VARIATIONS IN SPECTRA OF P WAVES RECORDED AT CANADIAN ARCTIC SEISMOGRAPH STATIONS

1966 ◽  
Vol 3 (5) ◽  
pp. 597-621 ◽  
Author(s):  
Tokuji Utsu
Keyword(s):  
Surface Layer ◽  
Epicentral Distance ◽  
Canadian Arctic ◽  
The Arctic ◽  
Spectral Amplitude ◽  
Layered System ◽  
Low Velocity ◽  
P Waves ◽  
Low Frequencies ◽  
Spectral Curves

To investigate the effects of location of a seismograph station on the records obtained, P waves from seismograms of Alaskan earthquakes recorded at four Canadian Arctic stations, Coppermine, Mould Bay, Resolute, and Alert have been analyzed spectrally. Differences in spectral amplitude at very low frequencies among the stations and between earthquakes can reasonably be explained by a consideration of earthquake magnitude, epicentral distance, and mechanism. Differences in the shape of the spectral curves between stations result mainly from local crustal structures beneath the station. Increased absorption of waves is observed beneath Resolute. Use of the vertical to radial-horizontal spectral amplitude ratios gives an approximate estimate of the thickness of the crust and surface layer beneath these stations, although some phenomena noted cannot be explained by the theory of signal reverberation in a horizontally layered system with perfect elasticity. This analysis suggests that the crust thins toward the Arctic Ocean: the best estimates of crustal thickness are about 45 km at Coppermine, about 33 km at Resolute, about 23 at Alert, and about 18 km at Mould Bay. The latter depth is the most uncertain. There is a low velocity surface layer with a thickness of several hundred meters at Mould Bay, Resolute, and Alert.

scholarly journals Photooxidation of dimethylsulfide (DMS) in the Canadian Arctic

2013 ◽  
Vol 10 (2) ◽  
pp. 2093-2126 ◽  
Author(s):  
A. Taalba ◽  
H. Xie ◽  
M. G. Scarratt ◽  
S. Bélanger ◽  
M. Levasseur
Keyword(s):  
Surface Layer ◽  
River Estuary ◽  
Canadian Arctic ◽  
Ventilation Rate ◽  
The Arctic ◽  
Apparent Quantum Yield ◽  
Photochemical Process ◽  
Photochemical Modeling ◽  
High Concentrations ◽  
Loss Term

Abstract. Photolysis of dimethylsulfide (DMS), a secondary photochemical process mediated by chromophoric dissolved organic matter (CDOM), has previously been demonstrated to be an important loss term of DMS in the surface layer of warm seas and the Southern Ocean. The role of photolysis in regulating the DMS dynamics in the Arctic Ocean, however, remains obscure. This study for the first time determined the apparent quantum yield (AQY) spectra of DMS photooxidation in northern polar marine milieus covering the Baffin Bay in the eastern Canadian Arctic and the Mackenzie River estuary, Mackenzie Shelf and Canada Basin in the western Canadian Arctic. The DMS AQY was fairly invariant at salinities < 25 but rose rapidly with further increasing salinity, which is well defined by a three-parameter exponential decay equation with a constant intercept. Salinity can therefore be used as a quantitative indicator of the DMS AQY. The DMS AQY in the ultraviolet (UV) wavelengths was linearly and positively correlated with the spectral slope coefficient (275–295 nm) of the CDOM absorption spectrum, suggesting that marine CDOM photosensitizes the degradation of DMS more efficiently than does terrestrial CDOM. High concentrations of nitrate (~12 μmol L−1) in deep water samples boosted DMS photooxidation by 70–80%, due likely to radical chemistry of nitrate photolysis. Coupled optical-photochemical modeling, based on the obtained DMS AQY spectra, shows that UV-A (320–400 nm) accounted for 60–75% of the DMS photolysis in the sunlit surface layer and that photochemistry degraded DMS on an e-folding time from 9 to 100 d (mean: 29 d). The photooxidation term on average accounted for 21% of the DMS gross loss rate and was comparable to the atmospheric DMS ventilation rate estimated for the same geographic regions.

High-frequency Pn attenuation in the Canadian shield

1989 ◽  
Vol 79 (4) ◽  
pp. 1039-1053
Author(s):  
Kin-Yip Chun ◽  
Richard J. Kokoski ◽  
Gordon F. West
Keyword(s):  
Velocity Structure ◽  
Epicentral Distance ◽  
Spectral Amplitude ◽  
Common Source ◽  
Spatial Decay ◽  
Geometrical Spreading ◽  
Eastern Canada ◽  
Frequency Dependent ◽  
Low Frequencies ◽  
Head Waves

Abstract Frequency-dependent spatial attenuation of Pn waves, incorporating the combined effects of geometrical spreading and anelastic dissipation, is investigated in eastern Canada between 3 and 15 Hz. Measurement of this total attenuation, instead of the two separate effects, circumvents the usual need for making a priori assumptions regarding the Pn geometrical spreading rate. The data consist of 77 Pn spectra, all amplitude-normalized using a set of previously measured spectral ratios of eastern Canadian earthquake sources. The normalization procedure eliminates the need for explicit source spectral assumptions, another common source of error in Pn attenuation measurements. An unconventional technique is introduced to account for differences in observed Pn spectra, which arise from geological site effects and instrument response error, both of which are frequency-dependent phenomena. We conclude that, at each frequency, the Pn amplitude falls off with distance according to: Δ−n, where Δ is epicentral distance. The exponent n is weakly frequency-dependent and takes the form: 2.2 + 0.02f. A unique interpretation of the behavior of the Pn spectral amplitude decay is unattainable, owing to the difficulty in separating the effects due to anelastic dissipation and the velocity structure in the uppermost mantle. It is interesting to note, however, that the spatial decay of pure elastic head waves follows the classical Δ−1/2L−3/2 relation, where L is the distance the waves travel in the mantle refractor. For the distance range of our interest (260-1087 km), this amounts to Δ−2.2. This indicates that towards low frequencies our n approaches a value which is consistent with the spatial decay rate expected of pure elastic head waves.

Zooplankton from the Arctic Ocean and Adjacent Canadian Waters

1965 ◽  
Vol 22 (2) ◽  
pp. 543-564 ◽  
Author(s):  
E. H. Grainger
Keyword(s):  
Surface Layer ◽  
Surface Water ◽  
Arctic Ocean ◽  
Canadian Arctic ◽  
Atlantic Water ◽  
The Arctic ◽  
Central Arctic Ocean ◽  
As Species ◽  
Calanus Glacialis ◽  
The Arctic Ocean

Zooplankton collections from the Arctic Ocean, the Beaufort Sea, and northwestern Canadian coastal waters are described, along with physical characteristics of the waters sampled. About 50 species are included.The collections are compared with records from the central Arctic Ocean and other waters adjacent to the present region. The species are shown to fall into three groups. One is characteristic of the surface water of the Arctic Ocean, one of the Atlantic water and to a lesser extent the deep layer of the surface water of the Arctic Ocean, and one of the shallow peripheral seas of the Arctic Ocean.The surface water group includes eight species which account for more than 95% of the copepod individuals found in the surface layer, and which appear to be the only copepods which breed in the surface layer of the central Arctic Ocean. The same species are the major constituents of the zooplankton found in the waters of the Canadian arctic, from the Arctic Ocean to Davis Strait. The deeper Atlantic species of the Arctic Ocean, more numerous as species but far less numerous as individuals than those of the surface water, occur only very rarely in the surface layers, show no evidence of breeding there, and appear to be almost entirely absent from Canadian archipelago waters inside the shelf. Clear continuity of the Arctic Ocean surface fauna through the waters of the Canadian arctic is shown, along with the almost total exclusion from archipelago waters of the deeper Atlantic fauna. This intrusion of Atlantic species into the waters of arctic Canada appears to be almost entirely restricted to the southeast part of the region, especially Hudson Strait and adjacent waters.Development rates of two copepods in the Arctic Ocean, Microcalanus pygmaeus and Calanus glacialis, are discussed.

On the travel times of P as determined from nuclear explosions

1964 ◽  
Vol 54 (1) ◽  
pp. 123-139 ◽  
Author(s):  
I. Lehmann
Keyword(s):  
Epicentral Distance ◽  
Test Site ◽  
Surface Velocity ◽  
Strong Increase ◽  
Travel Times ◽  
Low Velocity ◽  
P Waves ◽  
Small Depth ◽  
Low Velocity Layer ◽  
Velocity Layer

abstract A study has been made of the travel times of P waves as recorded from 14 shots on the Nevada Test Site (NTS) and from the Gnome (GN) shot. The travel times on different lines extending from the test sites were considered separately. Of special interest were the travel times obtained on the line joining the NTS and GN site. The two sets of travel times were in good agreement, but from epicentral distance 700 km onwards they were delayed and scattered. This was an indication of the presence of a low velocity layer at small depth on the line. Travel times on lines extending in other directions from the NTS differed somewhat but not very greatly from those on the NTS-GN line. On the line from the Gnome site to the northeast travel times are considerably smaller owing to a strong increase of velocity with depth close to the Gnome site. Travel times in agreement with those observed were calculated. Some California stations at distances around 1700 km observed P of the Gnome shot with an exceptional delay of 412 seconds. The new Madrid earthquake of February 2, 1962, had its epicenter on the Gnome northeast line, but the surface velocity of Pn of the earthquake is smaller on the line than that of the Gnome shot. Pn of the earthquake was well recorded in all directions from the epicenter; there is no low velocity layer at small depth in these regions. In an earlier study of some earthquakes in northeastern America Pn and also Sn were found to be well recorded phases. It may seem as if shallow, low-velocity layers are confined to the western mountain regions.

Local travel-time curves and their geologic implications for the Pacific Northwest states

1965 ◽  
Vol 55 (3) ◽  
pp. 587-607 ◽  
Author(s):  
Peter Dehlinger ◽  
E. F. Chiburis ◽  
M. M. Collver
Keyword(s):  
Travel Time ◽  
Pacific Northwest ◽  
Epicentral Distance ◽  
Gravity Data ◽  
Normal Velocity ◽  
Low Velocity ◽  
P Waves ◽  
The Pacific ◽  
Low Velocity Layer ◽  
Velocity Layer

Abstract Travel-time curves were constructed for the Pacific Northwest states based on recordings of recent local earthquakes. Average velocities of Pn and S waves were found to be 4 per cent lower in the region west of the Cascade Mountains than they are to the east of the Cascades, while velocities of P* and P¯ waves are essentially the same in the two provinces. West of the Cascades the velocities obtained are 7.67 km/sec for Pn, 4.37 for Sn, 6.61 for P*, and 5.48 for P¯. East of the Cascades they are 7.96 km/sec for Pn, 4.56 for Sn, 6.60 for P*, and 5.53 for P¯. Intercept times indicate that the crust (above the Mohorovicic discontinuity) is 5 to 10 km thinner to the west than east of the Cascades. Pn velocities are found to be independent of epicentral distance to distances of 1000 km, implying that the corresponding mantle materials and densities are uniform down to the low-velocity layer in each province. In both provinces Poisson's ratio in the mantle is 0.26. From the travel-time curves and gravity data, it appears that the section above the low-velocity layer east of the Cascades is approximately typical or “normal,” while the corresponding mantle west of the Cascades consists of a different or anomalous material. The likelihood of crystal alignment, temperature anomalies, and normal velocity-density relations in the upper mantle sections are discussed.

Logistic problems in the Canadian Arctic

Polar Record ◽  
1961 ◽  
Vol 10 (67) ◽  
pp. 365-371
Author(s):  
T. A. Harwood
Keyword(s):  
United States ◽  
Canadian Arctic ◽  
The United States ◽  
The Arctic ◽  
Weather Bureau ◽  
Weather Stations ◽  
Resolute Bay ◽  
States Weather

In 1946 the United States Weather Bureau and the Canadian Meteorological Service installed the first of the Joint Arctic Weather Stations at Resolute Bay. The network of satellite stations was extended into the Arctic archipelago in the following years on roughly a 275-mile spacing to Mould Bay, Isachsen, Eureka and Alert.

MOSAiC simulator in CMIP6

2021 ◽  
Author(s):  
Rajka Juhrbandt ◽  
Suvarchal Cheedela ◽  
Nikolay Koldunov ◽  
Thomas Jung
Keyword(s):  
Surface Layer ◽  
Arctic Ocean ◽  
Ease Of Use ◽  
Arctic Climate ◽  
The Arctic ◽  
Early Results ◽  
The Arctic Ocean ◽  
Virtual Field ◽  
Field Campaigns ◽  
Type Code

&lt;p&gt;The recently completed Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC) can serve as reference to evaluate current and future ocean state of the Arctic Ocean. With this premise, we perform a virtual MOSAiC expedition in historical and ssp370-scenario experiments in data generated by CMIP6 models.&lt;br&gt;&lt;br&gt;The timespan covered ranges from preindustrial times (1851-1860) through present-day up to a 4K world (2091-2100). Early results using AWI-CM model, suggest that for scenario simulations a thinning of the colder surface layer and a warming of the layer between 200 and 1200 m along the MOSAiC path can be expected, while there is no significant change in temperature below this depth. Results from other models will be presented.&lt;br&gt;&lt;br&gt;The Python-centric tool used for the analysis simplifies preprocessing of a pool of CMIP6 data and selecting data on space-time trajectory. It exposes an interface that is agnostic to underlying model or its grid type. Code snippets are presented along to demonstrate the tool's ease of use with a hope to inspire such virtual field campaigns using other past observations or arbitrary trajectories.&lt;/p&gt;

scholarly journals Regional variability of acidification in the Arctic: a sea of contrasts

2014 ◽  
Vol 11 (2) ◽  
pp. 293-308 ◽  
Author(s):  
E. E. Popova ◽  
A. Yool ◽  
Y. Aksenov ◽  
A. C. Coward ◽  
T. R. Anderson
Keyword(s):  
Climate Change ◽  
Primary Production ◽  
Arctic Ocean ◽  
Canadian Arctic ◽  
Atmospheric Co2 ◽  
The Arctic ◽  
Canadian Arctic Archipelago ◽  
Regional Variability ◽  
The Arctic Ocean ◽  
The Impact

Abstract. The Arctic Ocean is a region that is particularly vulnerable to the impact of ocean acidification driven by rising atmospheric CO2, with potentially negative consequences for calcifying organisms such as coccolithophorids and foraminiferans. In this study, we use an ocean-only general circulation model, with embedded biogeochemistry and a comprehensive description of the ocean carbon cycle, to study the response of pH and saturation states of calcite and aragonite to rising atmospheric pCO2 and changing climate in the Arctic Ocean. Particular attention is paid to the strong regional variability within the Arctic, and, for comparison, simulation results are contrasted with those for the global ocean. Simulations were run to year 2099 using the RCP8.5 (an Intergovernmental Panel on Climate Change (IPCC) Fifth Assessment Report (AR5) scenario with the highest concentrations of atmospheric CO2). The separate impacts of the direct increase in atmospheric CO2 and indirect effects via impact of climate change (changing temperature, stratification, primary production and freshwater fluxes) were examined by undertaking two simulations, one with the full system and the other in which atmospheric CO2 was prevented from increasing beyond its preindustrial level (year 1860). Results indicate that the impact of climate change, and spatial heterogeneity thereof, plays a strong role in the declines in pH and carbonate saturation (Ω) seen in the Arctic. The central Arctic, Canadian Arctic Archipelago and Baffin Bay show greatest rates of acidification and Ω decline as a result of melting sea ice. In contrast, areas affected by Atlantic inflow including the Greenland Sea and outer shelves of the Barents, Kara and Laptev seas, had minimal decreases in pH and Ω because diminishing ice cover led to greater vertical mixing and primary production. As a consequence, the projected onset of undersaturation in respect to aragonite is highly variable regionally within the Arctic, occurring during the decade of 2000–2010 in the Siberian shelves and Canadian Arctic Archipelago, but as late as the 2080s in the Barents and Norwegian seas. We conclude that, for future projections of acidification and carbonate saturation state in the Arctic, regional variability is significant and needs to be adequately resolved, with particular emphasis on reliable projections of the rates of retreat of the sea ice, which are a major source of uncertainty.

Claiming Spaces for Science

2017 ◽  
Vol 47 (2) ◽  
pp. 164-199
Author(s):  
Adam M. Sowards
Keyword(s):  
Canadian Arctic ◽  
The Arctic ◽  
Professional Literature ◽  
Popular Discourse ◽  
Scientific Authority ◽  
Competing Demands ◽  
Complicated Process ◽  
History Of ◽  
External Forces ◽  
Reciprocal Process

Exploration has always centered on claims: for country, for commerce, for character. Claims for useful scientific knowledge also grew out of exploration’s varied activities across space and time. The history of the Canadian Arctic Expedition of 1913–18 exposes the complicated process of claim-making. The expedition operated in and made claims on many spaces, both material and rhetorical, or, put differently, in several natural and discursive spaces. In making claims for science, the explorer-scientists navigated competing demands on their commitments and activities from their own predilections and from external forces. Incorporating Arctic spaces into the Canadian polity had become a high priority during the era when the CAE traversed the Arctic. Science through exploration—practices on the ground and especially through scientific and popular discourse—facilitated this integration. So, claiming space was something done on the ground, through professional literature, and within popular narratives—and not always for the same ends. The resulting narrative tensions reveal the messy material, political, and rhetorical spaces where humans do science. This article demonstrates how explorer-scientists claimed material and discursive spaces to establish and solidify their scientific authority. When the CAE claimed its spaces in nature, nation, and narrative, it refracted a reciprocal process whereby the demands of environment, state, and discourse also claimed the CAE.

An early nineteenth century meteorological register from the eastern Canadian Arctic

Polar Record ◽  
1995 ◽  
Vol 31 (178) ◽  
pp. 335-342 ◽  
Author(s):  
Paul A. Kay
Keyword(s):  
Nineteenth Century ◽  
Canadian Arctic ◽  
The Arctic ◽  
Research Centre ◽  
Historical Reconstruction ◽  
Early Nineteenth Century ◽  
Northwest Passage ◽  
Time Periods ◽  
Modern Experience ◽  
Eastern Canadian Arctic

AbstractSignificant warming in the Arctic is anticipated for doubled-CO2 scenarios, but temperatures in the eastern Canadian Arctic have not yet exhibited that trend in the last few decades. The spatial juxtaposition of the winter station in 1822–1823 of William Edward Parry's Northwest Passage expedition with the modern Igloolik Research Centre of the Science Institute of the Northwest Territories affords an opportunity for historical reconstruction and comparison. Parry's data are internally consistent. The association of colder temperatures with westerly and northerly winds, and wanner temperatures with easterly and southerly winds, is statistically significant. Temperatures are not exactly comparable between the two time periods because of differences in instrumentation, exposure, and frequency of readings. Nevertheless, in 1822–1823, November and December appear to have been cold and January to March mild compared to modern experience. Anomalously, winds were more frequently northerly (and less frequently westerly) in the latter months than in recent observations. Parry recorded two warm episodes in mid-winter, but, overall, it appears that the winter of 1822–1823 was not outside the range of modern experience.

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