Microbial ecology of the stratified water column of the Black Sea as revealed by a comprehensive biomarker study

The stratified water column of the Black Sea is partitioned into oxic, suboxic, and euxinic zones, each characterized by different biogeochemical processes and by distinct microbial communities. In 2003, we collected particulate matter by large volume in situ filtration at the highest resolution to date for lipid biomarker analysis and bacterioplankton for enumeration of major prokaryotic groups. Abundances of several prokaryotic groups were estimated using CARD-FISH probes specific for Bacteria, Archaea (Crenarchaeota and Euryarchaeota), epsilonproteobacteria (mainly sulfide oxidizers) and sulfate reducing bacteria. We also measured a wide range of bacterial and archaeal lipid biomarkers. Depth distributions of diagnostic biomarkers are matched with zonation of microbial processes, including aerobic bacterial oxidation of methane, oxidation of ammonium by bacteria and archaea, metal reduction, and sulfide oxidation at the chemocline, and bacterial sulfate reduction and anaerobic oxidation of methane by archaea in the anoxic zone. Cell densities for archaea and sulfate reducing bacteria are estimated based on water column biomarker concentrations and compared with CARD-FISH results.     

The influence of human activity in the Arctic on climate and climate impacts

Human activities in the Arctic are often mentioned as recipients of climate-change impacts. In this paper we consider the more complicated but more likely possibility that human activities themselves can interact with climate or environmental change in ways that either mitigate or exacerbate the human impacts. Although human activities in the Arctic are generally assumed to be modest, our analysis suggests that those activities may have larger influences on the arctic system than previously thought. Moreover, human influences could increase substantially in the near future. First, we illustrate how past human activities in the Arctic have combined with climatic variations to alter biophysical systems upon which fisheries and livestock depend. Second, we describe how current and future human activities could precipitate or affect the timing of major transitions in the arctic system. Past and future analyses both point to ways in which human activities in the Arctic can substantially influence the trajectory of arctic system change.     

Mineralogy and petrogenesis of lunar magnesian granulitic meteorite Northwest Africa 5744

Lunar meteorite Northwest Africa (NWA) 5744 is a granulitic breccia with an anorthositic troctolite composition that may represent a distinct crustal lithology not previously described. This meteorite is the namesake and first‐discovered stone of its pairing group. Bulk rock major element abundances show the greatest affinity to Mg‐suite rocks, yet trace element abundances are more consistent with those of ferroan anorthosites. The relatively low abundances of incompatible trace elements (including K, P, Th, U, and rare earth elements) in NWA 5744 could indicate derivation from a highlands crustal lithology or mixture of lithologies that are distinct from the Procellarum KREEP terrane on the lunar nearside. Impact‐related thermal and shock metamorphism of NWA 5744 was intense enough to recrystallize mafic minerals in the matrix, but not intense enough to chemically equilibrate the constituent minerals. Thus, we infer that NWA 5744 was likely metamorphosed near the lunar surface, either as a lithic component within an impact melt sheet or from impact‐induced shock.     

An analysis of Apollo lunar soil samples 12070,889, 12030,187, and 12070,891: Basaltic diversity at the Apollo 12 landing site and implications for classification of small‐sized lunar samples

Lunar mare basalts provide insights into the compositional diversity of the Moon's interior. Basalt fragments from the lunar regolith can potentially sample lava flows from regions of the Moon not previously visited, thus, increasing our understanding of lunar geological evolution. As part of a study of basaltic diversity at the Apollo 12 landing site, detailed petrological and geochemical data are provided here for 13 basaltic chips. In addition to bulk chemistry, we have analyzed the major, minor, and trace element chemistry of mineral phases which highlight differences between basalt groups. Where samples contain olivine, the equilibrium parent melt magnesium number (Mg#; atomic Mg/[Mg + Fe]) can be calculated to estimate parent melt composition. Ilmenite and plagioclase chemistry can also determine differences between basalt groups. We conclude that samples of approximately 1–2 mm in size can be categorized provided that appropriate mineral phases (olivine, plagioclase, and ilmenite) are present. Where samples are fine‐grained (grain size <0.3 mm), a “paired samples t‐test” can provide a statistical comparison between a particular sample and known lunar basalts. Of the fragments analyzed here, three are found to belong to each of the previously identified olivine and ilmenite basalt suites, four to the pigeonite basalt suite, one is an olivine cumulate, and two could not be categorized because of their coarse grain sizes and lack of appropriate mineral phases. Our approach introduces methods that can be used to investigate small sample sizes (i.e., fines) from future sample return missions to investigate lava flow diversity and petrological significance.     

A petrological,mineralogical, and chemical analysis of the lunar mare basalt meteorite LaPaz Icefield 02205, 02224, and 02226

Abstract— LaPaz Icefield (LAP) 02205, 02226, and 02224 are paired stones of a crystalline basaltic lunar meteorite with a low‐Ti (3.21–3.43% TiO₂) low‐Al (9.93–10.45% Al₂O₃), and low‐K (0.11–0.12% K₂O) composition. They consist mainly of zoned pyroxene and plagioclase grains, with minor ilmenite, spinel, and mesostasis regions. Large, possibly xenocrystic, forsteritic olivine grains (<3% by mode) contain small trapped multiphase melt inclusions. Accessory mineral and mesostasis composition shows that the samples have experienced residual melt crystallization with silica oversaturation and late‐stage liquid immiscibility. Our section of LAP 02224 has a vesicular fusion crust, implying that it was at one time located sufficiently close to the lunar surface environment to have accumulated solar‐wind‐implanted gases. The stones have a comparable major element composition and petrography to low‐Ti, low‐Al basalts collected at the Apollos 12 and 15 landing sites. However, the LAP stones also have an enriched REE bulk composition and are more ferroan (Mg numbers in the range of 31 to 35) than similar Apollo samples, suggesting that they represent members of a previously unsampled fractionated mare basalt suite that crystallized from a relatively evolved lunar melt.     

Lunar Palaeoregolith Deposits as Recorders of the Galactic Environment of the Solar System and Implications for Astrobiology

One of the principal scientific reasons for wanting to resume in situ exploration of the lunar surface is to gain access to the record it contains of early Solar System history. Part of this record will pertain to the galactic environment of the Solar System, including variations in the cosmic ray flux, energetic galactic events (e.g., supernovae and/or gamma-ray bursts), and passages of the Solar System through dense interstellar clouds. Much of this record is of astrobiological interest as these processes may have affected the evolution of life on Earth, and perhaps other Solar System bodies. We argue that this galactic record, as for that of more local Solar System processes also of astrobiological interest, will be best preserved in ancient, buried regolith (‘palaeoregolith’) deposits in the lunar near sub-surface. Locating and sampling such deposits will be an important objective of future lunar exploration activities.     

Preservation potential of implanted solar wind volatiles in lunar paleoregolith deposits buried by lava flows

The lunar surface is bathed in a variety of impacting particles originating from the solar wind, solar flares, and galactic cosmic rays. These particles can become embedded in the regolith and/or produce a range of other molecules as they pass through the target material. The Moon therefore contains a record of the variability of the solar and galactic particle fluxes through time. To obtain useful temporal snapshots of these processes, discrete regolith units must be shielded from continued bombardment that would rewrite the record over time. One mechanism for achieving this preservation is the burial of a regolith deposit by a later lava flow. The archival value of such deposits sandwiched between lava layers is enhanced by the fact that both the under- and over-lying lava can be dated by radiometric techniques, thereby precisely defining the age of the regolith layer and the geologic record contained therein. The implanted volatile species would be vulnerable to outgassing by the heat of the over-lying flow, at temperatures exceeding 300-700 °C. However, the insulating properties of the finely particulate regolith would restrict significant heating to shallow depths. We have therefore modeled the heat transfer between lunar mare basalt lavas and the regolith in order to establish the range of depths below which implanted volatiles would be preserved. We find that the full suite of solar wind volatiles, consisting predominantly of H and He, would survive at depths of ∼13-290 cm (for 1-10 m thick lava flows, respectively). A substantial amount of CO, CO₂, N₂ and Xe would be preserved at depths as shallow as 3.7 cm beneath meter-thick flows. Given typical regolith accumulation rates during mare volcanism, the optimal localities for collecting viable solar wind samples would involve stacks of thin mare lava flows emplaced a few tens to a few hundred Ma apart, in order for sufficient regolith to develop between burial events. Obtaining useful archives of Solar System processes would therefore require extraction of regolith deposits buried at quite shallow depths beneath radiometrically-dated mare lava flows. These results provide a basis for possible lunar exploration activities.     

Geochemical and Sr–O isotopic constraints on magmatic differentiation at Gede Volcanic Complex, West Java, Indonesia

The Gede Volcanic Complex (GVC) of the Sunda island arc (West Java, Indonesia) consists of multiple volcanic centres and eruptive groups with complex magmatic histories. We present new petrological, mineralogical, whole-rock major and trace element and Sr–O isotopic data to provide constraints on the relative importance of fractional crystallisation and magma mixing in petrogenesis, as well as on the role and nature of the arc crust. Banded juvenile scoria from Young and Old Gede provide unequivocal evidence for the (late-stage) interaction of distinct magmas at Gede volcano. However, the relatively small-degree compositional zoning observed in plagioclase phenocrysts of all eruptive groups (up to ~20 mol% An) may be attributed to physical changes in magma properties (e.g. P, T, and PH₂O) rather than changes in melt composition. Major element and trace element variations within each eruptive series are inconsistent with magmatic evolution through simple mixing processes. Instead, mixing of variably fractionated magma batches is suggested to account for the significant scatter in some element variation diagrams. No correlation is observed between textural complexity and/or mineral disequilibrium and whole-rock geochemistry. REE data and geochemical modelling indicate that fractional crystallisation involving amphibole in the mid- to lower crust, and fractionation of plagioclase, clinopyroxene, Fe–Ti oxide ± olivine ± orthopyroxene provide strong control on the geochemical evolution of GVC rocks. Two-pyroxene geothermobarometry provides pre-eruption crystallisation temperatures of 891–1,046°C and pressures of 3.4–6.5 kbar, equivalent to ~13–24 km depth beneath the volcanoes (mid- to lower crust). Low, mantle-like clinopyroxene δ¹⁸O values of GVC lavas and poor correlation of Sr isotope ratios with indices of differentiation precludes significant assimilation of isotopically distinct crust during magmatic differentiation. Therefore, we suggest that the geochemical character of the moderately thick West Javan arc crust is relatively immature compared to typical continental crust. Trace element ratios and strontium isotopes show that the magmatic source composition of the older geographical units, Gegerbentang and Older Quaternary, is distinct from the other GVC groups.