Northeast Siberian ice wedges confirm Arctic winter warming over the past two millennia

Arctic climate has experienced major changes over the past millennia that are not fully understood in terms of their controls and seasonality. Stable-data from ice wedges in permafrost provide unique information on past winter climate. Recently, an ice-wedge record from the Lena River Delta suggested for the first time that Siberian winter temperatures increased throughout the Holocene, contradicting most other Arctic paleoclimate reconstructions which are likely biased towards the summer. However, the representativeness of this single record and the spatial extent of its reconstructed winter warming signal is unclear. Here, we present a new winter temperature record based on paired stable oxygen (δ18O) and radiocarbon age data spanning the last two millennia from the Oyogos Yar coast in northeast Siberia. The record confirms the long-term winter warming signal as well as the unprecedented temperature rise in recent decades. This confirmation demonstrates that winter warming over the last millennia is a coherent feature in the northeastern Siberian Arctic, supporting the hypothesis of an insolation-driven seasonal Holocene temperature evolution followed by a strong warming likely related to anthropogenic forcing

10Be in the Akademii Nauk ice core – first results for CE 1590-1950 and implications for future chronology validation

Temporal variations of the radionuclide 10Be are broadly synchronous across the globe and thus provide a powerful tool to synchronize ice core chronologies from different locations. We compared the 10Be record of the Akademii Nauk (AN) ice core (Russian Arctic) for the time period CE 1590–1950 to the 10Be records of two well-dated Greenland ice cores (Dye3 and NGRIP). A high correlation (r = 0.59) was found between the AN and Dye3 records whereas the correlation with NGRIP was distinctly lower (r = 0.45). Sources of deviations may include local fluctuations in the deposition of 10Be due to changes in the precipitation patterns, and artefacts due to the core-sampling strategy. In general, the existing age model was validated, confirming the AN ice core to be a unique and well-dated source of palaeoclimate parameters for the Russian Arctic. We further used numerical simulations to test the influence of the core-sampling strategy on the results and derived an optimized sampling strategy for the deeper parts of the ice core

Magnetic excitations and amplitude fluctuations in insulating cuprates

We present results from light scattering experiments on three insulating antiferromagnetic cuprates, YBa$_2$Cu$_3$O$_{6.05}$, Bi$_2$Sr$_2$YCu$_2$O$_{8+\delta}$, and La$_2$CuO$_4$ as a function of polarization and excitation energy {using samples of the latest generation. From the raw data we derive symmetry-resolved spectra.} The spectral shape in $B_{1g}$ symmetry is found to be nearly universal and independent of the excitation energy. The spectra agree quantitatively with predictions by field theory [\onlinecite{Weidinger:2015}] facilitating the precise extraction of the Heisenberg coupling $J$. {In addition, the asymmetric line shape on the high-energy side is found to be related to amplitude fluctuations of the magnetization. In La$_2$CuO$_4$ alone minor contributions from resonance effects may be identified.} The spectra in the other symmetries are not universal. The variations may be traced back to weak resonance effects and extrinsic contributions. For all three compounds we find support for the existence of chiral excitations appearing as a continuum in $A_{2g}$ symmetry having an onset slightly below $3J$. In La$_2$CuO$_4$ an additional isolated excitation appears on top of the $A_{2g}$ continuum.Comment: 8 pages, 7 figure

Observing Muostakh Island disappear: erosion of a ground-ice-rich coast in response to summer warming and sea ice reduction on the East Siberian shelf

Observations of coastline retreat using contemporary very high resolution satellite and historical aerial imagery were compared to measurements of open water fractions and summer air temperatures. We analyzed seasonal and interannual variations of thawing-induced cliff top retreat (thermo-denudation) and marine abrasion (thermo-abrasion) on Muostakh Island in the southern central Laptev Sea. The island is composed of ground-ice-rich permafrost deposits of Ice Complex type that render it particularly susceptible to erosion along the coast, resulting in land loss. Based on topographic reference measurements during field campaigns, we generated digital elevation models using stereophotogrammetry, in order to block adjust and ortho-rectify aerial photographies from 1951 and GeoEye, QuickBird, WorldView-1, and WorldView-2 imagery from 2010 to 2012 for change detection. Coastline retreat for erosive segments ranged from −13 to −585 m and was −109 ± 81 m (–1.8 ± 1.3 m a−1) on average during the historical period. Current seasonal dynamics of cliff top retreat revealed rapid thermo-denudation rates of –10.2 ± 4.5 m a−1 in mid summer and –4.1 ± 2.0 m a−1 on average during the 2010–2012 observation period. Using sea ice concentration data from the Special Sensor Microwave Imager (SSM/I) and air temperature time series from Tiksi, we calculated seasonal duration available for thermo-abrasion, expressed as open water days, and for thermo-denudation, based on thawing degree days. Geomorphometric analysis revealed that total ground ice content on Muostakh is made up of equal amounts of intrasedimentary and macro ground ice, while its vertical hourglass distribution provides favorable local preconditions for subsidence and the acceleration of coastal thermo-erosion under intensifying environmental forcings. Our results showed a~close relationship between mean summer air temperature and coastal thermo-erosion rates, in agreement with observations made for various permafrost coastlines different from East Siberian Ice Complex coasts elsewhere in the Arctic. Seasonality and recent interannual variations of coastline retreat rates suggest that the combination of macro ground ice distribution in the ground and changes in enviromental forcing generate a cyclicity in coastal thermo-erosion, that is currently increasing in frequency

Permafrost hydrology in changing climatic conditions: seasonal variability of stable isotope composition in rivers in discontinuous permafrost

Role of changing climatic conditions on permafrost degradation and hydrology was investigated in the transition zone between the tundra and forest ecotones at the boundary of continuous and discontinuous permafrost of the lower Yenisei River. Three watersheds of various sizes were chosen to represent the characteristics of the regional landscape conditions. Samples of river flow, precipitation, snow cover, and permafrost ground ice were collected over the watersheds to determine isotopic composition of potential sources of water in a river flow over a two year period. Increases in air temperature over the last forty years have resulted in permafrost degradation and a decrease in the seasonal frost which is evident from soil temperature measurements, permafrost and active-layer monitoring, and analysis of satellite imagery. The lowering of the permafrost table has led to an increased storage capacity of permafrost affected soils and a higher contribution of ground water to river discharge during winter months. A progressive decrease in the thickness of the layer of seasonal freezing allows more water storage and pathways for water during the winter low period making winter discharge dependent on the timing and amount of late summer precipitation. There is a substantial seasonal variability of stable isotopic composition of river flow. Spring flooding corresponds to the isotopic composition of snow cover prior to the snowmelt. Isotopic composition of river flow during the summer period follows the variability of precipitation in smaller creeks, while the water flow of larger watersheds is influenced by the secondary evaporation of water temporarily stored in thermokarst lakes and bogs. Late summer precipitation determines the isotopic composition of texture ice within the active layer in tundra landscapes and the seasonal freezing layer in forested landscapes as well as the composition of the water flow during winter months

Ice-wedge stable isotopes at the Dmitry Laptev Strait (Northeast Siberian Arctic) – indications for Late Quaternary stratigraphy and paleoclimate

Ice wedges are the most abundant type of ground ice in the ice-rich permafrost deposits of the Northeast Siberian Arctic. They are formed by the periodic repetition of frost cracking and subsequent crack filling and refreezing in spring, mostly by melt water of winter snow. Ice wedges can be studied by means of stable-water isotopes. Their isotopic composition is directly linked to atmospheric precipitation (i.e. winter snow) and, therefore, indicative of past climate conditions during the cold season even though also genetic aspects, i.e. sublimation, melting and refreezing in the snowpack and the frost crack, have to be taken into account. In this contribution we present stable-water isotope data of ice wedges from the Oyogos Yar coast of the Dmitry Laptev Strait (72.7°N, 143.5°E). Ice wedges and surrounding sediments were studied and sampled in 2002 and 2007. Ice-wedge stable-water isotopes were analyzed in the stable-isotope lab of the Alfred Wegener Institute in Potsdam, Germany. Sediments and ice wedges were dated using (a) OSL dating, (b) 36Cl/Cl dating (Blinov et al., 2009), (c) radiocarbon dating as well as (d) stratigraphic correlation based on ice-wedge stable isotopes. Based on our chronology the studied ice wedges correspond to different stratigraphic units of the Late Quaternary. These are (1) an Ice Complex of MIS5 age (Wetterich et al., in press), (2) Early Weichselian (MIS4 to MIS3) flood plain deposits, (3) the Middle Weichselian Yedoma Ice Complex of MIS3 age and (d) Holocene themokarst deposits (Opel et al., 2011). Ice wedge stable-water isotope data indicate substantial variations in Northeast Siberian Arctic winter climate conditions (δ18O) as well as shifts in the moisture generation and transport patterns (d excess) during the Late Quaternary, in particular between Glacial and Interglacial but also over the last centuries. An ice wedge of the MIS5 Ice Complex exhibits mean δ18O and d excess values of -33‰ and 7‰, respectively, representing very cold winter temperatures. Small multi-stage ice wedges corresponding to the MIS4 to MIS3 flood plain deposits showed two clusters of isotope values: (1) in their lower parts, i.e. composite sand-ice wedges or “polosatics”, δ18O values of -31 to -28‰ (d excess of 0-5‰) and (2) in their upper parts (classical ice wedge) δ18O values of -34‰ (d excess of 5‰), reflecting rather different formation conditions than climate differences under very cold climate conditions. The huge syngenetic ice wedges of the Weichselian Yedoma Ice Complex (MIS3) are characterized by mean δ18O values of -33‰ to -29‰ and mean d-excess values between 4 and 8‰ corresponding to different altitude levels and reflecting cold to very cold winter temperatures. On top of the Ice Complex as well as in a thermokarst depression of Late Glacial origin, Holocene ice wedges could be found. They have been grown predominantly in the Middle to Late Holocene and exhibit mean δ18O values of about -25‰ and mean d-excess values of 8‰, mirroring distinctly warmer winter temperatures in the Holocene. Recently grown (modern) ice wedges of the last decades are characterized by mean δ18O values of about -21‰ and mean d excess values of 8‰, testifying the recent winter warming in the Arctic. Blinov A, Alfimov V, Beer J, Gilichinsky D, Schirrmeister L, Kholodov A, Nikolskiy P, Opel T, Tikhomirov D, Wetterich S. 2009. Ratio of 36Cl/Cl in ground ice of east Siberia and its application for chronometry. Geochemistry Geophysics Geosystems 10, Q0AA03. Opel T, Dereviagin AY, Meyer H, Schirrmeister L, Wetterich S, 2011. Palaeoclimatic Information from Stable Water Isotopes of Holocene Ice Wedges on the Dmitrii Laptev Strait, Northeast Siberia, Russia. Permafrost and Periglacial Processes 22, 84-100. Wetterich S, Tumskoy V, Rudaya N, Kuznetsov V, Maksimov F, Opel T, Meyer H, Andreev AA, Schirrmeister L, in press. Ice Complex permafrost of MIS5 age in the Dmitry Laptev Strait coastal region (East Siberian Arctic). Quaternary Science Reviews

The Akademii Nauk ice core and solar activity

Ice cores are well established archives for paleo-environmental studies, but this requires a reliable ice core chronology. The concentration of cosmogenic radionuclides in ice cores reflects the solar activity in the past and can be used as dating tool for ice cores. Accelerator mass spectrometry (AMS) allows the determination of nuclides in high resolution. Here we present results of a 10Be study in an ice core from Akademii Nauk (Severnaya Zemlya, Russian Arctic). AMS analyses of more than 500 samples were carried out using the 6 MV accelerator facility of the Ion Beam Centre of the Helmholtz-Zentrum Dresden-Rossendorf. For the time period 400 to 2000 CE the temporal variations of 10Be reflect the centennial variations of solar activity known from similar studies of Greenlandic ice cores and from 14C production reconstructions. The 10Be peak of 775 CE, today understood as result of the strongest known solar particle storm, was found by high resolution core analysis. This peak is used as tie point (additionally to volcanic reference horizons) for the development of the depth-age relationship of the Akademii Nauk ice core. Indications of the so called “Carrington Event” of 1859 CE, 20 to 30 times weaker than 775 CE, could also be detected in the core