Identification of Icelandic tephras from the last two millennia in the White Sea region (Vodoprovodnoe peat bog,northwestern Russia)

The generation of reliable age models for palaeoenvironmental and archaeological records in the Eurasian Arctic is often problematic when using conventional dating techniques. Tephrochronology can potentially improve the chronologies of such records and synchronise disparate sedimentary archives. However, to date, systematic tephra studies are lacking for this region. This paper presents the first cryptotephra data from the White Sea region (northwestern Russia) based on a peat core spanning the past ~1800 years. We identify seven geochemical glass populations that derive from six Icelandic volcanoes and correlate four of them to north European tephra isochrons; these include Askja ad 1875, the basaltic component of the ad 877 Landnám tephra, and tephras BTD-15 (c. ad 1750–1650) and SL-2/SB-2 (ad 803–767) from unknown eruptions of Katla and Snæfellsjökull, respectively. The remaining three populations originate from Grímsvötn, Hekla and Katla; however, their attribution to individual eruptions remains ambiguous. These findings highlight the potential to extend the Late Holocene tephrochronological framework of northern Europe to the west Eurasian Arctic. The detection of at least three basaltic tephras in the core suggests that basaltic shards can be transported over larger distances than previously known and that peatlands are well suited to preserve such components.     

Glacial landscape evolution in the Uummannaq region,West Greenland

The Uummannaq region is a mosaic of glacial landsystems, consistent with hypothesized landscape distribution resulting from variations in subglacial thermal regime. The region is dominated by selective linear erosion that has spatially and altitudinally partitioned the landscape. Low altitude areas are dominated by glacial scour and higher elevations are dominated by plateaux or mountain valley and cirque glaciers. The appearance and nature of each landscape type varies locally with altitude and latitude, as a function of bedrock geology and average glacial conditions. Selective linear erosion has been a primary control on landscape distribution throughout Uummannaq, leading to plateau formation and the growth of a coalescent fjord system in the Uummannaq region. This has allowed the development of the Uummannaq ice stream's (UIS) onset zone during glacial periods. Fjord development has been enhanced by a downstream change in geology to less‐resistant lithologies, increasing erosional efficiency and allowing a single glacial channel to develop, encouraging glacier convergence and the initiation of ice streaming. The landscape has been affected by several periods of regional uplift from 33 Ma to present, and has been subject to subsequent fluvial and glacial erosion. Uplift has removed surfaces from the impact of widespread warm‐based glaciation, leaving them as relict landsurfaces. The result of this is a regional altitude‐dependent continuum of glacial modification, with extreme differences in erosion between high and low elevation surfaces. This study indicates that processes of long‐term uplift, glacial erosion/protection and spatial variability in erosion intensity have produced a highly partitioned landscape.     

Recent hydrological behavior of the East African great lakes region inferred from GRACE,satellite altimetry and rainfall observations

We have jointly analysed space gravimetry data from the GRACE space mission, satellite altimetry data and precipitation over the East African Great Lakes region, in order to study the spatiotemporal variability of hydrological parameters (total water storage, lake water volume and rainfall). We find that terrestrial water storage (TWS) from GRACE and precipitation display a common mode of variability at interannual time scale, with a minimum in late 2005, followed by a rise in 2006–2007. We argue that this event is due to forcing by the strong 2006 Indian Ocean Dipole (IOD) on East African rainfall. We also show that GRACE TWS is linked to the El Niño-Southern Oscillation cycle. Combination of the altimetry-based lake water volume with TWS from GRACE over the lakes drainage basins allows estimating soil moisture and groundwater volume variations. Comparison with the WGHM hydrological model outputs is performed and discussed.     

朝鲜半岛的核试验时期

过去20年中, 北朝鲜在核不扩散问题的外交政策方面一直与西方国家争论不休. 迫于前苏联的压力, 北朝鲜于1985年勉强加入了1968年签订的《核武器不扩散条约》. 但是, 在加入该条约之后, 北朝鲜就停止了必须履行的谈判, 而且也没有令其与国际原子能机构（IAEA）签署的全面安全协议（CSA）生效. 该协议本应于1986年生效, 但直到1992年4月10日它才有了合法约束力. 同年, 国际原子能机构基于其在伊拉克的经验, 在核安全方面实施了新方法. 在原有系统下, 国际原子能机构采用了一种“材料审计”的方法, 该方法只是检查其所申报核材料的存货清单是否正确. 然而, 自1992年开始, 国际原子能机构对接受其检查的国家所申报内容的完备性也开展了评估工作.     

Towards an operational aqueous phase chemistry mechanism for regional chemistry-transport models: CAPRAM-RED and its application to the COSMO-MUSCAT model

Mechanism reductions of the detailed aqueous phase chemistry mechanism CAPRAM 3.0i are performed. Manual methods and automatic techniques are both applied in order to provide a less computationally intensive mechanism which is operational in regional chemistry transport models (CTMs). The finally reduced mechanism contains less than 200 reactions (4 times smaller than the detailed CAPRAM 3.0i) and describes the main characteristics of inorganic and organic aqueous phase processes occurring in tropospheric warm clouds. Most of the chemical reduction potential is realized in the CAPRAM 3.0i organic chemistry. The number of aqueous phase species decreases from 380 in the full mechanism to 130 in the final reduced version. The calculated percentage deviations between the full and reduced mechanism are on average below 5% for the most important organic and inorganic target compounds such as oxidants, inorganic and organic acids, carbonyls and alcohols. Comparisons of the required CPU times between the full and reduced mechanisms show reductions of approximately 40%. 2-D test simulations with the CTM MUSCAT were performed using prescribed meteorological conditions in order to examine the applicability of the reduced mechanism at regional scale. Simulations with the reduced CAPRAM 3.0i mechanism and a much less complex mechanism with only limited inorganic chemistry (INORG) were compared to evaluate the effects of more detailed chemistry. The model results show large differences in the level of oxidants and the inorganic and organic mass processing. Prospectively, the reduced mechanism represents the basis for studying aerosol cloud processing effects at regional scale with future CTMs and will allow more adequate interpretation of field data.     

Lithospheric structure and tectonics at Isidis Planitia, Mars

We characterize the lithospheric structure of Isidis Planitia on Mars by analyzing Mars Global Surveyor and Mars Odyssey gravity and topography data using a flexural model of a thin elastic shell including bending and membrane stresses. Isidis Planitia is a circular, relatively flat plain formed near the end of the Early Noachian, at the edge of the highlands-lowlands boundary and the site of a large free-air gravity anomaly, features consistent with modification and filling of an impact basin. Our results suggest that the bulk density of the fill material inside Isidis must be more than 2600 kg m⁻³ and higher densities are probable. A comparison of the faulting observed at Nili Fossae to the predicted zone of extensional strain northwest of Isidis constrains the thickness of the elastic lithosphere to be 100-180 km thick beneath the basin at the time of loading. We also find that loads outside of the basin play a significant role in the interpretation of the tectonics; simplified models tend to overestimate the lithospheric thickness. We place relatively narrow bounds on the thermal gradient (3.4-6.5 K km⁻¹) and heat flux (13.6-26 mW m⁻²) at Isidis at the time of loading.     

High-frequency fluctuations of surface temperatures in an urban environment

This study presents an attempt to resolve fluctuations in surface temperatures at scales of a few seconds to several minutes using time-sequential thermography (TST) from a ground-based platform. A scheme is presented to decompose a TST dataset into fluctuating, high-frequency, and long-term mean parts. To demonstrate the scheme’s application, a set of four TST runs (day/night, leaves-on/leaves-off) recorded from a 125-m-high platform above a complex urban environment in Berlin, Germany is used. Fluctuations in surface temperatures of different urban facets are measured and related to surface properties (material and form) and possible error sources. A number of relationships were found: (1) Surfaces with surface temperatures that were significantly different from air temperature experienced the highest fluctuations. (2) With increasing surface temperature above (below) air temperature, surface temperature fluctuations experienced a stronger negative (positive) skewness. (3) Surface materials with lower thermal admittance (lawns, leaves) showed higher fluctuations than surfaces with high thermal admittance (walls, roads). (4) Surface temperatures of emerged leaves fluctuate more compared to trees in a leaves-off situation. (5) In many cases, observed fluctuations were coherent across several neighboring pixels. The evidence from (1) to (5) suggests that atmospheric turbulence is a significant contributor to fluctuations. The study underlines the potential of using high-frequency thermal remote sensing in energy balance and turbulence studies at complex land–atmosphere interfaces.

     

Dynamics of decadal variability in the Atlantic subpolar gyre: a stochastically forced oscillator

Internal variability of the Atlantic subpolar gyre is investigated in a 600 years control simulation of a comprehensive coupled climate model. The subpolar gyre shows irregular oscillations of decadal time scale with most spectral power between 15 and 20 years. Positive and negative feedback mechanisms act successively on the circulation leading to an internal oscillation. This involves periodically enhanced deep convection in the subpolar gyre center and intermittently enhanced air-sea thermal coupling. As a result, anomalies of the large-scale atmospheric circulation can be transferred to the ocean on the ocean’s intrinsic time scale, exciting the oscillator stochastically. A detailed understanding of oscillatory mechanisms of the ocean and their sensitivity to atmospheric forcing holds considerable potential for decadal predictions as well as for the interpretation of proxy data records.     

A look at the ocean in the EC-Earth climate model

EC-Earth is a newly developed global climate system model. Its core components are the Integrated Forecast System (IFS) of the European Centre for Medium Range Weather Forecasts (ECMWF) as the atmosphere component and the Nucleus for European Modelling of the Ocean (NEMO) developed by Institute Pierre Simon Laplace (IPSL) as the ocean component. Both components are used with a horizontal resolution of roughly one degree. In this paper we describe the performance of NEMO in the coupled system by comparing model output with ocean observations. We concentrate on the surface ocean and mass transports. It appears that in general the model has a cold and fresh bias, but a much too warm Southern Ocean. While sea ice concentration and extent have realistic values, the ice tends to be too thick along the Siberian coast. Transports through important straits have realistic values, but generally are at the lower end of the range of observational estimates. Exceptions are very narrow straits (Gibraltar, Bering) which are too wide due to the limited resolution. Consequently the modelled transports through them are too high. The strength of the Atlantic meridional overturning circulation is also at the lower end of observational estimates. The interannual variability of key variables and correlations between them are realistic in size and pattern. This is especially true for the variability of surface temperature in the tropical Pacific (El Ni?o). Overall the ocean component of EC-Earth performs well and helps making EC-Earth a reliable climate model.