Decadal variability of temperature at a depth of 400 meters in the North Pacific Ocean

Abstract

The gyre‐scale structure and evolution of decadal ocean thermocline variability in the North Pacific is described by analyzing historical temperature data at a depth of 400 meters. Decadal thermocline anomalies are characterized by a distinct see‐saw pattern in the midlatitudes and subtropics that appears to circulate coherently in the North Pacific basin, with a period on the order of 20 years. There are coherent spatial and temporal relationships between temperature anomalies around the subtropical gyre, with phase differences at depth and at the sea surface, suggesting that thermocline variability evolves independently of local SST anomalies. In the subtropics, subsurface anomalies can be seen to propagate all the way across the basin and thereby lead SST anomalies, providing a possible phase transition mechanism for SST. The basinwide anomaly pathways suggest a clockwise advection of subsurface temperature anomalies around the subtropical gyre, an active role played by the mean geostrophic flow in decadal variability.