432 research outputs found

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

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    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.

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

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    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