The Impact of Recent Climate Change on the Seasonal Phenology of Arctic Ocean Phytoplankton Blooms

In the recent past, the Arctic Ocean (AO) has undergone extreme climate variations as17 sociated with extensive seasonal sea-ice loss, particularly the severe loss event in 2007, 18 2012, and 2019. Additionally, Arctic warming has caused both earlier sea-ice melting in 19 spring and delayed sea-ice formation in the fall, resulting in direct consequences for the 20 AO phytoplankton blooms phenology. In this study we gain mechanistic understanding 21 of the processes controlling the changing dynamics of AO phytoplankton bloom using 22 an ocean biogeochemistry model that is based on physical ocean and sea ice state esti23 mates from the Estimating the Circulation and Climate of the Ocean (ECCO) Project 24 and on simulated marine microbes from the Massachusetts Institute of Technology (MIT) 25 Darwin Project. We focus on the 2006{2013 period which includes the 2007 and 2012 26 drastic sea-ice loss events. Our simulations show that early sea-ice melt onset in 2007 27 and 2012 triggered phytoplankton blooms in the Barents, East Siberian, and Chukchi 28 Seas approximately 1 month earlier than during other simulated years. The 2007 phy29 toplankton bloom is dissipated earlier than during other years due to the earlier deple30 tion of nutrients in the euphotic zone. Our model also shows that the delayed formation 31 of sea ice during fall triggers second fall blooms in the eastern (Barents and Kara Seas) 32 and western AO (Chukchi, Beaufort Seas, Canadian Archipelago, and Ba n Bay), match33 ing previous observational studies. Our model also captures the northward migration of 34 the spring phytoplankton bloom following the retreating sea-ice edge.

近年间，北冰洋（Arctic Ocean, AO）经历了与大范围季节性海冰消退相关的极端气候波动，其中尤以2007年、2012年及2019年的严重海冰消融事件为甚。此外，北极变暖导致春季海冰消融提前、秋季海冰形成延后，直接影响了北冰洋浮游植物水华的物候特征。本研究依托海洋生物地球化学模型，对调控北冰洋浮游植物水华动态变化的过程开展机制性解析。该模型的数据基础包括：来自海洋环流与气候估算（Estimating the Circulation and Climate of the Ocean, ECCO）计划的物理海洋与海冰状态估算结果，以及麻省理工学院（Massachusetts Institute of Technology, MIT）达尔文项目（Darwin Project）模拟的海洋微生物参数。研究聚焦2006至2013年这一时间段，其中涵盖了2007年与2012年的极端海冰消融事件。模拟结果显示，2007年与2012年提前的海冰消融起始时间，使得巴伦支海、东西伯利亚海与楚科奇海的浮游植物水华较其他模拟年份提前约1个月发生。2007年的浮游植物水华较其他年份更早消散，这是由于真光层内的营养盐提前被耗尽。本模型同时发现，秋季海冰形成延后会触发北冰洋东部（巴伦支海与喀拉海）及西部（楚科奇海、波弗特海、加拿大北极群岛与巴芬湾）的秋季二次水华，这与此前的观测研究结果一致。此外，本模型还复现了春季浮游植物水华随海冰边缘退缩向北迁移的现象。