| 12 Jan 2026
Variability in the Cretan Sea (Eastern Mediterranean) from six years’ glider observations (2017–2023)
Abstract. The Cretan Sea is an intermediate and occasionally deep water formation area within the Eastern Mediterranean that accumulates and transforms water masses from the adjacent Aegean, Levantine and Ionian Seas. Six years of glider observations (2017–2023) in the Cretan Sea were analysed to study the properties, variability and dynamics of the water masses during the study period. The analysis revealed progressive warming and salinification of the intermediate and deep layers. The mean temperature increased by around 0.05–0.07 °C per year, and the salinity by approximately 0.02 per year. Furthermore, comparisons with climatological data from 2000 to 2015 show temperature departures of + 0.4 to 0.6 °C in the upper 400 m and salinity increases of up to + 0.3 at the surface. Both of these values decline with depth, highlighting the intensified warming and increased salinity near the surface and in the upper intermediate layers. Additionally, the analysis of salinity and temperature datasets revealed the formation of intermediate water annually, except in winter 2022 when an intense mixing event occurred in the Cretan Sea triggered by exceptionally cold atmospheric conditions. The mixed layer, as captured by the glider, extended below 600 m inside the Cretan basin. These newly formed waters almost reached the deep layers, significantly modifying the properties of the intermediate and deep waters, although full deep convection was not reached. The observed downward displacement of the TMW core below 1000 m is associated with the strong convective event as well as with the redistribution of the heat and salt in the intermediate and deep layers. These findings emphasize the importance of sustained, high-resolution observations in capturing both gradual trends and extreme events, and in improving our understanding of the evolving thermohaline circulation of the Eastern Mediterranean.
The authors present an analysis of a 6-year glider observational dataset in the Cretan Sea. The region is highly relevant to Eastern Mediterranean variability, and several changes described over the study period appear consistent with recent findings and with what is being observed more broadly in the area. However, the manuscript in its current form lacks a clear narrative and prioritization of objectives, and many conclusions are insufficiently supported by quantitative results and methodological detail. For these reasons, I recommend rejection in its current form, but encourage re-submission after substantial restructuring and additional analysis, which in my view go beyond a single major-revision cycle. I hope the authors will view these comments as guidance to strengthen the scientific robustness and clarity of the work.
Major comments
1. Clarify the main scope and re-balance the manuscript accordingly
At present, it is difficult to identify a single central research question (or a small set of clearly prioritized objectives). The abstract places strong emphasis on the winter 2022 convection/mixing event, but the manuscript does not consistently follow through with event-focused analysis beyond MLD and selected transects. If winter 2022 is intended as a main focus, it should be supported with additional diagnostics (see comment 5). If not, the abstract and discussion should be revised to better reflect the broader goals (seasonal/interannual variability, anomalies vs climatology, water-mass evolution, etc.).
2. Too many figures relative to the amount of quantified results
There are many figures (some could be merged), yet relatively few results are explicitly quantified in the text. In several places the figure captions/results text remain descriptive, while key numbers (magnitudes of changes, anomalies by layer, interannual differences, uncertainties) are not summarized clearly. I recommend reducing redundancy, merging related panels, and adding concise quantitative summaries (tables or compact metrics) to strengthen the Results section.
The inclusion of satellite ADT/geostrophic velocity is potentially valuable to interpret mesoscale control on the transects, but in the current manuscript it remains largely qualitative. Please either (i) reduce/relocate ADT panels (in a potential Appendix) if only illustrative, or (ii) leverage ADT quantitatively (eddy polarity/strength indices per mission; distance to eddy center; relation between ADT anomalies and isopycnal heave / T–S anomalies; simple eddy tracking) to demonstrate how mesoscale circulation explains the observed hydrographic variability.
3. Spatial definitions and data-selection methodology need to be explicit
Several analyses refer to “east/central/west” regions, specific profiles, or climatological comparisons, but the manuscript does not clearly define:
These definitions are critical for reproducibility and interpretation, and should be stated explicitly (ideally with a map and/or a table of coordinates/criteria).
4. Structure: Results vs Discussion are currently mixed
The Results section contains substantial interpretation and comparison that would fit better in the Discussion, while the Results themselves often lack quantitative reporting. I suggest a clearer separation:
5. Attribution and context for the 2022 strong convection/mixing event
If winter 2022 is a major highlight, it would benefit from stronger supporting evidence on the atmospheric forcing and buoyancy loss. For example, ERA5-based diagnostics over the event window (turbulent heat fluxes, wind stress, buoyancy flux components, evaporation–precipitation, air–sea temperature differences) could substantiate the proposed driver and help distinguish local vs basin-scale forcing.
6. Trend analysis: statistical methodology and significance need more detail
Given the short record (6 years), limited number of missions, and uneven seasonal sampling, I am cautious about strong statements regarding trends without detailed statistical justification. The manuscript should specify:
If possible, additional confirmation should be attempted via independent sources (e.g., regional in-situ data, Argo where available, and/or CMEMS reanalysis) over the same region and time span.
Finally, the E1M3A buoy time series is not described in enough methodological detail (sampling frequency, temporal coverage, QC/processing), and the manuscript does not explicitly discuss any discrepancies between buoy- and glider-derived trend estimates. Please add these details and a quantitative buoy–glider trend comparison over the overlapping period.
7. External references / climatology description should be more concrete
The manuscript refers to an external climatology and uses it as a reference. Please describe more clearly:
If additional historical observations are available (SeaDataNet/CMEMS/ship CTDs/Argo), they could be used to provide context beyond the 6-year record and to corroborate the reported changes.
8. Presentation and clarity
Several figures are difficult to read (small labels, low contrast, dark text on dark backgrounds). Increasing font sizes and improving contrast would substantially improve accessibility.
Consider merging figures and reducing the total number by combining related information into fewer, more information-dense plots.
Summary recommendation
The dataset and topic are valuable, but the manuscript requires substantial restructuring, clearer definitions and methods, stronger quantitative reporting in the Results, and more robust support for trend statements (including statistical significance and/or external validation). If the authors choose to resubmit a substantially reworked manuscript, the work could become a solid and publishable contribution to Eastern Mediterranean variability studies.