Northern Hemisphere Controls on Tropical Southeast African Climate During the Past 60,000 Years

Abstract

The processes that control climate in the tropics are poorly understood. We applied compound-specific hydrogen isotopes (deltaD) and the TEX(86) (tetraether index of 86 carbon atoms) temperature proxy to sediment cores from Lake Tanganyika to independently reconstruct precipitation and temperature variations during the past 60,000 years. Tanganyika temperatures follow Northern Hemisphere insolation and indicate that warming in tropical southeast Africa during the last glacial termination began to increase approximately 3000 years before atmospheric carbon dioxide concentrations. deltaD data show that this region experienced abrupt changes in hydrology coeval with orbital and millennial-scale events recorded in Northern Hemisphere monsoonal climate records. This implies that precipitation in tropical southeast Africa is more strongly controlled by changes in Indian Ocean sea surface temperatures and the winter Indian monsoon than by migration of the Intertropical Convergence Zone.

North Atlantic forcing of tropical Indian Ocean climate

“…Comparison of our data from the eastern tropical Indian Ocean with the Lake Tanganyika humidity record from East Africa 14 reveals a strong similarity (r = 0.43 with the range [0.11, 0.67], 95% confidence interval; Methods) with dry Younger Dryas and Heinrich stadials on both sides of the tropical Indian Ocean (Fig. 2), and suggests that zonally asymmetric changes within the Indian Ocean 14 were not the main control on Indian Ocean hydrology during these periods. Our results suggest that decreases in the monsoon intensity 28 stem from a reorganization of the Hadley cell over the Indian Ocean realm (Fig.…”

“…The age model of SO189-119KL is based on 14 accelerator mass spectrometry (AMS) 14 C dates and linear interpolation between them (Supplementary Table 1 and Extended Data Fig. 4).…”

“…Dry Younger Dryas and Heinrich stadials have been reported from various marine and terrestrial archives across the tropical Indian Ocean 4,9-14 .However, a few records suggest wet Younger Dryas or Heinrich stadials over northeast Australia 15 , southern Indonesia 5,16 and southeast Africa 12,17 . Although there seems to be strong evidence that the intertropical convergence zone (ITCZ) moved southwards in the tropical Atlantic 2 , a wide range of mechanisms have been offered to explain the connection between the cooling of the North Atlantic and tropical Indian Ocean hydroclimates: a weakening of the rainfall system in response to regional sea surface cooling 13,14 ; and changes in the monsoon intensity 4,10,16 associated with a southward shift in the mean 1 or winter 4,5,15 position of the ITCZ or in the position of oceanic fronts 18 .However, there are no high-resolution records from the region of the tropical Indian Ocean unaffected by monsoon seasonality. Records from this region are needed to evaluate whether the eastern and western Indian Ocean experienced similar or contrasting rainfall anomalies during abrupt climate events.…”

Forcing of wet phases in southeast Africa over the past 17,000 years

“…4 The C 4 plant dominance in the lower Zambezi floodplain is seen in the relative abundance of C 4 plants (Fig. 1c, d) 15 .…”

“…It has been inferred that these periods represent southward shifts of the ITCZ 2,3,6 . Dry conditions during the YD and Heinrich Stadial 1 (HS1) in Lake Tanganyika, located closer to the equator in East Africa, were interpreted to have been caused by lowered Indian Ocean SST 4 . Recently, widespread drought conditions during HS1 in East Africa have similarly been suggested to be driven by cold conditions in the Indian Ocean 5 .…”