Schmidt-hammer exposure ages from periglacial patterned ground (sorted circles) in Jotunheimen, Norway, and their interpretative problems

© 2016 Swedish Society for Anthropology and Geography Periglacial patterned ground (sorted circles and polygons) along an altitudinal profile at Juvflya in central Jotunheimen, southern Norway, is investigated using Schmidt-hammer exposure-age dating (SHD). The patterned ground surfaces exhibit R-value distributions with platycurtic modes, broad plateaus, narrow tails, and a negative skew. Sample sites located between 1500 and 1925 m a.s.l. indicate a distinct altitudinal gradient of increasing mean R-values towards higher altitudes interpreted as a chronological function. An established regional SHD calibration curve for Jotunheimen yielded mean boulder exposure ages in the range 6910 ± 510 to 8240 ± 495 years ago. These SHD ages are indicative of the timing of patterned ground formation, representing minimum ages for active boulder upfreezing and maximum ages for the stabilization of boulders in the encircling gutters. Despite uncertainties associated with the calibration curve and the age distribution of the boulders, the early-Holocene age of the patterned ground surfaces, the apparent cessation of major activity during the Holocene Thermal Maximum (HTM) and continuing lack of late-Holocene activity clarify existing understanding of the process dynamics and palaeoclimatic significance of large-scale sorted patterned ground as an indicator of a permafrost environment. The interpretation of SHD ages from patterned ground surfaces remains challenging, however, owing to their diachronous nature, the potential for a complex history of formation, and the influence of local, non-climatic factors

Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Nienow, Sole and Cowton’s Greenland research has been supported by a number of UK NERC research grants (NER/O/S/2003/00620; NE/F021399/1; NE/H024964/1; NE/K015249/1; NE/K014609/1) and Slater has been supported by a NERC PhD studentshipPurpose of the review:  This review discusses the role that meltwater plays within the Greenland ice sheet system. The ice sheet’s hydrology is important because it affects mass balance through its impact on meltwater runoff processes and ice dynamics. The review considers recent advances in our understanding of the storage and routing of water through the supraglacial, englacial, and subglacial components of the system and their implications for the ice sheet Recent findings:   There have been dramatic increases in surface meltwater generation and runoff since the early 1990s, both due to increased air temperatures and decreasing surface albedo. Processes in the subglacial drainage system have similarities to valley glaciers and in a warming climate, the efficiency of meltwater routing to the ice sheet margin is likely to increase. The behaviour of the subglacial drainage system appears to limit the impact of increased surface melt on annual rates of ice motion, in sections of the ice sheet that terminate on land, while the large volumes of meltwater routed subglacially deliver significant volumes of sediment and nutrients to downstream ecosystems. Summary:  Considerable advances have been made recently in our understanding of Greenland ice sheet hydrology and its wider influences. Nevertheless, critical gaps persist both in our understanding of hydrology-dynamics coupling, notably at tidewater glaciers, and in runoff processes which ensure that projecting Greenland’s future mass balance remains challenging.Publisher PDFPeer reviewe

Structure-Function Study of Mammalian Munc18-1 and C. elegans UNC-18 Implicates Domain 3b in the Regulation of Exocytosis

Munc18-1 is an essential synaptic protein functioning during multiple stages of the exocytotic process including vesicle recruitment, docking and fusion. These functions require a number of distinct syntaxin-dependent interactions; however, Munc18-1 also regulates vesicle fusion via syntaxin-independent interactions with other exocytotic proteins. Although the structural regions of the Munc18-1 protein involved in closed-conformation syntaxin binding have been thoroughly examined, regions of the protein involved in other interactions are poorly characterised. To investigate this we performed a random transposon mutagenesis, identifying domain 3b of Munc18-1 as a functionally important region of the protein. Transposon insertion in an exposed loop within this domain specifically disrupted Mint1 binding despite leaving affinity for closed conformation syntaxin and binding to the SNARE complex unaffected. The insertion mutation significantly reduced total amounts of exocytosis as measured by carbon fiber amperometry in chromaffin cells. Introduction of the equivalent mutation in UNC-18 in Caenorhabditis elegans also reduced neurotransmitter release as assessed by aldicarb sensitivity. Correlation between the two experimental methods for recording changes in the number of exocytotic events was verified using a previously identified gain of function Munc18-1 mutation E466K (increased exocytosis in chromaffin cells and aldicarb hypersensitivity of C. elegans). These data implicate a novel role for an exposed loop in domain 3b of Munc18-1 in transducing regulation of vesicle fusion independent of closed-conformation syntaxin binding

A competitive integration model of exogenous and endogenous eye movements

We present a model of the eye movement system in which the programming of an eye movement is the result of the competitive integration of information in the superior colliculi (SC). This brain area receives input from occipital cortex, the frontal eye fields, and the dorsolateral prefrontal cortex, on the basis of which it computes the location of the next saccadic target. Two critical assumptions in the model are that cortical inputs are not only excitatory, but can also inhibit saccades to specific locations, and that the SC continue to influence the trajectory of a saccade while it is being executed. With these assumptions, we account for many neurophysiological and behavioral findings from eye movement research. Interactions within the saccade map are shown to account for effects of distractors on saccadic reaction time (SRT) and saccade trajectory, including the global effect and oculomotor capture. In addition, the model accounts for express saccades, the gap effect, saccadic reaction times for antisaccades, and recorded responses from neurons in the SC and frontal eye fields in these tasks. © The Author(s) 2010

The engineering properties of glacial tills

Glacial tills are a product of the glacial processes of erosion, transportation and deposition and could have been subjected to several glacial cycles and periglacial processes to the extent that they are complex, hazardous soils that are spatially variable in composition, structure, fabric and properties, making them very difficult to sample, test and classify. An overview of the formation of glacial tills and their properties shows that they are composite soils which should be classified according to their lithology, their mode of deposition to link the glacial processes with the facies characteristics and their engineering behaviour. This enables representative design properties to be assigned using frameworks developed for composite soils

Evolutionary History of the Odd-Nosed Monkeys and the Phylogenetic Position of the Newly Described Myanmar Snub-Nosed Monkey Rhinopithecus strykeri

Odd-nosed monkeys represent one of the two major groups of Asian colobines. Our knowledge about this primate group is still limited as it is highlighted by the recent discovery of a new species in Northern Myanmar. Although a common origin of the group is now widely accepted, the phylogenetic relationships among its genera and species, and the biogeographic processes leading to their current distribution are largely unknown. To address these issues, we have analyzed complete mitochondrial genomes and 12 nuclear loci, including one X chromosomal, six Y chromosomal and five autosomal loci, from all ten odd-nosed monkey species. The gene tree topologies and divergence age estimates derived from different markers were highly similar, but differed in placing various species or haplogroups within the genera Rhinopithecus and Pygathrix. Based on our data, Rhinopithecus represent the most basal lineage, and Nasalis and Simias form closely related sister taxa, suggesting a Northern origin of odd-nosed monkeys and a later invasion into Indochina and Sundaland. According to our divergence age estimates, the lineages leading to the genera Rhinopithecus, Pygathrix and Nasalis+Simias originated in the late Miocene, while differentiation events within these genera and also the split between Nasalis and Simias occurred in the Pleistocene. Observed gene tree discordances between mitochondrial and nuclear datasets, and paraphylies in the mitochondrial dataset for some species of the genera Rhinopithecus and Pygathrix suggest secondary gene flow after the taxa initially diverged. Most likely such events were triggered by dramatic changes in geology and climate within the region. Overall, our study provides the most comprehensive view on odd-nosed monkey evolution and emphasizes that data from differentially inherited markers are crucial to better understand evolutionary relationships and to trace secondary gene flow