Holocene climate change in southernmost South Africa: rock hyrax middens record shifts in the southern westerlies

Influence of tropical easterlies in southern Africa's winter rainfall zone during the Holocene

“…Considering the strong links identified between humidity, cool conditions and enhanced westerly influence at the Seweweekspoort hyrax midden site (SWP-1 in Fig. 1; Chase et al, 2013), the results from KB-3-1, which is closer to the core of the winter rainfall zone, are perhaps unexpected. As discussed by Chase et al (2013), enriched d 15 N values (drier conditions) at Seweweekspoort (SWP-1, particularly 7000e5500 cal BP and 4500e3500 cal BP) coincide with elevated continental temperatures, as reconstructed from the Cango Cave d 18 O record (Talma and Vogel, 1992) and lower southern Cape SSTs, which indicate stronger local upwelling with increased easterly flow (Cohen and Tyson, 1995).…”

“…This variability was linked to overall wetter (drier) conditions in the continental interior, which is part of southern Africa's summer rainfall zone, and derives most its moisture from the tropical easterlies. Recent studies of rock hyrax middens from the southern Cape Fold Mountains have lent some support this model, finding that regional trends in water availability during the Holocene correlate strongly with higher south coast SSTs, continental temperature records (Talma and Vogel, 1992 [chronology after Chase et al, 2013]), and remote evidence for shifts in the westerly storm track (Lamy et al, 2001), which in turn can be linked to changes in Antarctic sea-ice extent (Fischer et al, 2007;Wolff et al, 2010). These findings highlight the importance of temperate moisture-bearing systems in the southwestern and southern Cape, but lacking are records from the western interior that indicate the extent to which increases in easterly flow may have brought increased summer rainfall to regions distal to the primary Indian Ocean moisture source.…”

African hydroclimatic variability during the last 2000 years

“…However, in southwestern Africa, a largely in-phase relationship between the hemispheres has been found (Chase et al, 2009;Chase et al, 2010;Collins et al, 2011), contradicting the prediction of orbitally-driven north-south anti-phasing in Holocene hydroclimate trends. In the temperate mid-latitude region of the southern Cape, a long-term trend toward more humid conditions seems to have been concurrent with generally cooler conditions since the mid-Holocene (Chase and Meadows, 2007;Chase et al, 2013). However, more precise higher-resolution records from this region are required before robust conclusions can be drawn.…”

“…This trend also seems to be reflected in Cango Cave δ 13 C variation (either as a function of an increase in C3 grasses or variations in water-use efficiency under more humid conditions; cf. Chase et al, 2013), and the Verlorenvlei diatom record, which indicates increased freshwater input over the last 1400 years (Stager et al, 2012). Although a greater number of highly resolved records is required to draw robust conclusions, it appears that a generally in-phase relationship may exist between the southwestern Cape and the western summer rainfall zone, with both exhibiting signals in opposition to those observed in the eastern summer rainfall zone.…”

Late Holocene Marine Radiocarbon Reservoir Correction for the Southern and Eastern Coasts of South Africa

“…Reinwarth et al 2013) from wetland and lake sediments, as well as novel evidence, including a range of biological and chemical characteristics of rock hyrax middens (e.g. Chase et al, 2013). Other investigations are underway, including those carried out recently within the RAiN project (Regional Archives for Integrated iNvestigations), which is a multidisciplinary and multi-institutional collaboration that aims to explore evidence from terrestrial and offshore sediments of changing climate and associated environmental conditions during the late Quaternary in southern Africa (Haberzettl 2014).…”