Crustal section across the polar continent–ocean transition in Canada

1986 ◽  
Vol 23 (5) ◽  
pp. 608-621 ◽  
Author(s):  
L. W. Sobczak ◽  
U. Mayr ◽  
J. F. Sweeney
Keyword(s):  
Transition Zone ◽  
Structural Model ◽  
Gravity Anomalies ◽  
The Arctic ◽  
Near Surface ◽  
Mafic Rocks ◽  
Gravity Effects ◽  
Sverdrup Basin ◽  
Crystalline Crust ◽  
Vertical Density

The Canadian Arctic Transect extends northwards from the Canadian Shield across a thick (about 18 km) and wide (over 800 km) sedimentary section consisting of four overlapping basins. These overlie a continental crystalline crust that thins from 48 to 8 km towards the Canada Basin. The latter overlies a relatively thin (5 – 10 km thick) oceanic crust below the Arctic Ocean. The calculated gravity effects of the upper sedimentary section were stripped away from the observed gravity anomaly, and the residual anomalies were used to determine the boundaries between sediment and crystalline crust and between crust and mantle. Residual anomalies with short wavelength and steep gradients were used to modify the initial near-surface structural model and to identify zones of evaporite and mafic rocks within the sedimentary rock column.Some interesting results emerge from this analysis: (1) analysis of the gradients of the shelf and slope suggests that shelf subsidence is hinged about a line near the central axis of the Sverdrup Basin; (2) continental crystalline crust thins oceanward from 48 km to 8 km at the transition zone over a distance of 825 km and appears to have stretched from an original width of 543 km, for an apparent stretch factor of about 1.5; (3) sediment thickness is usually inversely related to the crystalline crustal thickness; (4) the mantle below the ocean appears to be less dense than below the continental crust, with an assumed significant vertical density boundary between the two below the continental shelf (transition zone); (5) this analysis supports the concept that evaporites occur along the axis of the Sverdrup Basin, and mafic rocks appear to be concentrated along the flanks of the Sverdrup Basin; and (6) seismicity usually occurs over areas of relatively positive gravity anomalies that are considered to be the result of uncompensated sedimentary loads or mafic igneous intrusions or are areas of uplifted and folded rocks.

Shallow and deep crustal structure of the western Sverdrup Basin, arctic Canada

1984 ◽  
Vol 21 (8) ◽  
pp. 902-919 ◽  
Author(s):  
L. W. Sobczak ◽  
A. Overton
Keyword(s):  
Gravity Data ◽  
Seismic Refraction ◽  
Sediment Accumulation ◽  
Density Control ◽  
Gravity Effects ◽  
Sverdrup Basin ◽  
Deep Crustal Structure ◽  
Crystalline Crust ◽  
Free Air Anomaly ◽  
Drill Holes

An analysis of gravity data along two detailed profiles over the western Sverdrup Basin in the Canadian Arctic supports a seismic refraction model. Drill holes as deep as 5.4 km near the profiles provide excellent density control. Mean densities in the thickest part of the basin exceed those in the thinner parts by an average of 0.13 Mg/m3.Bouguer anomalies corrected for the effect of water, sedimentary, and crystalline layers indicate significant anomalies that vary in width from 20 to 275 km and in amplitude from 3 to 46 mGal (30 to 460 μm s−2). These can all be explained by density structures within the sedimentary column. Sedimentary thickness along the profiles varies from 9 to 17.4 km, crystalline thickness varies from 18 to 33 km, and the total crustal thickness varies from 34 to 42 km. The analysis also shows: (1) negative gravity effects of about 60 to 120 mGal (600 to 1200 μm s−2) due to the mass deficiency of the water and sediments are offset by positive gravity effects of similar magnitude due to crustal thinning; (2) isostatic compensation of water and sediments by a mantle antiroot is evident from a regional free-air anomaly near zero and the apparent inverse variation of sedimentary thickness with the thickness of the crystalline crust; (3) in the thickest part of the basin, undulations at the sedimentary–crystalline boundary are in phase with and smaller in amplitude than undulations at the crust–mantle boundary; conversely, in the thinnest part of the basin, these undulations are out of phase and larger in amplitude.These effects may be explained by stretching of a crystalline crust and a general decrease in crustal rigidity with depth during sediment accumulation and subsequent orogenic events.

scholarly journals A warm jet in a cold ocean

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Jennifer A. MacKinnon ◽  
Harper L. Simmons ◽  
John Hargrove ◽  
Jim Thomson ◽  
Thomas Peacock ◽  
...  
Keyword(s):  
The Arctic ◽  
Bering Strait ◽  
Near Surface ◽  
Ice Melt ◽  
Beaufort Gyre ◽  
The Pacific ◽  
Climate Simulations ◽  
Initial Evolution ◽  
Forecast Models

AbstractUnprecedented quantities of heat are entering the Pacific sector of the Arctic Ocean through Bering Strait, particularly during summer months. Though some heat is lost to the atmosphere during autumn cooling, a significant fraction of the incoming warm, salty water subducts (dives beneath) below a cooler fresher layer of near-surface water, subsequently extending hundreds of kilometers into the Beaufort Gyre. Upward turbulent mixing of these sub-surface pockets of heat is likely accelerating sea ice melt in the region. This Pacific-origin water brings both heat and unique biogeochemical properties, contributing to a changing Arctic ecosystem. However, our ability to understand or forecast the role of this incoming water mass has been hampered by lack of understanding of the physical processes controlling subduction and evolution of this this warm water. Crucially, the processes seen here occur at small horizontal scales not resolved by regional forecast models or climate simulations; new parameterizations must be developed that accurately represent the physics. Here we present novel high resolution observations showing the detailed process of subduction and initial evolution of warm Pacific-origin water in the southern Beaufort Gyre.

scholarly journals An Evaluation of Surface Atmospheric Changes over the Arctic Ocean for 2000–09 Using Recent Reanalyses

2015 ◽  
Vol 19 (2) ◽  
pp. 1-18 ◽  
Author(s):  
Ayan H. Chaudhuri ◽  
Rui M. Ponte
Keyword(s):  
Arctic Ocean ◽  
Extreme Event ◽  
Longwave Radiation ◽  
Remotely Sensed ◽  
Surface Radiation ◽  
Shortwave Radiation ◽  
The Arctic ◽  
Near Surface ◽  
The Arctic Ocean ◽  
Ice Retreat

Abstract The authors examine five recent reanalysis products [NCEP Climate Forecast System Reanalysis (CFSR), Modern-Era Retrospective Analysis for Research and Applications (MERRA), Japanese 25-year Reanalysis Project (JRA-25), Interim ECMWF Re-Analysis (ERA-Interim), and Arctic System Reanalysis (ASR)] for 1) trends in near-surface radiation fluxes, air temperature, and humidity, which are important indicators of changes within the Arctic Ocean and also influence sea ice and ocean conditions, and 2) fidelity of these atmospheric fields and effects for an extreme event: namely, the 2007 ice retreat. An analysis of trends over the Arctic for the past decade (2000–09) shows that reanalysis solutions have large spreads, particularly for downwelling shortwave radiation. In many cases, the differences in significant trends between the five reanalysis products are comparable to the estimated trend within a particular product. These discrepancies make it difficult to establish a consensus on likely changes occurring in the Arctic solely based on results from reanalyses fields. Regarding the 2007 ice retreat event, comparisons with remotely sensed estimates of downwelling radiation observations against these reanalysis products present an ambiguity. Remotely sensed observations from a study cited herewith suggest a large increase in downwelling summertime shortwave radiation and decrease in downwelling summertime longwave radiation from 2006 and 2007. On the contrary, the reanalysis products show only small gains in summertime shortwave radiation, if any; however, all the products show increases in downwelling longwave radiation. Thus, agreement within reanalysis fields needs to be further checked against observations to assess possible biases common to all products.

A new sedimentary cover model for the southern area of the East European Platform and the Pre-Caucasus based on decompensation gravity anomalies data

2021 ◽  
Author(s):  
Mikhail Kaban ◽  
Alexei Gvishiani ◽  
Roman Sidorov ◽  
Alexei Oshchenko ◽  
Roman Krasnoperov
Keyword(s):  
East European Platform ◽  
Sedimentary Cover ◽  
Gravity Anomalies ◽  
Sedimentary Basins ◽  
The Caucasus ◽  
Near Surface ◽  
New Model ◽  
Origin And Evolution ◽  
East European ◽  
Bouguer Anomalies

<p><span>A new model has been developed for the density and thickness of the sedimentary cover in a vast region at the junction of the southern part of the East European Platform, the Pre-Caucasus and some structures adjacent to the south, including the Caucasus. Structure and density of sedimentary basins was studied by employing the approach based on decompensation of gravity anomalies. Decompensative correction for gravity anomalies reduces the effect of deep masses providing compensation of near-surface density anomalies, in contrast to the conventional isostatic or Bouguer anomalies. . The new model of sediments, which implies their thickness and density, gives a more detailed description of the sedimentary thickness and density and reveals new features which were not or differently imaged by previous studies. It helps in better understanding of the origin and evolution of the basins and provides a background for further detailed geological and geophysical studies of the region.</span></p>

Toward a biogeographic regionalization of the Nearctic region: Area nomenclature and digital map

Zootaxa ◽  
2021 ◽  
Vol 5027 (3) ◽  
pp. 351-375
Author(s):  
TANIA ESCALANTE ◽  
GERARDO RODRÍGUEZ-TAPIA ◽  
JUAN J. MORRONE
Keyword(s):  
North America ◽  
Transition Zone ◽  
Rocky Mountain ◽  
Volcanic Belt ◽  
Neotropical Region ◽  
The Arctic ◽  
Digital Map ◽  
Biogeographic Regionalization ◽  
Sierra Madre ◽  
Nearctic Region

We provide a preliminary nomenclatural proposal and a digital map of the Nearctic region, based on published regionalizations, especially Dice (1943), and applying the International Code of Area Nomenclature. The Nearctic region is comprised of three subregions (one of them with two dominions), one transition zone and 29 provinces. The Arctic subregion, in northern North America and Greenland, includes the Eskimoan, Hudsonian, Aleutian and Sitkan provinces. The Western subregion, in western North America, includes the Californian dominion, with the Californian and Oregonian provinces; and the Rocky Mountain dominion, including the Montanian, Saskatchewan, Palusian, Artemisian, Coloradan, Kansan, Mohavian, Navahonian, Sonoran, Chihuahuan, Comanche, and Baja California provinces. The Alleghany subregion, in eastern North America, includes the Illinoian, Canadian, Carolinian, Texan, Austroriparian, and Tamaulipan provinces. The Mexican Transition Zone, situated in the area of overlap with the Neotropical region, includes the Sierra Madre Occidental, Sierra Madre Oriental, Transmexican Volcanic Belt, Sierra Madre del Sur and Chiapas Highlands provinces.  

scholarly journals Numerical investigation of the Arctic ice-ocean boundary layer; implications for air-sea gas fluxes

2016 ◽  
Author(s):  
A. Bigdeli ◽  
B. Loose ◽  
S. T. Cole
Keyword(s):  
Sea Ice ◽  
Water Column ◽  
Mixed Layer ◽  
Mixed Layer Depth ◽  
The Arctic ◽  
Layer Depth ◽  
Near Surface ◽  
Resolution Model ◽  
Simplifying Assumptions ◽  
Vertical Spacing

Abstract. In ice-covered regions it can be challenging to determine air-sea exchange – for heat and momentum, but also for gases like carbon dioxide and methane. The harsh environment and relative data scarcity make it difficult to characterize even the physical properties of the ocean surface. Here, we seek a mechanistic interpretation for the rate of air-sea gas exchange (k) derived from radon-deficits. These require an estimate of the water column history extending 30 days prior to sampling. We used coarse resolution (36 km) regional configuration of the MITgcm with fine near surface vertical spacing (2 m) to evaluate the capability of the model to reproduce conditions prior to sampling. The model is used to estimate sea-ice velocity, concentration and mixed-layer depth experienced by the water column. We then compared the model results to existing field data including satellite, moorings and Ice-tethered profilers. We found that model-derived sea-ice coverage is 88 to 98 % accurate averaged over Beaufort Gyre, sea-ice velocities have 78 % correlation which resulted in 2 km/day error in 30 day trajectory of sea-ice. The model demonstrated the capacity to capture the broad trends in the mixed layer although with a bias and model water velocities showed only 29 % correlation with actual data. Overall, we find the course resolution model to be an inadequate surrogate for sparse data, however the simulation results are a slight improvement over several of the simplifying assumptions that are often made when surface ocean geochemistry, including the use of a constant mixed layer depth and a velocity profile that is purely wind-driven.

scholarly journals Tropospheric BrO column densities in the Arctic derived from satellite: retrieval and comparison to ground-based measurements

2012 ◽  
Vol 5 (11) ◽  
pp. 2779-2807 ◽  
Author(s):  
H. Sihler ◽  
U. Platt ◽  
S. Beirle ◽  
T. Marbach ◽  
S. Kühl ◽  
...  
Keyword(s):  
Boundary Layer ◽  
The Arctic ◽  
Trace Gas ◽  
Natural Phenomenon ◽  
Satellite Measurements ◽  
Surface Layers ◽  
Vertical Column ◽  
Near Surface ◽  
The Vertical Distribution ◽  
Good Agreement

Abstract. During polar spring, halogen radicals like bromine monoxide (BrO) play an important role in the chemistry of tropospheric ozone destruction. Satellite measurements of the BrO distribution have become a particularly useful tool to investigate this probably natural phenomenon, but the separation of stratospheric and tropospheric partial columns of BrO is challenging. In this study, an algorithm was developed to retrieve tropospheric vertical column densities of BrO from data of high-resolution spectroscopic satellite instruments such as the second Global Ozone Monitoring Experiment (GOME-2). Unlike recently published approaches, the presented algorithm is capable of separating the fraction of BrO in the activated troposphere from the total BrO column solely based on remotely measured properties. The presented algorithm furthermore allows to estimate a realistic measurement error of the tropospheric BrO column. The sensitivity of each satellite pixel to BrO in the boundary layer is quantified using the measured UV radiance and the column density of the oxygen collision complex O4. A comparison of the sensitivities with CALIPSO LIDAR observations demonstrates that clouds shielding near-surface trace-gas columns can be reliably detected even over ice and snow. Retrieved tropospheric BrO columns are then compared to ground-based BrO measurements from two Arctic field campaigns in the Amundsen Gulf and at Barrow in 2008 and 2009, respectively. Our algorithm was found to be capable of retrieving enhanced near-surface BrO during both campaigns in good agreement with ground-based data. Some differences between ground-based and satellite measurements observed at Barrow can be explained by both elevated and shallow surface layers of BrO. The observations strongly suggest that surface release processes are the dominating source of BrO and that boundary layer meteorology influences the vertical distribution.

scholarly journals Geophysical imaging of permafrost in the SW Svalbard – the result of two high arctic expeditions to Spitsbergen

2020 ◽  
Author(s):  
Mariusz Majdanski ◽  
Artur Marciniak ◽  
Bartosz Owoc ◽  
Wojciech Dobiński ◽  
Tomasz Wawrzyniak ◽  
...  
Keyword(s):  
Surface Waves ◽  
Active Layer ◽  
High Arctic ◽  
The Arctic ◽  
Seismic Profiles ◽  
Frozen Ground ◽  
Near Surface ◽  
Seismic Processing ◽  
Reflection Seismic ◽  
Sea Coast

<p>The Arctic regions are the place of the fastest observed climate change. One of the indicators of such evolution are changes occurring in the glaciers and the subsurface in the permafrost. The active layer of the permafrost as the shallowest one is well measured by multiple geophysical techniques and in-situ measurements.</p><p>Two high arctic expeditions have been organized to use seismic methods to recognize the shape of the permafrost in two seasons: with the unfrozen ground (October 2017) and frozen ground (April 2018). Two seismic profiles have been designed to visualize the shape of permafrost between the sea coast and the slope of the mountain, and at the front of a retreating glacier. For measurements, a stand-alone seismic stations has been used with accelerated weight drop with in-house modifications and timing system. Seismic profiles were acquired in a time-lapse manner and were supported with GPR and ERT measurements, and continuous temperature monitoring in shallow boreholes.</p><p>Joint interpretation of seismic and auxiliary data using Multichannel analysis of surface waves, First arrival travel-time tomography and Reflection imaging show clear seasonal changes affecting the active layer where P-wave velocities are changing from 3500 to 5200 m/s. This confirms the laboratory measurements showing doubling the seismic velocity of water-filled high-porosity rocks when frozen. The same laboratory study shows significant (>10%) increase of velocity in frozen low porosity rocks, that should be easily visible in seismic.</p><p>In the reflection seismic processing, the most critical part was a detailed front mute to eliminate refracted arrivals spoiling wide-angle near-surface reflections. Those long offset refractions were however used to estimate near-surface velocities further used in reflection processing. In the reflection seismic image, a horizontal reflection was traced at the depth of 120 m at the sea coast deepening to the depth of 300 m near the mountain.</p><p>Additionally, an optimal set of seismic parameters has been established, clearly showing a significantly higher signal to noise ratio in case of frozen ground conditions even with the snow cover. Moreover, logistics in the frozen conditions are much easier and a lack of surface waves recorded in the snow buried geophones makes the seismic processing simpler.</p><p>Acknowledgements               </p><p>This research was funded by the National Science Centre, Poland (NCN) Grant UMO-2015/21/B/ST10/02509.</p>

scholarly journals Observation of HClO3 and HClO4 in the Arctic atmosphere

2020 ◽  
Author(s):  
Yee Jun Tham ◽  
Nina Sarnela ◽  
Carlos A. Cuevas ◽  
Iyer Siddharth ◽  
Lisa Beck ◽  
...  
Keyword(s):  
Gas Phase ◽  
Ozone Depletion ◽  
Surface Ozone ◽  
Negative Ion ◽  
The Arctic ◽  
Research Station ◽  
Visible Absorption ◽  
Data Set ◽  
Near Surface ◽  
Arctic Atmosphere

<p>Atmospheric halogens chemistry like the catalytic reaction of bromine and chlorine radicals with ozone (O<sub>3</sub>) has been known to cause the springtime surface-ozone destruction in the polar region. Although the initial atmospheric reactions of chlorine with ozone are well understood, the final oxidation steps leading to the formation of chlorate (ClO<sub>3</sub><sup>-</sup>) and perchlorate (ClO<sub>4</sub><sup>-</sup>) remain unclear due to the lack of direct evidence of their presence and fate in the atmosphere. In this study, we present the first high-resolution ambient data set of gas-phase HClO<sub>3</sub> (chloric acid) and HClO<sub>4</sub> (perchlorate acid) obtained from the field measurement at the Villum Research Station, Station Nord, in high arctic North Greenland (81°36’ N, 16°40’ W) during the spring of 2015. A state-of-the-art chemical ionization atmospheric pressure interface time-of-flight mass spectrometer (CI-APi-TOF) was used in negative ion mode with nitrate ion as the reagent ion to detect the gas-phase HClO<sub>3</sub> and HClO<sub>4</sub>. We measured significant level of HClO<sub>3</sub> and HClO<sub>4</sub> only during the springtime ozone depletion events in the Greenland, with concentration up to 9x10<sup>5</sup> molecule cm<sup>-3</sup>. Air mass trajectory analysis shows that the air during the ozone depletion event was confined to near-surface, indicating that the O<sub>3</sub> and surface of sea-ice/snowpack may play important roles in the formation of HClO<sub>3</sub> and HClO<sub>4</sub>. We used high-level quantum-chemical methods to calculate the ultraviolet-visible absorption spectra and cross-section of HClO<sub>3</sub> and HClO<sub>4</sub> in the gas-phase to assess their fates in the atmosphere. Overall, our results reveal the presence of HClO<sub>3</sub> and HClO<sub>4</sub> during ozone depletion events, which could affect the chlorine chemistry in the Arctic atmosphere.</p>

scholarly journals Dynamics of the relief and sesmotectonic activity of the modern structures in the delta of the river lena

2019 ◽  
pp. 62-77
Author(s):  
L. P. Imaeva ◽  
G. S. Gusev ◽  
V. S. Imaev
Keyword(s):  
Transition Zone ◽  
North American ◽  
Active Faults ◽  
River Delta ◽  
The Arctic ◽  
Main Element ◽  
Dominant Factor ◽  
Lena River ◽  
Lithospheric Plates ◽  
Lena River Delta

This paper presents seismogeodynamic analysis of modern structures located in the Lena river delta. These structures are key elements in the tectonic evolution of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates. The geological structure of the Lena river delta is predetermined by the junction of the ancient Siberian platform and the Mesozoic Laptev Sea plate. These two large geoblocks of the crust, which differ in age, are separated by a fragment of the Kharaulakh segment of the Verkhoyansk fold system. In our study aimed to reveal regularities in seismotectonic destruction of the crust, we analyzed the geological and geophysical data on the crustal structure, active faults, modern structural plan, dynamic characteristics of the modern relief, and hydrological features characterizing of the flow redistribution in the Lena riverbed. A system of active faults identified in the Lena river delta shows a contrasting kinematic plan of the junction zone of the main geostructures. According to the analysis results, shear faulting is a dominant factor of impact on the morphologic features and seismogeodynamic activation of the modern structures. A regional right-lateral strike-slip fault of the sublatitudinal strike is traced as a major structural boundary that cuts the Lena river delta into several geodynamic segments. Seismotectonic destruction of the crust in the segments differs in types (transpression, transtension and compression). The above-mentioned fault is not only the main element of the kinematic plan of the newest structures in the Lena river delta – it controls the general structural pattern and seismotectonic parameters of active fault zones in the entire northern sector of the Verkhoyansk marginal suture. The seismogeodynamic analysis results obtained in our study provide a reliable basis for estimating potential seismic hazard of the modern structures in the Lena river delta and updating the available seismic zoning maps of the shelf–continent transition zone in the Arctic segment of the boundary between the Eurasian and North American lithospheric plates.

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