Current state and trends in Canadian Arctic marine ecosystems: I. Primary production     

Jean-éric Tremblay  Dominique Robert  Diana E. Varela  Connie Lovejoy  Gérald Darnis  R. John Nelson  Akash R. Sastri 《Climatic change》2012,115(1):161-178

During the International Polar Year (IPY), large international research programs provided a unique opportunity for assessing the current state and trends in major components of arctic marine ecosystems at an exceptionally wide spatio-temporal scale: sampling covered most regions of the Canadian Arctic (IPY-Canada??s Three Oceans project), and the coastal and offshore areas of the southeastern Beaufort Sea were monitored over almost a full year (IPY-Circumpolar Flaw Lead project). The general goal of these projects was to improve our understanding of how the response of arctic marine ecosystems to climate warming will alter the productivity and structure of the food web and the ecosystem services it provides to Northerners. The present paper summarizes and discusses six key findings related to primary production (PP), which determines the amount of food available to consumers. (1) Offshore, the warming and freshening of the surface layer is leading to the displacement of large nanophytoplankton species by small picophytoplankton cells, with potentially profound bottom-up effects within the marine food web. (2) In coastal areas, PP increases as favourable winds and the deeper seaward retreat of ice promote upwelling. (3) Multiple upwelling events repeatedly provide food to herbivores throughout the growth season. (4) A substantial amount of pelagic PP occurs under thinning ice and cannot be detected by orbiting sensors. (5) Early PP in the spring does not imply a trophic mismatch with key herbivores. (6) The epipelagic ecosystem is very efficient at retaining carbon in surface waters and preventing its sedimentation to the benthos. While enhanced PP could result in increased fish and marine mammal harvests for Northerners, it will most likely be insufficient for sustainable large-scale commercial fisheries in the Canadian Arctic.  相似文献   

Elemental and stable isotopic constraints on river influence and patterns of nitrogen cycling and biological productivity in Hudson Bay     

Zou Zou A. Kuzyk  Robie W. Macdonald  Jean-Éric Tremblay  Gary A. Stern 《Continental Shelf Research》2010

Elemental (carbon and nitrogen) ratios and stable carbon and nitrogen isotope ratios (δ¹³C and δ¹⁵N) are examined in sediments and suspended particulate matter from Hudson Bay to study the influence of river inputs and autochthonous production on organic matter distribution. River-derived particulate organic matter (POM) is heterogeneous, nitrogen-poor and isotopically depleted, consistent with expectations for OM derived from terrestrial C3 vascular plant sources, and distinct from marine OM sources. Both δ¹³C and C/N source signatures seem to be transmitted to sediments with little or no modification, therefore making good tracers for terrigenous OM in Hudson Bay. They suggest progressively larger contributions from marine sources with distance from shore and secondarily from south to north, which broadly corresponds to the distribution of river inputs to Hudson Bay. Processes other than mixing of marine and terrigenous OM influence sedimentary δ¹⁵N values, including variability in the δ¹⁵N of phytoplankton in the Bay's surface waters due to differences in relative nitrate utilization, and post-production processes, which bring about an apparently constant ¹⁵N-enrichment between surface waters and underlying sediments. Variability in the δ¹⁵N of phytoplankton in the Bay's surface waters, in contrast, seems to be organized spatially with a pattern that suggests an inshore–offshore difference in surface water nitrogen conditions (open- vs. closed-system) and hence the δ¹⁵N value of phytoplankton. The δ¹⁵N patterns, supported by a simple nitrate box-model budget, suggest that in inshore regions of Hudson Bay, upwelling of deep, nutrient-rich waters replenishes surface nitrate, resulting in ‘open system’ conditions which tend to maintain nitrate δ¹⁵N at low and constant values, and these values are reflected in the sinking detritus. River inflow, which is constrained to inshore regions of Hudson Bay, appears to be a relatively minor source of nitrate compared to upwelling of deep waters. However, river inflow may contribute indirectly to enhanced inshore nutrient supply by supporting large-scale estuarine circulation and consequently entrainment and upwelling of deep water in this area. In contrast to previous proposals that Hudson Bay is oligotrophic because it receives too much fresh water (Dunbar, 1993), our results support most of the primary production being organized around the margin of the Bay, where river flow is constrained.  相似文献   

Historical variability of subfossil chironomids (Diptera: Chironomidae) in three lakes impacted by natural and anthropogenic disturbances     

Vicky Tremblay  Isabelle Larocque-Tobler  Pascal Sirois 《Journal of Paleolimnology》2010,44(2):483-495

In the eastern boreal forest of Quebec, Canada, harvesting strategies try to mimic the effects of fire on forest ecosystems, assuming that both disturbances have similar impacts. However impacts of both types of perturbations on lacustrine ecosystems, especially on chironomids (non-biting midges), are still poorly understood. The objectives of this study were to determine if logging and fire resulted in chironomid assemblages significantly different than pre-disturbance states and to see if the harvesting strategy (careful logging around advanced growth (CLAAG) and buffer zones) protect lakes from logging effects in the boreal forest. Three statistical tests were used to study the difference between pre- and post-disturbance assemblages: a principal component analysis (PCA), analysis of similarity (ANOSIM) and a non-metric multi-dimensional scaling (MDS) ordination. All statistical analyses suggested that fire did not have any effects on chironomid assemblages. The PCA analysis showed that two logging events in Lac aux Huards created chironomid assemblages slightly outside the pre-disturbance variability. However, ANOSIM showed that these differences were not significant at the 0.5% level of significance. These results suggest that the presence of a buffer zone probably limited the impacts of logging on lakes in this area.  相似文献   

Response of three krill species to hypoxia and warming: an experimental approach to oxygen minimum zones expansion in coastal ecosystems          下载免费PDF全文

Nelly Tremblay  Doris Abele 《Marine Ecology》2016,37(1):179-199

To understand the adaptation of euphausiid (krill) species to oxygen minimum zones (OMZs), respiratory response and stress experiments combining hypoxia‐reoxygenation exposure with warming were conducted. Experimental krill species were obtained from the Antarctic (South Georgia area), the Humboldt Current System (HCS, Chilean coast) and the Northern California Current System (NCCS, Oregon). Euphausia mucronata from the HCS showed oxyconforming pO₂‐dependent respiration below 80% air saturation (18 kPa). Normoxic subsurface oxygenation in winter posed a ‘high oxygen stress’ for this species. The NCCS krill, Euphausia pacifica, and the Antarctic krill, Euphausia superba, maintained respiration rates constant down to low critical pO₂ values of 6 kPa (30% air saturation) and 11 kPa (55% air saturation), respectively. Antarctic krill had low antioxidant enzyme activities, but high concentrations of the molecular antioxidant glutathione (GSH) and was not lethally affected by 6 h exposure to moderate hypoxia. The temperate krill species (E. pacifica) had higher superoxide dismutase (SOD) values in winter than in summer, which relates to a higher winter metabolic rate. In all species, antioxidant enzyme activities remained constant during hypoxic exposure at the typical temperature for their habitat. Warming by 7 °C above habitat temperature in summer increased SOD activities and GSH levels in E. mucronata (HCS), but no oxidative damage occurred. In winter, when the NCCS is well mixed and the OMZ is deeper, +4 °C of warming combined with hypoxia represents a lethal condition for E. pacifica. In summer, when the OMZ expands upwards (100 m subsurface), antioxidant defences counteracted hypoxia and reoxygenation effects in E. pacifica, but only at mildly elevated temperature (+2 °C). In this season, experimental warming by +4 °C reduced antioxidant activities and the combination of warming with hypoxia again caused mortality of exposed specimens. We conclude that a climate change scenario combining warming and hypoxia represents a serious threat to E. pacifica and, as a consequence, NCCS food webs.  相似文献   

Mechanical and Thermal Tests of the Containers of Liquid Mirrors     

E. F. Borra  R. Content  G. Tremblay  A. Daigle  Y. Huot 《Experimental Astronomy》2003,15(3):147-169

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Mechanisms to limit higher mode effects in a controlled rocking steel frame. 2: Large‐amplitude shake table testing     

Lydell Wiebe  Constantin Christopoulos  Robert Tremblay  Martin Leclerc 《地震工程与结构动力学》2013,42(7):1069-1086

This paper presents the results of 56 large‐amplitude shake table tests of a 30% scale eight‐storey controlled rocking steel frame. No significant damage or residual deformations were observed after any of the tests. The frame had four possible configurations on the basis of combinations of two higher mode mitigation mechanisms. The first mitigation mechanism was formed by allowing the upper section of the frame to rock, so as to better control the mid‐height overturning moment. The second mitigation mechanism was formed by replacing the conventional first‐storey brace with a self‐centering energy dissipative (SCED) brace, so as to better control the base shear. The mechanisms had little effect during records where higher mode effects were not apparent, but they substantially reduced the shear and overturning moment envelopes, as well as the peak floor accelerations, during more demanding records. The reduction in storey shears led to similarly reduced brace force demands. Although the peak force demands in the columns were not reduced by as much as the frame overturning moments, using an upper rocking joint allowed the column demands to be estimated without the need to assume a lateral force distribution. The tests demonstrated that multiple force‐limiting mechanisms can be used to provide better control of peak seismic forces without excessive increases in drift demands, thus enabling more reliable capacity design. These results are expected to be widely applicable to structures where the peak seismic forces are significantly influenced by higher mode effects. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

Diachronic metamorphic and structural evolution of the Connecticut Valley–Gaspé trough,Northern Appalachians     

Morgann Perrot  Alain Tremblay  Gilles Ruffet  Loic Labrousse  Félix Gervais  Fabien Caroir 《Journal of Metamorphic Geology》2020,38(1):3-27

The Connecticut Valley–Gaspé (CVG) trough represents a major, orogen-scale Silurian–Devonian basin of the Northern Appalachians. From Gaspé Peninsula to southern New England, the CVG trough has experienced a contrasting metamorphic and structural evolution during the Acadian orogeny. Along its strike, the CVG trough is characterized by increasing strain and polyphase structures, and by variations in the intensity of regional metamorphism and contrasting abundance of c. 390–370 Ma granitic intrusions. In southern Quebec and northern Vermont, a series of NW–SE transects across the CVG trough have been studied in order to better understand these along-strike variations. Detailed structural analyses, combined with phase equilibria modelling, Raman spectrometry, and muscovite ⁴⁰Ar/³⁹Ar dating highlight a progressive and incremental deformation involving south–north variation in the timing of metamorphism. Deformation evolves from a D₁ crustal thickening event which originates in Vermont and progresses to southern Québec where it peaked at 0.6 GPa/380°C at c. 375 Ma. This was followed by a D₂ event associated with continuous burial in Vermont from 378 to 355 Ma, which produced peak metamorphic conditions of 0.85 GPa/380°C and exhumation in Quebec from 368 to 360 Ma. The D₃ compressional exhumation event also evolved from south to north from 345 to 335 Ma. D₁ to D₃ deformation events form part of a continuum with an along-strike propagation rate of ~50 km/Ma During D₁, the burial depth varied by more than 15 km between southern Quebec and Vermont, and this can be attributed to the occurrence of a major crustal indenter, the Bronson Hill Arc massif, in the New England segment of the Acadian collision zone.  相似文献   

Isotopic heterogeneity in the Sudbury impact melt sheet     

J.R. Darling  C.J. Hawkesworth  P.C. Lightfoot  C.D. Storey  E. Tremblay 《Earth and Planetary Science Letters》2010,289(3-4):347-356

A unique terrestrial large impact melt sheet is preserved in the 1850 Ma Sudbury Structure, Ontario. We have undertaken a Pb isotope investigation of the southern limb of the melt sheet, termed the South Range Main Mass. The model initial Pb isotope ratios (²⁰⁷Pb/²⁰⁴Pb_m) vary stratigraphically through the predominantly quartz monzogabbroic Lower Unit, varying from 15.40 to 15.45 at the base to ca. 15.35 at the top of the sequence. Lateral variations of similar range occur in basal Lower Unit samples over scales of less than 5 km. The range of these variations is similar to those of locally exposed upper crustal target rocks, and it is evident that the melt sheet has efficiently preserved inherited variability. During the violent phases of crater formation superheated impact melts are expected to be well-mixed mechanically, therefore significant post-impact melting of target rocks, fallback material and entrained clasts is required to explain such heterogeneity.The Sudbury Structure hosts world class Ni-Cu-PGE sulphide ore deposits. Systematic variation in ²⁰⁷Pb/²⁰⁴Pb_m occurs throughout sulphide ores within the Creighton Embayment, from massive (15.42–15.45) to interstitial (ca. 15.40–15.41) and disseminated (ca. 15.39) sulphide. Linking the Pb isotope composition of these ores to the immediately overlying Lower Unit stratigraphy, a protracted sulphide segregation history is apparent. Massive sulphides segregated early, prior to or during initial silicate crystallisation, although the total time involved in sulphide accumulation spanned much of the crystallisation of the Lower Unit. It is also shown that lateral variations in Ni depletion throughout the Main Mass correlate with Pb isotopes. Those segments with the strongest chalcophile element depletion signatures, reflecting the accumulation of significant basal sulphides, have high initial Pb isotope values, consistent with early sulphide segregation. The characterisation of Pb isotopic heterogeneity has therefore provided insights into the evolution and scales of mixing of the melt sheet, with the identified chemical variability between melt cells having a significant influence on ore forming processes.  相似文献   

Trap‐based indicators of egg production following increases in minimum legal size in Homarus americanus fisheries     

M. John Tremblay  Marc Lanteigne 《新西兰海洋与淡水研究杂志》2013,47(3):775-783

Minimum legal size (MLS) is an important conservation measure in trap fisheries for Homarus americanus. MLS has increased in several management areas in the Canadian Maritimes since 1987. A key conservation objective has been to increase egg production, with predictions of the effects of MLS increase based on egg‐per‐recruit models. We evaluated whether expectations of increases in ovigerous females (OF) were realised when MLS was increased. Data were examined from at‐sea samples of the commercial trap catch from 11 ports from 1986 to 2003. OF indicators were developed based on the OF catch‐per‐unit‐effort (CPUE) of different sizes, and on the percentage (PCT) of females that were ovigerous. Because there were within‐season increases in CPUE and PCT, annual indicators were based on regressions of CPUE on day in the season. There was considerable variability in all the time series of OF annual indicators and any effects of smaller MLS increases could not be detected. Increases in OF indicators were evident in areas that undertook the largest MLS increases (6–6.5 mm CL).  相似文献   

More than a checkbox: engaging youth in disaster risk reduction and resilience in Canada     

Cox  Robin S.  Hill  Tiffany T.  Plush  Tamara  Heykoop  Cheryl  Tremblay  Crystal 《Natural Hazards》2019,96(1):213-224

Fire has become one of the main disturbances in terrestrial ecosystems worldwide. It is known that elevation influences the occurrence of fire events; however, this variable has been poorly studied, although it is of particularly relevance to the Mexican topography. The objective of this research was to analyze the altitudinal distribution of forest fires in Mexico over a period of 11 years. Elevation gradients were defined based on a Digital Elevation Model and the main ecoregions of the country: (1) shrubland and tropical forests (0–1000 masl), (2) grasslands (1001–2000 masl) and (3) temperate forests (>?2000 masl). Each ecoregion was divided into Climate Research Units and the number of fires per unit was quantified. The G Getis–Ord statistic was applied in order to define the spatial patterns presented by the fire events. A relationship between the occurrence of fires and the El Niño Southern Oscillation phenomenon was also determined through a Pearson correlation. The results showed that the occurrence of fire events presented variability along elevation gradients, with elevation a determining factor in their occurrence. Gradient 3, with the highest elevation, had the greatest number of fires and also presented the largest area of fire event clustering. These results contribute to the knowledge of the spatial distribution of forest fires in Mexico and are of value to appropriate decision-making for effective fire management.

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