Late Quaternary climate variability at Mfabeni peatland, eastern South Africa

Abstract

Abstract. The scarcity of continuous, terrestrial, palaeoenvironmental records in eastern South Africa leaves the evolution of late Quaternary climate and its driving mechanisms uncertain. Here we use a ∼7 m long core from Mfabeni peatland (KwaZulu-Natal, South Africa) to reconstruct climate variability for the last 32 000 years (cal ka BP). We infer past vegetation and hydrological variability using stable carbon (δ13Cwax) and hydrogen isotopes (δDwax) of plant-wax n-alkanes and use Paq to reconstruct water table changes. Our results indicate that late Quaternary climate in eastern South Africa did not respond directly to orbital forcing or to changes in sea-surface temperatures (SSTs) in the western Indian Ocean. We attribute the arid conditions evidenced at Mfabeni during the Last Glacial Maximum (LGM) to low SSTs and an equatorward displacement of (i) the Southern Hemisphere westerlies, (ii) the subtropical high-pressure cell, and (iii) the South Indian Ocean Convergence Zone (SIOCZ), which we infer was linked to increased Antarctic sea-ice extent. The northerly location of the high-pressure cell and the SIOCZ inhibited moisture advection inland and pushed the rain-bearing cloud band north of Mfabeni, respectively. The increased humidity at Mfabeni between 19 and 14 cal kyr BP likely resulted from a southward retreat of the westerlies, the high-pressure cell, and the SIOCZ, consistent with a decrease in Antarctic sea-ice extent. Between 14 and 5 cal kyr BP, when the westerlies, the high-pressure cell, and the SIOCZ were in their southernmost position, local insolation became the dominant control, leading to stronger atmospheric convection and an enhanced tropical easterly monsoon. Generally drier conditions persisted during the past ca. 5 cal ka BP, probably resulting from an equatorward return of the westerlies, the high-pressure cell, and the SIOCZ. Higher SSTs and heightened El Niño–Southern Oscillation (ENSO) activity may have played a role in enhancing climatic variability during the past ca. 5 cal ka BP. Our findings highlight the influence of the latitudinal position of the westerlies, the high-pressure cell, and the SIOCZ in driving climatological and environmental changes in eastern South Africa.

Glacial to interglacial climate variability in the southeastern African subtropics (25–20° S)

“…The SHW northward shift of ca. 5 • latitude is well documented (Chase and Meadows, 2007;Chevalier and Chase, 2015;Chase et al, 2017;Miller et al, 2020). The possibility of more frequent SHWrelated low-pressure systems bringing moisture to our study area during the Last Glacial Maximum (LGM) has previous been proposed by Scott et al (2012) in the framework of a regional pollen review paper.…”

“…However, the position of the ITCZ was more southerly during glacial periods (Nicholson and Flohn, 1980;Chiang et al, 2003;Chiang and Bitz, 2005), which may have allowed ITCZ shifts to reach much further south along the east African coast than today (see Johnson et al, 2002;Schefuß et al, 2011;Ziegler et al, 2013;Simon et al, 2015). At the same time, the southern hemispheric westerlies (SHWs), which presently influence only the southernmost tip of Africa, are hypothesized to have moved northward during glacial periods of increased south Atlantic sea ice extent (Anderson et al, 2009;Sigman et al, 2010;Miller et al, 2020). As suggested by Miller et al (2020), in such a scenario the temperate systems may have brought winter moisture to the southeast African coast and/or blocked South Indian Ocean Convergence Zone (SIOCZ) related precipitation during the summer months.…”

“…At the same time, the southern hemispheric westerlies (SHWs), which presently influence only the southernmost tip of Africa, are hypothesized to have moved northward during glacial periods of increased south Atlantic sea ice extent (Anderson et al, 2009;Sigman et al, 2010;Miller et al, 2020). As suggested by Miller et al (2020), in such a scenario the temperate systems may have brought winter moisture to the southeast African coast and/or blocked South Indian Ocean Convergence Zone (SIOCZ) related precipitation during the summer months. Regional studies integrating many of the available records have found that (i) several small-scale climatic dipoles exist due to the interaction of various driving mechanisms and that (ii) the spatial extent of these climatic regions has varied considerably since the last glacial (Chevalier et al, 2017;Chase et al, 2018;Miller et al, 2020).…”

“…As suggested by Miller et al (2020), in such a scenario the temperate systems may have brought winter moisture to the southeast African coast and/or blocked South Indian Ocean Convergence Zone (SIOCZ) related precipitation during the summer months. Regional studies integrating many of the available records have found that (i) several small-scale climatic dipoles exist due to the interaction of various driving mechanisms and that (ii) the spatial extent of these climatic regions has varied considerably since the last glacial (Chevalier et al, 2017;Chase et al, 2018;Miller et al, 2020). Miller et al (2020) compile paleo-records along the southeastern African coast and propose a conceptual model of climatic variability during the Holocene.…”

“…Regional studies integrating many of the available records have found that (i) several small-scale climatic dipoles exist due to the interaction of various driving mechanisms and that (ii) the spatial extent of these climatic regions has varied considerably since the last glacial (Chevalier et al, 2017;Chase et al, 2018;Miller et al, 2020). Miller et al (2020) compile paleo-records along the southeastern African coast and propose a conceptual model of climatic variability during the Holocene. The authors describe three climatic zones; a northern SRZ (summer rainfall zone) where the climate is driven by local insolation and a central and eastern SRZ and southern South African zone where climate is driven by shifts of the Southern Hemisphere westerlies, the South African high-pressure cell and the SIOCZ.…”