Diversity of igneous rocks from the Isachsen Dome, Ellef Ringnes Island, Canadian High Arctic Abstract The sedimentary deposits of the central Sverdrup Basin on Ellef Ringnes Island were affected by both salt diapirism and igneous activity of the Cretaceous High Arctic Large Igneous Province (HALIP). Occurrences of mafic igneous rocks on the centre of salt domes are usually assigned to the Cretaceous magmatism. Petrographic, geochemical, Sr–Nd isotope, and geochronological (Ar–Ar dating) studies on six rock fragments collected on the top of Isachsen Dome reveal a larger variability in the composition and the age compared to HALIP-related rocks from elsewhere on Ellef Ringnes Island. A blocky fragment of tholeiitic hornblende dolerite with an Ar–Ar age of 121 Ma is interpreted to originate from an in-situ intrusion and was uplifted by evaporite diapirism. The other samples are small, sub-rounded pebbles, which represent three different parent rock types. A kaersutite-bearing alkali basalt was possibly formed during the Triassic or Permian. A leucocratic, albitised rock fragment has experienced contact metasomatism at 102 Ma, and three very similar tholeiitic basalt fragments probably derived from the margin of a dyke were auto-hydrothermally affected at 69 Ma. The inferred source area of these exotic pebbles is the segment of the Arctic continental margin in the northeast that was repeatedly affected by igneous events between the Carboniferous and latest Cretaceous and that was uplifted and eroded during the Eocene. The rock fragments were probably deposited as Palaeogene sediments above the rising Isachsen diapir shortly before or as the head of the salt dome has pierced the Earth’s surface. Glacial transport up the top of Isachsen Dome during the Late Wisconsinan glaciation is not very likely due to the contrast between the north to northwest directed ice-flow direction reported in the literature and the assumed northeastern source area of the pebbles; however, it cannot be completely excluded.

Evolution of contourite drifts in regions of slope failures at eastern Fram Strait Abstract Geotechnical characteristics of contouritic deposition often lead to preconditioning slope instabilities and failures along glaciated and formerly glaciated continental margins. However, internal depositional geometry is also an important factor in triggering instabilities. This work highlights the importance of the tectonic and oceanographic evolution of the Northwestern (NW) Svalbard margin in determining the buildup and the internal structure of contourite drifts and the subsequent type of slope instability. The analysis of seismic reflection data reveals that the presence of two contourite drifts on the flank of an active spreading ridge in the Fram Strait—NW Svalbard margin—in an area of extensive slope instability had a major impact on the evolution of slope failure. The presence of a slope sheeted drift (or plastered drift) led to the development of rotational/translational mass movement at water depth < 2500 ms, whereas at water depth > 2500 ms the presence of sediment waves facilitated the formation of planes of shear that led to internal deformation of the lower slope through a process of slump/creep. The well-documented high seismicity of the area might have provided the necessary energy to trigger the slope instability.

Sedimentary processes and seabed morphology of the Southwest Greenland margin Abstract Bathymetric and seismic data from the Southwest Greenland margin have been used to provide an integrated shelf-to-basin overview of the margin architecture between 57° N and 64° N. A variety of glacially formed morphologic features, contour current-related erosion and sedimentary deposits, and evidence of downslope sediment transport via canyons, channels and gullies is found here. The study area is characterized by two major canyons bordering Fylla Bank in the northern part and a narrow shelf and steep slope to the south, where erosion due to strong boundary currents occur down to c. 3000 m water depth. The narrow shelf area appears to be an intra-ice stream area, and numerous channels and gullies on the upper slope point to hyperpycnal melt water release from a stable or retreating wide ice front. Further southward, the shelf is widening and the morphology indicates dominance of former ice stream activity. This difference in glaciation style may reflect the different bedrock types. Sedimentary and morphologic characteristics of the Fylla Bank canyons and some of the slope gullies and channels point to actual cascading of dense winter water or hyperpycnal melt water flow from the shelf. Deep-water channels at the base of the slope evidence transport of Greenland-derived sediment to the central Labrador Sea basin and buried channels further west indicate a former contribution to the Northwest Atlantic Mid-Ocean Channel (NAMOC) system. However, in contrast to widespread turbidite channels on the present seabed bordering NAMOC to the west, east of NAMOC contourite deposits have largely covered the deep-water tributary turbidite channels originating from the Greenland margin.

Sediment geochemical study of hydrocarbon seeps in Isfjorden and Mohnbukta: a comparison between western and eastern Spitsbergen, Svalbard Abstract Methane is the most widespread volatile hydrocarbon and one of the most potent greenhouse gases. Marine sediments form the largest methane reservoir, from where large quantities of methane from gas-saturated sediments are released into the sea water and into the shallow shelf seas, through the water column almost unaltered into the atmosphere. Craters on the sea floor known as pockmarks are often related to seepage of methane-rich fluids originating either from shallow (microbial) or deep (thermogenic) sources. This paper presents the geochemical characteristics of migrating hydrocarbon gas from selected pockmarks and surrounding seabed in Isfjorden and Mohnbukta in western and eastern Spitsbergen, respectively. Collected gas samples, including wet gas fraction, were analyzed for methane concentration and methane carbon stable isotope ratio. Mixtures of microbial and thermogenic methane, together with higher homologies were found in the pockmarks as well as in the adjacent undisturbed seafloor, suggesting that the seepage activity in both areas is currently on the same level. Although the methane concentration profiles and methane stable carbon isotope ratios in Isfjorden and Mohnbukta show signs of biological oxidation and elevated concentrations of ethane/propane indicate input from deeper thermogenic sources. The gas composition and methane carbon stable isotope ratio from Isfjorden and Mohnbukta areas show similar trends, most likely due to originating in the same Mesozoic organic-rich marine mudstone.

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

Middle Miocene magmatic activity in the Sophia Basin, Arctic Ocean—evidence from dredged basalt at the flanks of Mosby Seamount Abstract The area to the northwest of Svalbard was repeatedly affected by tectono-magmatic events during the opening of the Arctic Ocean including the formation of the Cretaceous High Arctic Large Igneous Province, the Late Cretaceous/early Cenozoic birth of the Eurasian Basin, and the establishment of a full seafloor-spreading regime along the Lena Trough/Fram Strait in the middle Miocene. These processes also affected the Sophia Basin located between the Yermak Plateau and the northern Svalbard Shelf. In 2013 a piece of basalt was dredged from the southern flank of the Mosby Seamount, the central landmark within the Sophia Basin. According to Ar–Ar dating on fresh plagioclase the basalt erupted at ~ 13 Ma, contemporaneous with incipient seafloor spreading in the nearby Lena Trough and volcanic activity on northern Svalbard. If the dredged basalt is temporally related to sediment-covered lava flows and sill intrusions around Mosby Seamount, which were revealed by seismic reflections, then the age of the sedimentary cover must be middle Miocene or younger. This finding will improve the regional seismo-stratigraphy.

Inheritance and style of rifting: incremental structural restoration of the Laptev Sea Rift System, north-eastern Russian Arctic Abstract The Laptev Sea Rift System, on the north-eastern continental margin of the Russian Arctic, is a key area to understand the opening of the Eurasia Basin. The rifts developed since Cretaceous/Early Cenozoic times and consists of five, roughly north–south trending depocentres, controlled by major listric normal faults. Three cross-sections from the rift system were incrementally restored to quantify the amount of extension over time and to reconstruct the geological evolution. We show that since the beginning of rifting, fault activity in the Anisin Basin was unevenly distributed between two symmetrical graben systems. The central Ust’ Lena Rift has a completely different structure: regularly spaced west-dipping faults are interrupted by minor east-dipping faults in only three places. Fault dip decreases from west to east, from 60° to 30°, respectively.

Late Weichselian glacial history of Forlandsundet, western Svalbard: an inter-ice-stream setting Abstract The last glacial maximum (LGM) and post-glacial Quaternary history of Forlandsundet, the strait between western Spitsbergen and Prins Karls Forland, are enigmatic. Previous terrestrial field studies report contradicting evidence for an ice sheet either overriding the entire strait or completely absent during the LGM. Here, we present a multi-proxy investigation of marine sediments, high-resolution bathymetric data and aerial imagery from Forlandsundet. We reveal glacial till present at 15 cal. ka BP and geomorphological landforms characteristic to an inter-ice-stream glaciated margin. This new evidence implies that the Forlandsundet region was fully glaciated during the LGM. This glaciation was followed by a stepwise retreat of glacial ice during the Bølling–Allerød (14.7–12.7 cal. ka BP) and Younger Dryas (12.7–11.7 cal. ka BP). The Holocene record from the marine sediments is incomplete, with a hiatus from approximately 11.8 to 7.4 cal. ka BP, interpreted as an erosive event. By the mid-Holocene (7.4 cal. ka BP), more temperate, Atlantic conditions based on the benthic foraminiferal assemblages prevailed, and are followed by gradual cooling into the late Holocene (< 4 cal. ka BP). This study provides new data to resolve the LGM extent of the Svalbard–Barents Sea ice sheet in the Forlandsundet region and sheds light on the deglacial ice dynamics in a palaeo-inter-ice-stream area driven by the inflow of warm Atlantic water.

Distribution of living benthic foraminifera in the northern Chukchi Sea Abstract Living (Rose Bengal stained) benthic foraminifera were studied in the topmost sediments of five multi- and box cores collected on the continental shelf, upper and lower slopes, of the Chukchi Sea to provide background information on modern benthic foraminiferal distribution, useful for future studies. Sediment cores were collected during August–September 2015, when the area is seasonally ice-free. Benthic foraminiferal contents in the 63–125 µm and > 125 µm size fractions are discussed in terms of water masses distribution, and sedimentological (grain size) and organic geochemical (total organic carbon, total nitrogen, C/N ratio and δ13Corg) characteristics of the surface sediments. Marine organic carbon-rich clay sediments characterize the faunal microhabitats. Despite relatively high organic carbon contents, standing stocks of living benthic foraminifera are generally low, especially for the 63–125 µm size fraction. This low living stock seems to reflect post-bloom conditions in August and September in the area. The reduced supply of fresh organic carbon also affects faunal microhabitats in the sediment with a concentration of living fauna in the upper 2 cm of the sediment. Over the Chukchi Sea shelf, a relatively mixed upper sediment layer likely due to bioturbation or bio-structures induces a disturbed vertical distribution in the sediment. Corrosive Pacific-derived bottom water over the shelf likely explains the relative importance of agglutinated vs. calcareous fauna in this shallow setting. Our results suggest that, in a post-bloom context, the main environmental control on benthic foraminiferal assemblages in the Chukchi Sea is the nature of the bottom water masses.

Arctic environmental change beyond instrumental records: introduction and overview