the Creative Commons Attribution-NonCommercial 4.0 Deed License.
the Creative Commons Attribution-NonCommercial 4.0 Deed License.
Solving dense shelf water cascading with a high-resolution ocean reanalysis
Abstract. Dense shelf water cascading (DSWC) is an oceanographic process occurring when dense shelf water overflows the shelf edge downslope towards the deep sea. Monitored in the Northwestern Mediterranean by moorings since 1993 in the Lacaze-Duthiers Canyon and since 2003 in the Cap de Creus Canyon, numerical modeling with reanalysis extends this timeline further into the past. This study investigates a regional reanalysis (1987 – 2021) validated against mooring observations at 750–1000 m depth. The reanalysis successfully reproduces observed Intense DSWC (IDSWC) events from 1999, 2000, 2005, 2006, 2012, 2013, and 2018, while identifying one previously unreported event in 1987, and detecting no IDSWC between 1988 and 1998. The reanalysis effectively matches 84 % of observed IDSWC days within the same week and 56 % on the exact date. Instead of assimilating IDSWC events from mooring observations to resolve the cascading process, the model relies solely on the seawater density on the shelf. Reanalysis data have revealed the seawater properties along the canyon that caused IDSWC and can be used to find other unreported cascading events elsewhere.
Status: open (until 23 May 2025)
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RC1: 'Comment on egusphere-2025-1309', Anonymous Referee #1, 16 Apr 2025
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Review of «Solving dense shelf water cascading with a high-resolution ocean reanalysis» by Hos et al.
The authors investigated the dense shelf water cascading (DSWC) process at two submarine canyons in the Gulf of Lion (northwestern Mediterranean Sea). The aim of the study is to evaluate the performance of the reanalysis in representing the DSWC. To achieve this goal, the authors compare the reanalysis data with in-situ observations from two moorings over the period 1993-2021 for Lacaze-Duthiers Canyon and 2011-2021 for Cape de Creus Canyon. From the results, they conclude that the MedSea reanalysis is able to successfully reproduce the interannual variability of the DSWC, although the timing and intensity of the phenomena are biased at the daily scale.
I found the topic interesting because the reanlysis performance in deep layers has not been thoroughly evaluated for the Mediterranean Sea. Thus, testing reanlysis skills in representing an oceanic proccess such as the DSWC is a good excersise. The manuscript is generally well written and the results are relevant to the scientific community, especially the Mediterranean community. However, I found some points that should be improved before its publication in OS.
1) Abstract : I find the statement "...can be used to find other unreported cascading events elsewhere" somewhat problematic. While the approach is compelling, it's important to note that the reanalysis product used in this study is specifically designed for the Mediterranean. This does not necessarily imply that other reanalysis products (e.g. global) would perform equally well in capturing cascading processes in different regions. In addition, it may be premature to extend the conclusions to other cascading areas within the Mediterranean basin, such as the Adriatic or Aegean Seas, given the different water mass characteristics and potentially different local dynamics in these regions. It would be helpful to evaluate reanalysis performance in these areas before making broader generalizations. Please rephrase.
2) Introduction: Since the manuscript was previously submitted to another journal with strict space limitations, I understand why the introduction may have been kept concise. However, Ocean Science does not have such constraints, and I found the current introduction somewhat brief and missing some important background information. I would recommend that the authors provide a more detailed description of the state-of-the-art, including the criteria (e.g., temperature, salinity, potential density, current velocity) used in previous studies to characterize DWSC in the Gulf of Lions, as well as a more thorough geographical description of the study area. I also strongly recommend including references when referring to water mass characteristics (e.g., LIW, WMDW) and their typical depths in the water column. I suggest more clearly highlighting the novelty of this work in comparison to previous studies. Finally, a short paragraph at the end of the section introducing the content of the next section might also be nice.
3) Data and Methods: I suggest to include a small table summarizing the main information related to the reanalysis data and those related to the measurements from in situ observations. This would help the reader to easily follow the methods section. L68-71: It is not clear to me whether the criteria used to define DSWC events come from observations or from reanalysis. This should be clarified. Are you defining DSWC events from in-situ observations or are you moving to values (model reality) where reanalysis successfully reproduces DSWC?
4) Results: In general, I found this section to be very descriptive, I would recommend the authors to go a little bit more in depth in the analysis in order to provide answers to the open questions (such as, what mechanisms might be involved ?).
- L84: Why is 2019 not considered a DSWC event? It seems clear from the observations that there was an event in the CCC in 2019. However, this event is not captured by the reanalysis.
-L87: ‘Events tend to occur in paired years, where the second year is weaker and usually hardly detectable in the LDC.’. Any explanation for why DSWC occurs in paired years? Why is it more difficult to detect in LDC than in CCC?
-Figure 2: Please use the same ranges on the y-axis to make LDC and CCC easy to compare. Avoid using acronyms in the caption (figure captions should be understandable to the reader without having to read the entire manuscript).
-Figure 3: Why is the year 2018 missing in 3j?
- L123: Here, after finishing the analysis of Figure 3, you come back to the analysis of Figure 2e, which seems a bit strange. Please reorganize. These volumes are calculated for waters σθ ≥ 29.05 kg/m³? Clarify in the caption of Figure 2.
5) Discussion: Have you identified any EMT signals in the reanlysis that prevent deep cascading from 1988 to 1998?
6) Conclusions : As I noted in the abstract, I would caution against generalization of conclusions without detailed analysis in other regions. In this section I would suggest to highlight the biased performance of reanalysis at the daily scale and the main deficiencies found. In this way you can provide some perspectives to suggest improvements to the reanalysis developers.
Minor remarks:
-L13: As I understood through the manuscript, the monitoring of Cape de Creus started in 2005/2006 for winters and then permanently from 2011, not from 2003 as stated.
-L27: you may want to include the common names for these dry and cold northerly winds (Mistral and Tramontana).
L35: basin floor → bottom
-L38-40: Any study under CMIP5 or CMIP6 scenario projections?
-L50: (CMEMS, https://marine.copernicus.eu/)
-L60: from 1987 to 2021→ the reanalysis provides data until 05/31/2023, but you focus your analysis on 1987-2021.
-L88: significant ‘anti-correlation’ → ‘negative correlation’
- L95: ‘temperature minma at CCC’ → and LDZ isn’t it?
-L96: (Sv; 1 Sv = 106 m³/s) → (Sv; 1 Sv = 106 m³/s). Please revise the use of superscripts throughout the manuscript.
Citation: https://doi.org/10.5194/egusphere-2025-1309-RC1 -
CEC1: 'Reply on RC1', Karen J. Heywood, 16 Apr 2025
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Thank you for your helpful comments and suggestions to strengthen this paper. You are correct that most papers in Ocean Science do not have a page or word limit. However this particular paper is submitted for consideration as an Ocean Science Letter, and Letters papers do have a word limit (more information is given here https://www.ocean-science.net/about/manuscript_types.html). If the reviewers and editor don't feel that the paper is suitable for publication as a Letter (for example it needs expanding with more information to support the conclusions) then the editor can request that it become a regular research article with no length restrictions. Or indeed the authors might make that decision when they have received the reviews. I hope this helps to clarify?
Karen Heywood (co-editor-in-chief)
Citation: https://doi.org/10.5194/egusphere-2025-1309-CEC1
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CEC1: 'Reply on RC1', Karen J. Heywood, 16 Apr 2025
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