Transport Barriers and the Retention of Calanus finmarchicus on the Lofoten Shelf in Early Spring

• Published in: Journal of Geophysical Research: Oceans
• Main Authors: Dong, Huizi, Zhou, Meng, Hu, Ziyuan, Zhang, Zhaoru, Zhong, Yisen, Basedow, Sunnje L., Smith, Walker O., Jr.
• Format: Report
• Language: English
• Published: AMER GEOPHYSICAL UNION 2021
• Subjects: transport barrier; Calanus finmarchicus; Lagrangian coherent structures; remote sensing; energy conversion rate; Oceanography; SEASONAL VERTICAL MIGRATION; MESOSCALE EDDY FIELD; NORTH-ATLANTIC; BAROCLINIC INSTABILITY; SURFACE TRANSPORT; MARINE COPEPOD; OCEAN; RECRUITMENT; PATTERNS; Lofoten; North Atlantic
• Online Access: http://ir.qdio.ac.cn/handle/337002/176199; https://doi.org/10.1029/2021JC017408

Large aggregations of the copepod Calanus finmarchicus occur each spring in the shelf-slope-oceanic regions off the Lofoten-Vesteralen Islands where productive fisheries have traditionally supported local economies. The retention and off-shelf transport of populations of C. finmarchicus populations were studied by analyzing ocean color remote sensing, satellite altimetry data, and Lagrangian Coherent Structures (LCS) between 2010 and 2019. Our analysis revealed the existence of a transport barrier reoccurring at the shelf break that retains C. finmarchicus on the shelf for 30-70 days in the spring when C. finmarchicus were seasonally ascending to the surface layer. The analysis of baroclinic and barotropic energy conversions indicated that the topographically steered Norwegian Atlantic Current is the primary mechanism in the formation of the transport barrier, which restricts exchanges of C. finmarchicus populations between shelf and oceanic waters. In the mid- to late April, an increase in baroclinicity leads to an increase in mesoscale eddies generated on the shelf break near Lofoten-Vesteralen Islands, breaking down transport barriers and causing off-shelf transport of C. finmarchicus. The transport barrier predictably reoccurs in early spring which supports the entrapment of C. finmarchicus in the shelf region.