ABSTRACT
Much of the Baltic Sea is currently classified as ‘affected by eutrophication’. The causes for this are twofold. First, current levels of nutrient inputs (nitrogen and phosphorus) from human ...activities exceed the natural processing capacity with an accumulation of nutrients in the Baltic Sea over the last 50–100 years. Secondly, the Baltic Sea is naturally susceptible to nutrient enrichment due to a combination of long retention times and stratification restricting ventilation of deep waters. Here, based on a unique data set collated from research activities and long‐term monitoring programs, we report on the temporal and spatial trends of eutrophication status for the open Baltic Sea over a 112‐year period using the HELCOM Eutrophication Assessment Tool (HEAT 3.0). Further, we analyse variation in the confidence of the eutrophication status assessment based on a systematic quantitative approach using coefficients of variation in the observations. The classifications in our assessment indicate that the first signs of eutrophication emerged in the mid‐1950s and the central parts of the Baltic Sea changed from being unaffected by eutrophication to being affected. We document improvements in eutrophication status that are direct consequences of long‐term efforts to reduce the inputs of nutrients. The reductions in both nitrogen and phosphorus loads have led to large‐scale alleviation of eutrophication and to a healthier Baltic Sea. Reduced confidence in our assessment is seen more recently due to reductions in the scope of monitoring programs. Our study sets a baseline for implementation of the ecosystem‐based management strategies and policies currently in place including the EU Marine Strategy Framework Directives and the HELCOM Baltic Sea Action Plan.
•Global-Arctic FVCOM can simulate observed multi-scale Arctic circulation.•Advantages of an unstructured grid ocean model in the Arctic Ocean.•Using dynamical scales to guide grid resolution improves ...steep slope currents simulation.
A high-resolution unstructured-grid global-regional nested ice-current coupled FVCOM system was configured for the Arctic Ocean and used to examine the impact of model resolution and geometrical fitting on the basin-coastal scale circulation and transport in the pan-Arctic. With resolving steep bottom slope and irregular coastal geometry, the model was capable of simulating the multi-scale circulation and its spatial variability in the Arctic Basin and flow through the Bering Strait, Fram Strait and Canadian Archipelago. The model-simulated annual-mean velocities were in good agreement with observations within the measurement uncertainty and variability due to insufficient sampling. The errors in the flow direction varied with the flow speed, larger in the weak velocity zone and smaller as the velocity increased. In the upper 50-m layer, the annual-mean circulation pattern was dominated by the wind- and ice-drifting-induced anticyclonic circulation in the Arctic Basin and a relatively strong cyclonic slope current along the edge of the continental shelf. In the deep 200–600-m layer, a relatively permanent cyclonic circulation occurred along the steep bottom slope. These annual-mean circulations accounted for ∼85% of the total kinetic energy variance. De-trending the mean flow, an empirical orthogonal function (EOF) analysis showed that the semi-annual and seasonal variability of the sub-tidal flow was dominated by the first and second modes that accounted for ∼46% and ∼30% of the total variance in the upper 50-m layer and ∼58% and 20% in the deep 200–600-m layer. Consistent with observations, the AO-FVCOM-simulated cyclonic slope flow was characterized by a large positive topostrophy. Sensitivity experiment results with various grid configurations suggested that the currents over slopes, narrow straits and water passages featured topographic and baroclinic frontal dynamical scales associated with bathymetric slope and internal Rossby deformation radius. Over the Arctic slope, since these two scales are in the same order, the along-slope current could be captured, as the cross-isobath model resolution was refined to resolve the steep bottom topography. Under this condition, there is no need to add Neptune forcing into the momentum equations. The accuracy of the estimation of the transport through the strait and narrow water passage was affected by the model resolution. In Fram Strait where the flow is characterized by strong lateral current shear resulting from the Atlantic inflow and Arctic outflow, the transport estimation could have a significant uncertainty due to both horizontal and vertical sampling resolutions.
Shallow-water carbonate sediments constitute the bulk of sedimentary carbonates in the geologic record and are widely used archives of Earth’s chemical and climatic history. One of the main ...limitations in interpreting the geochemistry of ancient carbonate sediments is the potential for post-depositional diagenetic alteration. In this study, we use paired measurements of calcium (44Ca/40Ca or δ44Ca) and magnesium (26Mg/24Mg or δ26Mg) isotope ratios in sedimentary carbonates and associated pore-fluids as a tool to understand the mineralogical and diagenetic history of Neogene shallow-water carbonate sediments from the Bahamas and southwest Australia. We find that the Ca and Mg isotopic composition of bulk carbonate sediments at these sites exhibits systematic stratigraphic variability that is related to both mineralogy and early marine diagenesis. The observed variability in bulk sediment Ca isotopes is best explained by changes in the extent and style of early marine diagenesis from one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the fluid (fluid-buffered) to one where the composition of the diagenetic carbonate mineral is determined by the chemistry of the precursor sediment (sediment-buffered). Our results indicate that this process, together with variations in carbonate mineralogy (aragonite, calcite, and dolomite), plays a fundamental and underappreciated role in determining the regional and global stratigraphic expressions of geochemical tracers (δ13C, δ18O, major, minor, and trace elements) in shallow-water carbonate sediments in the geologic record. Our results also provide evidence that a large shallow-water carbonate sink that is enriched in 44Ca can explain the mismatch between the δ44/40Ca value of rivers and deep-sea carbonate sediments and call into question the hypothesis that the δ44/40Ca value of seawater depends on the mineralogy of primary carbonate precipitations (e.g. ‘aragonite seas’ and ‘calcite seas’). Finally, our results for sedimentary dolomites suggest that paired measurements of Ca and Mg isotopes may provide a unique geochemical fingerprint of mass transfer during dolomitization to better understand the paleo-environmental information preserved in these enigmatic but widespread carbonate minerals.
Identifying spawning sites for broadcast spawning fish species is a key element of delineating critical habitat for managing and regulating marine fisheries. Genetic barcoding has enabled accurate ...taxonomic identification of individual fish eggs, overcoming limitations of morphological classification techniques. In this study, planktonic fish eggs were collected at 23 stations along the northwestern coast of Cuba and across the Florida Straits to United States waters. A total of 564 fish eggs were successfully identified to 89 taxa within 30 families, with the majority of taxa resolved to species. We provide new spawning information for Luvarus imperialis (Louvar), Bothus lunatus (Plate Fish), Eumegistus illustris (Brilliant Pomfret), and many economically important species. Data from most sites supported previously established patterns of eggs from neritic fish species being found on continental shelves and oceanic species spawning over deeper waters. However, some sites deviated from this pattern, with eggs from reef‐associated fish species detected in the deep waters of the Florida Straits and pelagic species detected in the shallow, continental shelf waters off the coast of northwestern Cuba. Further investigation using satellite imagery revealed the presence of a mesoscale cyclonic eddy that likely entrained neritic fish eggs and transported them into the Florida Straits. The technique of combining DNA‐based fish egg identification with remotely‐sensed hydrodynamics provides an important new tool for assessing the interplay of regional oceanography with fish spawning strategies.
The flow through the Bering Strait, the only Pacific-Arctic oceanic gateway, has dramatic local, regional, and global impacts. Advanced year-round moored technology quantifies challengingly large ...temporal (subdaily, seasonal, and interannual) and spatial variability in the ~85 km wide, two-channel strait. The typically northward flow, intensified seasonally in the ~10–20 km wide, warm, fresh, nutrient-poor Alaskan Coastal Current (ACC) in the east, is otherwise generally homogeneous in velocity throughout the strait, although with higher salinities and nutrients and lower temperatures in the west. Velocity and water properties respond rapidly (including flow reversals) to local wind, likely causing most of the strait's approximately two-layer summer structure (by "spilling" the ACC) and winter water-column homogenization. We identify island-trapped eddy zones in the central strait; changes in sea-ice properties (season mean thicknesses from <1 m to >2 m); and increases in annual mean volume, heat, and freshwater fluxes from 2001 to present (2013). Tantalizing first results from year-round bio-optics, nitrate, and ocean acidification sensors indicate significant seasonal and spatial change, possibly driven by the spring bloom. Moored acoustic recorders show large interannual variability in sub-Arctic whale occurrence, related perhaps to water property changes. Substantial daily variability demonstrates the dangers of interpreting section data and the necessity for year-round interdisciplinary time-series measurements.
Seamen usually select popular routes according to navigational and hydrographical characteristics when passing through a strait with congested traffic. In order to minimise the possibility of ...collisions, Principal Fairways (PFs) are commonly used by sailors. It is essential to delineate PFs quantitatively and objectively for designing or refining routing measures. In this paper, a space use method found in habitat evaluation of wildlife is applied to extract PFs of ship passages through a strait. Compared with existing methods, the proposed method helps to identify cumulative activity patterns for ship groups derived from mass ship trajectories, and provides a clearer interpretation of shifting space-use patterns within strait corridors. Moreover, it gives a better insight for directional and seasonal factor for PFs in straits. Finally, this novel method is used to extract PFs in western Taiwan Strait and its adjacent sea. The results indicate that the proposed method is helpful to identify gaps between current ship routing system plan and cumulative activity patterns recognised by real ship trajectories.
•A cross-disciplinary application of ecological methods for maritime engineering.•A rigorous mathematical framework for delineating principal fairways boundaries.•Geo-visualise the effect of seasonal and directional factors for maritime corridors.•Identify the gaps between existing TSSs and cumulative activity patterns for vessel groups.
Abstract During typhoon passage extreme wind conditions pose a challenge to the structural integrity of wind turbines. Particularly, wind shear and wind veer can influence wind turbine loads. This ...study investigates how Taiwan’s central mountain range affects wind shear and wind veer in the Taiwan Strait during three westward-moving typhoon cases. The typhoons are simulated with the Weather Research and Forecasting (WRF) model. We find that wind speed, shear, and veer vary over different regions in the Taiwan Strait. In large areas, the simulated wind shear is larger than modeled over the open ocean. In particular, mountain blockage leads to a spatially confined area of several 1000 km 2 downstream of Taiwan, that exhibits over several hours strongly modified shear and veer in all three analyzed cases. Shear exponents up to 0.75 and veer between 0.2 and 0.6° m −1 suggest that turbine loads are impacted by the vertical change in the wind field in this area. The shear exponent and wind veer vary strongly with height in the downstream area of Taiwan’s central mountain range. The location of the area with large wind shear and wind veer differs between the three simulated typhoon cases and primarily depends on the latitude of the typhoon track relative to the central mountain range.
► A ship movement simulation model is developed. ► Discrete event models are applied to generate vessels. ► Ten ship following rules and five ship crossing rules are proposed.
The traffic volume in ...the Singapore Strait will be significantly increased according to the prediction by the United Nations Conference on Trade and Development. Therefore, it is important for the maritime authorities (e.g. Maritime and Port Authority of Singapore) to capture a picture of ship movements in the Straits in the near future. This paper proposed a novel simulation model for ship movements in the narrow and busy shipping channel. The simulation approach is on the basis of a modified Cellular Automata model and takes interactions between consecutive ships into consideration by expert judgment from experienced personnel. Discrete event models are applied to generate vessels with different categories and velocities from four portals of the Strait. Ten ship following rules and five ship crossing rules are used to simulate the mariners’ response to various navigational scenarios. The model is further verified by comparing the actual travel time through the Strait and the time derived from the model. At last, applications of the model are illustrated.
Harmful algal blooms (HABs) were not new to the tropical semi-enclosed Johor Strait, with incident records that could trace back to the 1980s. HAB monitoring in the area, often, is reactive, focusing ...only on HAB taxa previously causing problems but neglecting potential emerging HABs. To develop datasets on HABs that can better inform and improve management practices, monitoring should expand to sample whole microphytoplankton communities. In this study, microphytoplankton community structure across the Strait was investigated. Abundances of microphytoplankton and a suite of in situ water parameters of temperatures, salinity, pH, dissolved oxygen levels, macronutrients, and chlorophyll-a contents were collected at ten sites across the Strait at monthly intervals from January 2017 to December 2018. A total of 48 genera (51 taxa) microphytoplankton were identified microscopically. Diatom was the most diverse group (32 genera), followed by dinophyte (15 genera). Bloom-forming species included diatoms Chaetoceros, Coscinodiscus, Eucampia, Pseudo-nitzschia, Rhizosolenia, Skeletonema, Thalassiosira, and dinophytes Blixaea quinquecornis and Scrippsiella. Diatom taxa that exhibit high in situ growth rates were predominant in the low-nutrient marine-influenced environment. Bloom-forming taxa including HAB taxa were found dominant in the environment with high nutrient levels and mesohaline, salinity-stratified conditions. This study provides valuable baseline data that could assist in monitoring and prediction of HABs in the Johor Strait and could be of reference to other similar tropical coastal systems.
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•Microphytoplankton communities were spatially heterogeneous across Johor Strait.•Environmental factors shape the microphytoplankton community structure of Johor Strait.•Diatoms with high in situ growth rates were predominant in low nutrient levels marine-influenced environments.•Bloom forming taxa dominated environment with high nutrient levels and mesohaline, salinity-stratified conditions.
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