Oceanologia最新文献

The Moroccan Southern Atlantic coast is mainly influenced by upwelling, Saharan dust and anthropogenic micropollutant input. These factors contribute to increasing the availability of metal elements in waters. To differentiate human impact from natural variability, knowledge of background concentrations of metals and their fluctuations in bioindicator organisms such as zooplankton is important. This work aims to determine the levels of metals elements (Zn, Mn, Pb, Cu, Cd, Cr, Co, Ni, Li, As, Sr, U, Fe and Ba) in zooplankton along the southern area of the Atlantic coast of Morocco. Zooplankton samples were collected in the summer (July 2013) and autumn (December 2013) at 27 stations from Sidi Ifni to the south of Dakhla. All stations were located on transects perpendicular to the coast. The analysis of metal elements in zooplankton was determined by ICP–MS. The results revealed that in all transects, metal concentrations were below the regulatory limits. Metal enrichments were observed in the south and decreased gradually to the north. This study can be used as baseline data for the metal contents of zooplankton in Moroccan South Atlantic coastal water. A comparison to worldwide reported data on zooplankton did not reveal any suggestions on increased metal presence in the area investigated.

Oceanic internal waves are an active ocean phenomenon that can be observed, and their relevant characteristics can be acquired using synthetic aperture radar (SAR). The locations of oceanic internal waves must be determined first to obtain the important parameters of oceanic internal waves from SAR images. An oceanic internal wave segmentation method with integrated light and dark stripes was described in this study. To extract the SAR image characteristics of oceanic internal waves, the Gabor transform was initially used, and then the K-means clustering algorithm was used to separate the light (dark) stripes of oceanic internal waves from the background in the SAR images. The regions of the dark (light) stripes were automatically determined based on the differences between the three classes, that is, the dark stripes, light stripes, and background area. Finally, the locations of the dark (light) stripes were determined by shifting a given distance along the normal direction of the long side with the minimum bounding rectangle of the light (dark) stripes. The best segmentation results were obtained based on the intersection over the union of the images, and the accuracy of segmentation was verified. Furthermore, the effectiveness and practicability of the proposed method in the light and dark stripe segmentation of SAR images of oceanic internal waves were illustrated. The proposed method prepares the foundation for future inversion studies of oceanic internal waves.

Understanding the changing levels of biochemical parameters and the factors that influence them throughout the seasons is crucial for comprehending the dynamics of marine ecosystems. It also helps us identify potential threats that could harm their condition, aiding decision-making processes related to their protection. This study focuses on examining the variations in nutrients (such as nitrates, phosphates, and silicates), dissolved oxygen, and phytoplankton within the Gulf of Gdańsk. Additionally, we analyze the primary production process at three representative locations. To achieve this, we used data from the EcoFish biochemical numerical model. To ensure the model's accuracy, we compared its results with in situ data from the ICES database. The comparison revealed high correlations and minimal errors. Furthermore, we investigated how limiting factors impact primary phytoplankton production and demonstrated how the intensity of spring diatom blooms influences the nature of cyanobacterial blooms in the summer.

The statistics suggest that extreme waves cause more damage in shallow waters and at the coast than in the deep sea. In the linear theory of the formation of extreme waves, their existence is interpreted as a local superposition of surface monochromatic waves. The event of excitation of extreme waves can be understood as an increase in natural oscillations of the water basin. The conditions for the excitation and sustaining of natural oscillations are the proximity of the periods of exciting traveling waves to the period of traveling waves and the speed of movement of the exciting current to the phase speed of propagation of traveling waves of the reservoir. Examples of stimulating natural oscillations are presented. We determined the range of expected periods of natural oscillations, which range from 30 seconds to 24 hours. Synchronously and in common-mode with the oscillations of standing waves between their antinodes, a "standing" current occurs with a measured speed of up to 11 km/h. We presented a hypothesis about the possibility of stimulating natural oscillations of water bodies by a standing current, which changes its direction due to the movement of the water surface from the trough of the wave to its crest, and back. A model of stimulating oscillations by the waves with a constant period and currents with constant and variable speeds has been developed.

Due to the Arctic amplification effect, the Svalbard archipelago is an important area for studying ongoing environmental changes. However, its marine ecosystem is extremely complex. In this study, we analyze modern assemblages of dinoflagellate cysts (dinocysts) and benthic foraminifera from surface sediment samples around Svalbard. We use multivariate statistical analyses to examine relationships between environmental conditions (summer and winter sea surface temperature and salinity, sea-ice cover, etc.) and both microfossil groups to evaluate their use as proxies for reconstructions of the marine environment in the region. Our results show that the most important factor controlling the environment around Svalbard is the Atlantic Water which mostly impacts the western coast, but its influence reaches as far as the eastern coast of Nordaustlandet. However, on a local scale, such factors as the sea-ice cover, the presence of tidewater glaciers, or even the morphology and hydrology of fjords become increasingly important. We found that two dinocyst species, cysts of Polarella glacialis and Echinidinium karaense, can be considered regional winter drift ice indicators. The relationships between environmental parameters and benthic foraminiferal assemblages are much more difficult to interpret. Although statistical analysis shows a correlation of benthic foraminiferal species with various environmental parameters, this correlation might be somewhat coincidental and caused by other factors not analyzed in this study. Nevertheless, the use of two complementary microfossil groups as (paleo)environmental indicators can provide a more comprehensive picture of the environmental conditions.

Coastal erosion is a natural process, that contributed to shaping the Nile Delta shoreline in Egypt over history. The objective of this research is to investigate shoreline changes, accretion, and erosion and to detect particularly vulnerable locations that require immediate attention. Another goal is to assess the efficiency of coastal installations that have been recently implemented along the study area and determine whether they have performed their role to the fullest or need additional modifications. Several Landsat images (TM, ETM+, and OLI) were utilized over 37 years to track the shoreline changes and were analysed using remote sensing (RS) and Geographic Information System (GIS). The digital shoreline analysis system (DSAS) was integrated with the LRR model for assessing historical changes for shorelines from 1985 to 2022 and forecasting future shoreline positions in 2030, 2050, and 2100. Most of the eight zones that make up the Delta region have lately seen the establishment of coastal projects, such as the development of the Abu Qir port's breakwater in 2021. From the results, it was found that the areas around Rosetta promontory, Burullus headland, and Damietta promontory experienced a significant and rapid retreat and with large rates over the study period, with average values of –15.7, –3.25, and –16.8 m/y, respectively. However, both the coast of Alexandria, and Gamasa embayment were subjected to accretion as a prevailing case, with average rates of 2.85, and 4.03 m/y, respectively. Many groins were installed in the east of the Rosetta promontory (zone 3) in 2016 to decrease the erosion process; however, it didn't pay off and could not solve the problem. In contrast, the groins system, which was implemented at the East Kitchener Drain (zone 5) in the same year, lowered erosion rates from 17.6 m/y from 2000 to 2010 to 7 m/y from 2010 to 2022. In 2019, Y-groins built in zone 7, east of Damietta Port, succeeded in slowing rates of erosion. Finally, inlet jetties at El-Gamil (zone 8) were constructed in 2016, resulting in the coastline advancing at 14.7 m/y on average in the period of 2010–2022. The findings of this study confirmed that hard structures are dangerous because they exacerbate the problem of shoreline erosion by disseminating it to the neighbouring beaches and acting as an impediment to the movement of longshore sediments. According to the expected future shoreline patterns, it is necessary for authorities to implement both short-term and long-term protective measures to stop the erosion of several areas of the beach.

The paper presents the results of the novel modelling of the wind-driven current in the southern Baltic Sea. The steady current is accompanied by wave-induced orbital velocities. The bed boundary layer related to wave-induced oscillatory flow gives rise to the appearance of additional shear stresses affecting the wind-driven current. This impact included in the wind-driven current model yields a modified logarithmic velocity distribution. Theoretical velocity profiles are compared with the field data. The measurement database includes wind, wave and current parameters. The velocities and directions of the wind were collected from the anemometer installed at the Coastal Research Station (CRS) in Lubiatowo. Wave-current parameters at a depth of about 17 m were obtained from a location of approx. 1.5 Nm from the shoreline in the vicinity of CRS Lubiatowo. The study site hydrodynamics is typical of the south Baltic coast. The analysis shows good agreement between the measured flow velocities and the theoretical vertical distributions in the form of the modified logarithmic profile.

The simulation of Lagrangian drift is an important task in applications such as dispersion of pollutants, larvae and search and rescue activities. In this study, the Eulerian current, Stokes drift and wind effect on the simulation of observed drifters were analysed. The Lagrangian OceanParcels model was used, and the surface trajectories were assessed by comparison with 9 GPS drifter trajectories in the Gulf of Finland, Gulf of Riga and Lithuanian coast. The Normalised Cumulative Lagrangian Separation (NCLS) distance between the simulated and the satellite-tracked drifter trajectories, and the mean absolute error (MAE) were used as comparison metrics. The present study suggests the need to consider the Stokes drift and the wind factor in addition to the modelled Eulerian currents to obtain a better description of the trajectories of particles. By making these considerations, the OceanParcels model could adequately simulate particle trajectories in the sub-basins within the Baltic Sea. The realized model tests showed that motion of surface drifters are strongly controlled by the Stokes drift when the significant wave height is >1 m, whereas the wind component and the Eulerian currents are crucial when the significant wave height is <0.6 m or the wave (Stokes drift) directions do not match the wind direction.

Variations of temperature, salinity and oxygen of the Baltic Sea on interannual to decadal timescales were studied for the period from 1950 to 2020. Both observational data and the output of a numerical circulation model of the Baltic Sea were analyzed. In addition, we investigated the influence of atmospheric parameters and river runoff on the observed hydrographic variations. Variability of sea surface temperature (SST) closely follows that of air temperature in the Baltic on all timescales examined. Interannual variations of SST are significantly correlated with the North Atlantic Oscillation in most parts of the sea in winter. The entire water column of the Baltic Sea has warmed over the period 1950 to 2020. The trend is strongest in the surface layer, which has warmed by 0.3–0.4°C decade⁻¹, noticeably stronger since the mid-1980s. In the remaining water column, characterized by permanent salinity stratification in the Baltic Sea, warming trends are slightly weaker. A decadal variability is striking in surface salinity, which is highly correlated with river runoff into the Baltic Sea. Long-term trends over the period 1950–2020 show a noticeable freshening of the upper layer in the whole Baltic Sea and a significant salinity increase below the halocline in some regions. A decadal variability was also identified in the deep layer of the Baltic Sea. This can be associated with variations in saltwater import from the North Sea, which in turn are influenced by river runoff: fewer strong saltwater inflows were observed in periods of enhanced river runoff. Furthermore, our results suggest that changes in wind speed have an impact on water exchange with the North Sea. Interannual variations of surface oxygen are strongly anti-correlated with those of SST. Likewise, the positive SST trends are accompanied by a decrease in surface oxygen. In greater depths of the Baltic Sea, oxygen decrease is stronger, which is partly related to the observed increase of the vertical salinity gradient.

The southwest coast of India is exposed to long-period swells propagated from the South Indian Ocean during pre- and post-monsoon seasons. Although swells from the Southern Ocean and Atlantic Ocean were identified in the North Indian Ocean, their existence and impact along the southwest coast of India were not well investigated. On 19 March 2019, the Valiyathura-Shangumukham coastal stretch along the southwest coast of India experienced an unexpected coastal inundation without having a prompt forecast/warning, and not induced by a storm/cyclone in its vicinity. The present study investigates the causative forces of this inundation and estimates the wave runup and inundation. The study reveals that an unusual swell system was developed in the Indian-Atlantic-Southern Oceans (IASO) interface during 10–12 March and propagated towards the southwest coast of India. The measured wave spectra off Varkala clearly depicts the presence of long-period swells (T_p>18 s), which dominantly occurred as single-peaked. Wave modelling has been carried out to characterize the wave transformation associated with the “IASO interface swells” along the southern Kerala coast. A wave runup of up to 0.93 m height and a coastal inundation of up to 83 m onshore have been estimated during this event.