the Creative Commons Attribution 4.0 License.
the Creative Commons Attribution 4.0 License.
| 28 Mar 2025
Dense shelf-water and associated sediment transport in the Cap de Creus Canyon and adjacent shelf under mild winter regimes: insights from the 2021–2022 winter
Abstract. This study examines dense shelf water cascading (DSWC) and estimates the dense shelf-water and associated sediment transport in the Cap de Creus Canyon (northwestern Mediterranean) during the mild winter of 2021–2022. The FARDWO-CCC1 multiplatform survey in March 2022 revealed dense shelf waters on the continental shelf, which were transported to the canyon head. These cold, dense, and turbid waters, rich in dissolved oxygen and chlorophyll-a, downwelled along the canyon’s southern flank to depths around 350 m. During the observed downwelling event, estimated water and suspended sediment transport within the dense water vein were 0.3 Sv and 105 metric tons, respectively, mainly confined to upper canyon reaches. These transports were low compared to extreme winters, likely due to the influence of freshwater inputs and moderate meteorological winter conditions. Transport magnitudes were higher in the upper canyon section than in the mid-canyon section, where transport was estimated at 0.05 Sv, including around 104 metric tons of sediment. This observation suggests that during mild winters, while most of the dense water either remains on the shelf or the shelf-edge area, or flows southward along the coast, the Cap de Creus Canyon acts only as a partial sink for cascading waters. Mediterranean Sea Physics reanalysis data showed that the cascading season lasted approximately three months, from January to early April 2022, with several cascading pulses within the canyon. The highest dense shelf water transport occurred in mid-March, associated with easterly/south-easterly windstorms. This study confirms that remarkable dense shelf water and sediment transport occurs in the Cap de Creus Canyon, particularly along its southern flank, even during mild winters in absence of deep cascading and limited external forcing. Nevertheless, this phenomenon appears to make a significant contribution to the formation of Western Intermediate Water (WIW) in the region.
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Status: open (until 23 May 2025)
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RC1: 'Comment on egusphere-2025-1310', Anonymous Referee #1, 24 Apr 2025
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Referee Comment on:
“Dense shelf-water and associated sediment transport in the Cap de Creus Canyon and adjacent shelf under mild winter regimes: insights from the 2021–2022 winter” by Arjona-Camas et al.
General Comments:
This manuscript presents a well-written and carefully conducted observational study of dense shelf water cascading (DSWC) and associated sediment transport in the Cap de Creus Canyon during a mild winter (2021–2022). The authors employ a multi-platform approach—including gliders, moorings, ship-based CTD profiles, and reanalysis data—to describe the cascading evolution and to estimate transport of water masses and suspended sediments.
The manuscript is well structured and clearly written, with high-quality figures and solid data processing. However, the conceptual novelty is limited, as the key findings align closely with what is already established in the DSWC literature. Specifically, prior studies—including Mahjabin et al. (2019, Continental Shelf Research; 2019, JMSE; 2020, Scientific Reports)—have demonstrated:
- That DSWC can occur under mild to moderate wind forcing;
- That wind direction is a key modulator of cascading strength;
- That such events result in substantial sediment and biogeochemical transport.
Moreover, these studies introduced predictive frameworks such as the Simpson number and energy balance models, and examined canyon-free shelf settings under similar climatic regimes. These works are not cited in the current manuscript.
While the present study is geographically focused on the Cap de Creus Canyon, the manuscript could benefit from a deeper exploration of canyon-specific dynamics—such as flow steering, internal hydraulics, or sediment redistribution mechanisms—which are only briefly mentioned. Additionally, while the observations are carefully described, the broader significance of this mild-winter case for global DSWC understanding is not yet fully articulated. A more explicit discussion of the study’s unique contribution—particularly in terms of sediment asymmetry, constrained cascade depth, and implications for WIW formation—would significantly enhance the manuscript’s impact.
Specific Comments:
- On Novelty and Contextualisation
The Gulf of Lions is among the most studied regions globally for DSWC, with numerous works documenting both mild and extreme cascading events. While the present manuscript focuses on a specific mild winter (2021–2022), the authors should more clearly state what new understanding this adds. For example: Is the sediment asymmetry across the canyon novel? Is the observed upper canyon confinement unusual for mild winters? More detailed differentiation from earlier work is encouraged. - Wind Direction and Episodic Forcing
The manuscript appropriately links SE wind events to episodic downwelling and DSWC initiation. However, this connection is largely descriptive. Including wind stress time series or Ekman transport estimates would strengthen the argument and provide a more quantitative link to the observed cascading pulses. - Canyon-Specific Dynamics
While the Cap de Creus Canyon is central to the title and framing, the manuscript does not deeply examine its dynamic role beyond being a conduit. Consider discussing whether canyon morphology contributes to observed sediment asymmetries or restricts flow depth. Alternatively, consider softening the canyon emphasis if the goal is to document a shelf-wide mild DSWC event. - Citation Inclusion
Please cite the following prior studies if relevant:
- Mahjabin, T., Pattiaratchi, C., & Hetzel, Y. (2019). Wind effects on dense shelf water cascades in south-west Australia. Continental Shelf Research, 189, 103975.
- Mahjabin, T., Hetzel, Y., & Pattiaratchi, C. (2019). Spatial and temporal variability of dense shelf water cascades along the Rottnest continental shelf in southwest Australia. JMSE, 7(1), 30.
- Mahjabin, T., Pattiaratchi, C., & Hetzel, Y. (2020). Dense shelf water cascading around the Australian continent. Scientific Reports, 10, 9930.
These studies support the notion that DSWCs can occur under non-extreme conditions and offer theoretical and methodological insights that are directly relevant here.
Technical Corrections
- Abstract: The opening sentence “This study examines…” is generic and does not effectively convey the study’s context or significance. I recommend replacing it with a more engaging and informative sentence that introduces DSWC and the knowledge gap being addressed. For example:
“Dense shelf water cascading (DSWC) is a key process in transferring water masses and sediments from continental shelves to deep basins, yet its dynamics under mild winter regimes remain poorly characterized.” - Introduction: While DSWC is mentioned early, it is not clearly defined. I recommend including a short, reader-friendly definition in the introduction, such as:
“DSWC refers to the downslope flow of cold, dense water formed on continental shelves due to surface cooling and/or evaporation, which descends under gravity into deeper ocean basins.”
- Line 236: Typo — "metter" should be corrected to "meter".
Citation: https://doi.org/10.5194/egusphere-2025-1310-RC1
Data sets
CC1000 observatory data A. Sanchez-Vidal et al. https://doi.org/10.17882/104746
BILLION observatory data X. Durrieu de Madron et al. https://doi.org/10.17882/45980
CTD and ADCP data collected during the cruise FARDWO CC1 A. Sanchez-Vidal et al. https://doi.org/10.17882/105499
Glider data F. Bourrin https://data-selection.odatis-ocean.fr/coriolis/uri/p83112098
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