Thermodynamics and environmental constraints make the biosphere predictable – a response to Volk

In his critique of Kleidon (Clim Change 66:271–319, 2004), Volk (Clim Change 85:3–4, 2007) concludes that maximum entropy production (MEP) has no great relevance for biological evolution and the time history of life on Earth. I think that most of his points are not justified but rather reflect (a) a lack of appreciation of the central importance of entropy production as the “universal currency” that measures what keeps systems working, including the biosphere, (b) a misunderstanding of how biotic activity is embedded in the global entropy budget, and (c) a lack of distinction between optimal environmental conditions that maximize productivity and result from environmental tradeoffs versus optimal function of organisms to some internal tradeoffs. The examples that he uses to support his conclusions show flaws in that these mostly discuss single environmental effects and immediate system responses. Optimal environmental conditions, however, requires at least two effects that result in a trade-off, so it is not surprising that his examples seem to contradict optimality and MEP. And the immediate response of a system to change can be very different than the response in steady state, for which MEP applies. This is specifically important to be considered in the context of the “cheater” problem. In summary, I do not think that Volk makes convincing arguments that contradict MEP, although I certainly agree that there is a lot more work to be done to fully recognize the great importance that thermodynamics and MEP play in shaping the Earth’s biosphere and its evolutionary history.     

Rapakivi granites

Rapakivi granites, especially the famous rapakivis from southern Finland, are some of the most attractive building and decorative stones, used world-wide because of their striking textures and beautiful colours. But rapakivi granites are more than just building material, they have also been studied scientifically for over 100 years to try to explain the formation of their plagioclase-mantled alkali feldspar ovoids, the rapakivi feldspars which are responsible for the unique texture of the rock. Despite all the work which has been done on them, the formation of this distinctive texture is still not fully understood. Rapakivi granite complexes are not just a 'pretty face', they are also associated with important tin deposits in Rondônia and Amazonas in Brazil.     

U-Pb-Hf isotopic data from detrital zircons in late Carboniferous and Mid-Late Triassic sandstones,and also Carboniferous granites from the Tauride and Anatolide continental units in S Turkey: implications for Tethyan palaeogeography

ABSTRACT

Zircons from Carboniferous sandstones (three samples) and Mid-Late Triassic sandstones (four samples) from the Tauride and Anatolide continental units were analysed for U-Pb-Hf isotopes. For comparison, zircons were also analysed from Carboniferous granites of the Afyon Zone, Anatolides (three samples). A NE African/Arabian source is inferred for both the Carboniferous sandstones of the Taurides (Alada?) and the Anatolides (Konya Complex). In contrast, the Carboniferous Karaburun Melange is characterised by a NW African provenance. A prominent Devonian population occurs in the Carboniferous Karaburun Melange, characterised by mainly positive ε_Hf(t) values that differ significantly from those of the Devonian granites of the Sakarya continental crustal unit (Pontides). Middle-Late Triassic Tauride sandstones include minor Palaeozoic and Early Mesozoic zircons. In contrast, Devonian and Carboniferous zircons are relatively abundant in Late Triassic sandstones of the Karaburun Peninsula. The Hf isotopic compositions of 25 Carboniferous-aged zircons from three samples of Mid-Late Triassic sandstone and one of Late Carboniferous age (one sample) overlap with the ε_Hf(t) values of Carboniferous arc-type granites in the Anatolides. Taking account of the available U-Pb and Lu-Hf isotopic data from comparative crustal units, the Devonian zircon populations from the melanges in the Karaburun Peninsula and the Konya Complex are inferred to have a westerly source (e.g. granitic rocks of Aegean region or central Europe). A tectonic model is proposed in which Palaeozoic Tethys sutured during the late Carboniferous in the west (Aegean region westwards), leaving an eastward-widening oceanic gulf in which sandstone turbidites accumulated, including Devonian zircons.     

Design of feedback-controlled wide-band seismographs with respect to undesired side-effects

Various modifications of a displacement-sensing seismometer controlled by negative first-order low-pass, first-order high-pass and second-order high-pass feedback are analysed. Undesired side-effects of the frequency-limited feedback on the response of the closed-loop system are investigated. Rules for “optimum tuning” of systems with a flat-displacement or flat-velocity response in a desired period range are given.     

The complex X-ray spectrum of the isolated neutron star RBS1223

We present a first analysis of a deep X-ray spectrum of the isolated neutron star RBS1223 obtained with XMM-Newton. Spectral data from four new monitoring observations in 2005/2006 were combined with archival observations obtained in 2003 and 2004 to form a spin-phase averaged spectrum containing 290 000 EPIC-pn photons. This spectrum shows higher complexity than its predecessors, and can be parameterised with two Gaussian absorption lines superimposed on a blackbody. The line centers, E ₂≃2E ₁, could be regarded as supporting the cyclotron interpretation of the absorption features in a field B∼4×10¹³ G. The flux ratio of those lines does not support this interpretation. Hence, either feature might be of truly atomic origin.      

In situ U–Pb dating of micro-baddeleyite by secondary ion mass spectrometry

We introduce a technique for U–Pb dating of baddeleyite using secondary ion mass spectrometry (SIMS) in situ analysis of ng-mass crystals that cannot be efficiently extracted by conventional mineral separation techniques. Average ²⁰⁷Pb/²⁰⁶Pb ages for Precambrian baddeleyite crystals are within < 0.3% of the respective isotope dilution thermal ionization mass spectrometry (ID-TIMS) ages. ²⁰⁶Pb/²³⁸U ratios are corrected for instrumental fractionation calibrated through linear regression in a Pb/U relative sensitivity vs. UO₂⁺/U⁺ calibration plot. Calibration is performed on separated baddeleyite crystals (～ 100–200 μm in maximum dimension) mounted in random crystallographic orientation. ²⁰⁶Pb/²³⁸U ages for baddeleyite from Duluth gabbro (FC4b) and Kovdor are accurate within 1–2% when averaging 15–30 individual spot analyses and relative sensitivities calibrated on Phalaborwa baddeleyite. The relative difference of ²⁰⁶Pb/²³⁸U between large crystals and micro-baddeleyite from FC4b is within ～ 1%. Comparison between silicate glass and baddeleyite, as well as replicate analysis of the same grains in different orientations relative to the incidence direction of the primary beam support previous evidence for bias in Pb/U sensitivity in baddeleyite due to variable crystal orientations. We successfully utilized oxygen flooding and a UO₂⁺/U⁺-based calibration to significantly reduce orientation dependent bias.     

In situ U–Pb SIMS (IN-SIMS) micro-baddeleyite dating of mafic rocks: Method with examples

An in situ U–Pb SIMS (IN-SIMS) method to date micro-baddeleyite crystals as small as 3 μm is presented with results from three samples that span a variety of ages and geologic settings. The method complements ID-TIMS geochronology by extending the range of dateable crystals to sizes smaller than can be recovered by physical separation. X-ray mapping and BSE imaging are used to locate target grains in thin section, followed by SIMS analysis on a CAMECA ims 1270, using the field aperture in the transfer column to screen out ions from host phases. Internal age precisions for the method are anticipated to range from 0.1% for Precambrian rocks to 3–7% for Phanerozoic rocks. Results establish a 2689 ± 5 Ma age for mafic dikes in the Wyoming craton, USA, a 1540 ± 30 Ma age for a subaerial lava flow from the Thelon Basin of northern Canada, and a 457 ± 34 Ma age for mafic dikes in the platform sequence of southeastern Siberia. The method is ideal for relatively non-destructive dating of small samples such as extraterrestrial rocks and precious terrestrial samples.     

Geophysical exploration of an active pockmark field in the Bay of Concarneau,southern Brittany,and implications for resident suspension feeders

About a decade ago, a large field of pockmarks (individual features up to 30 m in diameter and <2 m deep) was discovered in water depths of 15–40 m in the Bay of Concarneau in southern Brittany along the French Atlantic coast, covering an overall area of 36 km² and characterised by unusually high pockmark densities in places reaching 2,500 per square kilometre. As revealed by geophysical swath and subbottom profile data ground-truthed by sediment cores collected during two campaigns in 2005 and 2009, the confines of the pockmark field show a spectacular spatial association with those of a vast expanse of tube mats formed by a benthic community of the suspension-feeding amphipod Haploops nirae. The present study complements those findings with subbottom chirp profiles, seabed sonar imagery and ultrasonic backscatter data from the water column acquired in April 2011. Results show that pockmark distribution is influenced by the thickness of Holocene deposits covering an Oligocene palaeo-valley system. Two groups of pockmarks were identified: (1) a group of large (>10 m diameter), more widely scattered pockmarks deeply rooted (up to 8 ms two-way travel time, TWTT) in the Holocene palaeo-valley infills, and (2) a group of smaller, more densely spaced pockmarks shallowly rooted (up to 2 ms TWTT) in interfluve deposits. Pockmark pore water analyses revealed high methane concentrations peaking at ca. 400 μl/l at 22 and 30 cm core depth in silty sediments immediately above Haploops-bearing layers. Water column data indicate acoustic plumes above pockmarks, implying ongoing pockmark activity. Pockmark gas and/or fluid expulsion resulting in increased turbidity (resuspension of, amongst others, freshly settled phytoplankton) could at least partly account for the strong spatial association with the phytoplankton-feeding H. nirae in the Bay of Concarneau, exacerbating impacts of anthropogenically induced eutrophication and growing offshore trawling activities. Tidally driven hydraulic pumping in gas-charged pockmarks represents a good candidate as large-scale short-term triggering mechanism of pockmark activation, in addition to episodic regional seismic activity.