Lead-210 as a tracer for acidic deposition in areas of complex topography

This thesis reports an investigation into methods of determining the long term deposition field for atmospheric aerosols in areas of complex topography using the soil inventories of atmospherically derived radionuclides. Measurements of the radionuclides ²¹⁰Pb, ¹³⁷Cs, ¹³⁴Cs and ⁷Be in vegetation and soil have been made at five mountain locations in northern Britain. A description of the field sampling procedure, sample processing and y-ray analysis is given. Loss-on-ignition experiments to determine the organic fraction of sampled soils were also conducted on selected samples. The presence of frequent low level cloud shrouding mountain tops in the uplands of northern and western Britain leads to enhanced precipitation and also deposition of the major acidic ions, eg SO₃²⁻ and N0₃, due to the washout of the low level cloud by falling rain ('seeder-feeder scavenging') and also the direct deposition of cloud droplets ('occult deposition'). It is important to quantify the inputs of acidic deposition in these acid sensitive regions and direct measurements present many logistical problems. The radionuclide ²¹⁰Pb is attached to the same sub-micron aerosol size range in the atmosphere as the major acidic ions and following deposition attaches very strongly to organic matter in soils. In this study the soil inventory of atmospherically derived ²¹⁰Pb is used as a tracer of the deposition of acidic ions. As the half-life of ²¹⁰Pb is 22.3 years the soil inventory of ²¹⁰Pb(atmos), at a site undisturbed for - 100 years, represents deposition integrated over several decades. Initial sampling took place at the Merrick, an isolated mountain close to the coast in southwest Scotland, to test and develop the technique. Measurements showed the ²¹⁰Pb(atmos) inventory to increase with altitude at a greater rate than precipitation. Sampling at Great Dun Fell in Cumbria enabled the measured radionuclide inventories to be compared with detailed measurements of the variation of the wet deposition pattern with altitude, and also with a model of sulphate deposition. Close correspondence was found between the ²¹⁰Pb deposition profile and the deposition pattern, with altitude, for the major acidic ions. The three mountains Ben Cruachan, Beinn Dorain and Ben Lawers lie along an 80 km transect running roughly west to east from the western coast into the central Highlands. Sampling at these three mountains has yielded information on the change in the wet deposition field with distance inland. The measurements suggest that deposition of ²¹⁰Pb decreases, with distance from the western coast, at a greater rate than does precipitation. The soil inventory of ²¹⁰Pb(atmos) increases with altitude at a greater rate than rainfall at 4 of the 5 mountains. The results show that, around summits, on average, the concentration of ²¹⁰Pb in low level cloud is a factor of - 2 greater than in the frontal ('seeder') rain falling from higher altitude. This finding is in good agreement with detailed wet deposition measurements. The ²¹⁰Pb measurements are important in themselves as they help define the global and UK ²¹⁰Pb budget. From measurements made at 65 individual sites the mean ²¹⁰Pb(atmos) inventory is 0.44 ± 0.03 Bq cm⁻², with the mean of the average annual rainfall being 2,060 ± 70 mm yr⁻¹. These figures correspond to a mean concentration of ²¹⁰Pb in rainfall of 66 mBql⁻¹. The ¹³⁷Cs inventory has been separated into the fraction originating from nuclear weapons testing, ¹³⁷Cs(bomb), and the fraction due to the Chernobyl accident, ¹³⁷Cs(Chern). The measured ¹³⁷Cs(bomb) inventory ranges from a mean of 3,300 Bq m⁻² at Ben Lawers to 5,200 Bq m⁻² at Beinn Dorain. The ¹³⁷Cs(Chern) inventory is highly variable between locations ranging from a mean of 440 Bq m⁻² at Great Dun Fell to 14,900 Bqm⁻² at Ben Lawers reflecting the patchy nature of deposition, due largely to convective storms, during the passage of the radioactive plume. The radionuclide ¹³⁷Cs is shown to be relatively mobile in the organic soils which characterise the study areas. The cosmogenic radionuclide ⁷Be was measured in samples collected from the Merrick on 26th Oct 1988. The mean inventory was 0.039 Bq cm⁻², being associated with vegetation and the top few cm of the soil profile

Age and development of active cryoplanation terraces in the alpine permafrost zone at Svartkampan, Jotunheimen, southern Norway

Schmidt-hammer exposure-age dating (SHD) of boulders on cryoplanation terrace treads and associated bedrock cliff faces revealed Holocene ages ranging from 0 ± 825 to 8890 ± 1185 yr. The cliffs were significantly younger than the inner treads, which tended to be younger than the outer treads. Radiocarbon dates from the regolith of 3854 to 4821 cal yr BP (2σ range) indicated maximum rates of cliff recession of ~0.1 mm/year, which suggests the onset of terrace formation prior to the last glacial maximum. Age, angularity and size of clasts, together with planation across bedrock structures and the seepage of groundwater from the cliff foot, all support a process-based conceptual model of cryoplanation terrace development in which frost weathering leads to parallel cliff recession and hence terrace extension. The availability of groundwater during autumn freeze-back is viewed as critical for frost wedging and/or the growth of segregation ice during prolonged winter frost penetration. Permafrost promotes cryoplanation by providing an impermeable frost table beneath the active layer, focusing groundwater flow, and supplying water for sediment transport by solifluction across the tread. Snowbeds are considered an effect rather than a cause of cryoplanation terraces and cryoplanation is seen as distinct from nivation

A rock-surface microweathering index from Schmidt hammer R-values and its preliminary application to some common rock types in southern Norway

An index of the degree of rock-surface microweathering based on Schmidt hammer R-values is developed for use in the field without laboratory testing. A series of indices - I2 to In, where n is the number of successive blows with the hammer - is first proposed based on the assumption that the R-values derived from successive impacts on the same spot on a weathered rock surface converge on the value characteristic of an unweathered surface of the same lithology. Of these indices, the I5 index, which measures the difference between the mean R-value derived from first and fifth impacts as a proportion of the mean R-value from the fifth impact, is regarded as optimal: use of fewer impacts (e.g. in an I2 index) underestimates the degree of weathering whereas use of more impacts (e.g. in an I10 index) makes little difference and is therefore inefficient and may also induce an artificial weakening of the rock. Field tests of these indices on weathered glacially-scoured bedrock outcrops of nine common metamorphic and igneous rock types from southern Norway show, however, that even after ten impacts, successive R-values fail to approach the values characteristic of unweathered rock surfaces (e.g. bedrock from glacier forelands and road cuttings). An improved *I5 index is therefore preferred, in which the estimated true R-value of an unweathered rock surface is substituted. Weathered rock surfaces exposed to the atmosphere for ~10,000 years in southern Norway exhibit *I5 indices of 36-57%, values that reflect a similarly high degree of weathering irrespective of the rock type

Landform transitions from pronival ramparts to moraines and rock glaciers: A case study from the Smørbotn cirque, Romsdalsalpane, southern Norway

© 2016 Swedish Society for Anthropology and Geography. Landform transitions are defined as intermediate forms that represent transient developmental stages between conventional landform types. This study evaluates possible cases of landform transitions from pronival (protalus) ramparts to moraine ridges, and from pronival ramparts to lobate rock glaciers (protalus lobes) at the foot of the headwall of Smørbotn cirque in southern Norway. The five landforms had been previously classified as pronival ramparts. We conclude that only two (Smørbotn 2 and 3) are undisputed, active pronival ramparts, which developed under the seasonal-freezing regime of the Holocene. It is inferred that a third (Smørbotn 1) represents the transition to a moraine ridge formed during the ‘Little Ice Age’ of the last few centuries as a semi-permanent snowbed grew into a small temperate glacier. The two others (Smørbotn 7 and 8) appear to be relict embryonic rock glaciers that developed between the Last Glacial Maximum and the Younger Dryas Stadial under a permafrost regime and benefited from enhanced debris supply as a result of rock-slope instability affected by glacier debuttressing and permafrost degradation. Variable landscape settings and distinctive environmental histories contribute to the differences in the morphology of these landforms. We highlight continuing controversies over the modes of formation and diagnostic characteristics of pronival ramparts by positioning them, together with push/dump moraines, ice-cored moraines and rock glaciers, in a conceptual model of the periglacial-glacial landform continuum. The model links snow, ice and debris fluxes under seasonal-freezing and/or permafrost climatic regimes to the process thresholds between landform types

EXCAVATIONS AT CATHOLE CAVE, GOWER, SWANSEA

The discovery of an engraving in Cathole Cave in 2010 led to a decision to grille the cave. In 2012 excavations took place in the cave ahead of the grilling. Two areas of the cave were excavated; Trench A demonstrating that the cave held a faunal occupation dating to MIS 3, at a time, or times, between 50,000 and 30,000 BP. Two flint blades of Upper Palaeolithic appearance were discovered along with a faunal assemblage from within the shallow deposits across the line of the grille. The work demonstrated that the earlier excavations in the cave by Col. E.R. Wood were extensive and at this point in the cave he excavated to bedrock. The standing section (Trench B) which he left exposed further along the main cave passage was also cleaned, recorded and sampled. The deposits contain a faunal assemblage dominated by microfauna, but no cultural artefacts were found. The dating of key animal bones, the analysis of themicrofauna and the sedimentological analysis have together enabled a picture to be developed of the changes in this section from the mid-Devensian to Late Glacial and Holocene

Schmidt-hammer R-values from glacially-scoured bedrock surfaces across glacier-foreland boundaries: insights into Holocene weathering rates with implications for exposure-age dating

Schmidt-hammer R-values were measured on glacially-scoured bedrock outcrops located inside and outside of 11 ‘Little Ice Age’ glacier-foreland boundaries in the Jotunheimen and Jostedalsbreen regions of southern Norway. Analysing paired samples differing in exposure age by ~10,000 years constitutes a field experiment on chemical weathering rates within and between regions. Mean R-values (± 95% confidence intervals) from inside sites were 65.9 ± 0.6 and 66.9 ± 0.6 for rock surfaces composed of pyroxene-granulite gneiss in Jotunheimen at altitudes of 990–1360 m above sea level and granite and granitic gneiss in the Jostedalsbreen region at 270–620 m a.s.l. The corresponding values from outside sites of 39.9 ± 0.9 and 39.0 ± 0.9 were significantly lower, indicating a higher degree of chemical weathering. In contrast, regional differences in mean R-values were insignificant. A similar pattern is reflected in indices of rock weathering (39.0% for Jotunheimen and 41.6% for Jostedalsbreen), and weathering rate (2.8 R-value units and 3.0 units per 1000 years, respectively). These results imply an estimated minimum age resolution of Schmidt-hammer exposure-age dating of ~350–625 years and a maximum age range of ~20,000 years. They suggest potential application of the Schmidt hammer to both studies of weathering rates and exposure-age dating at the regional scale, despite lithological variation associated with different rock types and climatic variation associated with altitudinal differences of up to 1000 m between the sites

Schmidt-hammer exposure-age dating (SHD) of sorted stripes on Juvflye, Jotunheimen (central South Norway): Morphodynamic and palaeoclimatic implications

Measurements with an electronic Schmidt-hammer (RockSchmidt) were conducted on 23 sites of sorted stripes (periglacial patterned ground) on Juvflye, Jotunheimen (central South Norway). All were located above the current lower limit of alpine permafrost. Performing Schmidt-hammer exposure-age dating (SHD) based on application of a new local age-calibration equation for RRock-values yielded SHD-ages between 7975 ± 370 and 6660 ± 355 years ago, which are closely comparable to results obtained previously from sorted circles at the same location. The age estimates are interpreted as ‘composite’ ages indicative of upfreezing of boulders, lateral sorting, and subsequent stabilisation. Formation of patterned ground essentially ceased with the onset of the regional Holocene Thermal Maximum (HTM). Neither sorted stripe sites at higher altitude, continuously underlain by permafrost during the entire Holocene, nor those at lower altitudes affected by re-aggradation of permafrost in the late Holocene show signs of significant recent morphodynamic activity. Likely explanations for early- to mid-Holocene stabilisation include (1) substantial changes of soil moisture conditions and related thermodynamics within the active layer affecting frost action, (2) loss of fine-grained substrate matrix from the coarse stripes and hence reduced frost susceptibility, and (3) exhaustion of supply of boulders from the fines-dominated areas. Whereas the sorted stripe data set as a whole did not reproduce the altitudinal gradient characteristic of sorted circles on Juvflye, the strength of the relationship between sorted stripe mean RRock-values and altitude increased with declining slope gradient. Although interpretation of SHD-ages for patterned ground remains challenging, this successful application of the electronic Schmidt-hammer, with its increased efficiency and technical improvements over the mechanical Schmidt-hammer, offers considerable potential for future SHD-studies in both morphodynamic and palaeoclimatic contexts