Continental Shelf Research最新文献

Güllük Gulf, located in the southeastern Aegean Sea, is significantly impacted by diverse human activities, including urban development, tourism, and intensive aquaculture. This study aims to assess the spatial distribution of trace metals in the Gulf's sediments, identify their sources, and evaluate their environmental impacts to inform effective management strategies. It also examines sediment transport patterns, which are crucial in influencing the distribution and concentration of pollutants. Establishing background concentration levels for various elements provides a baseline to assess pollution levels and identify deviations due to anthropogenic impact. Sediment samples were collected from 45 stations and analyzed for grain size, organic carbon, carbonate content, and concentrations of 26 elements. Contamination was assessed using indices such as Enrichment Factor (EF), Geoaccumulation Index (I_geo), Contamination Factor (Cf), Degree of Contamination (C_deg), Pollution Load Index (PLI), Modified Pollution Index (MPI), and Toxic Risk Index (TRI). Statistical analyses, including Principal Component Analysis (PCA) and Cluster Analysis (CA), were used to identify pollution sources. Results indicated that Güllük Gulf's sediments are predominantly sandy, with significant silt and clay fractions in sheltered bays. Organic carbon content averaged 1.68%, with higher values near urban and aquaculture areas. Trace metal concentrations exhibited notable spatial variability, with elevated levels of Pb, Cu and Zn in specific areas, indicating both natural and anthropogenic sources. PCA identified five significant factors contributing to metal presence, linking them to lithogenic origins, aquaculture activities, and industrial inputs. TRI results showed moderate toxic risk in Asin Bay, primarily due to Ni, As and Cr. The sediment transport model of Güllük Gulf, crucial in understanding regional pollution dynamics, revealed a complex interplay of hydrodynamic forces. The study underscores the significant environmental impact of human activities on sediment quality in Güllük Gulf. Elevated trace metal levels near aquaculture sites emphasize the need for stringent environmental management practices. Effective strategies should include regular monitoring, sustainable aquaculture practices, and stakeholder engagement to mitigate environmental impacts and preserve the Gulf's ecological integrity. This comprehensive approach provides crucial insights for future research and environmental management policies aimed at addressing the complex challenges facing Güllük Gulf.

The Zhejiang-Fujian (Zhe-Min) coastal muddy area plays a crucial role in facilitating sediment exchange through a cross-front. The mud depocenter off the Zhe-Min coastal area is a source of suspended sediment that can be transported to the continental shelf of the East China Sea (ECS). Although the front of the inner shelf of the ECS has been extensively reported, the cross-front material transport off the coastal area of Zhe-Min in summer has not been well studied, especially using measured data. To reveal how the front controls the transport of suspended sediment, this study focuses on the impact of fronts on the dispersion of suspended sediment off the coastal area of Fujian Province in different seasons. The results indicate that the front acts as a barrier, inhibiting the dispersion of suspended sediment into the sea. The high-concentration suspended sediment is mainly found to the northwest of the front, with an average SSC of 8.5 mg/L in winter and 3.1 mg/L in summer. The suspended sediment concentration (SSC) follows a V-shaped distribution along the cross-isobath transects, with lower SSC observed at the 50-m isobath compared with the shallow water area and the deep water area. The SSC at the front was the lowest, with an average concentration of 2.3 mg/L in winter and 1.9 mg/L in summer. The front is crucial for the development of the Zhe-Min coastal muddy area. The winter monsoon is strong, resulting in a sufficient supply of suspended sediments in the muddy area and a high transport flux of suspended sediments in the nearshore. The front hinders the dispersion of high-concentrated sediment from the nearshore to the offshore, resulting in the deposition of fine-grained sediments in the nearshore and the formation of an inner shelf muddy sedimentary zone. The findings of this study will help improve our understanding of the sediment source-to-sink processes in the ECS and land–sea interactions.

The distribution of deep-water rose shrimp (Parapenaeus longirostris, FAO 3 alpha code DPS), the main target species of demersal fisheries in the Strait of Sicily, is investigated in relation to surface parameters and biogeochemical processes. Such processes are known to influence sea bottom habitats and may be particularly relevant to the Strait of Sicily because of its relative shallowness and high surface primary production. Shrimp abundances recorded during multi-annual and seasonal trawl surveys (2004–2008) are analyzed. A GAMM and GAM model analysis is performed comparing juvenile abundances to monthly mean spatial patterns of remotely-sensed sea surface temperature (SST) and surface chlorophyll (chl), as well as their frontal structures, with a time-lag of one month, given the pelagic behavior of DPS early life stages preceding settlement. Juvenile and total shrimp abundances are also compared to the flux of particulate organic carbon (POC) to the seabed. The POC flux is computed via 1-D and 3-D models simulating sinking, re-mineralization and horizontal advection and diffusion of surface POC. The latter is derived from surface primary production maps obtained from ocean color data. Results show that the abundance of the juvenile fraction of DPS is significantly correlated with depth, distance to SST fronts and the intensity of chl fronts (correlation R² = 80%). Furthermore, results strongly suggest the significant role of bottom POC flux in conditioning the distribution of DPS abundance, indicating that ecological processes occurring in surface waters influence food availability near the seabed in the investigated area.

This study presents comprehensive observations of currents and seawater properties (temperature, salinity and density) made with moored instruments on the continental slope in the eastern Ligurian Sea (Mediterranean) between 18 October and November 6, 2021. During this period, the depth of the surface mixed layer increased from 40 to 70 m. At the same time, near-inertial waves were consistently observed below the mixed layer. In particular, on 28 October, a depression in the mixed layer depth triggered the formation of a pronounced wave packet. This packet radiated downwards between 70 and 200 m and propagated southward. The wave packet had a vertical and horizontal wavelength of about 80 m and 150 km, respectively, an upward vertical phase speed of 100 m/d, a downward vertical group speed of 10–15 m/d, and a downward energy flux of 0.2–0.3 mW/m². The observed frequency appeared subinertial, likely due to the red-shifting of the effective inertial frequency by the background vorticity. From 1 November, a storm with wind speeds of up to 15 m/s prevailed in the region. Near-inertial motion was pronounced throughout the water column and manifested itself as a first baroclinic mode. This mode exhibited a maximum isopycnal vertical displacement in the thermocline, accompanied by oscillatory currents that reversed with depth. Mainly superinertial currents were observed. The temperature and velocity data collected from all moorings indicated a southwestward propagation with a horizontal wavelength of about 200 km. While a slab model was partially successful in predicting inertial currents in the surface mixed layer, the storm-induced dynamics presented a challenge that was beyond the scope of the model.

The South China Sea (SCS) is ones of the largest marginal seas on the Earth. Apart from IODP/ODP sites, limited progress has been made in establishing chronostratigraphy for long-term geological sequences spanning millions of years. In this study, we present findings from a sediment core (NH-01) collected from the eastern part of Hainan Island, northwest SCS, in terms of magnetostratigraphy and sedimentary/paleoenvironmental changes in the past 1 Myr. The main findings are as follows: (1) Two magnetic polarity zones in core NH-01 can be preliminarily correlated with the upper part of the intervening Matuyama chron and the Brunhes normal chrons, respectively. (2) By tuning the color indices of core NH-01 to the stacked benthic δ¹⁸O record, the age-depth model was refined, and the sediment accumulation rates are estimated as 10–30 cm/kyr (3) The sedimentary processes in the study area display a dominant 100-kyr cycle, with contributions from precession and obliquity bands, underscoring the influence of regional sea-level changes and monsoonal evolution. Comparisons between the NH-01 sedimentary record and various global climate proxies indicate a significant shift in regional sedimentary processes around 430 kyr, which can be attributed to the pronounced impact of the

Mid-Brunhes event, potentially linking it to climatic changes in the Southern Hemisphere. Consequently, sedimentary records from the northwest SCS not only capture regional environmental history but also provide insights into potential connections between different climatic systems.

We report on methane (CH₄) concentration measurements in the northern Black Sea area conducted during 6 cruises with R/V Professor Vodyanitsky from 2017 to 2019. Our work is a multi-season study at a uniform station grid covering an area of 88 × 10³ km² and including three latitudinal transects that comprises both surface and vertical profile water-column measurements. The main goal of the work was to assess the seasonal patterns of vertical CH₄ structure in the aerobic water column (upper 100 m) and its emission to the atmosphere.

In surface waters, the mean dissolved CH₄ concentration ranged from 2.6 nmol L⁻¹ detected in November 2018 to 11.5 nmol L⁻¹ measured in June–July 2018, respectively. Calculated CH₄ seawater-air fluxes and saturations were mostly positive (i.e. net flux to atmosphere), and winter fluxes (2.6 μmol m⁻² d⁻¹) were higher than summer fluxes (1.6 μmol m⁻² d⁻¹) due to the higher wind speed. The integral CH₄ flux from the whole study area (88 × 10³ km²) ranged from 84 to 235 kM day⁻¹.

It was shown that, on average, the methane concentration in the upper layer for deep-water stations where the seabed is located at depths >160 m (σt >16.2) was lower compared to stations at shallow water depths (28–140 m, σt <16.2). The most distinct difference was obtained for the summer season (June–July 2018) and a less significant difference – for spring (April–May 2019) and winter season (November–December 2018). During these seasons the water column was also considerably less saturated in CH₄ compared to the entire monitoring period. We observed subsurface maxima, which were generally located at the base of the thermocline and exceeded 100 nmol L⁻¹ at some stations. Exceptions were observed in October 2019 (cruise 110), when vertical CH₄ distributions were characterized by two-peaks at ∼20 and ∼50 m depth. The strong influence of the thermohaline structure on the water column CH₄ distribution has also been shown in studies of daily dynamics of CH₄ vertical profiles in the shallow water region. Despite the high variability of CH₄ concentrations, significant similarities in vertical distributions of CH₄ and chlorophyll-a for which sub-surface maxima coincided at some stations, are shown. Extremely high concentrations of CH₄ (up to 351 nmol L⁻¹) in the near-bottom water layer were revealed during all seasons at the station near the Dnieper paleo-channel at the northwestern edge of the study area. This enrichment is assumed to be caused by methane emissions from gas seeps densely located in this region.

The Northeast US Continental Shelf (NES) is a highly productive marine ecosystem that has experienced wide swings in phytoplankton chlorophyll concentration (CHL). To better understand this variability, we examined changes in CHL over the period 1998–2022, while also considering three indicators of the potential supply of nutrient source waters including cross-shelf advection via deep channels, transport from beyond the shelf edge via Gulf Stream warm core rings (WCR), and input from river and estuarine discharge. Traditionally, deep channel advection of water across the NES was assumed to be derived from Labrador Slope Water (LSW) and Warm Slope Water (WSW). These designations do not fully capture the range of water types contributing to cross-shelf advection. The contribution of LSW and WSW was reciprocal over time, with the presence of WSW at an increased level in recent years. There has been an increase in the number of WCRs off the NES represented by indices of ring occupancy. Precipitation increased over the study period as well, generally over the NES region and in particular in the Mid-Atlantic Bight drainage. We see evidence of the effect of increased precipitation on the NES proper through a change in the area of the ocean surface having 555 nm reflectance with sr⁻¹ > 0.004. Using a canonical analysis, CHL correlated positively with the proportion of LSW and negatively with WSW. These correlations suggest there are aspects of the nutrient content associated with these water masses that are key to phytoplankton growth. WCR frequency negatively correlated with CHL, which was expected since the nutrient loadings of WCRs tends to be low. Finally, CHL negatively correlated with precipitation rate, which suggests terrestrial origin nutrient inputs to the NES are minor. We suggest that in order to understand future CHL dynamics in the NES, careful consideration of advective sources of nutrients in the Northwest Atlantic is necessary.

The present study investigates the contributions of upwelling mechanisms (coastal upwelling from boundary divergence and Ekman pumping from spatially variable wind) at the northern margin of the Gulf of Cadiz (NMGoC) based on high-resolution wind. The effects of the spatiotemporal upwelling mechanisms variability are then explored using current observations along with sea surface temperature and sea level anomaly. Upwelling favourable conditions occur throughout the year along the NMGoC, with the strongest intensity near Cape São Vicente due to a persistent positive wind stress curl. In winter, the surface water divergence is restricted to the coastal boundary due to strong coastal upwelling events that result in a cross-shore sea-level gradient close to the coast. Towards the summer, the gradient increases and extends further offshore (over the slope) at the western region due to the intensification of the Ekman pumping. Therefore, the seasonal and spatial variability of coastal upwelling and Ekman pumping contributes significantly to the offshore position of the geostrophic Gulf of Cadiz Current over the western shelf slope. Furthermore, a permanent sea level depression corresponds to the location of the strongest Ekman pumping, near Cape São Vicente. The dynamic adjustment of this feature may drive the cyclonic cell and alongshore poleward currents often observed in the area.

Even though many studies refer to copepods as potential indicators of hydrographical settings and/or water masses, focused studies on this aspect are very scarce in Indian waters. Hence, this study assesses the hydrography and the copepod composition in a cross-shore transect (7–30 m depth zone) off Kochi along the southwest coast of India during different seasons to understand how seasonal hydrography alters the composition of copepods. The copepod community in the study area was found to consist of 36 species (26 dominant) during the Southwest Monsoon [(SWM) June to September], 31 species (16 dominant) during the Northeast Monsoon [(NEM) November to February], and 39 species (26 dominant) during the Pre-Monsoon [(PRM) March to May]. The salient observations in this study are (a) a higher contribution of cyclopoids (45–50%) during the oligotrophic PRM when the microbial food web was dominant; (b) the dominance of several truly estuarine copepods (Acartia plumosa, Acartiella keralensis, Pseudodiaptomous annandalei, and P. serricaudatus) during the SWM when the flushing of the adjacent estuarine system (Kochi backwaters) was the seasonal highest; and (c) the dominant occurrence of Temora turbinata, commonly referred to as an indicator of coastal upwelling, during both the SWM and the NEM indicates their conducive conditions in the study area during both seasons and (d) the occurrence of copepods Acartia danae, A. erythraea, Acrocalanus gibber, A. gracilis, Centropages orsinii, C. tenuiremis, Corycaeus catus, C. speciosus, Oithona similis, O. spinirostris, Oncaea venusta, Paracalanus parvus, and Undinula vulgaris in the study area regardless of seasons. The study concludes that, while the presence of truly estuarine copepods in the study area can be attributed to estuarine watermass indicators, the presence of several other dominant species found regardless of the season cannot, as their occurrence is widespread in the eastern Arabian Sea and the western Bay of Bengal, owing to seasonal water mass exchange between the two regions.

Aim

Assessing the potential of the Chabahar Bay coasts for classification as marine and coastal protected areas.

Location

Chabahar Bay, northeast of the Gulf of Oman.

Period

Two seasons from 2017 to 2019.

Major taxa studied

Macrobenthic invertebrates.

Methods

The evaluation was based on the 2008 International Union for Conservation of Nature (IUCN) ecological model categories and criteria/sub-criteria. The study investigated criteria such as biodiversity, naturalness, dependency, representativeness, uniqueness, productivity, vulnerability, and integrity; the study was conducted at four zones of three stations within three regions.

Results

The northern region of Chabahar Bay showed significant differences in community structure compared to the other two regions. The highest abundance of macrobenthic invertebrates was observed in the northern area of Chabahar Bay, whereas the lowest abundance was observed in Konarak. Macrobenthic abundance, salinity, and electrical conductivity (EC) were found to influence the community structure of macrobenthic organisms; each region was assigned a score, categorizing it as an IUCN Category II protected area.

Main conclusions

The AMBI analysis revealed that some ecosystems in the studied regions were alarmingly disturbed, indicating the need for management attention to protect and conserve these ecosystems.