Glacial Influence Research Articles

Predicting river ecosystem response to glacial meltwater dynamics: a case study of quantitative water sourcing and glaciality index approaches

Glacier retreat and thinning are occurring in many regions of the world, leading to significant changes in river discharge, water quality and aquatic ecosystems. Therefore, it is increasingly necessary for environmental scientists and managers to develop and adopt methods that link changes in meltwater dynamics and biotic response to better understand and predict future ecosystem change in glacially influenced rivers. To this end, two approaches have been developed recently: (1) the ARISE quantitative meltwater contribution approach of Brown et al. (Freshw Biol 54:1357–1369, 2009b) and (2) the glaciality index (GI) of Ilg and Castella (Freshw Biol 51:840–853, 2006), which provides a measure of glacial runoff influence on stream ecosystems based on four environmental variables (water temperature, channel stability, electrical conductivity and suspended sediment concentration). However, the relative performance and potential complementarities of these two approaches have yet to be evaluated. We conducted a methodological comparison using detailed hydrological, water quality and biological datasets collected over two summers in the French Pyrenees. Analyses revealed strong and significant correlation between ARISE meltwater contributions and the GI. However, the ARISE approach performed better when differentiating glacial influence between streams and over time. Both approaches were significant predictors of macroinvertebrate taxonomic richness, beta diversity, the number of EPT genera and total abundance, although regression models were typically stronger for the ARISE meltwater contribution approach. At the species level, ARISE performed better for predicting the abundance of 13 of the 20 most common taxa. We propose both approaches are valuable for assessing the effects of decreasing meltwater contributions on river ecosystems at the community level but this case study suggests ARISE was better able to identify subtle differences in hydrological change, community response and the abundance of individual taxa. Comparative studies from other catchments are required to further evaluate the two methods.

The Mintom Formation (new): Sedimentology and geochemistry of a Neoproterozoic, Paralic succession in south-east Cameroon

Abstract This paper presents a lithologic and stratigraphic description of the Neoproterozoic (ante- or syn- Pan-African orogeny) Mintom Formation (new) of southeastern Cameroon, and provides a new facies and geochemical analysis of the sedimentary succession, formerly referred to as the upper Dja series. The Mintom Formation can be subdivided from base to top into four members that record a general increase in carbonate content. The members (all new) from lower to upper are: Kol Member (diamictite and pelite), Metou Member (dolostone), Momibole Member (calcareous pelite), and Atog Adjap Member (limestone). Although the lithostratigraphic architecture looks very similar to that of well-documented syn- and post-glacial Neoproterozoic deposits, physical evidence of glacial influence is absent. By contrast with other Central African Neoproterozoic carbonates deposited in ramp settings, the succession does not contain open marine facies. Limestones consist of monotonous subhedral microsparitic calcite mosaics and display occasional microbial laminae. These observations force reevaluation of both previous paleoenvironmental interpretations of the deposits and their comparison with neighboring Ediacaran carbonates. We assume that the graded basal succession from diamictite to laminated pelitic facies is compatible with emplacement of mass flow deposits in toe-of-slope setting during regional uplift. Interpretation of the overlying Metou dolostone is uncertain though sedimentological and geochemical properties point to a likely quiet depositional setting. The upper part of the Formation, including the Momibole and Atog Adjap Members, is conspicuously laminated, in places rhythmically and ripple-bedded, suggesting shallow subaqueous and calm depositional conditions only interrupted by occasional slumps indicative of a locally steepened bottom topography. Evaporitic fabrics and fenestral pores further indicate shallow water, possibly peritidal, environmental conditions. In spite of indications of shale and post-depositional contamination, rare earth elements (REE) plus yttrium (Y) patterns obtained from carbonate samples point to a non-marine origin for the Atog Adjap limestone, but instead deposition in lacustrine or lagoonal settings under freshwater influence. This interpretation suggests that the Mintom Formation formed in a small-scale palaeodepression, isolated from the open marine environment, where confined lagoonal or lacustrine sedimentation developed. The final Neoproterozoic evolution of the Mintom Formation was dominated by erosional features, including striations and stair-cased groove structures reported for the first time here, and revealing the passage of glaciers of likely Ediacaran age.

Observed changes in streamflow at the headwaters of the Urumqi River, eastern Tianshan, central Asia

AbstractThe runoff records of streams draining basins with between 0 and approximately 54% glacier cover, located at the headwaters of the Urumqi River in eastern Tianshan, central Asia, have been examined for the purpose of assessing climatic and glacial influences on temporal patterns of streamflow for the period 1959–2006. Runoff in the highest glacierized basin is found to be inversely correlated with the glacier mass‐balance data and increased by 165·1 × 104 m3 or 1·5 times on average from 1959 to 2006, whereas flow from a glacier‐free basin reflects precipitation changes associated with temperature that may enable either ground ice formation or ice storage release. For the basin with a glacier cover of 18·5%, the runoff increased approximately 355·4 × 104 m3 or 29·6% on average from 1983 to 2006, which underscores expected results based on glacier melt and precipitation increase, especially after 2000. This is due to several possible reasons including enhanced evaporation, groundwater percolation, increased water consumption due to plant colonization and runoff decrease from glacier basins subject to area reduction. From the measurement at Urumqi glacier No. 1 gauging station and a simple water balance model, the glacial runoff during the period 1959–2006 was calculated and found to have increased by 145·5 × 104 m3 a−1 (a factor of 2) over the 48‐year span. A significant amount of the increase occurred after 1987, particularly after 1995, and coincides with increases in both temperature and precipitation. Copyright © 2009 John Wiley & Sons, Ltd.

Holocene foraminiferal assemblages from Firth of Tay, Antarctic Peninsula: Paleoclimate implications

The 77 m sediment core from Firth of Tay provides complete record of glacial retreat and Holocene climate change on the Weddell Sea side of the Antarctic Peninsula that began ~ 9400 yr BP. Benthic foraminiferal data indicate significant environmental changes as recorded at ~ 600 m water depth at the drill site. Three foraminiferal assemblages (FAs): Globocassidulina spp.– Fursenkoina fusiformis FA, Miliammina arenacea FA, and Paratrochammina bartrami– Portatrochammina antarctica FA reflect increasingly glacier-distal conditions. They started with most glacier-proximal conditions that lasted until ~ 8800 yr BP, which is indicated by Cribroelphidium cf. webbi, and continued with elevated input of coarse glacial sediment until ~ 7750 yr BP. The Mid-Holocene Climatic Optimum between 7750 and 6000 yr BP appears to be the time of highest primary production, which led to higher corrosiveness of bottom waters, and biased species composition of the M. arenacea FA. It was terminated by minor cooling. The Neoglacial, that took place after ~ 3500 yr BP, is marked by an increase in P. bartrami and P. antarctica, the major constituents of the P. bartrami– P. antarctica FA. This FA became periodically dominant after ~ 900 yr BP indicating increasingly glacier-distal conditions due to cooling coinciding with increasing aridity, rising altitude of the glacial equilibrium line, and less glacial influence on marine biota. Episodic high-abundances of a fourth foraminiferal assemblage ( Globocassidulina biora FA) that occurs practically throughout the core is difficult to interpret explicitly. Although there are some concerns if G. biora FA represents in situ fauna, it appears to be an opportunistic fauna that dominated during periods of more glacial sediment input and sediment remobilization leading to better carbonate preservation.

Hot Fan or Cold Outwash? Hypothesized Proglacial Deposition in the Upper Paleozoic Cutler Formation, Western Tropical Pangea

Abstract The Permo-Pennsylvanian Cutler Formation in the proximal Paradox basin (western equatorial Pangea) has long been interpreted as low-latitude alluvial-fan deposits shed from the Uncompahgre uplift during the Ancestral Rocky Mountains orogeny. Here, we employ sedimentologic analysis of the Cutler strata within 10 km of its exposed source to hypothesize the alternative interpretation of deposition in a tropical proglacial–periglacial system. At this proximal location, the Cutler Formation onlaps Precambrian basement and dips gently southwestward, such that the section youngs distally. Along the onlap contact, crudely bedded and subhorizontal granule to cobble conglomerate of traction-flow origin is angularly juxtaposed atop inclined (15–30°) boulder diamictite and granule conglomerate of mass-flow origin (inferred subaqueous mass flows). The steeper dips form a semi-radial pattern that, together with facies evidence, suggest a subaqueous fan near this location. Immediately basinward (1–3 km from the onlap) is a gently dipping (≤ 10°) assemblage of cobble diamictite, granule conglomerate, sandstone, and mudstone of inferred subaqueous mass-flow origin. We propose that these associations collectively record topset, foreset and proximal bottomset deposits, respectively, of a lacustrine Gilbert-type delta. The slightly younger Cutler Formation exposed from 3 to 10 km from the onlap contains subhorizontal (≤ 4–7°) granule conglomerate and subordinate sandstone deposited by hyperconcentrated flood flows and traction flow in a fluvial system characterized by frequent high-discharge flow. Scattered siltstone units form a distinct assemblage reflecting silt genesis and eolian sorting (loess deposits), but with common overprinting by lacustrine and fluvial processes. We propose that these facies document the presence of generally abundant water. However, chemical and mineralogical immaturity record relatively minimal chemical weathering most compatible with a cold and wet system. Lateral to the inferred topset exposure, the Cutler strata fill a paleotrough within the Precambrian basement and contain abundant lonestones interpreted to record ice rafting, suggesting that the lacustrine system was, at times, ice-contact. Abundant faceted clasts and loess are also consistent with a glacial influence. Ultimately, the onlap of the Cutler strata onto the Precambrian basement of ancestral Unaweep Canyon, which has elsewhere been hypothesized to be a late Paleozoic valley of glacial origin, establishes a potential link between the two. We propose that, as an alternative to the long-held view of an alluvial fan in a hot (tropical) climate, the facies and climate indicators of the proximal Cutler system record a proglacial to periglacial, largely lacustrine–fluvial system related to tropical glaciation of the Uncompahgre uplift during the late Paleozoic. The proximity of marine and paralic facies to the Cutler “fan” system further implies that such glaciation resulted from cold temperatures, rather than high elevations, thus indicating a globally cool planet during the time recorded by the study section. If valid, this hypothesis raises the possibility that upper Paleozoic strata in other, uplift-proximal equatorial systems record anomalously cold conditions, and perhaps merit reassessment.

Phylogeography of the Alcippe morrisonia(Aves: Timaliidae): long population history beyond late Pleistocene glaciations

BackgroundThe role of Pleistocene glacial oscillations in current biodiversity and distribution patterns varies with latitude, physical topology and population life history and has long been a topic of discussion. However, there had been little phylogeographical research in south China, where the geophysical complexity is associated with great biodiversity. A bird endemic in Southeast Asia, the Grey-cheeked Fulvetta, Alcippe morrisonia, has been reported to show deep genetic divergences among its seven subspecies. In the present study, we investigated the phylogeography of A. morrisonia to explore its population structure and evolutionary history, in order to gain insight into the effect of geological events on the speciation and diversity of birds endemic in south China.ResultsMitochondrial genes cytochrome b (Cytb) and cytochrome c oxidase I (COI) were represented by 1236 nucleotide sites from 151 individuals from 29 localities. Phylogenetic analysis showed seven monophyletic clades congruent with the geographically separated groups, which were identified as major sources of molecular variance (90.92%) by AMOVA. TCS analysis revealed four disconnected networks, and that no haplotype was shared among the geographical groups. The common ancestor of these populations was dated to 11.6 Mya and several divergence events were estimated along the population evolutionary history. Isolation by distance was inferred by NCPA to be responsible for the current intra-population genetic pattern and gene flow among geographical groups was interrupted. A late Pleistocene demographic expansion was detected in the eastern geographical groups, while the expansion time (0.2–0.4 Mya) was earlier than the Last Glacial Maximum.ConclusionIt is proposed that the complicated topology preserves high genetic diversity and ancient lineages for geographical groups of A. morrisonia in China mainland and its two major islands, and restricts gene exchange during climate oscillations. Isolation by distance seems to be an important factor of genetic structure formation within geographical populations. Although glacial influence to population fluctuation was observed in late Pleistocene, it seems that populations in eastern China were more susceptible to climate change, and all geographical groups were growing stably through the Last Glacial Maximum. Coalescence analysis suggested that the ancestor of A. morrisonia might be traced back to the late Miocene, and the current phylogeographical structure of A. morrisonia is more likely to be attributable to a series geological events than to Pleistocene glacial cycles.

Evidence for Dynamic Climate Change on Sub-106-Year Scales from the Late Paleozoic Glacial Record, Tamworth Belt, New South Wales, Australia

Abstract Models of late Paleozoic ice-age climate dynamics have remained enigmatic, in part because preservation of mid- to Late Carboniferous, ice-proximal, Gondwanan glacial deposits is limited to very few Gondwanan regions. As such, detailed sedimentologic and stratigraphic analysis of six formations comprising the well-preserved, mid-Carboniferous to Lower Permian (Namurian or Serpukhovian to late Sakmarian), terrestrial, glacially influenced record from the Tamworth Belt, New South Wales, Australia, provides a unique opportunity to test existing models of late Paleozoic climate, characterize regional glaciation, and resolve the internal pacing of climate during the late Paleozoic ice age. Facies analysis based on twelve logged vertical sections and lateral facies relationships suggests that sediment accumulated in an eastward-draining, volcaniclastically influenced alluvial fan (facies association FA1), fluvial (FA2), and lacustrine (FA3) landsystem. Evidence for proglacial outwash fan (sandar), glaciofluvial, and glaciolacustrine deposition is preserved in the form of texturally diverse diamictite, outsized clasts in fine-grained facies, and rhythmically laminated sandstone and siltstone. The association of these facies, which is termed herein as “distinctly glacial facies” and is taken as direct evidence of glaciation, does not occur through the stratigraphic extent of formations, suggesting that the Tamworth Belt of New South Wales, Australia, was subject to episodic, mountain/valley-type or outlet-type, temperate to subpolar glaciation during the Carboniferous and Early Permian. Climatic shifts and trends occurred on multiple timescales, termed herein “nested cyclicity.” Alternations between distinctly glacial facies and facies that lack evidence of glacial influence, interpreted to record alternating glacial and nonglacial conditions, occurred on timescales on the order of ~ 106 years. The cited age estimates are based on published estimates of glacial interval durations from the region, which in turn reconcile all available radiogenic isotopic data and biostratigraphic zonations. Facies trends within successions recording glacial intervals are interpreted in terms of glacial advance and retreat, which can be estimated to have occurred on timescales shorter than the duration of glacial intervals (shorter-term, sub-106-yr-order timescales) and may include Milankovitch-band cyclicity. These conclusions support the emerging view that the late Paleozoic was characterized by rapid and dynamic climatic shifts on multiple timescales, rather than as one, long protracted event as portrayed by earlier models of Gondwanan glaciation. Furthermore, this study provides an improved understanding of high-latitude climate dynamics and pacing, which may prove useful in constructing improved global models of late Paleozoic climate.

Hydroecological response of river systems to shrinking glaciers

AbstractAquatic ecosystems in high latitude and altitude environments are strongly influenced by cryospheric and hydrological processes due to links between atmospheric forcing, snowpack/glacier mass‐balance, river discharge, physico‐chemistry and biota. In the current phase of global climate warming, many glaciers are shrinking. Loss of snow and ice‐masses will alter spatial and temporal dynamics in bulk basin runoff with important changes in the relative contributions of snowmelt, glaciermelt and groundwater to stream flow. Accordingly, altered water source contributions will be accompanied by changes to fluvial, solute, sediment and thermal regimes and, thus, channel stability and habitat. The projected reduction in sediment load, warmer water temperature and increased channel stability will drive significant shifts in the floral and faunal composition of glacier‐fed rivers. This paper hypothesizes a general increase in the richness and production of micro‐organisms, algae, macroinvertebrates and fish as glacier hydrological influence shrinks under a warmer climate. With reduced glacial influence, macroinvertebrate species trait diversity will increase with more organisms possessing larger body size, less specialized body shape and lower adult mobility. In larger river systems, potential reduction of meltwater inputs will have a significant influence on off‐channel habitats (e.g. side‐channels and sloughs) that depend on glacial runoff to sustain habitat availability and connectivity, particularly for fish. Some species such as cold stenothermic taxa (including some endemic macroinvertebrates) may be vulnerable to extinction and therefore gamma (regional) diversity will be reduced. These sensitive macroinvertebrate taxa may be important biological indicators of environmental change in glacierized river basins. Moreover, high climatic sensitivity and low human perturbation make glacially influenced river basins early indicator systems for identifying hydrological and ecological responses to climate change/variability. It is concluded that glacier shrinkage and associated changes in runoff amount and timing, water source contributions and physico‐chemical habitat will be a major driver of the future biodiversity of stream communities in cold environments. Research imperatives and future directions are proposed for investigation of glacier‐fed river hydroecology. Copyright © 2008 John Wiley & Sons, Ltd.

Late Quaternary foraminiferal assemblages from western Ross Sea (Antarctica) in relation to the main glacial and marine lithofacies

Investigations on foraminifers from Upper Pleistocene–Holocene sediments were carried out on twelve cores from the western Ross Sea continental margin (Drygalski, Joides, North Victoria Land Basins) as part of a “Progetto Nazionale di Ricerche in Antartide” (P.N.R.A.) multidisciplinary project. Data on the foraminiferal frequency, species diversity, tests abundance and their state of preservation were presented as a synthesis of 404 core samples to establish their relationships with the main glacial and marine lithofacies of this area. A total of 126 benthic species, pertaining to 73 genera have been identified; just few taxa, such as Cibicides spp., Globocassidulina spp., Trifarina angulosa and Miliammina spp. being the most ubiquitous and in some cases the dominant species of these paleoenvironments. Two variants of Neogloboquadrina pachyderma, including thin and thick-shelled forms have been recovered. We propose to use these results to provide the degree of glacial control during the Last Glacial Maximum and the following Holocene retreat of the ice sheets. High test fragmentation, low diversity and density tests reflect higher glacial influence of the ice sheet in the Drygalski Basin, whereas the decreasing percentage of fragmentation and a relative increase of density and diversity in Drygalski, Joides and North Victoria Land Basins indicate the paleoenvironmental passage from the ice sheet to the ice shelf condition. The ice shelf retreat is well evidenced in the Joides Basin by a succession of levels barren of foraminifers alternating with high-density levels, rich in T. angulosa, followed by a total disappearance of the calcareous foraminifers. Open-marine settings indicative of lower glacial influence and increased corrosiveness of the water masses is testified by the Miliammina foraminiferal assemblage during the Holocene in Drygalski and Joides Basins cores. On the contrary, rich and abundant benthic and planktonic assemblages characterize the Holocene paleoenvironment of the North Victoria Land area, indicating that the water masses were less corrosive with respect to the other areas. In addition to the glacial reworking of the tests, and the dissolution due to the corrosive water mass conditions, the volcaniclastic sediments recovered in the North Victoria Land Basin cores also affected the condition of test preservation. In volcaniclastic sediments, older than about 20 ka BP, the foraminifers concentration tends to zero and, when present, their tests are highly damaged or completely broken.

The Lower Permian Wasp Head Formation, Sydney Basin: high‐latitude, shallow marine sedimentation following the late Asselian to early Sakmarian glacial event in eastern Australia

AbstractThe Lower Permian Wasp Head Formation (early to middle Sakmarian) is a ∼95 m thick unit that was deposited during the transition to a non‐glacial period following the late Asselian to early Sakmarian glacial event in eastern Australia. This shallow marine, sandstone‐dominated unit can be subdivided into six facies associations. (i) The marine sediment gravity flow facies association consists of breccias and conglomerates deposited in upper shoreface water depths. (ii) Upper shoreface deposits consist of cross‐stratified, conglomeratic sandstones with an impoverished expression of the Skolithos Ichnofacies. (iii) Middle shoreface deposits consist of hummocky cross‐stratified sandstones with a trace fossil assemblage that represents the Skolithos Ichnofacies. (iv) Lower shoreface deposits are similar to middle shoreface deposits, but contain more pervasive bioturbation and a distal expression of the Skolithos Ichnofacies to a proximal expression of the Cruziana Ichnofacies. (v) Delta‐influenced, lower shoreface‐offshore transition deposits are distinguished by sparsely bioturbated carbonaceous mudstone drapes within a variety of shoreface and offshore deposits. Trace fossil assemblages represent distal expressions of the Skolithos Ichnofacies to stressed, proximal expressions of the Cruziana Ichnofacies. Impoverished trace fossil assemblages record variable and episodic environmental stresses possibly caused by fluctuations in sedimentation rates, substrate consistencies, salinity, oxygen levels, turbidity and other physio‐chemical stresses characteristic of deltaic conditions. (vi) The offshore transition‐offshore facies association consists of mudstone and admixed sandstone and mudstone with pervasive bioturbation and an archetypal to distal expression of the Cruziana Ichnofacies. The lowermost ∼50 m of the formation consists of a single deepening upward cycle formed as the basin transitioned from glacioisostatic rebound following the Asselian to early Sakmarian glacial to a regime dominated by regional extensional subsidence without significant glacial influence. The upper ∼45 m of the formation can be subdivided into three shallowing upward cycles (parasequences) that formed in the aftermath of rapid, possibly glacioeustatic, rises in relative sea‐level or due to autocyclic progradation patterns. The shift to a parasequence‐dominated architecture and progressive decrease in ice‐rafted debris upwards through the succession records the release from glacioisostatic rebound and amelioration of climate that accompanied the transition to broadly non‐glacial conditions.

Loess record of the Pleistocene–Holocene transition on the northern and central Great Plains, USA

Various lines of evidence support conflicting interpretations of the timing, abruptness, and nature of climate change in the Great Plains during the Pleistocene–Holocene transition. Loess deposits and paleosols on both the central and northern Great Plains provide a valuable record that can help address these issues. A synthesis of new and previously reported optical and radiocarbon ages indicates that the Brady Soil, which marks the boundary between late Pleistocene Peoria Loess and Holocene Bignell Loess, began forming after a reduction in the rate of Peoria Loess accumulation that most likely occurred between 13.5 and 15 cal ka. Brady Soil formation spanned all or part of the Bølling-Allerød episode (approximately 14.7–12.9 cal ka) and all of the Younger Dryas episode (12.9–11.5 cal ka) and extended at least 1000 years beyond the end of the Younger Dryas. The Brady Soil was buried by Bignell Loess sedimentation beginning around 10.5–9 cal ka, and continuing episodically through the Holocene. Evidence for a brief increase in loess influx during the Younger Dryas is noteworthy but very limited. Most late Quaternary loess accumulation in the central Great Plains was nonglacigenic and was under relatively direct climatic control. Thus, Brady Soil formation records climatic conditions that minimized eolian activity and allowed effective pedogenesis, probably through relatively high effective moisture. Optical dating of loess in North Dakota supports correlation of the Leonard Paleosol on the northern Great Plains with the Brady Soil. Thick loess in North Dakota was primarily derived from the Missouri River floodplain; thus, its stratigraphy may in part reflect glacial influence on the Missouri River. Nonetheless, the persistence of minimal loess accumulation and soil formation until 10 cal ka at our North Dakota study site is best explained by a prolonged interval of high effective moisture correlative with the conditions that favored Brady Soil formation. Burial of both the Brady Soil and the Leonard Paleosol by renewed loess influx probably represents eolian system response that occurred when gradual change toward a drier climate eventually crossed the threshold for eolian activity. Overall, the loess–paleosol sequences of the central and northern Great Plains record a broad peak of high effective moisture across the late Pleistocene to Holocene boundary, rather than well-defined climatic episodes corresponding to the Bølling-Allerød and Younger Dryas episodes in the North Atlantic region.

Rivers and loess: The significance of long river transportation in the complex event-sequence approach to loess deposit formation

Rivers are essential for loess deposit formation. River systems which relate directly to loess deposit formation include the Danube and the Rhine; the Mississippi and the Missouri; the Thames and the Medway; the Indus, Ganges and Brahmaputra; the Dnepr, Don and Volga; the Clutha, Mataura and Rakaia—New Zealand rivers; the Yellow River; rivers in South America; Siberian rivers (flowing north); the Odra and the Wisla (between the mountains and the ice); the Syr-Darya and Amu-Darya (into the desert). The contention is that rivers are not just important in major loess deposit formation, they are mandatory (necessary, imperative, obligatory, essential, indispensable, requisite). For a complete and satisfactory study of a loess deposit, we need to know how the material is produced; how it is transported and distributed across the landscape; how intermediate deposits are formed; how transportation provides the defining properties (i.e., open structure, collapsibility, draping across the landscape); and what may happen post-deposition (e.g., chernozemisation, fragipan formation, increased collapsibility, etc.). If rivers are essential then it would appear that the British loess is probably Alpine material delivered by the proto-Rhine and the Polish loess is not derived from the ice-sheet to the north but from the mountains to the south. The lack of loess in Canada is explained by the absence of suitable rivers. The loess in Russia and neighbouring countries can be classified (as Jefferson et al. [Jefferson, I.F., Evstatiev, D., Karastenev, D., Mavlyanova, N.G., Smalley, I.J., 2003b. The engineering geology of loess and loess-like deposits: a commentary on the Russian literature. Engineering Geology 68, 333–351] suggested) on the basis of associated rivers. A ‘new’ deposit of glacial loess is recognised—associated with the Dnepr, Don and Volga rivers (the USWR loess). The Smalley–Leach [Smalley, I.J., Leach, J.A., 1978. The origin and distribution of the loess in the Danube basin and associated regions of East-Central Europe: a review. Sedimentary Geology 21, 1–26. Available from: 〈 www.geo.edu.ro/sgr/mod/downloads/PDF/Smalley-SedGeo-1978.pdf〉] vision of the loess in the Danube basin and East-Central Europe is probably misconceived. They assigned a great significance to glacial action and put loess in a ‘northern band’. It appears that this proposed glacial influence is minimal and that the Danube loess is essentially mountain loess—derived from the Alps, the Carpathians, the Sudeten mountains and other high regions. The Danube system is a classic example of a river controlling loess distribution.

New evidence for a postglacial homoploid hybrid origin of the widespread Central European Scabiosa columbaria L. s. str. (Dipsacaceae)

We have tested whether Scabiosa columbaria s. str. could have originated by recent homoploid hybrid speciation because it is of intermediate morphology and is distributed in areas under glacial influence. Existing morphological and new RAPD data for 11 ingroup populations were analysed using multivariate statistics. Most methods indicated that S. columbaria s. str. could be the first example for a homoploid hybrid origin from Central Europe although a rigorous proof was missing partly because of ongoing introgression. Sequence variation was absent for 5,000 bp from 11 regions supporting a postglacial origin of S. columbaria s. str. An analysis of realized macroclimatic niches using GIS data showed that the niches of S. columbaria s. str. were partly intermediate between its putative parental species rather than extreme as often found in other homoploid hybrids. This could be due to geographical preconditions: large new habitats were available in postglacial Europe while in the case of most other homoploid hybrids only ecologically challenging habitats were not occupied by parental taxa.

HydroTrend v.3.0: A climate-driven hydrological transport model that simulates discharge and sediment load leaving a river system

HydroTrend v.3.0 is a climate-driven hydrological water balance and transport model that simulates water discharge and sediment load at a river outlet, by incorporating drainage basin properties (river networks, hypsometry, relief, reservoirs) together with biophysical parameters (temperature, precipitation, evapo-transpiration, and glacier characteristics). HydroTrend generates daily discharge values through: snow accumulation and melt, glacier growth and ablation, surface runoff, and groundwater evaporation, retention and recharge. The long-term sediment load is predicted either by the ART- QRT module based on drainage area, discharge, relief, and temperature, or the BQART module that also incorporates basin-average lithology and anthropogenic influences on soil erosion. Sediment trapping efficiency of reservoirs is based on reservoir location in the river network and its volume that determines the residence time of water within the reservoir. Glacial influence is based on the extent of ice cover, equilibrium altitude, and freezing line mobility. HydroTrend v.3.0 captures the inter- and intra-annual variability of sediment flux by using either high-resolution climate observations or a stochastic climate generator for simulations over longer geological intervals. A distributary channel module simulates the flow conditions and transport capacity across a multiple deltaic channel system. Simulations of the Metauro and the Po rivers, in Italy, are used as case studies to demonstrate the applicability of the new model.

Distribution and spawning dynamics of capelin (Mallotus villosus) in Glacier Bay, Alaska: a cold water refugium

AbstractPacific capelin (Mallotus villosus) populations declined dramatically in the Northeastern Pacific following ocean warming after the regime shift of 1977, but little is known about the cause of the decline or the functional relationships between capelin and their environment. We assessed the distribution and abundance of spawning, non‐spawning adult and larval capelin in Glacier Bay, an estuarine fjord system in southeastern Alaska. We used principal components analysis to analyze midwater trawl and beach seine data collected between 1999 and 2004 with respect to oceanographic data and other measures of physical habitat including proximity to tidewater glaciers and potential spawning habitat. Both spawning and non‐spawning adult Pacific capelin were more likely to occur in areas closest to tidewater glaciers, and those areas were distinguished by lower temperature, higher turbidity, higher dissolved oxygen and lower chlorophyll a levels when compared with other areas of the bay. The distribution of larval Pacific capelin was not sensitive to glacial influence. Pre‐spawning females collected farther from tidewater glaciers were at a lower maturity state than those sampled closer to tidewater glaciers, and the geographic variation in the onset of spawning is likely the result of differences in the marine habitat among sub‐areas of Glacier Bay. Proximity to cold water in Glacier Bay may have provided a refuge for capelin during the recent warm years in the Gulf of Alaska.

The Neoproterozoic glacial record in the Río de la Plata Craton: a critical reappraisal

Abstract Neoproterozoic glacial successions have been described in South America, but the glacial deposits of the Río de la Plata Craton have been neglected in previous studies addressing the global distribution of glacially influenced successions. The Río de la Plata Craton contains Neoproterozoic glacial deposits in the Sierra del Volcán Formation (Tandilia System, Argentina), glacial influenced deposits in the Playa Hermosa and Zanja del Tigre formations (Dom Feliciano Belt, Uruguay) and suspected glacially influenced deposits in Passo da Areia (São Gabriel block, Brazil). The Tandilia System glacial record includes diamictites, dropstones and rhythmites deposited in glaciomarine conditions in a tectonically stable depositional setting. The Dom Feliciano Belt includes a thin section with ice-rafted clasts in carbonates and a thicker section containing diamictites, rhythmites, outsized clasts and deformed beds in a volcano-sedimentary succession. The São Gabriel block occurrence deserves more attention to confirm any glacial influence in the fine-grained part of the succession. Glaciation is considered to be contemporaneous with the Gaskiers glaciation (580 Ma), with the exception of the carbonates with dropstones that may represent a previous event correlative with one of the glaciations described in the Kalahari Craton, prior to Kalahari–Río de la Plata assembly in the proto-western Gondwana margin.

Seismic facies and stratigraphy of the Cenozoic succession in McMurdo Sound, Antarctica: Implications for tectonic, climatic and glacial history

Integration of data from fully cored stratigraphic holes with an extensive grid of seismic reflection lines in McMurdo Sound, Antarctica, has allowed the formulation of a new model for the evolution of the Cenozoic Victoria Land Basin of the West Antarctic Rift. The Early Rift phase (Eocene to Early Oligocene) is recorded by wedges of strata confined by early extensional faults, and which contain seismic facies consistent with drainage via coarse-grained fans and deltas into discrete, actively subsiding grabens and half-grabens. The Main Rift phase (Early Oligocene to Early Miocene) is represented by a lens of strata that thickens symmetrically from the basin margins into a central depocenter, and in which stratal events pass continuously over the top of the Early Rift extensional topography. Internal seismic facies and lithofacies indicate a more organized, cyclical shallow marine succession, influenced increasingly upward by cycles of glacial advance and retreat into the basin. The Passive Thermal Subsidence phase (Early Middle Miocene) is recorded by an evenly distributed sheet of strata that thickens somewhat into the depocentre but is continuous across and over the earlier rift strata to the margins of the basin. Internally, it contains similar facies to the underlying Main Rift, but preserves more evidence for clinoform sets and large channels, and in core comprises many short, condensed and strongly top-truncated stratal cycles with continued, periodic glacial influence. These patterns are interpreted to record accumulation under similar environmental conditions but in a regime of slower subsidence. The Renewed Rifting phase (Middle Miocene to Recent, largely unsampled by coring thus far) is represented by intervals that thicken significantly into the basin depocentre and that are complicated by evidence of magmatic activity (McMurdo Volcanic Group). This succession is further divided into lower and upper intervals, separated by a major unconformity that displays increasing angular discordance towards the western basin margin and Transantarctic Mountain Front. The youngest part of the stratigraphy was accumulated under the influence of flexural loading imposed by the construction of large volcanic edifices, and was formed in an environment in which little sediment was supplied from the western basin margin, suggesting a change in environmental (glacial) conditions at possibly c. 2 Ma. The Cenozoic stratigraphy of the southern Victoria Land Basin preserves archives of both climate change and the complex rift history of the basin, and coincidences between key stratal surfaces in seismic data and evidence for environmental change in drillcores suggest that tectonic and climatic drivers may be causally linked.

Deformation in the Neoproterozoic Smalfjord Formation, northern Norway: an indicator of glacial depositional conditions?

AbstractRecent studies on Neoproterozoic climate change have prompted renewed interest in Neoproterozoic glacial deposits and renewed debate over the criteria used to identify the nature of glacial influence on sedimentation. Analyses of soft sediment deformation structures have provided important clues to distinguish between competing palaeoenvironmental interpretations of Quaternary glacial deposits; a similar approach is presented here in the analysis of Neoproterozoic glacial deposits of the Smalfjord Formation, northern Norway. A detailed sedimentological and structural analysis at several sites in the Varangerfjorden area reveals complex soft sediment deformation at various scales in conglomerate, sandstone and diamictite. Deformation is predominantly ductile and includes anticlinal and synclinal folding, flow noses, flame structures, recumbent folding and shear structures. The deformed sediments are associated predominantly with conglomerate and sandstone, which record glaciofluvial and deltaic depositional conditions. Some deformations can be attributed to rapid deposition and slumping, whereas others appear to record shear stress associated with overriding ice. The scale, style and range of deformation, together with the coarse‐grained nature of the deformed sediments and facies associations, suggest that these were unfrozen outwash sediments that were overridden by ice and resedimented in a dynamic ice‐proximal setting. Whereas recent studies of diamictite‐bearing strata of the Smalfjord Formation had revealed no clear evidence of glacial influence on deposition, deformation structures documented here suggest that glacial conditions prevailed on the basin margin during deposition of Smalfjord Formation sediments, with sedimentary facies and deformation structures typical of temperate ice‐proximal settings.

Deglaciation sequences in the Permo-Carboniferous Itararé Group, Paraná Basin, southern Brazil

The Late Carboniferous–Early Permian Itararé Group is a thick glacial unit of the Paraná Basin. Five unconformity-bounded sequences have been defined in the eastern outcrop belt and recognized in well logs along 400 km across the central portion of the basin. Deglaciation sequences are present in the whole succession and represent the bulk of the stratigraphic record. The fining-upward vertical facies succession is characteristic of a retrogradational stacking pattern and corresponds to the stratigraphic record of major ice-retreat phases. Laterally discontinuous subglacial tillites and boulder beds occur at the base of the sequences. When these subglacial facies are absent, deglaciation sequences lie directly on the basal disconformities. Commonly present in the lowermost portions of the deglaciation sequences, polymictic conglomerates and cross-bedded sandstones are generated in subaqueous proximal outwash fans in front of retreating glaciers. The overlying assemblage of diamictites, parallel-bedded and rippled sandstones, and Bouma-like facies sequences are interpreted as deposits of distal outwash fan lobes. The tops of the deglaciation sequences are positioned in clay-rich marine horizons that show little (fine-laminated facies with dropstones) or no evidence of glacial influence on the deposition and likely represent periods of maximum ice retreat.

The northwestern Argentina Tarija Basin: Stratigraphy, depositional systems, and controlling factors in a glaciated basin

The Tarija Basin, shared by Bolivia and Argentina, was subjected to glacial conditions during the Late Carboniferous and Early Permian. The Macharetí and Mandiyutí groups deposited during these times record in their facies advances and retreats of the Gondwanan ice cap. The lithostratigraphic subdivision of these groups presents stages with minor glacial influence in the basal formations of each group (Tupambi and Escarpment formations), whereas in the upper units, glacially related deposition prevails (Tarija and San Telmo formations). Typical facies deposited in relation to glacial settings are diamictites and mudstones mainly related to proglacial, lacustrine environments. During the stages of main ice retreat, deposition was dominated by fluvial and deltaic sandstones. Significant erosion and deep valley incision characterize the basal surfaces of both groups. Conversely, the stratigraphic surface that separates the sandy formations from the overlying diamictites tends to be rather flat. The dynamics of the glacial cap are not only reflected in the facies distribution but also were a key factor in creating accommodation space; the changes in the glacial-driven subsidence linked to the advance and retreat of the ice were its main control.