AMOC Response to Dust Reduction and Greening of Sahara during the Mid-Holocene

Abstract:

The North Africa was green during the mid-Holocene (~9-6 ka) and emitting much less dust to the atmosphere than in the present day. Here we use a fully coupled atmosphere-ocean general circulation model, CESM1.2.2, to first test the influence of global dust reduction and greening of Sahara on AMOC (Atlantic Meridional Overturning Circulation) during this period. The results show that the atmospheric dust removal leads to a decrease of AMOC by 6.2% and reduces the oceanic poleward heat transport for the mid-Holocene. In contrast, the greening of Sahara with 100% shrubs (100% grasses) causes an enhancement of the AMOC by 6.1% (4.8%) and a strengthening of ocean meridional heat transport. The AMOC is increased by 5.3% (2.3%) considering both the dust reduction and green Sahara with 100% shrubs (100% grasses). The AMOC changes are associated with changes of density stratification in high latitudes of North Atlantic dominated by salinity anomalies, which result from ocean dynamics in the North Atlantic and atmospheric feedback between North Africa and West Atlantic. Evaporation and sea ice feedback also play important roles in the surface density anomalies over high latitudes.