Response of under-ice phytoplankton populations to light exposure during the Arctic spring bloom


Marine phytoplankton are responsible for approximately 50% of global primary production and are at the base of marine food webs. In the Arctic Ocean, one important factor controlling phytoplankton productivity is sunlight, as sea-ice and snow cover limits light penetration in the water column. Over the last three decades, the extent of the seasonal sea-ice and snow cover has decreased in response to climate change, resulting in changes in the dynamics of light penetration. These changes may cause important fluctuations of the spring and summer phytoplankton blooms dynamics with unknown effects on Arctic marine food webs and carbon cycle. In order to better understand the effects of light on Arctic nano- and pico-phytoplankton growth, a series of six incubation experiments were performed between May and July 2016 during an ice camp campaign ( in Baffin Island (67°28.78 N, 63°47,37 W). Sea-ice coverage at the ice camp was about 90% until mid-June and decreased rapidly down to approximately 10% at the end of July. The experiments were performed with surface sea-water collected through a permanent hole in the sea-ice and incubated in the laboratory for 7 to 8 days at 4°C in the dark (control) and in the light at 100 µE m-2 s-1. Phytoplankton growth was analyzed by flow cytometry. We observed a rapid increase in pico- and nano-phytoplankton cell concentration, up to 15-fold with light for the two experiments performed before the onset of the spring phytoplankton bloom. The four other experiments performed later in the season showed a clear decrease in cell concentration demonstrating that light was clearly not limiting any more. We are currently determining how the structure of community changed during these incubations by 18S rRNA metabarcoding.

ICOP meeting 2017