the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
Climate variability off Africa’s southern Cape over the past 260, 000 years
Abstract. During the late Quaternary the past climatic conditions of southern South Africa underwent fluctuations, influenced by various climatic factors, such as the impacts of both the Indian and Atlantic Oceans, as well as the effects of the southeasterly trade winds and Southern Hemisphere Westerlies (SHW), influenced by changes in orbital parameters. At the same time, this region exhibits some of the most abundant Middle Stone Age (MSA) archaeological sites containing records of Homo sapiens behavioural and technological evolution. Consequently, there is a pressing need for precise climatic reconstructions that can provide climate constraints during the MSA in this area. However, there is a lack of continuous high-resolution climate records covering the majority of the MSA, which spans from ~300 to ~60 ka. In this study, we present data obtained from a marine sediment core (MD20-3592) that spans approximately the last 260,000 (from m8 to 1) aiming to expand the spatial and temporal coverage of available climate archives. This marine sediment core documents both terrestrial and ocean hydroclimate variability because it is strategically positioned close to the South African coastline receiving terrestrial sediments via riverine input as well as being located under the marine influence of the Agulhas Current at the same time. X-ray fluorescence (XRF) core scanning, calibrated with discrete samples analyzed by XRF spectroscopy, was used to determine the variability of the bulk elemental composition of the core over time. Principal component analysis was performed to facilitate the interpretation of the data. Statistical analyses including frequency analysis, gaussian filtering, and wavelet analysis reveal that the regional hydroclimate was affected mostly by local insolation changes caused by orbital precession, and high latitude forcing that varies on timescales associated with orbital obliquity and eccentricity. Increased fluvial input was associated with a high precession index, during times of high local insolation, due to the effects of precession on local convergence and seasonal rainfall. Comparison with regional climate archives confirmed the dominant influence of precession on precipitation in southern South Africa. On glacial-interglacial timescales, lower precipitation observed during glacial intervals could be explained by a northward shift of the Southern Hemisphere Westerlies (SHW) and South Indian Ocean convergence zone (SIOCZ). Finally, the data from core MD20-3592 can provide a climatic context for the appearance of behavioral complexity in South Africa between ~ 120 ka and ~ 50 ka. Humid conditions in the river catchments going through the south coast and south-east coast of South Africa were present at approximately 117 ka, 93 ka, and 72 ka, alternating with dry conditions at approximately 105 ka, 83 ka, and 60–50 ka.
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RC1: 'Comment on egusphere-2024-2499', Anonymous Referee #1, 16 Sep 2024
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This paper presents climatic data derived from a marine core spanning the last 260,000 years off the southern Cape coast of South Africa. The southern Cape is a major focus of Quaternary climate research, both for its own sake as well as for understanding archaeological, ecological, and biogeographic change. The paper is appropriate for CP and I recommend publication pending revision.
Perhaps my biggest concern with the paper is the setup. Both in the abstract and introduction, the manuscript emphasizes the southern Cape’s Middle Stone Age (MSA) archaeological record and the “pressing need for precise climate data” to better understand this record. The archaeology appears to be the motivation for the paper. This would be an appropriate setup for the paper if there was going to be some serious engagement with the MSA record, and how the new climate record helps to understand it. However, outside of the abstract and introduction, there is very little meaningful engagement with the MSA record from the southern Cape. In the discussion section of the paper, the main reference to the archaeology is “Finally, the data from core MD20-3592 can be used to provide a climatic context for the ~ 120-50 ka time interval during which evidence of behavioural complexity in humans appears in South Africa. The general climatic trends inferred from the MD20-3592 PC1 record are as follows: 1) Initial humid conditions at ~120 ka become progressively more arid from ~117 to ~102 ka; 2) More humid conditions return between ~98 and 88 ka, after which a pronounced period of aridity centred on ~83 ka occurs; 3) Conditions become progressively more humid between ~ 83 and ~72 ka, after which progressive aridification occurs until ~60 ka; 4) Arid conditions persist until ~50 ka.” If that’s as deep as the authors want to dive into the archaeology, I don’t see why MSA archaeology is the main hook of the paper—i.e., the archaeology angle appears to be little more than window-dressing. Can we not write paleoclimate papers for the sake of learning more about paleoclimate? Why frame this great new record around an archaeological problem that you aren’t going to address?
The solution here is to (1) frame this paper (in the abstract/introduction) around paleoclimate—it’s fine to mention the archaeology where appropriate, but that isn’t what this paper is about; or (2) engage meaningfully in the implications of this record for the MSA archaeological record in the southern Cape. But if you go with option 2, just please, please avoid wiggle-watching and hand-waving!
Abstract line 12-13: The first sentence of the abstract is rather clunky
Abstract line 15: replace “exhibits” with “preserves”
Line 17: “during the MSA” I have been scolded many times for referring to the MSA as a period of time. It’s a technological industry that starts and ends at different times in different places. Reword to “…can provide climate constraints for the region’s MSA record”
Line 18: ~60 ka is early for the end of the MSA in southern Africa. I would say ~40 ka or even ~30 ka is reasonable.
Line 25-26: do you need to list the statistical analyses provided here? What about “Our results reveal that…”
Line 50-51: It’s also complicated by a lack of a robust mechanism for transmitting climatic cause to the proposed evolutionary effect (Behrensmeyer, 2006).
Line 57: “in the eastern Cape province…” Here and elsewhere, please be precise with your use of geography and place names. There is no Cape province anymore. There is an Eastern Cape province, but the paper cited here concerns a record from the Western Cape province.” Southern Cape would still be appropriate to use here.
Line 70: “…the African climate…” Beware of referring to the African climate. It is not a monolithic thing.
Line 123: Once again, be precise with geography and place names. “southern Cape coast and parts of the Western Cape.” A good part of the southern Cape coast falls within the Western Cape (province). So what parts of the Western Cape are you referring to here?
Line 133: geography again. The WRZ extends well north of the Western Cape (assuming you mean Western Cape the province).
Line 148: move the references cited here to the end of the sentence
Line 181-187: Do we need all the details about how a PCA works? A similar level of detail isn’t provided for other analyses.
Line 198: remove comma after “determine”
Line 208: … “and Fe/K” add “is shown in Figure 2g.
Figure 3: Not sure if this is required for the main text. Might be better off in the supplement.
Line 299: Italicize G. ruber
Line 316: remove comma after “reversals”
Table 2. Perhaps italicize or put in quotes “Undatable”; caption: insert comm after “calibration”
Figure 5 caption: “but here an age” to “but here the age”
Figure 8 caption: PC1 is referred to as PCI on two occasions here.
Line 434-435: for ease of reading, put the i.e. statements in parentheses: “…calcium input (i.e., marine productivity)…”
Line 463-465: It’s fine to mention the model, but you should also consult the terrestrial records that speak to wetter conditions and/or the intensification of winter rainfall in the region (e.g., Chase et al., 2017; Chase et al., 2018; Faith et al., 2019; Faith et al., 2024; Sealy et al., 2016; Sealy et al., 2020)
Line 548: “For the Cango Caves, a composite speleothem record named “Cape Fold composite” was produced by Chase et al. (2021)”. The Cape Fold Composite is not just from Cango Caves and it’s not just from speleothems, as it also includes hyrax midden records. Refer to it in the text (e.g., on lines 554, 555, 561, 622) as the Cape Fold Composite rather than the Cango Cave speleothem record.
Line 615: insert comma before “Collins”
Line 631: Again, it would be appropriate to refer to some of the terrestrial records (e.g., Chase et al., 2017; Chase et al., 2018; Faith et al., 2019; Faith et al., 2024; Sealy et al., 2016; Sealy et al., 2020). There’s no need to rely solely on a climate model when there are empirical data at hand!
Behrensmeyer, A.K., 2006. Climate change and human evolution. Science 311, 476-478.
Chase, B.M., Chevalier, M., Boom, A., Carr, A.S., 2017. The dynamic relationship between temperate and tropical circulation systems across South Africa since the last glacial maximum. Quaternary Science Reviews 174, 54-62.
Chase, B.M., Faith, J.T., Mackay, A., Chevalier, M., Carr, A.S., Boom, A., Lim, S., Reimer, P.J., 2018. Climatic controls on Later Stone Age human adaptation in Africa's southern Cape. Journal of Human Evolution 114, 35-44.
Faith, J.T., Chase, B.M., Avery, D.M., 2019. Late Quaternary micromammals and the precipitation history of the southern Cape, South Africa. Quaternary Research 91, 848-860.
Faith, J.T., Chase, B.M., Pargeter, J., 2024. The Last Glacial Maximum climate at Boomplaas Cave, South Africa. Quaternary Science Reviews 329, 108557.
Sealy, J., Lee-Thorp, J., Loftus, E., Faith, J.T., Marean, C.W., 2016. Late Quaternary environmental change in the Southern Cape, South Africa, from stable carbon and oxygen isotopes in faunal tooth enamel from Boomplaas Cave. Journal of Quaternary Science 31, 919-927.
Sealy, J., Naidoo, N., Hare, V.J., Brunton, S., Faith, J.T., 2020. Climate and ecology of the palaeo-Agulhas Plain from stable carbon and oxygen isotopes in bovid tooth enamel from Nelson Bay Cave, South Africa. Quaternary Science Reviews 235, 105974.
Citation: https://doi.org/10.5194/egusphere-2024-2499-RC1
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