The dynamic relationship between temperate and tropical circulation systems across South Africa since the last glacial maximum

Abstract

14A fundamental and long-standing question of southern African palaeoclimatology is the way 15 tropical and temperate climate system dynamics have influenced rainfall regimes across the 16 subcontinent since the Last Glacial Maximum. In this paper, we analyse a selection of recently 17 published palaeoclimate reconstructions along a southwest-northeast transect across South Africa. 18These records span the last 22,000 years, and encompass the transition between the region's winter 19 and summer rainfall zones. In synthesis, these records confirm broad elements of the dominant 20 paradigm, which proposes an inverse coeval relationship between temperate and tropical systems, 21with increased precipitation in the winter (summer) rainfall zone during glacial (interglac ia l) 22 periods. Revealed, however, is a substantially more complex dynamic, with millennial-sca le 23 climate change events being strongly -even predominantly -influenced by the interaction and 24 combination of temperate and tropical systems. This synoptic forcing can create same sign 25 anomalies across the South African rainfall zones, contrary to expectations based on the classic 26 model of phase opposition. These findings suggest a new paradigm for the interpretation of 27 southern African palaeoenvironmental records that moves beyond simple binary or additive 28 influences of these systems. 29 30

A high-resolution record of Holocene climate and vegetation dynamics from the southern Cape coast of South Africa: pollen and microcharcoal evidence from Eilandvlei

“…Chase et al . () highlight strong similarities in climate variability across the interior, from Seweweekspoort through the southern and central SRZ, suggesting that shifts in the westerly storm track act as a trigger for TTIs under a period of tropical dominance during the Holocene.…”

“…E, Iron (Fe) concentrations from the EV13 core (Wündsch et al ., ). F. Composite stable nitrogen isotope record from hyrax middens from Seweweekspoort (Chase et al ., ). G, Summer precipitation reconstruction (PWetQ) from the southern and central summer rainfall zone of South Africa (Chevalier and Chase, ).…”

“…Interactions between temperate and tropical systems and the subtropical anticyclones produce rainfall along the southern Cape in the form of a range of synoptic-scale disturbances such as ridging high-pressure systems (46% of annual rainfall total) and tropical-temperate troughs (28% of annual rainfall total) (Engelbrecht et al, 2015). It has been suggested that such tropical-temperate interactions (TTIs) have been a dominant driver of millennial-scale climate change across much of South Africa, including parts of the southern Cape (Chase et al, 2017) The ocean adjacent to the southern Cape coast is an additional important moisture source for the region, with many major rainfall events being associated with low-level advection of moisture onshore (originating from the warm Agulhas Current) and local intensification of frontal systems (Rouault et al, 2002;Engelbrecht et al, 2015;Engelbrecht and Landman, 2016).…”

“…Major atmospheric (white arrows) and oceanic (blue arrows) circulation systems and the austral summer positions of the Inter‐Tropical Convergence Zone (ITCZ) and the Congo Air Boundary (CAB) are indicated. B. Aridity index map of the south‐western Cape (Zomer et al ., ), with lower values indicating drier conditions (black box in A), and the locations of published palaeoenvironmental and archaeological records from the region: 1 Elands Bay Cave (Parkington et al ., ), 2 Grootdrift (Meadows et al ., ), 3 Verlorenvlei (Stager et al ., ; Carr et al ., a), 4 Klaarfontein Springs (Meadows and Baxter, ), 5 Pakhuis Pass (Scott and Woodborne, ,b), 6 Sneeuberg Vlei and Driehoek Vlei (Meadows and Sugden, ), 7 De Rif (Quick et al ., ; Valsecchi et al ., ; Chase et al ., ), 8 Truitjes Kraal (Meadows et al ., ), 9 Katbakkies (Meadows et al ., ; Chase et al ., ), 10 Rietvlei (Schalke, ), 11 Cape Flats (Schalke, ), 12 Princess Vlei (Neumann et al ., ; Kirsten and Meadows, ), 13 Cape Hangklip (Schalke, ), 14 Die Kelders (Klein and Cruz‐Uribe, ), 15 The Agulhas Plain vleis and lunettes (Soetendalsvlei, Voëlvlei, Renosterkop and Soutpan) (Carr et al ., ,b), 16 Blombos Cave (Henshilwood et al ., ), 17 Rietvlei‐Still Bay (Quick et al ., ), 18 Pinnacle Point (Bar‐Matthews et al ., ; Rector and Reed, ; Matthews et al ., ), 19 Seweweekspoort (Chase et al ., , , in press), 20 Cango Cave (Talma and Vogel, ) and Boomplaas Cave (Deacon et al ., ), 21 Norga peats (Scholtz, ), 22 Groenvlei (Martin, ; Wündsch et al ., ), 23 Vankervelsvlei (Irving and Meadows, ; Quick et al ., ), 24 Nelson Bay Cave (Cohen and Tyson, ), 25 Klasies River Mouth (Deacon et al ., ) and 26 Uitenhage Aquifer (Heaton et al ., ; Stute and Talma, ). C. Wilderness lakes region, indicating the location of Eilandvlei and the current distribution of dominant vegetation types (Mucina and Rutherford, ).…”

“…Chase et al ., , , ,b; Neumann et al ., ; Valsecchi et al ., ; Carr et al ., ; Quick et al ., ). Important questions remain, however, regarding the past dynamics of temperate and tropical systems in the region, particularly at the WRZ–SRZ interface, and their impact on regional environments (Chase et al ., , ). The developing regional dataset indicates that at multi‐millennial timescales variations in mid‐ to high‐latitude Southern Hemisphere atmospheric and oceanographic circulation have driven environmental changes in the southern Cape through changes in the position and influence of the westerly storm track (Chase et al ., , ).…”