Marine Chemistry最新文献

The pervasive increase of plastics in marine systems and subsequent trace metals (TM) adsorption represents a critical environmental challenge. This long-term study is first to investigate how duration of exposure and stratified water column impact TM adsorption on various plastics in an estuary. We exposed polypropylene (PP), polyethylene (PE), poly(ethylene terephthalate) (PET), and fluorinated ethylene propylene (FEP) to estuarine conditions, categorizing them into three distinct groups to capture diverse human activities: pre-production pellets (Pellets), single-use plastics (SUP) and laboratory plastics (Lab). Plastic and water samples were analyzed before deployment and 1, 4, 7 and 16 months after deployment at three depths in the stratified Krka River estuary (Croatia). We measured TM concentrations, pH and salinity in the water column, and adsorbed TM amounts on plastics. Additionally, we examined plastic sample surfaces by Raman spectroscopy and scanning electron microscopy. TM speciation was modeled from water column data to better explain adsorption processes. Statistical analysis indicates that Zn, Cd, Pb, Ni, and Co adsorption depends on both duration of exposure and stratified water column, while Cu is influenced solely by duration of exposure to estuarine environment. Adsorbed TM amounts varied significantly among the plastic groups (Pellets, SUP and Lab), but not among different polymer types (PP, PE, PET and FEP). A noteworthy observation was the difference in the results of statistical analysis when investigating TM amounts expressed by plastic sample mass and by plastic sample surface area. Results expressed by plastic sample mass showed a difference between SUP group versus Pellets and Lab groups, while results expressed by plastic sample surface area distinguished Pellets group compared to other two groups. Therefore, we suggest presenting TM adsorption results in similar studies both by plastic sample mass and by plastic sample surface area. This approach will improve the understanding of TM adsorption on plastics, and enable more effective comparisons among the scientific literature dealing with plastics of different specific surface areas.

While there is a significant body of research on the dynamics of chromophoric dissolved organic matter (CDOM) in coastal and offshore waters, our understanding of CDOM dynamics in tropical inland water bodies remains limited. To bridge this knowledge gap, a monthly in-situ investigation was carried out at 33 stations along a monsoon driven lagoon, Chilika, on the southeast coast of India for one year i.e., from July 2018 to June 2019. CDOM absorption at 440 nm [aCDOM(440)] data were analyzed as a proxy for CDOM concentration which varied between a range of 0.04–65.14 m⁻¹ with an average value of 2.77 ± 5.23 m⁻¹. A gradient in aCDOM(440) was observed from the river discharge dominated shallower northern sector (4.91 ± 8.32) m⁻¹ to the more isolated and less fresh water influenced deeper southern sector (1.21 ± 1.55) m⁻¹. Spectral slope (S), spectral slope ratio (S_R), and molecular weight proxy (M) were computed to understand the possible source and fate of CDOM in the lagoon. The average spectral slope of S_280–500 and S_350–500 vary between 0.002 and 0.096 nm⁻¹ and 0.001–0.095 nm⁻¹, respectively. The (S_R) and (M) values ranged between of 0.01–6.81 and 0.31–52.28. It was observed that large-sized, high molecular weight CDOM from terrestrial origin was prevalent during monsoon with lower (S_280–500), (S_R), and (M)values. In contrast, lower molecular weight CDOM fractions were prevalent during pre- and post-monsoon which were mainly of autochthonous origin with higher (S_350–500), (S_R), and (M) values. Our findings indicate significant spatio-temporal variations of CDOM in Chilika Lagoon, influenced by the monsoon-driven influx of freshwater and the mixing of fresh and marine water. In-situ changes in CDOM are likely shaped by microbial breakdown and photodegradation.

Inorganic nitrogen is the major limiting nutrient in the northern Indian Ocean. The published and unpublished data of nitrate (NO₃⁻) and ammonium (NH₄⁺) uptake rates and estimated f-ratios (new to total production) for the past 3 decades were compiled for the northern Indian Ocean. Though the data covered seasonality in the northern Indian Ocean, however, it is biased with reference to space. Both NO₃⁻ and NH₄⁺ uptake rates displayed significant spatial variability associated with hydrographic properties. The mean NO₃⁻ uptake rates at surface were not different in the Arabian Sea (0.07 ± 0.1 mmol m⁻³ d⁻¹) than Bay of Bengal (BoB; 0.04 ± 0.02 mmol m⁻³ d⁻¹), however, photic zone integrated rates were higher in the BoB (4.5 ± 2 mmol m⁻² d⁻¹) than Arabian Sea (2.7 ± 2 mmol m⁻² d⁻¹) due to higher uptakes rates at the subsurface chlorophyll-a (Chl-a) maxima region in the BoB. The basin average NH₄⁺ uptakes at the surface were almost same in the Arabian Sea (0.4 ± 0.3 mmol m⁻³ d⁻¹) and BoB (0.5 ± 0.5 mmol m⁻³ d⁻¹), the photic zone integrated NH₄⁺ uptake rates are 6 times higher in the Arabian Sea (15 ± 8 mmol m⁻² d⁻¹) than BoB (2.3 ± 1 mmol m⁻² d⁻¹). This difference is mainly caused by deeper photic depth in the Arabian Sea (75 ± 8 m) than BoB (62 ± 5 m) due to high suspended load from rivers in the latter basin. High f-ratios were observed in the BoB (>0.5) than that of Arabian Sea (<0.2) suggesting that about half of the primary production is potentially exported from the mixed layer in the BoB whereas less than one-fifth only exported in the case of the Arabian Sea. The photic-zone integrated NO₃⁻ uptake rates and f-ratios displayed a significant relationship with surface temperature, salinity, surface Chl-a and nutrients concentrations suggesting that nitrogen uptake rates were mainly controlled by hydrographic properties. The compiled nitrogen uptake rates and f-ratio may be useful to improve simulations of cycling of carbon, nitrogen, and oxygen in the numerical models.

Iron-bound organic carbon (Fe-OC) plays a significant role in the global marine carbon cycle, facilitating the long-term accumulation and storage of organic carbon. However, the conventional method for quantifying Fe-OC, known as the citrate-bicarbonate-dithionite (CBD) method, has limitations in terms of its efficiency in extracting both Fe-OC and iron (Fe). Another CBD method, commonly used for Fe speciation analysis in paleoenvironmental reconstructions, has shown efficient and selective extraction of Fe oxides; however, its effectiveness in extracting Fe-OC remains uncertain. To evaluate the efficiency of the two CBD methods, synthetic samples spiked with organic acid/environmental organic matter‑iron (hydr)oxide coprecipitates and a marine sediment sample were subjected to extraction. The CBD approach for Fe speciation analysis at pH 4.8 on spiked samples demonstrated higher efficiency compared to the conventional CBD method, but not for samples of marine sediment. This result suggests that the synthetic Fe-OC in the spiked samples did not accurately represent the realistic state of Fe-OC in marine sediments. We found that the pH of the leaching solution during the CBD extraction significantly influenced the efficiency of the Fe-OC and Fe extraction. Our tests at pH 4.8, 5.5, 6.0, 6.5, and 7.0 revealed that lower pH enhanced the extraction of Fe, but hindered the release of Fe-OC. Our study revealed that the new CBD (pH 6.5) method resulted in approximately 30% higher yields of Fe-OC and Fe compared to the conventional CBD method, despite of significant variability in the Fe-OC data. The modified CBD (pH 6.5) method uses lower concentration of extraction reagent and reaction temperature, both of which is considered beneficial. Therefore, we suggest that the new CBD method (pH 6.5) is at least of similar efficiency as the conventional method, and can be employed alongside the established method to facilitate the evaluation of the role of Fe-OC in the marine carbon cycle.

Coastal marine sediments can be either major scrubbers or eutrophication contributors to surface waters. Standard methods for direct measurement of nutrient fluxes at the sediment-water interface do not consider hydrodynamic forcing although several ex-situ studies suggest that sediment resuspension can dramatically increase dissolved fluxes. We provide a new model to quantify dissolved phosphate (PO₄³⁻) resuspension flux (J_R) based on physical representation of its identified components: diffusion stimulation by exposure of deeper sediment layer with higher PO₄³⁻ concentration in the porewater (J_D), pore water mixing with overlying water (J_M) and net adsorption/desorption from suspended sediments (J_K). This approach was applied to field data from a Seine intertidal mudflat periodically submitted to millimetric erosion. On a tidal scale, the model output reveals a J_R of 272.3 ± 360.0 μmol m⁻² h⁻¹ (± 52% from parameter uncertainty), well above flux calculated by application of Fick's first law (0.15 ± 0.85 μmol m⁻² h⁻¹) or by ex situ core incubation (40.8 μmol m⁻² h⁻¹). Iron bound phosphorus within suboxic layers buffers PO₄³⁻ concentrations in superficial sediments leading to negligible contributions of J_D and J_M to total fluxes. Conversely, J_K appears to be the main exchange pathway, even though improvements in turbidity measurement would allow this term to be defined more precisely. Correction required to enhance and control model robustness are described. These results show the importance of considering the dissolved PO₄³⁻ resuspension flux in dynamic environments.

Rare earth elements (REE) are widely used as tracers of geochemical and anthropogenic processes across diverse environments. We investigated the abundances, sources, and fractionation of REE and Y in 12 estuaries along the Southwest Atlantic Coast. Additionally, we assessed the concentrations of Al, Fe, Mn, and organic carbon (OC) to elucidate the influence of diagenetic remobilization and facilitate comparison between estuaries. The ƩREEY varied widely, ranging from 6 mg kg^-1 (Santa Cruz Channel; > 90% sand) to 337 mg kg^-1 (Piraquê-Açú; 30% silt+clay). Normalized REE abundances relative to post-Archean Australian shale (PAAS) revealed enrichment of light REE (LREE) over heavy REE (HREE). Moreover, the northern estuaries of the Todos os Santos Bay (São Paulo, Mataripe, Subaé), Vitória Bay, and the Doce River exhibited enrichment of medium REE (MREE) over HREE. Positive correlation between ƩREEY and Al, Fe, and Mn were observed in 5 of the studied estuaries. LREE showed a positive correlation with Al (r² > 0.7) and Fe (r² > 0.8) across most of the areas studied. Additionally, REE were significantly correlated with Mn (r² > 0.8) in only 5 out of the 12 estuaries, while a positive correlation with OC (r² > 0.8) was observed in 8 estuaries. The concentration of REEY, Al, Mn, Fe, and OC depends on the bottom types and position along the estuarine zones. The observed REEY abundances contribute to the characterization of estuaries along the east coast of Brazil and can serve as a baseline reference for the region.

The activity concentrations of Po-210 were determined in seawater (<0.45 μm), suspended particulate matter (0.45–20 μm), fractionated plankton (20–50 μm, 50–200 μm, >200 μm) and tissues from four fish species, namely European seabass (Dicentrarchus labrax), Golden grey mullet (Chelon auratus), Gilt-head bream (Sparus aurata) and Common pandora (Pagellus erythrinus), collected in the Gulf of Trieste (northern Adriatic Sea). The activity concentration of Po-210 in seawater varied from 0.4 to 2.2 mBq/L in the dissolved phase (<0.45 μm) and from 0.4 to 0.8 Bq/L in suspended particulate matter (0.45–20 μm). Plankton fractionation showed the levels of 62–395 Bq/kg Po-210 in the >200 μm mesoplankton fraction, 65–459 Bq/kg in 50–200 μm and 52–537 Bq/kg in 20–50 μm microplankton fractions. No significant differences were found between fractions. The Po-210 distribution trend in fish tissues was in order: liver > stomach with intestine > kidney > spleen > gonads > gills > muscle. Bioaccumulation factors were determined for fish tissues indicating that the amount of Po-210 mostly depends on fish feeding habits. Hence, the main pathway entry of Po-210 is through ingested food. The highest estimated average total annual effective ingestion doses of Po-210 are obtained via the consumption of Common Pandora (7.1 μSv/year to 16.5 μSv/year) while the lowest doses are due to the consumption of European seabass (0.32 μSv/year to 0.76 μSv/year). Comparison with levels reported for other Mediterranean and Atlantic areas showed that only activitiy concentrations of Po-210 in fish appear significantly different, most likely because different fish species were analysed. The human dose exposure via fish consumption in the area is rather low.

Marginal seas play a critical role in the earth's systems as hotspots of microbially-mediated nitrogen (N) cycling. Meanwhile, human activities and global changes strongly impact this land-ocean boundary. Understanding the key N cycling processes and their climatic feedback is crucial for predicting the status of earth in the future and developing global N-driven physical-biogeochemical models. Although N cycling processes in China marginal seas have received great attention, a systematic analysis over a large geographical scale from estuaries to the deep ocean is still missing. This gap hinders us from concretely determining the sources and fate of N and predicting their responses to changing environments. This review compiles and re-analyzes historical data of source terms, encompassing N fluxes from riverine inputs and atmospheric deposition, as well as N₂ fixation. We also examine sinks related to sedimentary N loss processes (denitrification and anammox), internal N cycling processes (uptake and nitrification), short-lived N intermediates, and nitrous oxide, by considering rates, spatiotemporal variability, and environmental factors. Finally, we outline future research directions pertaining to marine N cycling in China marginal seas.

The ballast hypothesis involving rapid sinking of organic carbon in association with riverine mineral particles is proposed in the Bay of Bengal (BoB) in 1991. The ballast hypothesis was used intensively to explain several biogeochemical processes, such as low primary production, weak oxygen minimum zone (OMZ), low bacterial respiration rates and lack of denitrification in the BoB. In contrast, the recent measurements indicated that high primary production, intense OMZ with occurrence of denitrification in the sinking particles but not in the water column. Hence the ballast hypothesis is re-visited using the recent experiments conducted on sinking particle flux using sediment traps, ²³⁴Thorium based particulate organic carbon export, particle back scatter, water column biogeochemistry, stable isotopic composition of carbon and nitrogen of sinking particles and surface sediment of shelf region. The isotopic data suggests the sinking organic matter is mainly contributed by in-situ production supported by dissolved organic nitrogen (DON). The amount of organic matter decomposed within the water column was higher in the north and decreased towards southern BoB and it is consistent with the spatial pattern of rate of sinking particle flux suggesting against ballast hypothesis of removal of organic matter to the sediment with weaker modifications in the water column. The higher organic carbon trapped in the middle and deep than shallow traps was observed and it is attributed to cross-shelf transport of sedimentary organic carbon as evidenced from the back-scatter of particles and isotopic composition carbon and nitrogen of shelf sediments. Variations in the river discharge did not show impact on the magnitude of sinking carbon fluxes indicating that river discharge is not a drive force for higher sinking carbon fluxes to deep BoB than hitherto hypothesized as ballast effect.

The concentrations of dissolved iron (DFe), iron-binding ligands (L_Fe), and electroactive humic-like substances (eHS) were revealed in the upper 200 m along the 170°W latitudinal transect of the central Pacific Ocean in summer, which was weakly influenced by terrestrial input. DFe was largely depleted throughout the transect, except in the Bering Sea, and below 100 m in the North Pacific Subarctic Gyre. The concentration of L_Fe was lowest within the subtropical gyres and was lower in the Southern Hemisphere, which is consistent with the results from the Atlantic Ocean. The vertical distribution of L_Fe was relatively constant in the subtropical regions, whereas in the subarctic regions the subsurface maximum appeared around or over the subsurface chlorophyll maximum at some stations. The higher concentration of L_Fe in the subarctic regions coincides with a lower stability constant, which suggests a higher contribution of weaker ligands, including humic and exopolymeric substances. The horizontal and vertical distribution patterns of eHS were largely similar to those of L_Fe, supporting their significant contribution to iron-binding capacity in the upper 200 m, particularly in the subarctic regions. However, the eHS concentration was only weakly correlated with that of the fluorescently determined humic-like substances, demonstrating the substantially different chemical properties of the two humic-like substances. The strong positive correlation between the concentrations of eHS and chlorophyll a and Synechococcus strongly suggests their biological origins. However, further research is required to examine whether eHS are directly produced by phytoplankton or released via relevant biological processes, such as grazing, bacterial composition, and viral lysis.