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Woolly mammoth (Mammuthus primigenius), horse (Equus spp.) and bison (Bison spp.) coexisted with a variety of mammalian megafauna across the Pleistocene mammoth steppe – a megacontinental ecosystem that spanned northern Eurasia and northwestern North America. Previous research has suggested that highly conserved niches with minimal niche overlap allowed high levels of species diversity on the mammoth steppe. Here we evaluate previously published and some new collagen carbon and nitrogen isotope data (δ 13C, δ 15N) for mammoth steppe megaherbivores using Stable Isotope Bayesian Ellipses in R (SIBER) and linear regression models to determine isotopic niches for individual species during broad time intervals (pre-, during and post-Last Glacial Maximum (LGM)) at multiple geographic regions across the mammoth steppe. Individual species maintained relatively consistent isotopic niche positions at different geographic locations and during different times. Diet and habitat niches for any given species appear to have been similar across the mammoth steppe. Between some regions and times, however, species' isotopic niches changed, suggesting adaptation to local climatic conditions and/or changes in the nitrogen isotope patterns at the base of the food web. Isotopic niche overlap, including at the level of core niche overlap (>60% overlap), was observed in at least one time and region for most species. This overlap suggests high levels of functional redundancy in the ecosystem, whereby one species could fulfil another's ecological role in the latter's absence. Despite spatial and temporal environmental variation, species' adaptability and functional redundancy within the ecosystem would have made the mammoth steppe a highly resilient ecosystem. • Herbivores across the mammoth steppe had broadly homogenous isotopic niches. • Some species shifted their niche in response to environmental conditions. • Overlap between species' isotopic niches suggests functional redundancy. • Functional redundancy made the mammoth steppe a highly resilient ecosystem. [ABSTRACT FROM AUTHOR]

Southwestern Ontario has a legacy of unplugged oil and gas wells drilled in the late 1800s and early 1900s before the advent of government regulatory controls. A number of these wells exhibit artesian flow of salty and/or sulphurous water at the surface, creating a liability to landowners and a possible threat to potable groundwater aquifers and the surface environment. Cost-effective plugging of these wells is hindered by incomplete drilling records regarding well depths, well construction, and geologic information on the sources of the leaking fluids. This study seeks to fill this knowledge gap by characterizing distinct geochemical ‘fingerprints’ for each of the major bedrock water-producing zones that may be the possible sources of the leaking fluids. To this end, over 130 groundwater samples were collected and analyzed for a broad suite of isotopic parameters ( δ 18 O, δ 2 H, δ 34 S SO4 , δ 18 O SO4 , δ 13 C DIC , 87 Sr/ 86 Sr, δ 37 Cl and δ 81 Br), and this dataset was combined with available data from previous studies in the area. A Bayesian mixing model, SIAR, was applied to these data to develop a statistical tool for identifying the probable source(s) of leaking fluids. Several hypothetical samples and one real-world example are presented here to demonstrate the model’s performance. [ABSTRACT FROM AUTHOR]

Abstract: The oxygen-isotope compositions (obtained by laser fluorination) of hand-picked separates of isolated forsterite, isolated olivine and chondrules from the Tagish Lake carbonaceous chondrite describe a line (δ17O=0.95*δ18O−3.24; R 2 =0.99) similar to the trend known for chondrules from other carbonaceous chondrites. The isolated forsterite grains (Fo99.6–99.8; δ18O=−7.2‰ to −5.5‰; δ17O=−9.6‰ to −8.2‰) are more 16O-rich than the isolated olivine grains (Fo39.6–86.8; δ18O=3.1‰ to 5.1‰; δ17O=−0.3‰ to 2.2‰), and have chemical and isotopic characteristics typical of refractory forsterite. Chondrules contain olivine (Fo97.2–99.8) with oxygen-isotope compositions (δ18O=−5.2‰ to 5.9‰; δ17O=−8.1‰ to 1.2‰) that overlap those of isolated forsterite and isolated olivine. An inverse relationship exists between the Δ17O values and Fo contents of Tagish Lake isolated forsterite and chondrules; the chondrules likely underwent greater exchange with 16O-poor nebular gases than the forsterite. The oxygen-isotope compositions of the isolated olivine grains describe a trend with a steeper slope (1.1±0.1, R 2 =0.94) than the carbonaceous chondrite anhydrous mineral line (CCAMslope =0.95). The isolated olivine may have crystallized from an evolving melt that exchanged with 16O-poor gases of somewhat different composition than those which affected the chondrules and isolated forsterite. The primordial components of the Tagish Lake meteorite formed under conditions similar to other carbonaceous chondrite meteorite groups, especially CMs. Its alteration history has its closest affinities to CI carbonaceous chondrites. [Copyright &y& Elsevier]

While the evolution of the Laurentian Great Lakes has been researched intensively, fewer studies have focused on reconstructing the history of Lake Simcoe, the fourth largest lake wholly within southern Ontario. This study uses proxy data, including ostracod valves, contained in lake sediments to reconstruct a ∼14 000-year history of paleoenvironmental change in the Lake Simcoe basin. First, oxygen-isotope compositions of ostracod valves (δ 18O valve) are used to estimate the oxygen-isotope composition of ancient lake water, δ 18O lake water. In Lake Simcoe, δ 18O lake water is insensitive to changes in lake level but sensitive to shifts in temperature, capturing periods such as the early Holocene warming. This δ 18O lake water record demonstrates that the delivery of meltwater from Lake Algonquin to Lake Simcoe began to slow at ∼12 050 cal yr BP, supporting previous research based on geophysical data. It also suggests that an isolated pulse of 16O-rich water from Early Lake Mattawa may have occurred from ∼10 699 to 10 591 cal yr BP. Next, stable carbon-isotope compositions of ostracod valves (δ 13C valve) are used to estimate the stable carbon-isotope composition of dissolved inorganic carbon (δ 13C DIC) in Lake Simcoe. These data, combined with ostracod assemblages, grain size, magnetic susceptibility (MS) and sediment mineralogy, support our interpretation of temperature-sensitive variation in δ 18O lake water and provide further insights into in-lake conditions. A pronounced increase in accumulation rate, and subtler increases in grain size and detrital carbonate contents, between ∼8300 and ∼8000 cal yr BP may reflect the abrupt transition from cold and dry to wet and warm conditions resulting from the collapse of the Laurentide Ice Sheet (LIS) at ∼8200 cal yr BP. In summary, this study refines our understanding of the evolution of Lake Simcoe and provides a holistic picture of environmental change over the last ∼14 000 years. • Ostracods reveal paleoenvironmental history of Lake Simcoe, Canada. • Glacial meltwater input to Lake Simcoe began to slow at ∼12 050 cal yr BP. • Early Lake Mattawa may have inundated Lake Simcoe ∼10 600 cal yr BP. • Proxies from Lake Simcoe reveal relative Holocene temperature change. • Physical properties of Lake Simcoe sediment record the 8.2 ka event. [ABSTRACT FROM AUTHOR]

The (Laurentian) Great Lakes region (GLR) of North America contains ∼20% of the world's freshwater by total area. Yet, the water quantity and quality of lakes in this region are threatened by water level fluctuations and excessive algal growth associated with climate warming. To understand the mechanisms that drive these changes, we have established a 900-year history of environmental change using sediments from a small kettle lake, Barry Lake, located within the GLR. To understand how water quantity changed over time, we used stable isotopes of oxygen and carbon in marl to reconstruct effective moisture. Our reconstruction for Barry Lake shows that the Little Ice Age (LIA) was wetter than present, whereas the Medieval Climate Anomaly (MCA) was drier than present. There is considerable spatiotemporal variation in effective moisture across the GLR and northeastern (NE) USA. This variation may reflect changes in the sign of the Pacific Decadal Oscillation (PDO) and Atlantic Multidecadal Oscillation (AMO), which can alter moisture delivery by modifying the strength and position of the polar and subtropical jet streams. To identify changes in water quality, we reconstructed primary production using sedimentary chlorophyll a (Chl- a (s)) contents and stable isotopes of carbon and nitrogen in organic matter. There was relatively little change until the last 150 years, revealing that shifts in effective moisture did not noticeably influence primary production. Rather, primary production was impacted by anthropogenic pressures such as land use change and associated increases in nutrient delivery. Our research contextualizes recent threats to water quantity and quality in the GLR against a backdrop of environmental change, while also synthesizing hydroclimate records from across this region and the NE USA. • At Barry Lake, effective moisture was variable throughout the last ∼900 years. • Barry Lake is more productive now than at any time in the last ∼900 years. • Variations in effective moisture are not driving these increases in production. • The western Great Lakes region is more sensitive to drought than the northeast USA. • Spatiotemporal moisture patterns in these regions match the PDO and AMO. [ABSTRACT FROM AUTHOR]