Yuanqi Wang: State Key Laboratory of Estuarine and Coastal Research, School of Marine Sciences, and Institute of Eco-Chongming, East China Normal University, Shanghai, China. ORCID
Zhixuan Feng: State Key Laboratory of Estuarine and Coastal Research, School of Marine Sciences, and Institute of Eco-Chongming, East China Normal University, Shanghai, China. zxfeng@sklec.ecnu.edu.cn. ORCID
Peigen Lin: School of Oceanography, Shanghai Jiao Tong University, Shanghai, China.
Hongjun Song: Observation and Research Station of Bohai Strait Eco-Corridor, First Institute of Oceanography, Ministry of Natural Resources, Qingdao, China. ORCID
Jicai Zhang: State Key Laboratory of Estuarine and Coastal Research, School of Marine Sciences, and Institute of Eco-Chongming, East China Normal University, Shanghai, China.
Hui Wu: State Key Laboratory of Estuarine and Coastal Research, School of Marine Sciences, and Institute of Eco-Chongming, East China Normal University, Shanghai, China.
Haiyan Jin: State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China.
Jianfang Chen: State Key Laboratory of Satellite Ocean Environment Dynamics, Second Institute of Oceanography, Ministry of Natural Resources, Hangzhou, China.
Di Qi: Polar and Marine Research Institute, Jimei University, Xiamen, China.
Jacqueline M Grebmeier: Chesapeake Biological Laboratory, University of Maryland Center for Environmental Science, Solomons, MD, USA.
The Arctic Ocean has experienced significant sea ice loss over recent decades, shifting towards a thinner and more mobile seasonal ice regime. However, the impacts of these transformations on the upper ocean dynamics of the biologically productive Pacific Arctic continental shelves remain underexplored. Here, we quantified the summer upper mixed layer depth and analyzed its interannual to decadal evolution with sea ice and atmospheric forcing, using hydrographic observations and model reanalysis from 1996 to 2021. Before 2006, a shoaling summer mixed layer was associated with sea ice loss and surface warming. After 2007, however, the upper mixed layer reversed to a generally deepening trend due to markedly lengthened open water duration, enhanced wind-induced mixing, and reduced ice meltwater input. Our findings reveal a shift in the primary drivers of upper ocean dynamics, with surface buoyancy flux dominant initially, followed by a shift to wind forcing despite continued sea ice decline. These changes in upper ocean structure and forcing mechanisms may have substantial implications for the marine ecosystem, potentially contributing to unusual fall phytoplankton blooms and intensified ocean acidification observed in the past decade.
