Role of environmental factors on phytoplankton bloom initiation under landfast sea ice in Resolute Passage, Canada

• Published in: Marine ecology. Progress series (Halstenbek) 2014-02, Vol.497, p.39-49
• Main Authors: Mundy, C. J., Gosselin, Michel, Gratton, Yves, Brown, Kristina, Galindo, Virginie, Campbell, Karley, Levasseur, Maurice, Barber, David, Papakyriakou, Tim, Bélanger, Simon
• Format: Article
• Language: English
• ISSN: 0171-8630; 1616-1599
• DOI: 10.3354/meps10587

It has been common practice in scientific studies to assume negligible phytoplankton production when the ocean is ice-covered, due to the strong light attenuation properties of snow, sea ice, and ice algae. Recent observations of massive under-ice blooms in the Arctic challenge this concept and call for a re-evaluation of light conditions prevailing under ice during the melt period. Using hydrographic data collected under landfast ice cover in Resolute Passage, Nunavut, Canada between 9 May and 21 June 2010, we documented the exponential growth phase of a substantial under-ice phytoplankton bloom. Numerous factors appeared to influence bloom initiation: (1) transmitted light increased with the onset of snowmelt and termination of the ice algal bloom; (2) initial phytoplankton growth resulted in the accumulation of biomass below the developing surface melt layer where nutrient concentrations were high and turbulent mixing was relatively low; and (3) melt pond formation rapidly increased light transmission, while spring-tidal energy helped form a surface mixed layer influenced by ice melt—both were believed to influence the final rapid increase in phytoplankton growth. By the end of the study, nitrate+nitrite was depleted in the upper 10 m of the water column and the under-ice bloom had accumulated 508 mg chl a m−2 with a new production estimate of 17.5 g C m−2 over the upper 50 m of the water column. The timing of bloom initiation with melt onset suggests a strong link to climate change where sea ice is both thinning and melting earlier, the implication being an earlier and more ubiquitous phytoplankton bloom in Arctic ice-covered regions.