A Single-Year Cosmic Ray Event at 5410 BCE Registered in 14C of Tree Rings.

The annual 14C data in tree rings is an outstanding proxy for uncovering extreme solar energetic particle (SEP) events in the past. Signatures of extreme SEP events have been reported in 774/775 CE, 992/993 CE, and ∼660 BCE. Here, we report another rapid increase of 14C concentration in tree rings from California, Switzerland, and Finland around 5410 BCE. These 14C data series show a significant increase of ∼6‰ in 5411-5410 BCE. The signature of 14C variation is very similar to the confirmed three SEP events and points to an extreme short-term flux of cosmic ray radiation into the atmosphere. The rapid 14C increase in 5411/5410 BCE rings occurred during a period of high solar activity and 60 years after a grand 14C excursion during 5481-5471 BCE. The similarity of our 14C data to previous events suggests that the origin of the 5410 BCE event is an extreme SEP event.

Radiocarbon signal of a low and intermediate level radioactive waste disposal facility in nearby trees.

Tree ring series were collected from the vicinity of a Hungarian radioactive waste treatment and disposal facility and from a distant control background site, which is not influenced by the radiocarbon discharge of the disposal facility but it represents the natural regional (14)C level. The (14)C concentration of the cellulose content of tree rings was measured by AMS. Data of the tree ring series from the disposal facility was compared to the control site for each year. The results were also compared to the (14)C data of the atmospheric (14)C monitoring stations at the disposal facility and to international background measurements. On the basis of the results, the excess radiocarbon of the disposal facility can unambiguously be detected in the tree from the repository site.

Accelerator mass spectrometry at Arizona: geochronology of the climatic record and connections with the ocean.

There are many diverse uses of accelerator mass spectrometry (AMS). 14C studies at our laboratory include much research related to paleoclimate, with 14C as a tracer of past changes in environmental conditions as observed in corals, marine sediments, and many terrestrial records. Terrestrial records can also show the influence of oceanic oscillations, whether they are short term, such as ENSO (El Niño/Southern Oscillation), or on the millennial time scale. In tracer applications, we have developed the use of 129I as well as 14C as tracers for nuclear pollution studies around radioactive waste dump sites, in collaboration with IAEA. We discuss some applications carried out in Tucson, AZ, for several of these fields and hope to give some idea of the breadth of these studies.

Accelerator mass spectrometry at Arizona: geochronology of the climate record and connections with the ocean.

There are many diverse uses of accelerator mass spectrometry (AMS). Carbon-14 studies at our laboratory include much research related to paleoclimate, both with 14C as a tracer of past changes in environmental conditions as observed in corals, marine sediments and many terrestrial records. Terrestrial records such as forest fires can also show the influence of oceanic oscillations, whether they are short-term such as ENSO, or on the millennial time scale. In tracer applications, we have developed the use of 129I as well as 14C as tracers for nuclear pollution studies around radioactive waste dump sites, in collaboration with IAEA. We discuss some applications carried out in Tucson for several of these fields and hope to give some idea of the breadth of these studies.

A reduced organic carbon component in martian basalts.

The source and nature of carbon on Mars have been a subject of intense speculation. We report the results of confocal Raman imaging spectroscopy on 11 martian meteorites, spanning about 4.2 billion years of martian history. Ten of the meteorites contain abiotic macromolecular carbon (MMC) phases detected in association with small oxide grains included within high-temperature minerals. Polycyclic aromatic hydrocarbons were detected along with MMC phases in Dar al Gani 476. The association of organic carbon within magmatic minerals indicates that martian magmas favored precipitation of reduced carbon species during crystallization. The ubiquitous distribution of abiotic organic carbon in martian igneous rocks is important for understanding the martian carbon cycle and has implications for future missions to detect possible past martian life.

Asynchronous extinction of late Quaternary sloths on continents and islands.

Whatever the cause, it is extraordinary that dozens of genera of large mammals became extinct during the late Quaternary throughout the Western Hemisphere, including 90% of the genera of the xenarthran suborder Phyllophaga (sloths). Radiocarbon dates directly on dung, bones, or other tissue of extinct sloths place their "last appearance" datum at approximately 11,000 radiocarbon years before present (yr BP) or slightly less in North America, approximately 10,500 yr BP in South America, and approximately 4,400 yr BP on West Indian islands. This asynchronous situation is not compatible with glacial-interglacial climate change forcing these extinctions, especially given the great elevational, latitudinal, and longitudinal variation of the sloth-bearing continental sites. Instead, the chronology of last appearance of extinct sloths, whether on continents or islands, more closely tracks the first arrival of people.

A possible tektite strewn field in the Argentinian Pampa.

Impact glass associated with 11 elongate depressions in the Pampean Plain of Argentina, north of the city of Rio Cuarto, was suggested to be proximal ejecta related to a highly oblique impact event. We have identified about 400 additional elongate features in the area that indicate an aeolian, rather than an impact, origin. We have also dated fragments of glass found at the Rio Cuarto depressions; the age is similar to that of glass recovered 800 kilometers to the southeast. This material may be tektite glass from an impact event around 0.48 million years ago, representing a new tektite strewn field.