Decadal-scale droughts disrupted the African Humid Period in the Sahara

Area of Science:

• Paleoclimatology
• Climate Dynamics
• African Climate History

Background:

• The early and mid-Holocene featured the African Humid Period (AHP), a wet phase in the Sahara and Sahel.
• The AHP, spanning from 14.8 kyr BP to 6.0 kyr BP, was marked by a significant humid interval but also experienced poorly dated short droughts.
• Understanding the precise timing and duration of these droughts is crucial for reconstructing past climate variability.

Purpose of the Study:

• To identify and precisely date decadal-scale droughts during the African Humid Period.
• To investigate the environmental impact of these droughts on the Lake Yoa region.
• To explore the teleconnections between African climate and North Atlantic circulation changes.

Main Methods:

• Analysis of a multiproxy time series from the annually layered sedimentary archive of Lake Yoa, Chad.
• Utilizing pollen, diatom, leaf-wax isotopes, and geochemical source area indicators.
• Employing climate simulations to link observed drought events with potential large-scale climate drivers.

Main Results:

• Identification of two decadal-scale droughts at approximately 9.3 kyr BP and 8.2 kyr BP, with a possible third at 6.3 kyr BP.
• Evidence of reduced local precipitation and fluvial supply during the 8.2 kyr BP drought, leading to lake-level drop and shoreline vegetation changes.
• Climate simulations suggest the 8.2 kyr BP drought was a rapid response to a weakened Atlantic Meridional Overturning Circulation (AMOC) due to North Atlantic freshwater input.

Conclusions:

• The African Humid Period was punctuated by significant decadal droughts, notably around 9.3 and 8.2 kyr BP.
• The 8.2 kyr BP drought event demonstrates a clear teleconnection between North Atlantic climate dynamics (AMOC weakening) and hydroclimate variability in the African Sahel.
• These findings highlight the sensitivity of African climate to abrupt climate shifts and underscore the need for improved decadal climate predictions.