Journal of Marine Systems最新文献

Small river basins represent an important source of dissolved nutrients to the coast, which are fundamental to coastal primary production. However, such transport is a resultant of nutrient fluxes from small rivers, estuarine modulation and, currently, anthropic emission loads. In this context, this study assessed ammonium (NH₄⁺) and phosphate (PO₄³⁻) dynamics in a small subtropical river-estuary system by addressing seasonal fluxes from the river to the estuary, as well as the estuarine spring-neap tidal modulation, the resultant fluxes to the coast, and the influence of natural processes and anthropogenic activities on the land-sea nutrient dynamics. The results indicated that NH₄⁺ and PO₄³⁻ fluxes in the small river-estuary system were influenced by anthropic emission loads and by estuarine modulation through amplification of river discharge and NH₄⁺ and PO₄³⁻ concentrations and fluxes within the estuary. During most of the time, the small river-estuary system exported such dissolved nutrients to the coast, likely contributing to coastal primary production.

Using the Simple Ocean Data Assimilation Version 2.2.4 dataset from 1950 to 2010, we analyzed the interannual variations in wintertime temperature inversions in the Gulf of Alaska (GOA), and the linkages to the Aleutian Low are also examined. The results show that the climatological wintertime temperature inversions is predominantly distributed in the northwestern GOA (NWGOA) and northern GOA (NGOA), in which it is stronger in the NWGOA than in the NGOA. Interannual variations in the temperature difference (∆T) are pronounced and are mainly controlled by the temperature minimum (T_min) of the inversions layer. The temperature inversions layer became warmer and shallower during 1950–2010, among T_min and the temperature maximum (T_max) was notably warming, and the upper edge depth (D_min) and lower edge depth (D_max) revealed significant shoaling. ∆T decreased by 0.12 °C from 1950 to 2010 in the NWGOA but had no trend in the NGOA. The interannual variations in wintertime temperature inversions are controlled by the mixed-layer temperature anomalies and are closely correlated with the changes in the Aleutian Low. The weakened (deepened) Aleutian Low during strong (weak) ∆T winters could cause the weakening (enhancement) of the cyclone wind field in the North Pacific subarctic region, which is conducive to slowing down (spinning up) the flow of the Alaskan Gyre and the transportation of warm air into the GOA. Thus, a negative (positive) T_min anomalies within the mixed layer is larger than T_max anomalies, resulting in a larger (smaller) ∆T; meanwhile, the strong (weak) cooling effect leads to a deeper (shallower) D_max. The interannual variations in the wintertime temperature inversions could be influenced by net heat flux and advection anomalies in the NWGOA, but only caused by net heat flux anomalies in the NGOA.

The Sea of Marmara, located in northwest Turkey, comprises challenging environmental conditions and is an important bridge between the Black Sea and the Aegean Sea. In this study, we assessed the trophic situation of the coasts of the Sea of Marmara using the benthic diatom composition and their relation to the environmental variables in the spring and autumn of 2019 and 2020. A total of 120 samples were collected and 452 species were observed; Navicula Bory and Nitzschia Hassal were represented with the highest numbers of taxa. Analysis of Similarity (ANOSIM) revealed that diatom communities differed significantly between the spring-autumn periods and years. Canonical Correspondence Analysis (CCA) showed that diatoms grouped under water, temperature, salinity, dissolved oxygen, and TIN influence. TRIX observations revealed a highly mesotrophic-eutrophic status along the coasts. Our study contributes to the knowledge of diatom diversity, distribution and community changes in spring and autumn on the coasts Sea of Marmara. Our findings suggest that marine benthic diatoms could be used as eutrophication indicators in the coastal waters for long-term monitoring with the support of environmental parameters.

Structure and functions of picophytoplankton and their links to the water column density stratification and nutrient vertical profiles were studied in the Black Sea open waters along a transect from the Western Gyre to the NW shelf during spring homothermy in April of 2017. Abundances of picocyanobacteria of the genus Synechococcus (0.85 ± 0.96 (SD) × 10³ cells ml⁻¹) and eukaryotic picoalgae (5.74 ± 5.99 × 10³ cells ml⁻¹) and their intracellular pigment (chl a, phycoerythrin) contents were quantified using flow cytometry. The distribution of these variables in the upper 100-m layer was non-uniform. Along the whole transect, Synechococcus and picoeukaryote abundance maxima (up to 4 × 10³ and 3 × 10⁴ cells ml⁻¹, respectively) were observed at the water temperature of 8–8.5°С in the depth range between 30 and 40 m. Picoeukaryotes dominated the total community. The share of Synecococcus averaged about 22% and increased with depth up to 80%. Picophytoplankton abundance dropped abruptly through the oxycline but the cells were found in the suboxic layer at about 10³ cells ml⁻¹ and in a sample from the anoxic zone at 10² cells ml⁻¹. Intracellular chl a maxima were revealed in the nitrate peak at sigma-t density of 15.5. In the surface and suboxic layers, non-specific green autofluorescence (GAF) was detected in picophytoplankton cells that might provide evidence of their stress state in adverse environment. Multivariate analysis has revealed tight coupling between abiotic and microbiological variables in three statistically distinct pelagic regions of the transect, corresponding to the abyss, the continental slope and the shelf.

Information on microbial metabolic activity is essential for quantifying carbon and energy flows through marine food webs. We quantified community (R_com) and prokaryotic (R_pro) respiration rates, bacterial production (BP), bacterial abundance (BA), and bacterial growth efficiencies (BGE) in the Perdido and Coatzacoalcos basins of the Gulf of Mexico (GOM) during summer and winter conditions in 2016. Our results showed seasonal, regional, and mesoscale eddy influences on those metabolic variables. R_pro accounted for >60% of total respiration in both regions, being three times higher in stations influenced by a cyclonic eddy (CE) in September (24.1 μM O₂ d⁻¹) than in stations affected by an anticyclonic eddy in March (7.2 μM O₂ d⁻¹) within the Coatzacoalcos basin where the eddy-trapping mechanism advected biomass-enriched waters from the Bay of Campeche. The eddy-stirring mechanism produced horizontal and vertical dipole patterns of metabolic variables increasing up to one order of magnitude R_com and R_pro while decreasing BGE to 25-fold from the southeastern to the northwestern edges in CEs. This finding indicates that dissolved organic matter is more actively taken up to build bacterial biomass on the eastern edge of CEs in the GOM, while R_pro and R_com increase on the western edges. Satellite integrated primary production was coupled with surface R_pro and R_com at CEs and no eddies. BP was mainly regulated by CEs and was about 50% higher in the Coatzacoalcos basin (~0.03–0.14 μmol C L⁻¹ d⁻¹). BP increased in zones with high R_pro and R_com, suggesting that R_com is associated with heterotrophic prokaryote activity in both basins. BGE was lower than 25% within the upper 500 m during both cruises, but the highest values were quantified in the euphotic zone and during the September cruise. Metabolic variables integrated over the water column showed that 40–80% of the microbial activity occurred between the base of the euphotic zone and 150 m depth. Our findings contribute to a better understanding of the metabolic activity of the microbial communities in two regions of the GOM influenced by mesoscale eddies.

Seasonal variations in hydrographic conditions, nutrients, and microplankton abundance and biomass were investigated inside and outside Kagoshima Bay in the northern Satsunan area. The area is a nursery ground for the migrating fish. During the mixing season from November to April, highly saline water (>34.5) originating from a branch of the Kuroshio Current, the western boundary current of the North Pacific Subtropical Gyre, intruded from the surface layer into the bay causing extrusion of coastal bottom water. This intrusion generated vertical mixing between surface water and nutrient-rich bottom water. Consequently, chlorophyll a concentrations increased (>1 μg l⁻¹) around the bay mouth. During the stratified season from May to August, the coastal surface water was extruded due to intrusion of saline water from the bottom layer. High chlorophyll a concentrations (>1 μg l⁻¹) were also observed in the surface layer in July during the rainy season. Such differences in hydrographic conditions between mixing and stratified seasons were due to vertical distribution of highly saline water from outside the bay, which seasonally migrated between surface and subsurface layers. Relatively distinct redundancy analysis plots and boxplots generated from a generalized linear model showed that microplankton community structure differed between mixing and stratified seasons. The mixing and stratified seasons were characterized by high diatom abundance and low microplankton abundance, respectively, suggesting that vertical mixing increases nutrient supply and consequently increases diatom abundance. Thus, microzooplankton (mainly naked ciliates and athecate dinoflagellates) abundance was related to the abundance of prey organisms, such as diatoms, thecate dinoflagellates and cryptophyte-like flagellates, rather than hydrographic conditions. Thus, saline water intrusion from a branch of the Kuroshio Current likely governs hydrographic conditions in Kagoshima Bay and consequently affects temporal variations in abundance and taxonomic composition of phytoplankton and microzooplankton communities.

This study provides the first observational evidence on the role of deep-water renewal in triggering phytoplankton blooms in a rare shallow-silled tropical fjord (Ambon Bay). Seasonal variation in the tidal-induced deep-water intrusions into inner Ambon Bay (IAB, the fjord basin) upwardly displaces water from the IAB deep layer towards the surface. The budget method was employed to quantify vertical mixing in the deep layer of IAB (below sill depth) post-intrusions (stagnant periods). Within a spring-neap sequence (~ 2 weeks), deep-water intrusion pulses in IAB were observed to be more frequent in the easterly monsoon (July, eight pulses) than the transitional season (October, three pulses). These intrusion pulses uplifted the resident deep waters of IAB with rates of 2.4 - 4.0 m/day in the easterly monsoon and 1.5 - 1.8 m/day in the transitional season. Depth-averaged vertical diffusion coefficient (K_v) in the deep layer of IAB slightly varied between easterly monsoon (3.3 × 10^-4 m²/s) and transitional season (3.7 × 10^-4 m²/s). The parameterization of the vertical mixing-stratification relationship (K_v ∝ [N²]^-β) in the IAB deep layer was found to be larger in easterly monsoon (β = 1.104) than in transitional season (β = 0.694). Chlorophyll-a concentration in the water column of IAB increased during uplifting events with phytoplankton bloom conditions (> 5 mg/m³) found only in the easterly monsoon. The described uplift mechanism as a driver of phytoplankton blooms should be included in future analyses of water quality for IAB.

The Ocean Weather Station M (OWSM) is situated at a fixed position in the Norwegian Sea, one of the major basins of the Nordic Seas, which represents an important area for uptake of atmospheric CO₂ as well as deep water formation. At OWSM, the inorganic carbon cycle has been regularly monitored since 2001, and significant interannual changes of the carbonate system have been determined. Data collected at this site since the 1990s have been included, and over the 28 last years the surface fugacity of CO₂ (fCO₂) has increased by 2.92 ± 0.37 μatm yr⁻¹, while surface pH and aragonite saturation (Ω_Ar) have decreased by −0.0033 ± 0.0005 yr⁻¹ and −0.018 ± 0.003 yr⁻¹, respectively. This corresponds to a surface pH change of −0.092 over 28 years, which is comparable to the global mean pH decrease of −0.1 since the onset of the industrial revolution. Our estimates suggest that 80% of the surface pH trend at OWSM is driven by uptake of CO₂ from the atmosphere. In the deepest layer, Ω_Ar has decreased significantly (−0.006 ± 0.001 yr⁻¹) over the last 28 years, now occasionally reaching undersaturated values (Ω_Ar < 1). As a rough estimate, the saturation horizon has shoaled by 7 m yr⁻¹ between 1994 and 2021. The increase in surface fCO₂ is confirmed by semi-continuous measurements of CO₂ from the site (2.69 ± 0.14 μatm yr⁻¹), and thus, the area has become less of a net sink for atmospheric CO₂, taking into consideration an atmospheric CO₂ increase at OWSM of 2.27 ± 0.08 μatm yr⁻¹.