Generation and fate of basal meltwater during winter, western Greenland Ice Sheet

Basal sliding in the ablation zone of the Greenland Ice Sheet is closely associated with water from surface melt introduced to the bed in summer, yet melting of basal ice also generates subglacial water year-round. Assessments of basal melt rely on modeling with results strongly dependent upon assumptions with poor observational constraints. Here we use surface and borehole measurements to investigate the generation and fate of basal meltwater in the ablation zone of Isunnguata Sermia basin, western Greenland. The observational data are used to constrain estimates of the heat and water balances, providing insights into subglacial hydrology during the winter months when surface melt is minimal or nonexistent. Despite relatively slow ice flow speeds during winter, the basal meltwater generation from sliding friction remains manyfold greater than that due to geothermal heat flux. A steady acceleration of ice flow over the winter period at our borehole sites can cause the rate of basal water generation to increase by up to 20 %. Borehole measurements show high but steady basal water pressure rather than monotonically increasing pressure. Ice and groundwater sinks for water do not likely have sufficient capacity to accommodate the meltwater generated in winter. Analysis of basal cavity dynamics suggests that cavity opening associated with flow acceleration likely accommodates only a portion of the basal meltwater, implying that a residual is routed to the terminus through a poorly connected drainage system. A forcing from cavity expansion at high pressure may explain observations of winter acceleration in western Greenland.

Variability of Basal Meltwater Generation During Winter, Western Greenland Ice Sheet

Basal sliding in the ablation zone of the Greenland Ice Sheet is closely associated with water from surface melt introduced to the bed in summer, yet melting of basal ice also generates subglacial water year-round. Assessments of basal melt rely on modelling with results strongly dependent upon assumptions with poor observational constraint. Here we use surface and borehole measurements to investigate the generation and fate of basal meltwater in the ablation zone of Isunnguata Sermia basin, Western Greenland. The observational data are used to constrain estimates of the heat and water balances, providing insights into subglacial hydrology during the winter months when surface melt is minimal or non-existent. Despite relatively slow ice flow speeds during winter, the basal meltwater generation from sliding friction remains many fold greater than that due to geothermal heat flux. A steady acceleration of ice flow over the winter period at our borehole sites can cause the rate of basal water generation to increase by up to 20 %. Borehole measurements show high but steady basal water pressure, rather than monotonically increasing pressure. Ice and groundwater sinks for water do not likely have sufficient capacity to accommodate the meltwater generated in winter. Analysis of basal cavity dynamics suggests that cavity opening associated with flow acceleration likely accommodates only a portion of the basal meltwater, implying a residual is routed to the terminus through a poorly connected drainage system. A forcing from cavity expansion at high pressure may explain observations of winter acceleration in Western Greenland.

Tuber melanoexcavatum sp. nov., an edible black truffle from China

A new black truffle species with a basal cavity, Tuber melanoexcavatum, is identified and described. The new species is morphologically similar to T. pseudobrumale, T. pseudoexcavatum, and T. mesentericum in having a basal cavity. However, T. melanoexcavatum differs from T. pseudobrumale and T. pseudoexcavatum in having black pyramidal warts and 5 to 8 spored asci, and differs from T. mesentericum by having spiny ascospores and 1 to 5 spored (rarely 6 spored) asci. Phylogenetic analysis indicates that T. melanoexcavatum is most closely related to T. pseudobrumale, but the two still clearly differentiate. Tuber melanoexcavatum grows as a mycorrhizal association with Cyclobalanopsis glaucoides. Tuber melanoexcavatum is considered an edible black truffle species and is indigenous to China.

Absolute Single Cavity Length Interrogation of Fiber-Optic Compound Fabry–Perot Pressure Sensors Through a White Light Non-Scanning Correlation Method

A white light non-scanning correlation interrogation system was proposed and built to interrogate absolute length of the air cavity of fiber-optic compound Fabry–Perot pressure sensors for the extraction of pressure value. By carefully choosing thickness range and tilt angle of the optical wedge used for cavity length matching, correlation interferometric signal of the basal cavity can be naturally filtered out. Based on peak positioning by Fourier transform, bandpass filtering in frequency domain, inverse Fourier transform back to time domain, envelope fitting and zero fringe finding through a gravity center method, cavity length can be determined with an accuracy of 0.04%. The system was used for the interrogation of a fiber-optic compound Fabry–Perot pressure sensor under different pressures. For a pressure range of 0.1~2.9 Mpa, the linear relationship between the air cavity length and the gas pressure imposed was successfully extracted.

A new species of Ponthieva (Cranichidinae, Orchidaceae) from Bolivia

A new species of Ponthieva, P. boliviensis, is described and illustrated based on Bolivian material. The novelty resembles P. pilosissima and P. hermiliae characterized by pilose leaves and free lateral sepals. From P. pilosissima the new species differs in the shallowly concave lip, ovate-triangular basal lip auricles which are more or less parallel to the claw and ovate lip disc. Unlike in P. boliviensis, the lip of P. hermiliae is yellowish-green to greenish-white, lanceolate-triangular, lacking basal lobes, concave on the proximal half, with a 6-toothed callus placed horizontally in front of the basal cavity.

Tuber pulchrosporum sp. nov., a black truffle of the Aestivum clade (Tuberaceae, Pezizales) from the Balkan peninsula

Knowledge on the diversity of hypogeous sequestrate ascomycetes is still limited in the Balkan Peninsula. A new species of truffle, Tuberpulchrosporum, is described from Greece and Bulgaria. Specimens were collected from habitats dominated by various oak species (i.e. Quercusilex, Q.coccifera, Q.robur) and other angiosperms. They are morphologically characterised by subglobose, ovoid to irregularly lobed, yellowish-brown to dark brown ascomata, usually with a shallow basal cavity and surface with fissures and small, dense, almost flat, trihedral to polyhedral warts. Ascospores are ellipsoid to subfusiform, uniquely ornamented, crested to incompletely reticulate and are produced in (1–)2–8-spored asci. Hair-like, hyaline to light yellow hyphae protrude from the peridium surface. According to the outcome of ITS rDNA sequence analysis, this species forms a distinct well-supported group in the Aestivum clade, with T.panniferum being the closest phylogenetic taxon.

Tarimspirafrom the Cambrian (Series 2, Stage 4) of Laurentia (Greenland): extending the skeletal record of paraconodontid vertebrates

Phosphatic sclerites of the problematicTarimspiraYue and Gao, 1992 (Cambrian Series 2) recovered by weak acid maceration of limestones display a unique range of mainly strongly coiled morphologies. They were likely organized into multielement scleritomes, but the nature of these is poorly known; some sclerites may have had a grasping function.Tarimspirasclerites grew by basal accretion in an analogous fashion to younger paraconodonts (Cambrian Series 3–4) but lack a basal cavity. Based on proposed homologies,Tarimspiramay provide an extension of the early vertebrate paraconodont–euconodont clade back into the early Cambrian.Tarimspirais described for the first time from Laurentia (North Greenland), extending its known range from China and Siberia in Cambrian Series 2. In addition to the type species,Tarimspira planaYue and Gao, 1992, the Greenland record ofTarimspiraincludes two morphotypes of a new species,Tarimspira artemi.UUID:http://zoobank.org/c7c536c8-cdaf-49a9-ae1d-77c392f553fc.

Mechanical forcing of water pressure in a hydraulically isolated reach beneath Western Greenland's ablation zone

ABSTRACTA suite of surface and basal measurements during and after borehole drilling is used to perform in situ investigation of the local basal drainage system and pressure forcing in western Greenland. Drill and borehole water temperature were monitored during borehole drilling, which was performed with dyed hot water. After drilling, borehole water pressure and basal dye concentration were measured concurrently with positions in a GPS strain diamond at the surface. Water pressure exhibited diurnal changes in antiphase with velocity. Dye monitoring in the borehole revealed stagnant basal water for nearly 2 weeks. The interpretation of initial connection to an isolated basal cavity is corroborated by the thermal signature of borehole water during hot water drilling. Measurement-based estimates of cavity size are on the order of cubic meters, and analysis indicates that small changes in its volume could induce the observed pressure variations. It is found that longitudinal coupling effects are unable to force necessary volume changes at the site. Sliding-driven basal cavity opening and elastic uplift from load transfer are plausible mechanisms controlling pressure variations. Elastic uplift requires forcing from a hydraulically connected reach, which observations suggest must be relatively small and in close proximity to the isolated cavity.

Kakadudessus tomweiri, a new genus and species of diving beetle from tropical northern Australia, based on molecular phylogenetic and morphological data (Coleoptera, Dytiscidae, Bidessini)

The diving beetle genus and species, Kakadudessus tomweiri gen.n., sp.n. are described from the Northern Territory (Kakadu National Park, headwaters of Mary River) and north-eastern Queensland (Cape York Peninsula) of Australia. The new species has an elongate, almost flat habitus and elytra with pale yellowish markings. The head has a cervical line between the hindmargin of the eyes and the clypeus is anteriorly bordered. Pronotum and elytra have well developed striae, the latter without sutural lines and accessory striae. The posterior part of the basal cavity of epipleura has no transverse carina, the fairly elongate and narrow prosternal process reaches the metaventrite. The latter is provided with rows of punctures at its midline and the metacoxal lines are longer than the distance between them and strongly diverging anteriorly. The parameres are bi-segmented, very thin, slender and elongate, and slightly bifid apically. The combination of all these characters separates the new species and, thus, also the new genus from all other Bidessini. Morphologically, Kakadudessus resembles species of Leiodytes Guignot, 1936, Limbodessus Guignot, 1939 and Uvarus Guignot, 1939, the parameres resemble those of species of Allodessus Guignot, 1953. DNA sequence data from the mitochondrial genes cytochrome oxidase subunit I (cox1) and the large ribosomal subunit (16S rRNA), however, suggest that Kakadudessus does not belong to any of the known Oriental and Australasian Bidessini genera. Most importantly, recognition of Kakadudessus does not create paraphyly. All specimens were collected in small pools of shaded and intermittent streams and rivers with sandy or gravely bottom and without any vegetation.

Rapid glacier sliding, reverse ice motion and subglacial water pressure during an autumn rainstorm

Measurements of basal water pressure from 15 boreholes located at both local (tens of meters) and regional (kilometers) length scales were used to elucidate the pressure/sliding relationship during an autumn rapid motion event on Bench Glacier, Alaska, USA. The 8 day event had two distinct phases, each with a ten-fold speed-up with respect to winter velocity. The water pressure in all 15 boreholes varied synchronously during the speed-up. The first phase of rapid sliding began after a peak in basal water pressure and continued while the pressure was elevated and stable, or decreasing. The second phase of rapid sliding occurred when the basal water pressure was low but increasing, and terminated before the pressure peaked. Pressure and velocity do not appear unrelated, but the pressure/sliding relationship was not consistently linked to increasing, decreasing or a critical water pressure. The pressure variations and sliding accelerations are a response to a warm rainstorm, although equally large input events occurred in weeks prior with no apparent response. Drainage system evolution therefore appears to play a key role in both the acceleration and the pressure/velocity relationship. Basal cavity dynamics are likely responsible for three episodes of reverse (up-valley) motion observed after enhanced sliding.