Oceanologia

The sandy seashore is a highly dynamic environment where the beach experiences constant change. If the granulometric composition of beach sediment does not change substantially and the sediment circulation is undisturbed, as well as the prevailing hydrometeorological situation does not substantially change, the beach can maintain its morphology quasi-stably on a decadal time scale, even when coastal erosion or accretion processes prevail. In this study, beach width and volume characteristics of coastal segments with prevailing erosion or accretion were assessed based on interannual beach leveling surveys from the Lithuanian Baltic Sea coast in 2002–2023 (72 cross-shore profiles in total). Study results revealed that the beach on both coastal stretches with prevailing erosion processes and coastal stretches with prevailing accretion processes maintains its morphometric characteristics. On coastal stretches with prevailing erosion, the beach maintains its profile by supplementing its sediment budget with the sediment reserves in the foredune, while on coastal stretches with prevailing accretion and seaward shoreline migration, the indefinite increase in beach width is limited by the formation of the incipient dunes at the foredune toe.

The round goby (Neogobius melanostomus) has expanded its range from the Ponto-Caspian region to new habitats in Europe and North America. It is an invasive species in many areas that has a significant impact on new environments. The round goby inhabits various ecosystems with different environmental conditions. Here, we investigated the optimal temperatures for round goby reproduction. Our experimental study on the development of round goby embryos demonstrated a high tolerance to different temperatures at this stage of ontogenesis. The development of round goby embryos was highly successful (over 90% of larvae hatching) at temperatures ranging from 12°C to 20°C. In contrast, embryo development was less successful at 25°C, while no effective embryo development was observed in temperatures below 12°C. We found that larvae hatching at temperatures between 12°C and 20°C have yolk remnants, which provide an additional supply of energy in the first days after hatching. A wide range of temperature tolerance, along with tolerance to other changing factors, are the features that contribute to successful population growth. Thus, temperature should not be a factor limiting the expansion of round goby in the temperate climate zone.

This study uses a fully coupled physical-biological model to study nutrient enrichment and plankton dynamics in a seasonal coastal upwelling system. This upwelling system, located in the eastern Great Australian Bight, Australia, provides the feeding ground for a range of predatory species including tuna, sea lions, sharks, and whales. The biological model describes the interactions between dissolved nitrogen, phytoplankton, zooplankton, and detritus in response to changes in the physical environment predicted by a standard three-dimensional hydrodynamic model. This study tests a “zonation hypothesis” claiming that, in coastal upwelling systems, zones of maximum nitrogen, phytoplankton and zooplankton develop spatially separated along the coast due to the advective effect of coastal upwelling currents and biological delays in the formation of phytoplankton and zooplankton. While the physical process of wind-driven coastal upwelling is well understood and predictable, several aspects of the biological response simulated in this study are surprising. (i) During the upwelling phase, maximum phytoplankton and zooplankton production occurs in shallower waters alongside the upwelling zone of maximum surface nitrogen. In this upwelling shadow, recycled nitrogen contributes the same amount as physical processes to the local nutrient flux. (ii) Conversely, physical effects offset most of the local phytoplankton growth in the upwelling zone. After wind relaxation, the shutdown of the upwelling process eventually also triggers phytoplankton blooms in this zone. (iii) Wind relaxation creates a narrow coastal countercurrent that operates to maintain the plankton biomass near the upwelling center. For these reasons, the zonation hypothesis does not hold for the coastal upwelling system studied in this work.

The northern South China Sea (SCS) is characterized by multiple oceanographic phenomena and has developed diverse patterns of distribution, migration and transformation of dissolved organic carbon (DOC). To better understand the DOC behavior and its relationship with the nepheloid layer, UV-visible absorption spectra and three- dimensional fluorescence spectra of dissolved organic matter (DOM) were obtained in the northern SCS, as well as beam attenuation (BA), major physicochemical parameters and chlorophyll �� (Chl-��) data. DOC and chromophoric dissolved organic matter (CDOM) gradually decrease from the surface to deeper layers, with high-low alternations occurring in the euphotic zone. The fluorescence intensity of DOM is primarily attributed to protein-like components, followed by humic-like components (24.6%). CDOM exhibits a typical marine origin and is produced mainly through bacterial production in situ. The spatial and temporal distributions of DOC and humic-like components are influenced by major physicochemical factors (such as temperature, salinity, and nutrients) and Chl-��. In contrast the protein-like components might be closely associated with bacterial activity. The distributions of DOC and humic-like components are significantly correlated with the presence of the nepheloid layer. In the euphotic zone, phytoplankton particulates are the primary source of humic-like components, while suspended particles affect the distribution of humic-like components below the euphotic zone. The results presented direct evidence for the function of the marine nepheloid layer in the organic carbon cycle.

Sea surface temperature (SST) is a crucial climate indicator for tracking atmospheric and oceanic interactions, particularly in coastal areas. The study focused on the simulation of SST in the region around the north coast of Penang Island, Malaysia, where the prediction of SST is challenging due to its complex atmospheric and oceanic interactions. The Regional Ocean Modeling System (ROMS), a sophisticated numerical model, is employed to predict the variation of SST in the study region. In the present study, HYCOM Global Ocean Forecasting System (GOFS) was incorporated to generate the boundary condition, initialisation, and climatology, while MERRA-2 datasets were considered as atmospheric forcing datasets. The generated SST from ROMS was compared with Aqua-MODIS observations of SST across six selected locations. Different methods, such as time series plots, linear modelling plots, and Taylor diagrams, and error estimation methods were employed to understand the accuracy of the model. The result indicates an underestimation of the SST using the ROMS model. Also, the root mean square error (RMSE) and mean absolute error (MAE) show an average of 2.58°C and 2.50°C in the study area, highlighting the requirement for bias correction. Three bias correction methods, such as Delta Change (DC), Linear Scaling (LS), and Quantile Mapping (QM), were considered to improve SST predictions. The comparative analysis of these three methods through time-series plots and statistical evaluations demonstrates that all three methods significantly reduce errors by bringing RMSE and MAE below 0.7°C. It is also noted that the best result was obtained by the QM method, as it not only reduces mean errors but also enhances correlation between the predicted and observed SST, the other two methods show no variation in the correlation value. The study confirms that the ROMS model can effectively capture the characteristics fluctuation of the SST in the dynamic regions like the north coast of Penang Island but bias correction is crucial for improving the prediction. In this case, the QM bias correction method provides the most balanced and effective adjustment compared to the other two methods.

Analyses of the spatial and interannual variability of suspended particulate matter (SPM) and chromophoric dissolved organic matter (CDOM) concentrations were carried out in the waters of the Gulf of Gdańsk in the summer season in 2016–2020. Additionally, the absorption properties of those substances were analyzed. The inflowing waters of the Vistula River are characterized by high concentrations of SPM, chlorophyll a (Tchla) and CDOM, significantly affecting the absorption properties in the mixture of river and sea waters. The high contribution of particulate organic matter, POM, in the total SPM in the Gulf of Gdańsk (80% on average) indicates high phytoplankton productivity in the summer. High concentrations of pigments characteristic of different size classes of algae and cyanobacteria (fucoxanthin and zeaxanthin, chlorophyll b, peridinin and alloxanthin) were recorded, being markers of diatoms, cyanobacteria, green algae, dinophytes and cryptophytes, respectively. Analysis of interannual variability showed changes of SPM, Tchla and CDOM concentrations, depending on volume and direction of the river inflow and weather conditions. The composition of individual pigments changed year to year in a mosaic (heterogeneous) manner. The average contribution of CDOM, phytoplankton and detritus in the total light absorption was determined (at 443 nm – 50%, 34% and 16%, and at 675 nm – 41%, 54% and 5%). Spatial and temporal variability of the light absorption coefficients by suspended particles and CDOM in sea water was examined, and the relationships between the individual light absorption coefficients by sea water components were determined as a function of the dependence on SPM and Tchla.

The South China Sea is a region frequently impacted by intense tropical cyclones (TCs). Recent super typhoons such as Yagi (2024), Haikui (2023), Saola (2023), Doksuri (2023), and Koinu (2023) have caused catastrophic damage. This study primarily investigates the oceanic response to westward-moving super typhoons. The cyclonic wind field is reconstructed based on reanalysis from the European Centre for Medium-Range Weather Forecasts (ECMWF), and the TC wind speed derived from measurements of five moored buoys shows a 4.01 m/s root mean squared error (RMSE), a 0.90 Pearson’s correlation (Cor), and a 0.48 scatter index (SI). A triangular-grid-based numerical circulation mode, namely the Finite-Volume Community Ocean Model (FVCOM), is employed to simulate sea surface currents and sea levels. The reconstructed TC winds act as the forcing field, and the FVCOM-simulated sea surface currents and sea levels are then incorporated into wave simulations conducted with the Simulating WAves Nearshore (SWAN) model. It is found that the hindcasting significant wave heights (SWHs) are most consistent with measurements from moored buoys when current and sea level are included, and this phenomenon is particularly significant around the Taiwan Strait. Two parameterizations of the drag coefficient ��_��, i.e., the ��_�� by Wu (1982) and the ��_�� by Hu et al. (2024), are used in SWAN. The improved ��_�� shows a clear advantage when SWH > 3 m, resulting in a reduction of over-estimation and an increase in SWH accuracy by 0.6 m. Wind and SWH exhibit opposing asymmetry trends due to swell influence. Along super typhoon tracks, sea surface temperature (SST) cooling reaches a maximum of 4°C; however, the Kuroshio Current and Zhejiang-Fujian Coastal Current mitigate this cooling, reducing it by approximately 1°C. These findings offer significant implications for understanding super typhoon responses to ocean dynamics and provide critical insights for enhancing disaster resilience strategies during extreme weather events.

Noctiluca scintillans, which is common in coastal waters, significantly affects coastal biomass through bloom formation. This study has measured the cellular carbon, nitrogen, and chlorophyll a (Chl-a) content of natural green Noctiluca from the western Upper Gulf of Thailand. The carbon content ranged from 195–556 ng-C cell⁻¹ (mean: 241 ± 132 ng-C cell⁻¹), while nitrogen content varied between 17–55 ng-N cell⁻¹ (mean: 36 ± 6 ng-N cell⁻¹). Chl-a content averaged 9.80 ± 0.78 ng cell⁻¹. Notably, green Noctiluca exhibited higher carbon content than red Noctiluca of identical cell size, potentially because of their endosymbionts.