Variability of size-fractionated chlorophyll a in the high-latitude Arctic Ocean in summer 2020

• Main Authors: Ting, Cai, Qiang, Hao, Youcheng, Bai, Musheng, Lan, Jianfeng, He, Jianfang, Chen
• Format: Article in Journal/Newspaper
• Language: English
• Published: Polar Research Institute of China - PRIC 2022
• Subjects: Fauna; Arctic; Arctic Ocean; Canada; Advances in Polar Science; canada basin; Phytoplankton; Polar Science; Sea ice; ice covered areas
• Online Access: http://library.arcticportal.org/2793/; http://library.arcticportal.org/2793/1/A2203006.pdf

The size structure of phytoplankton has considerable effects on the energy flow and nutrient cycling in the marine ecosystem, and thus is important to marine food web and biological pump. However, its dynamics in the high-latitude Arctic Ocean, particularly ice-covered areas, remain poorly understood. We investigated size-fractionated chlorophyll a (Chl a) and related environmental parameters in the highly ice-covered Arctic Ocean during the summer of 2020, and analyzed the relationship between Chl a distribution and water mass through cluster analysis. Results showed that inorganic nutrients were typically depleted in the upper layer of the Canada Basin region, and that phytoplankton biomass was extremely low (mean= 0.05 ± 0.18 mg·m−3) in the near-surface layer (upper 25 m). More than 80% of Chl a values were <0.1 mg·m−3 in the water column (0–200 m), but high values appeared at the ice edge or in corresponding ice areas on the shelf. Additionally, the mean contribution of both nanoplankton (2–20 μm) (41%) and picoplankton (<2 μm) (40%) was significantly higher than that of microplankton (20–200 μm) (19%). Notably, the typical subsurface chlorophyll maximum (0.1 mg·m−3) was found north of 80°N, where the concentration of sea ice reached approximately 100%. The Chl a profile results showed that the deep chlorophyll maximum of total-, micro-, nano-, and picoplankton was located at depth of 40, 39, 41, and 38 m, respectively, indicating that nutrients are the primary factor limiting phytoplankton growth in the ice-covered Arctic Ocean during summer. These phenomena suggest that, despite the previous literatures pointing to significant light limitation under the Arctic ice, the primary limiting factor for phytoplankton in summer is still nutrient.