For radiocarbon calibration, the arrow of time is pointing backwards but the entropy does not necessarily decrease in this direction…

The Swedish varve chronology, or Swedish Time Scale, is an annual chronology based upon the successive correlation of more than 1000 varve-thickness diagrams. The Late Glacial-Early Holocene varved clays were deposited as glaciolacustrine sediments in the Baltic Sea during the recession of the Scandinavian ice sheet. Formation of varved clays continued throughout the Holocene and is still going on in the estuary of River ångermanälven in northern Sweden. Accelerator mass spectrometry (AMS) radiocarbon measurements, which have been performed on terrestrial plant macrofossils extracted from the varved clays, show—in comparison with other annual chronologies—that several hundreds of varve years are missing in the varve chronology. These findings are supported by, among others, pollen stratigraphic investigations on time-equivalent varve year intervals. If an effort were undertaken to evaluate the erroneous parts, the Swedish Time Scale would have the potential of becoming a continuous annual chronology.

This paper presents radiocarbon dates of terrestrial macrofossils from Lakes Gościąż and Perespilno, Poland. These data agree very well with most of the German pine calibration curve. In the Late Glacial, they generally agree with the data from Lake Suigetsu, Japan, and indicate constant or even increasing 14C age between 12.9 and 12.7 ka BP, rapid decline of 14C age around 12.6 ka BP, and a long plateau 10,400 14C BP around 12 ka BP. Correlation with corals and data from the Cariaco basin seems to support the concept of site-speficic, constant values of reservoir correction, in contradiction to those introduced in the INTCAL98 calibration. Around the Allerød/Younger Dryas boundary our data strongly disagree with those from the Cariaco basin, which reflects large discrepancy between calendar chronologies at that period. The older sequence from Lake Perespilno indicates two periods of rapid decline in 14C age, around 14.2 and 13.9 ka BP.

During the last decade, several radiocarbon-dated varve chronologies have been produced. The main goal at first was the extension of the 14C calibration curve beyond 10,000 BP. This paper aims to discuss varve chronologies of Soppensee and Holzmaar Lakes. Although both chronologies encountered problems, high-resolution 14C dating and relative varve time have been obtained for events during the Late Glacial.

The Holocene varve chronology of annually laminated sediment sequences from Lake Meerfelder Maar agree for most of the record with dendro-calibrated accelerator mass spectronomy radiocarbon dates from the same site. Only between 9710 and 9950 cal BP does an offset of 240 yr appear between both data sets. At this position, a micro-disturbance in the varve succession has been detected by thin section analyses and was quantified in terms of missing varves. A comparison with the nearby record from Lake Holzmaar, as well providing high resolution AMS 14C and varve chronologies, revealed that such gaps (ca. 2% in time for the entire Holocene) are exceptional for these long-varved maar lake records. Moreover, since sections of missing years appear for both profiles at different stratigraphic positions, a combination of both the Meerfelder Maar and Holzmaar records enables us to bridge erroneous zones in varve chronologies. This confirms the high potential of two long-varved records in close vicinity to each other for the elimination of dating errors and for increasing chronological precision at a time resolution that is normally regarded as within the counting errors. Late Glacial varve and 14C data beyond the dendro-calibration from Meerfelder Maar and their tentative tele-connections to other high resolution data sets reveal unexplained age discrepancies in the calendar year time scale of about 200 years.

This paper presents an updated atmospheric radiocarbon calibration from annually laminated (varved) sediments from Lake Suigetsu (LS), central Japan. As presented earlier, the LS varved sediments can be used to extend the radiocarbon time scale beyond the tree ring calibration range that reaches 11,900 cal BP. We have increased the density of 14C measurements for terrestrial macrofossils from the same core analyzed previously. The combined data set now consists of 333 measurements, and is compared with other calibration data.

Uranium series and radiocarbon ages were measured in corals from the uplifted coral terraces of Huon Peninsula (HP), Papua New Guinea, to provide a calibration for the 14C time scale beyond 30 ka (kilo annum). Improved analytical procedures, and quantitative criteria for sample selection, helped discriminate diagenetically altered samples. The base-line of the calibration curve follows the trend of increasing divergence from calendar ages, as established by previous studies. Superimposed on this trend, four well-defined peaks of excess atmospheric radiocarbon were found ranging in magnitude from 100% to 700%, relative to current levels. They are related to episodes of sea-level rise and reef growth at HP. These peaks appear to be synchronous with Heinrich Events and concentrations of ice-rafted debris found in North Atlantic deep-sea cores. Relative timing of sea-level rise and atmospheric 14C excess imply the following sequence of events: An initial sea-level high is followed by a large increase in atmospheric 14C as the sea-level subsides. Over about 1800 years, the atmospheric radiocarbon drops to below present ambient levels. This cycle bears a close resemblance to ice-calving episodes of Dansgaard-Oeschger and Bond cycles and the slow-down or complete interruption of the North Atlantic thermohaline circulation. The increases in the atmospheric 14C levels are attributed to the cessation of the North Atlantic circulation.

The paper presents a comparison of U-series and radiocarbon dates of speleothems collected in several caves in central and southern Europe and southeast Africa. Despite a large spread of dates, mainly due to contamination with younger carbon, the group of corresponding 14C and 230Th/U ages of speleothem samples seems to be coherent with the previous suggestion of large deviation between the 14C and the absolute time scale between 35 and 45 ka BP. This agrees with the result of frequency analysis of published 14C and 230Th/U ages of speleothem.

The radiocarbon timescale has been calibrated by dendrochronology back to 11.8 ka cal BP, and extended to 14.8 ka cal BP using laminated marine sediments from the Cariaco Basin. Extension to nearly 23.5 ka cal BP is based on comparison between 14C and U-Th ages of corals. Recently, attempts to further extend the calibration curve to >40 kyr are based on laminated sediments from Lake Suigetsu, Japan, foraminifera in North Atlantic sediments, South African cave deposits, tufa from Spain, and stalagmites from the Bahamas. Here we compare these records with a new comparison curve obtained by 234U-230Th ages of aragonite deposited at Lake Lisan (the last Glacial Dead Sea). This comparison reveals broad agreement for the time interval of 20–32 ka cal BP, but the data diverge over other intervals. All records agree that Δ14C values range between ∼250–450‰ at 20–32 ka cal BP. For ages >32 ka cal BP, the Lake Suigetsu data indicate low Δ14C values of less than 200‰ and small shifts. The other records broadly agree that Δ14C values range between ∼250 and 600‰ at 32–39 ka cal BP. At ∼42 ka cal BP, the North Atlantic calibration shows low Δ14C values, while the corals, Lisan aragonites, and the Spanish tufa indicate a large deviations of 700–900‰. This age is slightly younger than recent estimates of the timing of the Laschamp Geomagnetic Event, and are consistent with increased 14C production during this event.

The purpose of this paper is to analyze the numerous holocene subfossil trees (Pinus silvestris) buried in alluvial deposits in the Southern French Alps. These trees lived between the Allerød and Subboreal periods, according to 14C dates. Our dendochronological studies explain the trees' sudden death as due to morphological crisis brought on by climatic oscillations. Tree-ring series could be used to identify the variability of early Holocene atmospheric 14C levels.

By correlating the climate records and radiocarbon ages of the planktonic foraminifera N. pachyderma(s) of deep-sea core PS2644 from the Iceland Sea with the annual-layer chronology of the GISP2 ice core, we obtained 80 marine 14C calibration points for the interval 11.4-53.3 ka cal BP. Between 27 and 54 ka cal BP the continuous record of 14C/cal age differences reveals three intervals of highly increased 14C concentrations coincident with low values of paleomagnetic field intensity, two of which are attributed to the geomagnetic Mono Lake and Laschamp excursions (33.5-34.5 ka cal BP with maximum 550 marine δ14C, and 40.3-41.7 ka cal BP with maximum 1215 marine δ14C, respectively). A third maximum (marine δ14C: 755) is observed around 38 ka cal BP and attributed to the geomagnetic intensity minimum following the Laschamp excursion. During all three events the A14C values increase rapidly with maximum values occurring at the end of the respective geomagnetic intensity minimum. During the Mono Lake Event, however, our A14C values seem to underestimate the atmospheric level, if compared to the 36Cl flux measured in the GRIP ice core (Wagner et al. 2000) and other records. As this excursion coincides with a meltwater event in core PS2644, the underestimation is probably caused by an increased planktonic reservoir age. The same effect also occurs from 38.5 to 40 ka cal BP when the meltwater lid of Heinrich Event 4 affected the planktonic record.