Journal Article

Extreme Ventilation of the North Pacific Central Mode Water by El Niño During Positive Phase of the Pacific Decadal Oscillation

Zheng, Xiao‐Tong, Liu, Jing, Li, Junliang, Xu, Lixiao, Wang, Keyao

2025

Overview

This study investigates the interannual variability of the North Pacific Central Mode Water (CMW) under the phase relationship of the El Niño–Southern Oscillation (ENSO) and the Pacific Decadal Oscillation (PDO), based on multiple observational data sets. Peaks and troughs of the CMW variability are primarily observed when ENSO and PDO are in phase, but only moderate variation when ENSO and PDO are out of phase. In El Niño spring during positive PDO, extreme CMW ventilation takes place in the central North Pacific (180°–155°W, 30°–40°N), where no local ventilation occurs for other cases. Such extreme CMW ventilation induces stronger temperature anomalies, which persist longer and penetrate deeper. Our results suggest that CMW, representing a long‐term ocean memory, may play a more significant role in tropical‐extratropical interactions than ever expected. Plain Language Summary The North Pacific Central Mode Water (CMW) is a vertically homogeneous thermocline water mass in the central North Pacific, affecting the subtropical gyre's large‐scale circulation and the storage of heat and carbon. Previous studies mainly focus on the CMW variability forced by Pacific Decadal Oscillation (PDO), without considering the relative phase of the El Niño–Southern Oscillation (ENSO). The present study finds that the interannual variability of CMW is significantly related to the ENSO‐PDO phase relationship. For in‐phase conditions, the CMW is strongest in the decay year of El Niño during positive PDO, and the CMW is weakest in the decay year of La Niña during negative PDO. For out‐of‐phase conditions, by contrast, the CMW variation is moderate. After El Niño winter during positive PDO, the strongest surface buoyancy loss sharply deepens the mixed layer and injects well‐mixed surface water into the thermocline in the central North Pacific (180°–155°W, 30°–40°N), where no such “ventilation” occurs for other cases. The extreme CMW ventilation favors the transport of anthropogenic heat, carbon, oxygen & nutrient rich waters into the deep ocean, important for the climate system. Key Points Abnormal ventilation of the North Pacific Central Mode Water (CMW) occurs east of the Dateline after El Niño winter during positive Pacific Decadal Oscillation (PDO) The CMW is strongest (weakest) in the decay year of El Niño (La Niña) when accompanied by a positive (negative) PDO When ENSO and PDO are in phase, the CMW temperature anomalies are stronger, persist longer and penetrate deeper

• Publisher: John Wiley & Sons, Inc,Wiley
• Subject: Aleutian low / Anthropogenic factors / Carbon / Climate system / Decay / El Nino / El Nino phenomena / El Nino-Southern Oscillation event / El Niño‐Southern Oscillation / Interannual variability / La Nina / Mixed layer / Nutrient transport / Oceans / ocean‐atmosphere interaction / Pacific Decadal Oscillation / Southern Oscillation / Subtropical circulation / subtropical mode water / Surface water / Temperature anomalies / Thermocline / Troughs / Variability / Ventilation / Water masses