ENSO and Sea Surface Temperature Anomalies in Association with Canadian Wheat Yield Variability

Interannual variations of spring wheat yields in Canadian agricultural regions are analyzed, together with the associated sea surface temperature (SST) anomalies in the northern hemisphere tropics and extratropics, from 1961 to 2015. The cubic trend is calculated and used to represent the trend related to advances in agricultural technology over this time period. The correlations between Canadian wheat yields at regional scales and the tropical El Niño–Southern Oscillation (ENSO) variability are not robust at any stage of the evolution of ENSO. Based on the power spectrum and cross-spectrum analysis, the most prominent yield variance is found in the Canadian Prairies, with a significant power peak of 4.5 years but does not co-vary significantly with interannual ENSO variability. ENSO weakly affects temperature and precipitation anomalies in the Canadian Prairie Region in summer—two important agroclimatic conditions for crop growth—and hence insignificantly impacts wheat yields. This indicates that there would be little benefit to including tropical ENSO indices in the operational wheat yield forecasting system. For Canadian wheat yield forecasting, attention should be paid to the preceding winter and spring SST anomalies in the northern extratropics. The SST anomalies associated with yields in the Canadian Prairie region and Central Region are generally stronger than those associated with yields in the Canadian Pacific Coast Region and eastern Maritime Region. In association with the Prairie Region and Central Region yields, SST shows pronounced anomalies in the mid-high latitudes of the North Pacific from winter to summer. The non-linearity of the SST anomalies associated with the Canadian yields is also clearly evident. Stronger (weaker) SST anomalies in the extratropical North Pacific correspond to low wheat yields in the Prairie (Central) Region, while weaker (stronger) SST anomalies correspond to high yields in the Prairie (Central) Region.     

Time relationships between volcanism–plutonism–alteration–mineralization in Cu-stratabound ore deposits from the Michilla mining district,northern Chile: a <Superscript>40</Superscript>Ar/<Superscript>39</Superscript>Ar geochronological approach

The Michilla mining district comprises one of the most important stratabound and breccia-style copper deposits of the Coastal Cordillera of northern Chile, hosted by the Middle Jurassic volcanic rocks of the La Negra Formation. ⁴⁰Ar/³⁹Ar analyses carried out on igneous and alteration minerals from volcanic and plutonic rocks in the district allow a chronological sequence of several magmatic and alteration events of the district to be established. The first event was the extrusion of a thick lava series of the La Negra Formation, dated at 159.9 ± 1.0 Ma (2σ) from the upper part of the series. A contemporaneous intrusion is dated at 159.6 ± 1.1 Ma, and later intrusive events are dated at 145.5 ± 2.8 and 137.4 ± 1.1 Ma, respectively. Analyzed alteration minerals such as adularia, sericite, and actinolite apparently give valid ⁴⁰Ar/³⁹Ar plateau and miniplateau ages. They indicate the occurrence of several alteration events at ca. 160–163, 154–157, 143–148, and 135–137 Ma. The first alteration event, being partly contemporaneous with volcanic and plutonic rocks, was probably produced in a high thermal gradient environment. The later events may be related either to a regional low-grade hydrothermal alteration/metamorphism process or to plutonic intrusions. The Cu mineralization of the Michilla district is robustly bracketed between 163.6 ± 1.9 and 137.4 ± 1.1 Ma, corresponding to dating of actinolite coexisting with early-stage chalcocite and a postmineralization barren dyke, respectively. More precisely, the association of small intrusives (a dated stock from the Michilla district) with Cu mineralization in the region strongly suggests that the main Michilla ore deposit is related to a magmatic/hydrothermal event that occurred between 157.4 ± 3.6 and 163.5 ± 1.9 Ma, contemporaneous or shortly after the extrusion of the volcanic sequence. This age is in agreement with the Re–Os age of 159 ± 16 Ma obtained from the mineralization itself (Tristá-Aguilera et al., Miner Depos, 41:99–105,2006).     

The relationship between glacial activity and sediment production: evidence from a 4450-year varve record of neoglacial sedimentation in Hector Lake, Alberta, Canada

A 4450-year sequence of varves, spanning the entire Neoglacialinterval, has been recovered from Hector Lake, Alberta. The varve record is compared to records of regional glacial history toevaluate therelationship between alpine glacial activity and sediment production. Glacial controls on sediment production vary with the timescale considered. Long-term variations in sedimentation rate, of centuries to millennial duration, reflect changes in ice extent of the same timescale. Superimposed on these long-term changes is decadal-scale variability that is complexly related to upvalley ice extent. Over the short term, high sedimentation rates may be associated with glacier maximum stands, or with periods of glacier advance or recession. Overthe last millennium at least, highest sedimentation rates appear to have been associated with transitional periods, preceding or post-dating maximum ice stands, rather than with times of maximum ice extent.     

A densely feathered ornithomimid (Dinosauria: Theropoda) from the Upper Cretaceous Dinosaur Park Formation,Alberta, Canada

A recently discovered articulated partial skeleton of Ornithomimus from the Upper Cretaceous Dinosaur Park Formation of Alberta, Canada is remarkable in the extent and quality of preservation of integumentary structures including feathers. It is the first ornithomimid to preserve a tail bearing extensive plumaceous feathers that are slightly more elongate in comparison to those present on the remainder of the body. However, the underside of the tail and the hind limb distal to the middle of the femur appear devoid of plumage. Overall, the plumage pattern in Ornithomimus is similar to that of Struthio camelus (ostrich) and other large palaeognaths, indicating a probable function in thermoregulation. The specimen also preserves the body outline around the legs, including a skin contour anterior to the femur, analogous to skin webs in extant birds. Whereas the knee web of birds bridges the knee to the abdomen, in Ornithomimus it spans from the mid-femoral shaft to the abdomen, and is herein referred to as an anterior femoral web. This is the first report of such soft tissue structures in non-avian theropods. It may indicate that the resting position of the femur was positioned more anteroventrally in ornithomimids than in most theropods, and in that sense may have been transitional to the situation in modern birds.     

The saturation of calcite and aragonite in the Arctic Ocean

We report on the chemical saturation of CaCO₃ in the waters of the Arctic Ocean calculated from total alkalinity (A_T) and total dissolved inorganic carbon (C_T). Data based on four different expeditions are presented: International Arctic Ocean Expedition (IAOE-91), Arctic Ocean Section 94 (AOS94), Polarstern Arctic '96 expedition (ACSYS 96), and Joint Ocean Ice Study 97 (JOIS 97). The results show a lysocline at around 3500 m for aragonite and that most of the Arctic Ocean sea floor lies above the lysocline for calcite. The only anomaly is the low degree of saturation at the shelf break depth in the Canadian Basin seen in the sections of the AOS94 and JOIS 97 cruises, correlated with nutrient maxima and very low O₂ concentration, suggesting decomposition of organic matter. The insignificant variability in degree of saturation between the deep waters of the different basins in the Arctic Ocean indicates a very low sedimentation/remineralisation of organic soft matter.     

Comparing various approaches for assessing groundwater recharge at a regional scale in the Canadian Shield

ABSTRACT

Estimating groundwater recharge is crucial to ensuring the proper management of aquifers. In this study, net regional recharge and spatial potential recharge are estimated at four watersheds within the Charlevoix–Haute-Côte-Nord (CHCN) regions, Quebec Province, Canada. Four methods are applied based on available data. The first two approaches are regional water budget methods. These two methods differ in their estimation of vertical inflow (VI), which is estimated from two hydrological models: GR4J and HYDROTEL. The third method estimates potential recharge spatially over the study area. Finally, the streamflow data are analysed using the Eckhardt baseflow separation method to obtain an estimation of recharge, assuming that discharge is equal to recharge. According to the results of all investigated methods, the mean annual recharge for the CHCN region is approximately 183 mm, which is 18% of the total annual precipitation (P). The discussion section highlights uncertainties due to the assumptions of each method and the reliability of the data.     

Crustal growth during back‐arc closure: Cretaceous exhumation history of Cordillera Darwin,southern Patagonia

The Cordillera Darwin metamorphic complex is unique in the Andes in exposing kyanite–staurolite schist north of the Beagle Channel in southern Patagonia. Garnet in amphibolite facies pelitic schists from Bahía Pia has patchy textures whereby some grains consist of clear, grossular‐rich garnet with fine‐grained S1 inclusion trails truncated by regions of turbid spessartine–pyrope‐rich garnet with biotite, muscovite, plagioclase and quartz inclusions. Micron‐scale aqueous inclusions in turbid garnet are consistent with recrystallization facilitated by fluid ingress; S2 inclusion trails indicate this was broadly contemporary with the growth of kyanite and staurolite in the matrix. Pseudosection modelling in Na₂O–CaO–K₂O–FeO–MgO–Al₂O₃–SiO₂–H₂O–TiO₂–Fe₂O₃ (NCKFMASHTO) is used to infer a P–T path dominated by decompression from 12 to 9 kbar at T ≈ 620 °C, coupled with garnet mode decreasing from ～5% to <1%. U–Th–Pb in situ dating of S2 monazite indicates that staurolite and kyanite growth and thus exhumation was underway before 72.6 ± 1.1 Ma. Contact aureoles developed adjacent to late granite intrusions include sillimanite‐bearing migmatites formed at P ≈ 6 kbar after 72 Ma. Metamorphism of southern Cordillera Darwin induced by continental underthrusting beneath the arc, related to closure of the Rocas Verdes back‐arc basin, was terminated by thrusting‐controlled exhumation, with the rocks at P ≈ 9 kbar by c. 73 Ma and 6 kbar by c. 70 Ma.     

Quantifying groundwater–surface water interactions in a proglacial valley,Cordillera Blanca,Peru

A myriad of downstream communities and industries rely on streams fed by both groundwater discharge and glacier meltwater draining the Cordillera Blanca, Northern Peruvian Andes, which contains the highest density of glaciers in the tropics. During the dry season, approximately half the discharge in the region's proglacial streams comes from groundwater. However, because of the remote and difficult access to the region, there are few field methods that are effective at the reach scale to identify the spatial distribution of groundwater discharge. An energy balance model, Rhodamine WT dye tracing, and high‐definition kite‐borne imagery were used to determine gross and net groundwater inputs to a 4‐km reach of the Quilcay River in Huascaran National Park, Peru. The HFLUX computer programme ( http://hydrology.syr.edu/hflux.html ) was used to simulate the Quilcay River's energy balance using stream temperature observations, meteorological measurements, and kite‐borne areal photography. Inference from the model indicates 29% of stream discharge at the reach outlet was contributed by groundwater discharge over the study section. Rhodamine WT dye tracing results, coupled with the energy balance, show that approximately 49% of stream water is exchanged (no net gain) with the subsurface as gross gains and losses. The results suggest that gross gains from groundwater are largest in a moraine subreach but because of large gross losses, net gains are larger in the meadow subreaches. These insights into pathways of groundwater–surface water interaction can be applied to improve hydrological modelling in proglacial catchments throughout South America. Copyright © 2016 John Wiley & Sons, Ltd.     

Snowmelt variability in Polar Bear Pass,Nunavut, Canada,from QuikSCAT: 2000–2009

Snowmelt onset and end date estimates are made from QuikSCAT scatterometer measurements in the Canadian High Arctic wetland of Polar Bear Pass (PBP) and the surrounding region of Bathurst Island, Nunavut. In situ data within PBP is used to validate QuikSCAT snowmelt onset/end date estimates. Results indicate that within PBP from 2000 to 2009, the mean snowmelt onset date was Year Day (YD) 162, the mean snowmelt end date was YD179, and the mean snowmelt duration was 17 days. More interannual variability was apparent in snowmelt end date and duration compared with onset, and only snowmelt end date was significantly correlated with mean June air temperature at ?0.78. Cooler air temperatures in 2004 contributed to a long snowmelt duration of 24 days, and the very short snowmelt duration in 2007 of just 11 days was caused by rapid and sustained increases in air temperature. For snowmelt end date and duration the mean spatial pattern revealed two centres of later snowmelt end date/longer snowmelt duration over Bathurst Island. They were separated by early snowmelt end date/short snowmelt duration in PBP. These patterns are in agreement with the spatial distribution of mean May to July air temperature over Bathurst Island and are likely influenced by the local‐scale topography of Bathurst Island. Given the correlation between air temperature and snowmelt end date, we might expect quicker snowmelt under increased warming. The latter process may have implications for the sustainability of the PBP wetland under a warmer climate. Copyright © 2011 John Wiley & Sons, Ltd.     

Metamorphic evolution of sapphirine‐ and orthoamphibole‐cordierite‐bearing gneiss,Okanogan dome,Washington, USA

Gneiss domes are commonly cored by quartzofeldspathic rocks that provide little information about the pressure–temperature–fluid history of the domes. Three northern Cordilleran migmatite domes (Thor‐Odin and Valhalla/Passmore, British Columbia, Canada; Okanogan, Washington, USA), however, contain Mg–Al‐rich orthoamphibole‐cordierite gneiss as layers and lenses that record metamorphic conditions and pressure–temperature (P–T) path information not preserved in the host migmatite. These Mg–Al‐rich rocks are therefore a valuable archive of metamorphic conditions during dome evolution, although refractory rocks such as these commonly contain reaction textures that may complicate the calculation of metamorphic conditions. In the Okanogan dome, Mg–Al‐rich layers are part of the Tunk Creek unit, which occurs at the periphery of an underlying migmatite domain. Bulk compositional layers (mm‐ to m‐scale) consist of gedrite‐dominated, hornblende‐dominated and biotite‐bearing layers that contain variable amounts of gedrite, hornblende, anorthite, cordierite, spinel, sapphirine, corundum, kyanite, biotite and/or staurolite. The presence of different compositional layers (some with reaction textures, some without) allows systematic analysis of metamorphic history by a combined petrographic and phase equilibrium analysis. Gedrite‐dominated layers containing relict kyanite preserve evidence of the highest‐P conditions; symplectitic and coronal reaction textures around kyanite indicate decompression at high temperature. Gedrite‐dominated layers lacking these reaction textures contain layers of sapphirine and spinel in apparent textural equilibrium and record a later high‐T–low‐P part of the path. Phase equilibria (pseudosection) analysis for layers that lack reaction textures indicates metamorphic conditions of 720–750 °C at a range of pressures (>8 to <4 kbar) following decompression. Elevated crustal temperatures and concordant structural fabrics in the Tunk Creek unit and underlying migmatite domain suggest that the calculated P–T conditions recorded in Tunk Creek rocks were coeval with anatexis, extension, and dome formation in Palaeocene–Eocene time. In contrast to orthoamphibole‐cordierite gneiss in the other Cordilleran domes, the Tunk Creek unit occurs as a discontinuous km‐scale layer rather than as smaller (m‐scale) pods, is more calcic, and lacks garnet. In addition, kyanite did not transform to sillimanite, and spinel commonly occurs as a blocky matrix phase in addition to vermicules in symplectite. These differences, along with the compositional layering, allow an analysis of bulk composition v. tectonic (P–T path) controls on mineral assemblages and textures. Pseudosection modelling of different layers in the Tunk Creek unit provides a basis for understanding the metamorphic history of these texturally complex, refractory rocks and their host gneiss domes, and other such rocks in similar tectonic settings.