EAST ASIA SUMMER MONSOON ONSET DATE CALCULATED FROM OBSERVED, REANALYZED AND COMBINED DAILY RAINFALL

In this paper, the East Asia summer monsoon onset date lines in East China are calculated by the definition similar to the traditional one, with the ECMWF reanalyzed 850 hPa daily wind and observed, reana-lyzed and combined daily rainfall during 1980～1993. To make the onset date line as close as possible to the previous work, the earliest onset date limits have to be applied for the regions with different latitude and the daily mean datasets have to be smoothed by space before calculation, therefore their space-resolution is reduced to about 3 longitude ×1°latitude. The results show that the multiyear mean summer monsoon onset date lines are quite similar to each other. Compared with the one from the reanalysis, the 14-year average onset date line form combination is obviously improved in the southern Sichuan Basin and the correlation between observed and combined onset date is also slightly higher over the Huaihe valley and Northeast China. Since daily rainfall combination also improved the long term daily mean and standard deviation through the pentad CMAP, if no better daily dataset is available, such a kind of daily rainfall combination can be used to get reasonable result in the Indian monsoon region without sufficient observatories or over the North Pacific without any ground observation at all in future study.     

Age constraints on faulting and fault reactivation: a multi-chronological approach

Movement within the Earth’s upper crust is commonly accommodated by faults or shear zones, ranging in scale from micro-displacements to regional tectonic lineaments. Since faults are active on different time scales and can be repeatedly reactivated, their displacement chronology is difficult to reconstruct. This study represents a multi-geochronological approach to unravel the evolution of an intracontinental fault zone locality along the Danube Fault, central Europe. At the investigated fault locality, ancient motion has produced a cataclastic deformation zone in which the cataclastic material was subjected to hydrothermal alteration and K-feldspar was almost completely replaced by illite and other phyllosilicates. Five different geochronological techniques (zircon Pb-evaporation, K–Ar and Rb–Sr illite, apatite fission track and fluorite (U-Th)/He) have been applied to explore the temporal fault activity. The upper time limit for initiation of faulting is constrained by the crystallization age of the primary rock type (known as “Kristallgranit”) at 325 ± 7 Ma, whereas the K–Ar and Rb–Sr ages of two illite fractions <2 μm (266–255 Ma) are interpreted to date fluid infiltration events during the final stage of the cataclastic deformation period. During this time, the “Kristallgranit” was already at or near the Earth’s surface as indicated by the sedimentary record and thermal modelling results of apatite fission track data. (U–Th)/He thermochronology of two single fluorite grains from a fluorite–quartz vein within the fault zone yield Cretaceous ages that clearly postdate their Late-Variscan mineralization age. We propose that later reactivation of the fault caused loss of helium in the fluorites. This assertion is supported by geological evidence, i.e. offsets of Jurassic and Cretaceous sediments along the fault and apatite fission track thermal modelling results are consistent with the prevalence of elevated temperatures (50–80°C) in the fault zone during the Cretaceous.     

‘Modelling the Arctic Boundary Layer: An Evaluation of Six Arcmip Regional-Scale Models using Data from the Sheba Project’

A primary climate change signal in the central Arctic is the melting of sea ice. This is dependent on the interplay between the atmosphere and the sea ice, which is critically dependent on the exchange of momentum, heat and moisture at the surface. In assessing the realism of climate change scenarios it is vital to know the quality by which these exchanges are modelled in climate simulations. Six state-of-the-art regional-climate models are run for one year in the western Arctic, on a common domain that encompasses the Surface Heat Budget of the Arctic Ocean (SHEBA) experiment ice-drift track. Surface variables, surface fluxes and the vertical structure of the lower troposphere are evaluated using data from the SHEBA experiment. All the models are driven by the same lateral boundary conditions, sea-ice fraction and sea and sea-ice surface temperatures. Surface pressure, near-surface air temperature, specific humidity and wind speed agree well with observations, with a falling degree of accuracy in that order. Wind speeds have systematic biases in some models, by as much as a few metres per second. The surface radiation fluxes are also surprisingly accurate, given the complexity of the problem. The turbulent momentum flux is acceptable, on average, in most models, but the turbulent heat fluxes are, however, mostly unreliable. Their correlation with observed fluxes is, in principle, insignificant, and they accumulate over a year to values an order of magnitude larger than observed. Typical instantaneous errors are easily of the same order of magnitude as the observed net atmospheric heat flux. In the light of the sensitivity of the atmosphere–ice interaction to errors in these fluxes, the ice-melt in climate change scenarios must be viewed with considerable caution.     

Preliminary Characterisation of New Reference Materials for Microanalysis: Chinese Geological Standard Glasses CGSG‐1, CGSG‐2, CGSG‐4 and CGSG‐5

Four silicate glasses were prepared by the fusion of about 1 kg powder each of a basalt, syenite, soil and andesite to provide reference materials of natural composition for microanalytical work. These glasses are referred to as ‘Chinese Geological Standard Glasses’ (CGSG) ‐1, ‐2, ‐4 and ‐5. Micro and bulk analyses indicated that the glasses are well homogenised with respect to major and trace elements. Some siderophile/chalcophile elements (e.g., Sn, Pt, Pb) may be heterogeneously distributed in CGSG‐5. This paper provides the first analytical data for the CGSG reference glasses using a variety of analytical techniques (wet chemistry, XRF, EPMA, ICP‐AES, ICP‐MS, LA‐ICP‐MS) performed in nine laboratories. Most data agree within uncertainty limits of the analytical techniques used. Discrepancies in the data for some siderophile/chalcophile elements exist, mainly because of possible heterogeneities of these elements in the glasses and/or analytical problems. From the analytical data, preliminary reference and information values for fifty‐five elements were calculated. The analytical uncertainties [2 relative standard error (RSE)] were estimated to be between about 1% and 20%.     

Ultrahigh pressure metamorphic rocks from the Chinese Continental Scientific Drilling Project: I. Petrology and geochemistry of the main hole (0–2,050 m)

The main hole (MH) of the Chinese Continental Scientific Drilling Project (CCSD) in southern Sulu has penetrated into an ultrahigh-pressure (UHP) metamorphic rock slice which consists of orthogneiss, paragneiss, eclogite, ultramafic rock and minor schist. Recovered eclogites have a UHP metamorphic mineral assemblage of garnet + omphacite + rutile ± phengite ± kyanite ± coesite ± epidote. Ultramafic rocks contain garnet + olivine + clinopyroxene + orthopyroxene ± Ti-clinohumite ± phlogopite. Gneisses and schists contain an amphibolite-facies paragenesis, but their zircons have coesite, garnet, omphacite (or jadeite) and phengite inclusions, indicating that eclogites and gneisses have been subjected to in situ UHP metamorphism. Using available geothermobarometers, P–T estimates of 3.1–4.4 GPa and 678–816°C for eclogites were obtained. If surface outcrops and neighboring shallow drill holes are considered together, we suggest that a huge supracrustal rock slab (> 50 km long × 100 km wide × 5 km deep) was subducted to a depth > 100 km and then exhumed to the surface. The depth interval (0–2,050 m) of the CCSD-MH can be divided into six lithological units. Unit 1 consists of alternating layers of quartz-rich and rutile-rich eclogites, with thin interlayers of gneiss and schist. Eclogites of unit 1 are characterized by Nb, Ta, Sr and Ti depletions, low Mg number and general LREE enrichment. Unit 2 comprises rutile- and ilmenite-rich eclogite and minor “normal” eclogite and is characterized by high TiO₂, total Fe, V, Co and Sr, and very low SiO₂, alkali, Zr, Ba, Nb, Ta and total REE contents, and LREE-depleted REE patterns with slightly positive Eu anomalies. Unit 3 contains ultramafic rock and minor MgO-rich eclogite. Protoliths of UHP rocks from units 1, 2 and 3 represent a layered mafic to ultramafic intrusion at crustal depth. Units 4 and 6 consist of interlayered eclogite and paragneiss; the eclogites are characterized by Th, U, Nb, Ta and Ti depletion and K enrichment and LREE-enriched REE patterns. Paragneisses show Nb, Ta, Sr and Ti depletions and LREE-enriched REE patterns occasionally with slightly negative Eu anomalies, indicating that their protoliths represent metamorphic supracrustal series. Unit 5 consists mainly of orthogneisses, showing distinct Nb, Ta, Sr and Ti depletions, and LREE-enriched REE patterns with pronounced negative Eu anomalies, suggesting granitic protoliths. In conclusion it is proposed that the southern Sulu UHP belt consists of a series of meta-supracrustal rocks, a layered mafic–ultramafic complex and granites.     

Contributions to the mineral chemistry of Hawaiian rocks

Phenocryst and groundmass pyroxenes in 24 rocks of the tholeiitic, alkalic, and nephelinic suites from Haleakala and West Maui volcanoes, Maui, Hawaii, were analyzed quantitatively by electron microprobe. Results and conclusions: i) Tholeiites contain augite, pigeonite, and bronzite; alkalic rocks contain salite, augite, and ferroaugite; and nephelinic rocks have salite, sometimes of Wo>50 mole %. ii) The three suites can be distinguished by Ca contents of pyroxenes: High-Ca pyroxenes of tholeiitic rocks have Wo_30–40; those of alkalic rocks have Wo_38–48; and those of the nephelinic rocks have Wo_47–51; i.e. Wo in clinopyroxene increases from tholeiitic, to alkalic, to nephelinic suites, iii). In the alkalic suite, rock types can be distinguished on the basis of clinopyroxene composition: Alkalic olivine and alkalic basalts have Wo_38–45, hawaiites and mugearites have Wo_45–48. Trachytes can be distinguished from both groups by higher Fe (Fs_22–30) and Ca contents (Wo_43–47). iv) Pyroxenes in tholeiitic rocks show higher intrarock variability (e.g. Fs₁₂Wo₄₀-Fs₃₇Wo₃₀) than those of the alkalic and nephelinic suites, v) Na₂O bulk-rock content affects Na₂O content of the precipitating high-Ca pyroxene; e.g. Na₂O in groundmass pyroxene increases from tholeiitic, to alkalic (mafic members only), to nephelinic suites; a similar relationship is present within the differentiated alkalic suite, vi) In tholeiites, changes in groundmass high-Ca pyroxene compositions are related to changes in bulk rock compositions, e.g. FeO/FeO+MgO+CaO in clinopyroxene increases as this ratio increases in the bulk rock; this is not true for alkalic and nephelinic rocks, vii) In groundmass high-Ca pyroxene, Al₂O₃, Na₂0, and TiO₂ contents increase and MnO content decreases with increasing Wo content from tholeiitic, to alkalic (mafic members only), to nephelinic suites, viii) Groundmass high-Ca pyroxenes are richer in MnO and Na₂O and poorer in Cr₂O₃ compared to coexisting phenocrysts. High-Ca pyroxene phenocrysts in nephelinic rocks and in one mugearite are depleted in SiO₂ and enriched in Al₂O₃ relative to coexisting groundmass clinopyroxene, indicating increased SiO₂ activity during crystallization. Some tholeiites show the reverse; this Si—Al relationship is not clear in other samples.     

Calcium Carbonate and Phosphate Reference Materials for Monitoring Bulk and Microanalytical Determination of Sr Isotopes

In situ laser ablation analyses rely on the microanalytical homogeneity of reference materials (RMs) and a similar matrix and mass fraction between unknown samples and RMs to obtain reliable results. Suitable carbonate and phosphate RMs for determination of Sr isotope ratios in such materials are limited. Thus, we determined ⁸⁷Sr/⁸⁶Sr ratios of several carbonate (JCt‐1, JCp‐1, MACS‐1, MACS‐3) and phosphate (MAPS‐4, MAPS‐5, NIST SRM 1400, NIST SRM 1486) international RMs using dissolved samples and two different multi‐collector inductively coupled plasma‐mass spectrometers (MC‐ICP‐MS). Our Sr isotope data are in agreement with published data and have an improved measurement precision for some RMs. For MACS‐1, we present the first ⁸⁷Sr/⁸⁶Sr value. We tested the suitability of these materials for microanalytical analyses by LA‐MC‐ICP‐MS, with two different laser ablation systems: a conventional nanosecond laser and a state‐of‐the‐art femtosecond laser. We investigated the RMs micro‐homogeneity and compared the data with our solution data. Both laser ablation systems yielded identical ⁸⁷Sr/⁸⁶Sr ratios within uncertainty to the solution data for RMs with low interferences of REEs. Therefore, these carbonate and phosphate RMs can be used to achieve accurate and precise results for in situ Sr isotope investigations by LA‐MC‐ICP‐MS of similar materials.     

What are robust strategies in the face of uncertain climate threshold responses?

We use an integrated assessment model of climate change to analyze how alternative decision-making criteria affect preferred investments into greenhouse gas mitigation, the distribution of outcomes, the robustness of the strategies, and the economic value of information. We define robustness as trading a small decrease in a strategy’s expected performance for a significant increase in a strategy’s performance in the worst cases. Specifically, we modify the Dynamic Integrated model of Climate and the Economy (DICE-07) to include a simple representation of a climate threshold response, parametric uncertainty, structural uncertainty, learning, and different decision-making criteria. Economic analyses of climate change strategies typically adopt the expected utility maximization (EUM) framework. We compare EUM with two decision criteria adopted from the finance literature, namely Limited Degree of Confidence (LDC) and Safety First (SF). Both criteria increase the relative weight of the performance under the worst-case scenarios compared to EUM. We show that the LDC and SF criteria provide a computationally feasible foundation for identifying greenhouse gas mitigation strategies that may prove more robust than those identified by the EUM criterion. More robust strategies show higher near-term investments in emissions abatement. Reducing uncertainty has a higher economic value of information for the LDC and SF decision criteria than for EUM.     

Stochastic riming of plate-like and columnar ice crystals

Riming growth of ice particles is simulated by numerically solving the stochastic collection equations, simultaneously considering coagulation of water droplets. By introducing a special criterion which defines the habit of a riming particle, the influence of this habit on the growth of several kinds of ice particles assumed to be formed during riming was investigated.It was found that (i) hexagonal rimed ice plates are growing more efficiently than lump graupel or rimed columns, (ii) the use of different collection kernels for the lump graupel evolution leads to widely differing results and that (iii) the time dependent decrease of liquid water substance and the size of the resulting ice particles were more strongly influenced by the initial ice crystal concentration than by the initial ice crystal size and the habit of the ice particles. By decreasing the number density of ice crystals gradually a critical ice crystal concentration was found at which the present liquid water was not completely consumed by the riming process even after 1800 s model time, causing large drops of radii >100 m to be formed in appreciable concentrations.     

Low-frequency climate variability of an aquaplanet

The long-term variability of an aquaplanet climate is analyzed with a coupled atmosphere–ocean–sea ice general circulation model. The main result of the 20,000 years simulation is a very dominant low-frequency oscillation with a period of approximately 700 years. All compartments of the aquaplanet (atmosphere, ocean, and sea ice) are involved as the climate alternates between warmer and colder states. Comprehensive time series analyses, as well as a comparison between mean states of cold and warm phases, give a detailed picture of the life cycle of the low-frequency oscillation. The warm phases are characterized by ice-free polar waters and a weaker meridional overturning circulation. During cold phases, the poles are completely covered by sea ice (down to 65^° N/S) and the overturning cells in the ocean are stronger. The climate state changes throughout atmosphere and ocean; however, surface areas in high latitudes are especially affected due to the changing sea ice cover. The meridional energy transport in atmosphere and ocean alternates with the climate regime, since the ocean is more efficient in transporting heat poleward when the poles are ice-free.