Decadal Spiciness Variability in the Subtropical-Tropical Pacific in the CESM2 Large Ensemble

Journal Article · Fri Apr 10 00:00:00 EDT 2026 · Journal of Climate

DOI:https://doi.org/10.1175/JCLI-D-25-0518.1· OSTI ID:3025316

Stockmayer, Vera ^[1]; Schneider, Niklas ^[1]; Stuecker, Malte F. ^[1]; Lübbecke, Joke F. ^[2]

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1. Univ. of Hawaii at Manoa, Honolulu, HI (United States)
2. Univ. of Bremen (Germany)

Tropical Pacific decadal variations impact weather and climate around the world and are also connected to variations in the global warming trend. The mechanisms driving these long-term modulations, particularly the role of subsurface ocean dynamics, are still debated. Here, we investigate the dynamics of spiciness (density-compensated temperature and salinity) anomalies in the tropical and subtropical Pacific, which are hypothesized as a possible driving mechanism of decadal climate variability. Based on the analysis of 100 realizations from the Community Earth System Model Version 2 Large Ensemble (CESM2-LE), we demonstrate a coupling between the subtropics and the equatorial Pacific by propagating spiciness anomalies at decadal time scales. The CESM2-LE simulates spiciness variability along a subduction path from the subtropics to the equator with frequency spectra that show the highest power at low frequencies and a power decay proportional to a −4 slope for frequencies greater than 0.01 cycles per months, corresponding to periods smaller than ∼8.5 years. Signals that originate in the Southern Hemisphere (SH) dominate and arrive with a larger magnitude at the equator compared to spiciness anomalies from the Northern Hemisphere (NH). Spiciness anomalies from the SH have shorter propagation times and are strengthened along their pathway as stochastic wind stress curl forcing generates anomalous baroclinic ocean pressure gradients. These pressure gradients generate spiciness anomalies via anomalous advection across climatological spiciness gradients in the SH. We conclude that the observed spiciness variance at decadal time scales is consistent with a forcing by stochastic wind variations that are low-pass filtered by ocean dynamics.

• Research Organization: Univ. of Hawaii at Manoa, Honolulu, HI (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Biological and Environmental Research (BER). Earth & Environmental Systems Science (EESS)
• Grant/Contract Number: SC0025595
• Other Award/Contract Number: NA22OAR4310616
• OSTI ID: 3025316
• Journal Information: Journal of Climate, Journal Name: Journal of Climate; ISSN 0894-8755; ISSN 1520-0442
• Publisher: American Meteorological Society
• Country of Publication: United States
• Language: English

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54 ENVIRONMENTAL SCIENCES