Phytoplankton community composition and molecular physiology in Arctic glacierized marine regions
Creators: White, Patrick
Publisher: name: University of Alberta Library
Year: 2024

<p>Climate change has resulted in the rapid loss of glacial ice mass in Arctic regions with consequences for recipient ocean waters. Recent work in high-latitude regions across the globe has established that glaciers can provide polar phytoplankton with essential nutrients either directly via the glacial meltwater itself (e.g., iron, manganese, silica) or indirectly, in the case of glaciers that terminate directly into the ocean (i.e., tidewater or marine-terminating glaciers), via meltwater-induced upwelling of deeper marine waters enriched in nitrate, phosphate and silica. The delivery of these bio-essential nutrients to the surface ocean likely enhances phytoplankton production at the base of the marine food web with positive effects for higher tropic levels (e.g., zooplankton, fish, marine mammals). Yet, while many studies have described increases in chlorophyll a and essential nutrients near tidewater glaciers, there has yet to be a systematic investigation into phytoplankton community composition and physiology across multiple tidewater glaciers and non-glacierized sites. Furthermore, it has yet to be conclusively shown which nutrient delivery mechanisms (upwelling or direct delivery) are most important for phytoplankton in regions impacted by glaciers at different stages of retreat. In the summer of 2021 in the Canadian Arctic Archipelago, we collected observations and samples from marine regions impacted by tidewater glaciers, and combined these with an experimental incubation to assess phytoplankton activity in response to real and simulated tidewater glacier activity. Using 16S chloroplast rRNA gene amplicon sequencing, we found that larger phytoplankton, like diatoms, were more abundant at sites with tidewater glaciers than at sites without tidewater glaciers. Additionally, measurements of Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) protein were higher at a select tidewater glacier site where surface ocean macronutrient concentrations were also high, suggesting increases in potential carbon fixation near tidewater glaciers due to deep seawater entrainment and upwelling. In contrast, marine regions without glaciers had a higher abundance of smaller phytoplankton with the potential to be to be mixotrophic, suggesting flexible nutritional strategies are favored in these nutrient-poor environments. Our experimental work confirmed that macronutrients, particularly nitrate, are key in enabling higher phytoplankton biomass proximate to tidewater glaciers. Communities amended with macronutrient additions mimicking upwelling of deep seawater observed the largest increases in chlorophyll a over the course of a week-long incubation. Metaproteomic measurements from our incubations reveal that diatoms in simulated upwelling treatments exhibited shifts in their molecular physiology associated with increases in growth, including greater investment in ribosomal protein, and increased expression of proteins associated with nitrogen metabolism and carbon fixation. Taken together, these findings indicate that upwelling driven by tidewater glaciers has important implications for phytoplankton community composition and molecular physiology, and that the retreat of tidewater glaciers from the ocean as a result of climate change may pose consequences for the base of Arctic marine food webs.</p>