Lomonosov Ridge Research Articles

Eurasian Arctic Rifted Margin Composite Tectono-Sedimentary Element

The Eurasian Arctic Rifted Margin (EARM) spans a poorly studied transition region between the Eurasian continental shelf and the deep-water Nansen Basin. It is a conjugate margin to the Lomonosov Ridge, as both domains were united before the opening of the oceanic Eurasia Basin. The EARM is considered as a Composite Tectono-Sedimentary Element (CTSE) consisting of two individual tectono-sedimentary elements (TSEs): (1) an undefined group of poorly known pre-rift Mesozoic and Paleozoic sedimentary successions; and (2) Late Cretaceous–Paleocene synrift strata. The latter are bounded by a c. 56 Ma break-up unconformity and are overlain by the Eurasia Basin prograded margin TSE, which is not included in EARM. In the absence of drilled wells, we utilize multichannel seismic reflection (MCS) data for seismic stratigraphic correlations with nearby, better-explored, areas. The EARM CTSE is subdivided into three along-strike segments (from west to east): Svalbard–Barents Sea, the North Kara Sea and the Taimyr–Laptev Sea. Across-strike, the EARM CTSE is composed of a proximal zone of stretched crust characterized by normal faulting and a relatively narrow distal transition zone that may contain unroofed serpentinized mantle. The lack of drilled wells makes it challenging to evaluate the petroleum potential of the CTSE, although some indications of a working petroleum system presence exist.

Rift to Post‐Rift Tectonostratigraphy of the Sverdrup Basin in Relation to Onset of the High Arctic Large Igneous Province (HALIP) in the Early Cretaceous, Arctic Canada

AbstractA summary of the Jurassic‐Cretaceous rift to breakup tectonostratigraphy of the onshore Sverdrup Basin is correlated to the offshore Amerasia Basin in order to reconstruct a tectonic setting for the High Arctic Large Igneous Province (HALIP). The rift climax from the Canadian rifted margin is correlated with hyper‐extension of the continent‐ocean‐transition zone. Hyper‐extension of the continental lithosphere can accommodate plate motions of Arctic Alaska‐Chukotka away from the Canadian Arctic Islands and Lomonosov Ridge between ∼155 Ma and 135–133 Ma. After lithospheric breakup at ∼135–133 Ma, correlation of the post‐rift stage to the seafloor spreading anomalies M10n to M4n that are associated with oceanic crustal domains can accommodate plate motions from 135–133 Ma to 128 Ma. The uncertainties associated with the earliest magmas of HALIP overlap with the uncertainties on the timing of the latest seafloor spreading. The first main pulse of HALIP in the Aptian at 124–120 Ma post‐dates seafloor spreading and so HALIP was emplaced in a tectonic setting that closely resembles the present state of the south and eastern Amerasia Basin. At the paleogeographic center of the HALIP, the Alpha Ridge complex is consistent with the magmatic character and history of similar Cretaceous oceanic plateau in terms of volume and duration.

Eurasia Basin Composite Tectono-Sedimentary Element

The Eurasia Basin formed by continental break-up and separation of the Lomonosov Ridge from the northern Barents–Kara Shelf at about 56–54 Ma. It was a restricted oceanic basin from its formation up until the Miocene, when extensive water circulation between the North Atlantic and Arctic oceans commenced through the Fram Strait gateway. The opening of the oceanic gateway had a large impact on palaeoceanography and palaeoclimate, which evolved from an Eocene greenhouse to a Neogene icehouse associated with northern hemisphere glaciations. The Eocene–present sedimentary fill of the Eurasia Basin was mainly sourced from surrounding shelf areas in the Barents, Kara and Laptev seas, which experienced widespread Cenozoic uplift and erosion during several phases. The stratigraphy of the Eurasia Basin is poorly constrained due to a lack of boreholes penetrating the basin fill. We therefore have to rely on seismic stratigraphy and tentative ages assigned to sequences and their boundaries terminating on top of oceanic basement of known age. This contribution covers two tectono-sedimentary elements (TSEs): the Eurasia Basin Oceanic TSE and the Eurasia Basin Prograded Margin TSE, which are closely connected and difficult to draw a distinct boundary between.

Content and Composition of Rock Debris at Lomonosov Ridge (83° N): Indication of Palaeoenvironmental Changes

Content and Composition of Rock Debris at Lomonosov Ridge (83° N): Indication of Palaeoenvironmental Changes

Unexpectedly High Magma Productivity Inferred From Crustal Roughness and Residual Bathymetry on the Eastern Part of the Ultra‐Slow Spreading Gakkel Ridge Since ∼45 Ma, Eurasian Basin, Arctic Ocean

AbstractThe Gakkel Ridge in the Eurasian Basin has the slowest seafloor spreading worldwide. The western Gakkel Ridge (3°W–85°E; 14–11 mm/a) alternate between magmatic and sparsely magmatic zones, while the eastern Gakkel Ridge (85–126°E; 11–6 mm/a) appears to be dominated by magmatic zones despite ultraslow spreading. Little is known about the seafloor spreading conditions in the past along the entire ridge. Here, we exploit the residual bathymetry and basement roughness to assess the crustal accretion process of the Gakkel Ridge over time using 23 published regional multichannel seismic reflection profiles. Full seafloor spreading rates were faster (20–24 mm/a) up to ∼45 Ma, and residual bathymetry for the older crust is deeper than the world average in the entire Eurasian Basin. There is a sharp transition to 300–400 m shallower residual bathymetry for seafloor <45 Ma in the eastern Eurasian Basin. The crustal roughness versus spreading rate of the western Eurasian Basin is on the global trend, while that of the eastern is significantly below. Both low roughness and shallow residual bathymetry of the eastern Eurasian Basin is close to that of oceanic crust for spreading rates above 30 mm/a, demonstrating increased magmatic production of the eastern Gakkel Ridge since ∼45 Ma. A recent mantle tomography model predicts partial melting in the upper mantle based on the low Vs anomaly underneath. The sedimentary pattern toward the Lomonosov Ridge indicates that this hot mantle anomaly started to cause dynamic uplift of the area at ∼45 Ma.

Isotopic constraints on the late Pleistocene glacial water and sediment inputs to the central Arctic ocean

The Quaternary history of the Arctic Ocean reflects pronounced periodic changes in marine and glacial environments. This variability is an important component of the Arctic paleoclimatic system. For more insight, we use isotopic measurements on the detrital (Nd-Sr-Pb) and authigenic (Nd) phases of the Quaternary sediments from the central Arctic Ocean. We analyze core ICE4 from ∼3 km water depth off the Lomonosov Ridge. This core was previously studied for other sedimentary proxies (Dong et al., 2022). The analyzed record is estimated to cover major Late Pleistocene Weichselian/Wisconsinian glaciations occurring over the last ∼100–200 ka. Our results provide new evidence that glacially-derived waters from the glaciated margins reached the bottom of the deep Arctic basins. We infer that these waters were delivered to the deep basins by hyperpycnal flows originating from subglacial outbursts accompanying overflow meltwater and iceberg discharge during glacial/deglacial events. Voluminous outbursts during the older, presumed Early/Middle Weichselian glaciation, ca. 115-35 ka, are traced to the West Siberian margin impacted by the Eurasian Ice Sheet. Similar sedimentary layers are found in longer records from the central Arctic Ocean at older stratigraphic intervals. Sediments constrained to the Last Glacial Maximum have less pronounced glacigenic inputs with a stronger Laurentide Ice Sheet signature. The circulation patterns were likely dependent on the interplay of the timing and extent of the Laurentide and Eurasian ice sheets.

Environmental controls on the distribution of brGDGTs and brGMGTs across the Seine River basin (NW France): implications for bacterial tetraethers as a proxy for riverine runoff

Abstract. Branched glycerol dialkyl glycerol tetraethers (brGDGTs) are bacterial lipids that have been widely used as environmental proxies in continental paleorecords. Another group of related lipids, branched glycerol monoalkyl glycerol tetraethers (brGMGTs), has recently been proposed as a potential paleotemperature proxy. Nevertheless, the sources and environmental dependencies of both brGDGTs and brGMGTs along the river–sea continuum are still poorly understood, complicating their application as paleoenvironmental proxies in some aquatic settings. In this study, the sources of brGDGTs and brGMGTs and the potential factors controlling their distributions are explored across the Seine River basin (NW France), which encompasses the freshwater-to-seawater continuum. BrGDGTs and brGMGTs were analyzed in soils, suspended particulate matter (SPM), and sediments (n=237) collected along the land–sea continuum of the Seine basin. Both types of compounds (i.e., brGDGTs and brGMGTs) are shown to be produced in situ, in freshwater and saltwater, based on their high concentrations and distinct distributions in aquatic settings (SPM and sediments) vs. soils. Redundancy analysis further shows that both salinity and nitrogen dominantly control the brGDGT distributions. Furthermore, the relative abundance of 6-methyl vs. that of 5-methyl brGDGTs (the IR6Me ratio), the total nitrogen (TN), the δ15N, and the chlorophyll a concentration co-vary in a specific geographical zone with low salinity, suggesting that 6-methyl brGDGTs are preferentially produced under low-salinity and high-productivity conditions. In contrast to brGDGTs, the brGMGT distribution appears to be primarily regulated by salinity, with a distinct influence on the individual homologues. Salinity is positively correlated with homologues H1020a and H1020b and negatively correlated with compounds H1020c and H1034b in SPM. This suggests that bacteria living in freshwater preferentially produce compounds H1020c and H1034b, whereas bacteria that primarily grow in saltwater appear to be predominantly responsible for the production of homologues H1020a and H1020b. Based on the abundance ratio of the freshwater-derived compounds (H1020c and H1034b) vs. their saltwater-derived homologues (H1020a and H1020b), a novel proxy, the Riverine IndeX (RIX), is proposed to trace riverine organic matter inputs, with high values (>0.5) indicating a higher riverine contribution. We successfully applied RIX to the Godavari River basin (India) and a paleorecord across the upper Paleocene and lower Eocene from the Arctic Coring Expedition at Lomonosov Ridge, showing its potential applicability to both modern samples and paleorecords.

Canada’s claim to the continental shelf in the Arctic

Canada ratified the UNCLOS in 2003 and thus had to submit scientific and technical data to the Commission on the Limits of the Continental Shelf (CLCS) no later than 2013 to extend its continental shelf beyond 200 miles from the coast. Initially the Canadian submission was to include data for both the Atlantic Ocean and the Arctic Ocean. However the requirement in 2013 by Canadian Prime Minister S. Harper to include the seabed at the North Pole in the submission forced the Canadian government to split the submission into two parts: in 2013 data on the outer limit of Canada's continental shelf in the Atlantic Ocean were submitted to the CLCS, and in 2019 - on the Arctic. In the 2019 submission Canada claimed a seabed area of 1.2 million square kilometers, including the North Pole. In December 2022 Canada submitted an addendum to its 2019 proposal to the CLCS, in which it further increased its claims to the continental shelf in the Arctic, bringing the boundaries of its shelf to the Russian exclusive economic zone. The increase in the area of disputed areas of the continental shelf between Russia, Canada and Denmark means that the decisive role in establishing the boundaries of the continental shelf of these countries in the Arctic will be played by the corresponding negotiations between these countries. The February 2023 approval by the CLCS of Russian claims to the Lomonosov Ridge and the Alpha-Mendeleev Rise is important for Canada as well, as it also legitimizes Canada's right to claim the continental shelf in the Arctic beyond 350 miles from its coast. The extreme aggravation of relations between Russia and the West since 2022 complicates the division of the continental shelf in the Arctic between the countries of this region.

Lomonosov Ridge Composite Tectono-Sedimentary Element, Arctic Ocean

Abstract The Lomonosov Ridge (LR) is a sliver of continental crust, a microcontinent that stretches across the Arctic Ocean and separates the Mesozoic Amerasia Basin from the Cenozoic Eurasia Basin. The LR is thought to have been separated from the northern Barents Sea–Kara Sea passive continental margin by continental rifting at about 56–53 Ma and the subsequent formation of the oceanic crust in the Eurasia Basin. Following the nomenclature of this volume, the sedimentary succession of the LR and nearby area forms a composite tectono-sedimentary element containing an assemblage of the following main tectono-sedimentary elements (TSEs): (1) an undefined group of pre-rift TSEs mostly composed of Mesozoic and poorly known Paleozoic successions; (2) the Cretaceous–Paleocene synrift TSE; and (3) the Eocene–Holocene post-rift TSE. The age of the LR's folded and metamorphosed basement can be inferred based on correlations to basement units of the northern Eurasian passive continental margin, which may include a variety of geological structures formed during Timanian, Caledonian, late Paleozoic and Mesozoic orogenic events. The pre-rift TSE includes the oldest and most poorly known offshore sedimentary succession in the Arctic region. The lithostratigraphic units of these basins were mainly characterized from a handful samples collected at the seafloor and by correlation with better known stratigraphy of the conjugate continental margin. The synrift TSE of Cretaceous–Paleocene age has been defined based on seismic data and samples of sedimentary rocks recovered during the Arctic Coring Expedition (ACEX), as well as from seismic facies correlation between the LR and the Podvodnikov–Makarov, Laptev and East Siberian Sea basins. The post-rift Cenozoic sedimentary record was documented by the ACEX well in the central part of the LR.

The High Arctic Large Igneous Province: first seismic-stratigraphic evidence for multiple Mesozoic volcanic pulses on the Lomonosov Ridge, central Arctic Ocean

We use seismic reflection data acquired by an over-winter expedition on drifting sea ice in the central Arctic Ocean to explore a possible spatial and temporal magmatic relation between the sub-bottom geology of part of the deep Arctic Ocean and the Mesozoic volcanic rocks found on the islands and the bordering continental shelf of Franz Josef Land and Svalbard. The new dataset from the North American segment (85–90°N) of the Lomonosov Ridge, central Arctic Ocean documents several Mesozoic volcanic pulses over a distance of c. 600 km along the ridge. This volcanism borders a domain of high magnetic field intensity over the adjacent Alpha Ridge in the deep basin where the magnetic source rocks and recent seismic reflection data indicate extensive Mesozoic magmatism. We suggest that the Mesozoic volcanism on the Lomonosov Ridge in its palaeo-position at the former continental margin north of Franz Josef Land and Svalbard spatially links the Mesozoic magmatic pulses of the continental High Arctic Large Igneous Province (HALIP) of polar Europe to volcanism on the adjacent Alpha Ridge in the deep Arctic Ocean. Increased input of heat to the upper crust on the Lomonosov Ridge enhanced maturation of hydrocarbon source rocks as manifested by the presence of gas or fluid escape pipes restricted to the area of volcanism.

Paleogene Stratigraphy and Foraminifera of the Submarine Lomonosov Ridge, Arctic Ocean

Paleogene Stratigraphy and Foraminifera of the Submarine Lomonosov Ridge, Arctic Ocean

Foraminifera and Paleogene Stratigraphy of the Submarine Lomonosov Ridge, Arctic Ocean

Materials on the Paleogene biostratigraphy of the Lomonosov Ridge in the Arctic Ocean are presented, including new data on foraminifers from the M0004A borehole section (interval 390–391 m) in its polar part. The studied benthic foraminifers are united into the complex with Reticulophragmium coksuvorovae of the upper Zelandian–the lower Thanetian stages, which includes some characteristic species of the North Atlantic and West Siberian basins. It also contains information about the connection of these Arctic seas in the Paleocene time.

Clay mineral and Nd, Pb, and Sr isotope provenance of a MIS 4-3 sediment record from the Lomonosov Ridge, central Arctic Ocean

Modern techniques for detrital mineral provenance were applied to sediment core 96/12-1pc from the Lomonosov Ridge in the central Arctic Ocean. The techniques include quantitative clay mineralogy analysis combined with determination of Nd, Pb, and Sr isotopes from clay fraction. The clay mineral assemblage and the isotope signatures depict distinct changes during the Marine Isotope Stage (MIS) 4-3 transition corresponding to the Middle Weichselian deglaciation. This transition is characterised by a homogenous, 48 cm thick, dark grey, silty clay layer with a distinctive IRD concentration, forming a prominent marker bed for the central Arctic Ocean sediments. The elevated smectite and kaolinite contents in the transitional interval are possible weathering products of the Siberian basaltic rocks, such as the Putorana Plateau, feeding the shelves of the Kara Sea and the western Laptev Sea. The Nd and Sr isotope values are compatible with input from the basaltic rocks and fall within the isotopic range of sediments from these shelves. The abrupt changes in the Nd, Pb and Sr isotopic data from the distinct grey layer attributed to the MIS 4-3 transition likely mark a pronounced deglaciation event. An increase in coarse debris in the grey layer indicates a change in the sedimentation regime with a strong iceberg rafting component. This change may also be related to a sudden release of meltwater from a large ice-dammed lake in the northern Siberia.

Amino acid racemization in Neogloboquadrina pachyderma and Cibicidoides wuellerstorfi from the Arctic Ocean and its implications for age models

Abstract. We report the results of amino acid racemization (AAR) analyses of aspartic acid (Asp) and glutamic acid (Glu) in the planktic Neogloboquadrina pachyderma, and the benthic Cibicidoides wuellerstorfi, foraminifera species collected from sediment cores from the Arctic Ocean. The cores were retrieved at various deep-sea sites of the Arctic, which cover a large geographical area from the Greenland and Iceland seas (GIS) to the Alpha and Lomonosov ridges in the central Arctic Ocean. Age models for the investigated sediments were developed by multiple dating and correlation techniques, including oxygen isotope stratigraphy, magnetostratigraphy, biostratigraphy, lithostratigraphy, and cyclostratigraphy. The extent of racemization (D/L values) was determined on 95 samples (1028 subsamples) and shows a progressive increase downcore for both foraminifera species. Differences in the rates of racemization between the species were established by analysing specimens of both species from the same stratigraphic levels (n=21). Aspartic acid (Asp) and glutamic acid (Glu) racemize on average 16 ± 2 % and 23 ± 3 % faster, respectively, in C. wuellerstorfi than in N. pachyderma. The D/L values increase with sample age in nearly all cases, with a trend that follows a simple power function. Scatter around least-squares regression fits are larger for samples from the central Arctic Ocean than for those from the Nordic Seas. Calibrating the rate of racemization in C. wuellerstorfi using independently dated samples from the Greenland and Iceland seas for the past 400 ka enables estimation of sample ages from the central Arctic Ocean, where bottom water temperatures are presently relatively similar. The resulting ages are older than expected when considering the existing age models for the central Arctic Ocean cores. These results confirm that the differences are not due to taxonomic effects on AAR and further warrant a critical evaluation of existing Arctic Ocean age models. A better understanding of temperature histories at the investigated sites, and other environmental factors that may influence racemization rates in central Arctic Ocean sediments, is also needed.

Океаническая кора, трансрегиональные зоны сдвига и Амеразийская микроплита в мел-кайнозойской геодинамике формирования океана в Арктике

The author has reconstructed the structural-tectonic setting of the Late Cretaceous-Early Cenozoic stage of the geodynamic evolution of the Arctic Ocean. It is shown that the oceanic crust in the Eurasian and Canadian basins occupies a much smaller area than previously thought and was formed in both on blocks of the continental basement strongly stretched by Cretaceous rifting. Due to the processes, large and extended transregional shear zones were set in motion: the Chukchi-Canadian during the opening of the Canadian basin in the Early Cretaceous, and the continental marginal ones — Khatanga-Lomonosov and Northern Greenland-Canadian, the activation of shear movements in which is associated with the Late Cretaceous-Paleocene time, when the consistent formation of the Makarov and Eurasian basins took place. As a result new composite Amerasian microplate was detached and set in motion, which combined the blocks of Arctic Alaska, the Canadian Basin, the Chukchi Rise, the Alpha–Mendeleev Rise, the Podvodnikov and Makarov Basins, and the Lomonosov Ridge. The movement of the microplate along approximately parallel large shear zones at the edges of the Canadian Arctic and Siberian-Chukotka shelves was directed towards the Pacific subduction zone. The movement of the Amerasian microplate was accompanied by rifting and detachment of the Lomonosov Ridge from the Barents-Kara margin, opening of the Eurasian Basin in the rear of the ridge, and transform displacements — right-sided along the Khatanga-Lomonosov zone and left-sided along the North Greenland-Canadian fault zone. At the same time, as a result of the movement of the Amerasian microplate, the previously unified area of Cretaceous plateau basalts (HALIP) was broken, and the Central Arctic province of magmatism was separated and moved away from the Barents Sea province.

Geophysical study of the Earthʼs crust (Northern regions of Russia and the Arctic sea shelf)

Research subject. The results of the geological and geophysical study of the Earth’s crust on the territory of two regions are presented: the northwestern part of the East European Platform and the adjacent water area, as well as the waters of the East Siberian, Chukchi Seas and the Russian eastern sector of the Arctic Ocean, including the Lomonosov ridge and the Mendeleev–Alpha rise. The research is focused on mapping the Moho, the thickness and type of the Earth's crust necessary to substantiate the outer boundary of the continental shelf.Materials and methods. The authors’ original materials obtained during the processing of gravimetry and magnetometry data in the VECTOR system were used. Based on the relationship between gravity anomalies and density variations of rocks, the shape, size of the studied objects, and their deep mutual position are characterized.Results. The constructed schemes and profiles of the deep structure of the Earth's crust, obtained using the VECTOR method, were tested using the European Moho global seismic model. The positive forms of the Moho section and the raised parts of the shelf surface correspond to the positive anomalies of the transformed gravitational field. The spread of the structure of the field of continental anomalies in the Pevek–Anadyr area to the marine part of the territory under consideration can indirectly confirm the belonging of the Lomonosov Cr., the Mendeleev and Alpha ridges to the continental type of crust.Conclusion. Global, i.e., related to the territory of the globe, three-dimensional models of Moho allow us to expand and deepen the amount of knowledge about the features of the shelf structure. Geopotential fields in the VECTOR system display the tectonics of the studied environment systematically and comprehensively compared to is representation according to the scheme of profile seismic studies.

A river of terrestrial dissolved organic matter in the upper waters of the central Arctic Ocean

The Transpolar Drift (TPD) is a mechanism for the rapid transport of shelf-modified Siberian river waters across the Arctic Ocean and out through Fram Strait. We present results from three trans-Arctic research cruises in August–September 2014–2016 to investigate the distribution and dynamics of dissolved organic matter (DOM) in the upper waters across the North Pole, from Svalbard to the Mackenzie River mouth, and in two important outflow gateways of the Arctic Ocean (Fram Strait and Lancaster Sound). Fluorescence measurements of DOM obtained using in situ sensor and laboratory-based spectroscopic analyses, coupled with parallel factor analysis (PARAFAC) were used to map components of DOM at high spatial resolution. The optical properties showed a completely different composition with a much stronger humic-like signal observed in surface waters in the Makarov Basin than in the adjacent Canada Basin, likely due to the substantial amount of Siberian runoff transported by the TPD. The high levels of humic-like in TPD-influenced surface waters were traced from southern Makarov shelves up to the Lomonosov Ridge near the North Pole. Lower DOM levels were observed in the eastern Amundsen basin waters, likely the result of mixing with terrestrial-poor DOM Atlantic waters. The annual flux of humic-like C2 transported to the Atlantic through Fram Strait was estimated at 1816 ±926 r.u. km3. This study reveals the importance of shelf processes and TPD in supplying humic-like material to the central Arctic Ocean to Fram Strait.

DIVIDING THE ARCTIC. ON THE ISSUE OF THE RUSSIAN ARCTIC BOUNDARIES

The reconfiguration of the international arena that is taking place at the moment cannot be characterized other than as a time of crises and sudden changes. It seems quite obvious that in the conditions of international tension, any division of states into “friendly” and “unfriendly”, accompanied by the mutual imposition of sanctions, by the growing desire of countries to realize their national interests, including the military methods, the most vulnerable points of intersection of geopolitical interests are under threat. For Russia, one of them is the Arctic, a region of high resource, industrial and infrastructural potential. Meanwhile, despite the importance of the Arctic for the state and the long history of exploration of the territory, the borders of the Russian Arctic space have not been clearly defined yet, which makes it possible to increase political pressure from unfriendly states and international organizations. Having ratified the UN Convention on the Law of the Sea in 1997, the Russian Federation undertook obligations to act in accordance with the established procedure in case of territorial claims to water and underwater spaces. Consequently, asserting its rights to the Lomonosov Ridge and other objects that are the extensions of the continental shelf, in 2001 the Russian Federation filed an application to the UN Commission on the Limits of the Continental Shelf. Currently, the procedure is still incomplete, although Russia in February 2023 received the recommendations of the Commission, which has recognized a significant part of the state’s territorial claims. However, the contemporary conditions are such that any further efforts to delimit the spaces with the Arctic states, which have overlapping interests with Russia, are fraught with the aggravation of the situation in the international arena and unconstructive co-operation in general.

A Eurasian Basin sedimentary record of glacial impact on the central Arctic Ocean during MIS 1–4

Pronounced Quaternary circulation and depositional changes in the Arctic Ocean basins remain poorly understood. We investigate sediment core ARC5-ICE4 (ICE4) in the Eurasian (Amundsen) Basin off the Lomonosov Ridge to reconstruct glacial-interglacial variability in sediment sources and circulation. The ICE4 record features variable lithologies including distinct glacigenic deposits with Ice Rafted Debris (IRD). The sediment age is constrained by a combination of the organic carbon 14C with paleomagnetic data and correlation to earlier developed stratigraphies. The derived sedimentation rates constitute several cm/kyr (6.5 cm/kyr average) consistent with estimates from regional geophysical data. The developed age model covers the time interval from ca. 10 to 75 ka including Late and Middle Weichselian/Wisconsinian glaciations. Respective glacigenic sediments were primarily deposited by pulsed iceberg discharge. The Last Glacial Maximum and deglaciation is expressed in sharp IRD peaks including mineral proxies of the Laurentide Ice Sheet with an apparent millennial-scale variability. The older glacigenic sedimentary unit with abundant IRD of predominantly Siberian provenance was deposited during deglaciation of the Middle Weichselian (MIS 4/3) Eurasian Ice Sheet. These sedimentary differences indicate diverging impacts of the two glaciations on the Arctic Ocean, including ice-sheet sizes/geometries and oceanic circulation.

Crustal structure and magmatism of the Marvin Spur and northern Alpha Ridge, Arctic Ocean

SUMMARYThe Marvin Spur is a 450-km-long east–west trending escarpment along the northernmost periphery of the Alpha Ridge, starting about 500 km from the coasts of Ellesmere Island and Greenland off the Arctic Ocean margin of North America and running subparallel to the Amerasian margin of the continental Lomonosov Ridge. This region was investigated as part of the Canada–Sweden Polar Expedition in 2016, from which two seismic profiles are presented. The first is a 165-km-long line along the crest of the Marvin Spur. The second is a 221-km-long line extending southwestward from the spur to the northern flank of the Alpha Ridge within the Cretaceous High Arctic Large Igneous Province (HALIP). Multichannel seismic reflection data were acquired along both lines using a 100-m-long streamer, and the airgun shots were also recorded using 16 sonobuoys and 5 stations on the sea ice to calculate a velocity model for the crust from forward modelling of seismic traveltimes. The Marvin Spur profile reveals up to 1100 m of sedimentary rocks on top of a 1-km-thick series of basalts (4.5–5.1 km s−1). Upper and lower crust have velocities of 5.8–5.9 km s−1 and 6.2–6.3 km s−1, respectively, with the upper crust being 1–2 km thick compared to around 13 km for the lower crust. A wide-angle double seismic reflection manifests the top and base of a 6-km-thick lower crustal layer that we interpret as magmatic underplating beneath the continental crust of the Marvin Spur. We correlate a high-amplitude magnetic anomaly on Marvin Spur with a comparable anomaly on Lomonosov Ridge by invoking 110 km of dextral strike-slip motion. Assuming that HALIP-related magmatic deposits generate these anomalies, the strike-slip motion pre-dates the main phase of magmatism (latest Cretaceous, 78 Ma). On the northern Alpha Ridge, sediments are around 1-km-thick and cover a 700 to 1700-m-thick series of basalts with velocities of 4.4–4.8 km s−1. Below is a 3-km-thick layer with intermediate velocities of 5.6 km s−1 and a lower crust with a velocity of 6.8 km s−1. Moho depth is not resolved seismically, but gravity modelling indicates a total thickness of 13 or 18 km for the igneous crust except for the Fedotov Seamount where Moho deepens by about 5 km. Construction of the seamount occurred in multiple magmatic phases, including flow eruptions during deposition of the Cenozoic sedimentary succession post-dating the main HALIP magmatism.