As offshore oil and gas exploration expands in the Arctic, it is important to expand the scientific understanding of arctic ecology and environmental impact to mitigate operational risks. Understanding the fate of oil in arctic seawater is a key factor for consideration. Here we report the chemical loss due to the biodegradation of Alaska North Slope (ANS) crude oil that would occur in the water column following the successful dispersion of a surface oil slick. Primary biodegradation and mineralization were measured in mesocosms containing Arctic seawater collected from the Chukchi Sea, Alaska, incubated at −1°C. Indigenous microorganisms degraded both fresh and weathered oil, in both the presence and absence of Corexit 9500, with oil losses ranging from 46−61% and up to 11% mineralization over 60 days. When tested alone, 14% of 50 ppm Corexit 9500 was mineralized within 60 days. Our study reveals that microorganisms indigenous to Arctic seawater are capable of performing extensive biodegradation of chemically and physically dispersed oil at an environmentally relevant temperature (−1°C) without any additional nutrients.

The acute toxicity of physically and chemically dispersed crude oil and the dispersant Corexit 9500 were evaluated for key Arctic species. The copepod Calanus glacialis, juvenile Arctic cod (Boreogadus saida), and larval sculpin (Myoxocephalus sp.) were tested under conditions representative of the Beaufort and Chukchi Seas during the ice-free season. The toxicity of 3 water-accommodated fractions (WAF) of Alaska North Slope crude oil was examined with spiked, declining exposures. A dispersant-only test was conducted with the copepod C. glacialis. Each preparation with oil (WAF, breaking wave WAF [BWWAF], and chemically enhanced WAF [CEWAF]) produced distinct suites of hydrocarbon constituents; the total concentrations of oil were lowest in WAF and highest in CEWAF preparations. The relative sensitivity for the different species and age classes was similar within each WAF type. Median lethal concentration values based on total petroleum hydrocarbons ranged from 1.6 mg/L to 4.0 mg/L for WAF and BWWAF treatments and from 22 mg/L to 62 mg/L for CEWAF. For Corexit 9500 exposures, median lethal concentration values ranged from 17 mg/L to 50 mg/L. The differences in the relative toxicity among the accommodated fractions indicated that the majority of petroleum hydrocarbons in the CEWAF are in less acutely toxic forms than the components that dominate the WAF or BWWAF. Further evaluation showed that the parent polycyclic aromatic hydrocarbon compounds, specifically naphthalene, were highly correlated to acute toxicity. Environ Toxicol Chem 2013;32:2284–2300.

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ABSTRACT. Permafrost temperatures have increased in Alaska since the 1960s, and many impacts of climate warming are associated with permafrost thaw. Thaw of permafrost caused by increases in permafrost temperature may result in thaw settlement and significant damage to infrastructure. The goal of this research is to identify regions of Alaska at risk from thaw subsidence related to climate warming and to determine the relative risk of those regions. We developed a Permafrost Settlement Hazard Index (PSHI) by analyzing anticipated climate warming and the ecological characteristics that regulate thaw subsidence. This analysis provides statistical verification that the discontinuous permafrost region is at more risk of thaw settlement than other regions of Alaska. In addition, it estimates future thaw subsidence risk in Alaska in 2050 using future temperature increases projected by published climate models. Results indicate increased thaw subsidence risk in northern Alaska in 2050, with the greatest increase expected in parts of northwest Alaska. However, in the interior and southwest Alaska, projected disappearance of permafrost from the surface will reduce the risk of thaw subsidence.Key words: Permafrost Settlement Hazard Index, permafrost, thaw subsidence, thaw settlement, thaw settlement risk in Alaska, climate warming RÉSUMÉ. Depuis les années 1960, les températures du pergélisol de l'Alaska ont augmenté, et de nombreuses incidences du réchauffement climatique sont liées au dégel du pergélisol. Le dégel du pergélisol découlant de l'augmentation des températures du pergélisol donne lieu au tassement dû au dégel et à d'importants dommages à l'infrastructure. L'objectif de cette recherche consiste à cerner les régions de l'Alaska qui sont à risque d'affaissement attribuable au dégel résultant du réchauffement climatique, ainsi qu'à déterminer le risque relatif qui existe dans ces régions. Nous avons mis au point un indice du danger de tassement du pergélisol (PSHI) en nous appuyant sur l'analyse du réchauffement climatique prévu et sur les caractéristiques écologiques qui régularisent les affaissements résultant du dégel. Cette analyse a permis d'obtenir la vérification statistique selon laquelle les zones à pergélisol discontinu sont plus à risque de subir du tassement dû au dégel que les autres régions de l'Alaska. Par ailleurs, l'analyse permet d'estimer les risques futurs de tassement dû au dégel en Alaska en 2050 en s'appuyant sur les augmentations de température projetées par les modèles climatiques publiés. Les résultats indiquent que le risque d'affaissement attribuable au dégel sera accru dans le nord de l'Alaska en 2050, et que l'augmentation la plus grande devrait se produire dans le nord-ouest de l'Alaska. Cependant, dans l'intérieur et le sud-ouest de l'Alaska, la disparition projetée du pergélisol de la surface réduira le risque d'affaissement attribuable au dégel.Mots clés : indice du danger de tassement du pergélisol, pergélisol, affaissement attribuable au dégel, tassement dû au dégel, risque de...