At 2 locations of the southern Spanish coast, we found indications for tsunamis induced by submarine earthquakes. Charcoal, which we sampled in 2 stratified, assumed tsunamigenic sediment (tsunamites) layers at the shore outside the ruins of the Roman city of Baelo Claudia, close to the Strait of Gibraltar (province of Cádiz), and radiocarbon dated, surprisingly turned out to be of identical age, about 465 BP. In the laguna of the Cabo de Gata (province of Almería), we found possible remnants of tsunamites in drilling cores deposited above organic sediments, 14C dated as 680 ± 30 BP.

High-precision radiocarbon age calibration for different terrestrial samples allows us to establish accurate boundaries for many climatic time series. At the same time, the fluctuations of 14C content reflect solar variability. A bispectrum analysis of long-term series of the 14C content deduced from decadal measurements in tree rings demonstrates the existence of amplitude modulation, with a period of main modulation of ∼2400 yr. In 14C time series for the last 11 kyr, major oscillations are distinguished at 8.5–7.8, 5.4–4.7, 2.6–2.2, and 1.1–0.4 cal kyr BP with ∼2400-yr periodicity. High amplitudes in cosmogenic isotope content with a periodicity of about 2400 yr appear synchronous to cooling events documented in Greenland ice cores, to the timing of worldwide Holocene glacier expansion, and to the periods of lake-level changes. This paper focuses on revealing solar forcing on the Earth's climate and about the nature, significance, and impact of sharp Holocene climate variability on human societies and civilizations.

High-resolution radiocarbon calibration for the last 14,000 cal yr has been developed in large part using European oaks and pines. Recent subfossil wood collections from the Great Lakes region provide an opportunity to measure 14C activity in decadal series of rings in North America prior to the White Mountains bristlecone record. We developed decadal 14C series from wood at the classic Two Creeks site (∼11,850 BP) in east-central Wisconsin, the Liverpool East site (∼10,250 BP) in northwestern Indiana, and the Gribben Basin site (∼10,000 BP) in the Upper Peninsula of Michigan. Initial AMS dates on holocellulose produced younger-than-expected ages for most Two Creeks subsamples and for a few samples from the other sites, prompting a systematic comparison of chemical pretreatment using 2 samples from each site, and employing holocellulose, AAA-treated holocellulose, alpha-cellulose, and AAA-treated whole wood. The testing could not definitively reveal the source of error in the original analyses, but the “best” original ages together with new AAA-treated holocellulose and α-cellulose ages were visually fitted to the IntCal04 calibration curve at ages of 13,760–13,530 cal BP for the Two Creeks wood, 12,100–12,020 cal BP for Liverpool East, and 11,300–11,170 cal BP for Gribben Basin. The Liverpool East age falls squarely within the Younger Dryas (YD) period, whereas the Gribben Basin age appears to postdate the YD by ∼300 yr, although high scatter in the decadal Gribben Basin results could accommodate an older age nearer the end of the YD.

We have carried out a multiproxy analysis of high-resolution eutrophic peat/mud, sand dune, and loess/paleosol sequences covering the Holocene period in both southern and northern China, in order to test the hypothesis of a time-transgressive Holocene optimum in the East Asian monsoon area (An et al. 2000). Samples were radiocarbon dated to establish the chronology. Our results indicate that the Holocene optimum occurred between ∼10,000–5000 cal yr ago in both southern and northern China, consistent with a global pattern rather than simply a local expression. Our data also support the conclusion that the evolution of Holocene climate in China is consistent with changes in Northern Hemisphere solar radiation.

Marine upwelling along coastal Peru can be intense and variable, making radiocarbon dating marine and coastal systems complex. Historical and proxy records of upwelling along coastal Peru are few, and long-lived species such as corals do not grow in the cold coastal waters. Mollusk shell carbonate, however, can record both the magnitude of the local marine reservoir correction, ΔR, and of seasonal oscillations in the ventilation age of coastal waters. If large, these seasonal oscillations would complicate radiocarbon dating of marine organisms. To examine this possibility, we sampled for δ13C, δ18O, and 14C content a set of pre-bomb Argopecten purpuratus shells collected from coastal Peru during 1908 and 1926. Intrashell variations of up to 216 14C yr were noted, but these were not consistently correlated with seasonal changes in δ18O or δ13C. Only an 11 yr difference was observed in the weighted average ΔR of Callao Bay shells collected during normal (1908) and El Niño (1926) years. Despite the intrashell 14C variation noted, weighted average ΔR values from all 3 sample sites and from normal and El Niño years all overlap at 1 σ. We report ΔR values of 183 ± 18 and 194 ± 23 yr from Callao Bay (12°4′S), 165 ± 24 yr from Salaverry (8°14′S), and 189 ± 23 yr from Sechura Bay (5°45′S).

Oxbow lake deposits of the Neris River at the Valakupiai site in Vilnius (Lithuania) have been studied by different methods including radiocarbon dating. A timescale was attained for the development of the oxbow lake and climatic events recorded in the sediments. 14C dates obtained for 24 samples cover the range 990–6500 BP (AD 580 to 5600 BC). Medieval human activity was found in the upper part of the sediments. Mollusk fauna found in the basal part of the terrace indicate contact between people living in the Baltic and the Black Sea basins. Mean rates were calculated for erosion of the river and for accumulation during the formation of the first terrace.

ΔR values have been calculated based on offsets in radiocarbon values exhibited in a series of stratigraphically paired charcoal and marine shell values, ranging from about 300 to 10,000 BP, excavated from archaeological sites on Cedros Island, Baja California, Mexico. Based on this data, there appears to be the equivalent of about an 800-yr range in inferred ΔR values (-400 to 400 yr) exhibited in Holocene-age marine shells from this portion of the central Baja California coast.

A surface-water Δ14C record of AD 1948–1999 in the tropical South China Sea (SCS) has been reconstructed from accelerator mass spectrometric radiocarbon measurements of annual bands of a Pontes coral collected from Con Dao Island, Vietnam. Results gave the following Δ14C time series: a steady state of −47.8 ± 2.8‰ (mean ± SD, n = 8) during 1948–1955 (i.e. in the pre-bomb period); a sharp increase during 1956–1966; a gradual increase during 1967–1973; a relatively high maximum value of ∼174‰ in 1973; and a gradual decrease for the following period to ∼86‰ in 1999. This Δ14C record having a sharp increase and a relatively high peak is similar to the records of subtropical corals (latitudes 21–27°) and is distinctly different from the records of equatorial/tropical corals (latitudes <10°), although our coral sample was collected from an equatorial/tropical region (8°39′N, 106°33′E). This can be explained by the geographic, oceanographic, and climatic setting of our study site. The SCS is a semi-enclosed marginal sea in the far western tropical Pacific and is little influenced by equatorial upwelling or related ocean currents. Our study site is located in the southwestern SCS, where an enormous submerged plain (the Sunda Shelf) spreads out with very shallow waters (mean depth <100 m). Furthermore, in the SCS, the East Asian monsoon (a strong, seasonally reversing wind system) enhances air-sea gas exchange especially in the mainland coastal waters, including our study site. Such semi-enclosed shallow waters with enhanced ventilation were probably very sensitive to the atmospheric nuclear explosions in the late 1950s and early 1960s and caused the sharp increase and high peak in the coral Δ14C record. Our coral Δ14C values in the southwestern SCS are significantly higher than the values in the northwestern SCS (Xisha Islands), which seems to suggest that meridional mixing of surface waters is not active in the SCS and that the open-ocean water intruding into the northern SCS (i.e. the Kuroshio intrusion) has only a limited influence on the southern SCS.

Radiocarbon concentrations in the northernmost region of the Japan Sea were observed during the summer of 2002. The averaged surface δ14C (above 100 m depth) was 52 ± 8%, which is significantly higher compared with the values of the Pacific Ocean and Okhotsk Sea. The δ14C in the deep water decreased with density, and the minimum value was −70%. By analyzing 14C and other hydrographic data, we found that i) the Tsushima Warm Current Water reaches to the surface layer in the southern Tatarskiy Strait; ii) deep convection did not occur in the northernmost region, at least not after the winter of 2001–2002; and iii) the bottom water that was previously formed in this region may step down southward along the bottom slope and mix with the Japan Sea Bottom Water. Furthermore, a new water mass characterized by high salinity (>34.09 psu) was found in the subsurface layer in the area north of 46°N.

Differences in the radiocarbon ages of closely associated marine mollusk shells and terrestrial material (charred wood or bones) from several Galician archaeological contexts are significant from the Iron Age to Medieval times. δR values show high variability, ranging from −280 ± 70 to 270 ± 40 14C yr. The set of δR values also presents a strong positive peak (δR = 270 ± 40 14C yr) at 860 ± 90 BP, which matches another peak found for western Portuguese coastal waters. The data obtained, namely the negative or close to zero δR values, suggest that the reduced offset between atmospheric and surface water 14C content is due to the existence of a strong stratification of the water column and environmental factors in the Galician rías during the Iron Age and the Medieval period.

A basin-scale repeat hydrography of the WOCE-P06 line along approximately 32°S has revealed decadal changes of bomb-produced radiocarbon in the subtropical South Pacific Ocean between 1992 and 2003. Surface δ14C decreased by about 30%. A δ14C decrease was also found in the upper thermocline from the surface to 400 m water depth. In the lower thermocline, from 400 m to 1100 m depth, however, δ14C increased, with a maximum increase of 25% at 700 m depth. This contrast between the upper and lower thermoclines resulted in an overall 10% increase of the specific column inventory of bomb 14C from 1992 to 2003. The global ocean inventory of bomb 14C was assessed based on the specific inventory increase in the subtropical South Pacific Ocean. The meridional distribution of bomb 14C in the early 1990s suggests that the bomb 14C increases observed along 32°S in 2003 were primarily caused by mixing along isopycnals.

This paper examines 2 potential sources of the radiocarbon offset between human and terrestrial mammal (horse) bones recovered from Norse (∼AD 870–1000) pagan graves in Mývatnssveit, north Iceland. These are the marine and freshwater 14C reservoir effects that may be incorporated into human bones from dietary sources. The size of the marine 14C reservoir effect (MRE) during the Norse period was investigated by measurement of multiple paired samples (terrestrial mammal and marine mollusk shell) at 2 archaeological sites in Mývatnssveit and 1 site on the north Icelandic coast. These produced 3 new δR values for the north coast of Iceland, indicating a δR of 106 ± 10 14C yr at AD 868–985, and of 144 ± 28 14C yr at AD 1280–1400. These values are statistically comparable and give an overall weighted mean δR of 111 ± 10 14C yr.

The freshwater reservoir effect was similarly quantified using freshwater fish bones from a site in Mývatnssveit. These show an offset of between 1285 and 1830 14C yr, where the fish are depleted in 14C relative to the terrestrial mammals. This is attributed to the input of geothermally derived CO2 into the groundwater and subsequently into Lake Mývatn. We conclude the following: i) some of the Norse inhabitants of Mývatnssveit incorporated non-terrestrial resources into their diet that may be identified from the stable isotope composition of their bone collagen; ii) the MRE off the north Icelandic coast during the Norse period fits a spatial gradient of wider North Atlantic MRE values with increasing values to the northwest; and iii) it is important to consider the effect that geothermal activity could have on the 14C activity of samples influenced by groundwater at Icelandic archaeological sites.

We measured radiocarbon ages of planktic foraminifera in 4 sediment cores from the northwestern Pacific region off northern Japan in order to estimate marine reservoir ages during the B⊘lling-Aller⊘d period. The ages of deglacial tephra markers from 2 Japanese source volcanoes identified in these sediment cores had been previously estimated from 14C ages of terrestrial charcoal and buried forests. By comparing the foraminiferal and tephra ages, we estimated the surface water reservoir age during the B⊘lling-Aller⊘d period to be ∼1000 yr or more in the region off northern Japan. The deglacial reservoir ages were more than 200 yr higher than the Holocene values of ∼800 yr. The older deglacial ages may have been caused by active upwelling of deep water during the last deglaciation and the consequent mixing of “older” deep water with “younger” surface waters.

Carbon isotopic and chemical compositions of freshwaters feeding the Dead Sea and the Sea of Galilee (i.e. perennial streams and floods along their stream profiles) were used to constrain the factors that dictate the reservoir ages (RA) of these lakes and the last glacial Lake Lisan. Runoff waters are characterized by high Ca2+, Mg2+, alkalinity, and radiocarbon contents (67–108 pMC), suggesting a major role for 14C atmospheric exchange reactions (carbonate rock dissolution alone will result in lower pMC values). These exchange processes were corroborated by dissolved inorganic carbon (DIC) and δ13C trends throughout the flood profile. During the evolution from rain to incipient runoff, the 14CDIC of the water increases and is accompanied by a DIC increase and δ13CDIC decrease, suggesting an addition of soil CO2, which is characterized by light δ13C and high 14C content. When incipient runoffs evolve to floods, the opposite trends are observed.

It appears that the Sea of Galilee, the Dead Sea, and its last glacial precursor, Lake Lisan, maintained uniform but specific RAs of 0.8 ± 0.1, 2.3 ± 0.1, and 1.6 ± 0.3 kyr, respectively. However, applying the 14C contents of modern Dead Sea water sources to the water mass balance of Lake Lisan reveals that the RA of Lake Lisan is higher than that predicted by the mass balance. This discrepancy may reflect enhanced dissolution of carbonatic dust, changes in the amount of 14C exchanged in Judean Desert floods, or variations in the contribution of brine and saline springs. Furthermore, the small fluctuations in the Lisan RA (1.6 ± 0.3 kyr) may reflect small, short-term changes in the relative contributions of these sources.

In the absence of identifiable macrofossils in lacustrine sediments, radiocarbon dating must rely on pollen or bulk sediment fractions. Bulk sediment fractions are not generally preferred because they contain an unknown mixture of organic material of variable age, they may contain dead carbon such as lignite that is difficult to eliminate, and material of aquatic origin may be subject to reservoir effects. If the various processes that contribute carbon to the system are relatively constant over time, however, changes in 14C activity with depth may be used to accurately estimate sediment accumulation rates even if the absolute ages are erroneous. In this study, fine-grained fractions (250–710 μm organic material, humic acids extracted from <250-μm fraction, and untreated <250-μm fraction combusted at low temperature) were analyzed and compared with terrestrial plant stems (twigs), charcoal, and wood fragments in sediments from an oxbow lake in Mississippi, USA. The 14C activities of the bulk fractions were highly linear with depth and produced consistent calculated sediment accumulation rates similar to, and perhaps more reliable than, rates determined using twigs or charcoal.

Rivers and streams in many parts of the world contain high concentrations of dissolved carbon dioxide, which is lost to the atmosphere by evasion (outgassing). Recent methodological advances now enable the carbon isotopic composition of this evaded CO2 to be measured directly, with early results from peatland streams showing it to be depleted in 13C relative to the atmosphere. The first direct measurements of the radiocarbon age of evaded CO2 for a stream draining a peatland site in the United Kingdom covered a large range, ranging from modern to >1400 yr BP. We investigated whether a proportion of the carbon fixed by plants growing adjacent to the stream was derived from evasion; this would have implications for the cycling of carbon in such streams, and lead to riparian plants having older, rather than contemporary, 14C ages.

13C analysis of riparian plants at the site suggested that up to 20% of the carbon they fixed was derived from evasion. Although the 14C content of the same samples suggested a similar proportion of plant carbon was derived from evaded CO2, the uncertainty in these estimates was greater. Fixation of evaded CO2 was greatest in plants growing within 1 m of the stream. Although the results for this site suggest a small amount of CO2 lost by evasion from the stream surface is incorporated in plant material, it may be a more important factor at other sites characterized by higher evasion rates, lower wind speeds, and different stream bank morphology.

We investigated the feasibility of using Melanopsis shells as radiocarbon chronometers of paleolakes and springs in the Jordan Valley, Israel. For this purpose, we analyzed the 14C content of aragonite of living Melanopsis shells from different freshwater bodies of the northern Jordan Valley and Lake Kinneret (Sea of Galilee) and compared them to the contemporaneous water values. The Melanopsis shells are in 14C equilibrium with their habitat waters, allowing to specify a particular reservoir age for various water types. We measured ∼750 yr for Lake Kinneret, ∼2300 yr for northern Jordan, ∼4600 yr for springs in the north Kinneret, and ∼7200 yr for streams flowing directly from carbonate aquifers. These results were tested and corroborated by analyzing fossil Melanopsis shells of known age, measured on contemporaneous organic matter. We conclude that Melanopsis shells are reliable 14C chronometers and have the potential to be used as paleohydrological tracers.

Lacustrine carbonate deposition in Hungary has been traditionally interpreted as the outcome of the dry, hot climate prevailing between 7500 and 5000 14C yr BP (hereafter BP) (∼6400 and 3800 BC), triggering the partial desiccation of minor ponds and lakes. A comparative analysis of 5 14C results from the site of Csólyospálos, central Hungary, with those of other Hungarian lacustrine carbonates yielded stunning new results. According to these new dates, carbonate deposition must have initiated much earlier, possibly around 10,000–11,000 BP (9500–11,000 BC) in the Carpathian Basin. Furthermore, the formation of lacustrine carbonates must have come to an end at very different times in different parts of the basin, contrasting previous views on the uniform and synchronous cessation of lacustrine carbonate formation in Hungary. According to the newest results presented here, carbonate deposition in the southern and southeastern parts of the basin ceased around 6000 BP (∼4900 BC). Meanwhile, in the central parts, deposition continued as long as the terminal Bronze Age (∼1300 BC).

Approximately 10% of Hungary is covered by dust sequences of the Quaternary period. Samples have been taken from more than 50 outcrops and boreholes during fieldwork in the past 20 yr. Some 81 bulk samples taken from 27 profiles of the Hungarian loess regions have been analyzed for radiocarbon. Based on the 14C results, loess layers that accumulated between 33,000 and 12,000 BP were selected for further investigation. The sedimentation rates of the 27 loess profiles suggest periods of slow and quick dust accumulation in the Carpathian Basin during the Upper Weichselian period. It seems to us that some soil development and intense weathering periods interrupted the loess development during the Upper Weichselian in Hungary. According to the 14C dates, the estimated average rate of sedimentation was 0.31 mm/yr in both the northern and southern parts of the Carpathian Basin between 33,000 and 12,000 BP.

The activity of radiocarbon in 14CO2 and 14CnHm chemical forms is measured in the vicinity of Paks nuclear power plant (NPP), Hungary, by sampling environmental air. Four differential sampling units at different sites collected samples less than 2 km away from the 100-m-high stacks of Paks NPP, and for reference a sampler was operated at a station ∼30 km away from Paks NPP. We present the results of continuous observations at the 5 stations covering the time span from 2000 to 2005. The samples have been analyzed by a proportional counting technique. During a cleaning tank incident at unit 2 of Paks NPP in April 2003, a significant release of radioactive isotopes took place from the damaged fuel assemblies, and gaseous products escaped through the chimney. We evaluate the possible short- and long-term impact of this incident on the 14C content of the atmosphere in the surroundings of Paks NPP. Comparing our 14CO2 measurements with data sets from Jungfraujoch and Schauinsland, as well as from Košetice (Czech Republic), we demonstrate that the incident had no definite influence on the 14C content of the atmosphere.