| 1. |
- Hogan, K. A., et al.
(författare)
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Revealing the former bed of Thwaites Glacier using sea-floor bathymetry: implications for warm-water routing and bed controls on ice flow and buttressing
- 2020
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Ingår i: Cryosphere. - : Copernicus GmbH. - 1994-0416. ; 14:9, s. 2883-2908
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Tidskriftsartikel (refereegranskat)abstract
- The geometry of the sea floor immediately beyond Antarctica's marine-terminating glaciers is a fundamental control on warm-water routing, but it also describes former topographic pinning points that have been important for ice-shelf buttressing. Unfortunately, this information is often lacking due to the inaccessibility of these areas for survey, leading to modelled or interpolated bathymetries being used as boundary conditions in numerical modelling simulations. At Thwaites Glacier (TG) this critical data gap was addressed in 2019 during the first cruise of the International Thwaites Glacier Collaboration (ITGC) project. We present more than 2000 km(2) of new multibeam echo-sounder (MBES) data acquired in exceptional sea-ice conditions immediately offshore TG, and we update existing bathymetric compilations. The cross-sectional areas of sea-floor troughs are under-predicted by up to 40% or are not resolved at all where MBES data are missing, suggesting that calculations of trough capacity, and thus oceanic heat flux, may be significantly underestimated. Spatial variations in the morphology of topographic highs, known to be former pinning points for the floating ice shelf of TG, indicate differences in bed composition that are supported by landform evidence. We discuss links to ice dynamics for an overriding ice mass including a potential positive feedback mechanism where erosion of soft erodible highs may lead to ice-shelf ungrounding even with little or no ice thinning. Analyses of bed roughnesses and basal drag contributions show that the sea-floor bathymetry in front of TG is an analogue for extant bed areas. Ice flow over the sea-floor troughs and ridges would have been affected by similarly high basal drag to that acting at the grounding zone today. We conclude that more can certainly be gleaned from these 3D bathymetric datasets regarding the likely spatial variability of bed roughness and bed composition types underneath TG. This work also addresses the requirements of recent numerical ice-sheet and ocean modelling studies that have recognised the need for accurate and high-resolution bathymetry to determine warm-water routing to the grounding zone and, ultimately, for predicting glacier retreat behaviour.
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| 2. |
- Klages, J. P., et al.
(författare)
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Temperate rainforests near the South Pole during peak Cretaceous warmth
- 2020
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 580:7801, s. 81-86
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Tidskriftsartikel (refereegranskat)abstract
- The mid-Cretaceous period was one of the warmest intervals of the past 140millionyears1–5, driven by atmospheric carbon dioxide levels of around 1,000parts per million by volume6. In the near absence of proximal geological records from south of the Antarctic Circle, it is disputed whether polar ice could exist under such environmental conditions. Here we use a sedimentary sequence recovered from the West Antarctic shelf—the southernmost Cretaceous record reported so far—and show that a temperate lowland rainforest environment existed at a palaeolatitude of about 82°S during the Turonian–Santonian age (92 to 83millionyearsago). This record contains an intact 3-metre-long network of in situ fossil roots embedded in a mudstone matrix containing diverse pollen and spores. A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric carbon dioxide concentrations of 1,120–1,680parts per million by volume and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo under high levels of atmospheric carbon dioxide. © 2020, The Author(s), under exclusive licence to Springer Nature Limited.
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| 3. |
- Wang, Jiu, et al.
(författare)
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In Situ Photo-Fenton-Like Tandem Reaction for Selective Gluconic Acid Production from Glucose Photo-Oxidation
- 2023
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Ingår i: ACS Catalysis. - : American Chemical Society (ACS). - 2155-5435. ; , s. 2637-2646
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Tidskriftsartikel (refereegranskat)abstract
- Biomass photorefining to selectively produce value-added bioproducts is an emerging alternative biomass valorization approach to alleviate energy crisis and achieve carbon neutrality. Here, we demonstrate an efficient and selective glucose photo-oxidation to gluconic acid via a rationally designed dual-functional carbon nitride photocatalyst that not only allows H2O2 production via 2e- oxygen reduction reaction (2e-ORR) but also realizes in situ photo-Fenton-like reaction. As a result, the essential oxidative species (•O2- and •OH) for glucose oxidation into gluconic acid are generated that achieves >60% glucose conversion and >60% of gluconic acid selectivity within 4 h. Density functional theory calculations demonstrate the superior performance of the photocatalyst for •O2- and H2O2 generation. Further experimental results reveal that the moderate concentration of H2O2 produced by 2e-ORR reaction plays a vital role in regulatinge gluconic acid selectivity. This work demonstrates a good example to realize selective biomass photorefining through tandem reaction of ORR and in situ photo-Fenton-like process, which could have profound impact on artificial photoenzyme systems involving moderate H2O2 modulation.
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| 4. |
- Wåhlin, Anna, 1970, et al.
(författare)
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Pathways and modification of warm water flowing beneath Thwaites Ice Shelf, West Antarctica
- 2021
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:15
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Tidskriftsartikel (refereegranskat)abstract
- Thwaites Glacier is the most rapidly changing outlet of the West Antarctic Ice Sheet and adds large uncertainty to 21st century sea-level rise predictions. Here, we present the first direct observations of ocean temperature, salinity, and oxygen beneath Thwaites Ice Shelf front, collected by an autonomous underwater vehicle. On the basis of these data, pathways and modification of water flowing into the cavity are identified. Deep water underneath the central ice shelf derives from a previously underestimated eastern branch of warm water entering the cavity from Pine Island Bay. Inflow of warm and outflow of melt-enriched waters are identified in two seafloor troughs to the north. Spatial property gradients highlight a previously unknown convergence zone in one trough, where different water masses meet and mix. Our observations show warm water impinging from all sides on pinning points critical to ice-shelf stability, a scenario that may lead to unpinning and retreat.
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