the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 19 Feb 2025
High-Resolution Paleo-Storm Reconstruction from Eastern Canada Aligns with Late-Holocene Northwestern Atlantic Hurricane Records
Abstract. Atlantic Canada experiences frequent major storms, particularly tropical cyclones transitioning into post-tropical storms. Events such as Hurricane Fiona (2022), Dorian (2019), and Juan (2003) have caused significant damage, loss of life, and coastal erosion, exacerbated by sea level rise and warming waters. Despite this, centennial- to millennial-scale storm records in the region remain scarce. Existing studies in North America focus primarily on marine and coastal overwash records, with limited use of aeolian mineral inputs in ombrotrophic peatlands as storm proxies. Here, we address these gaps by analysing grain-size and geochemical data from two peatlands in Quebec, Canada’s Magdalen Islands.
Our two peat records reveal consistent storm signals over the past 4000 years, with three key periods of heightened activity: 800–550 BCE, 600–800 BCE, and 1300–1700 CE. These signals align with marine and overwash records spanning the past 2000 years across eastern Canada, the US, and the Bahamas, indicating low storm activity during the Medieval Climate Anomaly, followed by increased activity during the Little Ice Age. Our findings suggest that storm records in these regions are influenced by local climatic factors. Negative phases of the Atlantic Multidecadal Variability, which typically suppress hurricane activity in the North Atlantic, are associated with conducive hurricane formation and intensification north of the Bahamas. Additionally, the position of the Bermuda High seems to play a more significant role in directing storm tracks during different climatic phases. Our findings highlight the potential antiphase relationship in storm activity between regions north of the Bahamas and those in the Gulf of Mexico, suggesting broader climatic mechanisms that warrant further investigations.
Despite the similarities between our two sites, discrepancies in geochemistry and mineralogical profiles highlight the importance of site-specific conditions in interpreting the storm record from peatlands, namely the distance of the sites to the coast and source of aeolian sediment, as well as peatland size. Challenges also remain in calibrating peat-based proxies with historical storm records, as identifying specific events from the past 150 years remains difficult.
Competing interests: At least one of the (co-)authors is a member of the editorial board of Climate of the Past. Dr. Pierre Francus is a member of the editorial board of Climate of the Past.
Publisher's note: Copernicus Publications remains neutral with regard to jurisdictional claims made in the text, published maps, institutional affiliations, or any other geographical representation in this preprint. The responsibility to include appropriate place names lies with the authors.- Preprint
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RC1: 'Comment on egusphere-2025-400', Anonymous Referee #1, 10 Mar 2025
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General Comments
The manuscript by Lachance and coauthors presents two new records of past storm activity from northeastern Canada. Methods of Aeolian Sediment Influx (using a sieving method) and ITRAX XRF analysis are used to measure the past aeolian sand deposits to the two bogs, spanning the late Holocene. The manuscript is very well written, with clear language, well presented figures and appropriate numbers of citations in most parts. The statistical analysis of the data appears to me (a non expert) to be appropriate, although as detailed below I have questions about the use of unnormalized itrax count data in parts of the paper and the chosen method of detecting storm events. The discussion is particularly interesting and well written, and includes comparisons between the storm records and individual recent storms, as well as a very good comparison of records from a latitudinal transect. The conclusion includes interesting take home messages, but could be strengthened by detailing more of the results and findings.
Major Corrections
1) Unnormalized ITRAX count data: the authors do a good job with the statistical analysis of the ITRAX data, converting it to Centered Log Ratios before doing the statistical analysis, because ITRAX data is compositional data. Therefore there is an acknowledgement that changes in one element can affect the counts of another element, and hence the need to normalize it. It was therefore surprising that following the statistical analysis the Ti records that are shown and on which the storm records are based were raw counts per second (kcps) results, rather than the CLR results. Previous studies (e.g. Löwemark et al. 2011; Weltje and Tjallingii, 2008; Croudace et al. 2019) have highlighted that ITRAX results should be normalized because otherwise variations in the amount of undetected organic matter, water content, surface roughness and counts of other elements can all influence the results. Appendix D shows photos of the cores, which have a very rough surface – was the surface smoothed at all prior to ITRAX scan as this would surely influence the ITRAX results greatly? This makes it important that the results are normalized as the variability in the surface would have likely influenced the measured Ti kcps. The CLR results (or natural log ratios with a carefully selected denominator) should provide the basis for the storm records.
2) Potential misinterpretation and overreliance on the Ti results
- Why was Ti selected as the element most indicative of mineral content over other elements? I think more justification of this decision is needed. The Principle Component Analysis in figure 4 shows that for TLM Ti is not strongly correlated with PC1, when the ASI results and other elements are. Figure 7 which shows the ASI overlaying the Ti record does support the use of Ti and perhaps this comparison should be done earlier in the paper (and using the full records), as currently much of the ITRAX results are discounted with little explanation in the results section.
- The event frequency was calculated using the number of times that Ti exceeded a threshold. The data was detrended using a 10/30 year moving average window and peaks above a threshold were marked as storm events. The authors state ‘To avoid overestimating the number of events due to consecutive Ti measurements associated with a single Ti peak, consecutive measurements were grouped together, and only the maximum value within each group was retained’. I wonder however whether some of the identified storm events are represented by single data points or small groups, which could be outliers or erroneous data points rather than sand layers. As noted above, in data that has not been normalized other factors could cause an increase or decrease in the kcps that is unrelated to mineral content in the peat. The authors should check the Mean Squared Error and total counts per second measurements through the records to see if any of the peaks in Ti are associated with anomalies and should be excluded as artefacts (see Lowemark et al. 2019).
- A point related to this one about the detection of storm events, is that the moving window used may be too narrow and single large events may be identified as several small events. If you look at Figure 5b and the record of TAC the red line of the moving average threshold goes up over some of the increases in Ti as a result of the concentrations increasing over a >10 year period (depending on the accumulation rate 10 years could be just 1-2cm within the peat). My concern is that if there was a large deposit of sand on the bog by a single large magnitude storm, then sand may settle on the bog at different depths due to the uneven surface, with some falling into pools and sinking down, some at the roots, others on the top of plants etc.. Further mixing could occur with root bioturbation potentially. You acknowledge in the discussion ‘downward movement of sediments in the spongey peat matrix may have dated sediments associated to Hurricane Dorien to an older interval’ to explain the timing of an event, so a similar mechanism could spread the sand from a single large event over a few cm’s within the consolidated peat. Therefore, this could lead to overestimation of the number of events if these larger increases in sand are removed by detrending and then small variations in Ti on these peaks are counted as events. Either the method should be adjusted to address this or these limitations should be discussed, with perhaps more cautious statements about the frequency of events.
3) Exclusion of part of the TAC record
You should be consistent about whether or not the period between ~600 BCE and ~1000 CE in TAC is useful as a storm record, or not given you interpret it as being not ombrotrophic. In Figure 5 you shaded out the section but in Figure 8 it is included. In the discussion you also observe that the Ti and storm events records of the two cores are similar over this section. While you have concluded that TAC was not ombrotrophic at this time, that is not to say that the peaks in Ti and sand shown by the TAC record were not deposited by the same storms that caused the deposits in TLM. Perhaps better not to discount this section of the TLM record but to rather use it with the caveat that deposits may come from other sources in addition to storms.
Minor and Moderate Corrections
Title – I would put ‘storm reconstruction’ as plural, and not sure Late Holocene should be hyphenated
Line 36 – ‘in Atlantic Canada ever’, I would suggest that this is changed to ‘on record’ or ‘to date’ rather than ‘ever’
Line 46 – ‘Answering these questions is aided by a long-term perspective’, the wording of this is a little unusual, perhaps ‘A long term perspective can help to answer these questions,’
Line 65 – the sentence ending ‘cyclone strikes’ needs citations. Currently these are put after the following sentence, but they should go after the first sentence, or the two sentences could be merged.
Line 68 – sentence ending ‘centennial data’. As with the above point, the citations should go after the first sentence rather than the following one.
Line 82 – NAO needs writing in full the first time it is mentioned
Line 97 – ‘composed of quartz and being the main sand source’, this is phased in an unusual way. I would suggest ‘ …quartz, which is the main sand source..’
Line 100 – ‘steady winds from all directions’. Remove this, as in a following sentence you discuss wind directions being seasonal and show this with the results in the appendix.
Line 111 – it depends on the journal guidelines perhaps, but shouldn't the ages be 'ka before present' and ka BP rather than just ka?
Figure 1d and 1e - TLM is in the center of the island so could have sand from a few directions. Perhaps also include a couple more arrows with distances to beaches. Also the distance of TAC to the cliffs may not be as relevant to highlight as the distance to sand sources.
Line 182 – I don’t think Bjorck has an ‘l’ at the end
Line 202 – in equation 2, were the denominator measurements all the elements measured, or just those terrigenous mineral elements listed above.
Figure 3 – some of the y axis labels are too close together and are overlapping
Line 345 – The statement that the storm records are based solely on the Ti results needs more justification
Figure 5 - 1) Could the colored dots on the storm events be made smaller? It is hard to see the results. 2) While the results on this figure are convincing, as they show similar patterns, I would like to also see the ASI results presented, as these results are surely also as relevant as Ti to showing past storminess. 3) The AMV results should be included on 8, rather than 5, as this is where they are discussed.
Line 402 – this sentence says that sand layers in TAC at 600BCE and 810 CE were not visible in TLM. But there was an increase in identified storm events coinciding with these times in TLM, so could it be that there was an enhanced sand deposition related to storms at these times, but just more sand reached TAC?
Line 403 – The sentence says that there was no abrupt contacts between the sand and overlying and underlying peat, supporting a gradual accumulation of sand over time. I am not sure about this interpretation as peat bog environments don’t seem to often have sharp boundaries in the same way as lakes. The surface of bogs are uneven and I could see that when sand blows in a single event over the surface it could fall into pools, sit on top of plants but also land or wash down to the base of the plant and so be incorporated within different depths giving a gradual boundary even for a single large event.
Line 406 – for the sentence about the likely explanation is the in-situ concentration of mineral matter I think you should say that this interpretation is based on the hiatus shown by the age model, and any other evidence you have. I was confused at first why this would be a more likely explanation than the proximity of the sand sources.
Line 413 - I would not include the Netherlands example, as the Netherlands are so far away and not relevant to the regional climate. Lots of other sites around the world probably show no change at this time.
Line 422 – the sentence suggests the proximity of TAC to the cliffs is the reason for the larger particles at TAC. But are the cliffs the sediment source during storms? Are sand sized particles being eroded from the cliffs and transported in land during storms? It looks like TAC is slightly closer to the beach to the west than TLM is, but the satellite photos seem to show the environment around TAC is dryer, so would exposed soil potentially be providing a source of minerals to TAC?
Line 426 – in this sentence again the assumption is that the windblown sands came from the cliffs and/or beaches. I expect the soil on the island would have a similar elemental composition to the bedrock, so could wind blown soil also be a contributor and spatial variations in vegetation a factor?
Line 431 – remove typo (sand written twice)
Line 432 - ‘Ti emerged as the common aeolian sand indicator in both TLM and TAC.’ I think this needs more justification earlier in the paper.
Line 446 – remove the link to Fig 6c because it doesn’t show evidence that supports the use of ASI and Ti
Line 458 – ‘winter westerlies storms’, maybe 'storms associated with the winter westerlies' would sound better here
Line 461 – recent calendar years need CE throughout this section
Line 467 – ‘despite it coming ashore’, its not clear what this means - did waves come ashore?
Line 526 – ‘active hurricane period’ perhaps
Section 5.3 – this is a really nice comparison of the different records along the transect
Figure 8 – 1) you could just have CE on the x axis label. 2) in the caption you write that there are similarities between the Ti record from TAC and the storm activity in TLM. The fact that you have two records close to each other showing similar patterns increases confidence in the records and I think this point should be made more prominent in the text. It also gives some support that the non-ombrotrophic section of TAC is still capturing a storm signal.
Line 560 - a citation is needed here
Conclusion – this part highlights some interesting challenges and lessons but doesn’t go into much detail about the results of the paper, in the same way as the abstract does for example. I would like to see the results summarized in the conclusions either at the start or incorporated in. An example is the paragraph at line 631, where there could be another sentence covering the point you make about regional versus tropical Atlantic SST's being important for hurricane impacts in different regions.
Appendix A - 30-40, 40-50 with hyphens might make this clearer
Citation: https://doi.org/10.5194/egusphere-2025-400-RC1
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