# Phytoplankton fatty acid proportions in the Canadian Arctic are strongly affected by temperature, salinity, and phosphate in late summer

## TL;DR

This study shows that temperature, salinity, and phosphate levels strongly influence the fatty acid composition of phytoplankton in the Canadian Arctic during late summer.

## Contribution

The study identifies specific physicochemical factors affecting phytoplankton fatty acid proportions in the Canadian Arctic, highlighting regional and seasonal variability.

## Key findings

- Monounsaturated fatty acid (MUFA) proportions varied significantly between deep and shallow water regions in 2019.
- Polyunsaturated fatty acids (PUFA) and Σω3% were higher in Baffin Bay compared to lower salinity regions in 2021.
- DHA/EPA ratios negatively correlated with phosphate levels across both years and water depths.

## Abstract

Phytoplankton form the base of the food web and act as the main source of both energy, and ω3 essential fatty acids in marine ecosystems. In the Arctic, the effects of climate change are exacerbated compared to lower latitudes. Expected shifts in phytoplankton growth due to climate change in the Arctic are dependent on water physicochemistry, especially temperature, salinity, and nutrient concentrations. The goal of this investigation was to, 1) assess which Canadian Arctic (CA) regions were significantly different based on biomarkers of phytoplankton condition and community assemblage, and 2) identify which hydrographic properties and dissolved inorganic nutrient concentrations correlated with those biomarkers. Phytoplankton samples were collected from the CA in 2019 (July-September) and 2021 (August-October). CA regions were clustered based on similar hydrographic properties, and then lipid and FA profiles were compared. In 2019, there was variation in monounsaturated fatty acid (MUFA) proportions: cluster groups in very deep water, with higher temperature and lower oxygen saturation (Davis Strait stations) were significantly lower compared to cluster groups defined by lower salinity and light transmission (East Barrow Strait and Lancaster Sound stations) in both surface (p = 0.001) and sub-surface chlorophyll maximum waters (SCM)(p = 0.008). In 2021, a year with more expansive coverage of the CA compared to 2019, Σω3% and polyunsaturated fatty acids (PUFA) were significantly higher in cluster groups containing Baffin Bay stations compared to the clusters defined by lower salinity (Beaufort Sea and the Canadian Arctic Archipelago stations) in both surface (p < 0.001) and SCM waters (p < 0.001). Across both years and both SCM and surface waters, DHA/EPA (two ω3 essential fatty acids) negatively correlated with phosphate. Overall, FA proportions in the CA are strongly affected by physiochemical conditions in late summer with MUFA responding mainly to physical changes, while PUFA responded heavily to phosphate changes.