Is High Topography Around the North Atlantic Supported From the Upper Mantle?

2020 ◽  
Vol 125 (9) ◽  
Author(s):  
Babak Hejrani ◽  
Niels Balling ◽  
Bo Holm Jacobsen ◽  
Søren Bom Nielsen
Keyword(s):  
North Atlantic ◽  
Upper Mantle ◽  
The North ◽  
The North Atlantic ◽  
High Topography

Seismic P- and S-wave velocity Tomography in Scandinavia

2020 ◽  
Author(s):  
Nevra Bulut ◽  
Valerie Maupin ◽  
Hans Thybo
Keyword(s):  
Travel Time ◽  
North Atlantic ◽  
Upper Mantle ◽  
Body Waves ◽  
Significant Heterogeneity ◽  
Finite Frequency ◽  
S Wave ◽  
The North ◽  
The North Atlantic ◽  
High Topography

<p>The causes of the high topography in Scandinavia along the North Atlantic passive continental margins are enigmatic, and two end-member models have been proposed. One opinion is that the high topography has been maintained since the Caledonian orogeny, because isostatic rebound has compensated for most of the erosion over >400 My. The other opinion is that the topography is Cenozoic and that it is related to plate tectonic or deep thermal / geodynamic processes. Onshore uplift is related to simultaneous offshore subsidence, and the rapid topographic changes may be the combined result of a series of complementary processes.</p><p>Here, we provide new evidence for the upper mantle structure by calculating a tomographic model for Fennoscandia (Scandinavia and Finland) by teleseismic inversion of finite-frequency P- and S- wave travel-time residuals. We use seismic signals from earthquakes at epicentral distances between 30° and 104° and with magnitudes larger than 5.5, gathered on 200 broad-band seismic stations installed by the ScanArray project in Norway, Sweden and Finland, which operated during 2012-2017, together with data from earlier projects and stationary stations..</p><p>We measure relative travel-time residuals of direct body waves in high- and low-frequency bands, and carry out an appropriate frequency-dependent crustal correction. The average residuals vary over the region, and show clear trends depending on location and and back-azimuthal directions. This demonstrates the presence of significant heterogeneity of seismic velocities in the upper mantle across the region. Based on the travel-time residuals<strong>,</strong> we carry out finite-frequency body-wave tomographic inversion to determine the P and S wave seismic velocity structure of the upper-mantle. By use of “relative kernels” we reduce problems related to station coverage with asynchronous datasets, which allows the use of data from different deployments for the inversion. The resulting seismic model is compared to the existing and past topography in order to contribute to the understanding of mechanisms responsible for the topographic changes in the Fennoscandian region, which we relate to the general tectonic and geological evolution of the North Atlantic region. The models provide basis for deriving high-resolution models of temperature and compositional anomalies that may contribute to the understanding of the observed, enigmatic topography.</p>

Upper mantle conditions during the opening of the North Atlantic Ocean

2020 ◽  
Author(s):  
Zsófia Zalai ◽  
Jenny Collier ◽  
Gareth Roberts ◽  
Thomas Funck
Keyword(s):  
Atlantic Ocean ◽  
North Atlantic ◽  
Upper Mantle ◽  
North Atlantic Ocean ◽  
Temperature Anomaly ◽  
Potential Temperature ◽  
The North ◽  
The North Atlantic ◽  
Break Up ◽  
Mantle Potential Temperature

<p>Mantle conditions during the opening of the North Atlantic Ocean and specifically the presence or otherwise of a deep mantle plume have been much debated. Current models fall into two groups: the plume impingement and the plate-driven models. The plume impingement model associates the arrival of the Icelandic plume with continental break-up of the North Atlantic and the observed excess magmatism is associated with passive upwelling and elevated mantle potential temperatures. However, the plate-driven model associates this excess magmatism with increased mantle fertility due to inherited lithospheric structure and/or small-scale convection induced by sub-lithospheric topography.</p><p>We examine the spatial and temporal variation of upper mantle conditions at the time of continental break-up using an inventory of 40 published seismic refraction velocity-depth profiles acquired between the Charlie Gibbs and the East Greenland Fracture Zones. We make use of the Hc-Vp method to estimate mantle potential temperature and the ratio of active to passive upwelling by extracting igneous crustal thickness, Hc, and its mean p-wave velocity, Vp. Finally, we compare the spatial and temporal patterns obtained to those predicted by previously proposed models of mantle conditions around the time of break-up.</p><p>Our results indicate an asymmetry in mantle potential temperature between the Greenland and the European side, the latter being 100°C hotter. The temperature anomaly also varies on a wavelength of 300-500 km along strike both margins. In most profiles, the mantle potential temperature decreases with time, with normal temperatures of 1300°C being reached 5-10 Ma after the onset of seafloor spreading at 55 Ma. This temperature appears to be “steady state” once reached. The exception to this is the Greenland-Iceland-Faroes Ridge where the “steady state” temperature is 100°C higher. However, the decreasing trend of mantle potential temperature with time is not uniform across the whole North Atlantic region: the temperature decreases by a 60°C/Ma rate at the Hatton margin, while at the Møre and Vøring margins it is considerably slower, at only 20°C/Ma. A 100°C lower than normal mantle potential temperature anomaly was found at the now extinct Aegir Ridge spreading centre even though it was located less than 300 km away from the proposed reconstructed position of the Icelandic plume. Nevertheless, the plume’s position coincides well with the highest calculated upwelling ratios. The NE Greenland margin is also characterised by moderate upwelling compared to the purely passive European side.</p><p>Overall the spatial distribution of high active upwelling ratios and widespread elevated mantle potential temperatures support the plume impingement model for the opening of the North Atlantic Ocean. This thermal anomaly was exhausted at a varying rate on the different margins in 5-10 Ma. Furthermore, the 300-500 km wide localised thermal anomalies and the proximity of the proposed plume location to a low temperature anomaly indicate moderation by local complexities that might be a manifestation of upper mantle flow induced by structural inheritance or plate tectonic processes.</p>

The Currents of the North Atlantic

1892 ◽  
Vol 34 (872supp) ◽  
pp. 13940-13941
Author(s):  
Richard Beynon
Keyword(s):  
North Atlantic ◽  
The North ◽  
The North Atlantic

NATO adaptation to current challenges and mechanisms of Ukraine’s cooperation with the North Atlantic Treaty Organization

2019 ◽  
pp. 73-81
Author(s):  
Oleh Poshedin
Keyword(s):  
North Atlantic ◽  
Task Force ◽  
Response Force ◽  
Cyber Attack ◽  
Adaptation Measures ◽  
Joint Force ◽  
Security Environment ◽  
The North ◽  
The North Atlantic ◽  
Area Of Influence

The purpose of the article is to describe the changes NATO undergoing in response to the challenges of our time. Today NATO, as a key element of European and Euro-Atlantic security, is adapting to changes in the modern security environment by increasing its readiness and ability to respond to any threat. Adaptation measures include the components required to ensure that the Alliance can fully address the security challenges it might face. Responsiveness NATO Response Force enhanced by developing force packages that are able to move rapidly and respond to potential challenges and threats. As part of it, was established a Very High Readiness Joint Task Force, a new Allied joint force that deploy within a few days to respond to challenges that arise, particularly at the periphery of NATO’s territory. NATO emphasizes, that cyber defence is part of NATO’s core task of collective defence. A decision as to when a cyber attack would lead to the invocation of Article 5 would be taken by the North Atlantic Council on a case-by-case basis. Cooperation with NATO already contributes to the implementation of national security and defense in state policy. At the same time, taking into account that all decision-making in NATO based on consensus, Ukraine’s membership in the Alliance quite vague perspective. In such circumstances, in Ukraine you often can hear the idea of announcement of a neutral status. It is worth reminding that non-aligned status did not save Ukraine from Russian aggression. Neutral status will not accomplish it either. All talks about neutrality and the impossibility of Ukraine joining NATO are nothing but manipulations, as well as recognition of the Ukrainian territory as Russian Federation area of influence (this country seeks to sabotage the Euro-Atlantic movement of Ukraine). Think about it, Moldova’s Neutrality is enshrined in the country’s Constitution since 1994. However, this did not help Moldova to restore its territorial integrity and to force Russia to withdraw its troops and armaments from Transnistria.

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