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.