[P002] Poster

1:00 PM - 1:50 PM JST(4:00 AM - 4:50 AM UTC)

[P01-042] Impact of Marine Heatwaves on Ocean-Atmosphere CO2 Fluctuations

○Pierre Simiganoschi¹ (1. Tohoku University (Japan))

Keywords:

Ocean biogeochemistry,Climate change,Sea surface temperature,Carbon cycle,Ocean-atmosphere interaction

Marine heatwaves (MHWs) are increasing in frequency, intensity, and duration under anthropogenic climate change, yet their impact on ocean–atmosphere CO2 exchange remains poorly quantified globally. Ocean warming reduces CO2 solubility (thermal effect), while biological and circulation processes (non-thermal effects) partially counteract this response, but no study has quantified compensation efficiency specifically during MHW events across the global ocean. This study investigates the thermal versus non-thermal compensation relationship during MHWs using daily-resolution data spanning 1982–2023. Daily sea–air CO2 flux from the Jena CarboScope product is decomposed into thermal and non-thermal components on a 2° × 2° grid, both detrended to remove long-term anthropogenic CO2 uptake. MHWs are detected from detrended NOAA OISST v2 sea surface temperatures using a 95th percentile threshold relative to a 1982–2011 climatology, with a minimum duration of five days. Event-mean thermal and non-thermal flux anomalies are computed per pixel, and ordinary least-squares regression yields a compensation slope at each grid cell, with effective degrees of freedom corrected via block-bootstrapping. The analysis is stratified by season, event intensity, and duration. The global mean compensation slope is −0.83, indicating non-thermal processes offset approximately 83% of thermally driven outgassing during MHWs, with incomplete compensation at 79% of ocean pixels. The equatorial Pacific is the sole major region of overcompensation, driven by upwelling suppression. Winter MHWs show the weakest compensation (mean slope −0.79) compared to spring and summer (−0.86), potentially related to weak biological production. Most notably, compensation efficiency degrades from short events (−0.85) to long events (−0.74), with 58.5% of pixels showing worsening compensation as events persist, concentrated in Northern Hemisphere subtropics to midlatitudes, suggesting prolonged stratification exhausts biological capacity to offset thermal outgassing. These results represent conservative estimates of actual compensation deficit, as background warming increases absolute thermal forcing beyond what anomaly-based detection captures. The 2° × 2° resolution may not fully resolve coastal upwelling dynamics, and 70% variance explained by the flux decomposition leaves residual terms unaccounted for. This study provides the first global, pixel-level quantification of thermal–non-thermal compensation efficiency during MHWs and its duration dependence. Systematic degradation of compensation with MHW persistence, combined with projected increases in MHW duration, implies that the ocean's capacity to buffer CO2 outgassing during extreme warming events will weaken in coming decades, particularly in midlatitude regions serving as major anthropogenic CO2 sinks.