Unexpected ice-edge diatom blooms occur as thin phytoplankton layers in Barrow Canyon, Chukchi Sea

Observations of environmental variables and photosynthetic pigments were carried out in and around Barrow Canyon, northeast Chukchi Sea, from 2008 to 2016. Barrow Canyon and its western flank are occupied by relatively cold waters (T < 0 °C) with high nutrient and chlorophyll concentrations, whereas the eastern flank is occupied by relatively warm waters (T > 0 °C) with low nutrient and chlorophyll concentrations. The variable dominance of these cold and warm waters appears to be the main driving factor of regional differences in phytoplankton distribution in and around Barrow Canyon. In 2014, an ice-edge phytoplankton bloom was detected in the nutrient-rich cold waters of the canyon, and pigment biomarkers indicated that diatoms were the major contributors. This diatom bloom occurred under the pycnocline, and the diatom cells were aggregated mainly in a thin (3-5 m thick) layer that may have been regulated by the combined effects of the euphotic depth and the nitracline. This is one of the few documented instances of diatoms blooms occurring as thin phytoplankton layers in the high-latitude Arctic Ocean to date.