Investigating δ18O of Turbo sarmaticus (L. 1758) as an indicator of sea surface temperatures

Azania: Archaeological Research in Africa

2016

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...

Section: Turbo Sarmaticus and Modern Calibration Datamentioning

confidence: 99%

Section: Turbo Sarmaticus and Modern Calibration Datamentioning

confidence: 99%

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

Azania: Archaeological Research in Africa

2016

“…In this study, we drilled closely spaced 426 samples using a micromill, which enables improved spatial and depth control to follow the 427 growth increments (Loftus et al 2017) compared to previous studies of this species (e.g. 428Henshilwood, 1995Henshilwood, , 2008Galimberti et al, 2017). This study rotated the sampling direction in 429…”

mentioning

confidence: 99%

Seasonal scheduling of shellfish collection in the Middle and Later Stone Ages of southern Africa

Journal of Human Evolution

Lee‐Thorp

Leng

et al. 2019

Self Cite

20 This study assesses the seasonal scheduling of shellfish harvesting among hunter-gatherer 21 populations along the southernmost coast of South Africa, based on a large number of serial 22 oxygen isotope analyses of marine mollusc shells from four archaeological sites. The south 23 coast of South Africa boasts an exceptional record of coastal hunter-gatherer occupation 24 spanning the Holocene, the last glacial cycle and beyond. The significance of coastal 25 adaptations, in this region in particular, for later modern human evolution has been 26 prominently debated. Shellfishing behaviours are an important focus for investigation given 27 the dietary and scheduling implications and the abundant archaeological shell remains in 28 numerous sites. Key to better understanding coastal foraging is whether it was limited to one 29 particular season, or year-round. Yet, this has proven very difficult to establish by conventional 30 archaeological methods. This study reconstructs seasonal harvesting patterns by calculating 31 water temperatures from the final growth increment of shells. Results from two Later Stone 32 Age sites, Nelson Bay Cave (together with the nearby Hoffman's Robberg Cave) and 33 Byneskranskop 1, show a pronounced cool season signal, which is unexpected given previous 34 ethnographic documentation of summer as the optimal season for shellfishing activities and 35 inferences about hunter-gatherer scheduling and mobility in the late Holocene. Results from 36 two Middle Stone Age sites, Klasies River and Pinnacle Point 5-6, show distinct seasonal 37patterns that likely reflect the seasonal availability of resources in the two locations. The 38Pinnacle Point 5-6 assemblage, which spans the MIS5-4 transition, records a marked shift in 39shellfishing seasonality at c. 71 ka that aligns with other indications of archaeological and 40 environmental change at this time. We conclude that the scheduling and intensity of 41shellfishing in this region is affected by a suite of factors including environmental and cultural 42 drivers, rather than a single variable, such as population growth. 43 44

“…This sampling strategy is unlike previous sampling efforts: continuous, curving arcs of individual holes 266 that followed the mid-line of the operculum (Galimberti et al, 2016;Henshilwood, 2008;Shackleton, 267 1982). Rather, the direction of sampling is shifted in accordance with the direction of growth changes, 268 forming sets of discontinuous, but overlapping, samples (see Figure 2B).…”

mentioning

confidence: 99%

“…Where two or more shells from a single depositional unit reflect similar mean 372 temperatures, one can infer with greater confidence that the shells record average environmental 373 parameters rather than microhabitat conditions. Yet, as demonstrated by the modern study of 374 Galimberti et al (2016), analysis of multiple shells allows for more accurate reconstruction of 375 parameters such as mean SST and seasonal amplitude. 376 Figure 5 shows the shell-derived SSTs for the Holocene and terminal Pleistocene dataset, according to 377 sub-context.…”

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confidence: 99%

A late Quaternary record of seasonal sea surface temperatures off southern Africa

Quaternary Science Reviews

Sealy

Leng

et al. 2017

14The southern Cape coastal region is important for understanding both the behavioural history of 15 modern humans, and regional and global climate dynamics, because it boasts a long archaeological 16 record and occupies a key geographical location near the intersection of two major oceans. The 17 western boundary Agulhas Current, implicated in global heat exchange dynamics, is an important 18 modulator of southern African climates and yet we understand its past behaviour only broadly as the 19 Current itself scours the coastal shelf and marine sediment core records necessarily provide little 20 detail. Numerous archaeological sites from both the late Pleistocene and Holocene provide the 21 opportunity for reconstruction of near-shore seasonal SST records, which respond both to localized 22 wind-driven upwellings and Agulhas temperature shifts, corresponding in turn with terrestrial 23 precipitation trends in the near-coastal and summer rainfall regions. Here we present a record of 24 seasonal SSTs extending over MIS5, MIS4, and the Holocene, from serial δ18O measurements of a 25 single gastropod species, Turbo sarmaticus. The results show that mean SST shifts accord well with 26 global SST trends, although they are larger than those recorded in the Agulhas Current from coarser-27 scale marine sediment records. Comparison with a record of Antarctic sea-ice suggests that annual 28 SST amplitude responds to Antarctic sea-ice extent, reflecting the positioning of the regional wind 29 systems that drive upwelling dynamics along the coast. Thus, near-shore SST seasonality reflects the 30 relative dominance of the westerly and easterly wind systems. These data provide a new climate 31 archive for an important but understudied climate system. 32