10Be evidence for the Matuyama-Brunhes geomagnetic reversal in the EPICA Dome C ice core.

An ice core drilled at Dome C, Antarctica, is the oldest ice core so far retrieved. On the basis of ice flow modelling and a comparison between the deuterium signal in the ice with climate records from marine sediment cores, the ice at a depth of 3,190 m in the Dome C core is believed to have been deposited around 800,000 years ago, offering a rare opportunity to study climatic and environmental conditions over this time period. However, an independent determination of this age is important because the deuterium profile below a depth of 3,190 m depth does not show the expected correlation with the marine record. Here we present evidence for enhanced 10Be deposition in the ice at 3,160-3,170 m, which we interpret as a result of the low dipole field strength during the Matuyama-Brunhes geomagnetic reversal, which occurred about 780,000 years ago. If correct, this provides a crucial tie point between ice cores, marine cores and a radiometric timescale.

Beryllium-10 mass spectrometry with a cyclotron.

The Grenoble cyclotron has been used as a mass spectrometer to measure ratios of beryllium-10 to beryllium-9 of 10(-8), 10(-9), and 10(-10) in standardized beryllium oxide samples. Similar measurements can be used to determine cosmogenic beryllium-10 (half-life, 1.5 x 10(6) years) profiles in various geophysical reservoirs such as sea sediments and polar ice. This procedure can be used either to date such samples or to give information about geophysical and astrophysical phenomena that have influenced the beryllium-10 production rate in the past.

Gastrointestinal absorption of aluminum in rats using 26Al and accelerator mass spectrometry.

Using the technique of Accelerator Mass Spectrometry (AMS), 26Al has been measured in plasma, liver, urine and bone of normal rats at 8, 24 and 48 hours after ingestion of trace amounts of Al (3.8 ng of 26Al and 63 ng of stable 27Al), both in citrate-free and citrate-containing solutions. Our data show that under physiological conditions, namely at normal levels of dietary intake, intestinal Al absorption is approximately 0.04%, and is not significantly enhanced by the presence of citrate. Interestingly, the amount of Al retained by bone (0.02%) is comparable to that excreted in urine during 48 h (0.02%). Our estimate of gastrointestinal absorption is more than two orders of magnitude smaller than that estimated by Day et al. [1991], also using 26Al, for a single human subject.

129I in the oceans: origins and applications.

The quantity of the long lived (half-life 15.7 million years) radioactive isotope 129I in the pre-nuclear age ocean was approximately 100 kg. Various nuclear related activities, including weapons testing, nuclear fuel reprocessing, Chernobyl and other authorized or non-authorized dumping of radioactive waste have increased the ocean inventory of 129I by more than one order of magnitude. The most important of these sources are the direct marine discharges from the commercial reprocessing facilities at La Hague (France) and Sellafield (UK) which have discharged approximately 1640 kg in the English Channel, and approximately 720 kg in the Irish Sea, respectively. We discuss how this 129I can be used as both a 'pathway' and 'transit time' tracer in the North Atlantic and Arctic oceans, as well as a parameter for distinguishing between reprocessed and non-reprocessed nuclear waste in the ocean, and as a proxy for the transport and dilution of other soluble pollutants input to the North Sea.

129I/127I, 129I/137Cs and 129I/99Tc in the Norwegian coastal current from 1980 to 1998.

Discharges of the nuclides 129I, 137Cs and 99Tc from the nuclear reprocessing facilities at Sellafield (UK) and La Hague (France) are very useful as oceanic tracers. On the basis of 129I/127I, 137Cs and 99Tc measurements in archived seaweeds, the ratios of 129I/127I, 129I/137Cs and 129I/99Tc have been estimated in seawater at two locations (Utsira and Kiberg) in the Norwegian Coastal Current from 1980 to 1998. These ratios, which vary up to two orders of magnitude over this period, are potentially very interesting for determining "transit times" in the Arctic and North Atlantic oceans. While the long-term trends in these ratios are quite clear, measurements in monthly and bimonthly samples show considerable structure. Further studies are required to determine the exact origin of this structure, which may be a limiting factor in the time resolution that can be obtained with these parameters.

Use of 129I and 137Cs in soils for the estimation of 131I deposition in Belarus as a result of the Chernobyl accident.

Using radioactivity measurements for 131I and 137Cs and nuclear activation analysis (NAA) or accelerator mass spectrometry (AMS) for 129I, ratios of 131I/137Cs and 129I/137Cs have been determined in soils from Belarus. We find that the pre-Chernobyl ratio of 129I/137Cs in Belarus is significantly larger than expected from nuclear weapons fallout. For the Chernobyl accident, our results support the hypothesis that there was relatively little fractionation of iodine and caesium during migration and deposition of the radioactive cloud. For sites having 137Cs > 300 Bq/kg, 129I can potentially give more reliable retroactive estimates of Chernobyl 131I deposition. However, our results suggest that 137Cs can also give reasonably good (+/-50%) estimates for 131I in Belarus.

Search for supernova-produced 60Fe in a marine sediment.

An 60Fe peak in a deep-sea FeMn crust has been interpreted as due to the signature left by the ejecta of a supernova explosion close to the solar system 2.8+/-0.4 Myr ago [Knie, Phys. Rev. Lett. 93, 171103 (2004)10.1103/PhysRevLett.93.171103]. In an attempt to confirm this interpretation with better time resolution and obtain a more direct flux estimate, we measured 60Fe concentrations along a dated marine sediment. We find no 60Fe peak at the expected level from 1.7 to 3.2 Myr ago. Possible causes for the discrepancy are discussed.

Orbital and millennial Antarctic climate variability over the past 800,000 years.

A high-resolution deuterium profile is now available along the entire European Project for Ice Coring in Antarctica Dome C ice core, extending this climate record back to marine isotope stage 20.2, approximately 800,000 years ago. Experiments performed with an atmospheric general circulation model including water isotopes support its temperature interpretation. We assessed the general correspondence between Dansgaard-Oeschger events and their smoothed Antarctic counterparts for this Dome C record, which reveals the presence of such features with similar amplitudes during previous glacial periods. We suggest that the interplay between obliquity and precession accounts for the variable intensity of interglacial periods in ice core records.

The last deglaciation of the southeastern sector of the Scandinavian ice sheet.

The Scandinavian Ice Sheet (SIS) was an important component of the global ice sheet system during the last glaciation, but the timing of its growth to or retreat from its maximum extent remains poorly known. We used 115 cosmogenic beryllium-10 ages and 70 radiocarbon ages to constrain the timing of three substantial ice-margin fluctuations of the SIS between 25,000 and 12,000 years before the present. The age of initial deglaciation indicates that the SIS may have contributed to an abrupt rise in global sea level. Subsequent ice-margin fluctuations identify opposite mass-balance responses to North Atlantic climate change, indicating differing ice-sheet sensitivities to mean climate state.

Gastrointestinal absorption, tissue retention, and urinary excretion of dietary aluminum in rats determined by using 26Al.

We used accelerator mass spectrometry (AMS) and 26AI to study the plasma concentration, urinary excretion, and retention in bone, brain, and liver of a single dose of a dietary concentration of aluminum ingested either with or without citrate by 2-month-old Wistar rats. In the absence of citrate, cumulative urinary excretion and skeleton retention were each approximately 0.05% of the total 26AI dose ingested. 26AI retention in brain and liver were approximately 4 x 10(-8) and 2 x 10(-6), respectively. Concomitant citrate intake increased these median values by about two- to fivefold, although this factor was highly variable in individual rats. Independent of citrate administration, 90% of the 26AI excreted in urine (measured cumulatively over 30 days) was excreted within the first 48 h. Uptake by bone was rapid (approximately 1 h) and permanent over the 30-day duration of the experiment.

Effects of silicon, citrate and the fasting state on the intestinal absorption of aluminium in rats.

1. The effect of silicon (Si) contained in drinking water and solid food on the intestinal absorption of aluminium (Al) remains a matter of debate. The present study was designed to readdress this issue in the experimental animal, and to examine concomitantly the effects of citrate and the fasting state, respectively. 2. Three groups of young, non-fasted rats (n = 8 per group) were gavaged by solutions containing 3.8 ng of 26Al, 63 ng of 27Al, and either distilled water (< 0.1 mg/l Si) or commercial mineral water with a medium (6 mg/l) or high (14 mg/l) Si concentration. 3. Two other groups of eight non-fasted rats each received the same distilled water or high-Si gavage solution, respectively, together with a high citrate concentration (62 g/l). In each case the animals had free access to drinking water for 5 days before and 2 days after the gavage, containing the same Si concentration as in the gavage solution. A sixth group of eight rats was gavaged by low-Si, Al and distilled water in the fasted state. 4. The animals were killed 48 h after gavage, and blood, tissue and urine samples were collected for 26Al measurements by accelerator mass spectrometry. 5. We found that the fraction of absorbed 26Al retained in the skeleton (0.025-0.030%) was of the same order of magnitude as the fraction excreted in the 48 h urine (0.035-0.037%). High Si concentrations in the drinking water failed to depress the 26Al fraction absorbed, as estimated on the basis of skeletal accumulation and urinary excretion. 6. The administration of citrate-containing fluid enhanced 26Al absorption 5- to 10-fold (P < 0.005), but again the Si content of drinking water did not interfere. Finally, the intestinal absorption of 26Al was approximately 15 times higher in the fasted than in the non-fasted state. 7. In conclusion, the provision of large amounts of Si in the drinking water failed to modify physiological intestinal Al absorption under basal conditions or after its stimulation by citrate. However, a prolonged fast greatly enhanced Al absorption, compared with the non-fasted state.