Influence of North Pacific subtropical mode water variability on the surface mixed layer through the heaving of the upper thermocline on decadal timescales

Abstract Decadal variability of the North Pacific subtropical mode water (STMW) and its influence on upper thermocline mixed layer are examined in a four-dimensional variational ocean re-analysis for Western over 30 years (FORA–WNP30). The STMW that forms south Kuroshio Extension becomes thick/cold thin/warm decadal timescales. These variations subducted advected to south, where thick (thin) causes heave up (down) above STMW, producing cold (warm) temperature anomalies at subsurface depths, with especially large depths seasonal thermocline. Temperature also appear from March November, except September. have same sign as although they due not reemergence surface but heaving In FORA–WNP30, because formation owes much increment introduced by data assimilation, mechanism remains unclear. A heat budget analysis layer, however, suggests importance entrainment and/or vertical diffusion base conveying layer. affects depth. shoals (deepens) thermocline, enhancing (weakening) stratification below thus hindering (favoring) development July