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Abstract This study investigates variability of the South Pacific western subtropical mode water (SPWSTMW), its physical processes, and relationship with El Niño‐Southern Oscillation (ENSO), using a gridded Argo data product from January 2004 to September 2019. On seasonal timescale, the SPWSTMW volume shows a significant variability, which involves three periods: the formation period (June–October), the isolation period (November–February), and the dissipation period (March–May). This seasonal variability is related to seasonal fluctuation of the mixed layer depth. During the Argo period from 2004 to 2019, interannual variability of the SPWSTMW volume is tightly linked to the ENSO, increasing during El Niño periods and decreasing during La Niña periods. Further analyses indicate that ENSO‐related anomalous winds are primarily responsible for interannual variability of the SPWSTMW volume. The anomalous winds first influence the surface heat flux through evaporation and then the mixed layer depth through convection, leaving an imprint of ENSO on the SPWSTMW. This study also shows that the SPWSTMW responds differently to the central Pacific (CP) El Niño and eastern Pacific (EP) El Niño.
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An Anti‐Phase Relationship Between the Subtropical Underwater and Eastern Subtropical Mode Water in the South Pacific During 2004–2020
Abstract Using the Roemmich‐Gilson Argo data set, this study investigates variability of the Subtropical Underwater (STUW) and eastern Subtropical Mode Water (ESTMW) in the South Pacific during 2004–2020. The STUW volume decreased during 2004–2013 and increased during 2013–2020, while the volume of the ESTMW shows the opposite phase. On interannual time scales, there is also a significant negative correlation in volume between the STUW and ESTMW. This anti‐phase relationship is attributed to changes in their volumetric subduction rates, which are in turn closely related to variability in the mixed layer depth (MLD). ENSO directly contributes to variability of the subduction rates by modifying the MLD. Equatorward propagation of spiciness anomalies is identified along isopycnal surfaces of the STUW and ESTMW cores. These spiciness anomalies in the downstream region are correlated with changes in volume of both water masses, and significant spiciness anomalies can reach the tropical Pacific.
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- PAR ID:
- 10362999
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 2
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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