Mechanisms of Persistent High Primary Production During the Growing Season in the Chukchi Sea

Abstract

Persistent high primary production during the growing season in the Chukchi Sea (Arctic Ocean) plays a key role in maintaining an efficient biological carbon pump and diverse Arctic ecosystem. We used a three-dimensional ocean–sea ice–biogeochemical model to simulate monthly averaged net primary production from 1998 to 2015. The results show that the growing season in the Chukchi Sea lasts more than 150 days, with an annual net primary production of 30.85 ± 3.67 Tg C y−1. The mechanisms for maintaining high primary production differ in the southern and northern Chukchi Sea biological hotspots. Nutrient-rich Pacific Winter Water triggers phytoplankton blooms in both hotspots as light intensity increased in spring. After these initial blooms, Bering Summer Water and remnant Pacific Winter Water are the main contributors to nutrient levels and drive primary production during the growing season (May to September) in the southern and northern hotspots, respectively. Nitrate budget estimations in the euphotic zone reveal that after the spring blooms, persistent high primary production in the southern hotspot is mainly fueled by advecting Bering Summer Water through the Bering Strait. In the northern area, vertical mixing plays a critical role in upwelling nutrient-rich Pacific Winter Water from around the Hanna Shoal, where Pacific Winter Water is trapped for a long duration as a result of topography-influenced ocean circulation. Hence, high primary production exists in the northern Chukchi Sea during the summer and early autumn.