Ultraclean field and laboratory procedures were used to examine trace element concentrations in northern Alaskan snow. Sixteen soluble trace elements and total mercury were determined in snow core samples representing the annual snowfall deposited during the 1993-94 season at two sites in the Prudhoe Bay oil field and nine sites in the Arctic National Wildlife Refuge (Arctic NWR). Results indicate there were two distinct point sources for trace elements in the Prudhoe Bay oil field-a source associated with oil and gas production and a source associated with municipal solid-waste incineration. Soluble trace element concentrations measured in snow from the Arctic NWR resembled concentrations of trace elements measured elsewhere in the Arctic using clean sample-collection and processing techniques and were consistent with deposition resulting from widespread arctic atmospheric contamination. With the exception of elements associated with sea salts, there were no orographic or east-west trends observed in the Arctic NWR data, nor were there any detectable influences from the Prudhoe Bay oil field, probably because of the predominant easterly and northeasterly winds on the North Slope of Alaska. However, regression analysis on latitude suggested significant south-to-north increases in selected trace element concentrations, many of which appear unrelated to the sea salt contribution.

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The Gulf of California hermit crab, Clibanarius digueti, forms discrete clusters at low tide consisting of as many as 700 individuals. To determine the adaptive value of clustering, hypotheses concerning resistance to strong currents, cold, and desiccation were evaluated experimentally. In addition, field observations of mating, shell exchange, grazing, and predator avoidance were made. Results suggest that aggregation improves survivorship of extreme cold and desiccation. When cover is lacking, clusters may also enable C. digueti to resist displacement by strong currents. Field experiments using empty, tagged shells also indicate a possible shell exchange role.