Initial measurement of beryllium-9 using high-resolution inductively coupled plasma mass spectrometry allows for more precise applications of the beryllium isotope system within the Earth Sciences

RATIONALE

Precise and accurate determination of the ratio of the cosmogenic nuclide ¹⁰ Be to the stable isotope ⁹ Be (¹⁰ Be/⁹ Be) is needed across multiple fields of research within the Earth Sciences. Current techniques used to measure the ⁹ Be content of geological materials generally require a large amount of sample or solution aliquot and present a large range of analytical precisions.

METHODS

A range of geological reference materials underwent whole-rock dissolution and "strong" (0.04 M NH₂ OH.HCl in 25% acetic acid) and "weak" (0.02 M NH₂ OH.HCl in 10% acetic acid) leaching to represent a range of potential applications within the geosciences. After treatment, the ⁹ Be and major element (Na, Ca, Mg, Fe, Mn, Al and Ti) content of sample solutions were determined by high-resolution inductively coupled plasma mass spectrometry (HR-ICP-MS) using a Thermo® ELEMENT XR instrument.

RESULTS

The ⁹ Be concentration of whole-rock and leaching solutions displayed a wide range of values within each geological reference material, generally following a uniform relationship implying a potential kinetic control on NH₂ OH leaching, as suggested by major element profiles. A precision of 0.1 to 1.4% is achieved independent of sample size or leaching strength.

CONCLUSIONS

Initial results suggest that the use of HR-ICP-MS improves the precision of ⁹ Be analysis for a range of geological reference materials. A high precision is maintained despite reducing the sample size or strength of leaching solution. This has implications for the use of the Be isotope system within the Earth Sciences by reducing the propagated uncertainty of ¹⁰ Be/⁹ Be ratios or the mass of sample or ⁹ Be aliquot used.

Conserving evolutionary history does not result in greater diversity over geological time scales

Alternative prioritization strategies have been proposed to safeguard biodiversity over macroevolutionary time scales. The first prioritizes the most distantly related species—maximizing phylogenetic diversity (PD)—in the hopes of capturing at least some lineages that will successfully diversify into the future. The second prioritizes lineages that are currently speciating, in the hopes that successful lineages will continue to generate species into the future. These contrasting schemes also map onto contrasting predictions about the role of slow diversifiers in the production of biodiversity over palaeontological time scales. We consider the performance of the two schemes across 10 dated species-level palaeo-phylogenetic trees ranging from Foraminifera to dinosaurs. We find that prioritizing PD for conservation generally led to fewer subsequent lineages, while prioritizing diversifiers led to modestly more subsequent diversity, compared with random sets of lineages. Importantly for conservation, the tree shape when decisions are made cannot predict which scheme will be most successful. These patterns are inconsistent with the notion that long-lived lineages are the source of new species. While there may be sound reasons for prioritizing PD for conservation, long-term species production might not be one of them.

Rapid glaciation and a two-step sea level plunge into the Last Glacial Maximum

The approximately 10,000-year-long Last Glacial Maximum, before the termination of the last ice age, was the coldest period in Earth's recent climate history¹. Relative to the Holocene epoch, atmospheric carbon dioxide was about 100 parts per million lower and tropical sea surface temperatures were about 3 to 5 degrees Celsius lower^2,3. The Last Glacial Maximum began when global mean sea level (GMSL) abruptly dropped by about 40 metres around 31,000 years ago⁴ and was followed by about 10,000 years of rapid deglaciation into the Holocene¹. The masses of the melting polar ice sheets and the change in ocean volume, and hence in GMSL, are primary constraints for climate models constructed to describe the transition between the Last Glacial Maximum and the Holocene, and future changes; but the rate, timing and magnitude of this transition remain uncertain. Here we show that sea level at the shelf edge of the Great Barrier Reef dropped by around 20 metres between 21,900 and 20,500 years ago, to -118 metres relative to the modern level. Our findings are based on recovered and radiometrically dated fossil corals and coralline algae assemblages, and represent relative sea level at the Great Barrier Reef, rather than GMSL. Subsequently, relative sea level rose at a rate of about 3.5 millimetres per year for around 4,000 years. The rise is consistent with the warming previously observed at 19,000 years ago^1,5, but we now show that it occurred just after the 20-metre drop in relative sea level and the related increase in global ice volumes. The detailed structure of our record is robust because the Great Barrier Reef is remote from former ice sheets and tectonic activity. Relative sea level can be influenced by Earth's response to regional changes in ice and water loadings and may differ greatly from GMSL. Consequently, we used glacio-isostatic models to derive GMSL, and find that the Last Glacial Maximum culminated 20,500 years ago in a GMSL low of about -125 to -130 metres.

Characteristics of high-energy neutrons estimated using the radioactive spallation products of Au at the 500-MeV neutron irradiation facility of KENS

We carried out a shielding experiment of high-energy neutrons, generated from a tungsten target bombarded with primary 500-MeV protons at KENS, which penetrated through a concrete shield in the zero-degree direction. We propose a new method to evaluate the spectra of high-energy neutrons ranging from 8 to 500 MeV. Au foils were set in a concrete shield, and the reaction rates for 13 radionuclides produced by the spallation reactions on the Au targets were measured by radiochemical techniques. The experimental results were compared with those obtained by the MARS14 Monte-Carlo code. A good agreement (between them) was found for energies beyond 100 MeV. The profile of the neutron spectrum, ranging from 8 to 500 MeV, does not depend on the thickness of the concrete shield.