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Large Arctic rivers are an important source of iron (Fe) to the Arctic Ocean, though seasonal variations in the terrestrial source and supply of Fe to the ocean are unknown. To constrain the seasonal variability, we present Fe concentrations and isotopic compositions (δ56Fe) for particulate (>0.22 µm) and colloidal (<0.22 µm–1 kDa) Fe from the Lena River, NE Russia. Samples were collected every month during winter baseflow (September 2012–March 2013) and every 2–3 days before, during and after river ice break-up (May 2015). Iron in particles have isotope ratios lower than crustal values during winter (e.g., δ56Fe Part = −0.37 ± 0.16‰), and crustal-like values during river ice break-up and spring flood (e.g., δ56Fe Part = 0.07 ± 0.08‰), indicating a change in the source of particulate Fe between winter and spring flood. Low isotope values are indicative of mineral dissolution, transport of reduced Fe in sub-oxic, ice-covered sub-permafrost groundwaters and near-quantitative precipitation of Fe as particles. Crustal-like isotopic compositions result from the increased supply of detrital particles from riverbank and soil erosion during river ice break-up and flooding. Iron colloids (<0.22 μm) have δ56Fe values that are comparable to or lower than crustal values during winter (e.g., δ56Fe Col = −0.08 ± 0.05‰) but similar to or higher than crustal values during spring flood (e.g., δ56Fe Col = +0.24 ± 0.11‰). Low δ56Fe ratios for colloidal Fe during winter are consistent with precipitation from isotopically light Fe(II) aq transported in sub-permafrost groundwaters. Higher colloidal δ56Fe ratios during the spring flood indicate that these colloids are supplied from surface soils, where Fe is fractionated via oxidation or organic carbon complexation, similar to during summer. Approximately half of the annual colloidal Fe flux occurs during spring flood while most of the remaining colloidal Fe is supplied during summer months. The total amount of colloidal Fe transported during winter was relatively low. The seasonal variation in colloidal Fe isotope values may be a useful tool to trace the source of colloidal Fe to the Arctic Ocean and monitor future changes in the sources and supply of Fe from the permafrost landscape to the Lena River basin. [ABSTRACT FROM AUTHOR]

The article discusses the strontium isotope signatures found in the Vendian Khorbusuonka group of the Olenek uplift river in the northeastern Siberian platform in Russia. It notes that the Vendian section of the Olenek uplift is one of the best reference successions for both regional and global correlation of Upper Precambrian deposits due to its unique paleontological characteristic and availability of geochronological dates. It states that no data are available for the chemostratigraphy of strontium isotope that prevents adequate assessment of age constraints for the Siberian hypostratotype. It also discusses the distribution of strontium isotope in carbonate rocks of the river aimed to assess their age to compare with other isotopic-chemostratigraphic methods.

Abstract: Detailed geochemical, isotope, and geochronological studies were carried out for the granitoids of the Chuya and Kutima complexes in the Baikal marginal salient of the Siberian craton basement. The obtained results indicate that the granitoids of both complexes are confined to the same tectonic structure (Akitkan fold belt) and are of similar absolute age. U–Pb zircon dating of the Kutima granites yielded an age of 2019±16 Ma, which nearly coincides with the age of 2020±12 Ma obtained earlier for the granitoids of the Chuya complex. Despite the close ages, the granitoids of these complexes differ considerably in geochemical characteristics. The granitoids of the Chuya complex correspond in composition to calcic and calc-alkalic peraluminous trondhjemites, and the granites of the Kutima complex, to calc-alkalic and alkali-calcic peraluminous granites. The granites of the Chuya complex are similar to rocks of the tonalite–trondhjemite–granodiorite (TTG) series and are close in CaO, Sr, and Ba contents to I-type granites. The granites of the Kutima complex are similar in contents of major oxides to oxidized A-type granites. Study of the Nd isotope composition of the Chuya and Kutima granitoids showed their close positive values of εNd(T) (+1.9 to +3.5), which indicates that both rocks formed from sources with a short crustal history. Based on petrogeochemical data, it has been established that the Chuya granitoids might have been formed through the melting of a metabasitic source, whereas the Kutima granites, through the melting of a crustal source of quartz–feldspathic composition. Estimation of the PT-conditions of granitoid melt crystallization shows that the Chuya granitoids formed at 735–776 °C (zircon saturation temperature) and >10 kbar and the Kutima granites, at 819–920 °C and >10 kbar. It is assumed that the granitoids of both complexes formed in thickened continental crust within an accretionary orogen. [Copyright &y& Elsevier]

Abstract: Reconstructing Quaternary glacial and environmental changes in the vast, high-northern latitudes of Siberia is essential for a better understanding of global past climate variability and its potential solar forcings. Two sediment outcrops in the Dyanushka Valley in the southwestern foreland of the Verkhoyansk Mountains, northeast Siberia, were investigated using a multi-proxy approach (lithostratigraphy, geochemistry, palynology, and radiocarbon and IRSL dating). Three piedmont glaciations reached the outcrop sites. The glacial advances are dated to >140, ∼119–92 and ∼78–53 ka and thus, within dating uncertainties, correspond to obliquity minima during marine isotope stages (MIS) 6, 5d, and 4. This chronology corroborates and refines previous studies that have documented the successively more restricted glacial extents in Siberia during the course of the last glacial cycle. The observed glaciation pattern is out of phase with global ice volume estimates and probably indicates a strong aridisation trend. Additionally, the results show that the geochemical and mineralogical composition of the sediments contains information about provenance. Sediments originating from the Verkhoyansk Mountains are generally enriched in TiO2, MgO, P2O5, Fe2O3, Cr, illite, and chlorite, whereas sediments derived from the Lena River contain more expandable clay minerals, Ba, Sr. Alkane patterns as biomarker proxies turn out to be particularly valuable where poor preservation of pollen is an issue, and, generally speaking, vegetation reconstruction helps distinguishing between ‘warm versus cold mode’ sediments. [Copyright &y& Elsevier]

A concept of an accelerator mass spectrometer intended for the Siberian Branch of the Russian Academy of Sciences is suggested. Preliminary tests have been conducted, and a carbon isotope having a mass of 14 amu has been detected in a charcoal sample. [ABSTRACT FROM AUTHOR]

Covering a vast area of the northern Siberian platform are the Siberian flood basalts (SFB), which make up one of the world’s largest magmatic provinces. Along the northeastern margin of the SFB province lies the Maymecha-Kotuy alkaline-ultramafic complex, consisting of a large volume of alkaline lavas, numerous dykes, and the Guli massif together with numerous other, smaller alkaline plutons. The genetic link between the SFB and the Maymecha-Kotuy complex continues to be a subject of active debate. Although the rocks in both units have essentially the same age close to the Permian-Triassic boundary, questions remain as to the relative order of emplacement and the contributing source materials of each lithology. This study builds upon earlier petrologic, geochemical, and isotopic work to further an understanding of the relationship between SFB and alkaline rocks. A whole-rock U-Pb age of 250 ± 9 Ma was determined for the Guli massif, which lies within the range of ages previously reported for the SFB. The Pb isotopic composition of the Guli rocks plot mainly in the lower portion of the OIB field, and dunite and carbonatite extend downward into the MORB field suggesting for them a more depleted source than the one that produced the SFB. The combined Pb, Sr, and Nd isotopic systematics of the SFB and the Guli alkaline rocks enable the identification of several discrete source components. The first component dominates many of the Guli rocks and is characterized by low 87Sr/86Sr (0.7031 to 0.7038), high εNd (+5.35 to +3.97), and relatively unradiogenic Pb (206Pb/204Pb = 17.88–18.31; 207Pb/204Pb = 15.38–15.46; 208Pb/204Pb = 37.33–37.70), which we associate with the depleted (MORB source) mantle. The second component representing most of the SFB demonstrates a notable chemical and isotopic uniformity with 87Sr/86Sr values of 0.7046 to 0.7052, εNd values of 0 to +2.5, and an average Pb isotopic composition of 206Pb/204Pb = 18.3, 207Pb/204Pb = 15.5, and 208Pb/204Pb = 38.0. This component, making up the majority of SFB, is speculated to be a relatively primitive lower mantle plume with a near-chondritic signature. Contamination by upper and lower continental crustal material, designated as components 3 and 4, is postulated to explain the isotopic characteristics of some of the higher SiO2 Guli rocks and SFB. Finally, metasomatic processes associated with the invasion of the Siberian super-plume add a fifth component responsible for the extreme enrichment in rare-earth and related elements found in some Guli rocks and SFB. [ABSTRACT FROM AUTHOR]

Permafrost soils are an important reservoir of carbon (C) in boreal and arctic ecosystems. Rising global temperature is expected to enhance decomposition of organic matter frozen in permafrost, and may cause positive feedback to warming as CO2 is released to the atmosphere. Significant amounts of organic matter remain frozen in thick mineral soil (loess) deposits in northeastern Siberia, but the quantity and lability of this deep organic C is poorly known. Soils from four tundra and boreal forest locations in northeastern Siberia that have been continuously frozen since the Pleistocene were incubated at controlled temperatures (5, 10 and 15°C) to determine their potential to release C to the atmosphere when thawed. Across all sites, CO2 with radiocarbon (14C) ages ranging between∼21 and 24 ka bp was respired when these permafrost soils were thawed. The amount of C released in the first several months was strongly correlated to C concentration in the bulk soil in the different sites, and this correlation remained the same for fluxes up to 1 year later. Fluxes were initially strongly related to temperature with a mean Q10 value of 1.9±0.3 across all sites, and later were unrelated to temperature but still correlated with bulk soil C concentration. Modeled inversions of Δ14CO2 values in respiration CO2 and soil C components revealed mean contribution of 70% and 26% from dissolved organic C to respiration CO2 in case of two permafrost soils, while organic matter fragments dominated respiration (mean 68%) from a surface mineral soil that served as modern reference sample. Our results suggest that if 10% of the total Siberian permafrost C pool was thawed to a temperature of 5°C, about 1 Pg C will be initially released from labile C pools, followed by respiration of∼40 Pg C to the atmosphere over a period of four decades. [ABSTRACT FROM AUTHOR]