ABSTRACT The Gaick is an enigmatic glaciated landscape in the Central Grampians, Scotland, dominated by an expansive dissected plateau. Previous studies have postulated widely differing interpretations of the glacial landforms and current understanding of the glacial events in this area is partly restricted by the absence of detailed glacial geomorphological mapping. To address this issue, we present a comprehensive 1: 46,000-scale glacial geomorphological map, covering an area of ∼520 km2. A combination of detailed field mapping and interpretation of aerial photographs and Digital Surface Models (DSMs) has revealed a variety of glacial, periglacial and fluvial landforms, including an abundance of moraines and meltwater channels within valleys. We also identify a glacial sediment-landform assemblage, dissected glaciogenic material, that has not previously been reported in the Scottish Highlands. The geomorphological map provides the necessary foundation for elucidating the extent, dynamics and timing of former glaciation in the area.
Younger Dryas ice‐marginal (‘hummocky’) moraines in Scotland represent valuable terrestrial archives that can be used to obtain important information on ice‐marginal dynamics and glacier thermal regimes during a period of rapid climatic change. In this paper, we present detailed sedimentological studies of Younger Dryas ice‐marginal moraines in the Gaick, central Scotland, the former site of a spatially restricted plateau icefield. Exposures demonstrate that moraines in the Gaick represent terrestrial ice‐contact fans, with evidence of proglacial and subglacial glaciotectonization, as reported elsewhere in Scotland. The exposures also reveal the influence of local hydrogeological conditions, with pressurization of the groundwater system leading to the formation of hydrofracture fills within some moraines. Clast shape analysis shows that all the moraines contain debris consistent with transport in the subglacial traction zone. The sedimentological data, and the planform arrangement of the moraines as nested arcs or chevrons, indicate that retreat of the Younger Dryas Gaick Icefield outlets was incremental and oscillatory. This evidence strongly suggests a mainly temperate thermal regime and short glacier response times, but with narrow cold‐ice zones near the margins facilitating the elevation of basal debris to the glacier surface. Analogous glaciodynamic regimes occur at modern ice‐cap and plateau icefield outlets in Iceland and Norway, although there are significant differences in the nature of ice‐marginal deposition. The glaciodynamic signature recorded by moraines in the Gaick has allowed us to shed new light on the ice‐marginal dynamics and thermal regime of one of the most easterly Younger Dryas icefields in Scotland.
<p>We present findings from detailed geomorphological and sedimentological investigations of small recessional moraines at Fjallsj&#246;kull, an active temperate outlet of &#214;r&#230;faj&#246;kull, southeast Iceland. The moraines are characterised by striking sawtooth or hairpin planforms that are locally superimposed, giving rise to a complex spatial pattern. We recognise two distinct populations of moraines, namely a group of relatively prominent moraine ridges (mean height ~1.2 m) and a group of comparatively low-relief moraines (mean height ~0.4 m). These two groups often occur in sets/systems, comprising one pronounced outer ridge and several inset smaller moraines. Using a representative subsample of the moraines, we establish that they form by either (a) submarginal deformation and squeezing of subglacial till or (b) pushing of extruded tills. Locally, proglacial (glaciofluvial) sediments are also incorporated within the moraines during pushing. For the first time, to our knowledge, we demonstrate categorically that these moraines formed sub-annually using repeat uncrewed aerial vehicle (UAV) imagery. We present a conceptual model for sub-annual moraine formation at Fjallsj&#246;kull that proposes the sawtooth moraine sequence comprises (a) sets of small squeeze moraines formed during melt-driven squeeze events and (b) push moraines formed during winter re-advances. We suggest the development of this process-form regime is linked to a combination of elevated temperatures, high surface meltwater fluxes to the bed, and emerging basal topography (a depositional overdeepening). These factors result in highly saturated subglacial sediments and high porewater pressures, which induces submarginal deformation and ice-marginal squeezing during the melt season. Strong glacier recession during the summer, driven by elevated temperatures, allows several squeeze moraines to be emplaced. This process-form regime may be characteristic of active temperate glaciers receding into overdeepenings during phases of elevated temperatures, especially where their englacial drainage systems allow efficient transfer of surface meltwater to the glacier bed near the snout margin.</p>
Over recent decades, glaciers outside of Greenland and Antarctica have displayed accelerating rates of mass loss and ice-frontal retreat, and this has been associated with unequivocal climatic and oceanic warming. Icelandic glaciers are particularly sensitive to climate variations on short-term timescales owing to their maritime setting, and have shown rapid rates of retreat and mass loss during the past decade. This study uses annual moraine spacing as a proxy for ice-frontal retreat to examine variability in glacier retreat at Skálafellsjökull, SE Iceland, over the last ~80 years. Two pronounced six-year periods (1936–1941 and 1951–1956) of ice-frontal retreat are recognised in the record for comparison with the most recent phase of retreat (2006–2011), and these three retreat phases are shown to be similar in style and magnitude. Analysis of climate data indicates that these periods of glacier retreat are associated with similar summer air temperature values, which is a key control on Icelandic terminus variations. This demonstrates that both the most recent phase of ice-frontal retreat at Skálafellsjökull and the recent warming of summer temperatures are not unusual in the context of the last ~80 years. These findings demonstrate the importance of placing observations of contemporary glacier change in a broader decadal- to centennial-scale context.
Severe extratropical winter storms are a recurrent feature of the European climate and cause widespread socioeconomic losses. Due to insufficient long-term data, it remains unclear whether storminess has shown a notable response to changes in external forcing over the past millennia, which impacts our ability to project future storminess in a changing climate. Reconstructing past storm variability is essential to improving our understanding of storms on these longer, missing timescales. Peat sequences from coastal ombrotrophic bogs are increasingly used for this purpose, where greater quantities of coarser grained beach sand are deposited by strong winds during storm events. Moving inland however, storm intensity decreases, as does sand availability, muting potential paleostorm signals in bogs. We circumvent these issues by taking the innovative approach of using mid-infrared (MIR) spectral data, supported by elemental information, from the inorganic fraction of Store Mosse Dune South (SMDS), a 5000-year-old sequence from a large peatland located in southern Sweden. We infer past changes in mineral composition and thereby, the grain size of the deposited material. The record is dominated by quartz, whose coarse nature was confirmed through analyses of potential local source sediments. This was supported by further mineralogical and elemental proxies of atmospheric input. Comparison of SMDS with within-bog and regionally relevant records showed that there is a difference in proxy and site response to what should be similar timing in shifts in storminess over the ∼100 km transect considered. We suggest the construction of regional storm stacks, built here by applying changepoint modelling to four transect sites jointly. This modelling approach has the effect of reinforcing signals in common while reducing the influence of random noise. The resulting Southern Sweden-Storm Stack dates stormier periods to 4495–4290, 3880–3790, 2885–2855, 2300–2005, 1175–1065 and 715-425 cal yr BP. By comparing with a newly constructed Western Scotland-Storm Stack and proximal dune records, we argue that regional storm stacks allow us to better compare past storminess over wider areas, gauge storm track movements and by extension, increase our understanding of the drivers of storminess on centennial to millennial timescales.
Iceland is situated in a climatically sensitive area close to both atmospheric and oceanic polar fronts, thus representing an important location for understanding North Atlantic climatic change. Icelandic glaciers are particularly sensitive to climatic fluctuations on annual to decadal timescales, and have exhibited accelerating rates of ice-marginal retreat and mass loss during the past decade. Understanding these current rapid glacier fluctuations is crucial to placing current atmospheric warming and associated glacier retreat in a broader context.
This study uses the characteristics of recessional (“annual”) moraines and complementary climate data to examine patterns, rates and drivers of ice-marginal retreat that has occurred at Skalafellsjokull, SE Iceland since the 1930s. High-resolution glacial geomorphological mapping reveals suites of minor moraines across the glacier foreland, with the features displaying distinctive sawtooth planform geometries. Chronological investigations of the Skalafellsjokull moraines, which integrate remote sensing observations and lichenometry, indicate that minor moraines on the northern and central parts of the glacier foreland formed on an annual basis. Sedimentological investigations reveal that these annual moraines form through a range of ice-marginal processes, with push/squeeze mechanisms being dominate. The geomorphological, chronological and sedimentological data therefore indicate these moraines represent successive annual ice-frontal positions. Thus, these annual moraines provide a framework for exploring patterns, rates and drivers of ice-marginal retreat at Skalafellsjokull.
Annual ice-margin retreat rates (IMRRs), equivalent to annual moraine spacing, indicate prominent periods of glacier recession at Skalafellsjokull are coincident with those at other Icelandic outlet glaciers, as well as those identified at Greenlandic outlet glaciers. Analysis of IMRRs and climate data suggests summer air temperature, sea surface temperature and North Atlantic Oscillation have an influence on IMRRs at Skalafellsjokull, with the glacier appearing to be most sensitive to summer air temperature. Based on this analysis, it is hypothesised that sea surface temperature may drive air temperature changes in the North Atlantic region, which in turn forces IMRRs. The increase in SST over recent decades may link to atmospheric-driven variations in North Atlantic subpolar gyre dynamics. Further research on glacier change in the North Atlantic region, and the controls thereon, is nonetheless required to test this hypothesis.
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