A 28-year-long (1997&ndash;2024) hydrographic dataset from the southern Baltic Sea

Rak, Daniel; Izabela Bulczak, Anna; Walczowski, Waldemar; Wieczorek, Piotr; Merchel, Małgorzata; Osiński, Robert; Goszczko, Ilona; Beszczynska-Moeller, Agnieszka; Strzelewicz, Agnieszka; Kitowska, Małgorzata

doi:10.5194/essd-2025-755

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https://doi.org/10.5194/essd-2025-755

Preprints

27 Dec 2025

| 27 Dec 2025

Status: this preprint is currently under review for the journal ESSD.

A 28-year-long (1997–2024) hydrographic dataset from the southern Baltic Sea

Daniel Rak, Anna Izabela Bulczak, Waldemar Walczowski, Piotr Wieczorek, Małgorzata Merchel, Robert Osiński, Ilona Goszczko, Agnieszka Beszczynska-Moeller, Agnieszka Strzelewicz, and Małgorzata Kitowska

Abstract. The data set presented here consists of Conductivity–Temperature–Depth (CTD) observations collected during 96 research cruises of R/V Oceania across the southern Baltic Sea between 1997 and 2024. The collection comprises towed and vertical station profiles acquired along a repeat transect spanning the Arkona Basin, Bornholm Basin, Słupsk Furrow, and Gdańsk Basin. Acquisition and post-processing procedures include standardized parsing of CNV/TXT files, robust time/position handling, pressure-binning to 1 dbar, median filtering, automated geolocation quality control, and pruning of incomplete profiles. The dataset enables analyses of seasonal to decadal variability in temperature and salinity, inflow propagation, ventilation events, and model validation. Manufacturer specifications for the principal instruments (Guildline 87104, Idronaut OS316/OS316Plus, Sea-Bird SBE49, Sea-Bird SBE19plus) are summarized to inform uncertainty assessment.

Received: 09 Dec 2025 – Discussion started: 27 Dec 2025

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RC1:
'Comment on essd-2025-755', Anonymous Referee #1, 04 Jan 2026 reply
Reviewer comments:
This manuscript presents a valuable, long-term CTD dataset spanning 28 years (1997–2024) in the southern Baltic Sea, a region with historically sparse high-resolution hydrographic observations—particularly within the Polish EEZ. The dataset, compiled from 96 cruises with over 55,000 profiles, fills a critical observational gap and provides a robust foundation for studies of seasonal-to-decadal variability, inflow dynamics, stratification, and model validation. The authors have demonstrated meticulous attention to data collection, calibration, QC, and standardization, making the dataset interoperable and accessible to the broader scientific community. Overall, this work is scientifically significant and well-structured, though several minor revisions would enhance its clarity, completeness, and utility. I recommend minor revision for publication.

Recommendations for Revision
As we known salinity measurements are usually affected by conductivity cell thermal inertia due to the lag between temperature and conductivity measurements, so it is of importance to conduct thermal lag correction for each profile. However, I cannot see any descriptions throughout the context.

The manuscript notes a sharp decline in sampling post-2020. While this is acknowledged, the authors should explicitly discuss how this discontinuity may impact specific analyses. For example, does the reduced sampling limit decadal trend analyses? Are there any supplemental observations, for example Argo or other observational data from WOD?

Line 284: Figure 7 shows below 50 dbar salinity exhibits a much more variability than the upper 50 dbar. This phenomenon is worth interpretation here.

Lines 230-231: A threshold of density inversion should be clarified here, e.g. 0.03 kg/m^3 is employed by QC of Argo TS profile.

Lines 314-316: In fact the Arkona Basin also shows the highest salinities and strong halocline from 30 dbar to the bottom. The authors shouldn’t neglect this.

Line 329: From Figure 10, the deep-layer signals in the Arkona Basin are stronger than in the Bornholm Basin and Slupsk Furrow. Can the authors interpret this?

Table 2: the unit of conductivity should be unified as S/m or mS/cm.

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Citation: https://doi.org/10.5194/essd-2025-755-RC1

Data sets

Southern Baltic Sea hydrographic CTD profiles along the Arkona–Bornholm–Słupsk–Gdańsk transect (1997–2024) Daniel Rak https://doi.org/10.48457/IOPAN.2025.531

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Short summary

This 28-year study collects vital oceanographic data from the southern Baltic. We used specialized instruments on a vessel to measure water temperature and saltiness along a repeated route, covering four major sea basins. This unique, long-term record is now publicly available and crucial for improving sea models and monitoring the health and dynamics of this important European Sea.


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