Journal of Marine Systems最新文献

Chile has high phytoplankton production due to being a classic example of an Eastern Boundary Upwelling System. Monthly averaged chlorophyll-α (Chl) and physical parameters (sea surface temperature, precipitation rate, southerly and westerly winds) were studied off the Chilean coast from 2002 to 2018, in order to understand the primary production along this important ocean margin. The coastal margin was split into three zones and ten sub-sections. The Northern Zone had a low phytoplankton production with small seasonal variability, except in its north. This pattern is due to a narrow shelf, weak winds, lack of precipitation and relatively stable weather conditions driven by the Southeast Pacific Subtropical Anticyclone (SPSA). The Central Zone presented a seasonally varying production, with a high Chl concentration in summer and early spring. This is linked to the SPSA movement and sunlight reduction during the winter. A high Chl activity is seen in the Southern Zone despite this Zone being at the limits of the SPSA effect, leading to weak longshore winds only during the warm season. Overall, this study has demonstrated the importance of shelf width and the upwelling driven by the presence or absence of the SPSA for ocean primary production. Thus, the most productive region is from 35°S to 45°S owing to both variables being present.

Fishes often use multiple habitats to complete their life cycles, leading to their unique otolith biogeochemical signatures. Interannual variability in otolith biogeochemical signatures is expected as fish respond to annual environmental variations in their distribution areas. In this study, we focus on Japanese Spanish mackerel Scomberomorus niphonius, an abundant commercial species in the Yellow Sea. As highly migratory fish that undergo their entire migratory cycle in a year, S. niphonius is susceptible to environmental variations. Consequently, they are believed to exhibit discernibly distinct migration patterns and varying timings of ontogenetic events across different years. Otolith biogeochemical signatures of 1-year-old spawning adults S. niphonius caught in the Yellow Sea from 2016 to 2018 were measured from core to edge using laser ablation inductively coupled plasma mass spectrometry (LAICP-MS). We hypothesized that the year-specific chemical signature could be found in 2016 as a strong El Niño Southern Oscillation event happened. From 2016 to 2018, converse ontogenetic changing patterns was observed for Sr/Ca and Ba/Ca, with Sr/Ca being positively correlated with sea surface salinity while Ba/Ca being negatively. As expected, the year-specific effect was identified for 2016 cohort but it was only significant on Ba/Ca. During this year, a stronger variation of elemental concentration and an earlier downward shift of Ba/Ca were found. These results provide evidence that otolith biogeochemical signatures have useful applications as natural tags, helping understand the interannual variability in migration of marine fish species.

Two hypothesis that can be responsible for the wind-driven migration of the salinity tongue in the bottom layer of the Gulf of Finland (GoF) are tested based on the NEMO and ERA5 reanalyses. The first hypothesis authored by Krauss and Brügge (1991) implies along-channel wind developing upwelling and downwelling jet-like currents in the wind direction at opposite lateral boundaries of the channel, and a compensatory countercurrent in the deep layer (the so-called coastal jet hypothesis). The second hypothesis implies the cross-channel wind developing the along-channel Ekman transport in the upper layer, and a countercurrent in the deep layer (so-called Ekman transport hypothesis). The salinity tongue migration velocity along the GoF thalweg as estimated from the NEMO output is found to be extremely correlated with the along-thalweg projection of the wind stress calculated from the ERA5 output. This is a convincing evidence in favor of the coastal jet hypothesis as opposed to the Ekman transport hypothesis to correctly describe the mechanism of the wind-driven migration of salinity tongue in GoF. Based on a theory of coastal upwelling/downwelling in a two-layer fluid, some analytical considerations and related empirical estimates are presented to explain the prevailing coastal jet mechanism in GoF.

A cost-effective particle-tracking model was implemented to study the transport and landing of sargassum in the Mexican Caribbean. Sensitivity analyses were performed to quantify the change in landing percentages varying some model factors: 1) windage factor, 2) the horizontal distribution of sargassum, 3) monthly variability of currents and winds, 4) sargassum growth, 5) thickness of the transporting ocean layer, 6) wind data source, and 7) ocean data source. The windage factor had the greatest effect on landing estimates: as it increased, the sargassum landing percentage increased by 19%. In second place, differences in the initial horizontal distribution of sargassum caused the landing percentage to change by ∼10%. In third place, the monthly variability of currents and winds changed the landing percentage by 6%. The northern shoreline of Mexican Caribbean (between 20.25°N and 20.75°N) was the most prone to sargassum landings. At the regional scale, this condition is related with a) the shoreline orientation in that region, which more clearly faces the northward flow of the Yucatán Current, and b) the position of Cozumel Island, which acts as an offshore barrier capturing sargassum. Most of landed sargassum in the Mexican Caribbean had floated 0–40 km east and south of Chinchorro Bank, within 18.25°N and 18.75°N (southern Mexican Caribbean), and then spread along the shore. Monitoring, containment, and collection of sargassum east and south of Chinchorro Bank could help predict and mitigate sargassum landings about 5 days in advance.

Antarctic krill (Euphausia superba) is a key species in the marine ecosystem of the Southern Ocean, but is also the target of a commercial fishery, with an important fishing ground in the South Orkney Islands region. The potential for competition for krill between predators and the fishery requires risk management strategies for the fishery, underpinned by an understanding of the key physical and behavioural drivers of krill movement and retention in target areas. Here, we present the results of a regional modelling study, combining a high-resolution ocean-sea ice model and an individual-based model parameterised for krill, to elucidate the roles of oceanographic variability and krill behaviour on patterns of transport and retention on and around the South Orkney Plateau. Simulations suggest that oceanic transport from sources around the Antarctic Peninsula is restricted by the northward flowing Antarctic Slope Current. Around the South Orkney Plateau, anticyclonic flows associated with the Weddell Front and the shelf edge transport krill rapidly towards the main fishing grounds to the northwest of the plateau. Transport onto the shelf and subsequent retention are influenced by the strength and direction of regional winds; weaker on-shelf transport and shorter retention times are associated with stronger westerly and northerly winds. The incorporation of sea-ice associated behaviour, whereby krill are moved with sea ice when sea ice is present, significantly modifies the patterns from purely oceanic transport; it reduces the influence of strong regional oceanic flows and increases transport of krill to the South Orkneys region from the Antarctic Peninsula. The inclusion of diel vertical migration also modifies predicted patterns from oceanic transport, but to a lesser extent, and moderates the impact of including sea-ice associated behaviour. We highlight the importance of understanding the behaviour of krill, including age-dependent behavioural changes in response to sea ice conditions, for modelling and management of Antarctic krill populations.

Fronts play an important role in ecological processes, having multiple effects on the structure of plankton communities. The Argentine Sea is characterized by the presence of the large and very productive Patagonian shelf-break front (PSBF). This is a permanent front, with high thermohaline gradients defined between the relatively warmer and fresher shelf waters and those of the Malvinas Current. We studied the effects of the PSBF in the vertical and horizontal structure of the copepod community along two transects crossing the front. For all the variables studied, the outer shelf plus the front behaves as a unity, different of the offshore oceanic region. The highest copepod abundances were recorded on the outer shelf and shelf-break front, while the highest diversity was verified in the oceanic regime. Three copepod assemblages were identified associated to different regions: outer shelf and front (OS-PSBF), upper (UMW) and deeper (DMW) Malvinas waters, each one characterized by its own set of indicator species, having different reproductive and feeding strategies. Sac-spawners, ambush or cruise-feeders, and detritivore or omnivore species, occurred in DMW, while broadcasters, filter-feeders and mainly herbivores dominated at UMW and OS-PSBF. The PSBF acts as a leaky boundary between the oceanic regime (UMW and DMW) and the outer shelf-front regime (OS-PSBF), the first one characterized by higher copepod diversity and several functional groups, and the last one depicted by higher copepod abundance and only one functional group. In addition to its high primary production, the PSBF and surroundings are important to provide diversity of pelagic habitats that promote the existence of different assemblages, which are characterized by species having similar functional traits and that could play a similar role in the ecosystem.

Climate change is causing an increase in the intensity and frequency of extreme weather events globally. In the summers of 2016 and 2020, two catastrophic floods occurred in the Changjiang (Yangtze) River basin, resulting in the first and second largest monthly discharges since 2000. Understanding of how the coastal environments response to these extreme floods is important. Therefore, during each of these two years, two cruises (four in total) were conducted in the Changjiang River estuary and the adjacent shelf, just before and after those floods. The floods brought more low-salinity and high-SPM (suspended particulate matter) waters into the shelf areas, along with higher concentrations of particulate and dissolved organic carbon (POC and DOC). Lower POC (%) and lower POC to particulate nitrogen (PN) ratios (POC/PN) also implied that SPM and POC substances in the surface of estuarine and shelf seawaters became more terrestrial-material dominated after the floods. The extra nutrient inputs did not stimulate uptake rates and enhance non-conservative degrees of nutrients in the shelf, suggesting that phytoplankton growth and biological biomass were not elevated by these floods. We hypothesized that the higher turbidities induced by the floods limited phytoplankton production by reducing the amount of sunlight penetration. The results of the current study further revealed that significant evolutions of nutrient regimes over long time scales of at least 10 years might have happened, i.e., lower uptake rates of nutrients in the estuarine area than before. The more frequently occurring catastrophic floods might have contributed, at least to some degree, to those evolutions.

The increasing human population and rapid development along the east coast of India pose potential threats to coastal water quality. To assess the water quality of two tropical estuaries of Odisha, India, diurnal and seasonal variations along with the influence of differential anthropogenic impacts have been studied. From the results, it was evident, the seasonal variations in the water quality were largely influenced by anthropogenic sources at both the estuaries. Relatively lower seasonal variations in salinity were recorded in Mahanadi compared to Dhamara. Dissolved inorganic nitrogen (DIN) concentrations were found to be higher in the Dhamara estuary when compared to the Mahanadi estuary that can be attributed to decay of organic materials followed by the nitrification process. A reverse trend was recorded for dissolved inorganic phosphate (DIP), with significantly higher values recorded in Mahanadi. The partial pressure of carbon dioxide (pCO₂) showed strong temporal variations in both the estuaries dominated by moderate CO₂ supersaturation with respect to the atmosphere. The mean annual pCO₂ was higher in the Mahanadi estuary and was largely attributed to its significant increase during the post-monsoon season. This study indicated the stronger influence of freshwater input and tidal activities compared to that of in situ biological processes in regulating the temporal variations in water quality of both the estuaries. The present study is helpful in understanding the natural state of the estuarine water and protection of ecosystems resources to fulfil the sustainable development at the regional level.

Coastal hypoxia can occur naturally in inshore areas of the Eastern Boundary Upwelling Systems, influenced by the nutrient-rich and low-oxygen upwelling waters. This study aims to explore the influence of water stratification and winds on bottom-water hypoxia of the Paracas Bay, an area subjected to the most intense alongshore winds and active coastal upwelling in the Peruvian coast. Monitoring data of the Pisco-Paracas water properties (dissolved oxygen, temperature, salinity and estimated stratification), the Pisco River flow, and the intensities of surface winds of the outside upwelling area, and of the local area, were analysed for the period 2006 to 2015. Bottom waters deeper than 8 m in the bay were shown undergoing a hypoxic regime (oxygen <1.4 mL L⁻¹) that becomes more frequent towards austral summer and less frequent towards winter. This seasonal difference was associated with changes in the oxygen content of incoming upwelling waters and changes in the intensity of both local and upwelling winds that drive the hydrodynamics of the bay. High frequency data analysis revealed that synoptic time-scale fluctuations of the upwelling-favourable and local winds modulate the intra-seasonal variability of hypoxia. Fluctuations of the former drive the inshore expansion of mixed and less hypoxic upwelling waters during June–September, whereas fluctuations of the latter during December–April drive the entrance and circulation of more hypoxic upwelling waters, and the development of stratification events that contribute to the persistence of bottom hypoxia.

Climate change is transforming Arctic ecosystems in ways that are influencing the transport and accumulation of contaminants. The spatial and temporal variability of heavy metal distribution was studied in two Spitsbergen fjords – Kongsfjorden and Hornsund. Sediment cores from five stations in Kongsfjorden and six in Hornsund were collected in 2018–2019 and used for measurement of heavy metal concentrations (Hg, Pb, Cd, Cu, and Zn). Sediment layers were dated by the ²¹⁰Pb method to reveal the history of contamination. Isotopic lead composition was used to study sources of Pb. Loads of heavy metals to fjord deposits were calculated based on mass sediment accumulation rates. The heavy metal loads varied spatially and reached ranged 0.3 mg m⁻² yr⁻¹ for Hg, 57.6 mg m⁻² yr⁻¹ for Pb, 0.5 mg m⁻² yr⁻¹ for Cd, 101 mg m⁻² yr⁻¹ for Cu, and 117 mg m⁻² yr⁻¹ for Zn. Heavy metal discharge from the glaciers to the glacial bays were much higher compared to discharge in central and outer fjord parts. This may suggest that glaciers can be important secondary sources of pollutants to fjords.