Sedimentation associated with glaciovolcanism: a review

Three discrete categories of sedimentary deposits are associated with glaciovolcanism: englacial cavity, jökulhlaup and lahar. Englacial cavity deposits are found in water-filled chambers in the lee of active glaciovolcanoes or at a locus of enhanced geothermal heat flux. The cavities provide a depocentre for the accumulation of debris, either abundant fresh juvenile debris with sparse dropstones (associated with active glaciovolcanism) or polymict basal glacial debris in which dropstones are abundant (associated with geothermal hot spots). Described examples are uncommon. By contrast, volcanogenic jökulhlaup deposits are abundant, mainly in Iceland, where they form extensive sandar sequences associated with ice-covered volcanoes. Jökulhlaups form as a result of the sudden subglacial discharge of stored meltwater. Analogous deposits known as glaciovolcanic sheet-like sequences represent the ultra-proximal lateral equivalents deposited under the ice. Glaciovolcanic lahars are associated with ice-capped volcanoes. They form as a result of explosive eruptions through relatively thin ice or following dome collapse, and they trigger mainly supraglacial rather than subglacial meltwater escape. Sediment transport and depositional processes are similar in jökulhaups and lahars and are dominated by debris flow and hyperconcentrated or supercritical flow modes during the main flood stage, although the proportions of the principal lithofacies are different.

Automated detection and analysis of surface calving waves with a terrestrial radar interferometer at the front of Eqip Sermia, Greenland

Glacier calving is a key dynamical process of the Greenland Ice Sheet and a major driver of its increasing mass loss. Calving waves, generated by the sudden detachment of ice from the glacier terminus, can reach tens of meters in height and provide very valuable insights into quantifying calving activity. In this study, we present a new method for the detection of source location, timing, and magnitude of calving waves using a terrestrial radar interferometer. This method was applied to 11 500 1 min interval acquisitions from Eqip Sermia, West Greenland, in July 2018. Over 7 d, more than 2000 calving waves were detected, including waves generated by submarine calving, which are difficult to observe with other methods. Quantitative assessment with a wave power index (WPI) yields a higher wave activity (+49 %) and higher temporally cumulated WPI (+34 %) in deep water than under shallow conditions. Subglacial meltwater plumes, occurring 2.3 times more often in the deep sector, increase WPI and the number of waves by a factor of 1.8 and 1.3, respectively, in the deep and shallow sector. We therefore explain the higher calving activity in the deep sector by a combination of more frequent meltwater plumes and more efficient calving enhancement linked with better connections to warm deep ocean water.

Late Cenozoic (13-0 Myr) Glacimarine Sedimentology, Facies Analysis, and Sequence Stratigraphy from the Western Ross Embayment, Antarctica: Implications for the Variability of the Antarctic Ice Sheets

<p>Sedimentary processes related to oscillations of the marine-based sector of Antarctic Ice Sheet (AIS) in the Ross Embayment over the past 13 Myr are examined at various timescales from stratigraphic records of glacial advance and retreat obtained from the McMurdo Sound region. An initial sedimentary model was developed from short (<2 m) sediment cores collected from beneath the present-day McMurdo Ice Shelf and seasonally open water in the Ross Island region. These cores document sedimentary processes associated with subglacial, ice shelf and open marine environments since the Last Glacial Maximum (LGM) in the Ross Sea Embayment. A radiocarbon chronology from these short cores implies that lift-off of grounded ice in the 900 m-deep marine basins surrounding Ross Island occurred by ~10,100 14C yr BP. Following lift-off, the ice shelf calving line retreated toward its present position. By ~8,900 14C yr BP, seasonally open marine conditions extended as far south as Ross Island. Glacial retreat was rapid and preceded the timing of Meltwater Pulse 1B. Since 8,900 14C yr BP, the calving line of the Ross Ice Shelf has remained pinned to Ross Island despite warmer-than-present temperatures during the mid-Holocene. Depositional models developed for the LGM to recent sediments were then applied to the interpretation of the 1284-m-long ANDRILL McMurdo Ice Shelf core (AND-1B) to documenting oscillations of the AIS in the Ross Embayment over the past 13 Myr. A sequence stratigraphic framework for grounding-line fluctuations of under a variety of glacial regimes, with three distinct types of glacimarine cycle (sequence motif) identified. Motif 1 (Pleistocene and Mid to early Late Miocene) is dominated by thick sub-glacial diamictite, deposited during glacial advance, with occasional thin interbeds of sparsely- to non-fossiliferous mudstone that marks an ice shelf setting during interglacial maxima. Motif 2 (Pliocene) comprises subglacial to glacimarine diamictite overlain by thin, proglacial deposits and capped with substantial beds of diatom-bearing mudstone or diatomite formed under open-marine conditions. Motif 3 (Late Miocene) extends from subglacial diamictite into a thick proglacial succession that includes a combination of stratified diamictite, graded sandstone, conglomerate, and rhythmically-stratified mudstone. The differences in these facies successions (motifs) are associated with the long-term evolution of the AIS in the Ross Embayment from a cold glacial regime with limited volumes of subglacial meltwater (Motif 1) to warmer styles (Motifs 2 and 3) of glaciation with increased subglacial meltwater discharge, before passing back to the cold style of glaciation that characterises the present-day AIS (i.e., limited subglacial meltwater). Each motif was interpreted on the basis of modern analogues of glacimarine sedimentation from a range of climatic/glacial settings, recording a fundamental change in the mass balance for the AIS in the Ross Embayment. For cold glacial regimes similar to the present day Antarctic Ice Sheets, ablation was largely controlled by calving at the marine margin and the melting of the underside of ice shelves by oceanic processes. For warmer regimes, in particular for Motif 3, ablation by melting was a significant influence on mass balance. This sedimentary model was then applied in detail to interpret the Pleistocene section of AND-1B (upper 150 m) with a chronostratigraphic interpretation constrained by sequence stratigraphy, 40Ar/39Ar dating of volcanic ashes, and magneto-stratigraphy. The glacimarine sequences in AND-1B drill core correlate one-to-one with cycles in the benthic delta 18 O record for the past ~0.8 Myr (Marine Isotope Stages 20-2), and are interpreted as recording fluctuations of the AIS in the Ross Embayment with a 100-kyr cyclicity. In this "100-kyr world", the AIS is relatively stable, with subglacial to grounding-zone sedimentation dominating at the AND-1B drill site, with only thin intervals of ice-shelf sedimentation during interglacials and little evidence for open-marine conditions during the Late Pleistocene "super-interglacials". An unconformity spans (~200 kyr) most of the Mid-Pleistocene Transition and is inferred to represent large scale expansion of AIS at ~0.8 Myr. Prior to this, Early Pleistocene glacial/interglacial cycles had a 40-kyr frequency, with interglacial periods characterised by open water deposits that contain volcanoclastic debris and diatomaceous sediments. This upper 150 m of AND-1B provides clear evidence for both a change in the frequency (40- to 100-kyr cycles), and a reduction in the sensitivity of a cooler marine-based AIS in the Ross Embayment.</p>

Late Cenozoic (13-0 Myr) Glacimarine Sedimentology, Facies Analysis, and Sequence Stratigraphy from the Western Ross Embayment, Antarctica: Implications for the Variability of the Antarctic Ice Sheets

<p>Sedimentary processes related to oscillations of the marine-based sector of Antarctic Ice Sheet (AIS) in the Ross Embayment over the past 13 Myr are examined at various timescales from stratigraphic records of glacial advance and retreat obtained from the McMurdo Sound region. An initial sedimentary model was developed from short (<2 m) sediment cores collected from beneath the present-day McMurdo Ice Shelf and seasonally open water in the Ross Island region. These cores document sedimentary processes associated with subglacial, ice shelf and open marine environments since the Last Glacial Maximum (LGM) in the Ross Sea Embayment. A radiocarbon chronology from these short cores implies that lift-off of grounded ice in the 900 m-deep marine basins surrounding Ross Island occurred by ~10,100 14C yr BP. Following lift-off, the ice shelf calving line retreated toward its present position. By ~8,900 14C yr BP, seasonally open marine conditions extended as far south as Ross Island. Glacial retreat was rapid and preceded the timing of Meltwater Pulse 1B. Since 8,900 14C yr BP, the calving line of the Ross Ice Shelf has remained pinned to Ross Island despite warmer-than-present temperatures during the mid-Holocene. Depositional models developed for the LGM to recent sediments were then applied to the interpretation of the 1284-m-long ANDRILL McMurdo Ice Shelf core (AND-1B) to documenting oscillations of the AIS in the Ross Embayment over the past 13 Myr. A sequence stratigraphic framework for grounding-line fluctuations of under a variety of glacial regimes, with three distinct types of glacimarine cycle (sequence motif) identified. Motif 1 (Pleistocene and Mid to early Late Miocene) is dominated by thick sub-glacial diamictite, deposited during glacial advance, with occasional thin interbeds of sparsely- to non-fossiliferous mudstone that marks an ice shelf setting during interglacial maxima. Motif 2 (Pliocene) comprises subglacial to glacimarine diamictite overlain by thin, proglacial deposits and capped with substantial beds of diatom-bearing mudstone or diatomite formed under open-marine conditions. Motif 3 (Late Miocene) extends from subglacial diamictite into a thick proglacial succession that includes a combination of stratified diamictite, graded sandstone, conglomerate, and rhythmically-stratified mudstone. The differences in these facies successions (motifs) are associated with the long-term evolution of the AIS in the Ross Embayment from a cold glacial regime with limited volumes of subglacial meltwater (Motif 1) to warmer styles (Motifs 2 and 3) of glaciation with increased subglacial meltwater discharge, before passing back to the cold style of glaciation that characterises the present-day AIS (i.e., limited subglacial meltwater). Each motif was interpreted on the basis of modern analogues of glacimarine sedimentation from a range of climatic/glacial settings, recording a fundamental change in the mass balance for the AIS in the Ross Embayment. For cold glacial regimes similar to the present day Antarctic Ice Sheets, ablation was largely controlled by calving at the marine margin and the melting of the underside of ice shelves by oceanic processes. For warmer regimes, in particular for Motif 3, ablation by melting was a significant influence on mass balance. This sedimentary model was then applied in detail to interpret the Pleistocene section of AND-1B (upper 150 m) with a chronostratigraphic interpretation constrained by sequence stratigraphy, 40Ar/39Ar dating of volcanic ashes, and magneto-stratigraphy. The glacimarine sequences in AND-1B drill core correlate one-to-one with cycles in the benthic delta 18 O record for the past ~0.8 Myr (Marine Isotope Stages 20-2), and are interpreted as recording fluctuations of the AIS in the Ross Embayment with a 100-kyr cyclicity. In this "100-kyr world", the AIS is relatively stable, with subglacial to grounding-zone sedimentation dominating at the AND-1B drill site, with only thin intervals of ice-shelf sedimentation during interglacials and little evidence for open-marine conditions during the Late Pleistocene "super-interglacials". An unconformity spans (~200 kyr) most of the Mid-Pleistocene Transition and is inferred to represent large scale expansion of AIS at ~0.8 Myr. Prior to this, Early Pleistocene glacial/interglacial cycles had a 40-kyr frequency, with interglacial periods characterised by open water deposits that contain volcanoclastic debris and diatomaceous sediments. This upper 150 m of AND-1B provides clear evidence for both a change in the frequency (40- to 100-kyr cycles), and a reduction in the sensitivity of a cooler marine-based AIS in the Ross Embayment.</p>

Sedimentary architecture and landforms of the late Saalian (MIS 6) ice sheet margin offshore of the Netherlands

Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding the relationships between global climate and sea-level change and to testing numerical ice sheet models. In this study, we integrate recently acquired high-resolution 2D seismic reflection and borehole datasets from two wind-farm sites offshore of the Netherlands to investigate the sedimentary, geomorphological, and glaciotectonic records left by the Saalian Drenthe substage glaciation, when Scandinavian land ice reached its southernmost extent in the southern North Sea (ca. 160 ka, Marine Isotope Stage 6). A complex assemblage of glaciogenic sediments and glaciotectonic structures is buried in the shallow subsurface. The northern wind-farm site revealed a set of NE–SW-oriented subglacial meltwater channels filled with till and glaciofluvial sediments and an E–W-trending composite ridge with local evidence of intense glaciotectonic deformation that denotes the maximum limit reached by the ice. Based on the identified glacial geomorphology, we refine the mapping of the maximum ice sheet extent offshore, revealing that the ice margin morphology is more complex than previously envisaged and displaying a lobate shape. Ice retreat left an unusual paraglacial landscape characterised by the progressive infilling of topographic depressions carved by ice-driven erosion and a diffuse drainage network of outwash channels. The net direction of outwash was to the west and southwest into a nearby glacial basin. We demonstrate the utility of offshore wind-farm data as records of process–form relationships preserved in buried landscapes, which can be utilised in refining palaeo-ice sheet margins and informing longer-term drivers of change in low-relief settings.

Sedimentary architecture and landforms of the Late Saalian (MIS 6) ice sheet margin, offshore the Netherlands

Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding the relationships between global climate and sea-level change, and to testing numerical ice sheet models. In this study, we integrate recently acquired high-resolution 2D-seismic reflection and borehole datasets from two windfarm sites offshore the Netherlands to investigate the sedimentary, geomorphological and glaciotectonic records left by the Saalian Drenthe substage glaciation, when Scandinavian land ice reached its southernmost extent in the southern North Sea (ca. 160 ka, Marine Isotope Stage 6). A complex assemblage of glaciogenic sediments and glaciotectonic structures are buried in the shallow subsurface. The northern windfarm site revealed a set of NE-SW oriented subglacial meltwater channels filled with till and glaciofluvial sediments and an E-W trending composite ridge with local evidence of intense glaciotectonic deformation that denotes the maximum limit reached by the ice. Based on the identified glacial geomorphology, we refine the mapping of the maximum ice-sheet extent offshore the Netherlands, revealing that the ice margin morphology is more complex than previously envisaged, displaying a lobate shape. Ice retreat left an unusual paraglacial landscape characterised by the progressive infilling of topographic depressions carved during the ice advance and a diffuse drainage network of outwash channels. The net direction of outwash was to the west and southwest into a nearby glacial basin. Antecedent topography influenced subglacial bed conditions, and their impact on ice dynamics during the glaciation and deglaciation stages. We demonstrate the utility of offshore windfarm data in refining palaeo ice margin limits, and the record of processes interactions preserved in buried landscapes to help inform longer-term drivers of change at low relief ice margins.

Drivers of Recurring Seasonal Cycle of Glacier Calving Styles and Patterns

Calving is a crucial process for the mass loss of outlet glaciers draining the Greenland ice sheet. Moreover, due to a lack of observations, calving contributes to large uncertainties in current glacier flow models and projections. Here we investigate the frequency, volume and style of calving events by using high-resolution terrestrial radar interferometer (TRI) data from six field campaigns, continuous daily and hourly time-lapse images over 6 years and 10-s time-lapse images recorded during two field campaigns. The results demonstrate that the calving front of Eqip Sermia, a fast flowing, highly crevassed outlet glacier in West Greenland, follows a clear seasonal cycle showing a distinct pattern in areas with subglacial discharge plumes, shallow bed topography and during the presence and retreat of proglacial ice mélange. Calving event volume, frequency and style vary strongly over time depending on the state in the seasonal cycle. Strong spatial differences between three distinctive front sectors with differing bed topography, water depth and calving front slope were observed. A distinct increase in calving activity occurs in the early melt season simultaneously when ice mélange disappears and meltwater plumes become visible at the fjord surface adjacent to the ice front. While reduced retreat of the front is observed in shallow areas, accelerated retreat occurred at locations with subglacial meltwater plumes. With the emergence of these plumes at the beginning of the melt season, larger full thickness calving events occur likely due to undercutting of the calving front. Later in the melt season the calving activity at subglacial meltwater plumes is similar to the neighboring areas, suggesting the presence of plumes to become less important for calving. The results highlight the significance of subglacial discharge and bed topography on the front geometry, the temporal variability of the calving process and the variability of calving styles.

Ice sheet scale subglacial meltwater conduit dimensions and processes: insights from 3D morphometry of a large sample of eskers

&lt;p&gt;Meltwater exerts an important influence on ice sheet dynamics and has attracted an increasing amount of attention over the last 20 years. However, the active subglacial environment remains difficult to study mainly due to its inaccessibility. Understanding of the dimensions, pattern, and extent of subglacial meltwater conduits at the ice sheet scale is limited to relatively sparse observations. We address this gap by using the geomorphological record of Quaternary ice sheets as a proxy to quantify the dimensions and pattern of subglacial conduits at the ice sheet scale. We present the results of a high-resolution (2 m), large sample (n&gt;50,000) study of three-dimensional esker morphometry at sample locations in SW Finland and Nunavut, Canada. Detailed mapping of esker crestlines and outlines permits the quantification of a number of parameters, including: length, width, height, cross-sectional area, volume, sinuosity, cross-sectional symmetry, and uphill/downhill trends. Whilst the dimensions of eskers reflect depositional processes as well as simply the size of the parent conduit, they nevertheless offer a powerful tool for understanding the size and shape of meltwater conduits and the configuration of subglacial drainage systems across large areas (entire ice sheets), and over long periods of time (from years to thousands of years) in both high spatial and temporal resolution. The results may be used to: (1) inform numerical models of subglacial meltwater drainage, (2) inform process models of esker formation, and (3) provide a dataset of esker morphometry against which other features may be compared (e.g. sinuous ridges on Mars).&lt;/p&gt;