An under‑ice bloom of mixotrophic haptophytes in low nutrient and freshwater‑influenced Arctic waters

• Published in: Scientific Reports
• Main Authors: Søgaard, Dorte, Sorrell, Brian Keith, Sejr, Mikael Kristian, Andersen, Per, Rysgaard, Søren, Hansen, Per Juel, Skyttä, Annaliina, Lemcke, Signe, Lund-Hansen, Lars Chresten
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2021
• Subjects: Arctic; Arctic Ocean; Sea ice
• Online Access: https://pure.au.dk/portal/en/publications/5199bc99-f85f-4670-a7db-174dc127ad75; https://doi.org/10.1038/s41598-021-82413-y

The pelagic spring bloom is essential for Arctic marine food webs, and a crucial driver of carbon transport to the ocean depths. A critical challenge is understanding its timing and magnitude, to predict its changes in coming decades. Spring bloom onset is typically light-limited, beginning when irradiance increases or during ice breakup. Here we report an acute 9-day under-ice algal bloom in nutrient-poor, freshwater-influenced water under 1-m thick sea ice. It was dominated by mixotrophic brackish water haptophytes (Chrysochromulina/ Prymnesium) that produced 5.7 g C m −2 new production. This estimate represents about half the annual pelagic production, occurring below sea ice with a large contribution from the mixotrophic algae bloom. The freshwater-influenced, nutrient-dilute and low light environment combined with mixotrophic community dominance implies that phagotrophy played a critical role in the under-ice bloom. We argue that such blooms dominated by potentially toxic mixotrophic algae might become more common and widespread in the future Arctic Ocean.