Major Δ14C excursions during the late glacial and early Holocene: changes in ocean ventilation or solar forcing of climate change?

The atmospheric 14C record during the Late Glacial and the early Holocene shows sharp increases simultaneous with cold climatic phases. These increases in the atmospheric 14C content are usually explained as the effect of reduced oceanic CO2 ventilation after episodic outbursts of large meltwater reservoirs into the North Atlantic. In this hypothesis the stagnation of the thermohaline circulation is the cause of both climate change as well as an increase in atmospheric 14C: As an alternative hypothesis we propose that changes in 14C production give an indication for the cause of the recorded climate shifts: changes in solar activity cause fluctuations in the solar wind, which modulate the cosmic ray intensity and related 14C production. Two possible mechanisms amplifying the changes in solar activity may result in climate change. In the case of a temporary decline in solar activity: (1) reduced solar UV intensity may cause a decline of stratospheric ozone production and cooling as a result of less absorption of sunlight. This might influence atmospheric circulation patterns (extension of Polar Cells and equatorward relocation of mid-latitude storm tracks), with effects on oceanic circulation, and (2) increased cosmic ray intensity may stimulate cloud formation and precipitation, while 14C production increases.

Radiocarbon Calibration for Japanese Wood Samples

The radiocarbon content of Japanese cedars was measured by accelerator mass spectrometry for decadal tree-ring samples from the period of 240 BC to AD 900. Conventional gas counting was also used for part of the samples. The data were compared with the INTCAL98 calibration curve. The results indicate that the difference in atmospheric 14C between Japan and North America or Europe is negligible at this period, less than 18 14C yr using an average of 50 yr. However, in the period of about AD 100 to about AD 200, we cannot exclude the possibility of a deviation of the order of 30 to 40 14C yr to the older ages.

A numerical approach to 14C wiggle-match dating of organic deposits: best fits and confidence intervals

14C wiggle-match dating (WMD) of peat deposits uses the non-linear relationship between 14C age and calendar age to match the shape of a sequence of closely spaced peat 14C dates with the 14C calibration curve. A numerical approach to WMD enables the quantitative assessment of various possible wiggle-match solutions and of calendar year confidence intervals for sequences of 14C dates. We assess the assumptions, advantages, and limitations of the method. Several case-studies show that WMD results in more precise chronologies than when individual 14C dates are calibrated. WMD is most successful during periods with major excursions in the 14C calibration curve (e.g., in one case WMD could narrow down confidence intervals from 230 to 36 yr).

Mesolithic Human Bones from the Upper Volga Basin: Radiocarbon and Trace Elements

Human bones from 3 Mesolithic sites in the Upper Volga basin were analyzed for trace elements, and dated by accelerator mass spectrometry (AMS). The radiocarbon dates of the bones correspond to the Mesolithic era. However, some dates differ from those obtained for the enclosing deposits and for the worked wood fragments in the cultural layer. The elemental composition of the bones is interpreted in terms of increased concentrations of some elements and their impact on human health and behavior.

Study of the 14C-contamination potential of C-impurities in CuO and Fe

The carbon concentration in CuO and iron was determined by isolating C. The values were in agreement with results reported in other studies. Contaminating carbon from CuO and Fe was transformed to AMS targets and measured for C-14. C-traces in CuO were shown to be the major contribution to the C-14 Sample processing blank. In addition, there is a significant variability in the C-14 content of CuO observed between different production batches. The combined contamination potential of CuO and Fe was found to be 4.47-8.92 mu g recent carbon, whereas the more realistic estimate for AMS-target preparation conditions ranged between 1.63 and 3.24 mu g recent carbon, depending on the C-14 level in CuO

Eine Interviewstudie zum Lesen von Diagrammen

Diagramme sind nicht nur in öffentlichen Medien ein gängiges Darstellungsmittel, sondern auch in den Lehrmaterialien vieler Unterrichtsfächer. Damit kommt dem sachgerechten Lesen von Diagrammen eine wichtige Rolle im Fachunterricht zu: struktur- und kontextspezifische Informationen müssen ausgelesen, eingebracht und zusammengedacht werden

Ingenieurinnen und Informatikerinnen: schöne neue Arbeitswelt?

In dem Kurzbericht wird auf der Basis amtlicher Statistiken sowie neuerer Untersuchungen ein Überblick über Erwerbstätigkeit, Arbeitsbedingungen und Arbeitslosigkeit von Informatikerinnen sowie von Ingenieurinnen vor allem der Fachrichtungen Maschinenbau, Elektrotechnik und Architektur/Bauingenieurwesen gegeben. "Vergleicht man die berufliche Situation von Ingenieurinnen und Informatikerinnen mit der aller Hochschulabsolventinnen, so ergibt sich ein differenziertes Bild: von Vorteilen (unbefristete Beschäftigung) über Gleichstand (Stellung in der betrieblichen Hierarchie) bis hin zu Nachteilen (Arbeitslosigkeit). Stellt man dagegen den Vergleich zwischen den Geschlechtern in den Vordergrund, müssen immer noch zum Teil ausgeprägte Benachteiligungen der Ingenieurinnen und Informatikerinnen gegenüber Ingenieuren und Informatikern festgestellt werden." Will man mehr Frauen für geschlechtsuntypische Studienfächer gewinnen, müssen auch deren Arbeitsmarktchancen und Beschäftigungsbedingungen verbessert werden

Stable carbon and radiocarbon isotope compositions of particle size fractions to determine origins of sedimentary organic matter in an estuary

Stable and radioactive carbon isotopic compositions of particle size fractions of a surface sediment from the Ems-Dollard estuary vary considerably with particle size. The organic material in the fine fractions (<20 µm) has considerably higher 14C values (14a~80%) than that in the coarse fractions (52%) and has higher δ13C values (average of -23‰ and -25.6‰, respectively). This shows that OM in the fine and the coarse fractions has different sources. The organic carbon in the fractions with particle sizes <20 µm is mainly imported from the North Sea. The contribution of material from the Ems river appears negligible. The carbon isotopic composition of the coarse fractions points to a terrestrial contribution. Discrete organic fragments are found of both terrestrial and marine/estuarine origin.