| 1. |
- Dulfer, Helen E., et al.
(författare)
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Reconstructing the advance and retreat dynamics of the central sector of the last Cordilleran Ice Sheet
- 2022
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 284
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Tidskriftsartikel (refereegranskat)abstract
- The advance of the Cordilleran Ice Sheet (CIS) towards its Last Glacial Maximum (LGM) configuration and its subsequent retreat remain poorly understood. We use the glacial landform record to determine ice dynamics for the central sector of the CIS in northern British Columbia, Canada, beneath the LGM ice divide. We classify seventy ice-flow indicator flowsets based on morphology, elevation, orientation and cross-cutting relationships into one of three stages, whereby stage 1 is oldest and stage 3 youngest. Combined with ice-contact geomorphology, our reconstruction highlights complex changes in ice flow over time as a result of ice divide migrations through the LGM and deglacial phases. The orientation and distribution of landforms indicates active post-LGM ice retreat westward through the Cassiar and Omineca mountains. We map the regional distribution of independent mountain glaciers, ice caps, and ice fields that regrew during a cooling event in the Late Glacial and show that some of these readvance glaciers were subsequently overrun by advancing outlet glaciers of the CIS. We use the cross-cutting relationship between readvance glaciers and CIS outlet glaciers and available chronological data to reconstruct the eastern CIS margin during the Late Glacial for the first time.
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| 2. |
- Lund Andersen, Jane, 1986-, et al.
(författare)
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A topographic hinge-zone divides coastal and inland ice dynamic regimes in East Antarctica
- 2023
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Ingår i: Communications Earth & Environment. - : Springer Science and Business Media LLC. - 2662-4435. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- The impact of late Cenozoic climate on the East Antarctic Ice Sheet is uncertain. Poorly constrained patterns of relative ice thinning and thickening impair the reconstruction of past ice-sheet dynamics and global sea-level budgets. Here we quantify long-term ice cover of mountains protruding the ice-sheet surface in western Dronning Maud Land, using cosmogenic Chlorine-36, Aluminium-26, Beryllium-10, and Neon-21 from bedrock in an inverse modeling approach. We find that near-coastal sites experienced ice burial up to 75–97% of time since 1 Ma, while interior sites only experienced brief periods of ice burial, generally <20% of time since 1 Ma. Based on these results, we suggest that the escarpment in Dronning Maud Land acts as a hinge-zone, where ice-dynamic changes driven by grounding-line migration are attenuated inland from the coastal portions of the East Antarctic Ice Sheet, and where precipitation-controlled ice-thickness variations on the polar plateau taper off towards the coast.
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| 3. |
- Mas e Braga, Martim, et al.
(författare)
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Antarctic ice stream thickening under Pliocene warmth
- 2024
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Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Ice streams regulate most ice mass loss in Antarctica. Determining their response to Pliocene warmth could provide insights into their future behaviour, but is hindered by poor representation of subglacial topography in ice-sheet models. We address this limitation using a high-resolution regional model for Dronning Maud Land (East Antarctica). We show that the region’s largest ice stream, Jutulstraumen, thickens by 700 m under warm late-Pliocene conditions despite ice-shelf collapse and a retrograde bed slope, while nearby ice streams thin. While it is known that unstable retreat on a retrograde slope can be slowed under certain conditions, this finding illustrates that an ice stream can thicken and gain mass. We attribute thickening to high lateral stresses at its flux gate, which constrict ice drainage. Similar stress balances occur today in 27% of East Antarctica, and understanding how lateral stresses regulate ice-stream discharge is necessary for accurately assessing Antarctica’s sea-level rise contribution.
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| 4. |
- Mas e Braga, Martim, 1991-
(författare)
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Modelling ice surface elevation changes in Dronning Maud Land, East Antarctica : Bridging the gap between in-situ and numerical model reconstructions
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Ice sheets are an active component of Earth's climate system. Their topography influences atmospheric circulation and changes in their volume alters freshwater fluxes to the oceans, affecting ocean water masses, atmospheric carbon uptake, and global sea level. Sea-level rise has a marked societal impact, and thus ice sheet models are indispensable tools to predict it. To increase confidence on sea-level rise projections, it is necessary that ice sheet models accurately represent the relevant processes governing ice sheet dynamics. Given the fact that ice sheets respond to geological-scale changes in Earth's system, it is necessary that their performance is compared with in-situ data of past geological periods, which are discrete in space and time. One useful constraint used for validating model results is past ice surface elevation, which is reconstructed based on rock samples taken from nunataks (mountain summits that pierce through the ice sheet surface). However, two main problems prevent reliable comparisons of past ice surface elevations between model and empirical results. First, data-model comparisons are hindered by the fact that most large-scale ice sheet models capture neither the timing nor the magnitude of ice thinning reconstructed for the last deglaciation. Second, the complex subglacial topography of regions where nunataks are present is also reflected on the ice sheet surface, through pronounced elevation gradients. As a result, the choice of a reference point on the present-day ice sheet, which can be subjective, is a significant source of uncertainty when computing thickness-change estimates. In this thesis, I aim to reconstruct changes in ice sheet geometry over Dronning Maud Land (DML, East Antarctica) during periods that were warmer and colder than present, and the climate drivers behind such changes. I assess whether the comparison between empirical and model results can be improved by resolving local features in ice sheet models, and by using data and models in an iterative way (using data to constrain the model, and models to interpret the data). The results of this thesis demonstrate that ice flow in areas of complex topography is poorly resolved in continental-scale ice sheet models and requires modelling in high resolution to match results from empirical constraints. High-resolution ice-sheet models, in turn, show that accurate ice sheet surface elevation reconstructions from empirical data require systematic sampling and definition of reference points over the modern ice sheet surface. Moreover, a consistent reconstruction of regional ice-thickness changes needs both empirical and ice sheet model results. Based on constrained models and empirical datasets, the ice sheet in DML responds to an interplay between sea level, ocean warming, surface mass balance, and subglacial topography. Samples from nunataks mainly reflect local ice surface elevation changes, potentially missing catchment-scale (regional) changes. Accurately determining regional changes using high-resolution modelling plays a significant role when interpreting the evolution of ice streams. Hence, the work presented here highlights that accurately reconstructing past ice sheet geometry is an effort that can only be truly successful if field scientists and ice sheet modellers work in tandem, at experiment-design, sampling, and result-interpretation stages.
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| 5. |
- Suganuma, Yusuke, et al.
(författare)
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Regional sea-level highstand triggered Holocene ice sheet thinning across coastal Dronning Maud Land, East Antarctica
- 2022
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Ingår i: Communications Earth & Environment. - : Springer Science and Business Media LLC. - 2662-4435. ; 3
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Tidskriftsartikel (refereegranskat)abstract
- The East Antarctic Ice Sheet stores a vast amount of freshwater, which makes it the single largest potential contributor to future sea-level rise. However, the lack of well-constrained geological records of past ice sheet changes impedes model validation, hampers mass balance estimates, and inhibits examination of ice loss mechanisms. Here we identify rapid ice-sheet thinning in coastal Dronning Maud Land from Early to Middle Holocene (9000–5000 years ago) using a deglacial chronology based on in situ cosmogenic nuclide surface exposure dates from central Dronning Maud Land, in concert with numerical simulations of regional and continental ice-sheet evolution. Regional sea-level changes reproduced from our refined ice-load history show a highstand at 9000–8000 years ago. We propose that sea-level rise and a concomitant influx of warmer Circumpolar Deep Water triggered ice shelf breakup via the marine ice sheet instability mechanism, which led to rapid thinning of upstream coastal ice sheet sectors.
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