Sea surface temperatures from oxygen isotopes in marine molluscs in Middle and Later Stone Age sites, South Africa

Abstract

The southernmost coast of South Africa has been proposed to have been a uniquely important region in later human evolution, in part due to the abundance of nutritious and dense coastal resources. Yet, strong contrasts in the Middle Stone Age (MSA) and subsequent Later Stone Age (LSA) archaeological records cast uncertainty on the significance of shellfish utilisation for processes of human evolution. Further, climatic shifts are frequently advanced as drivers of widespread technological change but few climate proxy records correspond adequately to the archaeological evidence at a temporal or spatial level to be unambiguously linked to human cultural activity. This thesis presents a temporally and spatially distributed record of near-shore seasonal sea surface temperatures (SSTs) from serial δ 18 O shell measurements of archaeological Turbo sarmaticus opercula. In addition, the annual timing of shellfish harvesting captured in the temperature signal of the shells' final few growth increments is indicative of the scheduling of foraging behaviours and social organisation.A non-destructive method for evaluating the preservation of the original aragonitic shell carbonate using Fourier transform infrared spectrometry with an attenuated reflectance attachment is presented, allowing for robust SST reconstructions. Nearshore SST reconstructions are presented from the LSA levels of Nelson Bay Cave and Byneskranskop 1, with new radiocarbon chronologies spanning the terminal Pleistocene and the Holocene, and the MSA deposits at Pinnacle Point 5-6 and Klasies River Main site, dated to periods in Marine Isotope Stage (MIS) 5 and across the MIS5/4 transition. These reconstructions confirm the utility of near-shore SST records for terrestrial climate reconstructions, indicating summer rainfall shifts during the Holocene and across MIS5/4. The annual timing of shellfish foraging is shown to be markedly different between the MSA and LSA, and more nuanced assessments of foraging behaviours within the MSA and LSA emerge. i capabilities of two instruments within RLAHA, FTIR-ATR and SEM, and noted the good potential for FTIR to provide quantitative measures of calcite contamination. I developed a method for evaluating small powder samples (described below in 3.3.2), published with Prof. Keith Rogers of Cranfield University, who assisted with comparative XRD analyses, as "Loftus E, Rogers KD, Lee-Thorp, JA. 2015. A simple method to establish calcite:aragonite ratios in archaeological mollusc shells. Journal of Quaternary Science. 30(8): 731-735."Another methodological issue only became apparent gradually during the first 18 months of my DPhil -the newly-acquired Sercon carbonate device in RLAHA could not analyse small samples with the precision necessary for palaeotemperature research. I had been analysing samples using the Kiel Device in the Department of Earth Sciences, Oxford, with the help of Dr. Chris Day, but that instrument was heavily utilised and experiencing recurring break-downs during this period. I also visited the Divisio...