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Climate of the Past An interactive open-access journal of the European Geosciences Union
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Volume 14, issue 9 | Copyright
Clim. Past, 14, 1331-1343, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 20 Sep 2018

Research article | 20 Sep 2018

Variations of the Somali upwelling since 18.5 ka BP and its relationship with southwest monsoon rainfall

Durairaj Balaji1,2, Ravi Bhushan2, and Laxman Singh Chamyal1 Durairaj Balaji et al.
  • 1Department of Geology, The Maharaja Sayajirao University of Baroda, India
  • 2Geoscience Division, Physical Research Laboratory, Ahmedabad, India

Abstract. Somali upwelling history has been reconstructed for the last 18.5kaBP based on biogenic silica fluxes estimated from a sediment core retrieved from the western Arabian Sea. Surface winds along the east African coast during the southwest monsoon (SWM) cause the Somali upwelling; thus, the intensity of this upwelling has been related to the variability of the SWM. Biogenic silica flux variation suggests periodic weakening and strengthening of the Somali upwelling. Weakened upwelling during the 18.5–15kaBP period and strengthened upwelling during the Bølling–Allerød (15–12.9kaBP) suggest the onset of the SWM. The Younger Dryas (12.9–11.7kaBP) is marked by reduced upwelling strength, with an intensification of the Somali upwelling observed at the beginning of the Holocene and a further decline at 8kaBP. The increase in the upwelling strength recorded since 8kaBP suggests SWM strengthening during the latter part of the Holocene. A comparison of upwelling variations with the SWM precipitation record demonstrates a reversal in the relationship between the strength of the Somali upwelling and SWM rainfall at the beginning of the Holocene. This observed shift has been attributed to the variation in the SWM strength due to the latitudinal shift of the intertropical convergence zone (ITCZ) associated with changes in moisture sources.

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Short summary
Understanding the causes of past climatic changes plays a major role in deciphering monsoon variability. This study aims to understand past changes in siliceous productivity in the Somali upwelling area, as well as the palaeo-upwelling strength and its relation with southwest monsoon (SWM) rainfall. It is found that the Somali upwelling has historically had a negative impact on SML rainfall; this has important implications as previous studies predict a future increase in the Somali upwelling.
Understanding the causes of past climatic changes plays a major role in deciphering monsoon...