Monsoonal response to mid-holocene orbital forcing in a high resolution GCM

Abstract

In this study we use a sophisticated high-resolution atmosphere-ocean coupled climate model, EC-Earth, to investigate the effect of Mid-Holocene orbital forcing on summer monsoons on both hemispheres. During the Mid-Holocene (6 ka), there was more summer insolation on the Northern Hemisphere than today, which intensified the meridional temperature and pressure gradients. Over North Africa, monsoonal precipitation is intensified through increased landward monsoon winds and moisture advection as well as decreased moisture convergence over the oceans and more convergence over land compared to the pre-industrial simulation. Precipitation also extends further north as the ITCZ shifts northward in response to the stronger poleward gradient of insolation. This increase and poleward extent is stronger than in most previous ocean-atmosphere GCM simulations. In north-westernmost Africa, precipitation extends up to 35° N. Over tropical Africa, internal feedbacks completely overcome the direct warming effect of increased insolation. We also find a weakened African Easterly Jet. Over Asia, monsoonal precipitation during the Mid-Holocene is increased as well, but the response is different than over North-Africa. There is more convection over land at the expense of convection over the ocean but precipitation does not extend further northward, monsoon winds over the ocean are weaker and the surrounding ocean does not provide more moisture. On the Southern Hemisphere, summer insolation and the poleward insolation gradient were weaker during the Mid-Holocene, resulting in a reduced South American monsoon through decreased monsoon winds and less convection, as well as an equatorward shift in the ITCZ. This study corroborates the findings of paleodata research as well as previous model studies, while giving a more detailed account of Mid-Holocene monsoons

Precessional control of Sr ratios in marginal basins during the Messinian Salinity Crisis?

“…[] (T03, orange), Bosmans et al . [] (without/with Chad basin: B11/B11c, light blue), and Murphy et al . [] (M09, green).…”

Impact of freshwater release in the Mediterranean Sea on the North Atlantic climate

“…The associated increased moisture transport led to the development of vegetation over part of the present-day Sahara Desert and potentially strengthening the flow of the Nile. Furthermore, local precipitation increase over the Mediterranean Sea (Bosmans et al 2012), runoff as well as melting from northern glaciers or ice sheets, associated with a connection to the Black Sea could have also strongly contributed to freshwater release in the Mediterranean Sea (Rohling et al 2015). All these freshwater inputs may have led to the onset of a strong halocline that isolated deeper oceanic water from the surface, leading to decreased available oxygen and therefore anoxic conditions.…”

The water cycle of the mid‐Holocene West African monsoon: The role of vegetation and dust emission changes

“…Changes in orbital forcing are a well‐known control of the MH monsoonal intensification (e.g., Kutzbach and Guetter, ; Street‐Perrott et al, ; Texier et al, ; Patricola and Cook, ; Marzin and Braconnot, ; Bosmans et al, ). A number of authors have also highlighted the importance of changes in vegetation cover as a feedback strengthening the response of the WAM to orbital changes and driving its northward extension during the AHP (e.g., Kutzbach and Liu, ; Claussen and Gayler, ; Claussen et al, ; Braconnot et al, , ; Su and Neelin, ; Krinner et al, ; Rachmayani et al, ).…”

“…In particular, we analyse how the timing, origin and convergence of moisture fluxes contributing to the monsoonal precipitation changes under a range of scenarios: MH orbital forcing; MH orbital forcing and surface greening; MH orbital forcing, surface greening and dust reduction. Previous studies have investigated either the MH WAM's water budget under orbital and land surface changes (e.g., Su and Neelin, ; Patricola and Cook, ; Bosmans et al, ; Rachmayani et al, ) or the dynamical changes driven by Saharan greening in combination with dust reduction (Pausata et al, ; Gaetani et al, ). However, no study has hitherto quantified the regional water budget's response to the reduced atmospheric dust loading resulting from a greening of the Sahara and Sahel.…”