| 1. |
- Alexanderson, Helena, et al.
(författare)
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The Seven Islands, Svalbard: glaciation at the margin
- 2018
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- On the Seven Islands, north of Nordaustlandet, Svalbard, decreasing snow cover has made previously inaccessible stratigraphic sections in coastal cliffs possible to investigate. Sections on two of the islands, Phippsøya and Parryøya, reveal mainly raised marine deposits, representing one or more coarsening upward sequences (emergence cycles) at each site, which in turn imply preceding regional glaciations (cf. Alexanderson et al. in press). Optically stimulated luminescence (OSL) ages are pending but radiocarbon (14C) ages and correlation to a previously studied site on Phippsøya (Forman and Ingólfsson 2000) suggest at least two events that occurred during the late Weichselian-early Holocene and prior to 40 14C ka BP, respectively. These results, along with observations of postglacial land uplift and of transport of erratic boulders to the islands, provide information on the glacial history and dynamics of an area close to the margin of the Svalbard-Barents Sea ice sheet.ReferencesAlexanderson, H., Henriksen, M., Ryen. H.T., Landvik, J.Y. and Peterson, G. in press. 200 ka of glacial events in NW Svalbard: An emergence cycle facies model and regional correlations. arktos. Forman, S.L. and Ingólfsson, Ó, 2000. Late Weichselian glacial history and postglacial emergence of Phippsøya, Sjuøyane, northern Svalbard: a comparison of modelled and empirical estimates of a glacial-rebound hinge line. Boreas 29, 16-25.
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| 2. |
- Farnsworth, Wesley R., et al.
(författare)
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Dynamic Holocene glacial history of St. Jonsfjorden, Svalbard
- 2017
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Ingår i: Boreas. - : Wiley. - 0300-9483. ; 46:3, s. 585-603
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Tidskriftsartikel (refereegranskat)abstract
- Evidence of a dynamic Holocene glacial history is preserved in the terrestrial and marine archives of St. Jonsfjorden, a small fjord-system on the west coast of Spitsbergen, Svalbard. High-resolution, remotely sensed imagery from marine and terrestrial environments was used to construct geomorphological maps that highlight an intricate glacial history of the entire fjord-system. The geomorphology and stratigraphy indicate an early Holocene local glacier advance constrained to the Lateglacial–early Holocene transition. Identification and 14C dating of the thermophilous bivalve mollusc Modiolus modiolus to 10.0±0.12 cal. ka BP suggest a rapid northward migration of the species shortly after deglaciation. Further evidence enhances the understanding of the onset and subsequent climax of the Neoglacial-Little Ice Age in inner St. Jonsfjorden. The present-day terminus of Osbornebreen, the dominating glacier system in St. Jonsfjorden, is located over 8.5 km up-fjord from its Neoglacial maximum extent. Cross-cutting relationships suggest subsequent advances of all the smaller glaciers in the area following the break-up of Osbornebreen. Glacial deposits, landforms and their cross-cutting relationships observed in both terrestrial and marine settings imply a complex and highly dynamic environment through the later part of the Holocene.
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| 3. |
- Farnsworth, Wesley R., et al.
(författare)
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Holocene glacial history of Svalbard : Status, perspectives and challenges
- 2020
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Ingår i: Earth-Science Reviews. - : Elsevier BV. - 0012-8252. ; 208
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Tidskriftsartikel (refereegranskat)abstract
- We synthesize the current understanding of glacier activity on Svalbard from the end of the Late Pleistocene (12,000 yrs. before present) to the end of the Little Ice Age (c. 1920 AD). Our glacier history is derived from the SVALHOLA database, the first compilation of Holocene geochronology for Svalbard and the surrounding waters, including over 1,800 radiocarbon, terrestrial cosmogenic nuclide and optically stimulated luminescence ages. Data have been categorized by geological setting, uniformly (re-)calibrated, quality assessed and ultimately used to constrain glacier fluctuations (deglaciation, ice free conditions, glacier re-advances and ice marginal positions). We advance existing knowledge by mapping the extent and distribution of ice-cover during the Holocene glacial maximum and the glacial minimum, as well as present retreat rates (and percentages) within Early Holocene fjord-systems. Throughout the Holocene, Svalbard glaciers have responded to a varying combination of climatic, environmental and dynamic driving factors which influence both the extent and behavior of ice margins. We discuss the complexities of glacier systems and their dynamics in response to changes in climate. This review provides a holistic state of the art of Holocene glaciers on Svalbard, suitable for orienting future works which address gaps in our current knowledge.
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| 4. |
- Flink, Anne E., et al.
(författare)
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Holocene glacial evolution of Mohnbukta in eastern Spitsbergen
- 2018
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 47:2, s. 390-409
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Tidskriftsartikel (refereegranskat)abstract
- Submarine geomorphology is one of the main tools for understanding past fluctuations of tidewater glaciers. In this study we investigate the glacial history of Mohnbukta, on the east coast of Spitsbergen, Svalbard, by combining multibeam-bathymetric data, marine sediment cores and remote sensing data. Presently, three tidewater glaciers, Heuglinbreen, Konigsbergbreen and Hayesbreen calve into Mohnbukta. Hayesbreen surged at the end of the Little Ice Age, between 1901 and 1910. The submarine landform assemblage in Mohnbukta contains two large transverse ridges, interpreted as terminal moraines, with debrisflow lobes on their distal slopes and sets of well-preserved geometric networks of ridges, interpreted as crevasse-squeeze ridges inshore of the moraines. The arrangement of crevasse-squeeze ridges suggests that both landform sets were produced during surge-type advances. The terminus position of the 1901-1910 Hayesbreen surge correlates with the inner (R.2) terminal moraine ridge suggesting that the R.1 ridge formed prior to 1901. Marine sediment cores display C-14 ages between 5700-7700cal. a BP derived from benthic foraminifera, from a clast-rich mud unit. This unit represents pre-surge unconsolidated Holocene sediments pushed in front of the glacier terminus and mixed up during the 1901 surge. An absence of retreat moraines in the deeper part of the inner basin and the observation of tabular icebergs calving off the glacier front during retreat suggest that the front of Hayesbreen was close to flotation, at least in the deeper parts of the basin. As the MOH15-01 core does not penetrate into a subglacial till and the foraminifera in the samples were well preserved, the R.1 ridge is suggested to have formed prior to the deposition of the foraminifera. Based on these data we propose that a surge-type advance occurred in Mohnbukta in the early Holocene, prior to 7700cal. a BP, which in turn indicates that glaciers can switch to and from surge mode.
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| 5. |
- Flink, Anne E., et al.
(författare)
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Past ice flow in Wahlenbergfjorden and its implications for late Quaternary ice sheet dynamics in northeastern Svalbard
- 2017
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 163, s. 162-179
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Tidskriftsartikel (refereegranskat)abstract
- Wahlenbergfjorden is a fjord situated in the western part of Nordaustlandet in northern Svalbard. It leads into the 400 m deep Hinlopen Strait located between Nordaustlandet and Spitsbergen. High-resolution multibeam bathymetric and sub-bottom data, as well as sediment cores are used to study the past extent and dynamics of glaciers in Wahlenbergfjorden and western Nordaustlandet. The submarine landform assemblage in Wahlenbergfjorden consists of landforms characteristic of subglacial, ice marginal and proglacial conditions. Glacial lineations indicate that Wahlenbergfjorden was occupied by streaming ice during the LGM and most likely acted as an ice stream onset zone. Westward ice flow in the fjord merged with the ice stream in Hinlopen Strait. Absence of ice recessional landforms in outer Wahlenbergfjorden suggests relatively fast deglaciation, possibly by flotation of the glacier front in the deeper parts of the fjord. The inner part of Wahlenbergfjorden and Palanderbukta are characterized by De Geer moraines, indicating episodic retreat of a grounded glacier front. In Palanderbukta, longer still stands of the glacier terminus resulted in the formation of larger terminal moraine ridges. The inner part of Wahlenbergfjorden was deglaciated prior to 11.3 +/- 55 Cal. ka BP. The submarine landform assemblages in front of Bodleybreen, Etonbreen, Idunbreen, Frazerbreen and Aldousbreen confirm that these glaciers have surged at least once during the Holocene.
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| 6. |
- Flink, Anne Elina, et al.
(författare)
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The evolution of a submarine landform record following recent and multiple surges of Tunabreen glacier, Svalbard
- 2015
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 108, s. 37-50
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Tidskriftsartikel (refereegranskat)abstract
- This study focuses on the glacial landform record associated with recent surge events of Tunabreen - a calving tidewater glacier in Tempelfjorden, Spitsbergen. Submarine geomorphology and recent terminal fluctuations of Tunabreen's glacier front were studied using high-resolution multibeam-bathymetric data and a range of published and remote-sensing sources, including topographic maps, satellite images and aerial photographs. The retreat moraines in the inner part of Tempelfjorden have been correlated with glacier terminus positions during retreat from the 2004 surge maximum. Glacier surface velocity and ice-front positions derived from high-resolution TerraSAR-X satellite data show ice movements at the glacier front during minor advances of the front in winter when calving is suppressed. This suggests that the moraines have formed annually during quiescent phase winter advances. Tunabreen has experienced three surges since the Little Ice Age (LIA). This is in contrast with most Svalbard surging glaciers which have long quiescent phases and have typically only undergone one or two surges during this time. The landform record in Tempelfjorden is distinguished from previously studied glacier-surge landsystems by four, well-preserved sets of landform assemblages generated by the LIA advance and three subsequent surges, all of which partly modify earlier landform records. Based on the unique landform record in Tempelfjorden, a new conceptual landsystem model for frequently surging glaciers has been put forward improving our understanding of the dynamics of the surging glaciers and, most importantly, how they can be distinguished from the climatically-controlled glaciers in the geological record.
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| 7. |
- Gowan, Evan J., et al.
(författare)
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ICESHEET 1.0 : a program to produce paleo-ice sheet reconstructions with minimal assumptions
- 2016
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Ingår i: Geoscientific Model Development. - : Copernicus GmbH. - 1991-959X .- 1991-9603. ; 9:5, s. 1673-1682
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Tidskriftsartikel (refereegranskat)abstract
- We describe a program that produces paleo-ice sheet reconstructions using an assumption of steady-state, perfectly plastic ice flow behaviour. It incorporates three input parameters: ice margin, basal shear stress and basal topography. Though it is unlikely that paleo-ice sheets were ever in complete steady-state conditions, this method can produce an ice sheet without relying on complicated and unconstrained parameters such as climate and ice dynamics. This makes it advantageous to use in glacial-isostatic adjustment ice sheet modelling, which are often used as input parameters in global climate modelling simulations. We test this program by applying it to the modern Greenland Ice Sheet and Last Glacial Maximum Barents Sea Ice Sheet and demonstrate the optimal parameters that balance computational time and accuracy.
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| 8. |
- Holmes, Felicity Alice, 1995-
(författare)
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Glacier-Ocean Interactions in the Arctic : Contemporary calving and frontal melt from field observations, remote sensing, and numerical modelling
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Globally, glaciers are losing mass as a result of the changing climate, with this mass loss having a considerable societal impact through rising sea levels. Glaciers which terminate in the oceans are particularly vulnerable to changing external conditions as a result of high sensitivity at their marine margins. Both changing meteorological patterns as well as changing ocean heat content and transport have been previously identified as potential drivers for contemporary rapid glacier retreat and acceleration. However, uncertainties remain and provide motivation for studies which improve our process understanding. Here, we use a combination of field data, remotely sensed data, and targeted numerical modelling experiments to investigate marine terminating glacier response to external changes. This is done in order to address uncertainties around mass loss at the inaccessible glacier-ocean interface. In particular, focus is paid to the processes of submarine melt and calving, together referred to as frontal ablation. Submarine melt is the melting of glacier termini by warm ocean waters below the waterline, whilst calving is the breaking off of icebergs from glacier termini. The two processes are interlinked, with submarine melting undercutting the glacier terminus and contributing to calving, whilst calving events can expose larger areas of the glacier margin to submarine melt. To look for relationships between frontal ablation and external forcings, four glacier-fjord systems were studied to varying extents; two grounded glaciers in Svalbard (Kronebreen and Tunabreen) and two glaciers with floating ice tongues in Greenland (Ryder glacier and Petermann glacier). Both submarine melt and calving were examined at various different scales, both temporally and spatially. Specifically, analysis was carried out from the scale of individual calving events up to decadal long time series of glacier margin change. Much of the data used focused on specific glaciological variables such as satellite-derived velocities, margin positions, model simulations, and time-lapse photography of calving events. However, as glaciers and their adjacent fjord or ocean environments impact on each other, data such as water temperatures were also collected from glacier proximal fjord environments. The results from both the observational data and model experiments suggest that ocean temperatures are of great importance for the frontal ablation of glaciers in the Arctic, but that the relationship is complex. Heterogeneous glacier response to external forcings highlights how site specific factors such as bathymetry and fjord geometry can add an additional layer of complexity and make it challenging to scale up results from one glacier to an entire region. However, there are some strong indications that it is the presence of warm air temperatures in conjunction with warm ocean temperatures that is most important for driving frontal ablation - highlighting the need to situate glacier behaviour within a wider environmental context.
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| 9. |
- Holmes, Felicity A., 1995-, et al.
(författare)
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Impact of tides on calving patterns at Kronebreen, Svalbard – insights from three-dimensional ice dynamical modelling
- 2023
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Ingår i: The Cryosphere. - 1994-0416 .- 1994-0424. ; 17:5, s. 1853-1872
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Tidskriftsartikel (refereegranskat)abstract
- Understanding calving processes and their controls is of importance for reducing uncertainty in sea level rise estimates. The impact of tidal fluctuations and frontal melt on calving patterns has been researched through both modelling and observational studies but remains uncertain and may vary from glacier to glacier. In this study, we isolate various different impacts of tidal fluctuations on a glacier terminus to understand their influence on the timing of calving events in a model of Kronebreen, Svalbard, for the duration of 1 month. In addition, we impose a simplified frontal melt parameterisation onto the calving front in order to allow for an undercut to develop over the course of the simulations. We find that calving events show a tidal signal when there is a small or no undercut, but, after a critical point, undercut-driven calving becomes dominant and drowns out the tidal signal. However, the relationship is complex, and large calving events show a tidal signal even with a large modelled undercut. The modelled undercut sizes are then compared to observational profiles, showing that undercuts of up to ca. 25 m are plausible but with a more complex geometry being evident in observations than that captured in the model. These findings highlight the complex interactions occurring at the calving front of Kronebreen and suggest further observational data and modelling work is needed to fully understand the hierarchy of controls on calving.
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| 10. |
- Holmes, Felicity A., et al.
(författare)
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Relating ocean temperatures to frontal ablation rates at Svalbard tidewater glaciers : Insights from glacier proximal datasets
- 2019
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Ingår i: Scientific Reports. - : NATURE PUBLISHING GROUP. - 2045-2322. ; 9
-
Tidskriftsartikel (refereegranskat)abstract
- Fjord-terminating glaciers in Svalbard lose mass through submarine melt and calving (collectively: frontal ablation), and surface melt. With the recently observed Atlantification of water masses in the Barents Sea, warmer waters enter these fjords and may reach glacier fronts, where their role in accelerating frontal ablation remains insufficiently understood. Here, the impact of ocean temperatures on frontal ablation at two glaciers is assessed using time series of water temperature at depth, analysed alongside meteorological and glaciological variables. Ocean temperatures at depth are harvested at distances of 1 km from the calving fronts of the glaciers Kronebreen and Tunabreen, western Svalbard, from 2016 to 2017. We find ocean temperature at depth to control c. 50% of frontal ablation, making it the most important factor. However, its absolute importance is considerably less than found by a 2013-2014 study, where temperatures were sampled much further away from the glaciers. In light of evidence that accelerating levels of global mass loss from marine terminating glaciers are being driven by frontal ablation, our findings illustrate the importance of sampling calving front proximal water masses.
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| 11. |
- Holmes, Felicity, 1995-, et al.
(författare)
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Impact of tides on calving patterns at Kronebreen, Svalbard -insights from 3D ice dynamical modelling
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- Understanding calving processes and their controls is of importance for reducing uncertainty in sea level rise estimates. The impact of tidal fluctuations and frontal melt on calving patterns has been researched through both modelling and observational studies, but remains uncertain and may vary from glacier to glacier. In this study, we isolate various different impacts of tidal fluctuations on a glacier terminus to understand their influence on the timing of calving events in a model of Kronebreen, Svalbard, for the duration of one month. In addition, we impose a simplified frontal melt parameterisation onto the calving front in order to allow for an undercut to develop over the course of the simulations. We find that calving events show a tidal signal when there is a small or no undercut but, after a critical point, undercut driven calving becomes dominant and drowns out the tidal signal. However, the relationship is complex and large calving events show a tidal signal even with a large modelled undercut. The modelled undercut sizes are then compared to observational profiles, showing that undercuts of up to c. 25 m are plausible but with a more complex geometry being evident in observations than that captured in the model. These findings highlight the complex interactions occurring at the calving front of Kronebreen and suggest further observational data and modelling work is needed to fully understand the hierarchy of controls on calving.
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| 12. |
- How, Penelope, et al.
(författare)
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Calving controlled by melt-under-cutting : detailed calving styles revealed through time-lapse observations
- 2019
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Ingår i: Annals of Glaciology. - : Cambridge University Press (CUP). - 0260-3055 .- 1727-5644. ; 60:78, s. 20-31
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Tidskriftsartikel (refereegranskat)abstract
- We present a highly detailed study of calving dynamics at Tunabreen, a tidewater glacier in Svalbard. A time-lapse camera was trained on the terminus and programmed to capture images every 3 seconds over a 28-hour period in August 2015, producing a highly detailed record of 34 117 images from which 358 individual calving events were distinguished. Calving activity is characterised by frequent events (12.8 events h(-1)) that are small relative to the spectrum of calving events observed, demonstrating the prevalence of small-scale calving mechanisms. Five calving styles were observed, with a high proportion of calving events (82%) originating at, or above, the waterline. The tidal cycle plays a key role in the timing of calving events, with 68% occurring on the falling limb of the tide. Calving activity is concentrated where meltwater plumes surface at the glacier front, and a similar to 5 m undercut at the base of the glacier suggests that meltwater plumes encourage melt-under-cutting. We conclude that frontal ablation at Tunabreen may be paced by submarine melt rates, as suggested from similar observations at glaciers in Svalbard and Alaska. Using submarine melt rate to calculate frontal ablation would greatly simplify estimations of tidewater glacier losses in prognostic models.
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| 13. |
- Jakobsson, Martin, et al.
(författare)
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In memoriam of Tom Flodén : obituary
- 2017
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Ingår i: GFF. - : Taylor & Francis. - 1103-5897 .- 2000-0863. ; 139:3, s. 241-242
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)
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| 14. |
- Jakobsson, Martin, et al.
(författare)
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The International Bathymetric Chart of the Arctic Ocean (IBCAO) Version 3.0
- 2012
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 39
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Tidskriftsartikel (refereegranskat)abstract
- The International Bathymetric Chart of the Arctic Ocean (IBCAO) released its first gridded bathymetric compilation in 1999. The IBCAO bathymetric portrayals have since supported a wide range of Arctic science activities, for example, by providing constraint for ocean circulation models and the means to define and formulate hypotheses about the geologic origin of Arctic undersea features. IBCAO Version 3.0 represents the largest improvement since 1999 taking advantage of new data sets collected by the circum-Arctic nations, opportunistic data collected from fishing vessels, data acquired from US Navy submarines and from research ships of various nations. Built using an improved gridding algorithm, this new grid is on a 500 meter spacing, revealing much greater details of the Arctic seafloor than IBCAO Version 1.0 (2.5 km) and Version 2.0 (2.0 km). The area covered by multibeam surveys has increased from similar to 6% in Version 2.0 to similar to 11% in Version 3.0. Citation: Jakobsson, M., et al. (2012), The International Bathymetric Chart of the Arctic Ocean (IBCAO) Version 3.0, Geophys. Res. Lett., 39, L12609, doi:10.1029/2012GL052219.
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| 15. |
- Jakobsson, Martin, et al.
(författare)
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The International Bathymetric Chart of the Arctic Ocean Version 4.0
- 2020
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Ingår i: Scientific Data. - : Springer Science and Business Media LLC. - 2052-4463. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- Bathymetry (seafloor depth), is a critical parameter providing the geospatial context for a multitude of marine scientific studies. Since 1997, the International Bathymetric Chart of the Arctic Ocean (IBCAO) has been the authoritative source of bathymetry for the Arctic Ocean. IBCAO has merged its efforts with the Nippon Foundation-GEBCO-Seabed 2030 Project, with the goal of mapping all of the oceans by 2030. Here we present the latest version (IBCAO Ver. 4.0), with more than twice the resolution (200 x 200m versus 500 x 500m) and with individual depth soundings constraining three times more area of the Arctic Ocean (similar to 19.8% versus 6.7%), than the previous IBCAO Ver. 3.0 released in 2012. Modern multibeam bathymetry comprises similar to 14.3% in Ver. 4.0 compared to similar to 5.4% in Ver. 3.0. Thus, the new IBCAO Ver. 4.0 has substantially more seafloor morphological information that offers new insights into a range of submarine features and processes; for example, the improved portrayal of Greenland fjords better serves predictive modelling of the fate of the Greenland Ice Sheet. Machine-accessible metadata file describing the reported data: 10.6084/m9.figshare.12369314
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| 16. |
- Kirchner, Nina, et al.
(författare)
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High-resolution bathymetric mapping reveals subaqueous glacial landforms in the Arctic alpine lake Tarfala, Sweden
- 2019
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Ingår i: Journal of Quaternary Science. - : Wiley. - 0267-8179 .- 1099-1417. ; 34:6, s. 452-462
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Tidskriftsartikel (refereegranskat)abstract
- In Arctic alpine regions, glacio-lacustrine environments respond sensitively to variations in climate conditions, impacting, for example,glacier extent and rendering former ice-contact lakes into ice distal lakes and vice versa. Lakefloors may hold morphological records of past glacier extent, but remoteness and long periods of ice cover on such lakes make acquisition of high-resolution bathymetric datasets challenging. Lake Tarfala and Kebnepakte Glacier, located in the Kebnekaise mountains, northern Sweden, comprise a small, dynamic glacio-lacustrine system holding a climate archive that is not well studied. Using an autonomous surface vessel, a high-resolution bathymetric dataset for Lake Tarfala was acquired in 2016, from which previously undiscovered end moraines and a potential grounding line feature were identified. For Kebnepakte Glacier, structure-from-motion photogrammetry was used to reconstruct its shape from photographs taken in 1910 and 1945. Combining these methods connects the glacial landform record identified at the lakefloor with the centennial-scale dynamic behaviour of Kebnepakte Glacier. During its maximum 20(th) century extent, attained c. 1910, Kebnepakte Glacier reached far into Lake Tarfala, but had retreated onto land by 1945, at an average of 7.9 m year(-1).
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| 17. |
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| 18. |
- Noormets, Riko, et al.
(författare)
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Glacial dynamics and deglaciation history of Hambergbukta reconstructed from submarine landforms and sediment cores, SE Spitsbergen, Svalbard
- 2021
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Ingår i: Boreas. - : Wiley. - 0300-9483 .- 1502-3885. ; 50:1, s. 29-50
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Tidskriftsartikel (refereegranskat)abstract
- The submarine landforms and shallow sediment record are presented from Hambergbukta, southeastern Spitsbergen using swath-bathymetric, subbottom acoustic, and sediment core data. The mapped landforms include large terminal and end-moraines with associated debrisflow aprons on their distal flanks, drumlinized till surface, glacial lineations, medial and retreat moraines, crevasse squeeze ridge networks, eskers, as well as iceberg-produced terraces and plough-marks. Analysis of the landforms and landform assemblages in combination with the sediment core data and aerial imagery studies reveal a complex and dynamic glacial history of Hambergbukta. We present a detailed history of Hambergbreen glacier indicating two previously unknown surges as well as new details on the nature of the subsequent ice-margin retreat. The results from two gravity cores combined with the shallow acoustic stratigraphy and high-resolution bathymetry suggest that the c. AD 1900 surge was less extensive than previously thought and the retreat was most likely rapid after the c. AD 1900 and 1957 surges of the Hambergbreen. Mixed benthic foraminifera collected from the outer fjord basin date to 2456 cal. a BP, suggesting older sediments were re-worked by the c. AD 1900 surge. This highlights the importance of exercising caution when using foraminifers for dating surge events in fjord basins enclosed by prominent end-moraines.
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| 19. |
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| 20. |
- O'Regan, Matt, et al.
(författare)
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The De Long Trough: A newly discovered glacial trough on the East Siberian continental margin
- 2017
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Ingår i: Climate of the Past. - : Copernicus GmbH. - 1814-9324 .- 1814-9332. ; 13:9, s. 1269-1284
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Tidskriftsartikel (refereegranskat)abstract
- Ice sheets extending over parts of the East Siberian continental shelf have been proposed for the last glacial period and during the larger Pleistocene glaciations. The sparse data available over this sector of the Arctic Ocean have left the timing, extent and even existence of these ice sheets largely unresolved. Here we present new geophysical mapping and sediment coring data from the East Siberian shelf and slope collected during the 2014 SWERUS-C3 expedition (SWERUS-C3: Swedish - Russian - US Arctic Ocean Investigation of Climate-Cryosphere-Carbon Interactions). The multibeam bathymetry and chirp sub-bottom profiles reveal a set of glacial landforms that include grounding zone formations along the outer continental shelf, seaward of which lies a > 65m thick sequence of glacio-genic debris flows. The glacial landforms are interpreted to lie at the seaward end of a glacial trough - the first to be reported on the East Siberian margin, here referred to as the De Long Trough because of its location due north of the De Long Islands. Stratigraphy and dating of sediment cores show that a drape of acoustically laminated sediments covering the glacial deposits is older than similar to 50 cal kyr BP. This provides direct evidence for extensive glacial activity on the Siberian shelf that predates the Last Glacial Maximum and most likely occurred during the Saalian (Marine Isotope Stage (MIS) 6).
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| 21. |
- Petrini, Michele, et al.
(författare)
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Interplay of grounding-line dynamics and sub-shelf melting during retreat of the Bjornoyrenna Ice Stream
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- The Barents Sea Ice Sheet was a marine-based ice sheet, i.e., it rested on the Barents Sea floor during the Last Glacial Maximum (21 ky BP). The Bjornoyrenna Ice Stream was the largest ice stream draining the Barents Sea Ice Sheet and is regarded as an analogue for contemporary ice streams in West Antarctica. Here, the retreat of the Bjornoyrenna Ice Stream is simulated by means of two numerical ice sheet models and results assessed against geological data. We investigate the sensitivity of the ice stream to changes in ocean temperature and the impact of grounding-line physics on ice stream retreat. Our results suggest that the role played by sub-shelf melting depends on how the grounding-line physics is represented in the models. When an analytic constraint on the ice flux across the grounding line is applied, the retreat of Bjornoyrenna Ice Stream is primarily driven by internal ice dynamics rather than by oceanic forcing. This suggests that implementations of grounding-line physics need to be carefully assessed when evaluating and predicting the response of contemporary marine-based ice sheets and individual ice streams to ongoing and future ocean warming.
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| 22. |
- Petrini, Michele, et al.
(författare)
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Simulated last deglaciation of the Barents Sea Ice Sheet primarily driven by oceanic conditions
- 2020
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 238
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Tidskriftsartikel (refereegranskat)abstract
- The Barents Sea Ice Sheet was part of an interconnected complex of ice sheets, collectively referred to as the Eurasian Ice Sheet, which covered north-westernmost Europe, Russia and the Barents Sea during the Last Glacial Maximum (around 21 ky BP). Due to common geological features, the Barents Sea component of this ice complex is seen as a paleo-analogue for the present-day West Antarctic Ice Sheet. Investigating key processes driving the last deglaciation of the Barents Sea Ice Sheet represents an important tool to interpret recent observations in Antarctica over the multi-millennial temporal scale of glaciological changes. We present results from a perturbed physics ensemble of ice sheet model simulations of the last deglaciation of the Barents Sea Ice Sheet, forced with transient atmospheric and oceanic conditions derived from AOGCM simulations. The ensemble of transient simulations is evaluated against the databased DATED-1 reconstruction to construct minimum, maximum and average deglaciation scenarios. Despite a large model/data mismatch at the western and eastern ice sheet margins, the simulated and DATED-1 deglaciation scenarios agree well on the timing of the deglaciation of the central and northern Barents Sea. We find that the simulated deglaciation of the Barents Sea Ice Sheet is primarily driven by the oceanic forcing, with prescribed eustatic sea level rise amplifying the ice sheet sensitivity to sub-shelf melting over relatively short intervals. Our results highlight that the sub-shelf melting has a very strong control on the simulated grounding-line flux, showing that a slow, gradual ocean warming trend is capable of triggering sustained grounded ice discharge over multi-millennial timescales, even without taking into account marine ice sheet or ice cliff instability.
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| 23. |
- Prakash, Abhay, 1992-
(författare)
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Petermann Glacier Ice Shelf in a warming world : Insights from 3-D numerical modelling of ice shelf-ocean interactions at Petermann Fjord, Northwest Greenland
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The Greenland Ice Sheet (GrIS) is currently the largest contributor to global mean sea level rise, and contemporary mass loss rates are likely lower bounds for the rates to be observed in decades to come. At present, marine outlet glaciers along the northern GrIS margin, with an ice volume estimated at 400 cm mean global sea level rise equivalent, are still largely buttressed by ice shelves. However, thinning and retreat of these ice shelves, combined with perturbations of the outlet glacier’s grounding line (GL) can lead to a loss of backstress and accelerated mass loss via dynamic ice discharge, and likely render the latter the major contributor (as opposed to surface mass balance) to GrIS mass loss towards the end of the century.Here, the focus is on processes that drive basal melting of the Petermann Glacier Ice Shelf (PGIS), northwest Greenland, because contemporary knowledge regarding the full spectrum of mechanisms that dictate basal melting, and how they respond to a warming climate, is incomplete. This often results in poorly constrained oceanic boundary conditions, and consequently, afflicts estimates of GrIS’s contribution to future sea level rise with uncertainty.To address these questions, a non-idealized, nested, three-dimensional ocean-sea ice-ice shelf setup centered on PGIS and Petermann Fjord (PF) was created, based on the Finite Volume Community Ocean Model. With the setup developed and a “standard run” validated against observations from the fjord, the following scientific questions were investigated: How are basal melt rates at PGIS affected by 1. the presence, and likely future absence, of sea ice arches in Nares Strait? 2. subglacial discharge (Qsg), through increased surface runoff from the GrIS and entering PF across the GL? 3. changes in the PGIS cavity geometry in a post future-calving scenario?Our results indicate that climate warming driven transition towards a mobile and thin sea ice cover from a landfast and thick one could result in up to twofold increase in melt. In such a scenario, wind and convectively upwelled warm Atlantic Water enter the PGIS cavity. Further, in summer, under the deeper regions of PGIS, more efficient melting occurs in a more turbulent cavity, without any noticeable increase in thermal driving. We find that the presence of Qsg at the GL, and its subsequent increase in a warming atmosphere, increases melt by more than threefold. Melting also shows strong sensitivity to how Qsg is routed across the GL. Importantly, we uncover that if Qsg increases beyond 100% of present summer mean estimates, PGIS cavity enters a shear-controlled regime. Here, enhanced turbulent heat delivered by the vertical shear of the Qsg intensified current is sufficient to drive substantial increase in melt, even if there is no further increase in ocean heat forcing. Following the loss of the outer regions of PGIS post-calving, we find that wind enhanced fjord-scale currents act in concert with the Qsg at the GL to strengthen the overturning circulation, thereby increasing the basal melt. In particular, we see up to threefold increase in melt in large sections of the basal channels under the deeper PGIS draft near the GL. These results suggest that intensified basal melting of PGIS in a warming climate; in particular, of its dynamically significant and resilient deeper regions, could accelerate mass loss from Petermann Glacier, with major implications for GrIS’s contribution to future sea level rise.
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| 24. |
- Steinbach, Julia, et al.
(författare)
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Source apportionment of methane escaping the subsea permafrost system in the outer Eurasian Arctic Shelf
- 2021
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Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 118:10
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Tidskriftsartikel (refereegranskat)abstract
- The East Siberian Arctic Shelf holds large amounts of inundated carbon and methane (CH4). Holocene warming by overlying seawater, recently fortified by anthropogenic warming, has caused thawing of the underlying subsea permafrost. Despite extensive observations of elevated seawater CH4 in the past decades, relative contributions from different subsea compartments such as early diagenesis, subsea permafrost, methane hydrates, and underlying thermogenic/ free gas to these methane releases remain elusive. Dissolved methane concentrations observed in the Laptev Sea ranged from 3 to 1,500 nM (median 151 nM; oversaturation by similar to 3,800%). Methane stable isotopic composition showed strong vertical and horizontal gradients with source signatures for two seepage areas of delta C-13-CH4 = (-42.6 +/- 0.5)/(-55.0 +/- 0.5) % and delta D-CH4 = (-136.8 +/- 8.0)/(-158.1 +/- 5.5) %, suggesting a thermogenic/ natural gas source. Increasingly enriched delta C-13-CH4 and delta D-CH4 at distance from the seeps indicated methane oxidation. The Delta C-14-CH4 signal was strongly depleted (i.e., old) near the seeps (-993 +/- 19/-1050 +/- 89%). Hence, all three isotope systems are consistent with methane release from an old, deep, and likely thermogenic pool to the outer Laptev Sea. This knowledge of what subsea sources are contributing to the observed methane release is a prerequisite to predictions on how these emissions will increase over coming decades and centuries.
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| 25. |
- Stokes, Chris R., et al.
(författare)
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On the reconstruction of palaeo-ice sheets : Recent advances and future challenges
- 2015
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Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791 .- 1873-457X. ; 125, s. 15-49
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Forskningsöversikt (refereegranskat)abstract
- Reconstructing the growth and decay of palaeo-ice sheets is critical to understanding mechanisms of global climate change and associated sea-level fluctuations in the past, present and future. The significance of palaeo-ice sheets is further underlined by the broad range of disciplines concerned with reconstructing their behaviour, many of which have undergone a rapid expansion since the 1980s. In particular, there has been a major increase in the size and qualitative diversity of empirical data used to reconstruct and date ice sheets, and major improvements in our ability to simulate their dynamics in numerical ice sheet models. These developments have made it increasingly necessary to forge interdisciplinary links between sub-disciplines and to link numerical modelling with observations and dating of proxy records. The aim of this paper is to evaluate recent developments in the methods used to reconstruct ice sheets and outline some key challenges that remain, with an emphasis on how future work might integrate terrestrial and marine evidence together with numerical modelling. Our focus is on pan-ice sheet reconstructions of the last deglaciation, but regional case studies are used to illustrate methodological achievements, challenges and opportunities. Whilst various disciplines have made important progress in our understanding of ice-sheet dynamics, it is clear that data-model integration remains under-used, and that uncertainties remain poorly quantified in both empirically-based and numerical ice-Sheet reconstructions. The representation of past climate will continue to be the largest source of uncertainty for numerical modelling. As such, palaeo-observations are critical to constrain and validate modelling. State-of-the-art numerical models will continue to improve both in model resolution and in the breadth of inclusion of relevant processes, thereby enabling more accurate and more direct comparison with the increasing range of palaeo-observations. Thus, the capability is developing to use all relevant palaeo-records to more strongly constrain deglacial (and to a lesser extent pre-LGM) ice sheet evolution. In working towards that goal, the accurate representation of uncertainties is required for both constraint data and model outputs. Close cooperation between modelling and data-gathering communities is essential to ensure this capability is realised and continues to progress.
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