Lomonosov Ridge Research Articles

To the question of the existence of a strike-slip fault in the Arctic Ocean between the underwater Lomonosov ridge and the adjacent shelf

The research object is the junction zone between the underwater Lomonosov ridge and East Siberian shelf. We intend to prove the absence of the strike-slip fault within this junction zone. The existence of the fault zone within this junction zone is still debatable. Formerly used geological and geophysical datawere unsufficient. To remove this ambiguity, seismological data obtained in neighboring areas was applied. Analysis of the earthquakes epicenters in the region showed that in cases of existence of such a fault zone, modern intraplate seismic activity should be certainly registered within its limits. The aseismicity of the junction zone between the underwater Lomonosov ridge and adjacent shelf areas clearly indicates the genetic unity exhisting between these tectonic structures.

Rises of the Amerasia Basin, Arctic Ocean, and Possible Equivalents in the Atlantic Ocean

Main positive morphostructures of the Amerasia Basin, the Lomonosov Ridge, Alpha Ridge, Mendeleev Rise, Chukchi Plateau and Northwind Ridge, have been considered from geomorphological, geological and geophysical aspects. Time and Depth seismic sections have been provided up to the Moho discontinuity from the Lomonosov Ridge and its junction with the Greenland and East-Siberian shelves. Time and Depth seismic sections of the Mendeleev-Alpha rises and Chukchi Plateau are presented too. The sections were set up based on seismic surveys: deep seismic sounding and multichannel seismic reflection. Some similarities have been reflected for the foregoing land structure depth sections and typical sections of the continental crust. Brief geological and geophysical data have been presented for the positive morphostructures of the Atlantic Ocean such as the Rockall and Voring plateaus, the continental nature of which is established beyond all doubt. Genesis of positive morphostructures in the northern Atlantic Ocean and the Arctic Ocean has been connected with processes of continental rifting and concomitant intraplate magmatism.

Structure of the Khatanga-Lomonosov fracture zone according to seismic data

According to the results of geophysical data interpretation considered the structural features of the Khatanga-Lomonosov fracture zones (HLZ), adapted to the strip joint part on the Laptev Sea continental margin with the structures of the spreading of the Eurasian basin and the Lomonosov ridge. Its reflection in anomalous geophysical fields, in a wave seismic picture on sections is shown on the example of separate links of HLZ and the character of its kinematic interrelations with heterogeneous tectonic elements is illustrated. The tectonic nature, role and place of this fault zone in the geodynamic evolution of the region are substantiated.

The Problem of the Existence of a Strike-Slip Fault in the Arctic Ocean between Lomonosov Submarine Ridge and the Adjacent Shelf

The junction zone between Lomonosov submarine ridge and the shelf of the East Siberian Sea was studied. The aim was to prove the absence of a strike-slip fault in the junction zone between Lomonosov Ridge and the East Siberian shelf. The problem of the existence of a fault zone in the region where the Lomonosov Ridge joins the East Siberian shelf is still currently debateable. The geological and geophysical data used to solve it are insufficient. To remove this ambiguity, seismological data obtained in neighboring areas were used. An analysis of the map of earthquake epicenters in the region showed that, if the fault zone mentioned existed, present-day intraplate seismic activity would certainly be observed within its limits. The absence of seismicity in the junction zone between Lomonosov Ridge and the adjacent shelf clearly indicates the genetic unity of these structures.

Basement segmentation and tectonic structure of the Lomonosov Ridge, arctic Ocean: Insights from bedrock geochronology

Apparent variations in the morphology of the Lomonosov Ridge and its along-strike segmentation are caused by the heterogeneity of the basement. Based on the morphological diversity, we divide the Lomonosov Ridge into three segments: Siberian, Central and North American. New petrographic and geochronological data from the rock clasts sampled in the “Arctika-2007-1” expedition, are integrated with seismic and relevant mineralogical, petrographic and isotopic data. Recovered fragments of the high-grade metamorphic and siliciclastic rocks are attributed to the bedrock of the Siberian and Central Segments of the Lomonosov Ridge respectively.The mineralogical and isotopic analysis of detrital zircons from Neoproterozoic arkose defines the Grenvillian age for the basement of the Siberian Segment of the Lomonosov Ridge. The U-Pb dating of the metamorphic zircons from gneisses and schists suggests that Timanian crystalline basement of the Central Segment was affected by an upper-Ordivician (∼450 Ma) felsic magmatism, followed by the mid- to high-grade Caledonian tectonometamorphic event (∼400 Ma). The Central Segment is therefore inferred to be a frontal part of Caledonian convergent shear and fold zone.Caledonian deformation front is suggested between the northeastern and southwestern islands of De Long archipelago. Northward from the shelf break, the orogenic front is expected between the Geophysicists Spur and the main horst of the Siberian Segment. Within the Central Segment the Caledonian deformation front is inferred to stretch along the western flank of the Lomonosov Ridge.

Arctic vegetation, temperature, and hydrology during Early Eocene transient global warming events

Early Eocene global climate was warmer than much of the Cenozoic and was punctuated by a series of transient warming events or ‘hyperthermals’ associated with carbon isotope excursions when temperature increased by 4–8 °C. The Paleocene-Eocene Thermal Maximum (PETM, ~55 Ma) and Eocene Thermal Maximum 2 (ETM2, 53.5 Ma) hyperthermals were of short duration (<200 kyr) and dramatically restructured terrestrial vegetation and mammalian faunas at mid-latitudes. Data on the character and magnitude of change in terrestrial vegetation and climate during and after the PETM and ETM2 at high northern latitudes, however, are limited to a small number of stratigraphically restricted records. The Arctic Coring Expedition (ACEX) marine sediment core from the Lomonosov Ridge in the Arctic Basin provides a stratigraphically expanded early Eocene record of Arctic terrestrial vegetation and climates. Using pollen/spore assemblages, palynofacies data, bioclimatic analyses (Nearest Living Relative, or NLR), and lipid biomarker paleothermometry, we present evidence for expansion of mesothermal (Mean Annual Temperatures 13–20 °C) forests to the Arctic during the PETM and ETM2. Our data indicate that PETM mean annual temperatures were ~2° to 3.5 °C warmer than those of the Late Paleocene. Mean winter temperatures in the PETM reached ≥5 °C (~2 °C warmer than the late Paleocene), based on pollen-based bioclimatic reconstructions and the presence of palm and Bombacoideae pollen. Increased runoff of water and nutrients to the ocean during both hyperthermals resulted in greater salinity stratification and hypoxia/anoxia, based on marked increases in concentration of massive Amorphous Organic Matter (AOM) and dominance of low-salinity dinocysts. During the PETM recovery, taxodioid Cupressaceae-dominated swamp forests were important elements of the landscape, representing intermediate climate conditions between the early Eocene hyperthermals and background conditions of the late Paleocene. • Arctic vegetation in the PETM and ETM2 included broadleaf forests, palms, and subtropical taxa. • Taxodioid swamp forests dominated Arctic landmasses during the PETM recovery. • Mixed conifer-broadleaf forests occupied Arctic sites during non-hyperthermals. • Proxy data indicate increased runoff and hypoxia during Eocene hyperthermals. • Bioclimatic and brGDGT indicators show ~2–3.5 °C warming during hyperthermals.

Kinematic model of the Midoceanic Gakkel ridge East areas development in the Eurasian basin of the Arctic ocean

The new map of linear magnetic anomalies axis for the mid-Arctic ridge east areas development in the Eurasian basin is made. The domestic geomagnetic investigations for the first time allow to determine paleomagnetic anomaly C25 and estimate the time of transfer rifting to spreading process as chrons С25r-С26n (57.656-59.237 ma). The eastablishing of Lomonosov ridge and Siberian margin splitting zone is made. The Euler pole for the splitting kinematic for first time calculated. The nocoinciding of conjugate isobaths related to process of sliding peripheral continental crust areas along lithosphere thrust plane for the first time is calculate.

Limited freshwater cap in the Eocene Arctic Ocean

Remains of the freshwater fern Azolla, found in Eocene (~50 Ma ago) sediments in the modern central Arctic Ocean, have been used to suggest that seasonal freshwater caps covered the entire Arctic Ocean during that time, with significant impact on global ocean circulation and climate. However, these records are located on the Lomonosov Ridge, which during the Eocene was a continental fragment barely rifted from Eurasia, separating the smaller Eurasian Basin from the much larger Amerasian Basin to the west. As such, the Lomonosov Ridge does not necessarily record environmental conditions of the broader Arctic Ocean. We tested the hypothesis of freshwater caps by examining sediment records from the western Amerasian Basin. Here we show that in the larger Amerasian Basin the Azolla event is associated with marine microfauna along with allochthonous (terrestrially sourced) organic matter. We propose that Azolla events are related to an increased hydrologic cycle washing terrestrially sourced Azolla, and other organics, into the Arctic Ocean. If freshwater caps did occur, then they were at best restricted to the small Eurasian Basin and would have had a limited impact on Eocene global climate, contrary to current models.

Mercury anomalies across the Palaeocene–Eocene Thermal Maximum

Abstract. Large-scale magmatic events like the emplacement of the North Atlantic Igneous Province (NAIP) are often coincident with periods of extreme climate change such as the Palaeocene–Eocene Thermal Maximum (PETM). One proxy for volcanism in the geological record that is receiving increased attention is the use of mercury (Hg) anomalies. Volcanic eruptions are among the dominant natural sources of Hg to the environment; thus, elevated Hg∕TOC values in the sedimentary rock record may reflect an increase in volcanic activity at the time of deposition. Here we focus on five continental shelf sections located around the NAIP in the Palaeogene. We measured Hg concentrations, total organic carbon (TOC) contents, and δ13C values to assess how Hg deposition fluctuated across the PETM carbon isotope excursion (CIE). We find a huge variation in Hg anomalies between sites. The Grane field in the North Sea, the most proximal locality to the NAIP analysed, shows Hg concentrations up to 90 100 ppb (Hg∕TOC = 95 700 ppb wt %−1) in the early Eocene. Significant Hg∕TOC anomalies are also present in Danish (up to 324 ppb wt %−1) and Svalbard (up to 257 ppb wt %−1) sections prior to the onset of the PETM and during the recovery period, while the Svalbard section also shows a continuous Hg∕TOC anomaly during the body of the CIE. The combination with other tracers of volcanism, such as tephra layers and unradiogenic Os isotopes, at these localities suggests that the Hg∕TOC anomalies reflect pulses of magmatic activity. In contrast, we do not observe clear Hg anomalies on the New Jersey shelf (Bass River) or the Arctic Ocean (Lomonosov Ridge). This large spatial variance could be due to more regional Hg deposition. One possibility is that phreatomagmatic eruptions and hydrothermal vent complexes formed during the emplacement of sills led to submarine Hg release, which is observed to result in limited distribution in the modern era. The Hg∕TOC anomalies in strata deposited prior to the CIE may suggest that magmatism linked to the emplacement of the NAIP contributed to the initiation of the PETM. However, evidence for considerable volcanism in the form of numerous tephra layers and Hg∕TOC anomalies post-PETM indicates a complicated relationship between LIP volcanism and climate. Factors such as climate system feedbacks, changes to the NAIP emplacement style, and/or varying magma production rates may be key to both the onset and cessation of hyperthermal conditions during the PETM. However, processes such as diagenesis and organic matter sourcing can have a marked impact on Hg∕TOC ratios and need to be better constrained before the relationship between Hg anomalies and volcanic activity can be considered irrefutable.

Geodynamics of the Lomonosov Ridge in the Central Arctic

Geodynamics of the Lomonosov Ridge in the Central Arctic

Extension Structures in the Central Arctic Submarine Elevations Complex

Abstract—The available body of geological and geophysical data indicates that the morphologic structures of the Central Arctic submarine elevations complex (CAE) form a single complex block of continental crust that broke away from the Barents–Kara continental margin in the late Paleocene. Seismostratigraphic interpretation of the multichannel seismic reflection data acquired within the CAE, based on seismostratigraphic benchmarks confirmed by drilling and continuous tracing of pre-Cenozoic unconformities from the offshore North Chukchi Trough to its deep-water extension (Vilkitsky Trough), makes it possible to draw the following conclusions: The sedimentary-basin depocenters of the Vilkitsky Trough and Chukchi basin include pre-Upper Jurassic sediments in addition to Cretaceous complexes. However, the former are not common in the rest area of the CAE.Synrift extension of the continental crust is the key factor that affected the tectonic evolution of morphologic structures of the Central Arctic basin. Multichannel seismic reflection data show the clearest signs of the synrift extension in the Lomonosov Ridge, Mendeleev Rise, Chukchi plateau, and their flanks sloping to the sedimentary basins of the Vilkitsky Trough and Chukchi basin. At the same time, the depocenters of these sedimentary basins formed by pre-Upper Jurassic deposits are characterized by an almost undisturbed bedding of all sedimentary complexes.Pre-Upper Jurassic deposits might be interpreted as a relic of the Ellesmerian structural stage preserved in the deep-water extension of the North Chukchi Trough since the preoceanic evolution stage. Pre-Upper Jurassic complexes seem to be affected by deep rift activity only within the elevations of the Central Arctic area and near-flank zones of the depressions separating them. Pre-Upper Jurassic deposits in the sedimentary basin depocenters of the Vilkitsky Trough and Chukchi basin structurally linked to the shallow-water shelf were barely affected by the rifting processes. The tectonic evolution of the depocenters and their submergence relative to the flank zones might have been affected not only by crustal extension processes but also by compensation mechanisms.

Kinematic Model of Development of Eastern Areas of the Gakkel Mid-Ocean Ridge in the Eurasian Basin of the Arctic Ocean

A new map of the axes of linear magnetic anomalies for eastern regions of the Eurasian Basin has been compiled. Based on the results of Russian geomagnetic surveys, paleoanomaly C25 was distinguished here for the first time, and the transition from rifting to spreading has been dated to the chron interval of С25r–С26n (57.656–59.237 Ma ago). The axis of the zone of splitting of marginal continental fragments of the Lomonosov Ridge from the Siberian shelf has been reconstructed. The Euler poles and angles of rotation that describe the splitting kinematics have been determined for the first time, as well as noncoincidence of conjugate isobaths related to sliding of peripheral continental crust areas along the lithospheric thrust plane.

Depositional Evolution of the Western Amundsen Basin, Arctic Ocean: Paleoceanographic and Tectonic Implications

AbstractA new stratigraphic model and estimated sedimentation rates of the western Amundsen Basin, Arctic Ocean, are presented based on multichannel seismic reflection data, seismic refraction data, magnetic data, and integrated with the sedimentary sequence from the central Arctic Ocean, obtained during the Arctic Coring Expedition. This places new constraints on the postbreakup Cenozoic depositional history of the basin, the adjacent Lomonosov Ridge, and improves the understanding of the tectonic, climatic, and oceanographic conditions in the central Arctic region. Four distinct phases of basin development are proposed. During the Paleocene‐mid‐Oligocene, high sedimentation rates are linked to terrestrial input and increased pelagic deposition in a restricted basin. Deposition of sedimentary wedges and mass transport into marginal depocenters reflect a period of tectonic instability linked to compression associated with the Eurekan Orogeny in the Arctic. During the late Oligocene‐early Miocene, widespread passive infill associated with hemipelagic deposition reflects a phase of limited tectonism, most likely in a freshwater estuarine setting. During the middle Miocene, mounded sedimentary buildups along the Lomonosov Ridge suggest the onset of geostrophic bottom currents that likely formed in response to a deepening and widening of the Fram Strait beginning around 18 Ma. In contrast, the Plio‐Pleistocene stage is characterized by erosional features such as scarps and channels adjacent to levee accumulations, indicative of a change to a higher‐energy environment. These deposits are suggested to be partly associated with dense shelf water‐mass plumes driven by supercooling and brine formation over the northern Greenland continental shelf.

Deciphering ∼45.000 years of Arctic Ocean lithostratigraphic variability through multivariate statistical analysis

Our understanding of past climate conditions in the Arctic Ocean has been hampered by poor age control caused in part by low sedimentation rates (<1 cm/kyr), hiatuses during glacial intervals as well as the scarcity and poor preservation of calcareous nanno- and microfossils in the sediments. Although recent advances using variations in single element (e.g. Mn) content or physical sediment properties (e.g. bulk density, grain size, colour) of the recovered sediments have aided Arctic core-to-core correlations, unique depositional events and post-depositional changes can complicate stratigraphic interpretations based on individual or even multiple, physical or chemical parameters. Furthermore, clear correlations between cores using physical and chemical parameters are not always possible to establish. To tackle this issue, we developed an algorithm that combines clustering and multivariate ordination to test the interrelation of multiple input parameters (e.g. an array of individual XRF elemental contents), and subsequently identifies statistically significant stratigraphic units on centimetre to decimetre scales. Our preliminary results show that a distinct sedimentological pattern during the past 45,000 years characterizes cores from the region of the Morris Jesup Rise and the Greenland side of the Lomonosov Ridge. Stratigraphic patterns of the Siberian Side of the Lomonosov Ridge yield distinct differences, thus allowing for novel insights into sedimentary processes shaping the different regions within the Arctic Ocean. We also argue that our approach can compensate for some of the weakness of single element or proxy applications, and hence aid the construction of a robust stratigraphic framework for a wide geographical range of Arctic Ocean sediments.

Модель откола Арлис спура от хребта Ломоносова в Северном Ледовитом океане

Модель откола Арлис спура от хребта Ломоносова в Северном Ледовитом океане

Structure and dynamics of mesoscale eddies over the Laptev Sea continental slope in the Arctic Ocean

Abstract. Heat fluxes steered by mesoscale eddies may be a significant, but still not quantified, source of heat to the surface mixed layer and sea ice cover in the Arctic Ocean, as well as a source of nutrients for enhancing seasonal productivity in the near-surface layers. Here we use 4 years (2007–2011) of velocity and hydrography records from a moored profiler over the Laptev Sea slope and 15 months (2008–2009) of acoustic Doppler current profiler data from a nearby mooring to investigate the structure and dynamics of eddies at the continental margin of the eastern Eurasian Basin. Typical eddy scales are radii of the order of 10 km, heights of 600 m, and maximum velocities of ∼0.1 m s−1. Eddies are approximately equally divided between cyclonic and anticyclonic polarizations, contrary to prior observations from the deep basins and along the Lomonosov Ridge. Eddies are present in the mooring records about 20 %–25 % of the time, taking about 1 week to pass through the mooring at an average frequency of about one eddy per month. We found that the eddies observed are formed in two distinct regions – near Fram Strait, where the western branch of Atlantic Water (AW) enters the Arctic Ocean, and near Severnaya Zemlya, where the Fram Strait and Barents Sea branches of the AW inflow merge. These eddies, embedded in the Arctic Circumpolar Boundary Current, carry anomalous water properties along the eastern Arctic continental slope. The enhanced diapycnal mixing that we found within EB eddies suggests a potentially important role for eddies in the vertical redistribution of heat in the Arctic Ocean interior.

Geological and paleooceanological significance of psephite from the cretaceous-cenozoic deposits from the near-pole part of the Lomonosove ridge

The article gives a characteristic of the psephitic material obtained in the IODP-302 well on the Lomonosov Ridge. We provide data on the shape of rock fragments, their roundness, petrographic composition and distribution over lithological units of the well. It is shown that the major part of the psephites was delivered to the drilling point with ice, but several samples have a local origin and characterize the composition of the Mesozoic rocks. The roundness of the psephites consistently deteriorates in the younger enclosing sediments. The paper presents arguments that link this trend with the intensification of the ice regime. The consequence of the ice cover increase is the shortening of the time of psephites occurrence in the wave-surf zone, where large-sized material is rounding, by activating the “anchor” mechanism of the rock fragments capture. The level of change in petrographic associations of psephites generally coincides with the level of change in the association of heavy minerals, which is a consequence of the appearance of more distant sources areas. It is shown that the “paleo–trans–polar” ice drift system began to function in the middle Miocene. The paper draws conclusions about the evolution of the ice regime in the Arctic Ocean during the Cenozoic.

Geodynamic Evolution Model of the Major Structures of Amerasian Basin

We have analyzed the geodynamic evolution of the lithosphere and upper mantle of the Amerasian basin based on the stress-strain state simulation. It is shown that the asthenospheric spreading in the return upflow region of the mantle convection, results in formation of two local uplifts, which can be interpreted as Lomonosov Ridge and Mendeleev/Alfa Ridge. The further long-term action of the mantle convection leads to formation of Makarov and Podvodnikov Basins.

Pre-rift sedimentation of the Lomonosov Ridge, Arctic Ocean at 84°N – A correlation to the complex geologic evolution of the conjugated Kara Sea

The Arctic Ocean region plays, and has played in the geological past, a key role for Earth’s climate and oceanic circulation and their evolution. Studying the Lomonosov Ridge, a narrow submarine continental ridge in the central Arctic Ocean, is essential to answer fundamental questions related to the complex tectonic evolution of the Arctic basins, the glacial history, and the details of known paleoceanographic changes in the Cenozoic. In this study, we present a new seismic dataset that provides insights into the sedimentary structures along the ridge, their possible origin, age and formation. We compare the structure and stratigraphy of the deeper parts of the ridge between 83°N and 84°30′N to its conjugate, the Severnaya Zemlya Archipelago at the Eurasia margin. We propose that some sediment sequences directly underlying the prominent HARS (High Amplitude Reflector Sequence) formed well before the ridge separated from the Barents and Kara shelves and represent a prolongation of the North Kara Terrane, most likely part of the Neoproterozoic Timanide orogen. Towards Siberia along the Lomonosov Ridge, we interpret the HARS to be underlain by Upper Proterozoic-Lower Paleozoic metasedimentary material that is correlated to metamorphic complexes exposed on Bol’shevik Island. Northward, this unit descends and gives way to a foreland sedimentary basin complex of presumed Ordovician/Devonian age, which underwent strong deformation during the Triassic/Jurassic Novaya Zemlya orogeny. The transition zone between these units might mark a conjugate continuation of the Eurasian margin’s Bol’shevik-Thrust Zone. A prominent erosional unconformity is observed over these strongly deformed foreland basins of the Eurasian and Lomonosov Ridge margins, and is conceivably related to vertical tectonics during breakup or a later basin-wide erosional event.

Numerical simulations of a kilometre-thick Arctic ice shelf consistent with ice grounding observations

Recently obtained geophysical data show sets of parallel erosional features on the Lomonosov Ridge in the central Arctic Basin, indicative of ice grounding in water depths up to 1280 m. These features have been interpreted as being formed by an ice shelf—either restricted to the Amerasian Basin (the “minimum model”) or extending across the entire Arctic Basin. Here, we use a numerical ice sheet-shelf model to explore how such an ice shelf could form. We rule out the “minimum model” and suggest that grounding on the Lomonosov Ridge requires complete Arctic ice shelf cover; this places a minimum estimate on its volume, which would have exceeded that of the modern Greenland Ice Sheet. Buttressing provided by an Arctic ice shelf would have increased volumes of the peripheral terrestrial ice sheets. An Arctic ice shelf could have formed even in the absence of a hypothesised East Siberian Ice Sheet.