbon dates for 365 samples associated with postglacial marine deposits of Eastern Canada and New England, U.S.A., yield a non-random statistical distribution. This distribution pattern is explained by two principal controls (that are partly interdependent): (1) secondary eustatic fluctuations, creating relative stabilizations of the sea level with an uplifting land; and (2) more generally the climatic variations. Other factors involved may include: (1) limitations of ¹⁴C dating method; (2) non-statistical sampling methodology adopted by the Quaternary geologists; (3) lack of intensive study of some of the marine basins; and (4) incidence of rapidly changing paleogeographic events (opening and shoaling of marine basins, glacial re-advances and changes in the ice flow). The statistical appraisal of errors in published ¹⁴C dates and the standard deviation, calculated with sliding means, enable us to screen out the influence of most of the non-climatic factors. With this technique, we are also able to draw a curve based on a general synthesis of all variations in ¹⁴C dates distribution. In this way, the irregularities observed in the synthesis curve are now correlated with paleoclimatic and paleogeographic events that took place in Eastern Canada between 15,000 years B.P. to present. That curve shows a close correlation during the Holocene with other climatic indicators and gives some original informations concerning the period 15,000–10,000 B.P. No attempt has been made to adjust radiocarbon years to calendar years for two reasons: (1) lack of agreement between comparative curves prior to 7,000 B.P.; and (2) lack of information concerning the effect of “old waters” on shell dates.     

Microbial Transformation of Polycyclic Aromatic Hydrocarbons in Pristine and Petroleum-Contaminated Sediments

To determine rates of microbial transformation of polycyclic aromatic hydrocarbons (PAH) in freshwater sediments, ¹⁴C-labeled PAH were incubated with samples from both pristine and petroleum-contaminated streams. Evolved ¹⁴CO₂ was trapped in KOH, unaltered PAH and polar metabolic intermediate fractions were quantitated after sediment extraction and column chromatography, and bound cellular ¹⁴C was measured in sediment residues. Large fractions of ¹⁴C were incorporated into microbial cellular material; therefore, measurement of rates of ¹⁴CO₂ evolution alone would seriously underestimate transformation rates of [¹⁴C]naphthalene and [¹⁴C]anthracene. PAH compound turnover times in petroleum-contaminated sediment increased from 7.1 h for naphthalene to 400 h for anthracene, 10,000 h for benz(a)anthracene, and more than 30,000 h for benz(a)pyrene. Turnover times in uncontaminated stream sediment were 10 to 400 times greater than in contaminated samples, while absolute rates of PAH transformation (micrograms of PAH per gram of sediment per hour) were 3,000 to 125,000 times greater in contaminated sediment. The data indicate that four- and five-ring PAH compounds, several of which are carcinogenic, may persist even in sediments that have received chronic PAH inputs and that support microbial populations capable of transforming two- and three-ring PAH compounds.     

The use of hair as an indicator of occupational 14C contamination

This paper presents a study in which the specific activity of ¹⁴C in hair has been investigated as an easily determined bio-indicator of the integrated ¹⁴C exposure (over several months). The study includes 28 Swedish workers handling ¹⁴C-labelled compounds, or working in a ¹⁴C-enriched environment. Hair samples from personnel at a Swedish nuclear power plant showed very low levels of ¹⁴C contamination, if any. In contrast, personnel at the investigated research departments showed ¹⁴C levels in hair of up to 60% above the natural specific activity of ¹⁴C. Much higher levels, up to 80 times the natural specific activity of ¹⁴C, were found in hair from individuals working at a pharmaceutical research laboratory. This contamination was, however, not solely an internal contamination. There were indications that most of the ¹⁴C in the hair originated from airborne ¹⁴C-compounds, which were adsorbed onto the hair. The difficulties in removing this external ¹⁴C contamination prior to analysis are discussed, as are the possibilities of using accelerator mass spectrometry to analyse various types of samples for retrospective dose assessment.     

Desert grassland dynamics estimated from carbon isotopes in grass phytoliths and soil organic matter

Abstract. We document the potential for using carbon isotopes in both soil organic matter (SOM) and grass phytoliths in soil to increase the temporal and taxonomic resolutions of long term vegetation dynamics. Carbon isotope values from both SOM and phytoliths are expected to describe both the age of material through ¹⁴C dating, and the photosynthetic pathway of the source plant material through ratios of ¹²C/¹³C. Taxonomic resolution is increased because the phytoliths examined are specific to grasses, whereas the SOM reflects the contribution of all the vegetation. Temporal resolution is increased because phytoliths are less mobile in the soil profile than SOM, and can therefore provide older dates from the same soil depth. Our results, from a desert grassland site in southwestern North America, largely confirm these expectations, and show that C₄ species have dominated the grass composition for the last 8000 yr, C₃ non‐grass vegetation increased about 100–350 yrBP, and no significant C₃ grass or non‐grass vegetation existed between 350–2000 yr BP.     

Calcium cycling and trophic relationships of arthropods in a 45Ca-Tagged cornfield

Summary The objectives of this study were to investigate (1) feeding relationships of arthropods on corn (Zea mays L.) and (2) cycling of calcium in a corn field.In May, 1966, a 0.6 hectare field on the Savannah River Plant, Aiken, South Carolina, was planted with ⁴⁵Ca tagged corn seeds. Corn plants and weeds were periodically sampled at random. Arthropods from corn were sampled from randomly selected circular quadrats (0.25 m²) centered on corn hills, using a portable suction insect sampler. Ashed samples were counted on a Tracerlab thin window gas flow detector equipped with sample changer. ⁴⁵Ca per corn plant decreased four-fold from June 2 to July 6. Leaching and the loss of the older (and more radioactive) leaves during growth were probably the sources of the calcium loss. Presence of ⁴⁵Ca in the soil, and an increasing standing crop of ⁴⁵Ca in the weeds from June through August, and in the corn during July and August, indicate that isotope lost to the soil by leaching was taken up again by the vegetation in the field. Distribution of ⁴⁵Ca within the corn plants was uneven, being much greater in old than in young leaves, and in leaves than in stems.Activity densities (amounts of isotope/gram of biomass) of the arthropods, because of the changing activity densities of the corn, could not by themselves show when they had attained equilibrium with the ⁴⁵Ca in the food plant. Therefore, the ratio of animal activity density/corn activity density was used in determining uptake curves, which showed the attainment of equilibrium when the ratio approached a constant value.The ratio of ⁴⁵Ca per gram of insect/⁴⁵Ca per gram of corn may illustrate differences in feeding behavior in three ways: (1) in the time (the inflection point) at which the uptake curve reaches equilibrium, (2) the level at which the ratio reaches equilibrium (the mean activity density ratio), and (3) the variability between sampling dates in the ratio after it reaches equilibrium.The date of inflection, though two weeks earlier in herbivores than in insect predators, occurred one month earlier in the pooled spiders, indicating that they became part of food chains beginning with corn much sooner than the other arthropods. Spiders, being predaceous, probably had fed on microarthropods not obtained in the samples.Mean activity density ratios (weighted average of activity density ratios beginning with the inflection date) were less than one (0.2 to 0.5) in most groups of arthropods, probably because of feeding on material with a lower activity density than the entier corn plant, or because of smaller calcium concentrations in the arthropods than in the plants.Variability of activity density ratios between sampling dates seemed correlated with the variability in activity densities of the food eaten. Thus the ratios for plant sap feeders were relatively constant, while the feeders on leaves (which had highly variable activity densities), had highly variable ratios.An estimated 0.5 per cent of the ⁴⁵Ca in the field was cycled by the arthropods during the entire study.From a thesis submitted to the University of Georgia in partial fulfillment of the Ph. D. degree