Variation of South Somalian upwelling during the last 160 ka: radiolarian and foraminifera records in core MD 85674

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Abstract
Indicators of upwelling activity and surface-water productivity for the last 160 ka have been studied in the ‘Marion Dufresne’ core MD 85674 taken off Somalia (3°11, 2 N-50°26, 3 E; 4875 m depth). Quantitative changes in the abundances of radiolarian species which are restricted to upwelling areas (A. murrayana, C. irregularis, D. infabricatus, L. nigriniae, P. caryoforma, P. crustula, and P. minythorax) were used to monitor the variation of vertical advection of deep water. These changes are compared with those recorded by the stable carbon isotopes of a foraminiferal thermocline dweller, N. dutertrei, and with quantitative variations of some planktonic foraminifers (N. dutertrei, G. bulloides, G. menardii, G. sacculifer and G. glutinata). Taken together, our data indicate that, under the south Somalian gyre, upwelling activity was maximal during transition between isotope stages 6 and 5, isotope stage 3, and transition between isotope stages 2 and 1 (respectively at about 130 ka, 65 to 25 ka, and 15 to 10 ka). These data also suggest that, at least during the last 60 ka, periods of increased activity in the Somalian, Arabian and Peruvian upwelling systems were synchronous.