Frost Activity Research Articles

Soil organic matter accumulation before, during, and after the last glacial maximum in Byers Peninsula, Maritime Antarctica

Organic matter is incorporated into soil by biological activity, and its preservation depends on composition and organic-mineral interactions. Frost activity, dry and cold climate, and glacial retreat-advance dynamics complexify soil organic matter storage in Antarctica. Byers Peninsula is the largest ice-free area in Antarctica and hosts a high diversity of vegetable and animal species. We hypothesize that (i) the SOM in the Byers Peninsula may reveal a distinct composition due to the antiquity of the ice-free areas not entirely obliterated by the advancing glaciers during the LGM; and (ii) the advancing ice caps at Byers allowed the accumulation of organic carbon at sheltered points of the Peninsula. Thus, the objectives of this work were: i) to characterize physically and chemically selected soils at Byers Peninsula, with emphasis on organic C and N stocks in different soil types, and ii) SOM dating of representative soil profiles. Thirteen soil profiles were dug, described, and classified. The plant species present at each site were identified. Chemical and physical attributes were determined. The C and N contents, δ13C and δ15N ratio isotopes were determined in the SOM physical size-fractionated particles. The C and N stocks were calculated for each SOM fraction. The deepest horizon of six soil profiles were dated by the 14C method.. Soils from Byers Peninsula showed a diverse and varied biochemical nature of SOM, resulting in varying content of C and N. The δ13C weighted mean of the SOM reflects the dominant vegetation type present in each sampling location, except for pre-Holocene soils and soils influenced by ornithogenesis. The highest organic C and N pools were recorded at subsurface horizons and attributed to the organo-mineral association fraction in upper platforms. For all soil groups, there was a significant overlap of δ13C and enrichment of δ15N in all fractions of SOM, requiring the combination of these two signatures to identify possible sources of contribution to SOM in this environment. The oldest soils, subjected to early-mid Holocene uplift, revealed an endolithic signature of pre-LGM age, the first recorded in Maritime Antarctica to this day. This first pre-LGM SOC record can indicate the initial modern colonization of Maritime Antarctica and suggests that ice caps advance during LGM was limited. Soils formed during and after the LGM in low platforms have a lacustrine signature indicating an influence of snowmelt, ice thawing, and permafrost degradation in selecting hygrophilous species. Soils formed in raised beaches have the lowest organic C and N stocks, and the isotopic composition of SOM indicates ancient ornithogenic influence.

Last Glacial Maximum active layer thickness in Western Europe, and the issue of ‘tundra gleys’ in loess sequences

AbstractLate Marine Isotope Stage (MIS) 3 and MIS 2 loess–palaeosol sequences in Western Europe comprise alternating loess layer and 3‐ to 30‐cm‐thick bleached soil horizons with Fe–Mn oxide precipitations, which are usually interpreted as waterlogged active layers and referred to as ‘tundra gleys’. Active layer thickness data derived from a regional climate model simulation and the fossils (shells, earthworm granules) found in ‘tundra gleys’ argue against such an assumption. Most of these horizons better correspond to Fe‐depleted, slightly humic topsoil horizons or subsurface eluvial horizons and should be referred to as (incipient) Ag or Eg horizons. They formed during climate ameliorations associated with vegetation (cryptogams, herbs) development, possibly limited by long‐lasting snow cover. Strong mixing usually occurred in these horizons due to the activity of anecic earthworms and frost activity.

Thermophysical Characterization of Cyclic Frost Formation in the Subsurface and Nominal Water Activity on Comets: Case Study of 67P/Churyumov-Gerasimenko

Abstract We use a generic thermophysical model to study in detail the formation of water-ice frost in the near-surface layers of comet 67P/Churyumov-Gerasimenko. We show that nightly frost formation is a common phenomenon. In particular, while abrupt landscapes may be conducive to frost formation, they are not a requisite condition. We show that the process of subsurface frost formation is similar to that of the condensed ice layer, or crust, underneath. The sublimation of frost produces regular, enhanced outgassing early in the morning. In the case of 67P, this activity is subordinate to and precedes the daily peak sourced from the ice-rich layers located above the diurnal skin depth. In any case, frost activity should be a nominal component of comet water activity.

Evolution in sandstone pore structures with freeze-thaw cycling and interpretation of damage mechanisms in saturated porous rocks

Measuring the evolution of pore structures is the most straightforward approach to assessing frost damage in porous rocks. Systematic and fine measurement of pore structures is critical to the interpretation of frost damage mechanisms. We conducted experiments where sandstone samples were subjected to 50 freeze-thaw cycles and their T2 spectra measured after each cycle via the nuclear magnetic resonance (NMR) method. This allowed the evolution in pore size distribution, porosity (pore volume), permeability (pore connectivity), tortuosity (pore curvature), and pore size uniformity coefficient (pore non-uniformity) to be comprehensively estimated. The results show that: (1) variation in pore structures is mainly caused by the propagation and expansion of nanopores and micropores and generation of new nanopores. (2) The porosity of sandstone has a three-stage trend of increasing-stabilizing- increasing, while tortuosity exhibits an opposite trend of decreasing-stabilizing-decreasing with freeze-thaw cycling. (3) The permeability and surface roughness of sandstone increase with freeze-thaw cycling, while the pore size uniformity coefficient decreases linearly. Based on the above results and scanning electron microscopic observations of the pore structure of sandstone, we found that: (1) the pore structure of layered sandstone can be simplified as a main stem type. (2) In this pore structure, there are two main damage processes: (a) where water in secondary cracks migrates to stem cracks and freezes, causing propagation and expansion of stem cracks; and (b) where unfrozen water in secondary cracks freezes in-situ, leading to the propagation, expansion and generation of secondary cracks. The above two damage processes coexist and alternately play pivotal roles during repeated frost activity, resulting in multistage changes to the porosity, permeability, and tortuosity of sandstone.

Growth of Grimmia mosses on volcanic tephra: Geoecological processes of biocrust development in Haleakalā crater (Maui, Hawai′i)

This research examines high-elevation biocrusts on volcanic tephra in Haleakalā Crater, Maui, Hawai′i; geomorphic, ecological, and pedological processes are discussed, in order to provide an integrated geoecological view of linkages that have influenced biocrust genesis. The study considers four spatial scales: (i) the landscape scale; (ii) the site scale; (iii) the miniature scale and, (iv) the microscopic scale. (i) Biocrusts grow at ~ 2335 m on a hydrologic basin circumscribed by four cinder cones which contributed tephra materials during eruptions between 11000 and 5000 BP, ~2700 BP, and 970 ± 50 BP. Basin landforms provide multiple clues about past geomorphic processes that have affected crust evolution, including intermittent runoff, which decreased the length of cryptobiosis periods, allowing poikilohydric mosses to gradually expand into dense biocrusts; and widespread frost activity, which caused tephra sorting and extensive slope creep on cinder cones. Ubiquitous signs of current frost disturbance are also found on basin soils. (ii) The study site, located amidst bare volcanic tephra—ash and lapilli—includes mainly two organisms: an acrocarpous moss, Grimmia torquata, and a foliose lichen, Peltigera rufescens. Biocrusts attained 40.23% groundcover;G. torquata was found on 64 undisturbed specimens, and showed 78.3% frequency on 46 sampling plots, whereas P. rufescens grew on 23.4% of specimens. Biocrusts also supported 13 vascular species. The most common were grasses, with 5.6% cover and 67.4% total frequency, including Trisetum glomeratum (47.8%) and Deschampsia nubigena (19.6%); other vascular plants reached just 0.85% combined cover. Tests show 72% of vascular-plant cover was statistically correlated with presence of biocrusts, suggesting these have beneficial—presumably pedological—effects on vascular plant growth. (iii) Biocrust microtopography was characterized by intermingling areas of rolling, 15–35 mm-high, protrusions, and 40–75 mm-high pinnacles. (iv) Soil micromorphology indicated crust growth was probably influenced by a host of genetic processes, including wind abrasion and erosion; aeolian dust deposition; soil desiccation during seasonal wet-dry cycles; rainwash and raindrop impact; diurnal temperature cycles; and bioturbation by burrowing fauna. The interactions among these agents are integrated into an idealized crust developmental sequence during the past few millennia.

Mapping the potential distribution of frozen ground in Tucarroya (Monte Perdido Massif, the Pyrenees)

This paper shows the creation of a map of frozen ground potential for the Tucarroya valley in Ordesa National Park. To create this map, it was necessary to combine the identified landforms associated to the presence of frozen ground by fieldwork, ground temperature data continuously recorded during two years by automatic loggers, a Basal Temperature of Snow (BTS) survey, and predictor variables derived from a high resolution Digital Elevation Model (DEM). Four environments have been differentiated: unfrozen ground, seasonal frozen ground, possible permafrost and probable permafrost. The map confirms a very limited variety and extension of permafrost, above 2700 m a.s.l. on gentle and shadowed slopes. Seasonal frozen ground is the most common thermal regime, as it can be developed above 2500 m a.s.l. Snow-pack duration and thickness tightly control the duration of frozen ground and the freezing-thawing cycles. Frost activity and unfrozen ground is restricted from 2570 to 2750 m a.s.l.

Formation of recurring slope lineae on Mars by rarefied gas-triggered granular flows

Active dark flows known as recurring slope lineae have been observed on the warmest slopes of equatorial Mars. The morphology, composition and seasonality of the lineae suggest a role of liquid water in their formation. However, internal and atmospheric sources of water appear to be insufficient to sustain the observed slope activity. Experimental evidence suggests that under the low atmospheric pressure at the surface of Mars, gas can flow upwards through porous Martian soil due to thermal creep under surface regions heated by the Sun, and disturb small particles. Here we present numerical simulations to demonstrate that such a dry process involving the pumping of rarefied gas in the Martian soil due to temperature contrasts can explain the formation of the recurring slope lineae. In our simulations, solar irradiation followed by shadow significantly reduces the angle of repose due to the resulting temporary temperature gradients over shaded terrain, and leads to flow at intermediate slope angles. The simulated flow locations are consistent with observed recurring slope lineae that initiate in rough and bouldered terrains with local shadows over the soil. We suggest that this dry avalanche process can explain the formation of the recurring slope lineae on Mars without requiring liquid water or CO2 frost activity.

Frost hollows of the boreal forest: a spatiotemporal perspective

Summary Frost hollows (FH) are small, confined lichen‐dominated ecosystems surrounded by lichen woodlands. FH are impacted by repetitive frosts occurring during the growing season. We evaluated the dynamics of FH across the boreal forest in eastern Canada and assessed the influence of latitude as the main geoclimatic factor controlling their development. The distribution and abundance of FH along 39 longitudinal transects were based on aerial photographs and field validation. Black spruce (Picea mariana) in FH and adjacent woodlands were sampled for age determination, year of tree establishment, height growth rate of spruce, and intensity and frequency of frost rings. Most FH are located in the southern part of the boreal forest, in depressions bordered by dry, open, lichen woodlands. The inception and development of FH are not dependent on latitude but rather on the presence of lichen woodlands. Frost‐induced thúfurs and frost rings were more frequent and abundant in the southernmost FH, whereas the northernmost FH were devoid of thúfurs. Black spruce established synchronously in FH across the boreal forest, an indication of a climatic control associated with cloudier, humid conditions reducing radiative frost activity. Most FH spruce established after 1933 and peaked in the 1980s. Fewer frost events were recorded in the 1980s than in the 1990s. In the latter decade, frost events became more frequent, intense and synchronous across the boreal forest. Synthesis. The distribution of frost hollows (FH) is related to the presence of dry lichen woodlands that exacerbate frost activity during the growing season. Synchronous frost‐ring frequency across the biome also suggests that shared climatic conditions, in particular freezing temperature, humidity and cloudiness, are at the origin of the dynamics of FH. A longer growing season creates propitious conditions for a higher frequency of frost events and more intense soil cryoturbation. FH are climate‐sensitive ecosystems which can be used as proxies of the impact of global change on the boreal biome.

Evaluating human-disturbed habitats for recovery planning of endangered plants

The recovery potential of endangered species is limited by the high prevalence of human-modified habitats, while effective in situ conservation strategies to identify and restore disturbed habitat within species ranges are lacking. Our goal was to determine the impact of human disturbance on the endangered endemic Barrens willow (Salix jejuna) to provide science-based protocols for future restoration of disturbed habitats; a key component of conservation and recovery plans for many rare plant species. Our study examined differences in substrate (e.g., % total plant cover, % species cover, substrate type) and vegetation in naturally- (via frost activity) vs human-disturbed limestone barrens (Newfoundland, Canada), across the entire species range of the endangered Barrens willow. There were distinct differences in substrate conditions and vegetation community structure between naturally- and human-disturbed limestone barrens habitat throughout the narrow range of this endemic willow. Human-disturbed sites are more homogeneous and differ significantly from the naturally-disturbed sites having a much coarser substrate (30% more gravel) with less fine grained sands, less exposed bedrock, decreased soil moisture, increased nitrogen content, and reduced phosphorus content. Substrate differences can inhibit return to the natural freeze-thaw disturbance regime of the limestone barrens, negatively affecting long-term persistence of this, and other rare plants. The structure of associated vegetation (specifically woody species presence) negatively affected willow abundance but was not linked to disturbance type. Human-disturbed sites are potential candidates for endangered plant recovery habitat if natural ecosystem processes, vegetation community structure, and habitat heterogeneity are restored, thereby supporting the establishment of long term viable populations.

Genesis of a till/sand breccia (Pleistocene, Noteć Valley near Atanazyn, central Poland)

The study area in Atanazyn in Noteć Valley, NW Poland, is located on the surface of terrace III in Toruń–Eberswalde ice-marginal valley. Terrace III is correlated with the Pomeranian Phase and the Oldest Dryas, during which most of the fluvio-periglacial sedimentation in the Noteć Valley took place. Four units are distinguished in the terrace: (1) horizontally stratified, ripple-drift cross-laminated and massive sand (unit Sh, Src, Sm) deposited in a shallow, sand-bed channel with a low-energy current; (2) a unique till/sand breccia formed by disintegration of a lodgement till due to drying out and frost activity under periglacial conditions, which was fluvially transported over a short distance; (3) a massive gravelly diamicton (DGm) representing a subaerial, cohesive debris flow; and (4) sand with low-angle cross-stratification (Sl) forming a coversand layer over the terrace. The presence of the till/sand breccia, which is unique for Quaternary sediments, sheds new light on the depositional conditions in ice-marginal valleys. The till/sand breccia lithofacies can be considered to be a diagnostic criterion for fluvio-periglacial conditions in ice-marginal valleys.

Frost‐ring chronologies as dendroclimatic proxies of boreal environments

Frost rings are formed in tree stems when growing‐season frosts affect immature wood cells, producing collapsed cells within annual tree rings. Open boreal forests are most susceptible to record growing‐season frost because they lack the greenhouse effect commonly observed in closed forests. Here we present a novel method to construct regional frost‐ring chronologies in lichen‐black spruce woodlands of the boreal forest zone. Because the ability of trees to form frost rings depends on several factors (including bark thickness and ring width), we used two models to produce a Frost Composite Index based on a frost susceptibility window of cambial age <30 years. The frost‐ring chronology showed alternating periods of high and low frost activity that were highly consistent within and among sites. Reconstruction of growing‐season frost activity may be used as dendroclimatic proxies of climate variability and may give insights into future risks of frost damage in a warming climate.

Biogeomorphic relationships between slope processes and globular Grimmia mosses in Haleakala's Crater (Maui, Hawai’i)

Globular mosses were found in Haleakala's crater (Maui) at five locations between 2175 and 2725 m; the highest-altitude site, with abundant epilithic mosses growing on alkali-olivine basalt outcrops and a large mossball population, was studied. Mossballs form when moss cushions are dislodged from rocks but continue growing unattached to substrate; detachment agents include rainsplash, desiccation, wind, frost, and disturbance by birds (dark-rumped petrels) that burrow nests under outcrops, or by goats. When loosened, moss polsters are transported down steep (26–34°) slopes by different geomorphic processes, including frost—mainly needle ice—activity, runoff, and wind. Mossballs contained two species, Grimmia trichophylla Grev. and Grimmia torquata Drumm., growing separately or commingled. Weight, size, and various shape indices were determined for 260 specimens. Shape and size were correlated; larger mosses become less spheroidal because heavier specimens are less disturbed by needle ice, remaining immobile for increasingly longer time periods, thus becoming flattened. Distance of downslope transport from source rockwalls was measured for 330 specimens; 83% shifted ≤ 100 cm, but only ∼ 5% had moved > 200–839 cm. Heavier mossballs moved short distances, thus ∼ 88% of all biomass remained within 200 cm from outcrops. Substrate soils were compared with those within globoids; surface site soils were much coarser than mossball grains. Twelve substrate samples had, on average, 21.3% gravel (≥ 2 mm), 6.1% fines (≤ 0.063 mm) and 2.1% organic matter; in contrast, 12 mossballs contained < 0.1% gravel, 47.9% fines, and 34.1% organic matter. G. torquata polsters had slightly finer soil (53.2%) than G. trichophylla (43.5%). This significant fine-grain concentration results as mosses trap aeolian dust among stems and leaves; ∼ 91% of moss grains were ≤ 0.25 mm, but only ∼ 30% of substrate particles measured ≤ 0.25 mm. Such fine texture, along with abundant organic matter contributed by moss growth, generates greater water-storage capacity in globoids (∼ 310%) than in site soils (16.8%); this is ecologically significant for mossball development and survival during drought periods. This area is frequently subjected to freezing temperatures, while fog interception from incoming tradewinds contributes significant moisture amounts to precipitation. Ground disturbance by frost activity seemed significant. Needle ice grows frequently on this slope, as evidenced by widespread presence of miniature sorted stripes, striated soils, fine-earth flags below stones, gaps around stones, and fine-soil raised patches, observed during multiple visits. Biogeomorphic interactions between mossballs and substrate at Haleakala are briefly discussed from the perspective of self-organized criticality, and interpreted to represent a self-replicating moss-dispersal system dependent on slope geomorphic processes.

Phytogeomorphic Influence of Stone Covers and Boulders on Plant Distribution and Slope Processes in High‐Mountain Areas

AbstractThis study reviews several effects stones have on slope geomorphic processes and plant distribution at high elevations, with emphasis on low‐latitude mountains and volcanic environments and rosette plants. It begins by considering how vegetation becomes established on relatively stable footslopes and the principal influences that outcrops and isolated boulders have on slope movement and vegetation development, moves to a comparison of the principal geomorphic processes affecting stone‐covered slopes and the disturbance agents influencing fine‐sediment zones that are devoid of clasts. The significance of stones for plant survival in areas subjected to frost activity, the strategies displayed by plants growing in unstable talus zones and the impacts stones have on plant development and slope dynamics are also considered. The study concludes by examining the role stones play in providing safe sites for plant development and the expansion of ecological niches, and with some speculations on possible future research directions.

A frost “buzzsaw” mechanism for erosion of the eastern Southern Alps, New Zealand

In the Southern Alps, New Zealand, large gradients in precipitation (< 1 to 12 m year − 1 ) and rock uplift (< 1 to 10 mm year − 1 ) produce distinct post-glacial geomorphic domains in which landslide-driven sediment production dominates in the wet, rapid-uplift western region, and rockfall controls erosion in the drier, low-uplift eastern region. Because the western region accounts for < 25% of the active orogen, the dynamics of erosion in the extensive eastern region are of equal importance in estimating the relative balance of uplift and erosion across the Southern Alps. Here, we assess the efficacy of frost cracking as the primary rockfall mechanism in the eastern Southern Alps using air photo and topographic analysis of scree slopes, cosmogenic radionuclide dating of headwalls, paleo-climate data, and a numerical model of headwall temperature. Currently, active scree slopes occur at a relatively uniform mean elevation (∼ 1450 m) and their distribution is independent of hillslope aspect and rock type, consistent with the notion that frost cracking (which is maximized between − 3 and − 8 °C) may control rockfall erosion. Headwall erosion rates of 0.3 to 0.9 mm year − 1 , measured using in-situ 10Be and 26Al in the Cragieburn Range, confirm that rockfall erosion is active in the late Holocene at rates that roughly balance rock uplift. Models of the predicted depth of frost activity are consistent with the scale of fractures and scree blocks in our field sites. Also, vegetated, paleo-scree slopes are ubiquitous at elevations lower than active scree slopes, consistent with the notion that lower temperatures during the last glacial advance induced pervasive rockfall erosion due to frost cracking. Our modeling suggests temporally-averaged peak frost cracking intensity occurs at 2300 m a.s.l., the approximate elevation of the highest peaks in the central Southern Alps, suggesting that the height of these peaks may be limited by a “frost buzzsaw.”

Late Middle Pleistocene climate in southwestern China: inferences from the stratigraphic record of Panxian Dadong Cave, Guizhou

Panxian Dadong Cave, situated in the subtropical zone of southwestern China, preserves a fan-like sedimentary sequence close to its entrance that spans the period between MIS 8 and 5 (300–130 ka). The frequent alternation of flowstone formation, cementation, clastic deposition, and frost activity in the depositional sequence makes it ideal for reconstructing the environmental conditions prevailing during the later Middle Pleistocene on the Guizhou Plateau. Macroscopic and microscopic sedimentary analyses determine that clastic deposits were entering the cave in the form of intermittent cohesive debris flows and sheetflows during cold and relatively dry climatic conditions when vegetation cover was reduced. Interlayered impure flowstones were forming during wetter phases but still under glacial conditions. Seasonally freezing temperatures are deduced from the frequent occurrence of cycles of well-developed freeze–thaw features affecting both the clastic parts of the sequence and the flowstones as they were deposited. The described depositional processes were responsible for lateral redistribution on the fan surface of bone remains and lithic artifacts that were accumulating on the surface as a result of hominid activities. During the intervening interglacial stages (MIS 7 and possibly MIS 5) clastic deposition was considerably reduced and only thin flowstone caps and weathering manganese–iron crusts were forming. It is suggested that precipitation was much higher during glacial intervals than interglacials under a predominantly cold climate. Dadong Cave provides a good example of very cold and wet climatic conditions during glacials in the subtropics of East Asia.

Short-term Periglacial Processes, Vegetation Succession, and Soil Development within Sorted Patterned Ground: Jotunheimen, Norway

Small (1 ≤ m diameter) sorted patterned ground features were studied on the Little Ice Age forelands of three Jotunheimen glaciers. Patterned ground appears to be most active near the ice margins, declining in intensity of activity with distance from the glaciers. Vegetation and soil development are negligible within patterned ground that is “Recent” (decadal time frame). Significant (P < 0.05) fine scale differences in vegetation and soil development occur within patterned ground on terrain ∼70 yr in age, with patterned ground borders having higher values of vegetation cover and thicker soils than that in patterned ground centers. With increasing age of terrain and patterned ground, soil development and vegetation encroach inward toward patterned ground centers, implying that a short-term, active periglacial zone exists near the ice margin, decaying with time and glacier retreat. Specifically, terrain that has been deglaciated for ∼70 years and is approximately ∼350–500 m from the ice margin shows a significant decline in frost activity, allowing for the initiation of pedogenesis and vegetation colonization.

From relict polygon patterns in South Scandinavia to active ice wedge polygons in Svalbard: A review of former studies

Scandinavian networks of relict ice wedge polygons are revealed by aerial photographs, (a) on the Swedish west coast and in south-western Jutland, Denmark, as vegetation patterns (crop marks) during dry seasons, and (b) in north-eastern Norway, as a pattern of shallow trenches enhanced by vegetation. The most regularly shaped and equally sized polygons occur in south-western Jutland. This is a result of the long period of periglacial frost activity in the environment outside the Weichselian Ice Sheet. The relict polygon areas on the Swedish west coast and in north-eastern Norway are situated in early deglaciated regions. Using dated shoreline records, it may be concluded that these polygons had their last period of activity in the Younger Dryas cold phase. Mean Annual Air Temperature (MAAT) values are discussed based on Péwé's temperature criteria for ice wedge formation. To gain experience of the dynamics of ice wedges, the high-arctic Adventdalen Valley, Svalbard, was chosen as test area. In active wedges in the valley plain, secondary wedges were observed. The climatological significance of the phenomenon is brought forward and discussed in view of the present climatic situation. The secondary wedges are interpreted as indicators of climatic cooling.

Temporal and Spatial Variability of Soil pH in Patterned-Ground Chronosequences: Jotunheimen, Norway

Glacier foregrounds of Jotunheimen, Norway are characterized by the occurrence of Little Ice Age end moraines, dating to approximately the mid 18th century. Patterned-ground features occurring within chronologically established time units were studied. Young patterned-ground features, forming ~ 10-20 years after deglaciation, are frost active with minimal soil development. With time and distance from the ice margin, frost activity declines within the patterned ground. Frost activity initially decreases at the borders of the features, with the centers later stabilizing. Sorted circles and sorted nets showed significant changes in soil pH across the chronosequences. Temporal thresholds were recognized on two of the chronosequences where patterned-ground features on terrain deglaciated ~ 1930 A.D. show increased acidification rates, suggesting a decline in frost activity and disturbance. Microsite variability was noted on one of the chronosequences with patterned-ground borders being more acidic than that of center positions. All glacier forelands showed a higher soil pH with depth in patterned-ground features. The importance of microsite variability and associated disturbance is stressed and should be incorporated when studying environmental change at traditional landscape scales.

Formation of patterned ground and fine-scale soil development within two late Holocene glacial chronosequences: Jotunheimen, Norway

Chronosequences of ∼250 to ∼130 years were established on two late Holocene glacier forelands in the Jotunheimen region of southern Norway. Patterned features occurring within chronologically established time units were studied. Young patterned features, forming ∼10–20 years after deglaciation, are frost active. Vegetation cover is minimal within the young patterned features, consisting of bryophytes/organic crusts. Soil development within patterned ground is also minimal/absent because frost action retards horizonization. With time and distance from the glaciated ice margin, frost activity declines within the patterned features, suggesting that a thin, active “periglacial zone” exists near the ice margin. Initially, frost activity decreases at the borders of the features with the centers stabilizing later in time. This results in fine-scale soil heterogeneity and variations of soil development. Fine-scale pedogenic development is first encountered at the borders of patterned ground that has developed on terrain exposed since the ∼1930s, yet soil development is predominantly absent at the centers of patterned ground. With time and distance from the ice margin, frost activity declines and allows patterned features to homogenize from border to center positions in regard to soil characteristics. Across the chronosequences, soils within patterned features pedogenically follow previous soil chronosequence studies, evolving from USDA classifications of Entisols into Inceptisols. Frost disturbance within patterned ground, however, produces a lag effect, that results in longer periods of time for pedogenesis to occur and thinner soils than that of the surrounding terrain.

Stratigraphy, age and formation of peaty earth hummocks (pounus), Finnish Lapland

Detailed investigations of peaty earth hummocks called pounus were carried out in northemmost Finnish Lapland in the vicinity of the Kevo Subarctic Research Station. Pounus are complex, often vegetated, cryogenic mounds formed partly of peat. Some have a core of mineral soil or several large stones, or just one frost-heaved boulder covered by peat. They belong to the same group of earth hummocks as thufur and non-sorted circles. The typology of pounus is described and compared with other types of cryogenic earth hummocks. Stratigraphical study of pounus shows how cryoturbation has deformed the previous soil horizons of typical Arctic podzols and has been followed by intense peat growth and later frost reactivation. Microstructures in pounus confirm the frost activity and several phases of peat growth during their formation. Alternating warmer and dryer conditions with water-table rise and renewed peat formation could be inferred. The present stage of development is frost reactivation and peat growth. Pounus are relatively young features. The maximum age for pounu development corresponds with the age of peat formation. Peat of a boulder pounu yielded a data of 330 + 70 BP and a minerogenic pounu gave an age of 710 + 50 BP. The Sphagnum peat formation on peat pounus started intensively about 1000 BP. They are random surficial forms with variable control by frost heave and vegetation growth, independent of the presence or absence of permafrost. They are related to a dynamic snowcover in areas of open birch stands or tundra and their development is polygenetic with alternating frost disturbance and phases of humification or podzolization. Pounus act thermally as a biological refuge in the autumn and spring. At present, perennial frozen cores seem to be common, especially in large peat pounus. Pounu development, as with other earth hummocks, occurs after the main phase of interglacial pedogenesis and can be considered as an indicator of a general cooling trend, developing mostly during the second half of the Holocene. Pounus' relation to climatic change is discussed. Pounus can be considered as an indication of a general cooling trend associated with progressive depletion of summer insolation. Hummock extent is coherent and parallel with trends in permafrost growth, but not directly linked to it.