Cross-Mean Flow Spreading of North Pacific Central Mode Water: Property Transport by Mesoscale Eddies

North Pacific Central Mode Water (CMW) is formed in the deep wintertime mixed layer near the northern edge of the subtropical gyre and subducted into the permanent pycnocline. While its spreading from the formation region had been considered to be generally in line with the mean gyre circulation, systematic deviation of the CMW distribution from the mean circulation pathway was suggested by recent analysis based on pre-Argo climatologial data and synoptic hydrographic section data. We examine the relation between locations of low potential vorticity signature of CMW from individual Argo profile data and the mean geostrophic streamlines in detail. It is demonstrated that CMW spreads across the mean flow, towards the gyre center or higher acceleration potential on isopycnals. With the aid of eddy-resolving ocean general circulation model simulation, we argue that the cross-mean flow spreading of CMW is due to southward/westward movement of mesoscale eddies trapping CMW. It is suggested that mesoscale eddies have significant effect on property distribution in the permanent pycnocline.