B. Sabbaghzadeh1, D. L. Arévalo-Martínez2*, V. Mohrholz1, L. C. Cotovicz Jr.1, S. Otto1, G. Dangl1, M. Glockzin1, and G. Rehder1 1 Leibniz Institute for Baltic Sea Research Warnemünde, Rostock, Germany, 2 GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany, * current address: Radboud University Nijmegen, NetherlandsCorrespondence to: B. Sabbaghzadeh, [email protected] ORCID NO: 0000-0002-1232-0576Key Points:The northern Benguela Upwelling System is a perennial source of long-lived greenhouse gases due to upwelling-driven winter peaks.Seasonal water column variations show rising pCO2, N2O and CH4 from winter to summer, confined to the inner shelf.It is imperative to consider non-CO2 greenhouse gases when assessing the far-reaching impacts of coastal waters on climate change.AbstractThe northern Benguela Upwelling System (nBUS) represents one of the ocean’s largest and most biologically productive marine ecosystems, crucial for the cycling of greenhouse gases (GHG). Despite its significance, there is a scarcity of direct evidence on the seasonal variability of GHG production and emissions in the nBUS and its major driving factors. Through multi-year observations, we examined the spatio-temporal dynamics in the nBUS to understand their influence on GHG dynamics. Our findings revealed coastal GHG hotspots with seasonal gradients, primarily influenced by upwelling. The nBUS consistently acted as a perennial source of GHG to the atmosphere, with peak CO2, CH4, and N2O sea-air fluxes during austral winter (increases of 97%, 47%, and 87% compared to austral summer, respectively). Winter CO2-equivalent (CO2-e) emissions accounted for 70 – 73% of GHG emissions, followed by N2O (23 – 24%) and CH4 (2 – 6%). In summer, these percentages shifted considerably, with CO2 contributing 23 – 30%, N2O 38 – 51%, and CH4 17 – 38%. We argue for the necessity of including non-CO2 GHG when assessing the impacts of coastal ecosystems on climate dynamics. Our results offer detailed insights into the primary drivers of spatial and seasonal variability in GHG dynamics within coastal upwelling waters. This study constitutes the first comprehensive simultaneously evaluation of all three GHG within the region. It serves as a foundational framework for subsequent model studies aimed at refining the sea-air flux variability, particularly in anticipation of projected ocean warming and the expanding oxygen minimum zones.