Biomarker Proxy Records of Palaeoenvironmental Change in the Mfabani Peatland, South Africa Since the Late Pleistocene

Abstract

Southern Africa’s unique global position has given rise to a dynamic climate influenced by large sea surface temperature gradients and seasonal fluctuations in the Inter Tropical Convergence Zone (ITCZ), however, uncertainty still surrounds the mechanism of interaction between these different climate drivers in the past. Moreover, it has been postulated that a bipolar seesaw interhemispheric mechanism dominated the relationship between the Northern and Southern hemisphere climates since the Pleistocene. Due to the region’s semi-arid climate, terrestrial palaeorecords are rare and our understanding of the long-term sensitivity of the region’s ecosystems to climatic drivers is ambiguous. The sub-tropical Mfabeni basin is the only known continuous coastal peat deposit that documents glacial and interglacial palaeoenvironmental conditions since the late Pleistocene (ca. 47 cal kyr BP) in southern Africa. Biomarker (n-alkane, n-alkanoic acid, and n-alkan-2-one) and molecular leaf wax isotopes (δ13Cwax) analysis, in conjunction with bulk geochemical data, was employed to reconstruct the Late Pleistocene and Holocene palaeoenvironment of the region, and due to the physical peat forming mechanisms in the basin, we were able to link these changes to regional precipitation and ambient air temperatures. By employing the n-alkane ratios and δ13Cwax OM source proxies and temperature sensitive n-alkanoic acid and n-alkan-2-one ratios, we reported dramatic variations in precipitation intensities, but subdued temperature fluctuations during the late Pleistocene. The Holocene period was characterised by overall elevated temperatures and precipitation compared to the preceding glacial period, interspersed with a millennial scale cooling event (c. 7 cal kyr BP). The Mfabeni archive displays a strong correlation with the adjacent Indian Ocean marine core records, confirming that regional ocean surface temperatures were the dominant climate driver in the region. A general anti-phase sequence was observed between the Mfabeni record and better established Northern Hemisphere events, underpinning the bipolar seesaw interhemispheric mechanism proposed for global climate forcing since the Late Pleistocene.

AAPG Datapages/Search and Discovery Article #90332 © 2018 AAPG International Conference and Exhibition, Cape Town, South Africa, November 4-11, 2018