the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 03 Sep 2026
Luminescence dating of offshore tsunami deposits from the Shetland Islands, United Kingdom
Abstract. With onshore geological evidence of three tsunami events, the Shetland Islands (UK) yield the most-detailed Holocene tsunami record in the North Sea region. Lately, tsunami deposits were also identified in shallow waters offshore the Shetland Islands. These offshore tsunami deposits may carry the potential to further improve our understanding of both local and basin-wide, long-term tsunami hazard. Making use of the offshore record, however, requires establishing robust event chronologies. By using cores collected from two shallow-marine embayments located in the eastern Shetlands (Dury Voe and Colgrave Sound), we present the first chronology for offshore tsunami evidence from this region based on luminescence dating by resolving critical methodological challenges. The offshore cores show four distinct layers that contrast with the background shelf sediments. We find micro X-ray fluorescence mapping to be a rapid and effective method for assessing the geometries and internal architectures of these candidate tsunami deposits, which helps to guide sampling for luminescence dating. Complex radiation fields and time-dependency of environmental dose rates are tackled by implementing representative water contents, site-specific internal potassium contents, modeled dose rates considering the effect of radioactive disequilibria, and stratigraphic heterogeneity on the scale of gamma radiation. We demonstrate how robust luminescence-based chronologies can be achieved through measuring silt- and sand-sized K-feldspars with a pIRIR130 protocol in combination with Bayesian age-depth modeling under these conditions. Our luminescence chronologies indicate sedimentary evidence of the Storegga tsunami at offshore Dury Voe and Colgrave Sound, and additionally of the late-Holocene tsunami at offshore Dury Voe. Overall, these results demonstrate both the great potential of luminescence dating for offshore tsunami deposits and the benefits of the associated chronologies for regional tsunami hazard assessment.
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Status: open (until 30 Oct 2026)
- RC1: 'Comment on egusphere-2026-3279', Anonymous Referee #1, 06 Oct 2026 reply
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Luminescence dating of offshore tsunami deposits from the Shetland Islands, United Kingdom Andreas Peffeköver, Max Engel, Stephan Opitz, Anja Zander, Maarten Van Daele, Pedro J. M. Costa, Sue Dawson, Rikza N. F. An Nahar, Juliane Scheder, Vanessa M. A. Heyvaert, Marc De Batist, and Dominik Brill https://doi.org/10.5281/zenodo.21363495
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- 1
The manuscript presents new data acquired from two sediment cores collected in two different shallow marine embayments offshore the South Shetland Islands. The study aims to investigate tsunami deposits and apply luminescence dating techniques to constrain the timing of the identified events.
Given my expertise, I focused particularly on the geological aspects and the interpretation of the sediment samples. Overall, I found the manuscript very interesting and potentially worthy of publication after addressing the comments below.
The manuscript is of high quality and represents a valuable contribution to the scientific community working on tsunamis and other high-energy depositional events, which are often challenging to date accurately. The study is well written, logically organized, and certainly merits publication after several revisions have been made to clarify some aspects of the interpretations, improve the presentation of the data, and provide stronger support for the conclusions drawn.
I found some difficulty in following the core descriptions, as outlined in the more detailed comments below. In addition, a few inconsistencies in the interpretation of the sedimentary units should be carefully reconsidered.
Although the study primarily focuses on the dating of the events, it makes extensive reference to another manuscript currently under review, in which cores collected from approximately the same locations were used to reconstruct sedimentary facies and the geological processes responsible for the deposition of the event layers. While this demonstrates that the dataset is robust and that the interpretations are supported by multiple lines of evidence, it also makes the manuscript difficult to follow, as the reader is frequently required to consult a second unpublished study in order to understand the basis of many of the interpretations presented here.
I therefore encourage the authors to include within the present manuscript the key information required for the discussion, either in the form of summary tables, figures, or concise descriptions in the text. Without these direct references, readers are forced to consult both manuscripts in parallel to understand how the interpretations were developed.
Specific comments
The introduction is well structured and provides a clear overview of the current state of knowledge and the associated uncertainties. I recommend verifying that all acronyms are properly defined and consistently reported throughout the text, figures, and figure captions.
The source and trigger of the late-Holocene tsunami have been interpreted as local. However, the related deposits have been identified over a remarkably wide geographical area onshore, as shown in Figure 1b. This point deserves further discussion.
Lines 185-190: It would be useful to summarize the main morphological, oceanographic, and geological characteristics that guided the site selection, as these factors are likely relevant for interpreting the results and also differences between the described cores and other cores in the area.
Line 192: Please explain why only these two cores were selected for this study. What was the rationale behind their selection?
Lines 203-204: Please specify which environmental conditions are being referred to and explain how these conditions are reflected in the chosen geochemical proxies.
Figure 1: Please indicate the source of panels c and d. Adding inset boxes highlighting the study areas would facilitate interpretation. In panel 1c and 1d it would be useful to see all the collected cores including those described in the paper by An Nahar et al (under review).
Figure 2: I am not sure what the red color assigned to the two coarse-grained units in the interpretative log represents. The meaning of the symbols used in the log is not explained either in the legend or in the figure caption. At present, understanding these units requires consulting the manuscript by An Nahar et al. (under review). Was grain-size analysis performed? Or does the grain-size information derive solely from visual core descriptions?
Figure 3: I am somewhat confused because the three event deposits are described using different sets of proxies. It would be more useful to consistently use the same parameters for all events, allowing similarities and differences among them to be more easily assessed.
For example, DV1 is described using Na/Mn, S/Mn, Br/Fe, and Na/Ti, but no information is provided regarding marine indicators such as Ca or Sr.
Figure 3e: The top of BV2 appears to be located at approximately 107 cm rather than extending upward as shown. What does the sharp transition at 107 cm depth represent?
Why is BV1 not included in Figure 3?
Is the very sharp upper boundary of DV1 real, or could it be an artifact of the XRF image? In the text (line 372), the upper boundary is described as gradual. Therefore, I am wondering whether the sharp boundary displayed in Figure 3a accurately reflects the sedimentary structure.
Line 362: Please verify the depths of the upper and lower boundaries of this unit (DV2). The depths reported in the text do not appear to match those shown in Figure 2. Based on the core photograph, the event seems to be located between 221 and 231 cm, as illustrated in Figure 2a, whereas the text and Figure 3c suggest a more restricted interval of 221-228 cm. Please clarify these discrepancies and explain why the XRF data do not show significant differences between the event deposit and the surrounding background sediments especially in the lowermost part of the event.
Results and Interpretation
Line 354 - The cores are described as consisting of different "facies" based primarily on texture and shell-fragment content. I suggest replacing the term facies with sedimentary units when referring to the subdivisions identified in the cores. The term “facies” generally implies a depositional and genetic interpretation, whereas sedimentary units is more appropriate for a strictly descriptive classification based on observed core characteristics.
In the introductory paragraph (lines 355-360), the succession of depositional environments is introduced based on the work of An Nahar et al. (under review). To allow readers of this manuscript to follow the interpretative workflow without consulting the companion paper, I recommend first describing the sedimentary units in purely observational terms and only subsequently discussing their depositional significance and environmental interpretation based on results from An Nahar (under review). This would make the manuscript more self-contained and easier to follow.
Lines 370-379 (Event DV1): Based on the core log (Fig2a), the event appears to be subdivided into two distinct sub-units: a lower red-colored interval and an upper interval characterized by finer-grained sediments. This subdivision is neither described nor discussed in the text. What do these two sub-units represent? Do they correspond to two depositional phases related to the same tsunami propagation, or are they interpreted as separate events? Why is the lower sub-unit highlighted in red?
Figure 2b: Why is BV2 colored in red? Does the upward fining trend reported in the core log (105 cm) have any interpretative significance? Could it indicate a subdivision into two sub-units (102-105 cm and 105-117 cm), potentially reflecting more complex depositional processes during tsunami propagation? Furthermore, why do the XRF data cover only the lower portion of the unit? The upper boundary is not included in Figure 3e.
Lines 385-386: The XRF data do not include the upper boundary of the deposit; therefore, this statement is not fully supported. The upper boundary appears to be located at approximately 102 cm depth, whereas the XRF interval extends only across approximately 104-120 cm. Consequently, the luminescence sample BAVO4, described as representing background sediment above the event deposit, actually appears to be located within the event layer itself, as clearly imaged in Figure 3e.
I note that the thickness of the luminescence samples varies between approximately 2 cm and 4 cm. I may have overlooked the explanation in the Methods section, but it would be useful to explain why different sample thicknesses were used and which criteria guided the choice of sampling interval. Such information may be of interest to future applications of the method.
If possible, I would also encourage the authors to include XRF data for BV1, or alternatively explain why these data are not necessary.
Discussion - Before discussing correlations with the cores described by An Nahar et al. (under review), it would be helpful to first summarize the main findings of the present study. Once the original results have been clearly synthesized, they can then be discussed within the broader stratigraphic and regional framework.
The beginning of the Discussion is particularly difficult to follow because it immediately introduces abbreviations for seismic-stratigraphic and sedimentary units derived from other studies. I recommend simplifying this section and making it more accessible to readers unfamiliar with the accompanying manuscript.
Rather than referring extensively to the manuscript under review, it would be beneficial to include a representative sub-bottom profile in the present paper and describe the acoustic characteristics of the event deposits directly from the geophysical data.
Lines 547-549: No Ca or Sr elemental maps are shown in Figure 3a. Therefore, it is currently not possible to verify the following statement: µXRF mapping of DV1 reveals reversed compositional patterns compared to DV2, because here, the event deposit shows as a terrestrial-dominated unit interbedded in marine background sedimentation.
Line 549: The two event deposits are described as being interbedded within two different facies. However, could the observed differences instead reflect changes in sediment source? How can these possibilities be discriminated? Is the interpretation based on the assumption that the event sediment originated from remobilization of pre-existing seafloor material? If the sediment source is external to the coring site, alternative explanations should also be considered.
Line 559: The event is also enriched in Si. Therefore, a mixed sediment source cannot be ruled out. Please explain why a predominantly marine origin is favored. Is Si considered diagnostic of a marine source in this context?
Line 568: Since the origin of BV1 remains uncertain, it would be particularly valuable to compare its XRF signature with those of the other event deposits. Such data could help distinguish tsunami deposits from storm-related deposits. The absence of XRF information for BV1 currently limits this type of analysis.
Finally, grain size appears to be the primary criterion used to identify event deposits in the studied cores. Given its importance, I wonder why detailed grain-size analyses were not performed. High-resolution granulometric measurements might provide valuable additional information and could potentially reveal more subtle grain-size changes associated with other tsunami events that are not readily identifiable from visual core descriptions alone.
Overall, this is a very interesting and potentially impactful contribution. However, the manuscript would benefit substantially from being made more self-contained and from presenting the observational evidence supporting the interpretations more directly within the paper. I hope to see it published soon.