General comments

• Multiple records suggest that the 8.2 ky event is the most significant climate anomaly of the Holocene. It is likely to have been triggered by melt waters in the North Atlantic region allowing us to examine a climate mechanism that may well operate in the near future. Thus, the authors certainly address a relevant subject.
• The authors select a cave from the North Atlantic region, close to the source of the perturbation.
• They provide a reconstruction of the hydroclimate of the regions using multiple proxies and with decent age control. They make a careful examination of the proxy interpretation within the record they produce, pointing out strengths and limitations.
• They further compare this record to others in the region providing regional context to the event.
• I think the goals of the project are highly relevant. My major comments address one technical calculation aspect and consideration of a recently published paper that is relevant to the conclusions in this paper.

Specific comments

• Growth rate calculations:
  • One of the strengths of using speleothems as a proxy archive is the strong age control. This is provided by absolute uranium-thorium dating with well-constrained uncertainties. Conversion of these absolute ages to an age-depth model has to incorporate uncertainties resulting from sampling resolution, averaging of time during sampling and other statistical considerations that the age-depth model may make.
  • I think a more robust way to go about growth rate calculations is to measure the growth rate between uranium-thorium dates, rather than stable isotope and trace element sample depths.
  • This study has made sufficient age measurements to make this approach feasible.
  • To examine the relationship between growth rate and stable isotopes and trace elements, I would then average these proxy measurements between uranium-thorium depth samples.
  • I would highly recommend that the authors carry out this exercise, if not as the main analysis, then at least for verification purposes.
• Timing and structure:
  • The recently published paper by Parker and Harrison on ‘examination of the timing, duration and magnitude of the 8.2 ka event in global speleothem records’ would be a useful reference to contextualize the region examined in this study to global records in the Parker and Harrison study.
• More nuanced characterization of the trigger region:
  • It is often the case that the driver of a climate events, such as the 8.2 ky event, is ‘found’ in distal locations such as the monsoon regions. This is not surprising, but nevertheless, it would be nice if the event could be better characterized at the source location.
  • The authors have a sample and experience with the climate of such a trigger source location. Where possible, it would be nice to see if the authors could discuss their results against modeled data and data from other archives and proxies in the region to give a better picture of the event. This would help understand the climate dynamics in other locations as well and would make the study more useful and impactful.

Specific comments

Line 45: Does the ice layer counting effect the start and end age or also the duration of the event?

Line 55: Please can you add references for ‘event, duration, shape and impacts’ as well as the attribution to ‘low resolution time series’.

Stay consistent with units of trace element measurements through the paper.

Figure 1: Show Cantabrian region and the Santander GNIP locations on the map.

Is it monthly averaged d18O or rainfall-weighted monthly averaged d18O?

Figure 2: Thanks for the photos! It would be great if you could provide some additional information. E.g. what is the height of the drip water from the stalagmite?  Do you know if the water is dripping through the stalactite, or if it is blocked, and flowing outside the stalactite.

Line 110: Rainfall ‘amount effect’ is a rather technical term used to describe an isotopic process more relevant to tropical convective systems. Perhaps this is rather upstream rainout?

Paragraph starting at 130: It’s great that so much cave exploration and monitoring has been done. At the moment, it is not clear how much of the information in this paragraph is from the Rossi and Lozano paper and how much is your interpretation.

Section 3.1 – Material: Was the mineralogy of the sample measured? Which method was used? Based on the measurement, what is the mineralogy of the sample?

Sections 3.3 and 3.4: Were stable isotopes and trace elements measured at the same resolution. Figure 4 suggests somewhat lower resolution trace element measurements.

Table 1: Please can you show this data as cross plots in the supplementary information section. It is a better way to understand the data. It would be helpful if this could be done wherever you refer to correlation coefficients.

Line 260: Perhaps the 30-point running correlation won’t be necessary if the data is examined between U-Th dates.

Figure 4: This is a tricky one. The anomaly in magnitude and duration is ever so small in all the proxies apart from the growth rate. The growth rate is the one that is expected to show an anomaly. I would be curious to see how the results would be after measuring growth rate between uranium-thorium dates. I also find it more intuitive to see warmer and wetter directed up. Perhaps the proxy plotting direction is this way to accommodate for the interpretation of the d18O isotopes. Maybe you could add ‘interpretative keys’ to the sides  of the records e.g. d18O = meltwater i.e. source water change / longer travel / upstream rainout etc. or something of the kind.

Figure 5 description: I am wary of language like ‘well-defined excursion’. The plot only covers the short duration from 9.2 to 7.8 ky. Even within the plot, neither the magnitude nor the duration of the d18O excursion stand out very clearly against the rest of the record.

Line 445: Reference Fig. S5 here. What are the pale lines in Figure S5?

Line 505: ‘prominent multi-pronged decrease’ again I would be wary of using such strong language.

Line 510: It could be change at moisture source and/or an increase in the distance of the moisture source from the cave location given circulations changes that maybe expected with such an event.

Line 515: Perhaps the Stoll et al paper (https://doi.org/10.1038/s41467-022-31619-3) is useful for thinking through how the location of meltwater release may impact the oxygen isotopic composition of the source region.

Line 520: Is the mechanism of …more effective recharge = low d13C = low Mg/Ca = low growth rate… does it not apply for slow growth phases of the speleothem? What is the ‘exception’ here?

Line 545: Add acronym for LAO here if you are going to use it later in the section.

Data availability: Maybe best to submit data to NOAA – more findable. And Zenodo or a University repository in SISAL format with the additional metadata since SISAL database updates are not frequent.

Review “The 8.2 ka event in northern Spain: timing, structure and climatic impact from a multi-proxy speleothem record” by Kilhawn et al.

This manuscript presents a speleothem record from northern Spain (El Soplao cave) that covers the 8.2 ka event with a well-stablished chronology. The record was presented in a previous paper focused on other time period (Rossi et al., 2018) and the chronology has now been improved. The main highlight is the combination of proxies to really infer the climate signal in this region as response to the 8.2 ka, combining growth rate, stable isotopes and trace elements with adequate resolution. There is a nice discussion to interpret the proxies and an excellent comparison with other speleothem records from W Mediterranean. The authors conclude that this event was synchronous in Greenland and S European records, with similar structure. I just have few comments that can be easily solved in a new version of the manuscript, previously to its acceptance.

1. The influence of temperature and amount of precipitation in the rainfall isotopic composition (i.e. d¹⁸O) is not easy to determine in this region. I like the approach of separating both influences as it is presented in Fig. S2 (lines 112-115 in the main text) but I think that, from the graphs, an acceptable correlation with temperature can be inferred, excepting for samples with very high precipitation. I think those samples may correspond to heavy summer storms that can provide very negative values although temperature is high. The authors may want to check it. Therefore, this figure and the obtained correlations need a more detailed consideration and probably giving a more important role to temperature variation.
2. Besides, in line 465, it is considered a d¹⁸O – temperature gradient between 0.24 – 0.34 ‰/°C, following GNIP results presented in (Domínguez-Villar et al., 2008), values that can be higher in other areas in northern Spain (please, check Moreno et al., 2021 for information at event-scale). If those values are higher, they won’t be counterbalanced by the temperature dependence of water-calcite isotope fractionation in the cave. Thus, I would not exclude so rapidly temperature as an important influence on d¹⁸O record. I think that temperature influence can be higher than 0.11 ‰/°C as pointed the authors in line 468. Still, I agree with the authors that very likely, the effective recharge was a more important factor on d¹⁸O values.
3. Although I agree that other records such as lake or marine sediments lack the adequate resolution (in the sampling and in the chronology) to provide information about the timing of the 8.2 ka, I don’t agree about neglecting the information they can offer on the impact of that event. I think that information can be of importance to get the regional picture and try to stablish the forcing mechanisms. It is important to include some lacustrine records and archaeological sites in the discussion section 5.2.3 since they are indicating, in general, a dry period during the 8.2 ka event, contrarily to what is observed in the speleothem records. I would recommend checking the Basa de la Mora record (a well-dated Holocene record from a lake in the Central Pyrenees) (Pérez-Sanz et al., 2013); the pollen record from marine core MD952043 and references therein (Fletcher et al., 2013) and a compilation of archaeological sites from the Ebro valley that were abandoned during the 8.2 ka due to dry conditions (González-Sampériz et al., 2009). There is also a recent paper on this topic (García-Escárzaya et al., 2022). I think all these records will enrich the discussion and may allow to define different regions in Iberia with distinct responses to the 8.2 ka event.

Minor comments:

• I miss the age model figure for SIR-1
• I am surprised that generating a new chronology for the presented records provides such differences in timing comparing with the previous ones (more than 200 years of temporal shift in some cases). This is important to me since considering one or the other way of generating the age model makes the 8.2 ka event to be synchronous or not. I wonder if the authors considered to improve the chronologies with more dates, not only with a different modelling approach to get a more robust approach here.
• Line 691: the reference Zielhofer et al., 2019 does not correspond to SW Europe (it may be better to talk about W Mediterranean).

References

Domínguez-Villar, D., Wang, X., Cheng, H., Martín-Chivelet, J., and Edwards, R. L.: A high-resolution late Holocene speleothem record from Kaite Cave, northern Spain: d18O variability and possible causes, Quaternary International, 187, 40–51, 2008.

Fletcher, W. J., Debret, M., and Goñi, M. F. S.: Mid-Holocene emergence of a low-frequency millennial oscillation in western Mediterranean climate: Implications for past dynamics of the North Atlantic atmospheric westerlies, The Holocene, 23, 153–166, https://doi.org/10.1177/0959683612460783, 2013.

Asier García-Escárzaga, Igor Gutiérrez-Zugasti, Ana B. Marín-Arroyo, Ricardo Fernandes, Sara Núñez de la Fuente, David Cuenca-Solana, Eneko Iriarte, Carlos Simões, Javier Martín-Chivelet, Manuel R. González-Morales & Patrick Roberts Human forager response to abrupt climate change at 8.2 ka on the Atlantic coast of Europe, Scientific Reports volume 12, 6481, 2022.

González-Sampériz, P., Utrilla, P., Mazo, C., Valero-Garcés, B., Sopena, M. C., Morellón, M., Sebastián, M., Moreno, A., and Martínez-Bea, M.: Patterns of human occupation during the Early Holocene in the Central Ebro Basin (NE Spain) in response to the 8.2 ka climatic event, Quaternary Research, 71, 121–132, 2009.

Moreno, A., Iglesias, M., Azorin-Molina, C., Pérez-Mejías, C., Bartolomé, M., Sancho, C., Stoll, H., Cacho, I., Frigola, J., Osácar, C., Muñoz, A., Delgado-Huertas, A., Bladé, I., and Vimeux, F.: Measurement report: Spatial variability of northern Iberian rainfall stable isotope values – investigating atmospheric controls on daily and monthly timescales, Atmospheric Chemistry and Physics, 21, 10159–10177, https://doi.org/10.5194/acp-21-10159-2021, 2021.

Pérez-Sanz, A., González-Sampériz, P., Moreno, A., Valero-Garcés, B., Gil-Romera, G., Rieradevall, M., Tarrats, P., Lasheras-Álvarez, L., Morellón, M., Belmonte, A., Sancho, C., Sevilla-Callejo, M., and Navas, A.: Holocene climate variability, vegetation dynamics and fire regime in the central Pyrenees: the Basa de la Mora sequence (NE Spain), Quaternary Science Reviews, 73, 149–169, https://doi.org/10.1016/j.quascirev.2013.05.010, 2013.

Rossi, C., Bajo, P., Lozano, R. and Hellstrom, J. Younger Dryas to Early Holocene paleoclimate in Cantabria (N Spain): Constraints from speleothem Mg, annual fluorescence banding and stable isotope records, Quaternary Science Reviews, 192, 71-85 2018 https://doi.org/10.1016/j.quascirev.2018.05.025.