The 2011 expedition to the El'gygytgyn impact structure,Northeast Russia: Toward a new geological map for the crater area

El'gygytgyn is a 3.6 Ma, 18 km diameter, impact crater formed in an approximately 88 Ma old volcanic target in Northeast Siberia. The structure has been the subject of a recent ICDP drilling project. In parallel to those efforts, a Russian‐German expedition was undertaken in summer 2011 to investigate the permafrost soil, lake terraces, and the volcanic rocks of the southern and eastern crater rim. This provided the unique opportunity for mapping and sampling of the volcanic target rocks around a large part of this complex impact structure. Samples from 43 outcrops were collected and analyzed petrographically and geochemically. The results were combined with earlier mapping outcomes to create a new geological map of this impact structure and its immediate environs, at the scale of 1:50,000. Compositions of our rock suites are compared with the lithologies of the 2009 ICDP drill core. The ignimbrite described as lower bedrock in the ICDP drill core shows petrographically and chemically strong similarities to the rhyolitic and rhyodacitic ignimbrites observed on surface. The suevite sequence exposed in the ICDP drill core is a mixture of all observed target rocks at their respective proportions in the area. In contrast to previous studies, the calculated average target composition of El'gygytgyn takes the contribution of the basic target rocks into consideration: mafic and intermediate rocks approximately 7.5%, and felsic rocks approximately 92.5%.     

Inference for the truncated exponential distribution

The constructed estimator is introduced for the right truncation point of the truncated exponential distribution. The new estimator is most efficient in important ranges of truncation points for finite sample sizes. The introduced inverse mean squared error clearly indicates the good behaviour of the new estimator. The estimation of the scaling parameter is considered in all discussions and computations. The methods and models of the extreme value theory are not appropriate to estimate the truncation point because they work only in the case of very large sample sizes. Furthermore, a procedure for a first goodness-of-fit test is introduced. All this has been researched by extensive Monte Carlo simulations for different truncation points and sample sizes. Finally, the new inference methods are applied at the end for the random distribution of wildfire sizes and earthquake magnitudes.     

Middle to Late Pleistocene lake‐level fluctuations of Lake El'gygytgyn,far‐east Russian Arctic

Lake El'gygytgyn, located in central Chukotka, Russian Arctic, was the subject of an international drilling project that resulted in the recovery of the longest continuous palaeoclimatic and palaeoenvironmental record for the terrestrial Arctic covering the last 3.6 million years. Here, we present the reconstruction of the lake‐level fluctuations of Lake El'gygytgyn since Marine Isotope Stage (MIS) 7 based on lithological and palynological as well as chronological studies of shallow‐water sediment cores and subaerial lake terraces. Reconstructed lake levels show an abrupt rise during glacial–interglacial terminations (MIS 6/5 and MIS 2/1) and during the MIS 4/3 stadial–interstadial transition. The most prominent lowstands occurred during glacial periods associated with a permanent lake‐ice cover (namely MIS 6, MIS 4 and MIS 2). Major triggering mechanisms of the lake‐level fluctuations at Lake El'gygytgyn are predominantly changes in air temperature and precipitation. Regional summer temperatures control the volume of meltwater supply as well as the duration of the lake‐ice cover (permanent or seasonal). The duration of the lake‐ice cover, in turn, enables or hampers near‐shore sediment transport, thus leading to long‐term lake‐level oscillations on glacial–interglacial time scales by blocking or opening the lake outflow, respectively. During periods of seasonal ice cover the lake level was additionally influenced by changes in precipitation. The discovered mechanism of climatologically driven level fluctuations of Lake El'gygytgyn are probably valid for large hydrologically open lakes in the Arctic in general, thus helping to understand arctic palaeohydrology and providing missing information for climate modelling.     

Treatment of frozen soil and snow cover in the land surface model SEWAB

Summary  The land surface model SEWAB (Surface Energy and Water Balance) is designed to be coupled to both, atmospheric and hydrological models. Its application in mid and high latitudes requires the inclusion of freezing and thawing processes within the soil and the accumulation and ablation of a snow cover. These winter processes are parameterised with a minimum number of empirical formulations in order to assure reasonable computation times for an application in climate and sensitivity studies yet accounting for all important processes. Meteorological forcing data and measurements of snow depth, soil temperature and liquid soil water content at two locations in the mid-west of North America are used to test the model. Generally the simulated snow depth matches the measurements, remaining differences in snow depth can be explained by uncertainties in snow density, blowing snow and errors in precipitation measurements. The simulated soil temperature and liquid soil water content compare well with the measurements, showing the isolating effect of the snow cover. Received August 25, 2000 Revised January 19, 2001     

Short-wave radiation flux divergence in arctic cirrus: a case study

Radiation and particle measurements have been performed with an aircraft in deep cirrus cloud fields near the island of Svalbard. The data of 12 March 1993, when measurements at 10 different levels could be obtained, are used in a comparative study with radiative transfer calculations. In a first analysis, the cirrus cloud field was assumed to be horizontally homogeneous and invariable during the time of measurements (frozen properties). Calculations of the up and downward radiative flux densities showed root mean square differences of 9 Wm⁻² from the measurements. To estimate the possible effect of changes of the optical properties of cirrus with time, the flux densities in the upper part (6000–8500 m) and the lower part (3000–5500 m) of the cirrus cloud were analyzed separately. In these simulations, the optical thickness in the lower (upper) part was increased (decreased) by 50%. By this treatment, most of all calculated flux densities were within one standard deviation of the natural variability in each leg. Finally, the effect of inhomogeneities in the cloud field on the solar flux density has been simulated using a Monte Carlo method, since the upper part of the cirrus field has indeed been very inhomogeneous. This paper is a result of a collaborative effort between the MRI in Tsukuba, Japan, and the GKSS in Geesthacht, Germany.     

Endolithische Wurm-Tunnelbauten (Lapispecus cuniculus n. g. n. sp. undDodecaceria [?] sp.) in Brandungsgeröllen der oberen Kreide im nördlichen Harzvorlande

The well known Santonian conglomerates from the area north of the Harz Mountains contain holes due to leached dolomitic pebbles of Kimmeridgian age, in which well preserved casts of “worm”-burrows have been observed. In smaller pebbles - caused by the lack of space — they were burrowed in narrow windings resembling the Serpulid genusGlomerula. However, their mode of winding differs from that of these Serpulids: The convex arches made by the boring organism must be regarded as a behavioural response when approaching the surface of the pebbles. In the loops of the burrows often a “Spreite” is found, but it is also observed in the convex windings and even parallel to the straight cylindrical burrows. That is in contradiction to the conventional definition of the “Spreite”. The burrows which may belong to the Polychaetes are described asLapispecus cuniculus n. g. n. sp. Other rare burrows have been identified asDodecaceria (?) sp.     

Zur Temperatur-Kurve der Oberen kreide in Europa

Zusammenfassung Wenn die auf Grund der¹⁶O¹⁶O-Methode konstruierte Temperatur-Kurve des Oberkreidemeeres (Lowenstam &Epstein 1954,Bowen 1961) richtig ist, welche für die Zeit des Coniac-Santon ein Wärmeoptimum gegenüber niedrigeren Temperaturen im Cenoman und Obermaastricht verzeichnet, so wäre zu erwarten, da\ diese Klimaveränderung auch in der Faunenzusammensetzung der einzelnen Oberkreidestufen deutlich zum Ausdruck kommt. Das ist merkwürdigerweise nicht oder kaum der Fall, wie aus der Verbreitung der mediterranen Faunenelemente in der borealen bzw. zentraleuropäischen Faunenprovinz hervorgeht. Gro\foraminiferen, Riffkorallen, Rudisten und andere Warmwasserformen zeigen zahlenmä\ig ihre grö\te Verbreitung au\erhalb der Tethys im Cenoman und im Obermaastricht. Die Globotruncanen-Verbreitung ergibt kein einheitliches Bild; doch ist die bisherige Vorstellung von einem allmählichen Rückzug der Globotruncanen (s. l.) nach Süden vom Coniac-Santon bis zum Obermaastricht zu revidieren. Die Aufgabe der vorliegenden Arbeit besteht in der Diskussion der sich aus der geochemischen und ökologisch-faunistischen Arbeitsweise ergebenden Resultate, die z. T. erheblich voneinander abweichen. Es ist zu hoffen, da\ es gelingt, die z. Z. noch bestehenden Widersprüche zu klären und sowohl die für die Paläoklimatologie so aussichtsreiche Isotopenmethode als auch die tiergeographisch-ökologische Arbeitsweise weiter zu vervollkommnen.Da mit einer späteren Umkristallisation auch der Belemnitenrostren, auf denen die erwähnten Temperaturmessungen beruhen, zu rechnen sein dürfte, wären neue Untersuchungen unter Berücksichtigung dieser Möglichkeit sehr wünschenswert.

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Summary The curve constructed for the temperatures of the Upper Cretaceous seas (Lowenstam &Epstein 1954,Bowen 1961) based on the¹⁶O¹⁸O ratios shows a temperature optimum in Coniacian-Santonian time, but lower temperatures in Cenomanian and Upper Maastrichtian time. These climatic changes ought to be visible in the faunistic composition within the different stages of the Upper Cretaceous too. Strangely, however, judging from the distribution of mediterranean faunal elements in the boreal and central european faunal provinces respectively, this seems not to be the case. Larger foraminifera, reef corals, rudistids, and other inhabitants of warm water are most widespread outside of the Tethys during Cenomanian and Upper Maastrichtian time. The distribution of Globotruncana gives no uniform picture, but the former conception of their gradual retreat towards the south from Coniacian-Santonian to Upper Maastrichtian time must be revised. The author discusses the results obtained by geochemical and by ecological-faunistical methods, which in part are at considerable variance. Hope is expressed that the present inconsistencies will be cleared up and that both methods will still further be improved that based on animal geography and ecology as well as the isotope method which is so very promising for paleoclimatology.The above-mentioned temperature measurements have been obtained from rostra of belemnoids. New investigations ought to make allowance for the probability of their having been recrystallized

     

The Baltic Sea Experiment BALTEX: A brief overview and some selected results of the authors

The mechanisms responsible for the transfer of energy and water within the climate system are under worldwide investigation within the framework of the Global Energy and Water Cycle Experiment (GEWEX) to improve the predictability of natural and man-made climate changes at short and long ranges and their impact on water resources. Five continental-scale experiments have been established within GEWEX to enable a more complete coupling between atmospheric and hydrological models. One of them is the Baltic Sea Experiment (BALTEX).In this paper, the goals and structure of BALTEX are outlined. A short overview of measuring and modelling strategies is given. Atmospheric and hydrological model results of the authors only are presented. These include also the validation of precipitation using station measurements as well as validation of modelled cloud cover with cloud estimates from satellite data. Furthermore, results of a large-scale grid based hydrological model to be coupled to atmospheric models are presented.This research has never been possible without the contribution of research groups and operational institutions from all 10 member countries. We concentrate here on results obtained at the GKSS research center.