Proglacial Basin Research Articles

Glacial Erosion Rates Since the Last Glacial Maximum for the Former Argentino Glacier and Present‐Day Upsala Glacier, Patagonia

AbstractRecovering the patterns of glacial erosion over time is key to understanding feedbacks between climate and tectonic processes. Glacial erosion rates have been shown to systematically increase worldwide toward the present since the late Cenozoic, a behavior interpreted as the response of glaciers to a cooling and increasingly variable climate. However, the validity of this signal has been questioned, and suggested to be affected by the incompleteness of the sedimentary record, which can introduce a time dependent bias in the time averaged rates. In this study, we present new glacial erosion rates estimated from sediment accumulations in Lago Argentino, Patagonia, a proglacial basin with a nearly complete preserved sedimentary record. The erosion rates are estimated through the past 20,000 years and averaged over time intervals ranging from sub‐decadal to millennial, allowing us to explore erosion rate variability through time and within a glacial cycle. The data show that erosion rates have varied substantially, from 0.43 0.12 to 82.38 17.58 mm/yr, with no systematic increase (or decrease) through time. Rather, erosion occurs during discrete, intense events separated by times of quiescence. In addition, we find that glacial erosion rates have comparable magnitudes when averaged over similar time intervals. Our data show a power‐law increase in glacial erosion rates with decreasing averaging time interval, consistent with other observations globally. Given our observed intermittent character of glacial erosion, we attribute this increase to a time averaging bias, rather than to an escalation in magnitude of erosional pulses toward the present.

LATE GLACIAL PALAEOENVIRONMENT AND DEVELOPMENT OF PROGLACIAL LAKES ON THE NORTHERN COAST OF THE SAMBIAN (KALININGRAD) PENINSULA<a href="#FN1"><sup>1</sup></a>

Comprehensive investigations of the northern coast of the Sambian (Kaliningrad) Peninsula, that included geomorphological survey, lithostratigraphic description of the section logs, diatom, botanical and LOI analyses, radiocarbon dating, and GNSS survey relating lithological boundaries and sampling levels to the sea level and determining terrace elevations, were performed. New data on the regional palaeogeographic settings of the Late Glacial period and the stages of development of the large proglacial basin, the Baltic Ice Lake (BIL) were obtained. It has been established that after the degradation of the last glaciation, erosional (subaquatic) processes prevailed in the coastal area, while in the interval of 14–13 cal kyr BP subaerial conditions established at the study site, and tree-moss phytocenoses formed during the Allerød warming. At the end of the warming period there was a shallow, isolated lake, with decreasing depth. During the Younger Dryas oscillation, ca. 12 000 cal kyr BP, the area was flooded by waters of a vast freshwater, ultra-oligotrophic basin with high content of suspended fine mineral particles. The conditions of a shallow bay of the BIL sheltered from the main basin by a moraine ridge at least 4–5 m high, are suggested for this period. The lake drainage took place around 11 660 cal kyr BP. Since then, no accumulation or alternating accumulation and erosion conditions prevailed in the study site until the late Holocene. The obtained results allow us to speak about two stages of flooding of the northern coast of the Sambia Peninsula during the Late Glacial, possibly caused by the BIL transgressions. The occurrence of BIL deposits in the northern part of the Sambia Peninsula above sea level suggests that the Late Glacial basin level in the study area may have exceeded the present sea level.

Позднеледниково-голоценовая стратиграфия донных отложений из котловин малых изолированных озер баренцевоморского побережья (Кольский регион)

Lithological study and diatom analysis of the bottom sediments from small lakes belonging to the category of isolated basins located on the Barents Sea coast of the Kola region was carried out. Stratigraphic subdivision of depositional sequences was performed based on the new data obtained from the Settlement Teriberka area, as well as on the published data from other areas; lithostratigraphic units (LSU), which are stratogens, were identified in them. We found out that the proglacial reservoir was marine during deglaciation on the Barents Sea coast, freshwater (LSU 1) sediments of the ice-marginal basins were not found here (LSU 1). In the lake basins isolated from the sea, the depositional sequences in deep parts of isolated basins is represented by: brackishwater sediments of the proglacial basin (LSU 2), Lateglacial brackishwater sediments (LSU 3), marine sediments (LSU 4), sediments of an isolating lagoon (LSU 5), sediments accumulated in a meromictic lake (LSU 6), sediments of an onshore freshwater lake (LSU 7), sediments of a freshwater lake with slightly increased water mineralization deposited during Early-Mid Holocene Tapes transgression (LSU 8) and lacustrine sediments (LSU 9) are represent in the sedimentary sequences from small isolated lakes in the Barents Sea coast.

Subglacial evolution from distributed to channelized drainage: Evidence from the Lake Murtoo area in SW Finland

AbstractDuring the last millennia of the Weichselian glaciation (c. 11 700–14 000 cal BP) and the first millennium of the Holocene interglacial (c. 10 500–11 700 cal BP), melting of the ice sheet and subsequent subglacial drainage resulted in the formation of murtoos and murtoo‐related landforms in the Fennoscandian Ice Sheet area in Finland and Sweden. Murtoos are composed of clay‐poor diamictons produced by sediment‐concentrated creep and material sorting in a subglacial environment under effective pressure close to zero, and potentially represent a transition form from non‐channelized to channelized subglacial drainage networks. Here, we explore the geomorphology and substratum characteristics of the Lake Murtoo area, one of the locations where murtoos were initially found and described in SW Finland. Our interpretation suggests an interconnected development from inefficient distributed or semi‐distributed cavities (murtoos) to efficient channelized drainage (esker) via erosional escarpments, all displayed in the same region. In addition, our excavation into a murtoo‐related erosional escarpment (MRE) revealed subglacial erosional channels alongside MREs that were filled with fine‐grained finely laminated sediments. We suggest that these channel fill sediments were deposited subglacially, because they are covered by flow till and show spatial and lithological characteristics that deviate significantly from the proglacial basin fill clay (varve) sediments in the area. The appearance of rhythmically laminated silt and clay sediments indicates sedimentation in a suspension‐load‐dominated environment in shallow subglacial channels with relatively low (but repetitiously changing) water flow velocities, possibly reflecting disconnected spill‐over routes of subglacial drainage in small tributaries that were only periodically used due to water pressure changes in the up‐ice direction.

Seasonal dynamics of meroplankton in a sub-Antarctic fjord (Southern Patagonia, Chile)

Knowledge of seasonal dynamics and composition of meroplankton (larvae of benthic invertebrates) is rather limited for sub-Antarctic regions. We studied the seasonal dynamics of meroplankton in a sub-Antarctic proglacial basin (Gallegos Sound, Chile), by examining changes in the meroplankton community in relation to hydrographic variables along four sampling cruises between early winter 2010 and late winter 2011. The local meroplankton community was composed of 39 larval morphotypes distributed among 11 major taxa, being polychaetes the best represented (15 larvae morphotypes), and bivalve the most abundant. We found distinct seasonal differences in terms of meroplanktonic composition and abundance, with higher abundance and larval morphotype number during austral spring and late winter, and lower in summer and early winter. The pattern observed for meroplankton was directly related to seasonal variations of fluorescence of chlorophyll a and temperature. We found meroplankton abundances lower than those of other sub- and Polar environments. However, meroplanktonic temporal dynamics showed a common pattern for sub- and Polar fjords, suggesting a strong link between benthic spawning and the occurrence of phytoplankton blooms.

A comparison of glacial and paraglacial denudation responses to rapid glacial retreat

AbstractGlacier thinning and retreat drives initial acceleration of glacier sliding and erosion, de-buttressing of steep valley walls, and destabilization of ice-marginal deposits and bedrock, which can lead to massive rock avalanching and accelerated incision of tributary watersheds. A compelling example of these changes occurred in Taan Fjord in SE Alaska due to the rapid thinning and retreat of Tyndall Glacier over the past half century. Increased glacier sliding speeds led to both increased rates of subglacial erosion and the evacuation of subglacially stored sediments into the proglacial basins. The shrinking glacier also exposed proglacial tributary watersheds to rapid incision and denudation driven by >350 m of baselevel fall in a few decades. Moreover, in October 2015 a large tsunamigenic landslide occurred at the terminus of Tyndall Glacier, largely due to thinning exposing oversteepened, unstable slopes. Sediment yields from the glacier, the landslide and the tributary watersheds, measured from surveys of the sediments in the fjord collected in 1999 and 2016, are compared to ongoing changes in glacier and fjord geometry to investigate the magnitude of glacial and paraglacial denudation in Taan Fjord during retreat. In the last 50 years, sediment yields from the glacier and non-glacial tributaries kept pace with the rapid rate of retreat, and were on par with each other. Notably, basin-averaged erosion rates from the paraglacial landscape were twice that from the glacier, averaging 58 ± 9 and 26 ± 5 mm a−1, respectively. The sharp increases in sediment yields during retreat observed from both the glacier and the adjacent watersheds, including the landslide, highlight the rapid evolution of landscapes undergoing glacier shrinkage.

Post-jökulhlaup geomorphic evolution of the Gígjökull Basin, Iceland

AbstractHow landscapes respond to, and evolve from, large jökulhlaups (glacial outburst floods) is poorly constrained due to limited observations and detailed monitoring. We investigate how melt of glacier ice transported and deposited by multiple jökulhlaups during the 2010 eruption of Eyjafjallajökull, Iceland, modified the volume and surface elevation of jökulhlaup deposits. Jökulhlaups generated by the eruption deposited large volumes of sediment and ice, causing significant geomorphic change in the Gígjökull proglacial basin over a 4-week period. Observation of these events enabled robust constraints on the physical properties of the floods which informs our understanding of the deposits. Using ground-based LiDAR, GPS observations and the satellite-image-derived ArcticDEMs, we quantify the post-depositional response of the 60 m-thick Gígjökull sediment package to the meltout of buried ice and other geomorphic processes. Between 2010 and 2016, total deposit volume reduced by −0.95 × 106 m3 a−1, with significant surface lowering of up to 1.88 m a−1. Surface lowering and volumetric loss of the deposits is attributed to three factors: (i) meltout of ice deposited by the jökulhlaups; (ii) rapid melting of the buried Gígjökull glacier snout; and (iii) incision of the proglacial meltwater system into the jökulhlaup deposits.

Spatial heterogeneity in the paraglacial response to post‐Little Ice Age deglaciation of four headwater cirques in the Western Alps

AbstractThis paper aims to understand how the paraglacial response to recent glacier retreat varies between four cirques in the Western Alps. Post‐Little Ice Age glacier retreat has created extensive forelands where a variety of gravitational and fluvial process operate on both till‐floored and rock‐floored cirques. These processes may affect transitions from subglacial to proglacial landsystems, by reworking sediment and reorganising drainage. Landsystems achieve a state of preservation once no more adjustment is possible due to buffering by channel network evolution, channel armouring, and sediment exhaustion. We find no consistent trajectory of change across all studied sites: paraglacial responses differ from the classical valley–glacier model, involving variable slope‐channel coupling. Proglacial drainage networks on till surfaces have become more integrated by reducing their low‐order bifurcation ratios, unlike streams locked into rock channels. Reasons for diverse and site‐specific behaviour include cirque floor width, gradient, and surface materials (bedrock, fine till, and/or blocky till). At some cirques, these restrict the downstream diffusion of a paraglacial “signal” of fluvial‐transported sediment. At others, increased sediment flux originated from the erosion of terminal moraines. A high proportion of glacial material generally remains within the glacier foreland, due to proglacial basin sediment traps, inefficiency of fluvial networks, armouring of floors by coarse tills, and rock‐controlled channels. The millennial‐timescale preservation potential of most recent primary glacial deposits and within‐cirque paraglacial landforms appears to be high.

Holocene pollen record from Lake Sokoch, interior Kamchatka (Russia), and its paleobotanical and paleoclimatic interpretation

A pollen record, obtained from sediments of Lake Sokoch in mountain interior of the Kamchatka Peninsula, covers the last ca. 9600years (all ages are given in calibrated years BP). Variations in local components, including pollen, spores and non-pollen palynomorphs, and related changes in sedimentation document the lake development from initially seepage and shallow basin to deeper lake during the mid Holocene and then to the hydrologically open system during the late Holocene. The studies of volcanic ashes from the lake sediment core show their complex depositional histories.Lake Sokoch occupies a former proglacial basin between two terminal moraines of the LGM time. The undated basal part of record before ca. 9600year BP, however, does not reflect properly cold conditions. At that time, although shrublands and tundra dominated, stone birch and white birch forests have already settled in surroundings; the presence of alder woodland indicates wet and maritime-like climate. The subsequent forest advance suggesting warmer conditions was interrupted by the ca. 8000–7600year BP spell of cooler climate. The following culmination of warmth is bracketed by the evidence of the first maximal forest extent between ca. 7400 and 5100year BP. During that time, dramatic retreat of alder forest suggests a turn from maritime-like to more continental climate conditions. The cool and wet pulse after ca. 5100year BP was pronounced as forests retreat while shrublands, meadows and bogs extended. An expansion of white birch forest since ca. 3500year BP reflected the onset of drier climate, strengthening continentality and seasonal contrast. The second maximum of forests dominated by both stone and white birches occurred between ca. 2200 and 1700year BP and indicated warming in association with relatively dry and increasingly continental climate. The following period was wetter and cooler, and minor outbreak of alder forest around ca. 1500year BP suggests a short-term return of maritime-like conditions. Since ca. 1300year BP forests retreated and replaced by shrublands, tundra and bogs, pointing to cool and wet climate and likely increased back continentality. A prominent re-advance of stone birch forest shown atop the record, most probably reflects recent warming trend.The reconstructed cool periods correlate well with Holocene glacial advances in neighboring mountain areas and with the tree ring and ice core records from the Central Kamchatka Depression. The Lake Sokoch pollen record, being consistent with the previously obtained regional paleoclimatic data, yet contributes new detailed information, especially for the late Holocene.

Late Weichselian varve archives re-explored to assess proglacial sedimentary chronologies using the principles of tree-ring analysis

Glaciogenic varves are formed annually in proglacial basins and provide detailed geochronological archives about the dynamics of deglaciation. Varve chronologies are constructed from multiple varve series measured at individual localities. Temporal connection between the series is traditionally achieved by visual comparison of varve-thickness variations. This connection method resembles that of dendrochronological cross-dating. By contrast, dendrochronological correlation proceeds through the routine of statistical (along with visual) comparisons between the tree-ring series, providing quantification of the dating results, their veracity and robustness. Here we demonstrate the advantages and convenience of applying tree-ring statistical methods to varve records, using an extensive varve archive originating from southern Finland. The data series of individual varve-thickness diagrams were metamorphosed by detrending, prewhitening and averaging, that is, by the methods adopted from tree-ring science. Subsequently, it was seen that the series having 80 or more varves have a higher potential to be unambiguously cross-dated than shorter series. The varve-thickness diagrams could be categorized into two types, those having regional chronological importance and those showing only subregional (distance < 20 km) correlativity. The varves of former type ought to be regarded as primary constituents of the geochronology. The varves of latter type have low geochronological validity although they may bear local sedimentological importance. The findings have the potential to modernize the science of varve-based geochronologies.

Lithofacies-genetic characteristics of sedimentary basins in the foreland of the Pomeranian Stage in the Drawsko Lakeland (northern Poland)

Lithofacies-genetic characteristics of sedimentary basins in the foreland of the Pomeranian Stage in the Drawsko Lakeland (northern Poland) The research carried out in the years 1995-98 in the area of the Złocieniec proglacial lake inclined its authors to take a broader view of the operation of proglacial basins in the Drawsko Lakeland (Paluszkiewicz 2004). Glaciolacustrine deposits in the studied lakeland area were discovered by Maksiak and Mróz in 1978. Until that time, the varved deposits at Złocieniec had not been subjected to lithological analysis. The more detailed studies conducted by the present authors in the years 2006-2007 at both Złocieniec and Wierzchowo sites with the help of geo-engineering methods allowed them to show that the two sites with varved clays in this region should be treated as separate sedimentary basins. The basins differ in thickness of varved deposits, in size, and processes responsible for the formation of the rhythmically stratified series.

Time‐transgressive tunnel valley formation indicated by infill sediment structure, North Sea – the role of glaciohydraulic supercooling

AbstractStructure and lithology of the infill sediments from 16 subglacial buried tunnel valleys of Pleistocene age in the North Sea were analyzed using 3D seismic data and geophysical log data from five hydrocarbon exploration wells. The infill sediments are characterized by three seismic facies: Facies I, the volumetrically most important and structurally most distinct, is composed of clinoform reflections downlapping axially up‐valley (up‐ice), Facies II is composed of near‐horizontal, continuous and well layered reflections onlapping the clinoform reflections and the valley walls and Facies III is composed of clinoform reflections downlapping axially down‐valley (down‐ice). A model of formation of this sediment architecture is proposed, in which valley incision and infill are causally linked. It is proposed that Facies I is related to glaciohydraulic supercooling of subglacial meltwater in the distal parts of tunnel valleys. The valleys formed time‐transgressively during ice retreat, whereby sediment eroded further up‐ice was re‐deposited along adverse subglacial slopes of the valleys close to the ice margin. The formation of Facies II and III is related to the deposition in proglacial basins during final deglaciation. Copyright © 2008 John Wiley & Sons, Ltd.

Variations in the influence of riverine discharge on the Kara Sea during the last deglaciation and the Holocene

Several sediment cores from the Kara Sea have been analyzed with a special emphasis on heavy-mineral, foraminiferal, and stable-isotopic composition of sediments. The temporal variations of these characteristics, controlled by 14C ages in some cores, allow us to reconstruct the history of latest Weichselian and Holocene sedimentation in the Kara Sea in relation to the discharge of the large Siberian Ob' and Yenisey rivers. We conclude that during the Last Glacial Maximum (LGM) these rivers were blocked by the Barents–Kara ice sheet that occupied the northern part of the Kara Sea. This blockage likely created a proglacial basin on the Kara Sea shelf; its effect on the Siberian drainage needs further investigation. With deglaciation and sea-level rise, river mouths migrated across the Kara Sea shelf to their modern estuaries. This retreat, combined with high early-Holocene insolation levels, had a profound influence on biota and sedimentation throughout the Kara Sea. Subsequent changes in riverine discharge did not affect the Kara Sea as strongly as during deglaciation and the early Holocene. A significant increase in discharge is inferred to have started after ca. 1.5 ka.

Sedimentological evidence of a meandering Younger Dryas subglacial conduit: Horn, SE central Sweden

The lateral displacement of a subglacial conduit, consisting of an area of subglacial conduit-mouth deposits covered by various subglacial and flow tills, is recognized in an abandoned gravel pit at Horn (near Nyköping). The displacement took place during a cold period (Younger Dryas) when the subglacial discharge of meltwater towards a proglacial basin was low. The sedimentary succession contains glaciofluvial deposits overlain by lodgement and flow tills. The superposition of tills may reflect oscillations of the ice in the frontal zone of the Scandinavian ice sheet during the Younger Dryas stadial. The tills are suggested to have been deposited in the conduit-mouth environment. The larger extent of the glaciofluvial unit, as compared to the limited range of the outcropping flow tills, is interpreted as evidence of lateral movement of the subglacial conduit in the frontal zone of the ice sheet. The study confirms a limited subglacial meltwater drainage in the study area during the Younger Dryas.