Journal of Marine Systems最新文献

Global climate change is altering the frequency and intensity of extreme weather events such as typhoons and cold fronts, and this is inducing physical changes and adaptions in estuaries and coasts. We conducted a field campaign on the subaqueous Changjiang Delta front in September 2019 to improve understanding of storm impact on short-term hydro-morphodynamics. Over an 11-day period, during which both typhoon and cold front events occurred, in-situ data including flow velocities, suspended sediment concentrations (SSC), and bed-level changes were acquired using bottom tripod and buoyage systems, Significant wave height reached 5.0 m during the typhoon, and the depth-averaged current velocity increased to 1.7 m/s. The net near-bottom sediment flux was in the same direction as the wind and was 5.5 times of that under calm weather. During the cold-front, significant wave height reached 2.5 m, and the near-bottom SSC increased to 7.0 kg/m³. Bed-level changes were small (<2 cm) under pre-storm weather, while net deposition and erosion reached 15.8 cm and 16.8 cm, respectively, during the typhoon. Short-term changes in the sediment source-to-sink regime were detected in the subaqueous Changjiang Delta. The cold front enhances seaward sediment flushing from the delta towards the sea, while the typhoon drives sediment transport from the subaqueous delta towards Hangzhou Bay. We also observed rapid bed-level recovery following these extreme events. These findings improve our understanding of sediment transport under stormy conditions.

An integrated habitat suitability index (HSI) model was developed in this study for Dosidicus gigas in the eastern equatorial waters of the Pacific Ocean to explore climate-related spatial and temporal variability in the habitat distribution pattern based on three crucial environmental variables: sea surface temperature (SST), sea surface salinity (SSS) and chlorophyll-a concentration (Chl-a). Results revealed that the HSI model could accurately predict potential habitats for D. gigas. The habitat suitability varied significantly by month, with highest suitability in April and lowest in March. Besides, from December to May, the longitudinal gravity center of the fishing grounds (LONG) and the HSI overall shifted eastward and the latitudinal gravity center shifted northward then southward. In comparison to the warm ENSO phases in 2019, the cold ENSO phases in 2018 produced increased suitable habitat from December to May, leading to a significantly higher CPUE. Prospective high-quality habitats in 2018 primarily occurred in the western regions, with the exception of December, which resulted in a more westward distribution of LONG from January to May. High-quality habitats moved northward from December to February and southward from March to May 2018, compared to minor latitudinal movement in 2019. It was inferred that annual variations in squid abundance and distribution were largely affected by the SST-related habitat pattern of D. gigas in the eastern equatorial waters. Our findings suggested that D. gigas habitats clearly varied by month and year and were greatly influenced by climate-induced environmental changes.

The pelagic zone is home to a large diversity of organisms such as macrozooplankton and micronekton (MM), connecting the surface productive waters to the mesopelagic layers (200-1000 m) through diel vertical migrations (DVM). Active acoustics complement net sampling observations by detecting sound-scattering layers (SL) of organisms, allowing to monitor the MM dynamics with a high spatio-temporal resolution. Multi-frequency analyses are a pertinent approach to better integrate the rich diversity of organisms composing SLs and their respective dynamics. However, analysing simultaneously emitted acoustic signals with distinct depth ranges and separating spatial from temporal variability is challenging and needs adapted tools to be fully exploited. This study examines the pelagic realm in a transition zone between the Southern Ocean and the subtropical Indian Ocean, crossing the Saint-Paul and Amsterdam islands’ natural reserve. We extended a Multivariate Functional Principal Component Analysis (mfPCA) to analyse the joint vertical variation of five frequencies from two oceanographic cruises (2016 and 2022), allowing the decomposition of the acoustic dataset into orthogonal vertical modes (VM) of variability. We found the first VM to be linked to the temporal variability due to DVM, while the following majorly depict patterns in spatial distribution. Overall, from the subantarctic to the subtropical zones, we observed (i) enrichment of densities in the surface layer (0–100 m), (ii) a decrease in densities in the intermediate layer during the daytime (100–300 m) and (iii) the apparition of an intensive deep scattering layer on the 38 kHz. We explored VMs’ connection with in-situ environmental conditions by clustering our observations into three distinct environmental-acoustic regions. These regions were compared with vertically integrated nautical area scattering coefficient distribution, a proxy for marine organisms’ biomass. Additionally, we analysed species assemblage changes from complementary cruises to further elucidate the observed acoustic distribution. We show that the mfPCA method is promising to better integrate the pelagic horizontal, vertical and temporal dimensions which is a step towards further investigating the control of the environment on the distribution and structuring of pelagic communities.

Buoyant material has a tendency to form dense clusters at the ocean surface. This has been observed in distributions of marine life and floating plastic contaminants. The main mechanism behind this is that particles with positive/neutral buoyancy do not behave as passive tracers in stratified flows. It could be expected that coextensive clustering between plankton and toxic ocean contaminants could lead to enhanced ecological risk. However, such interactions cannot be sufficiently modelled in a standard passive tracer approximation. Given the large uncertainty in the form of converging currents and how to model interactions of buoyant tracers, we opt for an idealised modelling approach. The simplicity of our model allows easy interpretation of the novel physical considerations. We demonstrate that the global dynamics of our biogeochemical model are significantly altered by clustering forces. Most notably, a new balance in the ecosystem exists in which reactions are dominated entirely by those within the dense clusters. This greatly enhances the impact of destructive pollutants through efficient mixing. There is evidence that this equilibrium will be robust moving to more complex and realistic models.

This work focuses on the freshwater contribution (water from the Ob’ and Yenisei rivers and ice meltwater) to the surface layer of the Kara Sea according to 2015–2020 expedition data. Salinity and hydrochemical data (total alkalinity and silicates) were used to calculate the proportion of freshwater in the desalinated layer of the Kara Sea. The ratio of the water fractions with the linear mixing of several sources was considered. Our results showed that riverine sources varied greatly, and the total contributions of the Ob’ and Yenisei runoff ranged from 10 to 60%, while the contribution of ice meltwater did not exceed 25%. The relationship between the period of seasonal ice retreat in the Kara Sea and its proportion in the surface desalinated layer was revealed. The interannual variability in freshwater source composition varied greatly from the southwestern to the eastern part of the sea owing to wind forcing and seasonality in river discharge.

This study highlights the importance of coupling the typology of planktonic food webs and their emerging properties to better describe the ecological status of an ecosystem under permanent disturbance mainly caused by phosphate industry. Linear inverse models were built to describe four stations under various levels of nutrient pressure, using the Markov Chain Monte Carlo method to estimate known and unknown carbon flows, later used to calculate food web typology ratios. Ecological network analysis (ENA) was used to describe the structural and functional properties of each food web. Based on the food web typology ratios, three planktonic trophic pathways (PTP) with different functional indices were distinguished according to nutrient stress. The microbial food web dominated in the least nutrient-rich environment. It mainly relied on phytoplankton production (picophytoplankton <2 μm) that was mainly transferred by the high microbivory of protozooplankton. In contrast, the herbivorous food web developed in the most nutrient-rich environment, where biogenic carbon was mainly produced by large phytoplankton (microphytoplankton >10 μm) and channeled to higher trophic levels by herbivorous protozooplankton and metazooplankton. In the other two stations – moderately nutrient-rich systems – the PTP acted as a multivorous food web. Phytoplankton (small and large size fractions) and non-living components (detritus and dissolved organic carbon) played a significant role in carbon production, and competed with protozooplankton and metazooplankton for its transport. ENA indices revealed that the herbivorous food web, with the highest total system throughput and lowest relative Ascendency and cycling, was the most active but the least organized and stable system. In contrast, the microbial food web, with the lowest total system flux and highest Ascendency, was least active but more organized than the herbivorous food web. The multivorous food web displayed the most recycling and most organized system, with high values of the detritivory-to-herbivory ratio, cycling and Ascendency. In addition to ENA indices, which are considered effective tools for studying the structural and functional properties of food webs, marine ecosystem management efforts heavily focus on using the “marine food web” as a descriptor of the system's ecological status. However, we suggest that the combination of food web typology and ecological indices could be used as an effective tool for the management and assessment of ecosystem health wherever possible, as well as for the study of anthropogenic pressures.

The Southwest Atlantic Ocean (SAO) is one of the largest global carbon sink areas. Therefore, the main objective of this study is to investigate turbulent CO₂ flux behavior and quantify it in the presence of an intense horizontal sea surface temperature (SST) gradient in the SAO under different atmospheric conditions. In-situ, satellite, and reanalysis data were used from October 14 to 27, 2018 to achieve this objective. The study area was divided into four areas based on satellite observations of SST, salinity, and chlorophyll. The CO₂ flux was calculated using the eddy covariance method. During the experiment the area absorbing the most CO₂ was the Brazil Current (BC) owing to its proximity to the chlorophyll-rich and less saline waters of the La Plata River and the cold and less saline waters from the Malvinas Current (MC). Moreover, intense wind speeds increased the CO₂ flux between the ocean and atmosphere. The Brazil Malvinas Confluence (BMC) also behaved as a CO₂ sink, and the modulation of CO₂ fluxes was due to the intense horizontal gradient of SST together with the moderate surface wind and turbulence. During the experiment, the MC sequestered less carbon than other regions because of the presence of high-pressure atmospheric systems near the region, resulting in high atmospheric stability, that inhibited mass exchange between the ocean and atmosphere. Vertical mixing mechanisms were identified at the BMC on the cold side, over MC waters. However, in the BC waters, the marine atmospheric boundary layer was modulated by the high-pressure atmospheric system, which suppressed the turbulent mixing. However, the intense mass exchange between the ocean and atmosphere was inhibited, and the area behaved as a mild CO₂ sink because of the high-pressure system. This research contributes to a better understanding of the role of the SAO in the global carbon balance in a climate change scenario, and we showed that area can act as a CO₂ sink or source, depending on the large-scale atmospheric conditions acting.

The Yellow Sea is a marginal sea in the Northwestern Pacific where the fishery resources have been overfished and the community structure has greatly changed over the past six decades. Ecosystem modeling approaches are valuable tools to uncover potential mechanisms behind the ecosystem changes. Here, we developed ‘OSMOSE-YS’, an individual-based multi-species OSMOSE model that includes important commercial pelagic and demersal fish and invertebrates in the Yellow Sea. Simulations were carried out under three fishing scenarios to investigate how different levels of fishing pressure may have impacted the Yellow Sea ecosystem. Results indicate that the biomass of demersal fish continued to decline during 1970–2014, while the biomass of pelagic fish and invertebrates fluctuated periodically. Long-term fishing pressure has led to the reduction of total biomass, body sizes, and longevity of the modelled species. Under low-fishing condition, the ecosystem biomass is restored and the proportion of elder and larger individuals increases. On the contrary, high-fishing condition further decreases the proportion of high-trophic-level species. OSMOSE-YS serves as a baseline model to investigate ecosystem responses to different fishing strategies, in support of ecosystem-based fisheries management in the Yellow Sea.

Franz Josef Land is located in the northern region of the Barents Sea and is subjected to the constant influx of cold Arctic water. Although this area is difficult to access, several benthic surveys have been conducted to evaluate the spatial patterns and community structure of the local fauna. However, there is a lack of information regarding the structure of bryozoan communities in this region during the ongoing climate change period. Therefore, we studied the species composition and spatial distribution of bryozoan diversity and biomass at 17 stations sampled by a 0.1 m² Van Veen grab in the southern region of the archipelago between 2006 and 2008. We found 151 bryozoan species, with Turbicellepora incrassata, Celleporina ventricosa, Leieschara subgracilis, Porella compressa, and Escharopsis lobata being the most prevalent. The proportions of Boreo-Arctic, Arctic, and boreal taxa were 55.6%, 35.8%, and 8.6%, respectively. Twenty-two species were recorded for the first time in this region, including seven boreal species (31.7% of their total number) probably as a result of climate change in the Arctic. Alpha-diversity ranged from 3 to 76, with a mean value of 26 species. Bryozoan biomass ranged from 0.1 to 742 g m⁻², averaging 139.4 g m⁻². Cluster analysis revealed three groups of stations following the depth gradient and sediment composition in shallow and deep waters. The primary environmental drivers of bryozoan communities were depth and temperature (negative association) and contents of stones and shells (positive link). Our research addresses crucial knowledge gaps, such as benthic diversity shifts during the climate change period and the impact of ecological factors on community structure.

Sea level and bottom water temperature variations caused by the Last Deglaciation climate warming impacted the stability of marine hydrates. In order to examine their influence on hydrate dissociation in the northern South China Sea (SCS), we conducted simulations to track the evolution of hydrate saturation and hydrate occurrence zone since the Last Deglaciation in the Dongsha Area, Shenhu Area, Xisha Area and Qiongdongnan Area. The amount of methane generated and subsequently released into seawater and atmosphere was also evaluated within the four areas. The simulation revealed the following results: (1) Hydrate dissociation induced by variations in sea level and bottom water temperature was observed in the Dongsha Area, Xisha Area and Qiongdongnan Area, but not in the Shenhu Area. (2) The water depth at which hydrate dissociation occurred ranged between 480 and 720 m, encompassing a hydrate dissociation area of approximately 1.54 × 10¹⁰ m². This accounted for 6.68% of the northern South China Sea Area. (3) Since the Last Deglaciation, an estimation of 3.08 × 10⁸–1.48 × 10¹⁰ m³ hydrates have dissociated, resulting in the release of 5.05 × 10¹⁰–2.43 × 10¹² m³ methane. The generated methane migrated through the overlying sediments by means of central migration mode. 9.9 × 10⁹–4.76 × 10¹¹ m³ methane entered into the seawater, which will result in the formation of a weak acid affecting the marine environment. Meanwhile, 2.02 × 10⁸–9.72 × 10⁹ m³ methane entered into the atmosphere, which leads to an increase in greenhouse gas concentrations.