Subnanomolar Sensitive Stable Isotopic Determination in CO2 by Tunable Infrared Laser Absorption Spectroscopy.

Oxygen and carbon stable isotope ratios (18O/16O, 13C/12C, and 17O/16O) of CO2 have been crucial in helping us understand Earth and planetary systems. These ratios have also been used in medicine for the noninvasive diagnosis of diseases from exhaled breath and for quantifying biochemical or metabolic reactions and in determining the production area of agricultural products. The current method for measuring the stable isotope ratios of CO2 is primarily gas-source isotope ratio mass spectroscopy (IRMS). Due to the recent demand for isotopic microanalysis of carbonates and organic compounds, the sample size required for isotopic measurements has been reduced to approximately 2 nmol CO2 (equivalent to 0.2 µg CaCO3 and 24 ng carbon) by using high-precision IRMS. We report a novel method using tunable mid-infrared laser direct absorption spectroscopy (TILDAS) for sensitive measurements of 18O/16O and 13C/12C in subnanomolar CO2. This method can accurately measure 18O/16O and 13C/12C in CO2 with a repeatability of less than 0.03‰ (n = 28) in a range of 0.3 nmol (equivalent to 0.03 µg CaCO3 and 3.8 ng carbon) to 30 nmol. This is a sample size 1 order of magnitude smaller than currently available sensitive analytical techniques. In addition, the TILDAS system measures 17O/16O simultaneously with a repeatability of less than 0.06‰ (n = 28). Our method is a major advance in supersensitive CO2 stable isotopic analyses for various fields.

Advanced maritime adaptation in the western Pacific coastal region extends back to 35,000-30,000 years before present.

Maritime adaptation was one of the essential factors that enabled modern humans to disperse all over the world. However, geographic distribution of early maritime technology during the Late Pleistocene remains unclear. At this time, the Indonesian Archipelago and eastern New Guinea stand as the sole, well-recognized area for secure Pleistocene evidence of repeated ocean crossings and advanced fishing technology. The incomplete archeological records also make it difficult to know whether modern humans could sustain their life on a resource-poor, small oceanic island for extended periods with Paleolithic technology. We here report evidence from a limestone cave site on Okinawa Island, Japan, of successive occupation that extends back to 35,000-30,000 y ago. Well-stratified strata at the Sakitari Cave site yielded a rich assemblage of seashell artifacts, including formally shaped tools, beads, and the world's oldest fishhooks. These are accompanied by seasonally exploited food residue. The persistent occupation on this relatively small, geographically isolated island, as well as the appearance of Paleolithic sites on nearby islands by 30,000 y ago, suggest wider distribution of successful maritime adaptations than previously recognized, spanning the lower to midlatitude areas in the western Pacific coastal region.

Sustained North Atlantic warming drove anomalously intense MIS 11c interglacial.

The Marine Isotope Stage (MIS) 11c interglacial and its preceding glacial termination represent an enigmatically intense climate response to relatively weak insolation forcing. So far, a lack of radiometric age control has confounded a detailed assessment of the insolation-climate relationship during this period. Here, we present 230Th-dated speleothem proxy data from northern Italy and compare them with palaeoclimate records from the North Atlantic region. We find that interglacial conditions started in subtropical to middle latitudes at 423.1 ± 1.3 thousand years (kyr) before present, during a first weak insolation maximum, whereas northern high latitudes remained glaciated (sea level ~ 40 m below present). Some 14.5 ± 2.8 kyr after this early subtropical onset, peak interglacial conditions were reached globally, with sea level 6-13 m above present, despite weak insolation forcing. We attribute this remarkably intense climate response to an exceptionally long (~15 kyr) episode of intense poleward heat flux transport prior to the MIS 11c optimum.

Noble gases and nitrogen in samples of asteroid Ryugu record its volatile sources and recent surface evolution.

The near-Earth carbonaceous asteroid (162173) Ryugu is expected to contain volatile chemical species that could provide information on the origin of Earth's volatiles. Samples of Ryugu were retrieved by the Hayabusa2 spacecraft. We measured noble gas and nitrogen isotopes in Ryugu samples and found that they are dominated by presolar and primordial components, incorporated during Solar System formation. Noble gas concentrations are higher than those in Ivuna-type carbonaceous (CI) chondrite meteorites. Several host phases of isotopically distinct nitrogen have different abundances among the samples. Our measurements support a close relationship between Ryugu and CI chondrites. Noble gases produced by galactic cosmic rays, indicating a ~5 million year exposure, and from implanted solar wind record the recent irradiation history of Ryugu after it migrated to its current orbit.

First asteroid gas sample delivered by the Hayabusa2 mission: A treasure box from Ryugu.

The Hayabusa2 spacecraft returned to Earth from the asteroid 162173 Ryugu on 6 December 2020. One day after the recovery, the gas species retained in the sample container were extracted and measured on-site and stored in gas collection bottles. The container gas consists of helium and neon with an extraterrestrial 3He/4He and 20Ne/22Ne ratios, along with some contaminant terrestrial atmospheric gases. A mixture of solar and Earth's atmospheric gas is the best explanation for the container gas composition. Fragmentation of Ryugu grains within the sample container is discussed on the basis of the estimated amount of indigenous He and the size distribution of the recovered Ryugu grains. This is the first successful return of gas species from a near-Earth asteroid.

Last glacial temperature reconstructions using coupled isotopic analyses of fossil snails and stalagmites from archaeological caves in Okinawa, Japan.

We applied a new geoarchaeological method with two carbonate archives, which are fossil snails from Sakitari Cave and stalagmites from Gyokusen Cave, on Okinawa Island, Japan, to reconstruct surface air temperature changes over the northwestern Pacific since the last glacial period. Oxygen isotope ratios (δ18O) of modern and fossil freshwater snail shells were determined to infer seasonal temperature variations. The observational and analytical data confirm that δ18O values of fluid inclusion waters in the stalagmite can be regarded as those of spring waters at the sites where snails lived. Our results indicate that the annual mean, summer, and winter air temperatures were lower by 6-7 °C at ca. 23 thousand years ago (ka) and 4-5 °C at ca. 16-13 ka than those of the present day. Our reconstruction implies that surface air cooling was possibly two times greater than that of seawater around the Ryukyu Islands during the Last Glacial Maximum, which potentially enhanced the development of the East Asian summer monsoon during the last deglaciation. Considering the potential uncertainties in the temperature estimations, the climatic interpretations of this study are not necessarily definitive due to the limited number of samples. Nevertheless, our new geoarchaeological approach using coupled δ18O determinations of fossil snails and stalagmite fluid inclusion waters will be useful for reconstructing snapshots of seasonally resolved time series of air temperatures during the Quaternary.

Pulsed Terahertz Radiation for Sensitive Quantification of Carbonate Minerals.

Quantification of natural carbonate minerals, namely, aragonite, high- and low-Mg calcite, and dolomite provides essential information about biomineralization, carbon cycling on Earth, and the evolution of ocean chemistry, and is also useful in many other scientific, pharmaceutical, and industrial fields. However, X-ray diffractometer has previously been the only practical tool to identify and quantify carbonate minerals, including calcium carbonate (CaCO3) polymorphs. We propose new fingerprint terahertz (THz) absorption and reflective index spectra in the 1-6 THz range that probe the lattice phonon modes and can be used for sensitive quantification of these four carbonate minerals, including polymorphs. In THz time-domain spectroscopy with our unique attenuated total reflection system, high- and low-Mg calcite and aragonite show different absorbance and reflective index amplitudes at 3.32 THz, which corresponds to the transverse optic mode. Dolomite shows a distinct absorbance peak and reflective index at 4.82 THz because its space group (R3̅) is different from that of calcite (R3̅c). THz absorbance and reflective index curves of the mixed carbonate materials, which typically occur in natural environments, correspond well to the curves calculated from the results of single-mineral samples (R 2 > 0.98). Remarkably, the absorbance and reflective index can quantify small fractions (<1%) of low-Mg calcite in an aragonite matrix with high linearity (R 2 = 0.99). Our findings provide a new method for screening low-Mg calcite diagenetic overprints on primary aragonitic skeletons such as corals, which is crucial for climate reconstructions using the isotopic analyses because a 1% overprint can cause estimated temperature deviations of ∼1 °C. THz spectra of carbonate minerals offer not only a new high-sensitivity quantification tool for interdisciplinary fields, but also safer light-source handling than X-ray diffractometer.

Cyanobacterial exopolymer properties differentiate microbial carbonate fabrics.

Although environmental changes and evolution of life are potentially recorded via microbial carbonates, including laminated stromatolites and clotted thrombolites, factors controlling their fabric are still a matter of controversy. Herein, we report that the exopolymer properties of different cyanobacterial taxa primarily control the microbial carbonates fabrics in modern examples. This study shows that the calcite encrustation of filamentous Phormidium sp. secreting acidic exopolymers forms the laminated fabric of stromatolites, whereas the encrustation of coccoid Coelosphaeriopsis sp. secreting acidic exopolymers and poor calcification of filamentous Leptolyngbya sp. secreting non-acidic exopolymers form peloids and fenestral structures, respectively, i.e. the clotted fabric of thrombolites. Based on these findings, we suggest that the rise and decline of cyanobacteria possessing different exopolymer properties caused the expansion of thrombolites around the Proterozoic/Cambrian boundary.

Biogeochemical Cycle of Methanol in Anoxic Deep-Sea Sediments.

The biological flux and lifetime of methanol in anoxic marine sediments are largely unknown. We herein reported, for the first time, quantitative methanol removal rates in subsurface sediments. Anaerobic incubation experiments with radiotracers showed high rates of microbial methanol consumption. Notably, methanol oxidation to CO2 surpassed methanol assimilation and methanogenesis from CO2/H2 and methanol. Nevertheless, a significant decrease in methanol was not observed after the incubation, and this was attributed to the microbial production of methanol in parallel with its consumption. These results suggest that microbial reactions play an important role in the sources and sinks of methanol in subseafloor sediments.