Distribution and changes of active layer thickness (ALT) and soil temperature (TTOP) in the source area of the Yellow River using the GIPL model

Active layer thickness (ALT) is critical to the understanding of the surface energy balance, hydrological cycles, plant growth, and cold region engineering projects in permafrost regions. The temperature at the bottom of the active layer, a boundary layer between the equilibrium thermal state (in permafrost below) and transient thermal state (in the atmosphere and surface canopies above), is an important parameter to reflect the existence and thermal stability of permafrost. In this study, the Geophysical Institute Permafrost Model (GIPL) was used to model the spatial distribution of and changes in ALT and soil temperature in the Source Area of the Yellow River (SAYR), where continuous, discontinuous, and sporadic permafrost coexists with seasonally frozen ground. Monthly air temperatures downscaled from the CRU TS3.0 datasets, monthly snow depth derived from the passive microwave remote-sensing data SMMR and SSM/I, and vegetation patterns and soil properties at scale of 1:1000000 were used as input data after modified with GIS techniques. The model validation was carried out carefully with ALT in the SAYR has significantly increased from 1.8 m in 1980 to 2.4 m in 2006 at an average rate of 2.2 cm yr^?1. The mean annual temperature at the bottom of the active layer, or temperature at the top of permafrost (TTOP) rose substantially from ?1.1°C in 1980 to ?0.6°C in 2006 at an average rate of 0.018°C yr^?1. The increasing rate of the ALT and TTOP has accelerated since 2000. Regional warming and degradation of permafrost has also occurred, and the changes in the areal extent of regions with a sub-zero TTOP shrank from 2.4×10⁴ to 2.2×10⁴ km² at an average rate of 74 km² yr^?1. Changes of ALT and temperature have adversely affected the environmental stability in the SAYR.     

Rodinia connections between Australia and Laurentia: no SWEAT,no AUSWUS?

Although geological comparisons between Australia and North America have provided a basis for various Neoproterozoic Rodinia reconstructions, quantitative support from precisely dated palaeomagnetic poles has so far been lacking. We report U–Pb ages and palaeomagnetic results for two suites of mafic sills within the intracratonic Bangemall Basin of Western Australia, one of which is dated at 1070 ± 6 Ma and carries a high‐stability palaeomagnetic remanence. Comparison of the Bangemall palaeopole with Laurentian data suggests that previous reconstructions of eastern Australia against either western Canada (SWEAT) or the western United States (AUSWUS) are not viable at 1070 Ma. This implies that the Pacific Ocean did not form by separation of Australia–Antarctica from Laurentia, and that up to 10 000 km of late Neoproterozoic passive margins need to be matched with other continental blocks within any proposed Rodinia supercontinent. Our results permit a reconstruction (AUSMEX) that closely aligns late Mesoproterozoic orogenic belts in north‐east Australia and southernmost Laurentia.     

A mineral and cumulate perspective to magma differentiation at Nisyros volcano,Aegean arc

Lavas and pyroclastic products of Nisyros volcano (Aegean arc, Greece) host a wide variety of phenocryst and cumulate assemblages that offer a unique window into the earliest stages of magma differentiation. This study presents a detailed petrographic study of lavas, enclaves and cumulates spanning the entire volcanic history of Nisyros to elucidate at which levels in the crust magmas stall and differentiate. We present a new division for the volcanic products into two suites based on field occurrence and petrographic features: a low-porphyricity andesite and a high-porphyricity (rhyo)dacite (HPRD) suite. Cumulate fragments are exclusively found in the HPRD suite and are predominantly derived from upper crustal reservoirs where they crystallised under hydrous conditions from melts that underwent prior differentiation. Rarer cumulate fragments range from (amphibole-)wehrlites to plagioclase-hornblendites and these appear to be derived from the lower crust (0.5–0.8 GPa). The suppressed stability of plagioclase and early saturation of amphibole in these cumulates are indicative of high-pressure crystallisation from primitive hydrous melts (≥ 3 wt% H₂O). Clinopyroxene in these cumulates has Al₂O₃ contents up to 9 wt% due to the absence of crystallising plagioclase, and is subsequently consumed in a peritectic reaction to form primitive, Al-rich amphibole (Mg# > 73, 12–15 wt% Al₂O₃). The composition of these peritectic amphiboles is distinct from trace element-enriched interstitial amphibole in shallower cumulates. Phenocryst compositions and assemblages in both suites differ markedly from the cumulates. Phenocrysts, therefore, reflect shallow crystallisation and do not record magma differentiation in the deep arc crust.     

Tree wave migration across an elevation gradient in the Altai Mountains,Siberia

The phenomenon of tree waves(hedges and ribbons) formation within the alpine ecotone in Altai Mountains and its response to observed air temperature increase was considered. At the upper limit of tree growth Siberian pine(Pinus sibirica) forms hedges on windward slopes and ribbons on the leeward ones. Hedges were formed by prevailing winds and oriented along winds direction. Ribbons were formed by snow blowing and accumulating on the leeward slope and perpendicular to the prevailing winds, as well as to the elevation gradient. Hedges were always linked with microtopography features, whereas ribbons were not. Trees are migrating upward by waves and new ribbons and hedges are forming at or near tree line, whereas at lower elevations ribbons and hedges are being transformed into closed forests. Time series of high-resolution satellite scenes(from 1968 to 2010) indicated an upslope shift in the position ribbons averaged 155±26 m(or 3.7 m yr~(-1)) and crown closure increased(about 35%–90%). The hedges advance was limited by poor regeneration establishment and was negligible. Regeneration within the ribbon zone was approximately 2.5 times(5060 vs 2120 ha~(-1)) higherthen within the hedges zone. During the last four decades, Siberian pine in both hedges and ribbons strongly increased its growth increment, and recent tree growth rate for 50 year-old trees was about twice higher than those recorded for similarly-aged trees at the beginning of the 20~(th) century. Hedges and ribbons are phenomena that are widespread within the southern and northern Siberian Mountains.     

Faunal communities at sites of gas- and oil-bearing fluids in Lake Baikal

Macro- and meiofaunal communities were examined at four geomorphologically distinct sites with different gas- and oil-bearing fluid characteristics in the northern, central and southern basins of Lake Baikal. All sites had elevated concentrations of bicarbonate, nitrate, sulphate and chloride ions in pore fluids, with highest values at the Frolikha vent. Elevated levels of iron ions were found in pore waters of the St. Petersburg methane seep and the Gorevoy Utes oil seep. The chemical composition of pore waters at the Malenky mud volcano was similar to that reported in earlier work. Consistent with published data, the Frolikha vent (northern basin) and the St. Petersburg methane seep (central basin) were characterised by methane of mixed genesis (thermogenic + biogenic), whereas the methane source was mainly thermogenic at the Gorevoy Utes oil seep (central basin) and biogenic at the Malenky mud volcano (southern basin). In contrast to marine seep ecosystems, the macrofauna was dominated only by amphipods, giant planarians and oligochaetes, whereas bivalves were absent; the meiofauna was similar to its marine counterpart, being dominated by nematodes, cyclops, harpacticoids and ostracods. A statistically significant positive relationship was revealed between faunal abundance and the availability of bacterial mats on seep sediments. Moreover, ANOVA tests showed significant increases in both meiozoobenthic and macrozoobenthic densities at “hot spot” vent/seep sites relative to discharge-free reference sites. The isotopic composition of carbon and nitrogen at various trophic levels of these benthic vent/seep communities was found to differ markedly from that reported by earlier studies for the pelagic and other benthic food webs in Lake Baikal. As in marine seeps, the macrofauna had variable isotopic signatures. Light δ¹³C and δ¹⁵N values suggest the utilization of chemosynthetically fixed and/or methane-derived organic matter. By contrast, the heavy δ¹³C signatures of some mobile amphipods likely reflect consumption of photosynthetically derived carbon. These findings would at least partly explain why Lake Baikal is a notable outlier in global temperature–biodiversity patterns, exhibiting the highest biodiversity of any lake worldwide but at an extremely cold average temperature.     

Middle to late Pleistocene record of explosive volcanic eruptions in marine sediments offshore Kamchatka (Meiji Rise,NW Pacific)

This paper presents the first detailed study of a late Pleistocene marine tephra sequence from the NW Pacific, downwind from the Kamchatka volcanic arc. Sediment core SO201-2-40, located on the Meiji Rise ~400 km offshore the peninsula, includes 25 tephras deposited within the last 215 ka. Volcanic glass from the tephras was characterized using single-shard electron microprobe analysis and laser ablation inductively coupled mass spectrometry. The age of tephras was derived from a new age model based on paleomagnetic and paleoclimate studies. Geochemical correlation of distal tephras to Kamchatkan pyroclastic deposits allowed the identification of tephras from the Karymsky, Gorely, Opala and Shiveluch eruptive centers. Three of these tephras were also correlated to other marine and terrestrial sites and hence are identified as the best markers for the north-west Pacific region. These are an early Holocene tephra from the Karymsky caldera (~8.7 ka) and two tephras falling into the Marine Isotope Stage (MIS) 6 glacial time: an MIS 6.4 tephra from Shiveluch (~141 ka) and the MIS 6.5 Rauchua tephra (~175 ka) from Karymsky. The data presented in this study can be used in paleovolcanological and paleoceanographic reconstructions.     

The Fazenda Largo off-craton kimberlites of Piauí State, Brazil

In the late 1990s, the Fazenda Largo kimberlite cluster was discovered in the Piauí State of Brazil. As with earlier known kimberlites in this area – Redondão, Santa Filomena-Bom Jesus (Gilbues) and Picos – this cluster is located within the Palaeozoic Parnaiba Sedimentary Basin that separates the São Francisco and the Amazonian Precambrian cratons. Locations of kimberlites are controlled by the ‘Transbrasiliano Lineament’. The Fazenda Largo kimberlites are intensely weathered, almost completely altered rocks with a fine-grained clastic structure, and contain variable amounts of terrigene admixture (quartz sand). These rocks represent near-surface volcano-sedimentary deposits of the crater parts of kimberlite pipes. By petrographic, mineralogical and chemical features, the Fazenda Largo kimberlites are similar to average kimberlite. The composition of the deep-seated material in the Fazenda Largo kimberlites is quite diverse: among mantle microxenoliths are amphibolitised pyrope peridotites, garnetised spinel peridotites, ilmenite peridotites, chromian spinel + chromian diopside + pyrope intergrowths, and large xenoliths of pyrope dunite. High-pressure minerals are predominantly of the ultramafic suite, Cr-association minerals (purplish-red and violet pyrope, chromian spinel, chromian diopside, Cr-pargasite and orthopyroxene). The Ti-association minerals of the ultramafic suite (picroilmenite and orange pyrope), as well as rare grains of orange pyrope-almandine of the eclogite association, are subordinate. Kimberlites from all four pipes contain rare grains of G10 pyrope of the diamond association, but chromian spinel of the diamond association was not encountered. By their tectonic position, by geochemical characteristics, and by the composition of kimberlite indicator minerals, the Fazenda Largo kimberlites, like the others of such type, are unlikely to be economic.     

Radiation balance variations of underlying surface from the long-term observations of the Meteorological Observatory of the Moscow State University

The data on the radiation balance of underlying surface, its components, and main factors defining their variations are systematized and generalized for 50 years (1958–2007) on the basis of continuous observations at the Meteorological Observatory of the Moscow State University. The climatic norms of radiation balance are obtained and its variability (diurnal, annual, and interannual) limits are estimated. The correlation dependences between its main components and factors influencing their variability are obtained and the probability of one or another diurnal radiation balance sum during the year is determined. The existence is demonstrated of the tendency toward the increase in the absorbed, effective, and atmospheric back radiation and terrestrial radiation balance mostly pronounced in the nighttime in winter months.     

The latest geodynamics in Asia: Synthesis of data on volcanic evolution,lithosphere motion,and mantle velocities in the Baikal-Mongolian region

From a synthesis of data on volcanic evolution,movement of the lithosphere,and mantle velocities in the Baikal-Mongolian region,we propose a comprehensive model for deep dynamics of Asia that assumes an important role of the Gobi,Baikal,and North Transbaikal transition-layer melting anomalies.This layer was distorted by lower-mantle fluxes at the beginning of the latest geodynamic stage(i.e.in the early late Cretaceous) due to avalanches of slab material that were stagnated beneath the closed fragments of the Solonker,Ural-Mongolian paleoceans and Mongol-Okhotsk Gulf of Paleo-Pacific.At the latest geodynamic stage,Asia was involved in east-southeast movement,and the Pacific plate moved in the opposite direction with subduction under Asia.The weakened upper mantle region of the Gobi melting anomaly provided a counterflow connected with rollback in the Japan Sea area.These dynamics resulted in the formation of the Honshu-Korea flexure of the Pacific slab.A similar weakened upper mantle region of the North Transbaikal melting anomaly was associated with the formation of the Hokkaido-Amur flexure of the Pacific slab,formed due to progressive pull-down of the slab material into the transition layer in the direction of the Pacific plate and Asia convergence.The early—middle Miocene structural reorganization of the mantle processes in Asia resulted in the development of upper mantle low-velocity domains associated with the development of rifts and orogens.We propose that extension at the Baikal Rift was caused by deviator flowing mantle material,initiated under the moving lithosphere in the Baikal melting anomaly.Contraction at the Hangay orogen was created by facilitation of the tectonic stress transfer from the Indo-Asian interaction zone due to the low-viscosity mantle in the Gobi melting anomaly.