A new formation model of the Atlantic-Arctic heterochronous rifting system: A concept and basic provisions

A new formation model of the global Atlantic-Arctic heterochronous rifting system is substantiated, according to which the Central and North Atlantics, Labrador-Baffin seas, and Arctic Ocean represent morpho-tectonic elements of different orders of the united recent Atlantic-Arctic Ocean. Evolution of the global rift system of this ocean includes three stages: the first stage (D–J1) was expressed by establishment of a tectonic zone in the lithosphere of Pangea with formation of the ophiolite ultrabasite-gabbro association; the second stage (J1–₽1) represented stretching of the continental crust to form depressions and uplifts with areal manifestation of trap magmatism of Cretaceous and other ages; and the third one (₽2–present) is neotectonic-magmatic reactivation with formation of a middle ridge, that is being accompanied by outpouring of glassy basalts and by hydrothermal manifestations. Within the framework of this model, the history of formation is reconstructed of the Eurasian Basin and the Gakkel Ridge, that were included in the Russia's updated application for expansion of the outer continental shelf border.

Testing the synchronicity of Pleistocene biostratigraphic events in the central Arctic – Do we have a consistent biostratigraphic framework?

<p>Harsh environmental and taphonomic conditions in the central Arctic Ocean make age-modelling for Quaternary palaeoclimate reconstructions challenging. Pleistocene age models in the Arctic have relied heavily on cyclostratigraphy using lithologic variability tied to relatively poorly calibrated foraminifera biostratigraphic events. Recently, the identification of <em>Pseudoemiliania lacunosa</em> in a sediment core from the Lomonosov Ridge, a coccolithophore that went extinct during marine isotope stage (MIS) 12 (478-424 ka), has been used to delineate glacial-interglacial units back to MIS 14 (~500 ka BP). Here we present a comparative study on how this nannofossil biostratigraphy fits with existing foraminifer biohorizons that are recognised in central Arctic Ocean sediments. A new core from the Alpha Ridge is presented, together with its lithologic variability and down-core compositional changes in planktonic and benthic foraminifera. The core exhibits an interval dominated by <em>Turborotalita egelida</em>, a planktonic foraminifer that is increasingly being adopted as a marker for MIS11 in sediment cores from the Amerasian Basin of the Arctic Ocean. We show that the new age-constraints provided by calcareous nannofossils are difficult to reconcile with the proposed MIS 11 age for the <em>T. egelida</em> horizon. Instead, the emerging litho- and coccolith biostratigraphy implies that Amerasian Basin sediments predating MIS5 are older than the egelida-based age models suggest, i.e. that the <em>T. egelida</em> Zone is older than MIS11. These results expose uncertainties regarding the age determination of glacial-interglacial cycles in the Amerasian basin and point out that future work is required to reconcile the micro- and nannofossil biostratigraphy of the Amerasian and Eurasian basin.</p>

Analysis of the effects of increased river runoff on the Arctic Ocean hydrology using numerical modeling

<p>The report discusses issues related to the influence of the increased discharge of Arctic rivers on the thermohaline structure of waters outside the Arctic shelf and, in particular, on the variability of Arctic Ocean heat content. The three-dimensional numerical model of the ocean and sea ice SibCIOM (Siberian Coupled Ice-Ocean Model), developed at the Institute of Computational Mathematics and Mathematical Geophysics SB RAS to study the climatic variability of the Arctic Ocean, and the NCEP/NCAR atmospheric reanalysis data are used.</p><p>To reveal the sensitivity of the model fields to the intensity of river runoff, numerical experiments assume the inclusion of variations in river discharge with unchanged remaining conditions, starting from 2000. The deviations of the monthly average values in a numerical experiment with increased discharge of individual Arctic rivers from the basic situation based on the monthly average climatic runoff assignment are considered.</p><p>An analysis of the numerical results obtained with increased discharge of the major Siberian rivers (Ob, Yenisei, Lena) by 1.3 times showed an increase in the Kara Sea's bottom temperature. This was followed by the warming of the subsurface layer of the waters propagating along the continental slope and increasing the heat content of the upper 200-meter layer of the Eastern Eurasian Basin. The heat preservation entering the deep-water part through the Kara Sea straits was facilitated by an increase in stratification's stability and a decrease of the mixed layer depth by 5-10 m on the continental slope of the Eurasian Basin. A similar process with a time delay (6-7 years) and on a smaller scale is developing on the Amerasian basin's continental slope and the Chukchi Sea shelf.</p><p>In the numerical experiment with an increased discharge of the Mackenzie River, deviations in the Beaufort Sea heat and freshwater content appear during the first two years. Still, their values are too small under the river's small discharge compared to the Siberian rivers' discharge.</p><p>The study is supported by the Russian Foundation for Basic Research, Grant No. 20-05-00536 A.</p>

The Western Eurasian Basin Halocline in 2017: Insights From Autonomous NO Measurements and the Mercator Physical System

<div> <div> <div> <p>We present the first sensor‐based profiles of the quasi‐conservative NO parameter obtained with an autonomous ice‐tethered buoy in the Arctic Ocean. Data documented the halocline in the Transpolar Drift and Nansen Basin in 2017. A NO minimum was found in the Nansen Basin on a σ‐horizon of 27.8 kg·m<sup>−3 </sup>corresponding to the lower halocline, while a lower NO minimum of 380 μM straddled the 27.4 σ‐horizon and marked the cold halocline in the Transpolar Drift. Back trajectories of water parcels encountered along the buoy drift were computed using the Mercator physical system. They suggested that waters within the NO minimum at 27.4 kg·m<sup>−3 </sup>could be traced back to the East Siberian Sea continental. These trajectories conformed with the prevailing positive phase of the Arctic Oscillation. The base of the lower halocline, at the 27.85 σ‐horizon, corresponded to the density attained in the deepest winter mixed layer north of Svalbard and cyclonically slowly advected from the slope into the central Nansen Basin. The 27.85 σ‐horizon is associated with an absolute salinity of 34.9 g·kg<sup>−1</sup>, a significantly more saline level than the 34.3 psu isohaline commonly used to identify the base of the lower halocline. This denser and more saline level is in accordance with the deeper winter mixed layers observed on the slopes of Nansen Basin in the last 10 years. A combination of simulations and NO parameter estimates provided valuable insights into the structure, source, and strength of the Arctic halocline.</p> </div> </div> </div>

On tectonic-geodynamic relationships of the Eurasian basin and the Lomonosov Ridge with the continental margin of Siberia according to new seismic data

Basing on the results of the interpretation of new seismic materials, the authors consider the structural features of the southern segments of the Eurasian Basin and the Lomonosov Ridge in the zone of junction with the continental margin of Siberia (the Laptev and East Siberian Seas). Interpretative analysis of the materials shows that the base of the sedimentary cover of the southern segment of the Eurasian Basin, where there are no regular linear magnetic anomalies, is predominantly represented by strongly stretched blocks of the continental basement. The formation the axial zone of spreading of the Gakkel Ridge here took place according to a three-stage development scheme: rifting in the Aptian-Alba and its telescoping development in the Late Cretaceous — Paleocene-Eocene, inherited valley formation in late neotectonic time. The development of the Severny Basin located in the zone of junction of the Lomonosov Ridge with the continental margin is similar to the scenario for the formation of pull-apart basins. Its formation was interconnected with the simultaneously opening adjacent extreme southeastern segment of the Amundsen Basin of the Eurasian Basin.