Fen ecosystem responses to water‐level fluctuations during the early and middle Holocene in central Europe: a case study from Wilczków,Poland

This paper presents a palaeoenvironmental reconstruction of the Wilczków fen (central Poland). The fen developed in an inactive valley at the onset of the Holocene (~11 ka BP) and peat accumulation lasted until 5.7 ka BP. Multi‐proxy reconstructions were made on the basis of palaeobotanical, cladoceran, chironomid, beetle and geochemical analyses. A Kohonen self‐organizing map (SOM, unsupervised artificial neural network) of the biotic sequence distinguished four stages of fen history. Stage X₁ (11.0–10.7 ka BP) was relatively wet and cool. Organic matter started to accumulate but the habitat conditions remained unstable. Moss, sedge and fern communities then developed. Sedimentary changes reveal an intensive groundwater supply at that time. Numerous and diverse chironomid and cladoceran subfossils indicate nearly permanent aquatic conditions. During stage Y₁ (10.6–9.2 ka BP) conditions were dry and the upper peat layer desiccated. Cladocera nearly disappeared whereas chironomids were represented by semi‐terrestrial and predatory (Tanypodinae) species. Conditions started to be more reducing. All the remaining samples belonged to the interweaving stages X₂ and Y₂. Stage Y₂ (mostly 9.1–7.3 and 6.0–5.7 ka BP) was also dry but humidity increased towards the top. Oxidizing conditions occurred and the pH became more alkaline, favouring Cladium mariscus. The basin received mostly allochthonous matter input at that time. Stage X₂ (mostly 6.8–6.1 ka BP) was humid and warm. The groundwater supply remained low but there was an increase in precipitation, changing local conditions to ombrotrophic. Species‐rich chironomid and cladoceran communities were associated with temporary pools. Finally, conditions returned to those characteristic of stage Y₂. The presented reconstruction documents long‐term abiotic and biotic changes determined by water supply, including groundwater outflow, which have rarely been detected at a multi‐proxy scale. We show that inactivated valley fens are sensitive to climate‐driven hydrological fluctuations. Kohonen neural networks appear to be a promising method for analysing variability in multi‐proxy data.     

Isotopic fingerprints of Milankovitch cycles in Pennsylvanian carbonate platform‐top deposits: the Valdorria record,Northern Spain

Sedimentary cyclic sequences deposited during the Late Palaeozoic Ice Age are widespread. Glacio‐eustatic control of the cyclic patterns is commonly accepted, and the durations of the cyclothems generally match the short‐ and long‐eccentricity Milankovitch orbital parameters. Nevertheless, geochemical fingerprints of orbital parameters are poorly documented in deep‐time sedimentary records. Here, we report on well‐exposed Bashkirian cyclothems of c. 123 ka and c. 400 ka durations from the Valdorria platform. The shorter‐term cyclothems can be grouped into longer‐term composite sequences that are consistent with generally accepted durations of c. 125 ka and c. 400 ka for Milankovitch eccentricity cycles. The stratigraphic pattern is mirrored by the isotope geochemical signals, which show distinct recurring trends. These trends are confirmed by statistical tests. Whereas intrinsic factors and/or subaerial exposure related to sea‐level lowstands might have truncated cycle patterns in tectonically stable basins, rapid subsidence of the Valdorria platform's foreland basin appears to have contributed to a faithful recording of cyclothems of different orders. The patterns and biostratigraphic constraint revealed in this study demonstrate the power of orbital forcing in imprinting sedimentary and geochemical signals in the rock record.     

Ensemble reconstruction of the atmospheric column from surface pressure using analogues

We present a statistical method to reconstruct continuous atmospheric fields on various pressure levels, given a constraint at the surface. The method is based on analogues of circulation and taking into consideration the time sequence of the analogues. The method is tested on the 2001–2011 period, with an emphasis on the year 2010. We base the atmospheric reconstruction on reanalysis data from 1948 to 2000, and use a constraint of sea-level pressure for 2001–2011. The pattern correlation scores appear to be significant most of the time, although score flaws are occasionally detected. Those flaws are mainly due to the time continuity constraint that is imposed on the reconstruction, which lowers the possibility of finding matching analogues. This method offers an ensemble of atmospheric reconstructions, and presents a computationally cheap alternative to data assimilation for a climate model, although with lower scores.     

Land use change scenarios and associated groundwater impacts in a protected peri-urban area

Land use changes in peri-urban areas are usually associated with significant impacts on groundwater resources due to alteration of the recharge regime as well as through the establishment of pollution sources. Quantifying the aforementioned impacts and assessing the vulnerability of the groundwater resources is an important step for the better management and protection of the aquifers. In the present study, a physically based, distributed hydrologic model has been used to identify the impacts from specific land use change scenarios in the protected area of Loutraki catchment. A vulnerability assessment method has been also implemented to provide a decision support tool to the land planning authorities and also hydrologic mitigation measures for the sustainable development of the area have been proposed. The hydrologic impacts of the land use scenarios include a 5% reduction in the annual recharge of the study aquifer for scenario 1 (doubling of the current urban areas) and 7% decrease for scenario 2 (tripling of the current urban areas). Nevertheless, these impacts can be minimised if small-scale artificial recharge infrastructure is developed and the land planning measures suggested through the vulnerability and recharge maps will be followed.     

Drilling the Waqf as Suwwan impact structure

The about 6-km diameter, near-circular Waqf as Suwwan structure located at E36°48′/N31°03′ in eastern Jordan was only recently recognized as a somewhat eroded, complex impact structure. Surface geological mapping, geophysical interpretation, remote sensing, and petrographic and mineralogical analyses have been carried out to understand the structure. In particular, the complex geology of the remnant of the central uplift has been scrutinized. A recent drilling project afforded an opportunity to expand the investigation of the structure to previously inaccessible strata of the ring syncline in the environs of the central uplift. Three boreholes were drilled, two to 140 and 110 m depth to the north and outside of the central uplift, and a further short hole to 5 m depth into the innermost part of the central uplift. Preliminary assessment of these cores has revealed the presence of around 11 m of fluvial breccias (wadi deposit) that are dominated by chert fragments at the top of the syncline fill. This is underlain by a normal succession of late Maastrichtian to Campanian strata. A variety of microstructures such as fracturing with vertical, as well as inclined at 45° and 30° fractures occurs throughout the cores. Some joints have slickensides along their walls. Limestone and marly limestone constitute the most abundant rocks in the boreholes. Distinct shock deformation effects are entirely lacking in the cores from the syncline. These observations are interpreted as a result of substantial erosion of the impact structure down to a level within the crater floor. The microstructures and the preliminary results of the analyses of sediment ages, textures, and compositions (nanofossils and sediment mineralogy) show that sediments as old as Campanian and as young as late Maastrichtian were affected by the impact. Unfortunately, the drilling did not expose any lithologies such as impact melt breccias that could lend themselves to absolute chronological analysis for a better constraint of the impact age.     

The Waqf as Suwwan crater,Eastern Desert of Jordan: aspects of the deep structure of an oblique impact from reflection seismic and gravity data

The deeply eroded Waqf as Suwwan ring structure was recently discovered to be a large impact, the first identified in the near east. Large-scale reflection seismic structure shows the impact situated high on the northeastern flank of the Jordan Uplift sloping into Wadi Sirhan Basin. If exhumation is linked to the Arabia–Eurasia collision, a likely time window for the impact event may be latest Eocene to Late Oligocene. Impact into a shallow sea seems an optional scenario. Old reflection seismic lines offer limited insight into the deep structure of the rim and part of the central uplift of the complex crater. An important structural clue is provided by a well-resolved seismic horizon of a yet tentative correlation with a Paleozoic black shale. The central gravity high is compatible with a mass surplus by the uplift of denser Paleozoic basement below the central uplift. The gravity model further indicates a ring of dense Paleozoic sediments rising from below into the ring syncline. Seismics show presumably radial synclines in the central uplift which are interpreted by centripetal constrictional flow during crater collapse. Beneath the final crater’s outer boundary, a shallow-dip normal fault zone, subtle seismic structure in uncollapsed footwall segments reveal an asymmetry of strain. The asymmetry is attributed to the cratering flow by an oblique impact directed toward NE. The finding provides independent support to an earlier suggestion of impact obliquity based on vergency of folds exposed on the central uplift.     

Modeling watershed-scale sequestration of soil organic carbon for carbon credit programs

Impending risks associated with climate change have forced the global community to devise tradable pollution permit or “cap and trade” approaches to control the release of greenhouse gases. In the U.S, soils have the potential to offset about 10 percent of annual CO₂ emissions; however, if carbon credits are to be included in greenhouse gas control programs, soil organic carbon (SOC) sequestration rates associated with agricultural land uses must be computed at a watershed scale. The Soil Water Assessment Tool (SWAT) water quality model, the Water Erosion Prediction Project (WEPP) erosion model, and the CENTURY 4.0 a soil carbon model were used to simulate carbon sequestration rates for 160 crop-tillage rotations in 272 sub-basins of the Big Creek watershed (12,300 hectares). Under annual crops, only no-till in a corn-soybean rotation, on low to moderate slopes results in net gains in SOC. Substantial annual rates of SOC sequestration occur only under perennial crops such as Conservation Reserve Program (CRP; 0.14 t/ha without erosion; 0.08 with erosion), pasture (0.67 t/ha without erosion; 0.58 with erosion), hay (0.88 t/ha without erosion; 0.52 with erosion), and forest (2.66 t/ha without erosion; 2.49 with erosion). Erosion thus has a large effect on the spatial distribution of field-measured SOC by moving it down slope and increasing its spatial variability. Because of this, carbon credit programs should be based on field practices, thus targeting the locations where the sequestration of atmospheric carbon actually occurs and minimizing monitoring costs. Developing model-based estimates of SOC sequestration rates of field practices at many locations would thus greatly serve the needs of carbon crediting programs.     

Stochastic downscaling method: application to wind refinement

In this article, we propose a new stochastic downscaling method: provided a numerical prediction of wind at large scale, we aim to improve the approximation at small scales thanks to a local stochastic model. We first recall the framework of a Lagrangian stochastic model borrowed from Pope. Then, we adapt it to our meteorological framework, both from the theoretical and numerical viewpoints. Finally, we present some promising numerical results corresponding to the simulation of wind over the Mediterranean Sea.