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

The Gulf of California is a tropical–subtropical, productive and biodiverse marine ecosystem that supports nearly 70 % of Mexico's fisheries. Despite its ecological and socio-economic importance, the basin-scale patterns and drivers of seasonal and interannual spatial variability in net primary productivity (NPP) remain incompletely understood. Here, we analyse 22 years (2003–2024) of satellite-derived NPP data to identify the principal spatio-temporal patterns of NPP and their environmental controls. Monthly climatology shows that the cold season (December–May) contributes 68 % of annual NPP, whereas the warm season (June–November) accounts for only 32 %. To characterise regional variability, we applied the k-means++ clustering algorithm, selected the optimal number of clusters using the elbow and silhouette criteria, and validated the resulting classification through discriminant analysis. This procedure identified three distinct productivity zones: low-productivity (LPZ; < 900 mgCm-2d-1), mid-productivity (MPZ; 900–1700 mgCm-2d-1), and high-productivity (HPZ; > 1700 mgCm-2d-1). Interannually, the LPZ covered 36 % of the area but produces only 16.9 % of total NPP, whereas the HPZ contributes 61.4 % of total NPP while occupying only 30 % of the gulf's area. A pronounced NPP negative anomaly during 2013–2019 reduced NPP by approximately 9 % relative to the long-term mean (124 Tg C yr ⁻¹ ). This decline coincided with sustained ocean warming, including multiple marine heatwaves and the strong 2015–2016 El Niño event. A partial recovery was observed during 2020–2024. Nitrate availability and water-column stratification were the dominant predictors of NPP, but their effects differed among productivity zones: nitrate was negatively associated with NPP and stratification index positively associated with NPP in the LPZ, whereas the opposite relationships were observed in the MPZ and HPZ. Wind forcing, sea-surface salinity and phosphate availability exerted additional zone-specific effects. Overall, our results indicate that anomalously warm conditions reduce the spatial extent of HPZ zones and favour the expansion of oligotrophic areas. Continued warming and enhanced stratification are therefore expected to increase the extent of LPZ, with potentially significant ecological consequences for the Gulf of California.