African Monsoon Variability over Past Millennia Peter B
African Monsoon Variability over Past Millennia Peter B. de. Menocal Jennifer Arbuszewski Jess Adkins Zhengyu Liu
Overview The African monsoon and orbital forcing The early Holocene African Humid Period Climate model simulations: … mechanisms for abrupt change
Sahel Drought (1960 s onward) Giannini et al. (2003)
The African Monsoon and Tropical Atlantic Upwelling Cool SSTs Maximum upwelling Steep thermocline slope W. Ruddiman, “Earth's Climate Past and Future”
Orbital Precession and the Monsoon Kutzbach (1981) W. Ruddiman, “Earth's Climate Past and Future”
Linear (? ) monsoon sensitivity
Precessional monsoon variability Med. Sapropels Tropical Upwelling African Climate (Mc. Intyre et al. , 1989; Molfino and Mc. Intyre, 1993; Pokras and Mix, 1985; Rossignol-Strick, 1983)
…persisted for millions of years! Miocene Mediterranean Sapropels (Sicily; Frits Hilgen)
NW African dust export Site 658
African Humid Period AHP de. Menocal et al. , 2000
African Humid Period Africa was much wetter between ca. 15 -5 kyr BP. Most of Saharan Desert vegetated, wetland fauna.
North Africa wet during early Holocene Paleolake sediments in Mali (NW Africa)
Climate-Controlled Occupation of the Eastern Sahara Kuper and Kroepelin, 2006
Faiyum Mirimde Egyptian Neolithic (6. 5 -4. 5 ka BP) Badari Nagada
AHP: A pan-North African event Liu et al. , 2007
Albedo-Vegetation feedback? Claussen et al. , 1999; de. Menocal et al. , 20
Fully coupled transient O-A-Veg GCM Liu et al. (QSR in press)
Climate Model insight African climate very sensitive to orbital radiation changes. Abrupt responses to gradual forcing due to some aspect of vegetation feedback. Humid-arid transitions occurred within centuries. SST influence uncertain but present in historical records.
Annual Evap - Precip Annual sea-surface temperature
Meridional ITZ displacements: LGM water-hosing experiments in temperature P-E (m/yr) (°C) Change in surface Vellinga and Wood (2002)
LGM Collapse of zonal SST Gradient
SST gradients along transect
Large and abrupt Deglacial ITCZ Swings Fresh Salty
Summary Past African climate changes were large. Moisture budget changes were abrupt. Likely importance of vegetation feedbacks, perhaps SSTs as well.
- Slides: 26