Evidence for cyanobacterial inputs and heterotrophic alteration of lipids in sinking particles in the Alboran Sea (SW Mediterranean)

The different sources of lipid compounds present in sinking particles collected in a sediment trap mooring deployed in the Alboran Sea (SW Mediterranean) were elucidated using the molecular marker concept. A significant contribution of cyanobacterial lipids was identified based on the occurrence of a series of 3- and 5-methylalkanes and dimethylalkanes. Further evidence of cyanobacterial inputs was obtained by principal component analysis of all data showing diploptene and n-alkanes in the range C₁₄–C₂₂ clustered together with those branched alkanes. The use of methyl and dimethyl alkanes to trace cyanobacterial sources in the water column is proposed with advantage to sterols which are usually masked by phytoplanktonic sterols. The sterol distribution indicates phytoplankton as a major source with a contribution from heterotrophic zooplanktonic. Both fossil and biogenic sources can be contributors to the large unresolved complex mixture (UCM) found in these samples.     

Microbial plankton abundance and heterotrophic activity across the Central Atlantic Ocean

The role of microorganisms in the transfer of carbon of marine systems is very important in open oligotrophic oceans. Here, we analyze the picoplankton structure, the heterotrophic bacterioplankton activity, and the predator-prey relationships between heterotrophic bacteria and nanoflagellates during two large scale cruises in the Central Atlantic Ocean (∼29°N to ∼40°S). Latitud cruises were performed in 1995 between March-April and October-November. During both cruises we crossed the regions of different trophic statuses; where we measured different biological variables both at the surface and at the deep chlorophyll maximum (DCM). The concentration of chlorophyll a varied between 0.1 and 0.8 mg m⁻³, the abundance of heterotrophic bacteria varied between <1.0 × 10⁵ and >1.0 × 10⁶ cells ml⁻¹, and that of heterotrophic nanoflagellates between <100 and >1.0 × 10⁴ cells ml⁻¹. The production of heterotrophic bacteria varied more than three orders of magnitude between <0.01 and 24 μgC L⁻¹ d⁻¹; and the growth rates were in the range <0.01-2.1 d⁻¹. In the Latitud-II cruise, Prochlorococcus ranged between <10³ and >3 × 10⁵ cells ml⁻¹, Synechococcus between <100 and >1.0 × 10⁴ cells ml⁻¹, and picoeukaryotes between <100 and >10⁴ cells ml⁻¹.Two empirical models were used to learn more about the relationship between heterotrophic bacteria and nanoflagellates. Most bacterial production was ingested when this production was low, the heterotrophic nanoflagellates could be controlled by preys during Latitud-I cruise at the DCM, and by predators in the surface and in the Latitud-II cruise. Our results were placed in context with others about the structure and function of auto- and heterotrophic picoplankton and heterotrophic nanoplankton in the Central Atlantic Ocean.     

Spacecraft trajectories to the L<Subscript>3</Subscript> point of the Sun–Earth three-body problem

Of the three collinear libration points of the Sun–Earth Circular Restricted Three-Body Problem (CR3BP), L₃ is that located opposite to the Earth with respect to the Sun and approximately at the same heliocentric distance. Whereas several space missions have been launched to the other two collinear equilibrium points, i.e., L₁ and L₂, taking advantage of their dynamical and geometrical characteristics, the region around L₃ is so far unexploited. This is essentially due to the severe communication limitations caused by the distant and permanent opposition to the Earth, and by the gravitational perturbations mainly induced by Jupiter and the close passages of Venus, whose effects are more important than those due to the Earth. However, the adoption of a suitable periodic orbit around L₃ to ensure the necessary communication links with the Earth, or the connection with one or more relay satellites located at L₄ or L₅, and the simultaneous design of an appropriate station keeping-strategy, would make it possible to perform valuable fundamental physics and astrophysics investigations from this location. Such an opportunity leads to the need of studying the ways to transfer a spacecraft (s/c) from the Earth’s vicinity to L₃. In this contribution, we investigate several trajectory design methods to accomplish such a transfer, i.e., various types of two-burn impulsive trajectories in a Sun-s/c two-body model, a patched conics strategy exploiting the gravity assist of the nearby planets, an approach based on traveling on invariant manifolds of periodic orbits in the Sun–Earth CR3BP, and finally a low-thrust transfer. We examine advantages and drawbacks, and we estimate the propellant budget and time of flight requirements of each.     

Non-nebular origin of dark mantles around chondrules and inclusions in CM chondrites

Our examination of nine CM chondrites that span the aqueous alteration sequence leads us to conclude that compact dark fine mantles surrounding chondrules and inclusions in CM chondrites are not discrete fine-grained rims acquired in the solar nebula as modeled by Metzler et al. [Accretionary dust mantles in CM chondrites: evidence for solar nebula processes. Geochim. Cosmochim. Acta56, 1992, 2873-2897]. Nebular processes that lead to agglomeration produce materials with porosities far higher than those in the dark mantles. We infer that the mantles were produced from porous nebular materials on the CM parent asteroid by impact-compaction (a process that produces the lowest porosity adjacent to chondrules and inclusions). Compaction was followed by aqueous alteration that formed tochilinite, serpentine, Ni-bearing sulfide, and other secondary products in voids in the interchondrule regions. Metzler et al. reported a correlation between mantle thickness and the radius of the enclosed object. In Yamato 791198 we find no correlation when all sizes of central objects and dark lumps are included but a significant correlation (r² = 0.44) if we limit consideration to central objects with radii >35 μm; a moderate correlation is also found in QUE 97990. We suggest that impact-induced shear of a plum-pudding-like precursor produced the observed “mantles”; these were shielded from comminution during impact events by the adjacent stronger chondrules and inclusions. Some mantles in CM chondrites with low degrees of alteration show distinct layers that may largely reflect differences in porosity. Typically, a gray, uniform inner layer is surrounded by an outer layer consisting of darker silicates with BSE-bright speckles. The CM-chondrite objects characterized as “primary accretionary rocks” by Metzler et al. did not form in the nebula, but rather on the parent body. The absence of solar-flare particle tracks and solar-wind-implanted rare gases in these clasts reflect their lithified nature and low surface/volume ratios during the period when they resided in the regolith and were subject to irradiation by solar particles. The clasts are analogous to the light-colored metamorphosed clasts in ordinary-chondrite regolith breccias (which also lack solar-flare particle tracks and solar-wind gas).     

The outburst of the κ Cygnids in 2007: clues about the catastrophic break up of a comet to produce an Earth-crossing meteoroid stream

Using high-resolution, low-scan-rate, all-sky CCD cameras and high-level CCD video cameras, the SPanish Meteor and fireball Network (SPMN) recorded the 2007 κ Cygnid fireball outburst from several observing stations. Here, accurate trajectory, radiant and orbital data obtained for the κ Cygnid meteor are presented. The typical astrometric uncertainty is 1–2 arcmin, while velocity determination errors are of the order of 0.3–0.6 km s⁻¹, though this depends on the distance of each event to the station and its particular viewing geometry. The observed orbital differences among 1993 and 2007 outbursts support the hypothesis that the formation of this meteoroid stream is a consequence of the fragmentation of a comet nucleus. Such disruptive process proceed as a cascade, where the break up of the progenitor body leads to produce small remnants, some fully disintegrate into different clumps of particles and other remaining as dormant objects such as 2008ED69, 2001MG1 and 2004LA12 which are now observed as near-Earth asteroids. In addition to the orbital data, we present a unique spectrum of a bright  κ  Cygnid fireball revealing that the main rocky components have chondritic abundances, and estimations of the tensile strength of those fireballs that exhibited a catastrophic disruption behaviour. All this evidence of the structure and composition of the κ Cygnid meteoroids is consistent with being composed by fine-grained materials typically released from comets.     

The restricted planar isosceles three-body problem with non-negative energy

We consider a restricted three-body problem consisting of two positive equal masses m ₁ = m ₂ moving, under the mutual gravitational attraction, in a collision orbit and a third infinitesimal mass m ₃ moving in the plane P perpendicular to the line joining m ₁ and m ₂. The plane P is assumed to pass through the center of mass of m ₁ and m ₂. Since the motion of m ₁ and m ₂ is not affected by m ₃, from the symmetry of the configuration it is clear that m ₃ remains in the plane P and the three masses are at the vertices of an isosceles triangle for all time. The restricted planar isosceles three-body problem describes the motion of m ₃ when its angular momentum is different from zero and the motion of m ₁ and m ₂ is not periodic. Our main result is the characterization of the global flow of this problem.     

Puerto Lápice eucrite fall: Strewn field,physical description,probable fireball trajectory,and orbit

Abstract— The fall of the Puerto Lápice eucrite occurred on May 10, 2007, at 17 h 57 m 30 ± 30 s UTC. Its daylight fireball was witnessed by hundreds of people from Spain, and produced a meteorite fall associated with a large strewn field of fragments. There were no direct pictures of the fireball, but several pictures of the fireball's train were taken from different locations in Spain. Additional theodolite calibrations of visual records were made in order to find the most probable fireball trajectory based on the available data. The shape of the meteorite strewn field was considered as well. Although the orbit of the Puerto Lápice meteoroid could not be computed due to the absence of velocity data, we assumed a likely range of geocentric velocities and computed a range of possible orbits. All solutions show that the body was in an Apollo‐type orbit, with low inclination and perihelion distance just below 1 astronomical unit (AU). This is the first case that an orbit can be discussed for an HED meteorite fall.     

Bedrock controls on the mineralogy and chemistry of PM<Subscript>10</Subscript> extracted from Australian desert sediments

Given the relevance of desert aerosols to environmental issues such as dust storms, climate change and human health effects, we provide a demonstration of how the bedrock geology of an arid area influences the mineralogy and geochemistry of even the finest particulate matter (i.e., the inhalable fraction <10 μm in size: PM₁₀). PM₁₀ samples extracted from desert sediments at geologically contrasting off-road sites in central and southeastern Australia (granitic, high grade metamorphic, quartzitic sandstone) were analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), inductively coupled plasma atomic emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS). The “granitic” PM₁₀ are highly alkali feldspathic and illitic, with a wide range of accessory minerals including rutile (TiO₂), monazite [(Ce, La, Nd, Th, Y) PO₄], xenotime (YPO₄), apatite [Ca₅(PO₄)₃ (F, OH, Cl)], hematite (Fe₃O₄), zircon (ZrSiO₄) and thorite (ThSiO₄). This mineralogy is reflected in the geochemistry which shows notable enrichments in rare earth elements (REE) and most high field strength elements (both held in the accessory minerals), and higher than normal levels of low (<2.0) ionic potential elements (Na, K, Li, Cs, Rb: held in alkali feldspar and illite). The “metamorphic” resuspended PM₁₀ define a mineralogy clearly influenced by local exposures of pelitic and calc-silicate schists (sillimanite, muscovite, calcite, Ca-amphibole), a dominance of monazite over other REE-bearing phases, and a geochemistry distinguished by enrichments in alkaline earth metals (Ca, Mg, Ba, Sr) and depletion in heavy REE. The “quartzite” PM₁₀, derived from rocks already recycled by Precambrian erosion and sedimentary transport, show a sedimentologically mature mineralogy of mostly quartz and kaolinite, detrital accessory ilmenite, rutile, monazite and hematite, and the strongest geochemical depletion (especially K, Rb, Cs, Na, Ca, Mg, Ba).