Revisiting the Gow Lake impact structure,Saskatchewan, Canada

The ~5 km diameter Gow Lake impact structure formed in the Canadian Shield of northern Saskatchewan approximately 197 Myr ago. This structure has not been studied in detail since its discovery during a regional gravity survey in the early 1970s. We report here on field observations from a 2011 expedition that, when combined with subsequent laboratory studies, have revealed a wealth of new information about this poorly studied Canadian impact structure. Initially considered to be a prototypical central peak (i.e., a complex) impact structure, our observations demonstrate that Gow Lake is actually a transitional impact structure, making it one of only two identified on Earth. Despite its age, a well-preserved sequence of crater-fill impactites is preserved on Calder Island in the middle of Gow Lake. From the base upward, this stratigraphy is parautochthonous target rock, lithic impact breccia, clast-rich impact melt rock, red clast-poor impact melt rock, and green clast-poor impact melt rocks. Discontinuous lenses of impact melt-bearing breccia also occur near the top of the red impact melt rocks and in the uppermost green impact melt rocks. The vitric particles in these breccias display irregular and contorted outlines. This, together with their setting within crater-fill melt rocks, is indicative of an origin as flows within the transient cavity and not an airborne mode of origin. Following impact, a hydrothermal system was initiated, which resulted in alteration of the crater-fill impactites. Major alteration phases are nontronite clay, K-feldspar, and quartz.     

Regime shifts in the marine environment: the scientific basis and political context

Regime shifts in the marine environment have recently received much attention. To date, however, few large-scale meta-analyses have been carried out due to insufficient data coverage and integration between sustained observational datasets because of diverse methodologies used in data collection, recording and archival. Here we review the available data on regime shifts globally, followed by a review of current and planned policies with relevance to regime shifts.We then focus on the North and Baltic Seas, providing examples of existing efforts for data integration in the MarBEF Network of Excellence. Existing gaps in data coverage are identified, and the added value from meta-analyses of multiple datasets demonstrated using examples from the MarBEF integrated data project LargeNet. We discuss whether these efforts are addressing current policy needs and close with recommendations for future integrated data networks to increase our ability to understand, identify and predict recent and future regime shifts.     

Nitrogen functionality in “oil window” rank range vitrinite rich coals and chars

X-ray photoelectron spectroscopy (XPS) was used to characterize organic nitrogen species in coals and chars. The coals comprise a set of vitrinite-rich samples from the Penn State Coal Bank set, ranging from vitrinite reflectance (R_r) 0.42-1.60%. Chars were obtained after coal pyrolysis under an inert atmosphere at 800 °C and fast heating rate. In the coals, pyrrolic nitrogen was the predominant form, steadily decreasing with coal rank, while pyridinic and quaternary nitrogen showed pronounced variation with rank. In contrast to the coals, the chars show much less pyrrolic and pyridinic nitrogen, and more quaternary nitrogen. The chars were also characterized by having oxidized nitrogen and nitro sub-peaks, which were not observed for the coals. Apparently the occurrence of these forms is related to the decrease in the pyridinic nitrogen.     

Sub-recent nitrogen-isotope trends in sediments from Skagerrak (North Sea) and Kattegat: Changes in N-budgets and N-sources?

We determined ¹⁵N/¹⁴N ratios of total nitrogen in surface sediments and dated sediment cores to reconstruct the history of N-loading of the North Sea. The isotopic N composition in modern surface sediments is equivalent to and reflects the isotopic mixture of oceanic nitrate on the one hand (δ¹⁵N = 5‰) and the imprint of river-borne nitrogen input into the SE North Sea (δ¹⁵N up to 12‰ in estuaries of the SE North Sea) on the other hand. We compare the results with δ¹⁵N records from pre-industrial sediment intervals in cores from the Skagerrak and Kattegat areas, which both constitute significant depositional centres for N in the North Sea and the Baltic Sea/North Sea transition. As expected, isotopically enriched anthropogenic nitrogen was found in the two records from the Kattegat area, which is close to eutrophication sources on land. Enrichment of δ¹⁵N in cores from the Skagerrak – the largest sediment sink for nitrogen in the entire North Sea – was not significant and values were similar to those found in sediment layers representing pre-industrial conditions. We interpret this isotopic uniformity as an indication that most riverine reactive nitrogen with its characteristic isotopic signature is removed by denitrification in shallow shallow-water sediments before reaching the main sedimentary basin of the North Sea.     

H<Subscript>2</Subscript>O solubility in basalt at upper mantle conditions

This study presents a new experimental approach for determining H₂O solubility in basaltic melt at upper mantle conditions. Traditional solubility experiments are limited to pressures of ~600 MPa or less because it is difficult to reliably quench silicate melts containing greater than ~10 wt% dissolved H₂O. To overcome this limitation, our approach relies on the use of secondary ion mass spectrometry to measure the concentration of H dissolved in olivine and on using the measured H in olivine as a proxy for the concentration of H₂O in the co-existing basaltic melt. The solubility of H₂O in the melt is determined by performing a series of experiments at a single pressure and temperature with increasing amounts of liquid H₂O added to each charge. The point at which the concentration of H in the olivine first becomes independent of the amount of initial H₂O content of the charge (added + adsorbed H₂O) indicates its solubility in the melt. Experiments were conducted by packing basalt powder into a capsule fabricated from San Carlos olivine, which was then pressure-sealed inside a Ni outer capsule. Our experimental results indicate that at 1000 MPa and 1200 °C, the solubility of H₂O in basaltic melt is 20.6 ± 0.9 wt% (2 × standard deviation). This concentration is considerably higher than predicted by most solubility models but defines a linear relationship between H₂O fugacity and the square of molar H₂O solubility when combined with solubility data from lower pressure experiments. Further, our solubility determination agrees with melting point depression determined experimentally by Grove et al. (2006) for the H₂O-saturated peridotite solidus at 1000 MPa. Melting point depression calculations were used to estimate H₂O solubility in basalt along the experimentally determined H₂O-saturated peridotite solidus. The results suggest that a linear relationship between H₂O fugacity and the square of molar solubility exists up to ~1300 MPa, where there is an inflection point and solubility begins to increase less strongly with increasing H₂O fugacity.     

Marine organic geochemistry of the Eastern Mediterranean: 1. Aliphatic and polyaromatic hydrocarbons in Cretan Sea surficial sediments

As part of a lipid biogeochemical study, aliphatic and polyaromatic hydrocarbons were determined in surficial sediments from the Cretan Sea (South Aegean Sea) in the Eastern Mediterranean. Total concentrations of both aliphatic (AHC) and polyaromatic (PAH) hydrocarbons were low (562–5697 and 14.6–158.5 ng/g, respectively) with respect to other coastal sediments worldwide and compare with concentrations found in open sea areas. The composition of AHC was dominated by unresolved complex mixture (UCM) indicating the presence of petroleum-related hydrocarbon inputs as confirmed by the detection of specific α,β-hopanes. PAH consisted mainly of pyrolytic four- to five-ring compounds. UCM and PAH amounts revealed that Cretan Sea receives low supply of anthropogenic material compared to NW Mediterranean. The spatial distributions of AHC and PAH indicated that urban run-off and transport from the continental self are the major input pathway of anthropogenic and biogenic hydrocarbons from terrestrial sources in the near shore area, whereas atmospheric transport might be the significant source of hydrocarbons in the deep area.     

The Size and Shape of the Oblong Dwarf Planet Haumea

We use thermal radiometry and visible photometry to constrain the size, shape, and albedo of the large Kuiper belt object Haumea. The correlation between the visible and thermal photometry demonstrates that Haumea’s high amplitude and quickly varying optical light curve is indeed due to Haumea’s extreme shape, rather than large scale albedo variations. However, the well-sampled high precision visible data we present does require longitudinal surface heterogeneity to account for the shape of lightcurve. The thermal emission from Haumea is consistent with the expected Jacobi ellipsoid shape of a rapidly rotating body in hydrostatic equilibrium. The best Jacobi ellipsoid fit to the visible photometry implies a triaxial ellipsoid with axes of length 1,920 × 1,540 × 990 km and density $2.6$  g cm $^{-3}$ , as found by Lellouch et al. (A&A, 518:L147, 2010. doi:10.1051/0004-6361/201014648). While the thermal and visible data cannot uniquely constrain the full non-spherical shape of Haumea, the match between the predicted and measured thermal flux for a dense Jacobi ellipsoid suggests that Haumea is indeed one of the densest objects in the Kuiper belt.     

New 40Ar/39Ar constraints for the “Grande Nappe”: The largest rhyolitic eruption from the Mont-Dore Massif (French Massif Central)

Since the 1960s, an early explosive activity in the Mont-Dore Massif is associated with a major pyroclastic rhyolitic eruption (5–7 km³) known as the “Grande Nappe” (GN). This event, linked to the formation of a 6-km-diameter cryptic caldera named “Haute Dordogne”, was before our investigation dated by ⁴⁰Ar/³⁹Ar at 3.07 ± 0.04 Ma. Our new single-crystal laser fusion ⁴⁰Ar/³⁹Ar dates obtained on two outcrops of the GN (Rochefort-Montagne and Ludières) questioned several hypotheses made concerning this “landmark” event of the Mont-Dore Massif history. We demonstrate that: (1) the GN rhyolitic eruption has occurred much later than previously estimated (i.e. 2.77 ± 0.02–0.07 Ma full external uncertainties); (2) the correlation made between the Vendeix rhyolitic complexes (intra-caldera position) dated back to 2.74 ± 0.04 Ma and the GN is proposed; (3) xenocryst contamination could be very high (i.e. 70% for the Rochefort-Montagne GN outcrop) and explains the noticeable older age obtained previously; (4) a link between the GN eruption and the formation of a caldera is questionable; the hypothesis of a northward-oriented blast channeled eastward toward the paleo-Allier River is thus proposed.