Tracing moisture pathways to understand AMOC–Amazon tipping interactions

The Atlantic Meridional Overturning Circulation (AMOC) and the Amazon rainforest are two vital components of the Earth system that regulate global climate and biosphere integrity. There is growing concern that both systems may approach critical thresholds beyond which they could, potentially irreversibly, tip to alternative stable states. However, it remains unclear how their stability changes when they are considered as an interlinked system rather than in isolation.

Although ecological rainforest processes and large-scale ocean circulation may appear distinct, they share a key coupling agent: freshwater. Here, we quantify these ocean–vegetation freshwater interactions by combining UTrack, a Lagrangian moisture tracking method, with complex network analysis. We first establish an empirical reference based on ERA5 reanalysis data to characterize present-day moisture pathways and recycling. Next, we extend this analysis to Earth System Model simulations under 2°C of global warming, as well as scenarios with additional AMOC collapse or Amazon rainforest dieback.

Under present-day conditions, easterly trade winds transport large amounts of moisture from the Atlantic Ocean to the Amazon (≈ 0.35 Sverdrups, 1 Sv = 10⁶ m³ s⁻¹), sustaining the rainforest and its self-amplifying moisture recycling mechanism (≈ 0.23 Sv). In turn, freshwater is returned to the Atlantic via the Amazon’s exceptionally large river discharge (≈ 0.21 Sv), and atmospheric moisture export (≈ 0.062 Sv), conceivably influencing the salt–advection feedback that drives the AMOC. Our findings suggest that a substantial weakening of the AMOC may alter the strength, spatial configuration, and seasonal variability of the trade winds, thereby affecting both moisture transport to the Amazon and internal moisture recycling within the basin. Conversely, large-scale Amazon forest dieback may influence freshwater fluxes that are relevant for the stability of the AMOC. Together, these results provide a foundation for exploring AMOC–Amazon interactions in (conceptual) coupled modelling frameworks, guiding future research on potential tipping cascades and Earth system resilience.