Droughts In The Sahara-Sahel Region: Lessons From Dust Records Of The Past 300 Years
Abstract
Mineral dust emitted from arid and semi-arid regions of North Africa is an important component of the Earth’s climate and has been causally related to prolonged periods of drought in the Sudano-Sahel region in the later part of the 20th century. To benchmark climate models and to understand how the Sahel will respond to climate change as global sea surface temperatures increase, we have reconstructed a record of dust export over the past 300 years using 4He as a tracer of dust. Our dust archives are (a) a fast growing coral (Porites lutea) from the northern Red Sea and (b) carbonate mud from the Bahama platform. High 4He fluxes in the Red Sea coral correspond to all major North African droughts of the 20th century. Hence, the 4He measurements in the Red Sea coral can be utilized to reconstruct an annual record of the drought patterns in North Africa over the past three centuries. We find that dust fluxes were high during the late 20th century and low in the early part of the 20th century. Dust emission rates from North Africa were high-at the terminal stages of the Little Ice Age (between 1830 and 1870) the average dust flux in the 19th century was 2.9 times higher than that in the 20th century. Dust fluxes are lower in the late 18th but increase in the early part of the 18th century. Overall, the 20th century dust emission rates are modest compared to those in the 18th and 19th centuries. These dust flux patterns are also reflected in the lower-resolution record of the North African dust flux from the carbonate platform in the Bahamas. Our 3-century long record of dust emission from North Africa shows a 12-year and a 65-year cycle. These frequencies are similar to the ‘Atlantic Dipole’ (N-S inter-hemispheric tropical Atlantic SST gradients) and the Atlantic Multidecadal Oscillation (AMO), respectively. Higher dust fluxes are strongly correlated with the negative phase of the Atlantic dipole (r=-0.7), i.e. severe droughts in the Sahel during a cold anomaly in the tropical North Atlantic (5-25N, 55W-15W) with respect to the tropical South Atlantic (20S-0, 30W-10E). Additionally, dust fluxes are modulated by the AMO and over the length of the record we observe that the highest dust fluxes follow the cold (negative) phase of the AMO (cooler North Atlantic). Hence, future drought patterns in North Africa are likely to depend on how global warming affects the AMO and the Atlantic dipole. However, North Africa remains susceptible to droughts more severe than those of the 20th century, particularly during the ramp up to the warm (positive) phase of the AMO.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMPP24B..02B
- Keywords:
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- 4901 PALEOCEANOGRAPHY / Abrupt/rapid climate change;
- 4906 PALEOCEANOGRAPHY / Aerosols;
- 4914 PALEOCEANOGRAPHY / Continental climate records;
- 4954 PALEOCEANOGRAPHY / Sea surface temperature