Contrasting land carbon uptake responses to El Niño–Southern Oscillation across North America

Abstract. El Niño–Southern Oscillation (ENSO) drives year-to-year variability in the land carbon sink. While responses of land carbon uptake to ENSO have been documented at aggregated continental scales over North America, these responses arise from ENSO's climate impacts that vary across subcontinental regions. Disentangling diverse regional responses is crucial for attributing ENSO's impacts on carbon uptake to climatic drivers. Here, we characterize ENSO-driven carbon–climate interactions across North America, a data-rich continent with prominent responses to ENSO, by leveraging fine-resolution (1° × 1°) top-down estimates of land carbon fluxes derived from tall-tower atmospheric CO₂ observations and spaceborne chlorophyll fluorescence measurements. We identify regions with distinct ENSO responses in the timing, direction, and magnitude of carbon uptake anomalies. Notably, regions where El Niño boosts carbon uptake, including the Pacific–Mountainous West and subtropical lands, are consistent with ENSO-driven shifts in the position of the subtropical jet. We further uncover contrasting patterns in how energy and water limitations mediate ENSO's impacts on carbon uptake across regions. These findings reveal key regional mechanisms connecting ENSO-driven climate variability with continental-scale carbon uptake responses and highlight the need to reassess tropical carbon–climate feedbacks in light of compensatory extratropical responses.