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Seasonal observations for tidal periods of 12 or 24 h in, or near, Bay of Fundy salmonid mariculture sites were made. Variables measured included dissolved oxygen, salinity, temperature, chlorophyll a, current velocity, dissolved inorganic nitrogen, phosphate, and silicate. Circumstantial evidence suggests that the following processes were most important in controlling levels of dissolved oxygen: advection which supplies oxygen-saturated water and removes dissolved oxygen deficits; photosynthetic oxygen production which supersaturates seawater with dissolved oxygen during the spring and summer; and chemical and biological oxidation processes which could be dominant in removing dissolved oxygen during the night and in the late summer/fall when temperatures remain high but photosynthetic activity is low. Levels of nitrate, phosphate, and silicate were not increased by the salmonid mariculture industry above those typical of the oligotrophic Bay of Fundy, although ammonia levels were higher near the salmon net pens. During the summer, levels of silicate and dissolved inorganic nitrogen were diminished coincident with uptake by the microalgal bloom.

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Classical nucleation theory describes the formation of the first solids from supercooled liquids and predicts an average waiting time for a system to freeze as it is cooled below the melting temperature. For systems at low to moderate undercooling, waiting times are too long for freezing to be observed via simulation. Here a system can be described by estimated thermodynamic properties, or by extrapolation from practical conditions where thermodynamic properties can be fit directly to simulations. In the case of crystallizing Earth's solid iron inner core, these thermodynamic parameters are not well known and waiting times from simulations must be extrapolated over approximately 60 orders of magnitude. In this work, we develop a new approach negating the need for freezing to be observed. We collect statistics on solidlike particles in molecular dynamic simulations of supercooled liquids at 320 GPa. This allows estimation of waiting times at temperatures closer to the melting point than is accessible to other techniques and without prior thermodynamic insight or assumption. Our method describes the behavior of nucleation at otherwise inaccessible conditions such that the nucleation of any system at small undercooling can be characterized alongside the thermodynamic quantities which define the first formed solids.

Geochemical observations of ocean island and mid-ocean ridge basalts suggest that abundances of heat-producing elements (HPEs: U, Th, and K) vary within the mantle. Combined with bulk silicate Earth models and constraints on the Earth's heat budget, these observations suggest the presence of a more enriched (potentially deep and undepleted) reservoir in the mantle. Such a reservoir may be related to seismically observed deep mantle structures known as large low shear velocity provinces (LLSVPs). LLSVPs might represent thermochemical piles of an intrinsically denser composition, and many studies have shown such piles to remain stable over hundreds of Myr or longer. However, few studies have examined if thermochemical piles can remain stable if they are enriched in HPEs, a necessary condition for them to constitute an enriched HPE reservoir. We conduct a suite of mantle convection simulations to examine the effect of HPE enrichment up to 25× the ambient mantle on pile stability. Model results are evaluated against present-day pile morphology and tested for resulting seismic signatures using self-consistent potential pile compositions. We find that stable piles can form from an initial basal layer of dense material even if the layer is enriched in HPEs, depending on the density of the layer and degree of HPE enrichment, with denser basal layers requiring increased HPE enrichment to form pile-like morphology instead of a stable layer. Thermochemical piles or LLSVPs may therefore constitute an enriched reservoir in the deep mantle. Plain Language SummaryThe amount and distribution of radioactive heat-producing elements within the mantle exert an important control on the thermal evolution of the mantle and core. Determining the composition of the mantle and its rate of heat production is difficult because several lines of evidence suggest that the Earth's mantle is not homogeneous, containing reservoirs of unmixed material. Such reservoirs may contain material enriched in radioactive elements and could be primordial, remaining isolated from the surface since Earth's formation. One possible physical location for such a reservoir is within "piles" of compositionally distinct material in the deep mantle. Such piles have been suggested by seismic observations, but it is unclear whether piles can persist if they are enriched in radioactive elements that heat the piles, promoting their buoyant rise and entrainment into the convecting mantle. We use geodynamic models to explore the dynamics of a compositionally distinct basal layer enriched in heat-producing radioactive elements. We determine the conditions under which the layer can be organized into piles that remain stable over geological timescales. We find that piles can remain stable, and we are able to reconcile the dynamical requirements for stability with seismic observations using models of lower mantle physical properties.

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Abstraet. The effects of mirex, a chlorinated hydrocarbon used to kill the imported red ant, Solenopsis saevissima richteri, on the complete larval development of two crabs, Rhithropanopeus harrisii and Menippe mercenaria are described. The duration of developmental stages of Rhithropanopeus and the total time of development is generally lengthened with an increase in concentration of mirex from 0.01 to 10.0 ppb. There are highly significant differences between survival of larvae in the control and in each concentration of mirex. In Menippe, there were no pronounced differences in duration of developmental stages with increased concentrations of mirex, but the percentage of extra 6th zoeae was greater as concentrations were increased. There was differential survival of the developmental stages in relation to concentration of mirex, and Menippe larvae were much more sensitive to mirex than Rhithropanopeus larvae, especially in the megalopal stage. Residue analysis revealed that Menippe concentrates mirex more efficiently during development to crab stages than does Rhithropanopeus.