Arctic phytoplankton spring bloom diversity across the marginal ice zone in Baffin Bay

Abstract

Phytoplankton under-ice blooms have been recently recognized as an important Arctic phenomenon for global primary production and biogeochemical cycling. Drastic sea-ice decline enables the development of early blooms, sometimes hundreds of kilometers beneath the pack ice. Baffin Bay is a semi-enclosed sea where Arctic and North Atlantic water masses interact. In the present work, we investigated the phytoplankton community structure across the marginal ice zone between the ice-free, Atlantic-influenced, east and the ice-covered, Arctic-influenced, west Baffin Bay using 18S rRNA high-throughput amplicon sequencing, and numerous environmental and biological data collected in the scope of the Green Edge project. Sampling was performed during June-July 2016 in a total of 16 stations with around 6 depths each. Stations were clustered into ″Under Ice″ (UI), ″Marginal Ice Zone″ (MIZ), and ″Open Water″ (OW) on the basis of its sea-ice cover upon sampling. The UI sector was characterized by a shallow nitracline, high pico-phytoplankton abundance, and a shared dominance between Micromonas and Phaeocystis in the 0.2-3 μm size fraction. Several amplicon sequence variants (ASVs) were flagged as indicators for the UI+MIZ sector group, including known ice-associated taxa such as the diatoms Melosira arctica and Pseudo-nitzschia seriata, but also specific ASVs assigned to the green alga Micromonas polaris, the cryptophyte Falcomonas daucoides, and a Pterosperma sp. rarely seen in other metabarcoding datasets, including from the Arctic. The OW sector harbored a community adapted to a nutrient-depleted/high light environment, with a significant contribution of the haptophyte Phaeocystis pouchetii and big centric diatoms, including several Thalassiosira species.

Temporal dynamics and biogeography of sympagic and planktonic autotrophic microbial eukaryotes during the under-ice Arctic bloom

“…Under high-light and low-nutrient conditions, such as those found during the ice-melt stage (Oziel et al 2019), blooming Phaeocystis species tend to form polysaccharide-based mucilaginous colonies that can be millimetres in diameter and serve the functions of energy storage and defence against grazers (Nejstgaard et al 2007; Schoemann et al 2005). The P. pouchetii ASV obtained during the Green Edge oceanographic campaign was flagged as an indicator of the marginal ice zone and open water sectors within the > 20 µ m size fraction, corroborating our results (Ribeiro et al 2022).…”

“…Similar to other time series studies under landfast ice (Mundy et al 2014), light availability and upper water column stabilization were the key factors triggering the under-ice bloom during the Green Edge campaign (Oziel et al 2019). A similar trend was also observed during a campaign in the marginal ice zone (Randelhoff et al 2019;Ribeiro et al 2022).…”

“…Among nanoplanktonic diatoms, a pennate-centric-pennate succession was observed in the surface water layer, where the relative abundance of centric diatoms represented by the genus Thalassiosira increased during stage II and receded during stage III (Figure 3). The succession observed at the ice camp was however not observed in under-ice samples collected during the Green Edge oceanographic campaign (Ribeiro et al 2022), which occurred simultaneously offshore throughout the central Baffin Bay (Bruyant et al 2022), during which the UIB community was co-dominated by centric and pennate diatoms, while centric diatoms were associated to development of the bloom in the marginal ice zone and open waters (Lafond et al 2019; Ribeiro et al 2022). These varying temporal dynamics within Baffin Bay highlight the differences in bloom phenology linked to the heterogeneity of Arctic outflow shelves (Michel et al 2015).…”