Interannual Variability of Lower Circumpolar Deep Water Transport in the North Pacific Influenced by Surface Wind Forcing

The deep-ocean circulation in the North Pacific plays a crucial role in redistributing ocean heat and carbon storage, but understanding its low-frequency variability is hindered by the complexity of its pathways, particularly regarding the relationships between different branches and the underlying dynamics. This study investigates the interannual variability of lower circumpolar deep water (LCDW) transport on a basin-wide scale using the Estimating the Circulation and Climate of the Ocean Version 4 Release 4 (ECCO v4r4) data set. Our findings indicate that interannual variations in LCDW transport in the North Pacific are primarily governed by barotropic processes. The first empirical orthogonal function (EOF) mode of interannual variability is characterized by a cyclonic circulation in the northwestern Pacific, while the second mode exhibits a basin-wide cyclonic structure. Utilizing barotropic vorticity equation and regression analysis, it is further demonstrated that EOF1 and EOF2 modes are associated with the spatial pattern of a wind stress curl, which are linked to the El Niño-Southern Oscillation (ENSO) and the Victoria mode, respectively. Thus, despite the lack of direct atmospheric coupling with the deep ocean, the wind-driven ocean bottom pressure anomalies modulate the interannual variability of LCDW transport.