Journal of Marine Systems最新文献

The seasonal and spatial variations of dissolved organic carbon (DOC), chromophoric dissolved organic matter (CDOM), and fluorescent dissolved organic matter (FDOM) were evaluated in the Bohai Sea (BS) and the Yellow Sea (YS) during three cruises. Two fluorescence components, such as marine humic-like (C1) and visible humic-like (C2), were identified using excitation-emission matrix fluorescence spectroscopy (EEMs) and parallel factor analysis (PARAFAC). The average values of DOC concentration, CDOM absorption coefficient (a_CDOM(355)) and fluorescence component intensities (C1 and C2) were significantly higher in the BS (2.14 mg C L⁻¹, 0.77 m⁻¹, 0.035 RU, 0.026 RU, respectively) than those in the YS (1.55 mg C L⁻¹, 0.50 m⁻¹, 0.025 RU, 0.019 RU, respectively). The average DOC value was highest in winter (2.16 mg C L⁻¹) and lowest in spring (1.62 mg C L⁻¹), while a_CDOM(355) was the opposite (winter: 0.45 m⁻¹; spring: 0.62 m⁻¹; summer: 0.58 m⁻¹). The average C1 (0.042 RU) and C2 (0.028 RU) values were highest during the winter and summer respectively, and lowest during spring (C1: 0.024 RU; C2: 0.016 RU). DOC and CDOM were mainly derived from terrestrial input, during the winter and spring, while they were primarily derived from phytoplankton production during the summer. C1 and C2 were not correlated with salinity or chlorophyll a during the three seasons. The SUVA₃₅₅ values generally decreased with increasing salinity during the spring and summer, indicating that sources and sinks of CDOM and DOC were uncoupled. DOC, CDOM, and FDOM were dominated by terrestrial input and phytoplankton production activities and their spatial distributions and seasonal variations were also affected by currents, microbial activities, and photobleaching.

Phytoplankton production controls the transfer of carbon dioxide from the atmosphere into the ocean through the biological carbon pump, facilitating the sequestration of carbon dioxide and thus, contributing to the regulation of global climate. In the Southern Ocean, a high-nutrient low-chlorophyll region, productivity is limited by micronutrients including iron. The limiting role of light is also important, especially in the context of Southern Ocean phytoplankton adaptation to the low-iron conditions. To investigate the relative dominance of iron and light limitation on phytoplankton growth, we conducted a series of incubation experiments during a 2019 summer research voyage off East Antarctica. Our results show that, while light was the primary limiting factor of phytoplankton growth, iron addition became favourable for growth under high light conditions. This supports similar findings from laboratory (Strzepek et al., 2019) and field experiments in the Ross Sea (Alderkamp et al., 2019) and provides a new insight from a different region of the Southern Ocean, at a later stage of the austral summer. Similar results have previously been documented in larger diatoms, and here we provide evidence that it is also true for smaller cells. Our findings add to the body of knowledge regarding iron and light limitation in the Southern Ocean, in a poorly sampled area, leading to a better understanding of how primary production will change in a future warming ocean.

Flocculation, triggered during estuarine mixing plays an important role in land-to-sea interactions and is a fundamental topic in near-shore oceanographic studies. Identifying in situ flocculation in large-river estuaries can be challenging due to the complex seawater circulation and heterogeneous suspended particulate matter (SPM) composition in these areas. In this study, three cruises were conducted in the Changjiang (Yangtze) River Estuary and the adjacent area in March, May, and July 2016. Vertical profiles of SPM total volume, mean size, and size spectra were determined using laser in situ scattering and transmissometry (LISST) measurements at 66–89 stations during the three cruises. Stable isotopic ratios of δ¹³C were also measured in the organic carbon contents of SPM collected at the surface, middle, and bottom layers of the sampling stations. LISST data were used to successfully identify the flocculation occurring in the field as well as to trace SPM size spectrum changes before and after the flocculation process. The δ¹³C values were utilized to study the response of biogeochemical parameters to the flocculation. Phytoplankton blooms occurring in May largely resulted in discontinuous variations in LISST parameters and δ¹³C from March to July. Although the pattern of SPM size spectra involved in flocculation differed among seasons, flocculation processes were always contributed by smaller particles with sizes of several tens of μm aggregating into larger ones >300 μm. Using LISST and δ¹³C measurements combined greatly improved our understanding of SPM dynamics in estuarine and coastal areas where estuarine flocculation was a critical component.

Understanding concurrent responses of habitat pattern of pelagic fish species to climate variability is favorable for sustainable exploitation and fisheries management. In this study, the key environmental factors affecting Dosidicus gigas (sea surface salinity (SSS), sea surface height anomaly (SSHA) and water temperature at 400 m (Temp_400m), and Trachurus murphyi (sea surface temperature (SST), mixed layer depth (MLD) and Temp_400m), were used in combination with the Pacific Decadal Oscillation (PDO) index to examine synchronous habitat variations off Chile based on habitat suitability index model (HSI). All environmental factors were significantly related to the PDO. A significantly negative relationship was found between the HSI of D.gigas and the PDO index, while a significantly positive correlation was observed in the HSI of T.murphyi. In the warm PDO regime, MLD was shallower, SST increased, and SSHA decreased from the northeast to the southwest off Chile. SSS and Temp_400m in northern waters off Chile were higher than those in southern waters. The suitable habitats of D.gigas contracted and shifted southwestward. While the area and distribution of T.murphyi changed little, but its habitat quality enhanced. In the cold PDO regime, SST and SSHA decreased, and MLD deepened. Variations in SSS and Temp_400m were consistent with those in the warm PDO regime. The suitable habitats of D.gigas enlarged and moved northeastward. Whereas the suitable habitats of T.murphyi slightly reduced with small change occurred with its spatial location. Our findings suggested that the PDO played important roles in the long-term concurrent habitat variations of Chilean T.murphyi and D.gigas.

Lagrangian particle tracking (LPT) models are used to study the transport and dispersal of marine organisms. In LPT studies, the accuracy of the circulation is essential for nearshore habitats of Eastern Boundary Current (EBC) regions that are areas of high productivity and economically important fisheries. We used the California Current System as an example of an EBC region, specifically the Oregon coast located in the northern California Current System because it has distinct upwelling and downwelling regimes and variable shelf width. More specifically, we developed and applied a LPT model to compare and contrast particle drift patterns during the spring transition as it is an important period for spawning. We contrasted years (2016–18) using Regional Ocean Modeling System (ROMS) with different horizontal spatial resolutions (2 km, 250 m). Lagrangian particles experience stronger downward velocities and displacements to greater depths in the 250 m ROMS simulations that used a finer resolution bathymetry. Consequently, retention along the Oregon coast increases in the 250 m ROMS compared to the 2 km ROMS. After 10 days, 37%–83% of particles forced with the 2 km ROMS remain in the model domain, compared to 61%–86% of particles remaining when using the 250 m ROMS. Particles in the 250 m ROMS are advected to depth at specific times and locations for each simulated year, coinciding with the location and timing of a strong and shallow alongshore undercurrent that is not present in the 2 km ROMS. Additionally, ageostrophic dynamics close to shore, in the bottom boundary layer, and around headlands emerge in the 250 m resolution model, while they are at best poorly resolved in the 2 km resolution case. We conclude that the higher horizontal model resolution and bathymetry used in the 250 m ROMS generates well-resolved mesoscale and submesoscale features (e.g., surface, subsurface, and nearshore jet) that vary annually. These physical features are significantly different than those modeled by the 2 km model and may be responsible for these differences in particle dispersal. These results have implications for modeling the dispersal, growth, and development of coastal organisms with dispersing early life stages.

ADCP current data and sea level data from tide gauges and satellite altimetry were used in order to analyze long-term variation of the Tsushima Warm Current (TWC) volume transport passing through the Korea/Tsushima Strait. The annual mean transport of the TWC estimated from ADCP current measurement for about 17 years (1997–2013) is 2.64 ± 0.41 Sv (Sv = 10⁶ m³s⁻¹) in the Korea/Tsushima Strait, 1.53 ± 0.36 Sv (about 58% of the total transport) in the western channel, and 1.11 ± 0.14 Sv (about 42%) in the eastern channel. The TWC shows the minimum transport (1.74 Sv) in January and the maximum transport (3.10 Sv) in October, with seasonal variation of up to 1.36 Sv (51.5% of the annual mean transport). The seasonal variation of the total TWC transport in the Korea/Tsushima Strait is mainly similar to that in the western channel. The annual mean transport of the TWC and its seasonal variation in the Korea/Tsushima Strait, the western and eastern channels are all similar in three datasets (ADCP, tide gauge, satellite altimetry). The annual mean volume transport of the TWC estimated from long-term tide gauge data was 2.57 ± 0.37 Sv (total volume transport) for 44 years (1975–2018) in the Korea/Tsushima Strait, 1.51 ± 0.32 Sv in the western channel and 1.06 ± 0.14 Sv in the eastern channel. Long-term variation of the TWC transport shows a decreasing trend for 1975 to 1988, and an increasing trend from 1989 to 2018. For the latter period (1989 to 2018), monthly transport tends to increase in all months throughout the years, showing a greater increase, especially in spring and summer months. The increase of the transport in the eastern channel was about 2.8 times larger than that in the western channel. It is suggested that the increasing trend of the TWC transport since 1989 is related to the Pacific Decadal Oscillation (PDO), which has been changed to negative direction since mid-1980s. During the period when the negative PDO index is strong, the negative wind stress curl weakens in the mid-latitudes of the North Pacific, and the Kuroshio in the East China Sea also weakens. As a result, the flow is strengthened toward the Korea/Tsushima Strait, increasing the TWC transport.

Variations in seawater temperature have a critical influence on marine ecosystems and aquaculture industries in coastal regions. From July 25 to August 5, 2017, the sea surface temperature off the southwestern coast of Korea rose rapidly from 17.1 °C to 27.3 °C, which induced environmental stress in marine organisms such as farmed abalone. This study investigated the cause of this abrupt sea temperature rise. Westerly winds from July 1 to 25 were favorable for the upwelling of cold subsurface water along the bottom slope in this coastal region, helping maintain cool surface water temperatures. As the wind changed to easterly, the cold subsurface water moved away and warmer, fresher surface water moved into the coastal region, where the surface currents changed from a southeastward flow to a northeastward flow from July 25 to August 5. Thus, to maintain stable, cool seawater temperatures during summer, both cold water supply and upwelling wind conditions are essential. The analysis of water masses indicated that the cold water was formed by the mixing of the Tsushima Warm Current Water and Yellow Sea Bottom Water in the northern East China Sea. The cold water advected eastward and formed a cold water pool in the intermediate depths (30–80 m) of the northern Jeju Strait, providing cold water to the coastal region during the upwelling period. The westerly winds were disrupted by the approach of a typhoon, which discontinued the supply of bottom cold water. The physical processes identified in this study will help predict short-term increases in water temperature and can assist in the development of countermeasures for the aquaculture industry against the negative effects of abrupt environmental changes.

High phytoplankton biomass usually appears off the coastal waters southeast of Vietnam (SV) during summer and southwest of the Luzon Strait (SLS) in winter. Although this seasonal upwelling has been recognized in SV and SLS for more than half a century, there has been limited documentation comparing the characteristics and formation mechanisms of these two upwelling systems. To understand the dynamic features of phytoplankton growth in SV and SLS, seasonal and interannual variabilities of Chlorophyll-a (Chl-a) concentration were studied based on decadal-scale satellite-derived datasets (2003–2018). Bivariate wavelet coherence (BWC) and multiple wavelet coherence (MWC) were performed to evaluate the temporal variability of multiple controlling factors. The results demonstrated that there were different patterns of seasonal cycles and interannual variability of Chl-a concentrations in the two upwelling regions. In SV, high Chl-a concentrations during summer were primarily formed by the interactions of multiple factors, causing the mixed layer depth to increase during summer and sufficient nutrient concentrations on the surface (supplied by the mixed water column). In contrast, the high Chl-a concentrations in SLS are caused by a combination of deep mixing (induced by wind and buoyancy forcing) and enhanced upward advection (induced by strong eddy activities). These factors support intense levels of phytoplankton biomass during winter. The sea surface temperature (SST) was the best single factor to explain the Chl-a variance in both regions. The addition of more factors to the MWC analysis changed the main factors influencing the Chl-a variations. The two-factor combination of SST-Niño 3.4 in SV and the SST-mixed layer depth (MLD) in SLS controlled the Chl-a variations on an interannual scale. Moreover, the three-factor combination of SST-Niño 3.4-MLD was still meaningful for explaining the Chl-a variations. This indicated that the influencing the Chl-a variations differed in these two upwelling systems.

When Antarctic glaciers retreat, high sediment loads from geomorphological and glaciological sources can disturb the biota, especially filtering organisms, and thereby significantly alter the ecology of the Antarctic coast. We applied the Finite volumE Sea-ice Ocean-Coastal Model (FESOM-C), a numerical tool equipped with a sediment module, to simulate for the first time the suspended particulate matter (SPM) dynamics in a fjordic environment at the northern West Antarctic Peninsula, Potter Cove as a case study. Depth-averaged SPM dynamics during a meteorologically representative austral summer (120 days from December to March) considered tidal and atmospheric forcing. Additionally, idealised experiments with passive particles based on post-processing Lagrangian module identified and followed possible material trajectories in Potter Cove. Particle dynamics in the area show them to be primarily tidal and wind-driven, sensitive to bathymetry, with the higher SPM concentrations in the inner cove and the highest hydrographical complexity in the transitional area between the fjordic and marine habitat. The SPM plume covers 5.5 km² of the total inlet of 9 km², with monthly mean values between 15 and 330 mg/l. The maximum SPM concentrations are during January (790 mg/l), and the maximum plume expansion during February. The model was validated with available in situ measurements. With this study, we can identify areas in Potter Cove (and similar coastal fjordic environments, prospectively) of increasing physical stress by longer SPM residence time and high accumulation rates induced by glacial meltwater. These factors are crucial for pelagic and benthic assemblages dependent on light and food availability, as well sediment deposition.