Slow Senonian and fast Palaeocene–Early Eocene uplift of the granitoids in the Central Eastern Pontides, Turkey: apatite fission-track results

Dating and forward modelling of the fission-track data of apatite samples from the Dereli– ebinkarahisar region, south of Giresun in the Eastern Turkish Pontides, provides quantitative data on the regional tectonics resulting from the closure of neo-Thetys and the collision of Eurasia and Gondwana. The age vs. elevation profiles identified Senonian (80.7±3.2 to 62.4±2.5 Ma) slow uplift and denudation, interpreted as the result of the diapiric ascent of subduction-related plutons above the neo-Tethyan subduction zone beneath the Eurasian continent. This was followed by rapid differential uplift during the Palaeocene–Early Eocene (57.4±2.4 to 47.8±2.4 Ma), which juxtaposed granitoid units of different ages, compositions, and emplacement levels in the crust, and is thought to be related to the collision between the Pontide (Eurasian) and Anatolide (Gondwana) basements. The modelling results must be interpreted with caution, but appear to indicate a period of Mio-Pliocene (ca. 5 Ma) reheating related to volcanism associated with the westward escape of the Anatolian plate and uplift from the Pliocene (ca. 3.5 Ma) up to the present.     

Crustal structure of the ancestral northwestern California forearc region from seismic reflection imaging: implications for convergent margin tectonics

Analysis of a suite of 2-D seismic reflection profiles reveals that the northwestern Sacramento Valley and eastern Coast Range foothills, northern California, are underlain by a system of blind, west-dipping thrust faults. Homoclinally east-dipping and folded Mesozoic marine forearc strata exposed along the western valley margin define the forelimbs of northeast-vergent fault-propagation folds developed in the hanging walls of the thrusts. Exhumed coherent blueschists of the accretionary complex and attenuated remnants of the ophiolitic forearc basement presently exposed in the eastern Coast Ranges are in the hanging wall of the blind thrust system, and have been displaced from their roots in the footwall. Deep, east-dipping magnetic reflectors in the footwall of the thrust system may be fragments of sheared, serpentinized and attenuated ophiolitic basement. Restoration of slip on the thrusts suggests that the Coast Range fault, which is the exposed structural contact between the coherent blueschists and attenuated ophiolite, originally dipped east and is associated with the east-dipping magnetic reflectors in the footwall. This interpretation of the reflection data is consistent with previous inferences about the deep structure in this region, and supports a two-stage model for blueschist exposure in the eastern Coast Ranges: (1) blueschist exhumation relative to the forearc basin by attenuation of the ophiolitic basement along the east-dipping Coast Range fault system in late Cretaceous; (2) blueschists, attenuated ophiolite, and forearc strata all were subsequently uplifted and folded in the hanging wall of the blind thrust system beginning in latest Cretaceous–early Tertiary. The blind thrust system probably rooted in, and was antithetic to, the east-dipping subduction zone beneath the forearc region. Active transpressional plate motion in western California is locally accommodated, in part, by reactivation of blind thrust faults that originally developed during the convergent regime.     

European winter temperature variability in a long coupled model simulation: the contribution of ocean dynamics

The interannual variability of the European winter air temperature is partially caused by anomalous atmospheric circulation and the associated advection of air masses, mainly linked to the North Atlantic Oscillation (NAO). However, a considerable part of the temperature variability is not linearly described by atmospheric circulation anomalies. Here, a long control simulation with a coupled atmosphere-ocean climate model is analyzed, with the goal of decomposing the European temperature (ET) anomalies in a part linked to the anomalous atmospheric circulation and a residual. The amount of interannual variability of each contribution is roughly 50%, although at subdecadal (overdecadal) time scales the variability of the residuals is dominant. These residuals are found to be linked to temperature anomalies of the same sign in the whole North Atlantic and Greenland, in contrast to the well-known temperature zonal seesaw associated with the NAO. The association between the residuals and other processes in the North Atlantic has been also analyzed. The thermohaline circulation, closely connected in the model to the intensity of the Gulf Stream, lags the evolution of the temperature residuals by several years and thus is not able to control their evolution. The variability of the oceanic convection in the Northern North Atlantic, on the other hand, correlates with the temperature residual at lags close to zero. It is hypothesized that oceanic convection produces a sea-surface temperature fingerprint that leads to the ET residuals. The implications of these results for multi-year predictability and for empirical climate reconstructions are discussed.     

Dune sand transport as influenced by wind directions, speed and frequencies in the Ordos Plateau, China

The Ordos Plateau in China is a region with extensive wind erosion, severe desertification and various aeolian sand hazards. In order to determine aeolian sand transport in this region, the relationship between the sand transport rate and wind speed at 10 min frequencies was established by field observation in both the Qubqi Sand Desert and the Mu Us Sandy Land. Threshold wind speeds (2 m above the ground) for mobile, semi-fixed and fixed dune surfaces were estimated by field observations. The sand transport rate increased with the increase of the bare land ratio and near-bed wind speed. High-resolution meteorological 10 min average wind velocity data at 10 m above the ground were converted into velocity values at a height of 2 m to calculate sand transport potential based on three specific parameters decisive for sand transport: wind speed, duration and direction. The quantity of aeolian sand transported was calculated for various wind speed levels and directions, and the overall characteristics of sand transport on different dune surface types were determined by vector operation techniques. Sand transporting winds took place mainly in springtime. The prevailing wind directions were W, WNW and NW, with a frequency of more than 60% in total, and sand transport in these directions made up more than 70% of the total transport, corresponding to a general southeastward encroachment of aeolian sand in the study area. The relationship between wind frequency and speed can be expressed by a power function. High magnitude strong winds had a low frequency, but they played a dominant role in aeolian sand transport.     

Constructed wetland technology and mosquito populations in Arizona

Constructed wetlands and other aquatic habitat creation or restoration efforts offer both potential benefits and problems for arid areas. An unintentional consequence of these efforts has been the potential for an increase in local adult mosquito populations. Shallow water-emergent plant zones may provide ideal conditions for mosquito larval growth, and areas of high humidity, dense vegetation, and abundant birds and other wildlife may provide ideal conditions for adult mosquitoes. Three constructed wetlands in southern Arizona were studied over a period of years before and after they were constructed and operational. Mosquito populations were sampled using a variety of methods, primarily trapping of adults with CO₂-baited traps. Populations apparently increased, sometimes by several orders of magnitude, after wetlands became operational. Several methods of mosquito abatement were initiated and their results are discussed. However, no definitive conclusions can be drawn because no untreated areas were available for comparison and many factors that may have affected mosquito populations also changed. Based on the experience gained at these three sites, mosquito control is an especially important design and management component for constructed wetlands in arid environments with low background populations of mosquitoes.     

Late Pleistocene and Holocene history of Lake Terrasovoje,Amery Oasis,East Antarctica,and its climatic and environmental implications

A 5.52 m long sediment sequence was recovered from Lake Terrasovoje, Amery Oasis, East Antarctica, in order to reconstruct the regional environmental history. The basal sediments, which are dominated by glacial and glaciofluvial clastic sediments, attest to a Late Pleistocene deglaciation of the lake basin. These sediments are overlain by 2.70 m of laminated algal and microbial mats and a few interspersed moss layers. Radiocarbon dating, conducted on bulk organic carbon of 12 samples throughout the organic sequence, provides a reliable chronology since the onset of biogenic accumulation at c. 12,400 cal. year BP. Successful diatom colonization, however, was probably hampered by extensive ice and snow cover on the lake and restricted input of nutrients until 10,200 cal. year BP. A subsequent increase of nutrient supply culminated between 8600 and 8200 cal. year BP and is related to warm summer temperatures and reduced albedo in the catchment. Warm conditions lasted until 6700 cal. year BP, supporting the establishment of a diatom community. Colder temperatures from 6700 cal. year BP culminated in several periods between 6200 and 3700 cal. year BP, when high amounts of sulphur and low abundances of diatoms were deposited due to a perennial ice and snow cover on the lake. During the late Holocene, relatively warm conditions between 3200 and 2300 cal. year BP and between 1500 to 1000 cal. year BP, respectively, indicated by high accumulation of organic matter and reducing bottom water conditions, were interrupted and followed by colder periods.     

GNSS/INS integration: still an attractive candidate for automatic landing systems?

During the last years, the International Symposia on Precision Approach and Automatic Landing (ISPA) have shown a considerable change in the significance of integrated landing systems. At the first ISPA conference in 1995, the combination of inertial sensors and GNSS receivers was thoroughly discussed and appeared to be a very promising concept, especially with respect to ‘Integrity’ and ‘Continuity’. Ever since, this particular combination of sensors has received little attention. A comprehensive discussion of the technical background of this setback for integrated landing systems did not take place, primarily because of the popular opinion that the Kalman filter algorithm, which is the system integration kernel, is not sufficiently stable. The true reason has meanwhile been identified. The aiding of an inertial navigation system by only one GNSS antenna is insufficient in phases of low aircraft dynamics such as in the case of final approach. Instead, a multi-antenna system is required with antennas widely distributed over the aircraft structure. This latter approach, however, causes problems due to structural flexibilities. To show that an integrated system based on inertial sensors and widely distributed GNSS antennas is technically feasible, the paper discusses the following topics. (1) Unstable system performance during final approach for 1-antenna-aiding. (2) Improving the system performance prior to using additional antennas. (3) Effect of the antenna distribution. (4) Integrated systems for distributed sensors and flexible aircraft structures. The paper shows that integrated systems are still an attractive candidate for automatic landing equipment preserving the advantages with respect to ‘Integrity’ and ‘Continuity’.     

Drought 2002 in Colorado: An Unprecedented Drought or a Routine Drought?

The 2002 drought in Colorado was reported by the media and by public figures, and even by a national drought-monitoring agency, as an exceptionally severe drought. In this paper we examine evidence for this claim. Our study shows that, while the impacts of water shortages were exceptional everywhere, the observed precipitation deficit was less than extreme over a good fraction of the state. A likely explanation of this discrepancy is the imbalance between water supply and water demand over time. For a given level of water supply, water shortages become intensified as water demands increase over time. The sobering conclusion is that Colorado is more vulnerable to drought today than under similar precipitation deficits in the past.     

New strategies to detect life on Mars

If we are to find unequivocal evidence for life on Mars, we will need new ways to search for it. Jeff L Bada and the MOD team describe the innovative strategy developed for the ExoMars mission.     

Paleoshoreline geomorphology of Böön Tsagaan Nuur, Tsagaan Nuur and Orog Nuur: the Valley of Lakes, Mongolia

We conducted a preliminary study of paleoshoreline features associated with Böön Tsagaan Nuur, Tsagaan Nuur, and Orog Nuur, lakes located in the Gobi–Altai transition zone of the Valley of Lakes (Dolina Ozor) which stretches from central to western Mongolia. The paleoshoreline features were first identified on RADARSAT satellite SAR imagery. We investigated the features during the 1998 field season of the Joint Mongolian–Russian–American Archaeological Expedition to the Gobi–Altai region. We identified paleoshorelines of multiple elevations in the field, which are considered to be relict beach ridges and wave-cut terraces. Other paleolake landforms include spits and Gilbert-type deltas. These landforms are complex, large and well established, implying that the paleolakes were stable for extended periods. The reconstructed paleolakes cover extensive areas of the valley floor, implying that hydrological and climatic conditions were very different in the past. Paleolake expansions may have occurred under a variety of circumstances. One hypothesis is that the high lake stands occurred during the wetter period corresponding to the Oxygen Isotope Stage 3 prior to the Last Glacial Maximum (LGM), during the warmest early Holocene and the late Holocene, or during all these periods. If low evaporation rates due to lower temperatures, glacier meltwater and possibly increased precipitation are important factors, then the expansions may have occurred during the terminal Late Glacial period after the Last Glacial Maximum. The greatly expanded lakes in the Gobi–Altai could have significantly affected the Quaternary human demography and migration in the region.