Submarine landform assemblages and sedimentary processes related to glacier surging in Kongsfjorden, Svalbard

High-resolution swath-bathymetry data from inner Kongsfjorden, Svalbard, reveal characteristic landform assemblages formed during and after surges of tidewater glaciers, and provide new insights into the dynamics of surging glaciers. Glacier front oscillations and overriding related to surge activity lead to the formation of overridden moraines, glacial lineations of two types, terminal moraines, associated debris lobes and De Geer moraines. In contrast to submarine landform assemblages from other Svalbard fjords, the occurrence of two kinds of glacial lineations and the presence of De Geer moraines suggest variability in the landforms produced by surge-type tidewater glaciers. All the landforms in inner Kongsfjorden were deposited during the last c. 150 years. Lithological and acoustic data from the innermost fjord reveal that suspension settling from meltwater plumes as well as ice rafting are dominant sedimentary processes in the fjord, leading to the deposition of stratified glacimarine muds with variable numbers of clasts. Reworking of sediments by glacier surging results in the deposition of sediment lobes containing massive glacimarine muds. Two sediment cores reveal minimum sediment accumulation rates related to the Kongsvegen surge from 1948; these were 30 cm a-1 approximately 2.5 km beyond the glacier front shortly after surge termination, and rapidly dropped to an average rate of 1.8 cm a-1 in ∼ 1950, during glacier retreat

Sedimentary ancient DNA from Lake Skartjorna, Svalbard: assessing the resilience of arctic flora to Holocene climate change

Reconstructing past vegetation and species diversity from arctic lake sediments can be challenging because of low pollen and plant macrofossil concentrations. Information may be enhanced by metabarcoding of sedimentary ancient DNA (sedaDNA). We developed a Holocene record from Lake Skartjørna, Svalbard, using sedaDNA, plant macrofossils and sediment properties, and compared it with published records. All but two genera of vascular plants identified as macrofossils in this or a previous study were identified with sedaDNA. Six additional vascular taxa were found, plus two algal and 12 bryophyte taxa, by sedaDNA analysis, which also detected more species per sample than macrofossil analysis. A shift from Salix polaris-dominated vegetation, with Koenigia islandica, Ranunculaceae and the relatively thermophilic species Arabis alpina and Betula, to Dryas octopetala-dominated vegetation ~6600–5500 cal. BP suggests a transition from moist conditions 1–2°C warmer than today to colder/drier conditions. This coincides with a decrease in runoff, inferred from core lithology, and an independent record of declining lacustrine productivity. This mid-Holocene change in terrestrial vegetation is broadly coincident with changes in records from marine sediments off the west coast of Svalbard. Over the Holocene sedaDNA records little floristic change, and it clearly shows species persisted near the lake during time intervals when they are not detected as macrofossils. The flora has shown resilience in the presence of a changing climate, and, if future warming is limited to 2°C or less, we might expect only minor floristic changes in this region. However, the Holocene record provides no analogues for greater warming

Geomorphology and development of a high-latitude channel system: the INBIS channel case (NW Barents Sea, Arctic)

This is a post-peer-review, pre-copyedit version of an article published in Arktos. The final authenticated version is available online at: http://dx.doi.org/https://doi.org/10.1007/s41063-019-00065-9 .The INBIS (Interfan Bear Island and Storfjorden) channel system is a rare example of a deep-sea channel on a glaciated margin. The system is located between two trough mouth fans (TMFs) on the continental slope of the NW Barents Sea: the Bear Island and the Storfjorden–Kveithola TMFs. New bathymetric data in the upper part of this channel system show a series of gullies that incise the shelf break and minor tributary channels on the upper part of the continental slope. These gullies and channels appear far more developed than those on the rest of the NW Barents Sea margin, increasing in size downslope and eventually merging into the INBIS channel. Morphological evidence suggests that the Northern part of the INBIS channel system preserved its original morphology over the last glacial maximum (LGM), whereas the Southern part experienced the emplacement of mass transport glacigenic debris that obliterated the original morphology. Radiometric analyses were applied on two sediment cores to estimate the recent (~ 110 years) sedimentation rates. Furthermore, analysis of grain size characteristics and sediment composition of two cores shows evidence of turbidity currents. We associate these turbidity currents with density-driven plumes, linked to the release of meltwater at the ice-sheet grounding line, cascading down the slope. This type of density current would contribute to the erosion and/ or preservation of the gullies’ morphologies during the present interglacial. We infer that Bear Island and the shallow morphology around it prevented the flow of ice streams to the shelf edge in this area, working as a pin (fastener) for the surrounding ice and allowing for the development of the INBIS channel system on the inter-ice stream part of the slope. The INBIS channel system was protected from the burial by high rates of ice-stream derived sedimentation and only partially affected by the local emplacement of glacial debris, which instead dominated on the neighbouring TMF systems

Modern agglutinated foraminifera from the Hovgård ridge, fram strait, west of Spitsbergen: Evidence for a deep bottom current

Deep-water agglutinated foraminifera on the crest of the Hovgârd Ridge, west of Spitsbergen, consist mostly of large tubular astrorhizids. At a boxcore station collected from the crest of Hovgârd Ridge at a water depth of 1169 m, the sediment surface was covered with patches of large (1 mm diameter) tubular forms, belonging mostly to the species Astrorhiza crassatina Brady, with smaller numbers of Saccorhiza, Hyperammina, and Psammosiphonella. Non-tubutar species consisted mainly of opportunistic forms, such as Psammosphaera and Reophax. The presence of large suspension-feeding tubular genera as well as opportunistic forms point to the presence of deep currents at this locality that are strong enough to disturb the benthic fauna. This is confirmed by data obtained from sediment echosounding, which exhibit lateral variation in relative sedimentation rates within the Pleistocene sedimentary drape covering the ridge, indicative of winnowing in a south-easterly direction

A review of the scientific knowledge of the seascape off Dronning Maud Land, Antarctica

Despite the exclusion of the Southern Ocean from assessments of progress towards achieving the Convention on Biological Diversity (CBD) Strategic Plan, the Commission for the Conservation of Antarctic Marine Living Resources (CCAMLR) has taken on the mantle of progressing efforts to achieve it. Within the CBD, Aichi Target 11 represents an agreed commitment to protect 10% of the global coastal and marine environment. Adopting an ethos of presenting the best available scientific evidence to support policy makers, CCAMLR has progressed this by designating two Marine Protected Areas in the Southern Ocean, with three others under consideration. The region of Antarctica known as Dronning Maud Land (DML; 20°W to 40°E) and the Atlantic sector of the Southern Ocean that abuts it conveniently spans one region under consideration for spatial protection. To facilitate both an open and transparent process to provide the vest available scientific evidence for policy makers to formulate management options, we review the body of physical, geochemical and biological knowledge of the marine environment of this region. The level of scientific knowledge throughout the seascape abutting DML is polarized, with a clear lack of data in its eastern part which is presumably related to differing levels of research effort dedicated by national Antarctic programmes in the region. The lack of basic data on fundamental aspects of the physical, geological and biological nature of eastern DML make predictions of future trends difficult to impossible, with implications for the provision of management advice including spatial management. Finally, by highlighting key knowledge gaps across the scientific disciplines our review also serves to provide guidance to future research across this important region.publishedVersio

Mid-Pleistocene climate transition drives net mass loss from rapidly uplifting St. Elias Mountains, Alaska

Erosion, sediment production and routing on a tectonically active continental margin reflect both tectonic and climatic processes; partitioning the relative importance of these processes remains controversial. Gulf of Alaska contains a preserved sedimentary record of Yakutat Terrane collision with North America. Because tectonic convergence in the coastal St. Elias orogen has been roughly constant for 6 Myr, variations in its eroded sediments preserved in the offshore Surveyor Fan constrain a budget of tectonic material influx, erosion, and sediment output. Seismically imaged sediment volumes calibrated with chronologies derived from Integrated Ocean Drilling Program boreholes shows that erosion accelerated in response to Northern Hemisphere glacial intensification (~2.7 Ma) and that the 900-km long Surveyor Channel inception appears to correlate with this event. However, tectonic influx exceeded integrated sediment efflux over the interval 2.8-1.2 Ma. Volumetric erosion accelerated following the onset of quasi-periodic (~100-kyr) glacial cycles in the mid-Pleistocene climate transition (1.2-0.7 Ma). Since then erosion and transport of material out of the orogen has outpaced tectonic influx by 50-80%. Such a rapid net mass loss explains apparent increases in exhumation rates inferred onshore from exposure dates and mapped out-of-sequence fault patterns. The 1.2 Myr mass budget imbalance must relax back toward equilibrium in balance with tectonic influx over the time scale of orogenic wedge response (Myrs). The St. Elias Range provides a key example of how active orogenic systems respond to transient mass fluxes, and the possible influence of climate driven erosive processes that diverge from equilibrium on the million-year scale

Sea-ice dynamics in an Arctic coastal polynya during the past 6500 years

The production of high-salinity brines during sea-ice freezing in circum-arctic coastal polynyas is thought to be part of northern deep water formation as it supplies additional dense waters to the Atlantic meridional overturning circulation system. To better predict the effect of possible future summer ice-free conditions in the Arctic Ocean on global climate, it is important to improve our understanding of how climate change has affected sea-ice and brine formation, and thus finally dense water formation during the past. Here, we show temporal coherence between sea-ice conditions in a key Arctic polynya (Storfjorden, Svalbard) and patterns of deep water convection in the neighbouring Nordic Seas over the last 6500 years. A period of frequent sea-ice melting and freezing between 6.5 and 2.8 ka BP coincided with enhanced deep water renewal in the Nordic Seas. Near-permanent sea-ice cover and low brine rejection after 2.8 ka BP likely reduced the overflow of high-salinity shelf waters, concomitant with a gradual slow down of deep water convection in the Nordic Seas, which occurred along with a regional expansion in sea-ice and surface water freshening. The Storfjorden polynya sea-ice factory restarted at ~0.5 ka BP, coincident with renewed deep water penetration to the Arctic and climate amelioration over Svalbard. The identified synergy between Arctic polynya sea-ice conditions and deep water convection during the present interglacial is an indication of the potential consequences for ocean ventilation during states with permanent sea-ice cover or future Arctic ice-free conditions