the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 20 Aug 2024
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
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 -
RC2: 'Comment on egusphere-2024-2499', Anonymous Referee #2, 18 Dec 2024
Review of egusphere pre-print 2024-2499 of Purcell et al. entitled “Climate variability off Africa’s southern Cape over the past 260,000 years”
Purcell et al. present XRF data from a study core MD20-3592 from off the coast of South Africa and apply a number of data analysis techniques (principal component analyses, filtering) to derive the dominant mechanisms driving sediment composition, primarily precipitation in nearby river catchments and terrigenous sediment supply, marine productivity changes as well as adjustments in wind circulation. The authors compare their data to speleothem records in South Africa and other sediment records around South Africa. They find a dominant impact of precession on continental aridity and precipitation patterns via its impact on land-ocean temperature contrasts, river discharge, and hence sediment composition at their study sites. This appears to be consistent, as the authors argue, with earlier findings based on sediment cores nearby.
The study addresses an important aspect of the climate system, namely the interplay of orbital forcing, local wind patterns and land-ocean interactions via sediment supply in South Africa and the adjacent ocean. These findings are not fully new, but I find the comprehensive comparison of local records spanning speleothems and sediment cores bears strong value.
The study is well-motivated and well-illustrated. I do, however, find that the study is not streamlined enough, lacks clarity, and is longwinded in parts. Also, I find that a clear scientific hypothesis is lacking. The link to hominin evolution is oversold and irrelevant because the study does not provide a clear comparison of suggested climate evolution and robust evidence from archaeological sites for mobility, technological advances of Homo species. I also recommend major restructuring of some parts of the study.
I outline major and minor criticism below and hope that the authors find them useful to improve and revise their study.
Major comments:
Motivation of the study and streamlining of the Introduction: I am missing a clear scientific question that is addressed in the study. It is therefore unclear what the goals of the PCA and spectral analysis etc. actually are. Writing “Principal component analysis (PCA) was conducted to facilitate interpretation of the XRF data.” is in my view not enough. The motivation for these types of time series analyses needs to be clear from the introduction in association with the scientific question(s) or hypothese(s). Please revise accordingly.I understand that the focus of the study is on studying sediment composition at the study site and how this is driven by precipitation changes in South Africa. However, there are a number of studies mentioned in the Discussion section that addresses these issues based on numerous cores nearby, and it is not clear how the study of Purcell et al. addresses an open question within the background of these existing studies. This needs to be emphasized in the Introduction and the scientific question(s) or hypothese(s) highlighted accordingly. In other words, the study of Purcell et al. would benefit from a clear introduction of what is known, what is debated and what remains an open question? Phrases such as l. 678 “Core MD20-3592 is the first marine sediment core off the coast of southern South Africa which allows for a reconstruction of the climatic conditions over the past two glacial cycles.” should be avoided because they are clearly wrong given the numerous records. Instead, it is more valuable to highlight what kind of assessments *specifically* the record does allow, such as potential river discharge changes in Southeast African river systems due to adjustments of the hydrological cycle over the past two glacial cycles.
I also recommend that the authors make a clear list of XRF elemental ratios that are important for the study and elaborate in clear fashion, what this XRF elemental ratio can be used as proxy for, in what capacity in the study area it was used before, and what purpose it serves in the study. Figure 2, 4 and 9 shows a number of XRF elemental ratios although they are never properly introduced. The description of the XRF ratio Fe/K in line 424-432 is somewhat inconclusive, as variations in K are not discussed. Please elaborate. If the authors are primarily interested in the ratio of a terrigenous versus biogenic element, then it is not clear why Fe/Ca is not used.
The importance of the analyses for the evolution of Homo sapiens in South Africa is overemphasized as no robust comparison between the marine and archaeological findings are made. The final sentence in the abstract is too vague and oversells the findings (without accurately proving the assertion). Thus, rather than elaborating at length about Homo sapiens evolution in the Introduction, I recommend to elaborate on the state-of-the-art of our knowledge of the hydrological cycle in South Africa (winds, precipitation, river discharge, etc.) and the open questions that remain and will accordingly be addressed in the study. This link made between hominin evolution and adjustments in the hydrological cycle in the final paragraph of the Conclusions is poor and not convincing. Remove or rewrite by providing convincing figures/argumentation showing a possible relationship between the two and sufficient background of the existing state-of-the-art of the archaeological literature.
Statements are often too vague in my view
Name available climate archives (l. 20 and l. 30)
Specify what exact purpose PCA serves in the study (l. 25) (stating “Principal component analysis was performed to facilitate the interpretation of the data.” is not enough)
Specify “this variability” (l. 56)
Clarify preference of whom (l. 61)
Specify in what way “at coastal environments, a strong influence of the Agulhas Current on hydroclimate is apparent” (l. 64)
Specify what is meant by climate signal (l. 78, -> sediment?),
Specify what is meant by “marine proxy records provide age constraints and palaeoceanographic conditions” (l. 103, -> age constraints for what?, what conditions specifically?)
Include “increased proportion of sediments from local southern African sources” (l. 118)
Link the information in the supplement by stating the figure, text and/or table to steps 1-3 (l. 204)
Statement “although the general pattern displays variability” (l. 209) is too vague, please remove or specify what is the general pattern and what is meant with “variability”.
Specify what is meant by “marine processes” (l. 216)
Specify what is meant by “large” and “relatively lower amount” in l. 240 (The explanation in lines 240-242 is incomprehensive, please revise)
Specify what the type of soil has a notable impact on (l. 424)
Specify the most important paleoclimate archives used for comparison, i.e., core name and region (Simon et al., 2015; Chase et al., 2021) (l. 681)
Specify what exactly drives variations in terrestrial input and what is controlled by orbital forcing; “climate change” is too vague (l. 688)
Specify what parameter shows the main frequency (l. 689)
Specify “other mechanisms” (l. 707)
Specify “successive technocomplexes” (l. 711)
Specify what is meant with “elemental oxide ratios” and “calcium input” (l. 434). Do you mean the sediment composition and the deposition of CaCO3 at the study site, respectively? Give details on “other elements”.
Elaborate on what way “this could affect the interpretation of the XRF data” (l. 438). I think you mean the postulation that XRF elemental ratios are primarily driven by riverine input of terrestrial material. Please say so in that case.
Elaborate on why the data do not support this (l. 440)
Rephrase “downcore variations in geochemistry” into “downcore variations in sediment composition” (l. 448)
Give more details on “significant sedimentation rates changes” (l. 453) and make a reference to a figure showing these changes.
Give details on the “exposed Agulhas bank”, the timing and drivers of exposure. Give appropriate references. (l. 462)
Please revise these sentences as they are incomprehensive (l. 473-476) Use MIS to refer to time intervals (or “Late Holocene”).
Statement “This observation is confirmed with the cross wavelet transform, as indicated by the arrows in fig. S6.” is unclear (l. 516). More specification is needed in the main text.
Specify what parameter is referred to here. (l. 555)
Give details on what “statistically significant amount of precessional forcing component” means (l. 577)
Specify “terrestrial paleoenvironmental evidence” (l. 604)
Specify “patterns” (l. 611).I find that key methodological information is missing or is unclear:
In section 3.1.1., specify the dimensions of the detector and the energies used? How was the core prepared (scraped clean, use of foil)? I am missing key aspects of the XRF methodology here. Rephrase “most easily interpretable signal” (“most reliable signal reflecting true sediment proportions” or similar). Name specifically how “previous study have used variations in sediment geochemistry” as this statement is too vague. “Rate” should likely also be rephrased into “proportion”.Section 3.1.2. specify how the sediments were digested/prepared for ICP-AES measurements? How were the samples introduced into the system? Where were the HR-ICP-MS analyses completed? How were the samples prepared for introduction into the mass spectrometer? What standards were used for the solution-based analyses? What is the accuracy/precision of the analyses? Or was a laser used throughout?
Also, I am confused whether the first and second paragraph describe two separate ways of XRF calibrations and I recommend clarification/specification accordingly. I also recommend that the authors describe their methods following an order of sampling, sample preparation, sample analyses, data processing/data quality check (if applicable). If “The results from VU were chosen for calibration because they included SiO2 which is the most abundant oxide in core MD20-3592.” (l 237), then I am confused why the other method is included. Please clarify. The comparison of the two methods is inadequate and too short (237-239) as it is not clear what elements were compared and how the numbers given come about (here a comparative figure is needed).
Line 156-158: These statements are very vague and unclear. Specify. What do you mean by “quantitative results”? How does this constrain “the interpretation of proxies” and what “paleoclimatic information” is relevant?
Avoid over-describing: lines 181-190 overdescribe PCA and is redundant in the paper. The same level of detail was not applied to explain XRF scanning, ICP-AES and HR-ICP-MS analyses (and rightly so); hence, it should be removed for PCA. Instead, explain in more detail what elements went into the PCA and what criteria were used to include or exclude elements. Specify what counts as “strongest XRF counts”, used to define the elements that went into the PCA. I also find lines 247-254 redundant and trivial. This is an over-description of the application of linear regressions. The same applies to lines 311-319 and to lines 487-490. Also, the description of the orbital parameters in 517-521 and 526-529 can and should be more succinct.
Age model:
The age model section definitely needs to go into the Methods section. It forms the basis for the spectral analysis and as such should not appear in the Results section. Also, this makes lengthy descriptions of XRF patterns against depth redundant as the reader is mostly interested in temporal changes in XRF elemental ratios only, as depths are difficult to link with ages for those who do not know the core inside out. This would make the paper much more streamlined and clearer, when section 4.1.1. will be shortened and the important observations will be highlighted against age.I am also not convinced of the use of N. incompta d18O for pinpointing the transition from MIS5-4, and find the choice of different species for different intervals dubious. The N. incompta d18O data are awfully low in resolution and it is not clear why the G. ruber data is *particularly* noisy in that area and not in other areas where tiepoints are based on G. ruber d18O. Particularly, transitions do not seem to match between N. incompta d18O and G. ruber d18O within few thousand years for instance at the MIS8-7 transition, which I find worrying. Please revise. I would strongly recommend to stick with G. ruber at the MIS5-4 transition accordingly. In addition, the G. ruber tiepoint at ~100 kyr is not convincing.
Please specify why AICC2012 was chosen as tuning target timescale and not AICC2023 (Bouchet et al., 2023) – the updated ice age scale for EDC. Please elaborate and adjust accordingly.
Principal component analyses (section 4.3):
Line 362: This first sentence is too trivial and should be rephrased. PC1 *always* explains the majority of the variance in the dataset. I also find that the scree-plot in Figure 7a is obsolete because variances of PC1-3 are given in the text and >PC3 is not relevant in the study.Line 364-366: I wonder why the loadings PC2 and PC3 are described, as they do not play a role in the remaining study. The text can accordingly be removed. Please use “positive loading” instead of “positive pole”. Please focus here on the most relevant findings, otherwise it becomes too confusing.
The assertion that “Ratios like Fe/K display a comparable pattern with PC1, suggesting that PC1 can be used to represent terrestrial element variability.” is incomprehensive. First of all, this is not demonstrated in a figure. I therefore recommend to do a comparison of Fe/K and other relevant XRF elemental ratios (Fe/Ca shown in Fig. 9) together with PC1 in Figure 7e in landscape as in Figure 2 and 4. Additionally, the use of the XRF elemental ratio Fe/K as indicator of “terrestrial element variability” is unclear to me and insufficiently explained. What is meant specifically by variability (supply? Relative proportion of different terrigenous sediment types? Please specify.)? This comes back to the issue that elemental ratios are not carefully introduced and hence because Fe and K were introduced as terrigenous elements, how Fe/K and accordingly PC1 is interpreted is not clear here.
Figure 7. Please specify what dataset the principal component analysis is based on and from what core this dataset stems.
Spectral- and wavelet analysis (section 4.4):
Please specify on the basis of which “the power spectra of eccentricity” and “the power spectra of obliquity” was calculated. Is this based on an astronomical solution of Laskar?Line 386-399: It would also help the reader if Marine Isotope Stages are also given here rather than using “older than 175 kyr” and “starting from the bottom of the core” and “in the younger half of the core”. The same applies to l. 696-697, l. 710-719 and l. 550-552.
Line 389. Elaborate on the “notable differences in amplitude” and refer to a figure. It does not suffice to simply say that. If these differences do not matter for the later discussion, remove the statement here.
Specify what window size has been used to calculate the Gaussian filters.
Line 396-399: the information on the cone of influence is in my review redundant. This is general knowledge.
Figure 8: Specify on what core and on what dataset the timeseries analysis was conducted. PCI should read PC1. AR(1) as abbreviation is not defined: please revise. “See text for explanation” is redundant and can be removed. “It can be seen that between ∼25 and ∼125 ka the cyclicity centred at ∼23 ka dominates, while deeper in the core the cyclicity centred at ∼41 ka dominates. The 122 ka cyclicity is outside the cone of influence.” is also redundant as this is explained in the text. For Figure 8b, give reference of the orbital data. The statement “The morlet wavelet is used as it usually performs best (Hammer et al., 2001).” is odd in the figure caption as this should be clear from the Methods section and it remains unclear what “usually” means and whether this also applies to the study of Purcell et al.
Avoid (lengthy) descriptions of figures in the main text. All information relevant to understand figures must become clear from the figure captions. In my view the authors should choose to link the observation and/or the finding with the figure in brackets after the statement. Please revise E.g. lines 208, 235, 246, 254, 275, 378, 394, 542-546, 584 This would make the reading flow much more efficient and the study clearer.
Discussion:
Comprehensibility of the discussion: Descriptions are often not streamlined and long-winded. Often the authors attempt to explain changes seen in other records rather than focusing on the study site.L. 434-540: The authors argue that XRF elements of terrigenous type are primarily driven by input fluxes via rivers. However, relative changes in the proportion in biogenic carbonate and biogenic silica, changes in carbonate preservation and changes in winnowing/focusing could also play a role. The assumption of constant or low fluctuations in carbonate flux out of the euphotic zone given strong changes in alkenone fluxes (e.g., Martínez-Garcia et al., 2014) seems misleading. The arguments based on CaO percentages in the study core are weak because the data are very low in resolution and XRF Ca intensity counts could be influenced by water content variations. Here I recommend that the authors make a thorough assessment of possible variations in the export flux of carbonates, and show the CaO assessment for the full core length.
Also, the authors discuss possible influences of carbonate preservation changes based on change in circulation, namely the influence from GPDW. However, NADW and AABW have likely a much stronger influence on the carbonate ion saturation of the study site (e.g., Hodell et al., 2001; Gottschalk et al., 2018), which are not addressed. More information is needed here, to exclude the effect of variations in the carbonate preservation on the sediment composition at the study site (e.g., Hodell et al., 2001; Gottschalk et al., 2018).
L. 453: How can high sedimentation rates unequivocally explain increased sediment supply by rivers? How about increased aeolian dust input, increased productivity through dust driven input, increased sediment focusing? How about ACC changes? I would expect that other factors are unequivocally excluded before making such statement.In the discussion section 5.2, the authors have chosen to compare their record to other sediment cores and archives, one by one. There is a lot of potential to streamline this because commonalities could be pointed out first, essentially confirming postulations made based on the study core, then followed by differences and how they can be explained. I find the one-to-one discussion of the different archives with the study core long-winded. At the moment, some of the comparisons are insufficient. For instance, l. 580 explanation is needed why “there are differences between the study core and MD96-2048”.
Purcell et al. assess the role of obliquity on the sediment composition in their study core. The find that “The inconsistent phasing makes it difficult to explain a mechanistic relationship between obliquity and the signal observed in MD20-3592.” This is somewhat disappointing and I wonder what the scientific hypothesis was that was tested based on the filtering. Please elaborate, if possible. Maybe a more important outcome would be that obliquity did *not* have a strong control on the sediment composition at the study site via shifts its control on the southern hemisphere westerlies (Timmermann et al., 2014). Would that be a valid conclusion?
Also, the wavelet analysis shows that the early record indicates a dominance of obliquity and the later record a dominance of precession. This is not mentioned in the discussion and remains unexplained. Please elaborate on that in the discussion.
The role of the southern hemisphere westerlies is not well addressed in the discussion. The statement in l. 650 leaves a role of the SHW unclear. A better integration of the possible changes in the SHW on glacial-interglacial timescales (Gray et al., 2023; Toggweiler et al., 2006) and/or driven by obliquity (Timmermann et al., 2014) is needed in the discussion.
Minor comments:
L. 72: Please revise the following statement “The hydroclimate of southern Africa is recorded in multiple terrestrial and marine climate archives (e.g., Chase, 2021). However, the southern part of South Africa is poorly resolved, especially on orbital timescales (Fig. 1). So far, to the author’s best knowledge, there are no published marine sediment cores records offshore the Southern Cape which span the last two glacial cycles.” It cannot be the only motivation of the study that this record is the first one right off the Cape and that spans the last two glacial cycles. There are other cores nearby that are similarly valuable although they only span one glacial cycle. Rather mention here what the open questions are that the new core allows to address! Also, why is this the “first high-resolution and continuous record of terrestrial climate and palaeoceanographic conditions for the study region” (l. 76)? There are a number of other similarly important records in Figure 9 and 10, including Simon et al., 2015 and Caley et al., 2018 which mainly show the same sedimentary features on a precession scale. Please refrain from such statements even if it is the first covering the last two glacial cycles. Another core will be the first one to cover two and a half glacial cycles, which is trivial.Figure 1. Text on land (river labels) is not legible at all. I also recommend to list all sites from Figure 1 (sediment cores, speleothems, archaeology) with associated metadata (lat, long, depth, references, interval covered) in a table for clarity. At the moment symbols overlay each other and it is not clear what the different sites refer to (caves, archaeological sites and craters are not clearly separated).
Line 124-126: statement requires reference(s)
Line 131-133: statement requires reference(s)
Figure 2. specify that the figure shows “XRF element ratios from sediment core xxx. What does CCSF refer to? “Lower variability in d and e causes the running average to overlap closely with the full resolution.” in the figure caption can be removed. Why does the figure not show logarithmic ratios of the elemental ratios as announced in the Methods section? The abbreviation cps should be defined.
Line 245 and 338: Tables have headers and not captions.
Line 259: Specify what “some peaks” and “general variability” refers to. Also, this sentence is entirely unclear: “This shows that the calibration yields effective individual elemental concentrations”. Please specify and elaborate.
Line 277: please specify the correct name for the radiocarbon facility at ETH Zurich.
Line 279: specify what is meant by “nearest 5 measured points”
Line 284: define the use of d18O- and dD-notation.
Line 304: µg instead of mg
Line 320: specify how the density of the sediment was determined.
Table 2: include CaCO3 weights for each sample
Figure 3. Why are the XRF element ratios (ln or not) not plotted against the oxide analyses? I understand from the text that this was used to calibrate the XRF data, and not the regression lines that are actually shown in Fig. 3. I must say that I am quite confused at this stage. The grey shading is not visible in the figure.
Figure 4. See my comments on Figure 2. Figure 2 and Figure 4 should be combined; there is a lot of redundancy there.
Figure 5 and Figure 6 e show some redundancy too. Please combine the figures accordingly.
Line 331: “EDC dD values from the Antarctic EDM ice core” is inconclusive. Please correct. EDM should read EDC, but then it would be a double mention.
Line 492: period instead of frequency
Line 584-591: this paragraph contains a lot the phrase “this record”. It is hard to follow. Please revise accordingly. This paragraph also requires a concluding sentence as the results of Engelbrecht et al. (2019) are not effectively linked with the observations.
Line 595: correct MD20-3992
Line 601-603: provide reference of the dataset in the first sentence.
Line 626-630: add references in association with external datasets.
Figure 9. For the EDC dD record Jouzel et al. 2007 should be referenced. Rephrase “PC1 of XRF”.
Figure 10. Specify what is compared against what in the introductory line. Rephrase “PC1 of XRF”. For the EDC dD record Jouzel et al. 2007 should be referenced. Provide the references for Figure 10c, d and e in the figure caption. The MD20-3592 data superimposed in c-e is hardly visible.
References:
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