Modeling the Responses of Phytoplankton Assemblage and Biological Pump Efficiency to Environmental Changes in the Chukchi Borderland, Western Arctic Ocean

• Published in: Journal of geophysical research. Oceans 2024-08, Vol.129 (8), p.n/a
• Main Authors: Luo, Xiaofan, Dong, Chunming, Wei, Hao, Zhao, Wei, Nie, Hongtao
• Format: Article
• Language: English
• Subjects: Advection; Arctic Ocean; Bacillariophyceae; basins; Biological models (mathematics); biological pump efficiency; Biomass; Canada; Carbon; Carbon sinks; Chukchi Borderland; Continental margins; continental shelf; Continental shelves; Deep water; Diatoms; Dominance; Efficiency; Environmental changes; Evolution; geophysics; Growing season; Habitats; Horizontal advection; Marine biology; Marine ecosystems; Marine microorganisms; Mathematical models; model simulation; nitrate concentration; Nitrates; Numerical models; Numerical simulations; Ocean models; Oceans; Oligotrophic waters; Organic carbon; Particulate organic carbon; Phytoplankton; phytoplankton assemblage; Plankton; Primary production; primary productivity; Residence time; Sea ice; Upper ocean
• ISSN: 2169-9275; 2169-9291
• DOI: 10.1029/2023JC020780

The Chukchi Borderland, connecting the Chukchi continental shelf and the Canada Basin, has become a hotspot for studying how ecosystems respond to rapid environmental changes in the Arctic Ocean. Based on a long‐term hindcast simulation during 1998–2015 using a coupled ocean‐sea ice‐biogeochemical model, this study investigates the responses of phytoplankton assemblage and the biological carbon pump efficiency within the upper layers (0–100 m) of the Chukchi Borderland. The nitrate concentration is found to be a crucial factor controlling the total phytoplankton biomass and determining the spatiotemporal variations in the evolution pattern of phytoplankton assemblage. In the shelf break adjacent region, nitrate concentration increased after 2009, boosting phytoplankton biomass with diatoms persistently dominating. In the Canada Basin adjacent region, the westward expansion of the Beaufort Gyre after 2009 extended the influence of oligotrophic water, leading to phytoplankton miniaturization and a shift in phytoplankton assemblage evolution, from a pre‐2009 pattern that non‐diatoms at start were succeeded by diatoms, to a post‐2009 scenario that non‐diatoms dominated throughout the growing season. The biological pump efficiency evidently increased in the shelf break region after 2009, due to heightened biomass and intensified horizontal advection‐induced particulate organic carbon (POC) supply. The western Canada Basin adjacent region presented the reduced primary production and vertical POC flux. However, the deeper nitracline deepened the phytoplankton habitat, shortening POC residence time in the upper layers and enhancing the biological pump efficiency. Plain Language Summary The responses of marine phytoplankton and the biological carbon pump efficiency to rapid changes in the Chukchi Borderland are studied through analyzing a numerical model simulation spanning 1998–2015. In the upper ocean (0–100 m depth), the nitrate concentration is found to be a crucial factor for space‐time variations of the total biomass and the dominance of phytoplankton groups. Over the continental shelf and shelf break, nitrate increased after 2009, promoting the growth of larger‐size phytoplankton (diatoms) and sustaining their dominance throughout most of the growing season. In the region near western Canada Basin, the westward expansion of the Beaufort Gyre (nitrate‐low water) favored the smaller‐size phytoplankton growth. This shift is expected to reduce the quality of eco