Climatic regions as an indicator of forest coarse and fine woody debris carbon stocks in the United States

Background  

Coarse and fine woody debris are substantial forest ecosystem carbon stocks; however, there is a lack of understanding how these detrital carbon stocks vary across forested landscapes. Because forest woody detritus production and decay rates may partially depend on climatic conditions, the accumulation of coarse and fine woody debris carbon stocks in forests may be correlated with climate. This study used a nationwide inventory of coarse and fine woody debris in the United States to examine how these carbon stocks vary by climatic regions and variables.     

Evaluation of osmium isotopes and iridium as paleoflux tracers in pelagic carbonates

New osmium (Os) isotope and platinum group element (PGE) concentration data are used in conjunction with published ³He and Th isotope data to determine the relative proportions of lithogenic, extraterrestrial and hydrogenous iridium (Ir) in a Pacific pelagic carbonate sequence from the Ocean Drilling Program (ODP) Site 806 on the Ontong Java Plateau (OJP). These calculations demonstrate that lithogenic and extraterrestrial contributions to sedimentary Ir budget are minor, while hydrogenous Ir accounts for roughly 85% of the total Ir. Application of analogous partitioning calculations to previously reported data from a North Pacific red clay sequence (LL44-GPC3) yields very similar results. Total Ir burial fluxes at Site 806 and LL44-GPC3 are also similar, 45 and 30 pg cm⁻² kyr⁻¹, respectively. Average Ir/³He and Ir/xs²³⁰Th_initial ratios calculated from the entire Site 806 data set are similar to those reported earlier for Pacific sites. In general, down-core profiles of Ir, ³He and xs²³⁰Th_initial, are not well correlated with one another. However, all three data sets show similar variance and yield sediment mass accumulation rate estimates that agree within a factor of two. While these results indicate that Ir concentration has potential as a point-paleoflux tracer in pelagic carbonates, Ir-based paleoflux estimates are likely subject to uncertainties that are similar to those associated with Co-based paleoflux estimates. Consequently, local calibration of Ir flux in space and time will be required to fully assess the potential of Ir as a point paleoflux tracer. Measured ¹⁸⁷Os/¹⁸⁸Os of the OJP sediments are systematically lower than the inferred ¹⁸⁷Os/¹⁸⁸Os of contemporaneous seawater and a clear glacial-interglacial ¹⁸⁷Os/¹⁸⁸Os variation is lacking. Mixing calculations suggest Os contributions from lithogenic sources are insufficient to explain the observed ¹⁸⁷Os/¹⁸⁸Os variations. The difference between the ¹⁸⁷Os/¹⁸⁸Os of bulk sediment and that of seawater is interpreted in terms of subtle contributions of unradiogenic Os carried by particulate extraterrestrial material. Down-core variations of ¹⁸⁷Os/¹⁸⁸Os with Pt/Ir and Os/Ir also point to contributions from extraterrestrial particles. Mixing calculations for each set of several triplicate analyses suggest that the unradiogenic Os end member cannot be characterized by primary extraterrestrial particles of chondritic composition. It is noteworthy that in efforts aimed at determining the effect of extraterrestrial contributions, ¹⁸⁷Os/¹⁸⁸Os of pelagic carbonates has greater potential compared to abundances of PGE. An attempt has been made for the first time to estimate sediment mass accumulation rates based on amount of extraterrestrial Os in the OJP samples and previously reported extraterrestrial Os flux. Throughout most of the OJP record, Os isotope-based paleoflux estimates are within a factor of two of those derived using other constant flux tracers. Meaningful flux estimates cannot be made during glacial maxima because the OJP sediments do not record the low ¹⁸⁷Os/¹⁸⁸Os reported previously. We speculate that this discrepancy may be related to focusing of extraterrestrial particles at the OJP, as has been suggested to explain down-core ³He variations.     

Occurrence of Almandine, and Its Implications for Ancient High Temperature Activity of the Orakeikorako Geothermal Field, Taupo Volcanic Zone, New Zealand

Abstract: Exploration drilling at Orakeikorako provides information on the hydrologic and thermal regime of the geothermal system, which is presently as high as 265C. The presence of almandine in Drillhole OK–1, at 1312. 5m drilled depth, is the only known occurrence of hydrothermal garnet in an active geothermal system from New Zealand. The formation temperature of the almandine, is not consistent with measured (bore) temperatures, but does coincide with fluid inclusion data and temperatures inferred from other secondary minerals, which suggest it formed at >240C, and possibly as much as 310C. Almandine is an important mineral geothermometer in active hydrothermal systems, and implications for its occurrence should not be discounted in fossil (mineralised) epithermal-type hydrothermal systems.     

Polar orbits around binary stars

Oks proposes the existence of a new class of stable planetary orbits around binary stars, in the shape of a helix on a conical surface whose axis of symmetry coincides with the interstellar axis, and rotates with the same orbital frequency as the binary pair. We show that this claim relies on the inappropriate use of an effective potential that is only applicable when the stars are held motionless. We also present numerical evidence that the only planetary orbits whose planes are initially orthogonal to the interstellar axis that remain stable on the time scale of the stellar orbit are ordinary polar orbits around one of the stars, and that the perturbations due to the binary companion do not rotate the plane of the orbit to maintain a fixed relationship with the axis.     

El Niño–Southern Oscillation diversity and Southern Africa teleconnections during Austral Summer

Climate Dynamics - A wide range of sea surface temperature (SST) expressions have been observed during the El Niño–Southern Oscillation events of 1950–2010, which have occurred...     

Soluble organic compounds in the Tagish Lake meteorite

The C2 ungrouped Tagish Lake meteorite preserves a range of lithologies, reflecting variable degrees of parent‐body aqueous alteration. Here, we report on soluble organic compounds, including aliphatic and aromatic hydrocarbons, monocarboxylic acids, and amino acids, found within specimens representative of the range of aqueous alteration. We find that differences in soluble organic compounds among the lithologies may be explained by oxidative, fluid‐assisted alteration, primarily involving the derivation of soluble organic compounds from macromolecular material. In contrast, amino acids probably evolved from precursor molecules, albeit in parallel with other soluble organic compounds. Our results demonstrate the role of parent‐body alteration in the modification of organic matter and generation of prebiotic compounds in the early solar system, and have implications for interpretation of the complement of soluble organic compounds in carbonaceous chondrites.     

Time-variable emission from transiently accreting neutron stars in quiescence due to deep crustal heating

Transiently accreting neutron stars in quiescence ( L _X ≲10³⁴ erg s⁻¹) have been observed to vary in intensity by factors of few, over time-scales of days to years. If the quiescent luminosity is powered by a hot neutron star core, the core cooling time-scale is much longer than the recurrence time, and cannot explain the observed, more rapid variability. However, the non-equilibrium reactions which occur in the crust during outbursts deposit energy in isodensity shells, from which the thermal diffusion time-scale to the photosphere is days to years. The predicted magnitude of variability is too low to explain the observed variability unless – as is widely believed – the neutrons beyond the neutron-drip density are superfluid. Even then, the variability due to this mechanism in models with standard core neutrino cooling processes is less than 50 per cent – still too low to explain the reported variability. However, models with rapid core neutrino cooling can produce a variability by a factor as great as 20, on time-scales of days to years following an outburst. Thus, the factors of ∼ few intensity variability observed from transiently accreting neutron stars can be accounted for by this mechanism only if rapid core cooling processes are active.