© Inter-Research 2016. We examined phytoplankton biomass and community composition (mostly based on pigments) as well as cell viability with the cell digestion assay in surface waters of the Canadian Beaufort Sea during the spring-summer transition. Our aim was to understand phytoplankton responses to the large environmental changes (irradiance, temperature and nutrients) occurring during this period. Two categories of stations were visited in May and June 2008: ice-covered (IC), exposed to low irradiances, and open-water (OW), exposed to higher irradiances. We observed a large variation in the percentage of living cells (%LC) relative to the total community. No relationship was found between %LC and nitrate concentration (the nutrient potentially limiting in this environment). The in situ irradiance influenced the status of the cells at OW stations. Mean surface mixed layer irradiances >600 μmol photons m-2 s-1 were associated with low cell viability and a decline in photosynthetic performance (Fv/Fm). For IC stations, %LC declined at temperatures above 0°C, whereas for OW stations, it increased, suggesting that ice melting resulted in the release into surface waters of unhealthy cells from the bottom ice in one case, and that seasonal warming favored the communities present in open waters. A chlorophyll degradation pigment tentatively identified as pyropheophorbide a-'like' showed a significant negative relationship between its concentration (relative to chlorophyll a) and the %LC and Fv/Fm. Our results suggest that the melting conditions influence the distribution of this pigment and that it may be useful as a marker for low cell viability of ice algae being released into surface waters.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: This work is a contribution to the International Polar Year-Circumpolar Flaw Lead system study (IPY-CFL 2008), supported through grants from the Canadian IPY Federal Program office and the Natural Sciences and Engineering Research Council (NSERC) of Canada. E.A.-F. received post-graduate scholarships from the Institut des sciences de la mer de Rimouski (ISMER) and Universite du Quebec a Rimouski and a stipend from Quebec-Ocean (through a grant from the Fonds de recherche du Quebec Nature et technologies). NSERC discovery grants to S.R. and to M.G. also helped to support this work. We thank the officers and crew of the CCGS 'Amundsen' for logistical support; and M. Palmer, J. Salcedo, M. Lionard, and M. Simard for assistance in the field and/or laboratory. We are grateful to P. Guillot for processing of CTD cast data; J. Gagnon for nutrient analysis; S. Lessard for algal counts and identification; Dr. T. Papakyriakou for providing incident PAR data; and 3 anonymous reviewers for their constructive comments on the manuscript. This is a contribution to the research programs of CFL, ArcticNet, ISMER, and Quebec-Ocean.