Dynamics and glacial history of the Drangajökull ice cap, Northwest Iceland

This thesis describes the glacial history, glacier dynamics, sediments and landforms of the Drangajökull ice cap as well as the glacial history and dynamics of the eastern Vestfirðir peninsula in northwest Iceland from the Late Weichselian until present. The aim was to reconstruct and improve the present understanding of the glacial history, surge history and dynamics of the Drangajökull ice cap. The results reveal a topographically controlled ice sheet which more and less covered the Vestfirðir peninsula during the last glaciation. Cold-based non-erosive sectors of the ice sheet covered most of the mountains while fjords and valleys were occupied by dynamical, warm-based ice. Ice thinning and deglaciation started over the mountain plateaux ca. 26 ka BP; the deglaciation was stepwise and asynchronous, uplands and some valleys were deglaciated 14-15 ka BP while valleys draining the main outlets of Drangajökull were occupied by outlet glaciers until c. 9 ka BP. The forefields proximal to the present Drangajökull ice cap are characterised by thin, coarse grained till and locally weathered bedrock, except for the sandur covered valley floors. The landforms mapped at the surging outlet glaciers are not unique for surging glaciers, and furthermore the mapped landform assemblage does not resemble landsystem models for surging glaciers. The surge-type outlets of Drangajökull reached their LIA maximum extent asynchronously during surges in the period ca. 1700-1846 AD. Review of historical data and geomorphological mapping revealed twice as many surges than previously recorded. The surge interval varies from 10-140 years between and within the outlets. Surges were most frequent during the 19th century and the earliest 20th century. No clear relationship between surge initiation or periodicity and climate could be established. A distinct ice discharge occurs during surges, reflected in 10-30 m surface thinning of the upper reservoir areas and 10-120 m thickening of the receiving areas. During the present quiescent phase, the reservoir areas thicken by c. 0.5-0.7 m a-1 and the receiving areas thin by c. 1 m a-1, which might bring the glacier surface to a pre-surge stage in 45-65 years. Future studies could focus on extensive morphological mapping and direct dating of glacial features, aiming to add further details to the glacial history and test the reconstructions of Drangajökull presented here. Further investigation of the surge-type glaciers, e.g. extensive monitoring of weather and the glacier conditions, geophysical surveys both of the glaciers and their forefields, might also contribute to an improved understanding of the Drangajökull surging glaciers.Í þessari ritgerð er fjallað um jöklunarsögu, sveiflur, setmyndanir og landmótun Drangajökuls. Einnig er fjallað um jöklunar- og afísunarsögu Vestfjarða, frá seinni hluta síðusta jökulskeiðs til nútíma. Aðalmarkmið rannsóknarinnar var að kanna betur sögu jöklunar og framhlaupa Drangajökuls. Niðurstöðurnar benda til þess að Vestfirðir hafi að langmestu leiti verið huldir ís á hámarki síðasta jökulskeiðs, íshellan var undir sterkum áhrifum djúpra dala og fjarða Vestfjarðskagans. Þýðjöklar/ísstraumar flæddu tiltölulega hratt eftir fjörðum og dölum og rufu undirlag sitt. Ofarlega í fjallshlíðum eða yfir fjalllendi voru snörp skil í eiginleikum jökulíssins. Þar uppi var gaddjökull ráðandi sem flæddi hægt við innri aflögun og lét undirlag sitt að mestu ósnortið. Jökulhörfun hófst á hæstu fjöllum fyrir 26 þúsund árum, jöklaleysingin var ósamstíga milli svæða, en fyrir um 14-15 þúsund árum voru hærri landsvæði og sumir dalir þegar íslausir á meðan aðrir firðir og dalir máttu þola ágang meginskriðjökla Drangajökuls þangað til fyrir u.þ.b. 9 þúsund árum síðan. Svæðið umhverfis Drangajökul einkennist af þunnum og grófum jökulruðningi í bland við ísmótaðar og veðraðar klappir en aðliggjandi dalbotnar eru að mestu huldir ármöl og áreyrum. Framhlaupsjöklar Drangajökuls náðu hámarksstærð hver í sínu lagi á árunum 1700-1846. Sögulegar heimildir og kortlagning á landmótunarsvæðum þeirra leiddi í ljós jökulgarða sem voru tvöfalt fleiri en áður skráð framhlaup Drangajökuls. Framhlaupahlé eru mjög óregluleg, 10-140 ár, en framhlaup virðast hafa verið einna tíðust á 19. öld og í upphafi 20. aldarinnar. Ekkert augljóst samband loftlags við eignleika og tíðni framhlaupanna er greinanlegt. Í nýyfirstöðnum framhlaupum Drangajökuls var algengasta yfirborðsþynning söfnunarsvæðanna á bilinu 10-30 m á meðan þykknun leysingasvæðanna var mun breytilegri, eða um 10-120 m. Þrátt fyrir neikvæða meðal afkomu Drangajökuls, það sem af er yfirstandandi kyrrfasa framhlaupsjöklanna, þykkna söfnunarsvæði þeirra að meðaltali um 0.5-0.7 m árlega. Uppbygging söfnunarsvæðanna ásamt um 1 m árlegri meðalþynningu leysingasvæðanna leiðir til brattara yfirborðs jökulsins og á 45-65 árum gæti yfirborðið orðið sambærilegt því sem var fyrir síðasta framhlaup jöklanna. Rannsóknin hefur leitt í ljós allflókið mynstur íseiginleika, sveiflna og jöklunarsögu Drangajökuls. Vitneskju okkar um þessa þætti mætti auka með áframhaldandi kortlagningu, aldursgreiningu jökulmyndaðra landforma og jökulættaðs sets. Þannig mætti sannreyna þær niðurstöður sem hér eru kynntar og skerpa línur varðandi sögu og eiginleika síðasta jökulskeiðs. Eignleikum, eðli og sögu framhlaupsjöklanna í Drangajökli mætti gera betri skil. Gagnlegt gæti verið að beita fleiri aðferðum, t.d. langtíma vöktun á veðri og afkomu jöklanna, jarðeðlisfræðilegar kannanir á íseignleikum, undirlagi jöklanna og landmótunarumhverfi þeirra gætu einnig aukið skilning okkar

Effects of abiotic stressors on lutein production in the green microalga Dunaliella salina.

BackgroundRecent years have witnessed a rising trend in exploring microalgae for valuable carotenoid products as the demand for lutein and many other carotenoids in global markets has increased significantly. In green microalgae lutein is a major carotenoid protecting cellular components from damage incurred by reactive oxygen species under stress conditions. In this study, we investigated the effects of abiotic stressors on lutein accumulation in a strain of the marine microalga D. salina which had been selected for growth under stress conditions of combined blue and red lights by adaptive laboratory evolution.ResultsNitrate concentration, salinity and light quality were selected as three representative influencing factors and their impact on lutein production in batch cultures of D. salina was evaluated using response surface analysis. D. salina was found to be more tolerant to hyper-osmotic stress than to hypo-osmotic stress which caused serious cell damage and death in a high proportion of cells while hyper-osmotic stress increased the average cell size of D. salina only slightly. Two models were developed to explain how lutein productivity depends on the stress factors and for predicting the optimal conditions for lutein productivity. Among the three stress variables for lutein production, stronger interactions were found between nitrate concentration and salinity than between light quality and the other two. The predicted optimal conditions for lutein production were close to the original conditions used for adaptive evolution of D. salina. This suggests that the conditions imposed during adaptive evolution may have selected for the growth optima arrived at.ConclusionsThis study shows that systematic evaluation of the relationship between abiotic environmental stresses and lutein biosynthesis can help to decipher the key parameters in obtaining high levels of lutein productivity in D. salina. This study may benefit future stress-driven adaptive laboratory evolution experiments and a strategy of applying stress in a step-wise manner can be suggested for a rational design of experiments

The role of antigen availability during B cell induction and its effect on sustained memory and antibody production after infection and vaccination-lessons learned from the SARS-CoV-2 pandemic

© The Author(s) 2022. Published by Oxford University Press on behalf of the British Society for Immunology. All rights reserved. For permissions, please e-mail: [email protected] importance of antibodies, particularly neutralizing antibodies, has been known for decades. When examining the immune responses against a pathogen after a vaccination or infection it is easier to measure the levels of antigen-specific antibodies than the T-cell response, but it does not give the whole picture. The levels of neutralizing antibodies are harder to determine but give a better indication of the quality of the antibody response. The induction of long-lived antibody-secreting plasma cells is crucial for a persistent humoral immune response, which has been shown for example after vaccination with the vaccinia vaccine, where antibody levels have been shown to persist for decades. With the SARS-CoV-2 pandemic ravaging the world for the past years and the monumental effort in designing and releasing novel vaccines against the virus, much effort has been put into analysing the quantity, quality, and persistence of antibody responses.Peer reviewe

Geomorphology and surficial geology of the Femmilsjøen area, northern Spitsbergen

Climate change is amplified in the Arctic, and establishing baseline data for its current character is important. Here we present a map of the geomorphology of the Femmilsjøen area, Spitsbergen, northern Svalbard. The regional physiography is characterised by a low-relief, high elevation mountain plateau, its high-relief steep slopes, and low-relief coastal lowlands. The results indicate that glaciers were most likely warm-based and erosive in the low terrain, whereas there are signatures of colder, less erosive ice on the plateaus during the Late Weichselian. Our study highlights the ongoing glacial and periglacial morphological processes in an area of hard and weathering-resistant bedrock, situated in northern Svalbard

The 2014 Lake Askja rockslide-induced tsunami: Optimization of numerical tsunami model using observed data

A large rockslide was released from the inner Askja caldera into Lake Askja, Iceland, on 21 July 2014. Upon entering the lake, it caused a large tsunami that traveled about ∼3 km across the lake and inundated the shore with vertical runup measuring up to 60–80 m. Following the event, comprehensive field data were collected, including GPS measurements of the inundation and multibeam echo soundings of the lake bathymetry. Using this exhaustive data set, numerical modeling of the tsunami has been conducted using both a nonlinear shallow water model and a Boussinesq-type model that includes frequency dispersion. To constrain unknown landslide parameters, a global optimization algorithm, Differential Evolution, was employed, resulting in a parameter set that minimized the deviation from measured inundation. The tsunami model of Lake Askja is the first example where we have been able to utilize field data to show that frequency dispersion is needed to explain the tsunami wave radiation pattern and that shallow water theory falls short. We were able to fit the trend in tsunami runup observations around the entire lake using the Boussinesq model. In contrast, the shallow water model gave a different runup pattern and produced pronounced offsets in certain areas. The well-documented Lake Askja tsunami thus provided a unique opportunity to explore and capture the essential physics of landslide tsunami generation and propagation through numerical modeling. Moreover, the study of the event is important because this dispersive nature is likely to occur for other subaerial impact tsunamis.Nordic Centre of Excellence on Resilience and Societal Security (NORDRESS) Research Council of Norway -231252 Icelandic Avalanche and Landslide Fund Vatnajokull National ParkPeer Reviewe

Cross-cutting palaeo-ice streams in NE-Iceland reveal shifting Iceland Ice Sheet dynamics

Ice streams are thought to have regulated the past Iceland Ice Sheet (IIS) during and following the Last Glacial Maximum (LGM) by discharging ice and sediment from the interior of the ice sheet towards the shelf edge. Previous assessments of ice streams within the IIS have produced contradictory reconstructions of ice sheet dynamics and location of ice divides. Here, we reconstruct palaeo-ice streams in NE-Iceland based on detailed mapping of streamlined subglacial bedforms (SSBs) and other glacial lineations. The morphometrics, distribution and orientation of the SSBs indicate the flow-sets of several cross-cutting palaeo-ice streams and the location and migration of ice divides, while high density and packing of SSBs possibly suggest the axial zones of the ice streams. North-trending flow-sets suggest that during maximum glaciation and ice-sheet thickness, ice flow within the study area was largely unaffected by underlying topography allowing ice to flow northwards across valleys and fjords. This ice flow direction correlates with the orientation of previously identified troughs on the north-eastern shelf and indicates that an E-W orientated ice divide was located to the south of the study area. During deglaciation and ice sheet thinning, a N-S orientated ice divide was located to the west of the study area, and palaeo-ice streams became confined to valleys and fjords, so that associated flow-sets crosscut the older ones. The absolute ages of these flow-sets are uncertain, but the simplest interpretation is that the older ones pertain to the LGM and the younger ones to the following deglaciation. This study sheds light on the dynamics and evolution of palaeo-ice streams within the IIS and highlights the importance of further efforts to understand the subglacial processes responsible for the formation of the streamlined subglacial bedforms as well as to constrain the evolution of shelf glaciation and chronology of ice stream retreat.University of Iceland Research Fund, the Icelandic Road and Coastal Administration, and the Energy Research Fund of Landsvirkjun.Pre-print (óritrýnt handrit

Glacial history of the Åsgardfonna Ice Cap, NE Spitsbergen, since the last glaciation

The response of glaciers and ice caps to past climate change provides important insight into how they will react to ongoing and future global warming. In Svalbard, the Holocene glacial history has been studied for many cirque and valley glaciers. However, little is known about how the larger ice caps in Svalbard responded to Late Glacial and Holocene climate changes. Here we use lake sediment cores and geophysical data from Femmilsjøen, one of Svalbard’s largest lakes, to reconstruct the glacial history of the Åsgardfonna Ice Cap since the last deglaciation. We find that Femmilsjøen potentially deglaciated prior to 16.1 ± 0.3 cal ka BP and became isolated from the marine environment between 11.7 ± 0.3 to 11.3 ± 0.2 cal ka BP. Glacial meltwater runoff was absent between 10.1 ± 0.4 and 3.2 ± 0.2 cal ka BP, indicating that Åsgardfonna was greatly reduced or disappeared in the Early and Middle Holocene. Deposition of glacial-meltwater sediments re-commenced in Femmilsjøen at c. 3.2 ± 0.2 cal ka BP, indicating glacier re-growth in the Femmilsjøen catchment and the onset of the Neoglacial. The glacier(s) in the Femmilsjøen catchment area reached sizes no smaller than their modern extents already at c. 2.1 ± 0.7 cal ka BP. Our results suggest that larger Svalbard ice caps such as Åsgardfonna are very sensitive to climate changes and probably melted completely during the Holocene Thermal Maximum. Such information can be used as important constraints in future ice-cap simulations

Spatial Analysis of Cirques from Three Regions of Iceland: Implications for Cirque Formation and Palaeoclimate

This study is a quantitative analysis of cirques in three regions of Iceland: Tröllaskagi, the East Fjords and Vestfirðir. Using Google Earth and the National Land Survey of Iceland Map Viewer, we identified 347 new cirques on Tröllaskagi and the East Fjords region, and combined these data with 100 cirques previously identified on Vestfirðir. We used ArcGIS to measure length, width, aspect, latitude and distance to coastline of each cirque. Palaeo‐equilibrium‐line altitudes (palaeo‐ELAs) of palaeo‐cirque glaciers were calculated using the altitude‐ratio method, cirque‐floor method and minimum‐point method. The mean palaeo‐ELA values in Tröllaskagi, the East Fjords and Vestfirðir are 788, 643 and 408 m a.s.l, respectively. Interpolation maps of palaeo‐ELAs demonstrate a positive relationship between palaeo‐ELA and distance to coastline. A positive relationship between palaeo‐ELA and latitude is observed on Vestfirðir, a negative relationship is observed on Tröllaskagi and no statistically significant relationship is present on the East Fjords. The modal orientation of cirques on Tröllaskagi and Vestfirðir is northeast, while orientation of cirques in the East Fjords is north. Palaeo‐wind reconstructions for the LGM show that modal aspect is aligned with the prevailing north‐northeast wind directions, although aspect measurements demonstrate wide dispersion. Cirque length is similar on Tröllaskagi and the East Fjords, but cirques are approximately 200 m shorter in Vestfirðir. Cirque widths are similar in all three regions. Comparisons with a global data set show that cirques in Iceland are smaller and more circular than cirques in other regions of the world. Similar to glaciers in Norway and Kamchatka, our results demonstrate that access to a moisture source is a key parameter in determining palaeo‐ELAs in Iceland. Temperatures interpreted from palaeo‐ELA depressions suggest that these cirques may have been glaciated as recently as the Little Ice Age

Reversible glacial-periglacial transition in response to climate changes and paraglacial dynamics: a case study from Héðinsdalsjökull (northern Iceland)

The objective of this work is to chronologically establish the origin of the different glacial and rock glacier complex landforms deposited by Héðinsdalsjökull glacier (65°39′ N, 18°55′ W), in the Héðinsdalur valley (Skagafjörður fjord, Tröllaskagi peninsula, central northern Iceland). Multiple methods were applied: geomorphological analysis and mapping, glacier reconstruction and equilibrium-line altitude calculation, Cosmic-Ray Exposure dating (in situ cosmogenic 36Cl), and lichenometric dating. The results reveal that a debris-free glacier receded around 6.6 ± 0.6 ka, during the Holocene Thermal Maximum. The retreat of the glacier exposed its headwall and accelerated paraglacial dynamics. As a result, the glacier terminus evolved into a debris-covered glacier and a rock glacier at a slightly higher elevation. The front of this rock glacier stabilized shortly after it formed, although nuclide inheritance is possible, but its sector close the valley head stabilized between 1.5 and 0.6 ka. The lowest part of the debris-covered glacier (between 600 and 820 m altitude) collapsed at ca. 2.4 ka. Since then, periods of glacial advance and retreat have alternated, particularly during the Little Ice Age. The maximum advance during this phase occurred in the 15th to 17th centuries with subsequent re-advances, namely at the beginning of the 19th and 20th centuries. After a significant retreat during the first decades of the 20th century, the glacier advanced in the 1960s to 1990s, and then retreated again, in accordance with the local climatic evolution. The internal ice of both the debris-covered and the rock glacier have survived until the present day, although enhanced subsidence provides evidence of their gradual degradation. A new rock glacier developed from an ice-cored moraine from around 1940–1950 CE. Thus, the Holocene coupling between paraglacial and climatic shifts has resulted in a complex evolution of Héðinsdalsjökull, which is conflicting with previously proposed models: a glacier, which had first evolved into a debris-covered and rock glacier, could later be transformed into a debris-free glacier, with a higher sensitivity to climatic variability.info:eu-repo/semantics/publishedVersio

Population size of Oystercatchers Haematopus ostralegus wintering in Iceland

The first ever survey of Oystercatchers wintering in Iceland found around 11 000 individuals. This is an estimated 30% of the Icelandic population, including juveniles, suggesting that approximately 26 000 Icelandic Oystercatchers migrate to western Europe in the autumn. More Oystercatchers winter in Iceland than at similar latitudes elsewhere in Europe, which may reflect the remoteness and milder winter temperatures on this oceanic island