Oceanologia No. 66 (2) / 24

Original research article

Short Communications

Original research article

Fluctuations of ice in a lake due to the impact of the North Atlantic Oscillation (1960/61–2009/10) – a case study of Łebsko Lake
Oceanologia 2024, 66(2), 153-166

Artur Młodzik, Roman Cieśliński*, Izabela Chlost
Department of Hydrology, Faculty of Oceanography and Geography, University of Gdańsk, Gdańsk, Poland;
e-mail: arturro19@onet.pl, georc@univ.gda.pl, izabela.chlost@ug.edu.pl
*corresponding author

keywords: Ice conditions, North Atlantic Oscillation, Air temperature, Global warming, Satellite imagery

Received 13 July 2022, Revised 2 July 2023, Accepted 13 October 2023, Available online 13 November 2023, Version of Record 16 May 2024.


The paper represents an attempt to understand the impacts produced by the North Atlantic Oscillation on the ice cover regime of the largest coastal lake in Poland situated in the northern part of the country. The purpose of the study was to estimate the impact of the North Atlantic Oscillation on selected ice cover parameters. The study also attempts to examine other factors that may affect its significant impact on observed changes in the climate. Water temperature data are used to assess temperature conditions in aqueous ecosystems as well as determine the heat absorption capacity of these systems. This allows one to then determine cooling rates in the event of ice cover formation. The data analysis provided in the paper focuses on selected characteristics of ice cover conditions (i.e. dependent variables) including the number of days with ice and maximum ice thickness in relation to NAO index changes (i.e. independent variables) for the reference period 1960/61–2009/10. In addition, the paper divides the studied period into 10-year subperiods in order to capture the weakest and strongest phases of NAO and assess the extent to which they affect the duration of ice cover. A large increase in the mean air temperature (1.8°C) occurred in the years 1960–2010. Trendline analysis indicates that the number of days with ice cover declined by about 60 days and the maximum thickness of ice cover decreased by about 10 cm. Oceanographic research employs satellite image data in order to accurately assess human impact. Therefore, ice cover forecasts generated for consecutive winter seasons may become an important tool in this type of assessment.

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Cooperation between the fishery sector and science: CTD probe measurements during fishing catches on the feeding grounds of herring (Culpea harengus) and sprat (Sprattus sprattus) in the south-eastern part of the Baltic Sea
Oceanologia 2024, 66(2), 167-179

Piotr Pieckiel1,*, Diana Dziaduch1, Lidia Dzierzbicka-Głowacka2, Marcin Kalarus1
1Gdynia Maritime University, Gdańsk, Poland;
e-mail: ppieckiel@im.umg.edu.pl
2Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland
*corresponding author

keywords: Temperature, Salinity, Hypolimnion layer, Pelagic fishery, Catch results

Received 23 February 2023, Revised 4 September 2023, Accepted 13 October 2023, Available online 21 October 2023, Version of Record 16 May 2024.


282 CTD probe measurements were analysed for the parameters of temperature, salinity, depth and oxygen saturation of the water column. These measurements were taken during commercial pelagic fishing for herring (Clupea harengus) and sprat (Sprattus sprattus). These species are currently the main target of commercial fishing in the Baltic Sea. Research was carried out throughout the years 2018–2022 in the south-eastern Baltic Sea, mainly in the Gdańsk Deep, mostly during the daytime. The main factor that influenced both, fishing strategy and the increase in catch per unit effort throughout each year, was temperature. Regardless of the season, the most frequent temperature measured was around 5.8°C during fishing, and 5°C in the most abundant winter season. This is the value occurring within the boundaries of the formation of the thermocline and the hypolimnion layer in the Baltic Sea. The formed shoals of fish moved dynamically with this layer in the daytime and occurred throughout the year at various depths in a range of up to 65.7 m. A stronger reaction to temperature changes was also observed for sprat, which is the most exploited fish in the Baltic Sea. This species was observed to be more numerous in the deeper layers of the water column and at lower temperatures than herring. In the winter, shoals of fish were observed at the level of the halocline, which may be strongly related to the presence of a preferred optimal food base in this season.
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Long-term statistics of atmospheric conditions over the Baltic Sea and meteorological features related to wind wave extremes in the Gulf of Gdańsk
Oceanologia 2024, 66(2), 180-195

Witold Cieślikiewicz1,*, Aleksandra Cupiał2
1Institute of Hydro-Engineering, Polish Academy of Sciences, Gdańsk, Poland;
e-mail: ciesl@ibwpan.gda.pl
2Department of Physical Oceanography and Climate Research, University of Gdańsk, Gdynia, Poland
*corresponding author

keywords: Atmospheric pressure, Wave climate, Extreme waves, EOF analysis

Received 5 October 2021, Revised 22 September 2023, Accepted 13 October 2023, Available online 7 November 2023, Version of Record 16 May 2024.


The goal of this study is to describe wind wave climate and wave extremes of the Gulf of Gdańsk in the southern Baltic Sea and associated meteorological conditions over the Baltic Sea. We obtain the characteristic features of 34 severe historical storms in the Gulf of Gdańsk during the period 1958–2001 and link them with extreme significant wave heights hindcast for five grid points in this gulf. The long-term statistics of atmospheric pressure systems over central and northern Europe, and the north-eastern Atlantic Ocean are derived from a 44-year REMO reanalysis database. A link between the mean, minimum and variability range of atmospheric pressure has been quantified. In general, the higher the mean pressure the smaller its variability and vice versa. Long-term characteristic features of winds over the Baltic Sea have been estimated from the REMO database. Strong winds directions vary from W, WSW to SW in the southern Baltic to more southerly SSW directions in the northern part of the Baltic Sea. The Empirical Orthogonal Functions (EOF) analysis shows that more than 50% of the variability in the atmospheric pressure in the Baltic Sea can be explained by the first EOF mode. The first four EOF modes can reproduce above 90% variability of the hindcast pressure time series. Statistical properties of the hindcast significant wave height over the Gulf of Gdańsk are computed based on the 44-year HIPOCAS database. All the computed statistics of wave heights reveal a very strong sheltering effect caused by the Hel Peninsula.
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Seasonal enhancement of phytoplankton biomass in the southern tropical Indian Ocean: Significance of meteorological and oceanography parameters
Oceanologia 2024, 66(2), 196-219

Chinnadurai Karnan*, Sreedharan Gautham
CSIR – National Institute of Oceanography, Dona Paula, Goa, India;
e-mail: karnanc@nio.org
*corresponding author

keywords: Southern Tropical Indian Ocean, Chlorophyll a, Primary production, Seasonality, Oligotrophy

Received 19 October 2022, Revised 11 September 2023, Accepted 13 October 2023, Available online 31 October 2023, Version of Record 16 May 2024.


The present study focused on understanding the seasonality of the phytoplankton biomass (chlorophyll a) distribution in the oligotrophic, Equatorial, and Southern Tropical Indian Ocean (ESTIO; 0–30°S and 60–90°E). The long-term satellite data analyses (2003–2020) showed a strong seasonality in sea surface temperature (SST), wind, currents, mean sea level anomaly (MSLA), photosynthetically available radiation (PAR), euphotic depth (ZEU) and mixed layer depth (MLD). As a response to the hydrographical changes, the phytoplankton biomass showed noticeable seasonal variation with the highest biomass during the Austral Winter (AW; June–September; avg. 0.11 ± 0.03 mg/m³) and lowest during the Austral Summer (AS; November–February; avg. 0.07 ± 0.03 mg/m). High chlorophyll patches (>0.1 mg/m³) were found between 0°–8°S during the AS and expanded over 0°–18°S during the AW. As multi-year mean chlorophyll a was higher (>0.1 mg/m³) in the northern part of the ESTIO (north of ∼13°S; HCD: high chlorophyll a domain) than the southern side (LCD: low chlorophyll a domain), the study area was divided into two domains and all the variables were analysed. In the HCD, enhancement of chlorophyll a was positively correlated with variables such as wind speed, wind stress, Ekman pumping, stronger northward and westward winds, as well as the presence of cyclonic eddies. These features are likely to stimulate primary production by uplifting the thermocline and enhancing nutrient supply. In the LCD, mixed layer depth also showed a strong positive correlation with elevated chlorophyll a, apparently because it is deep throughout the year (thereby keeping lower biomass) and deepens more strongly in winter than in the HCD. Another contrast with the HCD is that the cyclonic eddies appear to be insufficiently abundant to influence its chlorophyll a. Pearson's multivariable correlation analysis and principle component analysis confirmed the statistical significance of the above parameters on the enhancement of chlorophyll a in the ESTIO.
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Low abundance and high patchiness of decapod fauna sampled with van Veen grab on the West African continental margin (Gulf of Guinea, Ghana)
Oceanologia 2024, 66(2), 220-238

Krzysztof Podwysocki1,*, Krzysztof Pabis1, Ferran Palero2, Magdalena Błażewicz1, Bjørn Serigstad3
1Faculty of Biology and Environmental Protection, University of Lodz, Łódź, Poland;
e-mail: krzysztof.podwysocki@biol.uni.lod
2Cavanilles Institute of Biodiversity and Evolutionary Biology, Valencia, Paterna, Spain
3Institute of Marine Research, Bergen, Norway
*corresponding author

keywords: Benthos, Deep sea, Depth gradient, Distribution patterns, Diversity

Received 15 December 2022, Revised 29 September 2023, Accepted 16 November 2023, Available online 4 December 2023, Version of Record 16 May 2024.


Sixty morphospecies of Decapoda (Malacostraca: Crustacea) representing 34 families were recorded in the material collected in 2012 from 265 van Veen grab (0.1 m2) samples, from the nine transects distributed along the coast of Ghana in the 25–1000 m depth range. The examined material was dominated by the Diogenidae, Panopeidae, Leucosiidae, Pilumnidae and Xanthidae families. Species accumulation curves showed undersampling of the studied area and a large number of the morphospecies comprised singletons and doubletons. Panopeus africanus was the most frequent morphospecies in the analysed material (9.1% of all samples). We observed a substantial decrease of diversity (Shannon Index) and abundance along a depth gradient. Species richness also decreased with depth, starting from the highest number of morphospecies ‒ 38 at 25 m depth, then 33 at 50 m, 17 at 100 m, 11 at 250 m, 8 at 500 m and ending with 1 morphospecies at 1000 m bottom depth. Higher diversity was observed on the continental shelf (25–250 m – 57 morphospecies), while on the slope (500–1000 m) only eight morphospecies were recorded. Numerous factors of natural and anthropogenic origin may affect decapod communities on the coast of Ghana. Since our material was collected using a sampler collecting material at a very small scale, the observed patterns might be affected by the sampling method.
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Characterization of suspended particles at different glacial bays at Spitsbergen
Oceanologia 2024, 66(2), 239-249

Katarzyna Dragańska-Deja*
Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland;
e-mail: katarzyna@iopan.pl
*corresponding author

keywords: Glacial meltwater, Svalbard, Geology, Particular Size Distribution, Mineralogy

Received 11 May 2023, Revised 19 October 2023, Accepted 6 December 2023, Available online 14 December 2023, Version of Record 16 May 2024.


Particle size distribution (PSD) and concentration of mineral-suspended sediment released from melting glaciers are important factors affecting the local marine ecosystem, e.g. affecting the light availability in water columns, thus changing underwater light climate for photosynthetic organisms. We examined the characteristics of various samples of natural mineral assemblages suspended in different glacial bays in Hornsund and Kongsfjord at Spitsbergen. The concentrations of the total mass of particles (TSM) in suspended sediment as well as particular organic matter (POM) and particular inorganic matter mass (PIM) together with mineralogical composition and particular size distribution (PSD) were determined.

In this study, we investigated the PSD properties and variability in the front of different tidewater glaciers based, laser diffractometer measurements (LISST-100x), and XRD – techniques to obtain the mineralogical composition of the particles. The sampled sites are under the strong influence of freshwater discharge from the glacier. At each station, inorganic particulate matter contributed up to 98% to total suspended matter with the particle concentration of the particle reaches up to 111 mg/l with mean surface PSD slopes ranging from 3.24 to 3.85. The result provides valuable baseline information on the observed range of variability of the size of suspended particles due to glacial runoff and the presence of particles of different mineral origin in the glacial bays.

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Rapid coastal erosion, its dynamics and cause – an erosional hot spot on the southern Baltic Sea coast
Oceanologia 2024, 66(2), 250-266

Grzegorz Uścinowicz1,*, Szymon Uścinowicz2, Tomasz Szarafin1, Elżbieta Maszloch1, Kamila Wirkus1
1Polish Geological Institute – National Research Institute, Marine Geology Branch, Gdańsk, Poland;
e-mail: grzegorz.uscinowicz@pgi.gov.pl
2Institute of Hydro-Engineering, Polish Academy of Sciences, Gdańsk, Poland
*corresponding author

keywords: Nontidal, Sea ice, Barrier coast, Storminess

Received 30 January 2023, Revised 7 June 2023, Accepted 14 December 2023, Available online 26 December 2023, Version of Record 16 May 2024.


Coastal erosion is one of the major problems in coastal management. To adapt to it, and prevent it where possible and needed, it is important to recognize the temporal and spatial scale of the phenomenon as well as its causes. This paper describes the rapid erosion rate along an approximately 2.25 km stretch of the southern Baltic coast. The erosion occurs within a nature reserve, which is not subject to direct anthropogenic impact. Historical maps and modern remote sensing were used to trace changes in the shoreline position from 1875 to the present, and detailed DTMs derived from airborne LiDAR were used to trace elevation changes of the beach and dunes over the past years. The weighted maximum annual erosion rate since 1875 averages 2.3 m. An increase in this annual erosion rate has been observed since the turn of the millennium. The maximum average erosion rate from 2001 to 2005 was 15 m/year. The erosion has caused serious changes in elevation within the inland part of the coastal zone, manifested by a reduction in the width of the beach and a decrease in the height of the beach and dunes.
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Evaluating and enhancing the performance of the K-Means clustering algorithm for annual coastal bed evolution applications
Oceanologia 2024, 66(2), 267-285

Andreas Papadimitriou*, Vasiliki Tsoukala
Laboratory of Harbour Works, School of Civil Engineering, National Technical University of Athens, Zografou, Greece;
e-mail: andrewtnt@mail.ntua.gr
*corresponding author

keywords: Wave input reduction, Cluster analysis, Morphological bed evolution, K-Means algorithm, Numerical modelling

Received 28 December 2022, Revised 28 July 2023, Accepted 17 December 2023, Available online 6 January 2024, Version of Record 16 May 2024.


The prediction of the coastal bed evolution at an annual scale utilizing process-based models is usually a complex task requiring significant computational resources. To compensate for this, accelerating techniques aiming at reducing the amount of input parameters are often employed. In the framework of this research, a comprehensive evaluation of the capacity of the widely-used K-Means clustering algorithm as a method to obtain representative wave conditions was undertaken. Various enhancements to the algorithm were examined in order to improve model results. The examined tests were implemented in the sandy coastline adjacent to the port of Rethymno, Greece, utilizing an annual dataset of wave characteristics using the model MIKE21 Coupled Model FM. Model performance evaluation was carried out for each test simulation by comparing results to a “brute force” one, containing the bed level changes induced from the annual time series of hourly changing offshore sea state wave characteristics, deeming the results very satisfactory. The best-performing configurations were found to be related to the implementation of a filtering methodology to eliminate low-energy sea states from the dataset. Employment of clustering algorithms utilizing “smart” configurations to improve their performance could become a valuable tool for engineers desiring to obtain an accurate representation of annual bed level evolution, while simultaneously reducing the required computational effort.
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Coverage estimation of benthic habitat features by semantic segmentation of underwater imagery from South-eastern Baltic reefs using deep learning models
Oceanologia 2024, 66(2), 286-298

Andrius Šiaulys1,*, Evaldas Vaičiukynas2, Saulė Medelytė1, Kazimieras Buškus2
1Marine Research Institute, Klaipeda University, Klaipeda, Lithuania;
e-mail: andrius.siaulys@ku.lt
2Faculty of Informatics, Kaunas University of Technology, Kaunas, Lithuania
*corresponding author

keywords: Underwater video, Epibenthos, Mosaicking, Segmentation, Computer vision, PSPNet, ResNet, Baltic Sea

Received 10 July 2022, Revised 28 August 2023, Accepted 17 December 2023, Available online 4 January 2024, Version of Record 16 May 2024.


Underwater imagery (UI) is an important and sometimes the only tool for mapping hard-bottom habitats. With the development of new camera systems, from hand-held or simple “drop-down” cameras to ROV/AUV-mounted video systems, video data collection has increased considerably. However, the processing and analysing of vast amounts of imagery can become very labour-intensive, thus making it ineffective both time-wise and financially. This task could be simplified if the processes or their intermediate steps could be done automatically. Luckily, the rise of AI applications for automatic image analysis tasks in the last decade has empowered researchers with robust and effective tools. In this study, two ways to make UI analysis more efficient were tested with eight dominant visual features of the Southeastern Baltic reefs: 1) the simplification of video processing and expert annotation efforts by skipping the video mosaicking step and reducing the number of frames analysed; 2) the application of semantic segmentation of UI using deep learning models. The results showed that the annotation of individual frames provides similar results compared to 2D mosaics; moreover, the reduction of frames by 2–3 times resulted in only minor differences from the baseline. Semantic segmentation using the PSPNet model as the deep learning architecture was extensively evaluated, applying three variants of validation. The accuracy of segmentation, as measured by the intersection-over-union, was mediocre; however, estimates of visual coverage percentages were fair: the difference between the expert annotations and model-predicted segmentation was less than 6–8%, which could be considered an encouraging result.
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Influence of wind and waves on ambient noise and bubble entrainment depth in the semi-enclosed Baltic Sea
Oceanologia 2024, 66(2), 299-318

Agata Dragan-Górska1,*, Natalia Gorska1, Piotr Markuszewski2,3,4, Zygmunt Klusek1
1Marine Physics Department, Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland;
e-mail: adgorska@iopan.pl
2Physical Oceanography Department, Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland
3Department of Environmental Science, Stockholm University, 10691 Stockholm, Sweden
4Bolin Centre for Climate Research, Stockholm University, 10691 Stockholm, Sweden
*corresponding author

keywords: Breaking waves, Underwater ambient noise, Gas bubbles, Semi-enclosed Baltic Sea

Received 23 December 2022, Revised 10 August 2023, Accepted 16 December 2023, Available online 30 December 2023, Version of Record 16 May 2024.


Semi-enclosed, fetch-limited waters create unique conditions for wind wave development and breaking. Parameters of breaking waves influence bubble entrainment depth and associated noise, which is why they differ in semi-enclosed sea compared to open waters. While the established noise-wind speed relationship holds in oceanic conditions, it differs in land-constrained basins like the Baltic Sea. To explore noise level, bubble entrainment depth and wind speed relationships, we conducted noise and sub-surface bubble measurements, coupled with wind observations, in the selected area of the Baltic Sea during two consecutive summers. A novel method was employed to estimate bubble entrainment depth under conditions of strong backscatter. Model data of wave field parameters were employed to assess their influence on noise level and bubble entrainment depth. Results suggest stronger connections between noise level and wind speed, as well as wave height, compared to wave age and wind sea steepness. The same patterns hold true for the correlation between bubble entrainment depth and both wind speed and wave field parameters. The parameterized noise level-wind speed relationship differs from that obtained for oceanic conditions and also varies across measurement periods. Observed differences were shaped by varying wind-wave conditions, notably differences in wind speed, direction, wave height, and the presence of swell. The noise level-bubble entrainment depth relation is reported for the first time for Baltic Sea conditions. For a thorough analysis of the influence of these factors on noise and bubbles, longer measurements under diverse wind-wave conditions are required to account for site-specific wave field characteristics.
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Soft postglacial cliffs in Poland under climate change
Oceanologia 2024, 66(2), 319-333

Grzegorz Różyński*, Grzegorz Cerkowniak*
Institute of Hydro-Engineering, Polish Academy of Sciences, Gdańsk, Poland;
e-mail: grzegorz@ibwpan.gda.pl, grzegorzcerkowniak@ibwpan.gda.pl
*corresponding author

keywords: Baltic Sea, Sea level rise, Soft cliffs, Mixed sediments, Extreme events

Received 25 January 2023, Revised 31 May 2023, Accepted 10 January 2024, Available online 3 February 2024, Version of Record 16 May 2024.


The paper presents the results of the simulations of soft cliff erosion in Poland under future sea level rise. Two locations were investigated: one situated on the Wolin island, and the second near the town of Ustka. The cliffs will be suffering enhanced erosion for a number of reasons. First, the adopted sea level rise of 0.7 m results in a direct attack on cliff foot, leading to enhanced erosion with rates being roughly twice as high as that occurring without the rise. A high rate of erosion can persist because the cliff cannot reconfigure itself by moving landward and will permanently remain exposed to wave attack even under milder regimes. Second, the wave climates in the Baltic Sea release most energy in close shoreline proximity. Third, longer storm event durations can lead to ‘erosion saturation’, but this result requires further investigations, which will include alongshore effects induced by local bathymetry and longshore currents, ignored in 1-D simulations. Finally, the granulometry was found less important; finer grains offer less resistance to depletion, leading to greater erosion. The results demonstrate the need for vast follow-up research: (1) detailed mapping of the bathymetry near cliffs in order to properly reproduce alongshore redistribution of sediment during storms and achieve better estimates of cliff erosion, (2) detailed mapping of cliff lithology in order to properly reproduce their sediment composition and thus achieve better estimates of built-in susceptibility to erosion, (3) preparation of 2-D modeling suites for improved assessment of the rates of erosion of cliffs subjected to sea level rise.
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Knowledge Transfer Platform FindFISH – Numerical Forecasting System for the Marine Environment of the Gulf of Gdańsk for Fisheries
Oceanologia 2024, 66(2), 334-352

Lidia Dzierzbicka-Głowacka1,*, Maciej Janecki1, Dawid Dybowski, Artur Nowicki, Agata Zaborska1, Piotr Pieckiel2, Michał Wójcik2,3, Tomasz Kuczyński2, Jacek Wittbrodt4
1Institute of Oceanology, Polish Academy of Science, Sopot, Poland;
e-mail: dzierzb@iopan.pl
2Maritime Institute – Gdynia Maritime University, Gdynia, Poland
3Gdańsk University of Technology, Gdańsk, Poland
4The Association of Marine Fishermen – Producers' Organization in Władysławowo, Poland
*corresponding author

keywords: Sustainable fishing; Numerical modeling; Forecasting habitat

Received 1 September 2023, Revised 21 December 2023, Accepted 30 January 2024, Available online 19 February 2024, Version of Record 16 May 2024.


Fast access to expert knowledge is very valuable, especially in the context of decision-making. Fishermen can use this knowledge to diagnose hydrological and hydrochemical conditions in which fish stocks should be the most abundant. In response to this need, a digital service has been developed. It is a service created within the FindFISH project, which provides the results of all developed models: hydrodynamic, biochemical, and Fish – for selected commercially caught fish species (herring, sprats, cod, and flounder). Our research revealed that the FindFISH service can enhance fishing efficiency and quality by approximately 40%, significantly increasing expected profits. In practical applications, we observed a 50% to 70% concordance between the fishing grounds recorded by fishermen and those identified by the FindFISH Platform. The website runs dynamically in operational mode, allowing visualization of forecasts in the form of maps, time series, spatial data, and tables.
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The zooplankton community of Baltic Sea ports: diversity and seasonal dynamics
Oceanologia 2024, 66(2), 353-364

Bartosz Witalis1, Anna Iglikowska2,*, Marta Ronowicz3, Agata Weydmann-Zwolicka1, Piotr Kukliński3
1National Marine Fisheries Research Institute, Gdynia, Poland;
e-mail: bwitalis@mir.gdynia.pl
2University of Gdańsk, Faculty of Biology, Department of Evolutionary Genetics and Biosystematics, Laboratory of Biosystematics and Ecology of Aquatic Invertebrates, Gdańsk, Poland;
e-mail: anna.iglikowska@ug.edu.pl
3Institute of Oceanology Polish Academy of Sciences, Marine Ecology Department, Sopot, Poland;
e-mail: kuki@iopan.pl
4University of Gdańsk, Faculty of Oceanography and Geography, Department of Marine Biology and Biotechnology, Laboratory of Plankton Biology, Gdynia, Poland;
e-mail: agata.weydmann@ug.edu.pl
*corresponding author

keywords: Seasonal dynamics, Plankton diversity, Copepoda, Invasive species, Gulf of Gdańsk

Received 8 February 2023, Revised 26 October 2023, Accepted 2 February 2024, Available online 26 February 2024, Version of Record 16 May 2024.


In this study, we investigated zooplankton composition and seasonal dynamics, as well as the influence of selected environmental factors on the zooplankton community in three ports on the Polish Baltic coast: Władysławowo, Gdynia and Gdańsk. Our aim was to determine whether harbours’ heavy traffic, chemical pollution and physical disturbances affect the zooplankton community, and whether new nonindigenous planktonic species occur in these habitats. Forty three zooplankton taxa were found in all three ports; however, it is important to note that no new nonindigenous species were observed in the port basins. The most influential environmental factors affecting the zooplankton community were: seawater temperature (17% of explained zooplankton variability) and transparency (4%), which were related to seasonal changes. Acartia spp. (although of different development stages) was the dominant taxon during the study, and the examined ports/seasons differed in the presence and proportions of less abundant taxa: the autumn and winter assemblages were dominated by Acartia spp. nauplii, the spring assemblage by numerous Polychaeta larvae, while Cirripedia nauplii and early development stages of Eurytemora affinis were particularly abundant in summer. In addition, changes in salinity (2% explained variability) had a particular impact on the zooplankton community and especially on the assemblage of Gdańsk Port, which was influenced by freshwater inflow from the Motława and Dead Vistula rivers. Our study has clearly shown that, despite severe physical and chemical disturbances in all studied ports, the composition and seasonal dynamics of the zooplankton community were similar to those of the Gulf of Gdańsk outside the ports.
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Variability of chlorophyll a concentration in surface waters of the open Baltic Sea
Oceanologia 2024, 66(2), 365-380

Małgorzata Stramska*, Jaromir Jakacki
Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland;
e-mail: mstramska@wp.pl
*corresponding author

keywords: Baltic Sea, Remote sensing, Annual cycles, Chl variability

Received 2 December 2022, Revised 14 February 2023, Accepted 27 February 2024, Available online 12 March 2024, Version of Record 16 May 2024.


In situ, satellite and reanalysis data from numerical models were used to study the characteristic features of Chl variability in the Baltic Sea. The analysis is focused on the years 2003–2020 when regular observations of ocean color with the MODIS AQUA are available. In the Baltic Sea, there is a pronounced annual cycle in physical conditions in the water column, driven by seasonal cycles in atmospheric forcing. The seasonal cycle of Chl concentration does not conform to the picture known from classical models, with low phytoplankton concentration when nutrients are low. In contrast, in the Baltic Sea, the concentration of Chl is high even during the summer months when nutrients are depleted. This can be explained by a continuous supply of nutrients by runoff from land, as well as by a significant contribution to primary production by phytoplankton able to survive in environment poor in dissolved nutrients. There is also a considerable interannual variability in Chl. There are many possible cause/effect interactions involved, but the data series are still too short to make clear which of them are the most important. The most striking event was a spring bloom in 2008.
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Distribution and biogeochemical perspectives of nutrients in the Eastern Equatorial Indian Ocean
Oceanologia 2024, 66(2), 381-393

Madhusudan Paul1, Prasun Sanyal1, Rishmita Mukherjee1, Vandana Kumari Gupta1, Sneha Bakshi1, Avanti Acharya1, Trishneeta Bhattacharya2,4, Kunal Chakraborty2, Sandip Kumar Mukhopadhyay1,3,*
1Department of Marine Science, University of Calcutta, Kolkata, India;
e-mail: Sandip.m@gov.in
2Indian National Centre for Ocean Information Services (INCOIS), Ministry of Earth Sciences, Government of India, Hyderabad, India
3Ministry of Earth Sciences, Government of India, New Delhi, India
4Faculty of Ocean Science and Technology, Kerala University of Fisheries and Ocean Studies, Kochi, India
*corresponding author

keywords: Eastern Equatorial Indian Ocean, Nutrients, Preformed nutrients, Nitrate deficit

Received 22 March 2023, Revised 31 July 2023, Accepted 27 February 2024, Available online 16 March 2024, Version of Record 16 May 2024.


The seasonal reversal of ocean circulation associated with seasonal change in the direction of prevailing winds and the occurrence of several anomalous events in the Eastern Equatorial Indian Ocean (EEIO) make this region dynamic and complex in terms of its biogeochemical characteristics. Two multidisciplinary cruises were conducted to measure nutrients and associated physicochemical parameters across the water column (up to 1000 m) of the EEIO during boreal summer and winter monsoons to understand the distribution of nutrients and their spatio-temporal variability from a biogeochemical perspective. The seasonality in the thermohaline structure of the region is indistinct except for surface salinity drop during summer monsoon due to more precipitation on-site and in adjoining areas. Low concentrations of chlorophyll at the surface and in the deep chlorophyll maxima represent the oligotrophic nature of this region. Surface water was found nutrient-depleted (0.03–0.4 µM Nitrate, 0.02–0.13 µM Phosphate). The maxima of vertical profiles of nitrate and phosphate were recorded at a shallower depth (150–200 m) when compared to its maxima in usual oceanic conditions, but a silicate maximum was recorded in deeper water. In the surface and upper mixed layer paucity of nutrients resulted in low N:P and N:Si ratios. Therefore, nitrogen limitation is evident. The overall ratio of N:P yielded a mean value of 15.33 and matched with the representative literature value for the Indian Ocean. The minimum oxygen values (<50 µM) in the deep water (150–200 m) indicated a hypoxic condition. No signature of denitrification and a moderate nitrate deficit were observed in deep waters. The negative values of Nitrate anomaly (N-tracer) at 50–100 m depth were attributed to a Watermass influenced by denitrification. The prevailing oligotrophic condition caused limited synthesis of organic matter and subsequently little decomposition in deep water. The maxima in the apparent oxygen utilization (AOU) profile are confined to 150 to 200 m depth and represent the most active zone for regeneration that is limited to shallow depth. Regenerated nutrients reached maxima at shallower depth and primarily control material cycling in this region. Supply of nitrate to the surface water based on the preformed values of prevailing water mass was primarily by Bay of Bengal water. According to the findings of this study, preformed nitrate concentrations between 100 and 200 metres below the surface were found very low, indicating that Indonesian Through Flow (ITF) has little impact on the distribution of nutrients in this area.
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Assessing the effect of coastal upwelling on the air temperature at the south-eastern coast of the Baltic Sea
Oceanologia 2024, 66(2), 394-404

Toma Dabulevičienė*, Laura Nesteckytė, Loreta Kelpšaitė-Rimkienė
Marine Research Institute, Klaipeda University, Klaipėda, Lithuania;
e-mail: toma.dabuleviciene@ku.lt
*corresponding author

keywords: Upwelling, Baltic Sea, Air temperature, Satellite data, Coastal meteorology

Received 31 January 2023, Revised 27 December 2023, Accepted 6 March 2024, Available online 3 April 2024, Version of Record 16 May 2024.


Coastal upwelling along the SE Baltic Sea coast is a common feature, especially during the warm season. It significantly lowers sea surface temperature (SST) in the coastal areas, and, therefore, may be responsible for modifying meteorological conditions in those coastal areas, where upwelling is most frequently observed. This study aims to assess the effect of coastal upwelling on the air temperature at the south-eastern coast of the Baltic Sea based on long-term period observations (2002–2021) from coastal hydrometeorological stations and satellite data. Overall, our study revealed that due to its high frequency and spatial extent, upwelling is responsible for lowering the mean summer season SST of the SE Baltic Sea coast by about 1°C. And even though upwelling is a short-term event, upwelling-induced SST drop results in cooling air temperatures in the coastal areas, i.e., the mean air temperatures during upwelling are typically 2−4°C lower than before. It was also observed that upwelling is favouring the development of advective fog. Thus, sudden changes in meteorological parameters during upwelling can have versatile effects on various socio-economic activities. The results of this study contribute to the understanding of upwelling feedback onto the lower atmosphere and, therefore, are important for advancing the accuracy of weather forecasts that are needed for coastal communities, including marine and coastal industries.
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Phytoplankton pigments in the Baltic Sea – mathematical description of chlorophylls and carotenoids content in different seasons and regions
Oceanologia 2024, 66(2), 405-423

Joanna Stoń-Egiert1,*, Mirosława Ostrowska1, Roman Majchrowski2
1Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland;
e-mail: aston@iopan.pl
2Institute of Geography, Pomeranian University in Słupsk, Słupsk, Poland
*corresponding author

keywords: Baltic Sea, Chlorophylls, Carotenoids, Seasonal approximations

Received 20 February 2023, Revised 19 December 2023, Accepted 27 March 2024, Available online 10 April 2024, Version of Record 16 May 2024.


This study aimed to trace the spatial and seasonal changes in pigment composition and to develop mathematical formulas to quantitatively describe their composition in different seasons in two regions: the open Baltic Sea region and the Gulf of Gdańsk. The analyses were carried out based on a 20-year database of empirical data from 1999 to 2018 obtained using the HPLC method. The proportion of chlorophyll a in the total content of pigments was stable irrespective of the season and region (62% ± 5%). In summer and autumn, a higher total amount of photoprotective carotenoids (about 15–17% in total pigment content) than photosynthetic ones was recorded. The concentrations of marker pigments are related to periodic increases in the corresponding algal classes. The spring bloom dominated by diatoms and dinoflagellates results in 40% of fucoxanthin and 70% of peridinin in relation to their total content throughout all seasons. The highest percentage of chlorophyll b (up to 10% in open waters) and other pigments specific to green algae (neoxanthin, violaxanthin, lutein) were observed during summer and autumn. The 30% percentage of fucoxanthin confirms the occurrence of diatoms in autumn. The concentrations of groups and individual pigments have been determined as a function of chlorophyll a concentration. The best approximation results were obtained for the seasonal dependence of marker pigments for specific classes of algae. In summer and autumn – for chlorophyll b concentrations – zeaxanthin, fucoxanthin, alloxanthin and peridinin standard error factor ranges between 1.56 and 1.84.
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Short communication

Apparent return of free-living Fucus vesiculosus to the Polish Baltic waters
Oceanologia 2024, 66(2), 424-428

Piotr Balazy*, Józef Wiktor, Agnieszka Tatarek, Jan Marcin Węsławski
Institute of Oceanology, Polish Academy of Sciences, Sopot, Poland;
e-mail: balazy@iopan.pl
*corresponding author

keywords: Underwater meadows, Fucus mats, Puck Lagoon, Re-discovery

Received 21 December 2023, Accepted 27 February 2024, Available online 12 March 2024, Version of Record 16 May 2024.


The underwater meadows of the Puck Bay, once thriving with eelgrass Zostera marina, bladderwrack Fucus vesiculosus and black carrageen Furcellaria lumbricalis, experienced a decline in water quality during the 1960s and 1970s due to untreated sewage pollution. This, together with commercial exploitation, led to the disappearance of bladderwrack in 1977, with unsuccessful attempts at reintroduction in the early 2000s. In December 2023, a SCUBA survey near Rzucewo revealed a numerous bladderwrack in a benthic free-living form after 46 years of absence. The algae were found between 1.7 and 2.7 m depth, loosely positioned on the seabed, often within Z. marina beds, and with blue mussels Mytilus edulis attached. This reappearance suggests a positive trend in seawater quality and overall state of the Puck Bay, especially when combined with recent recovery of other algae species. The apparent return of bladderwrack could enhance ecosystem functionality, benefiting fish recruitment, grazer and algal biomass. Further investigations on bladderwrack's reappearance are needed in order to verify whether this is the only ecotype currently present in the Puck Bay.
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