Impacts of crude oil on Arctic sea-ice diatoms modified by irradiance

Abstract

Anthropogenic climate change is reducing ice and snow thickness in the Arctic. The loss of summer sea ice has led to increased access to Arctic waters and the development of marine resources, which raises the risk of oil spills. Thinning ice and snow also increases irradiance in the upper ocean which is predicted to increase primary productivity, disfavoring shade-adapted sea-ice algae while benefitting phytoplankton and cryopelagic taxa. Studies have confirmed the lethality of crude oil and its distillates to Arctic phytoplankton; less well-constrained are the sublethal impacts to sea-ice algae in combination with other drivers. This study investigates the combination of two drivers, crude oil exposure and irradiance, on the growth rate and maximum cell concentration of four sea-ice diatoms (Attheya septentrionalis, Fragilariopsis cylindrus, and two strains of Synedropsis hyperborea) isolated from landfast sea ice near Utqiaġvik, Alaska. Crude oil inhibition of growth was complex and dependent on species and irradiance level. A. septentrionalis was generally tolerant to crude oil exposure, but toxicity was enhanced at the highest irradiance. The cryopelagic taxon, F. cylindrus, exhibited strong growth inhibition at TPH concentrations greater than approximately 6 mg L−1. Growth rates of S. hyperborea strains were stimulated at low concentrations of oil at all light levels. A simple numerical model was used to simulate an oil spill under varying snow depths to follow composition of a mock community comprised of these four isolates across a spring season. Results highlight that the reduction of algal biomass accumulation and the community composition change following a crude oil spill are more severe in a simulated low-snow spring, due to the relative sensitivity of F. cylindrus. We show that a brighter Arctic, which is predicted to increase the relative importance of cryopelagic taxa like F. cylindrus, may render the Arctic ecosystem more vulnerable to crude oil spills.