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

Abstract

Abstract. We present a continuous and well-resolved record of climatic variability for the past 100,000 yrs from a marine sediment core taken in Delagoa Bight, off southeastern Africa. In addition to providing a sea surface temperature reconstruction for the past ca. 100,000 yrs, this record also allows a high-resolution continental climatic reconstruction. Climate sensitive organic proxies, like the distribution and isotopic composition of plant-wax lipids as well as elemental indicators for fluvial input and weathering type provide information on climatic changes in the adjacent catchment areas (Incomati, Matola, and Lusutfu rivers). At the transition between glacials and interglacials, shifts in vegetation correlate with changes in sea surface temperature in the Agulhas current. The local hydrology, however, does not follow these orbital-paced shifts. Instead, precipitation patterns follow millennial scale variations with different forcing mechanisms in glacial versus interglacial climatic states. During glacials, southward displacement of the Intertropical Convergence Zone facilitates a transmission of northern hemispheric signals (e.g. Heinrich events) to the southern hemispheric subtropics. Furthermore, the southern hemispheric westerlies become a more direct source of precipitation as they shift northward over the study site, especially during Antarctic cold phases. During interglacials, the observed short-term hydrological variability is also a function of Antarctic climate variability, however, it is driven by the indirect influence of the southern hemispheric westerlies and the associated South African high-pressure cell blocking the South Indian Ocean Convergence Zone related precipitation. As a consequence of the interplay of these effects, small scale climatic zones exist. We propose a conceptual model describing latitudinal shifts of these zones along the southeastern African coast as tropical and temperate climate systems shift over glacial and interglacial cycles. The proposed model explains some of the apparent contradictions between several paleoclimate records in the region.

Terrestrial temperature evolution of southern Africa during the late Pleistocene and Holocene: Evidence from the Mfabeni Peatland

“…Similarly, on longer timescales, temperature in south-east Africa is also influenced by glacial and CO 2 feedback controls (Chevalier et al, 2020). But in addition, some records indicate a connection with Northern Hemisphere climate change (Hahn et al, 2021a(Hahn et al, , 2021b and the impact of abrupt changes during Greenland stadials and associated changes in East Asian Monsoon intensity (Simon et al, 2015). This is similar to hydroclimate records found in south-western Africa (Chase et al, 2010), equatorial east Africa (Johnson et al, 2002;Tierney et al, 2008), andsouth-eastern Africa (Schefub et al, 2011).…”

“…It is possible that the hydroclimate follows precession (insolation) forcing in some south-east African areas and West Indian Ocean sea surface temperatures in others (Neumann et al, 2014;Simon et al, 2015), while temperatures predominantly follow SSTs. However, hydroclimate in the region is also inferred to be driven by the interplay of tropical and subtropical atmospheric processes, as well as the position of the westerly winds due to changes in Southern Ocean sea ice extent (e.g., Miller et al, 2019Miller et al, , 2020Hahn et al, 2021aHahn et al, , 2021b. This suggested interplay is consistent with dynamics affecting south, south-west and interior South Africa (Chase and Meadows, 2007;Gasse et al, 2008;Stager et al, 2012;Chase et al, 2020;2015a).…”

“…Lower water temperatures in the south-western Indian Ocean may have contributed to the decline in Mfabeni air temperatures, and at the same time also affected hydrological conditions (Baker et al, 2014(Baker et al, , 2016(Baker et al, , 2017Miller et al, 2019;Finch and Hill, 2008;Grundling et al, 2013;Esteban et al, 2020). A potential scenario explaining lower temperatures in the south-western Indian Ocean is that Southern Ocean sea ice expansion and subsequent cooling (e.g., Bianchi and Gersonde, 2004) pushed the Southern Hemisphere westerlies further north (Hahn et al, 2021a). This northward displacement of the Southern Hemisphere westerlies caused a shift to drier and cooler conditions in the region, as also recorded by the intensification of the aeolian flux during the LGM (Fig.…”

“…Of particular interest for contemporary climate in south-east Africa is the warm Agulhas current and Indian Ocean to the east, the Intertropical Convergence Zone (ITCZ) to the north, and the Southern Ocean and westerlies to the south. In this context, southeast African archives record spatially and temporally heterogenous responses to climate drivers during the late Quaternary (e.g., Schmidt et al, 2014;Singarayer and Burrough, 2015;Scott and Neumann, 2018;Miller et al, 2020) that likely differed between glacial and interglacial periods (e.g., Chevalier and Chase, 2015;Simon et al, 2015;Hahn et al, 2021a).…”

“…For example, local insolation has been suggested as a major driver for some hydroclimate changes in south-east Africa (Partridge et al, 1997), while mean annual temperatures in the region do not seem to follow local summer insolation (Chevalier and Chase, 2015). On glacial-interglacial time scales a coupling of south-eastern African hydroclimate and vegetation with Agulhas sea surface temperatures (SSTs) has been inferred from proxy records (Dupont et al, 2011;Schmidt et al, 2014;Caley et al, 2018;Hahn et al, 2021a). A similar terrestrial to sea surface temperature relationship has been proposed for the past glacial-interglacial cycle (Truc et al, 2013;Chevalier and Chase, 2015).…”