We first adapt a method due to Skjelbred–Sund to classify p-nilpotent restricted Lie algebras. It turns out that any p-nilpotent restricted Lie algebra of dimension n can be constructed as a central ...extension of a p-nilpotent restricted Lie algebra of dimension n−1. We apply these techniques to classify all p-nilpotent restricted Lie algebras of dimension 5 over a perfect field of characteristic p⩾5.
In this article, we provide an algorithm with Wolfram Mathematica code that gives a unified computational power in classification of finite dimensional nilpotent algebras using Skjelbred-Sund method. ...To illustrate the code, we obtain new finite dimensional Moufang algebras.
Glaciers erode their beds and the adjacent landscape by abrasion and plucking and entraining sediment on their way downwards driven by gravity. Ice becomes a sediment transport agent. To determine ...glacial transport of sediment, measurements of both the ice flux and its concentration of sediment are needed. Once glaciers reach the ocean, ice and its entrained sediment is released into the ocean by calving. Further transport takes place by icebergs. Quantification of IRD (ice‐rafted debris) fluxes, which upon ultimate deposition on the ocean floor is an important climate indicator, becomes even more complicated as icebergs topple and differentially melt while being in transport. While the volume of tidewater glacier ice released by recent calving is quite well constrained by satellite measurements, there is a lack of measurements of the concentration of sediment within the moving ice. Here, we describe a method to collect samples of ice from icebergs systematically for the first time in Greenland together with a strategy to obtain representative samples. Our method is tested in Scoresby Sound, East Greenland in order to describe the transport of sediment into the fjord system related to calving from known glacial source areas. Our data clearly demonstrate that biased and sparse sampling potentially produces unrealistic values of sediment concentrations. Seventy‐two samples from 24 icebergs had an average concentration of sediment of 35.5 g/L of ice with a standard deviation of 97%, between the 24 individual icebergs. The origin of the sediment is related to specific source areas. Based on the samples, we present an estimate of the annual transport of sediment out of Scoresby Sound related to calving ~100 (0.3–200) million t year−1. Finally, we discuss the uncertainties of our estimate.
Calved ice and related sediment transport in Scoresby Sound, East Greenland.
Volumes of calved ice are based on measurements of ice velocity and cross sections.
Sediment concentrations in ice are based on in situ quasi‐random sampling from icebergs.
The Impact of Lithology on Fjord Morphology Bernard, M.; Steer, P.; Gallagher, K. ...
Geophysical research letters,
28 August 2021, 2021-08-28, Volume:
48, Issue:
16
Journal Article
Peer reviewed
Open access
Assessing the impact of glaciations on topography and the co‐evolution of ice‐sheet dynamics requires a thorough understanding of the factors that control fjord morphology. We investigate the role of ...lithology on glacial valley form using topographic analyses and numerical landscape evolution models. We measure fjord depths and widths from East Central Greenland (68°N–75°N), and find a control of lithology on fjord width, with wider fjords in softer rocks (i.e., sedimentary rocks). This dependency of fjord width to bedrock properties is predicted by a quarrying erosion law, but not by an abrasion one, when considering results from a simple two‐dimensional model and a more detailed three‐dimensional ice flow model (iSOSIA). Our analyses and numerical results reveal a potential control of lithology on the width of glacial valleys with glacial quarrying as a plausible responsible mechanism.
Plain Language Summary
The present dynamics of the Greenland ice sheet is strongly influenced by fjords, which drain most of the continental ice into the ocean. Fjords are distinct geomorphological features formed by glacial erosion. They have spectacular dimensions with depths greater than 1 km, and width reaching up to 40 km (Scoresby Sund fjord, East Greenland). Understanding the factors that controlled the development of these glacial valleys can enable us to better evaluate the past and future evolution of the ice sheet and its sensitivity to climate change. In East Central Greenland (ECG), fjords show contrasting morphologies at the boundaries between different lithologies. To understand the role of lithology in controlling fjord morphology, we couple quantitative topographic analyses in ECG and numerical modeling of fjord development. We find that lithology controls fjord morphology with softer rocks leading to wider fjords. Next, we show that a classical glacial abrasion erosion law in numerical models does not reproduce the observations in ECG, while a process‐based erosion model of rock quarrying by ice does. We therefore advocate that the mechanics of ice erosion, and its sensitivity to lithology, should be considered as a fundamental aspect in the feedbacks between ice‐sheet dynamics, topography, and climate change.
Key Points
Observations in East Central Greenland show that lithology controls the width of fjords with softer rocks leading to wider fjords
Glacial erosion models reproduce the observations with a quarrying law but not when varying the erodibility factor in an abrasion law
The lithological contribution to glacial erosion law needs more careful description
The mass loss at Nioghalvfjerdsbræ is primarily due to rapid submarine melting. Ocean data obtained from beneath the Nioghalvfjerdsbræ ice tongue show that melting is driven by the presence of warm ...(1°C) Atlantic Intermediate Water (AIW). A sill prevents AIW from entering the cavity from Dijmphna Sund, requiring that it flow into the cavity via bathymetric channels to the south at a pinned ice front. Comparison of water properties from the cavity, Dijmphna Sund, and the continental shelf support this conclusion. Overturning circulation rates inferred from observed melt rates and cavity stratification suggest an exchange flow between the cavity and the continental shelf of 38mSv, sufficient to flush cavity waters in under 1 year. These results place upper bounds on the timescales of external variability that can be transmitted to the glacier via the ice tongue cavity.
Key Points
Pathway for Atlantic water at 79North unexpectedly found to be via pinned ice front
Bulk circulation in ice tongue cavities estimated using data
Renewal timescales for this ice tongue cavity are less than 1 year
The Greenland Ice Sheet is a major component of the Arctic cryosphere and the magnitude of its response to future climate changes remains uncertain. Longer-term records of climate near the ice sheet ...margin provide information about natural climate variability and can be used to understand the causes of past changes in the Greenland Ice Sheet. As a proxy for Holocene climate near the ice sheet margin, we reconstruct the fluctuations of Bregne ice cap in the Scoresby Sund region of central east Greenland. Bregne is a small ice cap (2.5 km2 in area) and responds sensitively to summer temperatures. We employ a multi-proxy approach to reconstruct the ice cap fluctuations using geomorphic mapping, 10Be ages of boulders and bedrock and lake sediment records.
Past extents of Bregne ice cap are marked by moraines and registered by sediments in downvalley lakes. 10Be ages of bedrock and boulders outboard of the moraines indicate that Bregne ice cap was within ∼250 m of its present-day limit by at least 10.7 ka. Multi-proxy data from sediments in Two Move lake, located downvalley from Bregne ice cap, indicate that the ice cap likely completely disappeared during early and middle Holocene time. Increasing magnetic susceptibility and percent clastic material from ∼6.5 to ∼1.9 cal ka BP in Two Move lake sediments suggest progressively colder conditions and increased snow accumulation on the highlands west of the lake. Laminated silt deposited at ∼2.6 cal ka BP and ∼1.9 cal ka BP to present registers the onset and persistence of Bregne ice cap during the late Holocene. 10Be ages of boulders on an unweathered, unvegetated moraine in the Bregne ice cap forefield range from 0.74 to 9.60 ka. The youngest 10Be age (0.74 ka) likely represents the age of the moraine whereas older ages may be due to 10Be inherited from prior periods of exposure. This late Holocene moraine marks the second largest advance of the ice cap since deglaciation of the region at the end of the last ice age. The oldest moraine in the forefield dates to ≤2.6 cal ka BP. The fluctuations of Bregne ice cap were likely influenced by Northern Hemisphere summer insolation throughout the Holocene and abrupt late Holocene cold events.
•10Be dates indicate Bregne ice cap was within its late Holocene extent by 10.7 ka.•Bregne ice cap was small or nonexistent from ∼10.0 to ∼2.6 cal ka BP.•The ice cap was expanded at ∼2.6 and ∼1.9 cal ka BP to present.•Ice cap fluctuations coincide with decreasing insolation and abrupt cooling events.•Bregne ice cap affords a Holocene climate record near the Greenland Ice Sheet margin.
This paper describes presently applied sailing rules and environmental conditions on Danish waters such as Kattegat and the Sund. Those rules were established in late 70’s of the twentieth century by ...Danish authorities as Denmark is a coastal country and has the legal right to do so. Presently International Maritime Organization – IMO is in the process of approving a new set of routeing measures and traffic separation schemes which should comply with resolution A.257(14) – General provisions on ships’ routeing, and will be introduced by Organization.
We present a 10Be chronology of late glacial to early Holocene fluctuations of a Greenland ice sheet outlet glacier and the adjacent Milne Land ice cap in central East Greenland. Ages of boulders on ...bedrock indicate that both ice masses receded during the Younger Dryas (YD), likely due to rising summer temperatures. Since Greenland ice core records register cold mean annual temperatures throughout the YD, these ice‐marginal data support climate conditions characterized by strong seasonality. The ice sheet outlet glacier and ice cap deposited inner Milne Land Stade moraines at 11.4 ± 0.8 ka and 11.4 ± 0.6 ka, respectively (mean moraine ages and 1σ uncertainties). Based on the coeval moraine ages, we suggest that both ice masses responded to climate conditions acting on the ice margins, specifically ablation. Moreover, the ice sheet responded sensitively (i.e., on the same time scale as a small ice cap) to climate conditions.
Key Points
Beryllium‐10 ages show deglaciation during the Younger Dryas in central East Greenland
The inner Milne Land Stade moraines of the Greenland ice sheet and a local glacier date to ~11.4 ka
Both ice masses responded in unison to late glacial and early Holocene climate conditions
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