Glacial-interglacial vegetation dynamics in South Eastern Africa coupled to sea surface temperature variations in the Western Indian Ocean

Abstract

Abstract. Glacial-interglacial fluctuations in the vegetation of South Africa might elucidate the climate system at the edge of the tropics between the Indian and Atlantic Oceans. However, vegetation records covering a full glacial cycle have only been published from the eastern South Atlantic. We present a pollen record of the marine core MD96-2048 retrieved by the Marion Dufresne from the Indian Ocean ∼120 km south of the Limpopo River mouth. The sedimentation at the site is slow and continuous. The upper 6 m (spanning the past 342 Ka) have been analysed for pollen and spores at millennial resolution. The terrestrial pollen assemblages indicate that during interglacials, the vegetation of eastern South Africa and southern Mozambique largely consisted of evergreen and deciduous forests. During glacials open mountainous scrubland dominated. Montane forest with Podocarpus extended during humid periods was favoured by strong local insolation. Correlation with the sea surface temperature record of the same core indicates that the extension of mountainous scrubland primarily depends on sea surface temperatures of the Agulhas Current. Our record corroborates terrestrial evidence of the extension of open mountainous scrubland (including fynbos-like species of the high-altitude Grassland biome) for the last glacial as well as for other glacial periods of the past 300 Ka.Correspondence to: L. M. Dupont (dupont@uni-bremen.de)

Southern Hemisphere anticyclonic circulation drives oceanic and climatic conditions in late Holocene southernmost Africa

“…In the past, it was relatively uncontroversial that long term (glacial-interglacial timescale) climate variations in southernmost Africa are directly forced by local insolation (Daniau et al, 2013;Simon et al, 2015). However, recently several paleorecords have emerged showing either no evidence of direct insolation as a climatic driver (Chase et al, 2009(Chase et al, , 2010Dupont et al, 2011) or evidence for opposing trends (i.e., synchrony with the Northern Hemisphere) (Tierney et al, 2008;Stager et al, 2012;Truc et al, 2013). Furthermore, on shorter timescales, recent datasets reveal strong indications for a highly complex local climate system.…”

“…Due to the strongly erosive Agulhas Current, very few marine records from the Agulhas Bank exist and the influence of SSTs on the regional precipitation patterns therefore remains under dispute. On the one hand, it has been suggested that decreased SSTs on the southwestern coast of South Africa lead to decreasing precipitation in southernmost South Africa (Rouault et al, 2003) and positive SST anomalies along the east coast associated with Agulhas strengthening enhance summer precipitation in the eastern South Africa (Jury et al, 1993;Dupont et al, 2011;Scott et al, 2012). On the other hand, the oxygen isotope composition of marine mollusk shells preserved in Nelson Bay archaeological cave deposits indicates that during periods of wetter conditions over the southern African interior, the Agulhas surface water temperatures were actually lower than during arid periods (Cohen and Tyson, 1995).…”

South African Climates (Agulhas LGM Density Profile)

“…document precession-paced changes in the African monsoonal rainfall belt with enhanced rainfall during periods of increased Southern Hemisphere summer insolation, superimposed by wet conditions during high-latitude Northern Hemisphere abrupt cold events. Farther south, a 342 ky pollen record from marine sediment Core MD96-2048 from 660 m water depth ~120 km south of the Limpopo River mouth shows glacial-interglacial and precessioncorrelated climate variations in the extent of the subtropical biome (Dupont et al, 2011). On land the sediment record from Tswaing Crater, a meteorite impact north of Pretoria, provides the longest terrestrial record of climate variability in South Africa, spanning the last 200 ky. Clastic particle size variations from Tswaing Crater have also been used to suggest that cyclic changes in precipitation were linked with the long-term effect of regional insolation changes driven by orbital precession (Partridge, et al, 1997(Partridge, et al, , 2004.…”

Untitled

“…Progressing south, a 342 ky long pollen record from marine sediment Core MD96-2048 from 660 m water depth ~120 km south of the Limpopo River mouth shows glacial-interglacial and precession-driven climate variations in the extent of the subtropical biome (Dupont et al, 2011). On land the sediment record from Tswaing Crater, a meteorite impact north of Pretoria, provides the longest terrestrial record of climate variability located directly in South Africa, spanning the last 200 ky. Clastic particle size variations from this site have been used to suggest that cyclic changes in precipitation were linked with the long-term effect of regional insolation changes driven by orbital precession (Partridge, et al, 1997(Partridge, et al, , 2004.…”

“…Did variable Agulhas Current warm-water transport contribute to and modulate the impacts of shifting air boundaries and rainfall patterns over southeast Africa, and possibly offset these patterns from those over southwest Africa and the Namib (Dupont et al, 2005(Dupont et al, , 2011Maslin et al, 2012)?…”