Response of Oceanic Meridional Overturning Circulation to Vegetation Removal on Different Continents

Vegetation on different continents is often subject to substantial changes due to climate change, anthropogenic activities, or vegetation evolution, but how it affects the oceanic meridional overturning circulation (MOC) is unclear. This study explores both the transient evolution and equilibrium response of MOCs to vegetation removal on each continent except Antarctica using an atmosphere-ocean general circulation model, CESM1.2.2, under preindustrial climate conditions. The results indicate that at equilibrium, removing Eurasian vegetation slightly weakens the Atlantic MOC (AMOC) (−2.5 Sv, −16.5%) but enhances the Pacific MOC (PMOC) (+6.0 Sv, +58.3%). Conversely, removing North American vegetation strengthens the AMOC (+2.7 Sv, +17.6%) while weakening the PMOC (−1.8 Sv, −17.7%). Vegetation removal over low-latitude regions produces minimal impact on either AMOC or PMOC. Global vegetation removal causes a substantial weakening of AMOC (−5.7 Sv, −36.9%) and a pronounced strengthening of PMOC (+4.8 Sv, +47.3%), different from the linear sum of individual effects described above. The transient evolution of both AMOC and PMOC is complex, exhibiting distinct (even opposite) responses in the multidecadal timescale and centennial or millennial timescale. Abrupt changes in both AMOC (by ∼10 Sv) and PMOC (by ∼2 Sv) occur around 2700 years after the global vegetation removal. This highlights the long timescale of surface-climate responses to external forcings, which is easily overlooked in shorter simulations. Process diagnostics show that salinity anomalies—modulated by net precipitation and sea ice melt—govern the AMOC response, whereas surface temperature anomalies dominate the PMOC response.