Marine Chemistry最新文献

The distribution and cycling of biogenic silica (BSi) and lithogenic silicon (LSi) in the ocean play crucial roles in the global silicon cycle and marine ecosystem dynamics. This is especially the case in the Southern Ocean where diatoms constitute the predominant phytoplankton and participate in a major way to the biological carbon pump. This study presents an assessment of BSi and LSi concentrations along the GEOTRACES South West Indian Ocean Section (SWINGS, late austral summer 2021), where several and contrasting regions were encountered: oligotrophic Mozambique basin, HNLC (High Nutrient Low Chlorophyll) areas and regions fertilized by the Subantarctic islands. Suspended particles were sampled from Niskin bottles and in situ pumps, along with scanning electron microscope (SEM) observations and specific pigments measurements to support BSi and LSi analyses. With samples coming from a contrasting study area prone to diverse continental influences, our BSi and LSi results showed a reproducibility of 13 ± 7%, in the same range as the established protocol. BSi concentrations show a north-south gradient with maxima encountered in the Antarctic Zone, and contrasted results between HNLC open ocean areas and naturally fertilized regions in the vicinity of the Subantarctic islands. Some open ocean stations have unusually high BSi (e.g. > 5 μmol L⁻¹) likely resulting from fertilization by aerosols, upwelling or island mass effect when they are downstream of the islands. Coupling of BSi with SEM observations and pigments measurements respectively showed diatoms were the most representative of the carrying phase of BSi and suggested silicification changes, induced either by heavily silicified diatoms or by micronutrient limitation in HNLC regions. BSi is often dominated by the smallest size fraction (0.45–5 μm) which represent 47 ± 23% of the total BSi based on 29 measurements on size fractionated samples. LSi results highlighted atmospheric inputs at the surface and nepheloid layers in the water column, which makes LSi overall a good indicator of the origin of lithogenic materials. SEM observations supported these results, enabling characterization of the diversity of lithogenic materials in the vicinity of the Subantarctic islands, more specifically volcanic ash around Heard Island, and within the nepheloid layers.

Iron (Fe) and manganese (Mn) are crucial micronutrients that limit oceanic primary productivity in the Southern Ocean. It has been recently suggested that hydrothermal activity may be an important source of oceanic dissolved iron, yet, this contribution is still not fully understood and only one active hydrothermal site has been reported on the Southwest Indian Ridge (SWIR), south of 40°S.

Using a multi-proxy approach, this study demonstrates the occurrence of hydrothermal venting on the SWIR in the near vicinity of the location 44°51.690 S, 36°10.460 E, which is likely to be a low or moderately high temperature fluid. Indeed, we report high values of dissolved methane to manganese ratios (up to 11.1 ± 1.2 mol mol⁻¹), low particulate iron (pFe) and manganese (pMn) concentrations (with maximum values of 0.7 nmol L⁻¹ and 0.06 nmol L⁻¹, respectively) associated with the presence of few oxyhydroxides, as well as high ²²³Radium (Ra) and ²²⁴Ra activities near the seafloor. The Fe and Mn data revealed a significant enrichment at depths influenced by hydrothermal circulation on the seafloor, within the Upper Circumpolar Deep Water. Dissolved Fe (dFe) and dissolved Mn (dMn) concentrations were enriched by 3- and 7-fold, respectively, and pFe and pMn by 2- and 1.5-fold, respectively, compared to a reference station located outside the SWIR. They were however lower than concentrations reported so far near high temperature vents, suggesting a weaker influence of this hydrothermal system on deep Fe and Mn reservoirs. We show that a large fraction of the dFe could be stabilized by organic complexation with humic substances (eHS, estimated 27–60% of dFe). High prokaryotic abundance related to the proximity of the hydrothermal vent suggests that other Fe-complexing ligands of biological origin might also stabilize Fe in its dissolved form. Collectively, these measurements integrated within the concept of a “multi-proxy approach”, helped painting a more detailed picture of the complex interactions and processes in this region of the SWIR. Although the system is a source of both dFe and dMn to the deep ocean, the low current velocities and the bathymetry likely limit the fertilization of surface water by dFe and dMn along this section of the SWIR.

Iron plays a pivotal role in marine primary production and the carbon cycle. Glaciers have been recognized as a regional iron source to the ocean. Understanding both the endmember values and the transport processes of glacial iron passing through coastal waters to the ocean is essential to comprehend the fate and flux of iron derived from glaciers to the ocean. Fjords are typical coastal pathways in polar marine environments, connecting glacial meltwater to the open ocean. To better estimate iron transport from glacial meltwater to the ocean, we examined dissolved iron (dFe), dissolved aluminum (dAl), iron stable isotopes (δ⁵⁶Fe), and other biochemical parameters, including dissolved organic carbon, total suspended matter, and chlorophyll a in an Arctic fjord system, Kongsfjorden, Svalbard. In surface Kongsfjorden, low dFe levels averaging 5.23 ± 0.43 nM were detected in the inflow along the southern bank of the outer fjord, while elevated dFe concentrations were observed in both the inner and middle fjord regions (10.74 ± 5.22 nM), as well as in the outflow along the northern bank of the outer fjord (9.37 ± 2.85 nM). The association of dFe distribution with circulation patterns, in addition to the correlation between dFe and salinity, emphasizes that both glacial input and circulation regulate dFe distribution in Kongsfjorden. dFe and dAl endmember values from glacial meltwater were estimated as 82 ± 21 nM and 1089 ± 200.7 nM, respectively. The summer flux of glacier-derived dissolved iron and aluminum in Kongsfjorden were calculated to be 4.6–19 Mg/summer and 29 ± 5.4 Mg/summer, respectively. A short residence time for dFe in the Surface Water of Kongsfjorden was estimated at approximately a few days to a week, while dAl exhibited nearly conservative behavior, suggesting a possible application as a tracer for glacier input. The average δ⁵⁶Fe value in Kongsfjorden surface water was 0.08 ± 0.19‰, and our extrapolated glacial δ⁵⁶Fe input fingerprint ranged from 0.1‰ to 0.3‰ as iron traveled from the glacier towards the ocean. Our results emphasize the transport pattern of glacier-derived iron towards the ocean through Arctic fjord systems.

Ocean acidification poses a substantial threat to global marine ecosystems, estuaries are more vulnerable to ocean acidification compared to open oceans due to their weaker buffering capacity. This study examined the carbonate parameters off the Yangtze River estuary (YRE) during summer 2019 and investigated seasonal variations in total alkalinity (TA) and dissolved inorganic carbon (DIC) transport in the lower Yangtze River in 2019. Monthly DIC (1566–2164 μmol/kg) and TA (1471–2128 μmol/kg) in the Yangtze River were negatively correlated with water discharge. Buffer factor (β_DIC) was calculated and used to evaluate the buffering capacity, which ranged from 65 to 256 μmol/kg and increased seaward along the YRE. Conservative mixing models indicated that the estuary had a minimum buffer zone (MBZ) at salinity of 2–9 during the high discharge periods. And the salinity of the MBZ was positively correlated with the riverine DIC:TA ratio. The construction of the Three Gorges Dam has resulted in a decrease in the Yangtze River's DIC:TA ratio, leading to the migration of the estuarine MBZ towards lower salinity regions. The effect of anthropogenic CO₂ invasion on estuarine buffering capacity was opposite to that of dam construction, leading to the migration of the estuarine MBZ towards higher salinity regions. Biological influences on the buffering capacity in the YRE were also quite considerable. Net autotrophy slightly enhanced the buffering capacity of the estuarine surface water, while net heterotrophy significantly weakened the buffering capacity of the estuarine bottom water. Eutrophication could intensify the biological influences on the buffering capacity. Globally, mid-latitude estuaries, such as the YRE, generally exhibit the strongest buffering capacity, while estuaries in Arctic regions tend to have the weakest buffering capacity.

Microplastics (MPs) have been recognized globally as a new environmental pollutant and can be transported in water environments all over the world. Diatoms contribute about 20% of marine primary productivity and play an important role in global carbon sequestration, climate regulation, and the biogeochemical cycling of biogenic elements. Understanding the impact of MPs on the primary biomass productivity of phytoplankton is crucial for assessing ecosystem resilience and maintaining essential ecosystem services. Here the relationships between phytoplankton physiological indicators and trace metal uptake were investigated to delineate how polystyrene microplastics (PS-MPs) affect the primary biomass productivity and alter the dynamics of trace metal sinks in marine ecosystems. We innovatively proposed that the influence of MPs on phytoplankton was not only shading effects on algae and causing oxidative damage, but also limiting the accumulation of trace metals in algae. The accumulation of Mn, Fe and Ni in algae is positively correlated with the content of chlorophyll a (Mn: r = 0.824; Fe: r = 0.697; Ni: r = 0.822), photosynthetic activity (Mn: r = 0.631; Fe: r = 0.467; Ni: r = 0.816) and β-carotene (Mn: r = 0.773; Fe: r = 0.307; Ni: r = 0.786), but negatively correlated with superoxide dismutase activity (Mn: r = −0.714; Fe: r = −0.730; Ni: r = −0.908). This provides a new perspective to reveal the influence mechanisms of MPs on primary biomass and trace metal sinks.

Simultaneous determination of dissolved silver (dAg) with other key GEOTRACES trace metals is difficult because dAg in seawater tends to form negatively charged chloride species that result in only 75% recovery efficiency with commonly used NOBIAS PA-1 chelating resins. In this study, we developed a method using solid phase extraction coupled with isotope dilution that enables full quantification (97.9 ± 2.1%) of dAg along with other major trace metals including cadmium (Cd), copper (Cu), manganese (Mn), nickel (Ni), and lead (Pb) (recovery efficiency = 100% to 102%) in seawater samples. Seawater samples were first spiked with Ag-109 and allowed to reach isotopic equilibrium before extraction using NOBIAS PA-1 chelating resin. Then, dAg isotope ratios (Ag-109/Ag-107) before and after solid phase extraction were determined and used to quantify dAg. Determination of dAg with dissolved Cd, Cu. Mn, Ni, and Pb in reference seawater material CASS-6 resulted in deviations of between 1.0% and 8.8% from the consensus values, which are well within the standard error of measurement. We then successfully determined the concentrations of dissolved Cd (0.05–0.2 nM), Cu (0.5–13 nM), Mn (10–140 nM), Ni (2–12 nM), Pb (5–110 nM), and Ag (10–40 pM) in Otsuchi Bay, Japan and its surrounding rivers. Evaluation of the behavior of dAg under a salinity gradient using estuarine samples collected from Samunsam River, Malaysia shows increasing dAg concentration with salinity (R² = 0.68), which suggests release of sedimental Ag under high ambient chloride concentrations. Our new method enables rapid and simultaneous measurements of dAg with other key GEOTRACES trace metals in a single analysis, which is expected to expedite analysis and increase availability of oceanic dAg data globally.

New seawater stable oxygen isotope (δ¹⁸O) samples were collected from the southeast Indian Ocean as part of the Coring to Reconstruct Ocean Circulation and Carbon dioxide Across 2 Seas (CROCCA-2S) expedition in November – December of 2018. These data fill a gap in the δ¹⁸O sampling coverage of the southern Indian basin, providing new insights into the hydrologic and oceanographic processes influencing the δ¹⁸O distribution of the region and its relationship to salinity in the upper ocean. Our surface ocean data (<100 m)—in combination with decades of observations from the broader south Indian Ocean—show distinct δ¹⁸O – salinity characteristics on either side of ∼85°E. The balance between evaporation and precipitation yields a strong, robust δ¹⁸O – salinity relationship west of 85°E (δ¹⁸O = 0.50(±0.01) * S – 17.2(±0.22)). However, within the mesoscale eddy field initiated by the Leeuwin Current further east (∼85–120°E), our observations fall along a mixing line between the southwest Indian Ocean and data collected from the Australian coastal margin, illustrating for the first time how the unique eastern boundary system of the south Indian Ocean drives regional-scale variability in the δ¹⁸O – salinity relationship of the surface ocean. A comparison between our observations in the shallow subsurface (100–1000 m) and those from neighboring surveys reinforces this upper ocean connection across the Indo-Australian basin. Antarctic Intermediate Water from the Indian Ocean can be isotopically distinguished from the more regional Tasman Intermediate Water occupying the South Australian Bight, suggesting exchange between the two regions is most prevalent at surface and mode water depths. In deeper waters (> ∼1500 m), we observe a notable 0.87‰ spread in δ¹⁸O. This variability may represent interactions between distinct deep water masses in the region, although additional data are needed to confirm. Overall, our data provide a new look at the hydrography and isotopic chemistry of the southeast Indian Ocean, emphasizing the impact of the region's mesoscale eddy field and its interconnectivity with neighboring basins.

Polysulfides (S_x²⁻) are important reduced sulfur species (RSS) that play a role in numerous environmental processes. A sound analytical method for the measurement of S_x²⁻ in euxinic waters is lacking. In this work, differential pulse voltammetry (DPV) at the Hg electrode was used to measure the presence of S_x²⁻ in a model seawater solution and an euxinic marine lake (Rogoznica Lake - RL Croatia), in which the concentration of RSS, mainly HS⁻, varies between 100 and 4000 μM. In the DPV, an adsorption phenomenon associated with S_x²⁻ reduction on Hg produces a characteristic current minimum at −1.0 V (vs. Ag/AgCl), the magnitude of which is proportional to the concentration of polysulfidic sulfur.

The DPV current minima were recorded in the model solution K₂S_x NaCl/NaHCO₃ (pH ∼ 8.2) in a concentration range from 10 to 100 μM of polysulfidic sulfur. Total RSS was measured by cyclic voltammetry, and sampled DC voltammetry showed the ratio between HS⁻ and S⁰ within the S_x²⁻. Using the same methodology, the presence of S_x²⁻ below the chemocline enriched by photoptrophic sulfur bacteria was measured in the euxinic layer of RL at concentrations of up to 70 μM of polysulfidic sulfur. The results suggest that euxinic RL samples can be considered as polydisperse solutions of S⁰ or of S-rich compounds that can change their physicochemical properties and speciation during sample manipulation. These changes can be detected by electrochemistry. Atomic force microscopy proved the release of bacterial cellular S⁰ during the acidification and purging step in the electrochemical measurements, which contributed to the voltammetric RSS signal.

The fate of microplastics (MPs) in the ocean is mostly driven by (i) photo-oxidation to smaller particles and dissolved constituents, which fuel the dissolved organic carbon pool (plastic-derived DOC, pDOC), and (ii) interactions with organic matter forming sinking aggregates (marine plastic snow). Two separate laboratory experiments were conducted to investigate the two pathways of MPs. In the first experiment, we measured potential rates of microbial pDOC utilization in bottle incubations over 15 days with microbial assemblages from coastal and offshore waters. Microbial utilization of pDOC was more efficient in the coastal (72% bioreactive pDOC) compared with the offshore experiment (32% bioreactive pDOC) 15 days. Changes in bacterial cell abundance and extracellular enzyme activities (glucosidase, peptidase, esterases) indicated that a fraction of pDOC was repackaged into microbial exopolymeric substances (EPS), stimulating growth of known EPS degrading bacteria within the phyla Verrucomicrobiota and Planctomycetota. Microbial EPS likely also played a key role in our second experiment that showed the formation of marine plastic snow in roller tanks with cultured cells of Emiliana huxleyi but not with cells of an Isocrysis sp. culture. Average sinking velocities of marine plastic snow were a factor of 1.2 lower compared with marine snow without MPs. Both aggregate types showed reduced sinking velocities in a density stratified sinking column. Our results from the two experiments on (i) microbial utilization of pDOC and (ii) the formation and sinking of marine plastic snow indicate potential effects of plastic-derived compounds on microbial elemental cycles (i.e., pDOC repackaged into EPS) with consequences for the efficiency of the biological carbon pump (i.e., marine plastic snow reduces carbon export) and the fate of plastic-derived compounds in the ocean.

The pronounced seasonal variation over the Bay of Bengal affects trace metals concentration and distribution. Trace metals distribution in the Bay of Bengal has been best characterized during spring and fall intermonsoon, while limited studies were conducted during the southwest monsoon. This study reports the full-depth profiles of trace metals, including dissolved iron, manganese, lead, cadmium, copper, and zinc (Fe, Mn, Pb, Cd, Cu, and Zn) in the Bay of Bengal (BoB) during southwest monsoon, from July to August 2013. At coastal and ocean scales, transect observations covering the entire water depth provided a comprehensive picture of the circulation and biogeochemical cycles of these elements in seawater during the southwest monsoon. Water samples were obtained from one station in the northeastern Indian Ocean (NR-1) and from three shallow coastal stations with maximum depths <60 m (BA-1, BA-3, and BA-5), as well as from three offshore stations with maximum depths exceeding 2000 m (MY-7, MY-9, and MY-11). In the surface layer (5 m depth), the trace metal concentrations at the shallow near-coastal station BA-5 were higher than those at the ocean station NR-1. Surface trace metal concentrations in offshore regions encompassing stations MY-11, MY-9, and MY-7 were relatively higher than those reported for other seasons in a similar salinity region, indicating seasonal variation associated with freshwater intrusion and coastal-derived input. Below the mixed layer depth, the trace metal/phosphate (P) ratio was higher than that previously reported in the eastern Indian Ocean, suggesting an input from continental margins and mildly reducing sediments, particularly for Fe, Mn, and Cu. Moreover, at intermediate depths (190–800 m), where the North Indian Central Water (NICW) is the main water mass, the Cd/P ratio (0.55 ± 0.11 nmol/μmol) deviated from the global trend (∼0.3 nmol/μmol) owing to oxygen-deficient conditions. Intriguingly, at some stations, specifically MY-9 and MY-7, the intermediate dFe concentrations were relatively higher than those at station NR-1 at the same depth. Continental margin sediment, water mass movement, and ventilation may control the transport of Fe from locations with high Fe concentrations, including near the continental shelf (station MY-11 in this study) and the Andaman Sea.