Net primary productivity in the Gulf of California: spatiotemporal patterns and drivers in a warming climate (2003–2024)

Abstract. The Gulf of California is a highly productive and diverse ecosystem that supports nearly 70 % of Mexico's fisheries. Despite its ecological and socio-economic importance, basin-scale analysis of seasonal and interannual variability in net primary productivity (NPP). This study analyses 22 years (2003–2024) of satellite-derived NPP data to identify its main spatiotemporal patterns and environmental drivers. The monthly climatology reveals that the cold season (December–May) accounts for 68 % of the annual NPP, while the warm season (June–November) contributes only 32 %. To characterize regional variability, we applied the k-means++ clustering algorithm, and validated the resultant classification using discriminant analysis. This procedure robustly identified three productivity zones: high (HPZ; > 1700 mg C m^-2 d^-1), mid (MPZ; 900–1700 mg C m⁻² d⁻¹), and low (LPZ; < 900  mg C m^-2 d^-1). Interannually, the HPZ contributes 61.4 % of total NPP despite occupying only 30 % of the gulf’s area, whereas the LPZ covers 36 % of the area but produces just 16.9 %. A significant negative anomaly between 2013 and 2019 led to a 9 % decline in NPP relative to the long-term mean (124 Tg C y^-1), a period coincided with intense warming episodes, including multiple marine heatwaves and the strong 2015–2016 El Niño. A partial recovery occurred between 2020 and 2024. The dominant environmental drivers of NPP differ among zones: sea surface temperature and mixed-layer depth control NPP in the HPZ, temperature and euphotic zone depth in the MPZ, and euphotic depth and phosphate availability in the LPZ. Overall, our analysis demonstrates that anomalously warm years compress the spatial extent of productive zones. Continued warming and stratification are therefore likely to expand oligotrophic conditions, increasing the area of low-productivity waters with profound ecological consequences for the Gulf of California.