Improved collection of rooftop micrometeorites through optimized extraction methods: The Budel collection

The scientific value of micrometeorites collected from deep-sea sediments or glacial deposits can be limited by poorly constrained accumulation times or severe alteration, coupled with a complex infrastructure of sampling expeditions. Collecting micrometeorites from rooftops has recently become a feasible alternative, but extraction methods have not been optimized or standardized to date. Here, we show that existing methods for the recovery of melted cosmic spherules (CSs) can be strongly improved by using a sequence of mineral separation techniques, including shape separation with an asymmetric vibrator and heavy liquid density separation with overflow centrifuges. We retrieved 1006 micrometeorites from the gutter of a barn in Budel, the Netherlands. Particle diameters are 80–515 μm, with the major mode at 130 μm and a slope exponent of −4.88. Differences in size distributions among various types of CSs indicate a multi-source influx, with CS textures controlled by their parent body's mineralogy and orbital parameters. Repeated sampling of the rooftop after accumulation times of 959 and 333 days allows for a time-integrated global mass flux estimate of 472 t year⁻¹. This estimate is notably higher than previous rooftop-based estimates but is still severely affected by micrometeorite loss from the gutter through drainage. The mass flux peaks at an equivalent particle diameter of ~200 μm. The Budel collection is the first rooftop collection to contain abundant vitreous micrometeorites and include the coarse-grained S-type CS class. Unmelted and I-type micrometeorites remain difficult to extract from rooftop samples. Vitreous micrometeorites display various stages of weathering, showing that severe alteration of glass can progress at a faster rate in populated regions than previously assumed. This study demonstrates that methodological adjustments can drastically increase the scientific potential of rooftop micrometeorite collections.     

Fast numerics for the spin orbit equation with realistic tidal dissipation and constant eccentricity

We present an algorithm for the rapid numerical integration of a time-periodic ODE with a small dissipation term that is \(C^1\) in the velocity. Such an ODE arises as a model of spin–orbit coupling in a star/planet system, and the motivation for devising a fast algorithm for its solution comes from the desire to estimate probability of capture in various solutions, via Monte Carlo simulation: the integration times are very long, since we are interested in phenomena occurring on timescales of the order of \(10^6\)–\(10^7\) years. The proposed algorithm is based on the high-order Euler method which was described in Bartuccelli et al. (Celest Mech Dyn Astron 121(3):233–260, 2015), and it requires computer algebra to set up the code for its implementation. The payoff is an overall increase in speed by a factor of about 7.5 compared to standard numerical methods. Means for accelerating the purely numerical computation are also discussed.     

Channelization of a large Alpine river: what is left of its original morphodynamics?

The Adige River drains 12 200 km² of the Eastern Alps and flows for 213 km within this mountain range. Similar to other large rivers in Central Europe, the Adige River was subject to massive channelization works during the 19th century. Thanks to the availability of several historical maps, this river represents a very valuable case study to document the extent to which the morphology of the river changed due to channelization and to understand how much is left of its original morphodynamics. The study was based on the analysis of seven sets of historical maps dating from 1803–1805 to 1915–1927, on geomorphological analysis, on the application of mathematical morphodynamic theories and on the application of bar and channel pattern prediction models. The study concerns 115 km of the main stem and 29 km of its tributaries. In the pre‐channelization conditions, the Adige River presented a prevalence of single‐thread channel planforms. Multi‐thread patterns developed only immediately downstream of the main confluences. During the 19th century, the Adige underwent considerable channel adjustment, consisting of channel narrowing, straightening, and reduction of bars and islands. Multi‐thread and single‐thread reaches evolved through different evolutionary trajectories, considering both the channel width and the bar/vegetation interaction. Bar and channel pattern predictors showed good correspondence with the observed patterns, including the development of multi‐thread morphologies downstream of the confluences. Application of the free‐bar predictor helped to interpret the strong reduction – almost complete loss – of exposed sediment bars after the channelization works, quantifying the riverbed inclination to form alternate bars. This morphological evolution can be observed in other Alpine rivers of similar size and similar massive channelization, therefore, a simplified conceptual model for large rivers subjected to channelization is proposed, showing that a relatively small difference in the engineered channel width may have a strong impact on the river dynamics, specifically on bar formation. Copyright © 2017 John Wiley & Sons, Ltd.     

Metazoan/microbial biostalactites from present‐day submarine caves in the Mediterranean Sea

Biostalactites formed by metazoan–microbialite associations from three submerged marine caves in the Plemmirio Peninsula (south of Syracuse, Ionian Sea) are randomly distributed and show different sizes and morphologies, as well as variations in surface roughness/smoothness. The biostalactites consist of crusts a few centimeters thick of small serpulids and other metazoans, associated with fine‐grained carbonate; the larger ones often include a nucleus of serpulid tubes (Protula). The metazoans include mainly serpuloideans, sponges, bryozoans and foraminifers but microbial carbonates are also significant components. The composition of both the living communities and thanatocoenoses on the outer surfaces, as well as the composition and fabric of the internal framework, were analysed and used to reconstruct the history of the caves. All of the identified sessile faunas mainly consist of cryptic and sciaphilic dwellers that reflect cave conditions and their variations through time. The distribution pattern, composition and abundance of the present‐day dwellers largely depend on the degree of roughness of the biostalactite surfaces and their positions within the caves. It has been suggested that the Protula specimens in the nuclei represent pioneer populations that formed aggregates during the early cave colonization phase, in response to relatively high food supply from seawater inflow and intruding continental waters. By contrast, the outer metazoan–microbialite carbonates reflect more confined conditions in the caves caused by Holocene sea‐level rises. Hypotheses are proposed for biostalactite growth, taking into account information about the growth rates of some constituents, and evidence of dissolution effects. Similarities and differences between these biostalactites and other Holocene deposits previously described from submarine caves in the Mediterranean Sea and in tropical reefs are discussed.     

Evidence of multiple thermokarst lake generations from an 11 800‐year‐old permafrost core on the northern Seward Peninsula,Alaska

Permafrost degradation influences the morphology, biogeochemical cycling and hydrology of Arctic landscapes over a range of time scales. To reconstruct temporal patterns of early to late Holocene permafrost and thermokarst dynamics, site‐specific palaeo‐records are needed. Here we present a multi‐proxy study of a 350‐cm‐long permafrost core from a drained lake basin on the northern Seward Peninsula, Alaska, revealing Lateglacial to Holocene thermokarst lake dynamics in a central location of Beringia. Use of radiocarbon dating, micropalaeontology (ostracods and testaceans), sedimentology (grain‐size analyses, magnetic susceptibility, tephra analyses), geochemistry (total nitrogen and carbon, total organic carbon, δ¹³C_org) and stable water isotopes (δ¹⁸O, δD, d excess) of ground ice allowed the reconstruction of several distinct thermokarst lake phases. These include a pre‐lacustrine environment at the base of the core characterized by the Devil Mountain Maar tephra (22 800±280 cal. a BP, Unit A), which has vertically subsided in places due to subsequent development of a deep thermokarst lake that initiated around 11 800 cal. a BP (Unit B). At about 9000 cal. a BP this lake transitioned from a stable depositional environment to a very dynamic lake system (Unit C) characterized by fluctuating lake levels, potentially intermediate wetland development, and expansion and erosion of shore deposits. Complete drainage of this lake occurred at 1060 cal. a BP, including post‐drainage sediment freezing from the top down to 154 cm and gradual accumulation of terrestrial peat (Unit D), as well as uniform upward talik refreezing. This core‐based reconstruction of multiple thermokarst lake generations since 11 800 cal. a BP improves our understanding of the temporal scales of thermokarst lake development from initiation to drainage, demonstrates complex landscape evolution in the ice‐rich permafrost regions of Central Beringia during the Lateglacial and Holocene, and enhances our understanding of biogeochemical cycles in thermokarst‐affected regions of the Arctic.     

Source and turnover of organic matter in agricultural soils derived from n-alkane/n-carboxylic acid compositions and C-isotope signatures

Agricultural soils are regarded as one potential sink for atmospheric CO₂ via photosynthetic fixation in plant biomass and subsequent transformation into soil organic matter upon soil diagenesis. The difference in C-isotope signatures of C₃- vs. C₄-plants allows for a natural isotopic labelling of soil organic matter after changes from C₃- to C₄-cropping. In this study, we demonstrate that isotopic shifts are paralleled by molecular signatures of C₃- vs. C₄-crop alkyl lipids. Turnover times vary significantly, based on cropping techniques. For grain-maize cropped soils at steady state average turnover times of 40 years for bulk SOC, 35 years for n-alkanes and 21 years for n-carboxylic acids were determined. Turnover times for silage-maize cropped soil at steady state were on average 250 years for bulk SOC, 60 years for n-alkanes and 49 years for n-carboxylic acids. Turnover times reported here for silage-maize cropped soils may be taken as maximum values only, because they derive from a single trial, which was affected by addition of anthropogenic refractory carbon. Discrimination of input from various plant parts (roots, stems and leaves) based on bulk C-isotopes is not feasible but can easily be achieved using compositions of carboxylic acids, especially the ratio of n-C₂₄ vs. n-C₂₂₊₂₆ and their respective C-isotope values. This enables delineation of the influence of different cropping techniques, e.g., silage- or grain-maize, on carbon storage in soils. Admixture of external sources of organic matter to the soil organic carbon pool of an urban site in Halle, Germany was identified based on alkyl lipid distributions. Nearby lignite mining was identified as a source for non-crop-derived alkyl lipids, primarily based on the elevated n-C₂₆-carboxylic acid content and heavier carbon isotopic signatures.