High-Pressure Melting of Eclogite and the P-T-X History of Tonalitic to Trondhjemitic Zoisite-Pegmatites, Munchberg Massif, Germany

Zoisite-bearing high-pressure pegmatites from the MünchbergMassif, Germany, provide an excellent example of the characteristicsof the onset of metabasite melting at eclogite-facies conditions.The pegmatites were derived by partial melting of a mid-oceanridge basalt (MORB)-like eclogite at T 680°C/2·3GPa to 750°C/3·1 GPa, which produced small amountsof tonalitic to trondhjemitic melt. The melt concentrated locallyin isolated, small melt pockets and crystallized primary zoisiteas liquidus phase at P 2·3 GPa/680°C to 2·1GPa/750°C. Compositional zoning of pegmatite zoisite recordsan ensuing multi-stage uplift history with successive, discretecrystallization events at 1·4 ± 0·2 GPa/650–700°Cand 1·0 ± 0·1 GPa/620–650°C.Resorption textures indicate reheating and thermal perturbationof the whole system prior to each successive crystallizationevent. Final solidification of zoisite-pegmatites occurred at0·9 ± 0·1 GPa/620–650°C. Thedata suggest that isolated melt + zoisite crystal mush pocketsformed an integral part of the eclogite throughout uplift frommelt formation at T 680°C/2·3 GPa to 750°C/3·1GPa to final solidification at 0·9 GPa/620–630°C;that is, over a depth range of 45–60 km. The entire pegmatite-formingprocess was probably fluid conserving: fluid present duringmelt formation was trapped by fully or nearly water-saturatedsiliceous melts, whereas fluid liberated during pegmatite crystallizationinteracted with dehydrated eclogite-facies assemblages to formamphibolite-facies hydrous minerals. A set of empirical D^{melt/eclogite}values based on mean zoisite-pegmatite and eclogite compositionwere used to model the onset of partial high-pressure meltingof metabasites. KEY WORDS: adakite; high-pressure melting; pegmatite; trondhjemite; zoisite     

How to operationalize accounting under Article 6 market mechanisms of the Paris Agreement

The role of market mechanisms was far from certain in the lead up to the 2015 Paris Climate Conference. The use of ‘constructive ambiguity’ led to Article 6 of the Paris Agreement, with Article 6.2 specifying a mechanism with limited international oversight, and Article 6.4 establishing a ‘Sustainable Development Mechanism’ (SDM) subject to detailed rules. Clear operationalization of these mechanisms remains a challenge, especially regarding the critical accounting issue that could not be resolved at the 2018 Katowice Climate Conference (COP24) – how to apply corresponding adjustments, especially regarding sectors not covered by targets under nationally-determined contributions (NDCs). By using fictitious examples, we explain two possible approaches to using Internationally Transferred Mitigation Outcomes (ITMOs) under Article 6.2 for achieving NDCs: a ‘target-based’ one where the acquiring Party adds the ITMO amount to the target level of its NDC; and a ‘tally-based’ one where the acquiring Party removes the ITMO amount from the final tally of its NDC. We discuss how these approaches influence the way to make corresponding adjustments and to avoid ‘double counting’. The first one leads to ‘target/budget-based accounting’, the second one to ‘emission-based accounting’. For mitigation outside the scope of the host Party's NDC, we propose using a tally-based interpretation of ITMO use, as opposed to the target-based variety used in the 1997 Kyoto Protocol, and stress the need for additionality testing. This interpretation allows for mandatory corresponding adjustments for all ITMO usage, while the host Party NDC level remains unchanged. A buffer registry is created for corresponding non-NDC adjustments of the selling party.

Key policy insights

• Under the Paris Agreement, transfers of emissions units between two countries through the Article 6 mechanisms need a corresponding adjustment on both sides to prevent double counting.

• Corresponding adjustments can be applied either to emissions targets under NDCs or measured emissions levels.

• The transfer of emissions reduction credits generated outside an NDC should lead to a corresponding adjustment of a buffer registry of the selling country, but not its emissions level/NDC target. Such credits should only be generated if additionality of the reductions is shown.

     

Late Wenlock carbon isotope excursions and associated conodont fauna in the Podlasie Depression,eastern Poland: a not‐so‐big crisis?

The middle Silurian ‘big crisis’ refers to a graptolite extinction event and faunal turnover at the onset of a double‐peaked positive carbon isotope excursion. The crisis has been proposed to affect conodonts, giving rise to a sophisticated palaeoecological model of their stepwise extinction, known as the Mulde Event. However, the impact of the event on conodont faunas outside Gotland and the Silurian Baltic Basin remains unknown. Here, it is examined in the Widowo IG‐1 core (E Poland). The middle Silurian succession in this core represents foreshoal, shoal, and lagoonal settings on a tropical carbonate ramp on the shelf of the Eastern European Craton. Three positive δ¹³C_carb excursions have been identified; the two upper excursions correlate with the Mulde isotope anomaly and with two global eustatic regressions. Conodont species proposed to be affected by the extinction event either were not observed or ranged through the extinction interval. Changes in their frequencies are best explained by the sequence stratigraphic architecture of the late Wenlock strata in the Widowo IG‐1 core. The little impact of the ‘big crisis’ may reflect facies homogeneity across the studied interval, supporting the hypothesis that the late Wenlock conodont turnover in epicontinental settings was primarily driven by eustatically controlled facies shifts. Copyright © 2015 John Wiley & Sons, Ltd.     

The German Bight (North Sea) is a nursery area for both locally and externally produced sprat juveniles

To better understand the role of the German Bight (GB) as a nursery area for juvenile North Sea sprat Sprattus sprattus we sought to determine whether the area may receive only locally or also externally produced offspring. We sampled juveniles during 3 trawl surveys in the GB in August, September, and October 2004 and applied otolith microstructure analysis in order to reconstruct their distributions of the day-of-first-increment-formation (dif). These were contrasted with spatial and seasonal patterns of sprat egg abundance in the GB and its adjacent areas, observed during 6 monthly plankton surveys. It was found that the majority of juveniles originated mainly from April/May 2004, coinciding with high spawning activity west of the GB, whereas spawning and larval production inside the GB peaked notably later, in May/June. This indicated that a large proportion of juveniles was produced outside the GB and transported subsequently into it through passive and/or active migration. Shifts to later mean difs from one survey to the next and length distributions indicative of the simultaneous presence of multiple cohorts, supported the notion that the GB is a complex retention and nursery area for sprat offspring from different North Sea spawning grounds and times. Later born juveniles had significantly faster initial growth rates than earlier born conspecifics, which was likely temperature-mediated, given the strong correlation between back-calculated growth histories and sea surface temperature as a proxy for thermal histories of juveniles (r² = 0.52).     

Testing the preservation potential of early diagenetic dolomites as geochemical archives

Early marine diagenetic dolomite is a rather thermodynamically-stable carbonate phase and has potential to act as an archive of marine porewater properties. However, the variety of early to late diagenetic dolomite phases that can coexist within a single sample can result in extensive complexity. Here, the archive potential of early marine dolomites exposed to extreme post-depositional processes is tested using various types of analyses, including: petrography, fluid inclusion data, stable δ¹³C and δ¹⁸O isotopes, ⁸⁷Sr/⁸⁶Sr ratios, and U-Pb age dating of various dolomite phases. In this example, a Triassic carbonate platform was dissected and overprinted (diagenetic temperatures of 50 to 430°C) in a strike-slip zone in Southern Spain. Eight episodes of dolomitization, a dolostone cataclasite and late stage meteoric/vadose cementation were recognized. The following processes were found to be diagenetically relevant: (i) protolith deposition and fabric-preservation, and marine dolomitization of precursor aragonite and calcite during the Middle–Late Triassic; (ii) intermediate burial and formation of zebra saddle dolomite and precipitation of various dolomite cements in a Proto-Atlantic opening stress regime (T ca 250°C) during the Early–Middle Jurassic; (iii) dolomite cement precipitation during early Alpine tectonism, rapid burial to ca 15 km, and high-grade anchizone overprint during Alpine tectonic evolution in the Early Eocene to Early Miocene; (iv) brecciation of dolostones to cataclasite during the onset of the Carboneras Fault Zone activity during the Middle Miocene; and (v) late-stage regression and subsequent meteoric overprint. Data shown here document that, under favourable conditions, early diagenetic marine dolomites and their archive data may resist petrographic and geochemical resetting over time intervals of 10⁸ or more years. Evidence for this preservation includes preserved Late Triassic seawater δ¹³C_DIC values and primary fluid inclusion data. Data also indicate that oversimplified statements based on bulk data from other petrographically-complex dolomite archives must be considered with caution.     

A Late Cretaceous theropod caudal vertebra from the Sultanate of Oman

A caudal vertebra collected from conglomerates of the Al-Khod Formation (Late Cretaceous) in the Al-Khod area, Sultanate of Oman, is assigned to a medium-sized theropod dinosaur. The Al-Khod discovery represents one of the very few dinosaur records from the Middle East.     

Bioavailability and bacterial degradation rates of dissolved organic matter in a temperate coastal area during an annual cycle

The bioavailability and bacterial degradation rates of dissolved organic matter (DOM) were determined over a seasonal cycle in Loch Creran (Scotland) by measuring the decrease in dissolved organic carbon (DOC), nitrogen (DON) and phosphorous (DOP) concentrations during long-term laboratory incubations (150 days) at a constant temperature of 14 °C. The experiments showed that bioavailable DOC (BDOC) accounted for 29 ± 11% of DOC (average ± SD), bioavailable DON (BDON) for 52 ± 11% of DON and bioavailable DOP (BDOP) for 88 ± 8% of DOP. The seasonal variations in DOM concentrations were mainly due to the bioavailable fraction. BDOP was degraded at a rate of 12 ± 4% d^– 1 (average ± SD) while the degradation rates of BDOC and BDON were 7 ± 2% d^– 1 and 9 ± 2% d^– 1 respectively, indicating a preferential mineralization of DOP relative to DON and of DON relative to DOC. Positive correlations between concentration and degradation rate of DOM suggested that the higher the concentration the faster DOM would be degraded. On average, 77 ± 9% of BDOP, 62 ± 14% of BDON and 49 ± 19% of BDOC were mineralized during the residence time of water in Loch Creran, showing that this coastal area exported C-rich DOM to the adjacent Firth of Lorne. Four additional degradation experiments testing the effect of varying temperature on bioavailability and degradation rates of DOM were also conducted throughout the seasonal cycle (summer, autumn, winter and spring). Apart from the standard incubations at 14 °C, additional studies at 8 °C and 18 °C were also conducted. Bioavailability did not change with temperature, but degradation rates were stimulated by increased temperature, with a Q₁₀ of 2.6 ± 1.1 for DOC and 2.5 ± 0.7 for DON (average ± SD).     

The atmospheric sulfur cycle in ECHAM-4 and its impact on the shortwave radiation

 The atmospheric general circulation model ECHAM-4 is coupled to a chemistry model to calculate sulfate mass distribution and the radiative forcing due to sulfate aerosol particles. The model simulates the main components of the hydrological cycle and, hence, it allows an explicit treatment of cloud transformation processes and precipitation scavenging. Two experiments are performed, one with pre-industrial and one with present-day sulfur emissions. In the pre-industrial emission scenario SO₂ is oxidized faster to sulfate and the in-cloud oxidation via the reaction with ozone is more important than in the present-day scenario. The atmospheric sulfate mass due to anthropogenic emissions is estimated as 0.38 Tg sulfur. The radiative forcing due to anthropogenic sulfate aerosols is calculated diagnostically. The backscattering of shortwave radiation (direct effect) as well as the impact of sulfate aerosols on the cloud albedo (indirect effect) is estimated. The model predicts a direct forcing of −0.35 W m^-2 and an indirect forcing of −0.76 W m^-2. Over the continents of the Northern Hemisphere the direct forcing amounts to −0.64 W m^-2. The geographical distribution of the direct and indirect effect is very different. Whereas the direct forcing is strongest over highly polluted continental regions, the indirect forcing over sea exceeds that over land. It is shown that forcing estimates based on monthly averages rather than on instantaneous sulfate pattern overestimate the indirect effect but have little effect on the direct forcing. Received: 16 October 1996/Accepted: 24 October 1996