Chondrites are samples from undifferentiated asteroids that contain components that formed in the early solar system. One of the components found in chondrites is chondrules, which are small igneous spherules that formed from the melting of precursor dust ball assemblages during very short, high-temperature events in the solar nebula. Chondrules typically contain olivine and pyroxene, a glassy mesostasis, Fe-Ni metal, and sulfides. Type I chondrules contain FeO-poor and volatile-poor mineral assemblages. Approximately 10% of type I chondrules, including type IA, IAB, and IB textures, also contain igneous plagioclase. While dynamic cooling experiments have put constraints on the formation conditions of chondrules based on olivine and pyroxene textures and morphologies, plagioclase has not been produced in previous experimental chondrule analogs. In this study, we investigated common chondrule textures in CO chondrites and determined mineral and bulk compositions for plagioclase-bearing type I chondrules in CO chondrites. We also performed one-atmosphere dynamic cooling experiments in order to establish formation conditions for type I chondrules. We attempted to optimize vi viii conditions for plagioclase nucleation and growth by conducting experiments at slow cooling rates, low quench temperatures, in the presence of a Na-rich atmosphere, and with anorthite seeds present in the starting material. Experimental run products closely resemble textures of type I chondrules in ordinary and carbonaceous chondrites. Olivine is commonly poikilitically enclosed in euhedral low-Ca pyroxene. Ca-pyroxene appears as overgrowths on larger low-Ca pyroxene grains. Compositions of olivine, pyroxene, and mesostasis from experimental charges are also very similar to those observed in natural chondrules. Therefore, peak temperatures (1500-1600°C) and slow cooling rates (5-25°C/hr) used are plausible conditions for type I chondrule formation. These conditions are also predicted by the shock wave model for chondrule formation. While our experiments were conducted at conditions that we considered optimized for plagioclase crystallization, plagioclase was not observed in any experiment. Defining the conditions necessary for plagioclase nucleation may place important constraints on chondrule thermal histories. vii ix TABLE OF CONTENTS LIST OF FIGURES .

The notion that Lake Superior proper is inhospitable to dreissenid mussel survival has been challenged by recent finds on shipwrecks and rocky reefs in the Apostle Islands region. Motivated by concerns surrounding these finds, we conducted an intensive sampling campaign of Apostle Islands waters in 2017 to understand Dreissena prevalence and distribution. The 100-site effort combined random and targeted sites and collected zooplankton, benthos, video, environmental DNA, and supporting water quality data. We did not find settled Dreissena in any video footage or benthos samples, and quantitative PCR applied to eDNA samples was negative for Dreissena. Dreissena veligers were found in almost half the zooplankton samples but at orders of magnitude lower densities than reported from other Laurentian Great Lakes. Veligers were most prevalent around the western islands and associated with shallower depths and slightly higher phosphorus and chlorophyll, but did not spatially match known (still very localized) settled Dreissena colonies. This is the first study to conduct veliger-targeted sampling in western Lake Superior and the first to report consistent detection of veligers there. We speculate that these Apostle Islands veligers are not a new locally-spawned component of the zooplankton community, but instead are transported from an established population in the St. Louis River estuary (~100 km away) by longshore currents; i.e., low-density propagule pressure that may have been present for years. Small-mesh zooplankton data collected along a gradient from the Apostle Islands to the St. Louis River estuary and enumerated with thorough veliger searching would help elucidate these alternatives.

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Underwater video is increasingly used to study aspects of the Great Lakes benthos including the abundance of round goby and dreissenid mussels. The introduction of these two species have resulted in major ecological shifts in the Great Lakes, but the species and their impacts have heretofore been underassessed due to limitations of monitoring methods. Underwater video (UVID) can "sample" hard bottom sites where grab samplers cannot. Efficient use of UVID data requires affordable and accurate classification and analysis tools. Deep Lake Explorer (DLE) is a web application developed to support crowdsourced classification of UVID collected in the Great Lakes. Volunteers (i.e., the crowd) used DLE to classify 199 videos collected in the Niagara River, Lake Huron, and Lake Ontario for the following attributes: round goby, Dreissena, and aquatic vegetation presence, and dominant substrate type. We compared DLE classification results to expert classification of the same videos to evaluate accuracy. Depending on the attribute, DLE had 77% (hard substrate) to 90% (vegetation presence) agreement with expert classification of videos. Detection rates, or the number of videos with an attribute detected by both volunteers and an expert divided by the number where only the expert detected the attribute, ranged from 62% (hard substrate) to 95% (soft substrate) depending on the attribute. Many factors affected accuracy, including video quality in the application, video processing, abundance of species of interest, volunteer experience, and task complexity. Crowdsourcing tools like DLE can increase timeliness and decrease costs but may come with tradeoffs in accuracy and completeness.