Increased amplitude of the North Pacific Gyre Oscillation towards recent: Evidence from tree‐ring‐based reconstruction since 1596.

The North Pacific Gyre Oscillation (NPGO) is the second leading mode of the sea surface height (SSH) of the North Pacific Ocean, playing a key role in causing regional ecosystem changes and large‐scale climate anomalies. However, its long‐term evolution prior to the industrial era is largely unknown. This study provides a reconstruction of the NPGO from 1596 onwards from 19 NPGO‐sensitive tree‐ring chronologies in the Himalayan Mountains, the Rocky Mountains, the Coastal Mountains and the Alaskan Mountain Range, which explained 57.1% of the observed NPGO variations. The selected tree‐ring chronologies showed strong linkages with the NPGO but weak or no correlations with the Pacific Decadal Oscillation (PDO), another leading mode of the North Pacific Ocean. The reconstruction revealed that the NPGO variance and amplitude are not only the strongest towards recent in the instrumental period but also in the reconstruction period. The linkages between the NPGO and El Niño–Southern Oscillation (ENSO) became strengthened towards recent, which may be attributed to the increased occurrence of central Pacific ENSO during the anthropogenic warming period. In addition, close linkages were found between the NPGO and the multidecadal Pacific variability (MPV), the North Atlantic Oscillation (NAO), the Atlantic Multidecadal Oscillation (AMO) at the interannual and multidecadal scales, indicative of strong teleconnections between the ocean–atmosphere modes of the Pacific and Atlantic. [ABSTRACT FROM AUTHOR]