Microplastics contamination of Lake Ontario sediments is investigated with the aim of identifying distribution patterns and hotspots in nearshore, tributary and beach depositional environments. Microplastics are concentrated in nearshore sediments in the vicinity of urban and industrial regions. In Humber Bay and Toronto Harbour microplastic concentrations were consistently >500 particles per kg dry sediment. Maximum concentrations of ~28,000 particles per kg dry sediment were determined in Etobicoke Creek. The microplastic particles were primarily fibres and fragments < 2 mm in size. Both low-and high-density plastics were identified using Raman spectroscopy. We provide a baseline for future monitoring and discuss potential sources of microplastics in terms of how and where to implement preventative measures to reduce the contaminant influx. Although the impacts of microplastics contamination on ecosystem health and functioning is uncertain, understanding, monitoring and preventing further microplastics contamination in Lake Ontario and the other Great Lakes is crucial . 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 Ballent, Anika Manuscript page 1Sources and sinks of microplastics in Canadian Lake Ontario nearshore, tributary and beach sediments. AbstractMicroplastics contamination of Lake Ontario sediments is investigated with the aim of identifying distribution patterns and hotspots in nearshore, tributary and beach depositional environments. Microplastics are concentrated in nearshore sediments in the vicinity of urban and industrial regions. In Humber Bay and Toronto Harbour microplastic concentrations were consistently >500 particles per kg dry sediment. Maximum concentrations of ~28,000 particles per kg dry sediment were determined in Etobicoke Creek. The microplastic particles were primarily fibres and fragments < 2 mm in size. Both low-and high-density plastics were identified using Raman spectroscopy. We provide a baseline for future monitoring and discuss potential sources of microplastics in terms of how and where to implement preventative measures to reduce the contaminant influx. Although the impacts of microplastics contamination on ecosystem health and functioning is uncertain, understanding, monitoring and preventing further microplastics contamination in Lake Ontario and the other Great Lakes is crucial.

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The ~180-km-diameter Chicxulub peak-ring crater and ~240-km multiring basin, produced by the impact that terminated the Cretaceous, is the largest remaining intact impact basin on Earth. International Ocean Discovery Program (IODP) and International Continental Scientific Drilling Program (ICDP) Expedition 364 drilled to a depth of 1335 m below the sea floor into the peak ring, providing a unique opportunity to study the thermal and chemical modification of Earth’s crust caused by the impact. The recovered core shows the crater hosted a spatially extensive hydrothermal system that chemically and mineralogically modified ~1.4 × 105 km3 of Earth’s crust, a volume more than nine times that of the Yellowstone Caldera system. Initially, high temperatures of 300° to 400°C and an independent geomagnetic polarity clock indicate the hydrothermal system was long lived, in excess of 106 years.

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Stable isotope analysis is an increasingly valuable tool in ecological studies and shows promise as a measure of nutritional stress in wild animals. Thus far, however, the only studies on endotherms that have conclusively shown changes in delta(15)N and delta(13)C values in response to nutritional stress were conducted on fasting animals and animals growing under extreme levels of food restriction. We conducted a laboratory experiment to test whether delta(15)N and delta(13)C values provide a general index of nutritional stress. We compared the isotopic composition of whole blood, liver, muscle and feathers between two groups of juvenile song sparrows (Melospiza melodia) hand-reared in captivity under identical conditions except for feeding regime. To verify that our experimental treatment induced a biologically meaningful level of nutritional stress, we simultaneously measured the effects on physiology, growth and development at multiple scales. While food-restricted birds were physiologically stressed, physically smaller, and showed poorer growth and brain development compared to ad libitum-fed birds, there was no effect of feeding regime on either delta(15)N or delta(13)C values in any tissue. Instead of a continuum where the level of change in (15)N or (13)C contents corresponds to the level of nutritional stress, we suggest there may be a threshold level of nutritional stress below which such isotopic changes are likely to be negligible.

Abstract-The Tagish Lake C2 (ungrouped) carbonaceous chondrite fall of January 18, 2000, delivered ∼10 kg of one of the most primitive and physically weak meteorites yet studied. In this paper, we report the detailed circumstances of the fall and the recovery of all documented Tagish Lake fragments from a strewnfield at least 16 km long and 3 to 4 km wide. Nearly 1 kg of "pristine" meteorites were collected one week after the fall before new snow covered the strewnfield; the majority of the recovered mass was collected during the spring melt. Ground eyewitnesses and a variety of instrument-recorded observations of the Tagish Lake fireball provide a refined estimate of the fireball trajectory. From its calculated orbit and its similarity to the remotely sensed properties of the D-and P-class asteroids, the Tagish Lake carbonaceous chondrite apparently represents these outer belt asteroids. The cosmogenic nuclide results and modeled production indicate a prefall radius of 2.1-2.4 m (corresponding to 60-90 tons) consistent with the observed fireball energy release. The bulk oxygen-isotope compositions plot just below the terrestrial fractionation line (TFL), following a trend similar to the CM meteorite mixing line. The bulk density of the Tagish Lake material (1.64 ± 0.02 g/cm 3 ) is the same, within uncertainty, as the total bulk densities of several C-class and especially D-and P-class asteroids. The high microporosity of Tagish Lake samples (∼40%) provides an obvious candidate material for the composition of low bulk density primitive asteroids.