1Laboratoire d'Océanographie et du Climat: Expérimentation et Approches Numériques (LOCEAN), UPMC, CNRS, UMR7159, Paris, France
2Laboratory of Marine Ecosystem and Biogeochemistry, Second Institute of Oceanography, SOA, PRC, Hangzhou 310012, China
3Department of Oceanography, Pusan National University, 30, Jangjeon-dong, Busan 609–735, South Korea
4School of Oceanography, University of Washington, 373 Marine Science Building, P.O. Box 357940, Seattle, WA, USA
5Laboratoire des Sciences du Climat et de l'Environnement (LSCE), IPSL, CNRS/CEA/UVSQ, 91198 Gif-sur-Yvette, France
6LEGOS/UMR5566/CNRS, 18 Avenue Edouard Belin, 31401 Toulouse Cedex 4, France
Abstract. A large part of the Pacific Arctic basin experiences ice-free conditions in summer as a result of sea ice cover steadily decreasing over the last decades. To evaluate the impact of sea ice retreat on the marine ecosystem, phytoplankton in situ observations were acquired over the Chukchi shelf and the Canadian basin in 2008, a year of high melting. Pigment analyses and taxonomy enumerations were used to characterise the distribution of main phytoplanktonic groups. Marked spatial variability of the phytoplankton distribution was observed in summer 2008. Comparison of eight phytoplankton functional groups and 3 size-classes (pico-, nano- and micro-phytoplankton) also showed significant differences in abundance, biomass and distribution between summer of low ice cover (2008) and heavy ice summer (1994). Environmental parameters such as freshening, stratification, light and nutrient availability are discussed as possible causes to explain the observed differences in phytoplankton community structure between 1994 and 2008.