Oceanologia最新文献

The Salish Sea is a marginal inland sea of the NE Pacific (NW North America) that includes the Georgia Strait-Gulf Islands Archipelago of British Columbia, Canada and the San Juan Archipelago, Strait of Juan de Fuca, and the Lower Puget Sound of Washington State, USA. This marginal seafloor has been extensively mapped and according to criteria presented and discussed at GeoHab conferences critical marine benthic habitat types are identified. One such habitat that is the focus of this paper is the deep-water sub-tidal habitat of Pacific sand lance (PSL). The PSL (Ammodytes personatus) is a critical forage fish for a variety of mammals, birds and fish including minke whales and salmon as it preys upon zooplankton and acts as an energy transfer species from the lower to higher trophic levels. Pacific sand lance seeks refuge and overwinters in sand-wave fields consisting of dynamic bedforms. The species prefers loosely packed, well-aerated, well-sorted, medium- to coarse-grain (∼1 phi [φ], 500 µm) sand that it can burrow into easily. Such geomorphic features as active dynamic bedforms provide preferable habitats for PSL and depends on specific and unique oceanographic processes that can maintain the habitat's morphology and grain sizes. Understanding these processes is essential in forecasting alteration or destruction of such features, including changes that may be brought about by sea level rise. Using the five-person submersible Cyclops 1, we recently examined a well-studied sand-wave field in the San Juan Archipelago of Washington State, USA, which has been reported to harbor up to 12 million PSL. Observations, video recordings, and photography from this vehicle allowed us to assess modern seafloor processes of the central Salish Sea that can be used along with fish and sediment sample data to determine physical preferences this fish needs to sustain its population. Changes in the seafloor current regime, sediment source, and anthropogenic disturbances can critically alter these dynamic bedforms. This research provides insight into the structure of these bedforms, their composition, their persistence, their resilience to disturbance, and the susceptibility as an impact and becoming impacted.

The morphological evolution of two mud depocenters in the southwestern Baltic Sea is investigated by comparison of numerical model results to geological and oceanographic data. The pathways of dense currents during episodic dense-water inflows from the North Sea are shown to correspond to current pathways inferred from contouritic depositional geometries in the flow-confining channels within the study area. A favorable comparison of model results to published current speed observations shows that the mesoscale dynamics of individual inflow events are reproduced by the model, indicating that external forcing and basin geometry rather than internal dynamics control the mesoscale dynamics of inflow events. The bottom current directions during inflows show high stability in the flow-confining channels and explain the contouritic depositional geometries. Asymmetric depositional features in the channels are qualitatively reproduced in the model. Bottom currents are less stable in areas without contouritic features, possibly resulting in an overall diffusive effect on sediment distribution in those areas. In a simulation of resuspension by bottom-contacting fishing gear, inter-basin sediment transport is increased by 4–30%, depending on the area, compared to the case of natural hydrodynamic resuspension. The model predicts an increased winnowing of the finest sediment fraction due to bottom trawling, leading to an overall coarsening-to-fining trend in the direction of net sediment transport. The results show that rather than hemi-pelagic background sedimentation, episodic events with high bottom current velocities as well as bottom-trawling induced resuspension are responsible for the present-day and future morphological configuration of the mud depocenters in the southwestern Baltic Sea.

The Institute of Marine Sciences (ISMAR) and the Institute of Polar Sciences (ISP) of the Italian National Research Council (CNR) have gathered a substantial amount of heterogeneous geodata through the years in the Adriatic Sea, with different methodologies and for multiple scopes regarding geological, oceanographic, biological, anthropogenic aspects, and their interactions.

To overcome challenges in datasets heterogeneity and fragmentation, a Marine Spatial Data Infrastructure (MSDI) has been set up, with the aim to integrate and preserve geodata, foster their reuse (e.g. the generation of scenarios for geological past and future developments by the application of numerical models), and ensure a good degree of FAIRness (FAIR: Findable, Accessible, Interoperable, and Reusable). The MSDI consists of a Spatial Relational Database Management System (RDBMS) based on specific data models designed following in part the INSPIRE Directive data specifications, a WebGIS, a metadata catalogue, and a cloud system. This paper shows the potentialities of this MSDI and discusses the main implementation steps, the elements that make up the infrastructure, the level of FAIRness reached, the main elements promoting FAIRness, and the gaps to be covered.

Compliance with the FAIR principles represents a fundamental step to developing interoperability with European and international marine data management infrastructures for handling and exchanging multidisciplinary data.

This work analyses the monthly spatial distribution of extreme sea levels in the Baltic Sea as well as the relationship of these levels with the NAO and AO indicators. The research was based on hourly sea level data from the 45 tide gauge stations gathered in the years 1960 to 2020. The analysis shows that the duration of extreme sea levels tends to increase moving from along the line joining the open sea and the gulf end. This is associated with the narrowing of the gulf and the geomorphological and bathymetric configuration of the coastal zone. The duration of high and low sea levels in the Baltic Sea decreases from a maximum in January to a minimum in the months of May to August, then it increases again until the end of the year. This cycle corresponds well to the annual occurrence of storm surges, which are affected by the annual changes in atmospheric circulation. The impact of the variations of the circulation on extreme sea levels was confirmed by examining the relation between maximum, minimum and mean levels of the Baltic waters and the zone circulation indices NAO and AO for each month of the year and the seasons in the multiyear period 1960–2020. The results indicate that the strongest correlations exist between sea levels and NAO/AO in the winter months. There is a spatial differentiation of the correlation and its increase from the southwest to the northeast in Baltic Sea.

Efforts towards the numerical simulation of the Baltic Sea wave properties, started in the 1950s, have reached maturity by the implementation of contemporary third generation spectral wave models, such as WAM and SWAN. The purpose of this paper is to give an overview of the relevant efforts since the beginning of numerical wave simulations. The Sverdrup-Munk-Bretschneider (SMB) type models are still valuable tools for rapid estimates of some properties of wave climate in single locations. The spatial resolution of spectral wave models for the entire sea has increased from about 20 km to 1 km, and to 100–200 m in specific areas. The number of directional bins has increased from 10–15 to 24–36 and the number of spectral frequency bins from about 15 to 35–42. The models replicate all main features of the wave climate of the Baltic Sea, such as an overall mild but intermittent wave climate, the predominance of short windseas and the scarcity of long swell, east-west asymmetry, the strong impact of seasonal ice, and the specific properties of wave growth in some areas. The wave climate changes involve variations in regional wave intensity, core properties of wave-driven sediment transport and wave set-up. Reconstruction of wave properties in the nearshore, archipelago areas, and in narrow subbasins remains a challenge. These areas require finer spatial resolution and possibly advancement of wave physics to account for changes in the spectral composition of wave fields and specific features of wave growth in narrow basins. Progress in these fields is a pillar for a number of applications, from the quantification of sediment transport to proper input into management issues of the coastal zone.

Chinese continental margins are experiencing remarkable environmental changes driven by anthropogenic activities and climate change. As an important habitat and sea-based fish farming resource in China, the Bohai was selected as a case study to understand how ecosystems and social interactions are influenced by multi-stressors. The Bohai ecosystem has been considerably modified. The Bohai coastline has been significantly changed (e.g., total sea area decreased and morphology changed) by sea reclamation and riverine sediment transport related to agriculture and erosion. Therefore, the strict reclamation policy and “Grain-for-Green” program have been issued to protect the coastline. Nutrient concentrations and composition have been changed by fertilizer application, wastewater discharge, and variations in seasonal patterns of riverine nutrient fluxes. Hence, pollution control and prevention are necessary. More seriously, fishing resources have been altered, as a result of environmental changes and overfishing. Therefore, a summer fishing ban and stock enhancement should be vital besides environmental improvement. This study can help to predict and mitigate impacts on global continental margins that are experiencing similar environmental stress.

Marine transgressions-regressions have profoundly shaped marginal seas following global sea-level fluctuations driven by climate change. This study on a sedimentary core profile SO219/31-4 from the Beibu Gulf, northwestern South China Sea (SCS), reveals information about paleoenvironment, paleoceanography and paleoclimate changes through fossil diatom assemblages and grain size distributions during the last ca. 12900 cal. yr. BP. Eight local diatom assemblage zones were distinguished and assigned to paleoenvironmental fluctuations recording sea-level and depositional environment changes in eight stages, ca. 12900–11700 (stage 1), ca. 11700–9500 (stage 2), ca. 9500–7200 (stage 3), ca. 7200–5800 (stage 4), ca. 5800–3800 (stage 5), ca. 3800–2400 (stage 6), ca. 2400–800 (stage 7) and ca. 800–0 (stage 8), cal. yr. BP. After the low sea level of stage 1 within the last deglaciation, rapid increases in sea level in stages 2 and 3 were recorded as meltwater events pulse-1B and pulse-1C resulting in marine transgression rates of ca. 16 m/kyr and 8 m/kyr, respectively. The high sea level, above the present level, in stages 4 and 5, in the Middle Holocene Climatic Optimum period, was clearly documented by more significant open sea/tropical diatom species and coastal planktonic species percentages, respectively. The late Holocene regression of sea levels was marked by a pronounced reversion of diatom taphocoenosis, responding to neoglacial climate. Fossil diatom assemblages outlined responded to paleoclimate of global warming in the deglacial and early Holocene. This study provides additional insights into the late Pleistocene and Post-glacial history of a tropical-subtropical shallow water gulf, in the NW-SCS.

Closely spaced CTDO profiling on the pathway of saltwater flow in the southeastern Baltic Sea in August and December 2019 revealed low oxygen intermediate layers-plumes with dissolved oxygen concentration (DOC) less than 2 mg/l under the upper boundary of permanent halocline. At the same time, DOC in the underlying layers was higher and reached 5.0–5.3 mg/l. In order to test the hypotheses about the origin of the intermediate hypoxic plumes, numerical hydrodynamic modelling was performed for time intervals including the measurement periods. The model was validated against bottom current velocity instrumental measurements by a TCM (Tilt Current Meter) moored on the track of the CTDO profiling. Numerical experiments with Lagrangian particles of neutral buoyancy coupled with the operational circulation model showed that sub-halocline hypoxic intermediate layers in the southern part of the Eastern Gotland Basin and in the Gdańsk Basin could be formed as a result of intrusion into the underlying bottom layer of denser, moderately oxygenated water from the Słupsk Furrow, which replaced the old anoxic and hypoxic water of Gotland and Gdańsk origin. It is assumed that cyclonic eddy activity above the saltwater flow along sloping bottom caused fragmentation of the hypoxic intermediate layer into separate plumes. The hypoxic intermediate layers in the Słupsk Furrow, in accordance with the results of monitoring measurements and modelling the motion of particles of neutral buoyancy, could be formed in the Bornholm Basin and moved eastward over the Słupsk Sill.

In a series of ad-hoc surveys at different academic institutions in the Baltic Sea region, students and young scholars were asked about their views about the environmental issues of the Baltic Sea, and who would be responsible for the management of the Baltic Sea. Overfishing, climate change and waste were considered the most significant issues, while tourism and constructions (of bridges, etc.) were less often recognized as severe. The responsibility for the management of the Baltic Sea was mostly attributed to the European Union or to the respective national governments.

Since climate is one of these issues, one question has dealt with the main task of climate science. It turns out that the most frequent assertion was not the genuine scientific task of generating knowledge about the dynamics of the system. Instead, the task of solving the problem and, equally often, supporting climate activism was favored.

The results are not representative – neither for the separate surveys, nor for the selection of the sites of surveying. However, when taken all surveys together, the emergence of consistent perceptions may be considered evidence for a general attitude among students and young scholars in the Baltic regions. However, differences between groups – in terms of nationality, seniority and discipline - may be related to sampling randomness.

The work is focused on the assessment of microplastics transport and distribution in the eastern part of the Gulf of Finland by means of numerical modeling. In the present study only the riverine sources of microplastics are taken into account. The presented model also accounts for possible sink of suspended microplastic particles into sediments due to simple parameterization of biogeochemical processes such as biofouling and ingestion by zooplankton. Two basic scenarios with different initial fall velocities of suspended microplastic particles, 0.2 m/day and 1.2 m/day, are discussed. The distribution of microplastics coming with the riverine waters of the Neva, Luga, and Narva rivers has been investigated, based on a numerical hydrodynamical hindcast of the year 2018. Model simulations show that the transport of suspended microplastics occurs along the northern coast of the considered area more intensively compared to the southern coast, especially in the easternmost shallow part of the gulf. The results are in a good agreement with other studies focused on the microplastic pollution of the Neva Bay, and with available observational data. The presented results and developed model can be useful tools aimed to assess the intensity and mechanisms of microplastic pollution of the eastern Gulf of Finland. The results can be used in the selection of areas for future environmental monitoring of microplastics pollution of the eastern part of the Gulf of Finland.