Seawater Interaction Research Articles

Nanoscale interaction mechanism between bubbles and microplastics under the influence of natural organic matter in simulated marine environment.

Bubble-microplastic (MP) interaction is a significant process that changes the routes of MP circulation in marine environment and thereby determines the risk of MPs, which could be strongly influenced by natural organic matter (NOM) in oceans. However, the quantitative interaction mechanisms between bubbles and MPs under the effect of NOM remain elusive. Herein, bubble-MP interactions in simulated seawater were quantified at nanoscale based on atomic force microscope coupled with the Stokes-Reynold-Young-Laplace model. Bubble-polystyrene (PS)/polyvinyl chloride (PVC) MP interactions exhibited stronger hydrophobic interactions (decay length D0 of 0.60 ± 0.03 nm/0.43 ± 0.02 nm for PS/PVC MP) than polymethyl methacrylate (PMMA) MPs. Humic acid (HA) considerably reduced the D0 of hydrophobic interaction from 0.43-0.60 nm to 0.30-0.32 nm for PS and PVC MPs by introducing oxygen-containing components as evidenced by spectroscopic analysis. In contrast, alginate (Alg) accumulated less on PS/PVC MP surfaces, thereby negligibly affecting the D0 value. While for PMMA MPs, virtually identical D0 values were observed despite the presence of HA/Alg. Therefore, the bubble-driven transport of PS/PVC MPs were modulated by different types of NOM, whereas PMMA MPs could only be slightly affected. This work provides nanoscale insights into quantitative bubble-MP interactions, shedding light on understanding MPs global cycling.

Evolution of a seafloor massive sulfide deposit on axial volcanic ridges: a case study of the Duanqiao hydrothermal field, Southwest Indian Ridge

The mineralization process below the surface of the seafloor in a hydrothermal field has an important influence on the distribution and enrichment of elements. The Duanqiao hydrothermal field (DHF) is located on the new axial volcanic ridge of the ultraslow-spreading Southwest Indian Ridge. Owing to the limited surface sulfide samples, the metallogenic processes occurring below the seafloor surface such as the element enrichment mechanism and the temporal evolution of the sulfide deposits remain unclear. In this study, we conducted mineral texture, geochemical, 230Th/U dating, and laser ablation inductively coupled plasma mass spectrometer analyses of a drill core containing shallow sulfide deposits to study their evolution process. The results revealed that pyrite is enriched in Mn, Co, As, Mo, Ag, Cd, Sb, Tl, and Pb, chalcopyrite is characterized by high concentrations of Se, Sn, In, As, Ag and Pb, and sphalerite is enriched in Co, Ga, Ge, As, Ag, Cd, Sb, and Pb. The 230Th/U dating data suggested five different mineralization periods during 4,552–2,297 years. Apart from the top and bottom, the core exhibited obvious characteristics of gradual accumulation of mineralization. Results revealed that the variations in the elemental contents of different layers and different types of pyrite were controlled by the interaction of seawater and hydrothermal fluids within the sulfide mound over five different mineralization periods. Compared with other hydrothermal fields on other mid-ocean ridges, DHF pyrite is generally enriched in Zn, Pb, As, Ag, Cd, Mo, and Sb, which might reflect shallow subsurface mixing during different periods of hydrothermal activity.

Enrichment of massive sulfdes from the Semenov hydrothermal cluster (Mid-Atlantic ridge) in barite: a result of E-MORB involvement and magmatic contribution

The paper reviews and compares the barite fndings in hydrothermal felds of the mid-oceanic ridges. The genetic signifcance of barite is considered for the Semenov hydrothermal sulfde cluster associated with an oceanic core complex (OCC) at 13°30? N of the Mid-Atlantic Ridge. Massive sulfdes of the Semenov-1, -3, and -4 felds are enriched in barite (up to 20 vol. %) and therefore Ba (up to 4.12 wt. %). The presence of a signifcant amount of barite and a high Ba content of massive sulfdes of the OCC-related felds link their formation with E-MORBs. Magmartic contribution for the formation of massive sulfdes from some Semenov felds is supported by negative values of S isotopic composition of sulfdes associated with barite, the presence of magmatic gases (CO2 and SO2) in Raman spectra of fuid inclusions in barite and the results of physicochemical modeling, which indicate the formation of barite-sulfde assemblage upon the interaction of E-MORBs, seawater, and magmatic gas. The results of modeling of the system with felsic rocks show that oceanic plagiogranites from OCC structure could be an additional supplier of Ba.

Impact of submarine volcanic versus hydrothermal activity onto the strontium and lithium isotopic signatures of the water column (TONGA)

During the TONGA cruise (2019), seawater samples were collected to assess the effect of volcanic eruption versus submarine hydrothermal system on the water column. For this purpose, two locations were investigated, the first one located directly under the influence of the New Late’iki island (eruption in October 2019), and the second one showing ongoing submarine hydrothermal activity. At both locations, the total strontium (TSr) and lithium (TLi) concentrations vary between 94.4 and 152.3 µmol/L and 13.2 and 203.5 µmol/L, respectively. When combined, TSr and TLi concentrations of all samples in the water column are higher than those of the oligotrophic water. Both volcanic eruption and submarine hydrothermal activity (e.g. volcanic ashes, particles, gas condensate) can deliver substantial amount of TSr and TLi to the water column. The distribution of TSr versus TLi evidences linear trends either with a negative or positive slope. The negative correlation is observed in the water column at both sites, directly under the influence of the eruption and in the vicinity of the volcano with hydrothermal activity. The positive TSr versus TLi correlation is observed at site under submarine hydrothermal influence and is in line with black smokers related hydrothermal plumes. The 87Sr/86Sr ratios vary between 0.709147 and 0.709210 and δ7Li values vary between +10.1 and +37.6 ‰. While 92% of the measured 87Sr/86Sr ratios are in line with the mean value of oligotrophic waters, once combined with the δ7Li values, only 20% of them remains within this field. The wide range of δ7Li values decreases from sea-surface down to ~140 mbsl, before increasing at greater depth, while defining different linear trend according to the dissolved inorganic carbon concentrations. The variability of δ7Li values reflect hydrothermal contribution, mineral–seawater interaction and potentially biology–environment interaction. In the particular geological setting of the study, where both hydrothermal and volcanic activities were at play, disentangling both contributions on water column implies a combined use of elemental and isotopic signatures of Sr and Li tracers.

Identification of stiffness and damping characteristics of magnetorheological elastomers due to immersion in seawater

ABSTRACT Magnetorheological elastomer (MRE) materials are commonly used as vibration dampers in offshore structures. Therefore, it is urgent to investigate the degradation of this smart material because of seawater interaction. This work focuses on the immersion of MRE material in seawater, which alters its rheological and mechanical characteristics. Hence, it is important to investigate the impact of seawater immersion on the rheological characteristics of substances. This study contributes to the assessment of the stiffness and damping characteristics of MRE materials after exposure to seawater for one year. The MRE samples comprise MRE with a silicone matrix devoid of any Carbonyl Iron Particle (CIP) and MRE with 70% CIP, exhibiting both isotropic and anisotropic properties. Immersing the subject in seawater was carried out for one year. The study involved doing multiple tests, such as scanning electron microscope (SEM), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and rheological testing. The findings indicated that the samples underwent harm, erosion, and deterioration of their rheological characteristics during immersion. The stiffness values for isotropic MRE and anisotropic MRE decreased by 97% and 11%, respectively. Meanwhile, the deterioration of the damping characteristics values of isotropic MRE and anisotropic MRE was 96% and 14%, respectively.

Geochemical constraints on depositional environment of metacarbonate rocks from the Neoproterozoic Cauvery Suture Zone, Southern Granulite Terrane, India

ABSTRACT Metacarbonates serve as proxies for understanding the chemical oceanography of the present, as well as the past-day ocean’s evolution history and these are extensively described in the Neoproterozoic-Cambrian collisional belts of East Gondwana. The Cauvery Suture Zone (CSZ), Southern Granulite Terrane (SGT), India, is one such prominent example of their occurrence, along with several Precambrian dismembered ophiolites, arc-related intrusions and other metamorphic rocks. These are dominantly exposed in the western, southern and south-central parts of the suture, around the Neoproterozoic Kadavur Gabbro-Anorthosite and Manamedu Ophiolite Complexes. Their whole-rock geochemistry reveals the protoliths of metacarbonates have been derived from different sources of continental inputs and deposited under open to passive margin settings. The δ13C(V-PDB)) - δ18O(V-SMOW) data (−0.01 to + 3.03‰; +15.81 to + 24.84‰) reveal as high-temperature carbonates of typical limestone variety, deposited under warmer palaeoclimatic conditions of the marine environment and later subjected to metamorphism. The presence of higher 87Sr/86Sr ratios (0.707514 to 0.71511) and negative εNd values (−17.3 to −10) suggests that they originated from large crustal inputs with more interactions of seawater with the sediments, evolved during Ediacaran to early Cambrian periods. The above results reveal that these are possible remnants of the Neoproterozoic Mozambique Ocean and coeval with the metacarbonates of Sør Rondane Mountains-East Antarctica, Highland Complex-Sri Lanka, Madagascar and Mozambique Belts of Neoproterozoic Gondwana.

Identifying seawater interaction with coastal aquifers using hydrochemical and GIS for Nagapattinam district, southeast coast of India

Groundwater chemistry of the two different seasons collected between 2020–2021 from the coastal areas of Nagapattinam, Mayiladuthurai and Karaikal in Tamil Nadu state of southeast India were evaluated for seawater intrusion into coastal aquifers. Groundwater types, its classification was evaluated to know the extension of seawater intrusions into coastal aquifers using the Groundwater Quality Indices (GQI) such as GQIPiper(mix), GQIPiper(dom), fsea, GQIfsea and GQISWI. Piper diagram grouped most samples (GQIPiper(mix) and GQIPiper(dom)) in domain-II, representing Na-Cl water type, followed by domain-IV, indicating mixed Ca-Mg-Cl water for both the seasons. As measured by the saltwater Intrusion as Groundwater Quality Index (GQISWI), about 62.5 % and 37.5 % of the pre-monsoon samples showed low saltwater intrusion and moderate seawater intrusion, respectively. In the post-monsoon samples, the low saltwater intrusion increased to around 82.5 % and the moderate seawater intrusion decreased to 17.5 % of the groundwater samples. The GIS framework was used to display the geographical distribution of groundwater types as well as the delineation of vulnerable zones from seawater intrusion.

Distinct diversity, assembly, and co-occurrence patterns of the prokaryotic microbiome in coral ecosystems of the South China Sea

Coral reefs are among the most energetic marine ecosystems, taking a place in ecological balance. Microbes participate in the energy exchange in coral ecosystems, which may affect coral resistance and resilience. However, there is still a lack of understanding regarding the microbial structure between corals and seawater. In this study, microbial structure and interactions in coral and seawater were studied using quantitative PCR and high-throughput sequencing. We found that the abundance and diversity of microbes in corals were higher than those in seawater. Corals, as nonfluidic ecosystems, limited the dispersal of microbes, causing broader stochasticity in the ecological shaping process, whereas ecological drift and homogeneous selection were the most important assembly mechanisms in seawater. The microbial niche width was larger in the coral group than in the seawater group, indicating strong adaptability. A group of microbes (e.g., Caldilineaceae, Burkholderiaceae, and Nitrosopumilaceae) may become microbial indicators which differentiate seawater samples (e.g., SAR11 and SAR86 clades, Cryomorphaceae), which may be due to separated habitats and nutrition. Coral microbes may participate in nitrogen-metabolism to maintain a nitrogen limited microenvironment. Nodes linked in the coral co-occurrence network showed coexisting interactions and higher complexity based on the comparison of topological values. Collectively, significant differences in microbial fractions were demonstrated observed in terms of diversity, composition, co-occurrence patterns, assembly processes and predicted functions between coral and seawater samples, showing potential microbial interactions and providing in-depth insights into the metacommunity diversity in coral reef ecosystems.

Effects of Wind Speed on Size-Dependent Morphology and Composition of Sea Spray Aerosols.

Variable wind speeds over the ocean can have a significant impact on the formation mechanism and physical-chemical properties of sea spray aerosols (SSA), which in turn influence their climate-relevant impacts. Herein, for the first time, we investigate the effects of wind speed on size-dependent morphology and composition of individual nascent SSA generated from wind-wave interactions of natural seawater within a wind-wave channel as a function of size and their particle-to-particle variability. Filter-based thermal optical analysis, atomic force microscopy (AFM), AFM infrared spectroscopy (AFM-IR), and scanning electron microscopy (SEM) were employed in this regard. This study focuses on SSA with sizes within 0.04-1.8 μm generated at two wind speeds: 10 m/s, representing a wind lull scenario over the ocean, and 19 m/s, indicative of the wind speeds encountered in stormy conditions. Filter-based measurements revealed a reduction of the organic mass fraction as the wind speed increases. AFM imaging at 20% relative humidity of individual SSA identified six main morphologies: prism-like, rounded, core-shell, rod, rod inclusion core-shell, and aggregates. At 10 m/s, most SSA were rounded, while at 19 m/s, core-shells became predominant. Based on AFM-IR, rounded SSA at both wind speeds had similar composition, mainly composed of aliphatic and oxygenated species, whereas the shells of core-shells displayed more oxygenated organics at 19 m/s and more aliphatic organics at 10 m/s. Collectively, our observations can be attributed to the disruption of the sea surface microlayer film structure at higher wind speeds. The findings reveal a significant impact of wind speed on morphology and composition of SSA, which should be accounted for accurate assessment of their climate effects.

Effects of the 2021 La Palma volcanic eruption on groundwater hydrochemistry: Geochemical modelling of endogenous CO2 release to surface reservoirs, water-rock interaction and influence of thermal and seawater

Volcanic islands face unique challenges in protecting and managing their water resources due to their small size, limited freshwater availability, and vulnerability to natural hazards. The recent 2021 eruption of the Tajogaite volcano on La Palma Island in the Canary Islands, Spain, raised concerns regarding the potential impact on groundwater hydrochemistry. This work aimed to characterize and model the processes that lead to the measured hydrochemical impacts in the groundwater of La Palma as a consequence of the volcanic eruption. The study involved conducting three groundwater sampling campaigns during the eruption, and six after the eruption ceased. A total of 15 monitored points, including piezometers, wells, water galleries, and the main gully collector of the island, all relatively close (2 to15 km) to the erupted volcano, were sampled for the analysis of major solutes and SiO2. Unpublished hydrochemical data previous to the eruption were provided by the local water management authorities of La Palma (CIALP) and the Geological Survey of Spain (IGME). Statistical analyses were performed to assess the differences in groundwater composition before, during, and after the eruption, and a Principal Component Analysis (PCA) mixing model was calculated. Three compositional extreme waters were defined as end members in the system: (1) a high SiO2 computed thermal end member; (2) a low salinity computed fresh groundwater; (3) and seawater. The results of the mixing model showed two main events of maximum mixing ratios in the fresh groundwater reservoirs of La Palma after the eruption; the first one of seawater in July 2022, and the next one of thermal fluids in December 2022. This water mixing during and after the eruption, together with a volcanic CO2 input to the reservoirs, led to significant increases in the concentrations of Na, Ca, SiO2 and SO4 in fresh groundwater, as well as a drop in pH. The significance of these findings relies in improving our understanding of the effects of volcanic eruptions on groundwater, emphasizing the necessity for frequent monitoring and evaluation, given the scarcity and vulnerability of groundwater resources in volcanic islands.

Mineralogical Evolution of High-pH/Low-pH Cement Pastes in Contact with Seawater

In facilities for the geological disposal of radioactive waste in coastal areas, the long-term alteration of cementitious materials in engineered barriers is expected to occur due to the ingress of groundwater derived from seawater. Although the reaction between cement and seawater has been studied, the alteration behavior caused by the reaction between seawater and low-pH cement, which is expected to be used in a disposal facility, has not yet been clarified. In this study, the effects of cement type on cement–seawater interactions were investigated, and the chemical stability and mineral evolution of cement pastes caused by reactions with seawater were determined. The dissolution of cement hydrates occurred upon increased contact with seawater, and the formation of secondary minerals, including carbonate and Mg-containing minerals, was observed. The progress of dissolution depended on the mineral composition of the initially formed cement hydrates, and low-pH cement containing pozzolanic materials showed less resistance to seawater. Differences in pH and Si concentration that are due to the type of cement used had a strong influence on the evolution of minerals (especially Mg-containing minerals), implying that the formed mineral species possibly affect the migration characteristics of radionuclide.

Ligand exchange provides new insight into the role of humic substances in the marine iron cycle

Organic complexation of iron plays a crucial role in preventing its precipitation, facilitating its transport, and modulating its reactivity and bioavailability in natural waters. Although humic substances (HS) complexes serve as the primary source of terrestrial iron reaching ocean waters, the transition from Fe-HS species to other forms of organic complexation with ocean autochthonous ligands has not yet been properly described. Taking advantage of the electrolability of Fe-HS complexes, we monitored the ligand exchange of iron-saturated Suwannee River fulvic and humic acids (SRFA and SRHA) after the addition of desferrioxamine B (DFOB) and other ligands for comparison. We observed that Fe-HS concentrations gradually decreased until reaching an apparent steady state, typical of a reversible reaction within 1 to 15 h. The dissociation kinetics and species partitioning of Fe-SRHS complexes at the equilibrium showed some features contrary to the current paradigm of HS iron complexation. The affinity of SRFA to bind iron is close to that of DFOB and for SRHA is even higher. The heterogeneity of the HS iron binding groups was confirmed, although experiments in NaCl solutions revealed that in seawater it is substantially caused by the interaction of major divalent ions. The different dissociation kinetics of Fe-SRHS complexes obtained with different competing ligands and the absence of Fe-DFOB dissociation in the presence of iron-free SRFA indicate an intimate associative mechanism of ligand exchange, with the presence of a ternary complex (SRHS-Fe-DFOB) that does not form if the departing complex is Fe-DFOB. We hypothesize that at the concentrations of HS and siderophores found in the open ocean, iron ligand exchange is limited and organic iron speciation will be close to being regulated on a “first come, first served” basis. Experiments conducted under saturation of all iron complexes support the formation of a permanent concentration of a ternary complex. Our findings show the real complexity of cation-ligand interactions in seawater, with implications for the interpretation of recent chromatographic and electrochemical measurements and for the understanding of iron partitioning in the presence of ubiquitous HS.

Incorporation of the riser-seabed-seawater interaction effects into the trench formation and fatigue response of steel catenary risers in the touchdown zone

The existing Steel Catenary Riser (SCR)-seabed interaction models do not account for the contribution of seawater as a key influential factor. The present study has examined the effect of SCR-seabed-seawater interaction on the trench enlargement and consequently on the fatigue performance of the SCR in the touchdown zone (TDZ). Coupled Eulerian-Lagrangian (CEL) analysis with three domains of SCR, seabed soil, and seawater were performed using ABAQUS. A parametric study was conducted to investigate the impact of seawater interaction along with incorporation of the shear strain rate and softening effects. The conventional bearing capacity approach for analysing pipe penetration into the seabed was also reviewed, and modifications were proposed to account for the effects of water entrainment into the trench. The results obtained from CEL analysis were integrated with a global SCR model to incorporate the SCR-seabed-seawater interaction effects into the fatigue analysis. The study showed that the entrainment of seawater into the trench can be coupled with SCR oscillations to further soften the seabed and erode the trench resulting in an enlarged trench profile affecting the fatigue damage in the TDZ.

Evolution mechanism of permeability of hot dry rock under coupled effect of thermal fatigue and seawater interaction during coastal geothermal development

Using seawater as a heat transfer fluid for developing hot dry rock (HDR) geothermal energy in coastal areas is a frontier of engineering worth exploring; however, only a few studies have considered this research topic. During the development of HDR based on enhanced geothermal system (EGS) technology, the thermal shock fatigue effect of low-temperature seawater on high-temperature reservoirs leads to changes in the permeability of the HDR, notably impacting the reservoir reconstruction design and heat transfer efficiency. Accordingly, the changes in pore structure, pore distribution, porosity, and permeability of HDR in the Guangdong-Hong Kong-Macao Greater Bay Area were investigated based on nuclear magnetic resonance (NMR) techniques and fractal theory after treatment to different temperatures and numbers of thermal shocks due to seawater interaction. The experimental results showed that with an increase in temperature and the number of seawater interactions, the pore structure distribution of the HDR underwent significant changes, with the proportion of mesopores and macropores increasing by 24.29 % and 10.52 %, respectively. Moreover, the porosity and permeability increased with increasing temperature and number of thermal shock cycles, especially above 300 °C. When the temperature increased from 100 °C to 500 °C, the total porosity increased from 0.98 % to 3.85 %, an increase of 292.9 %, while the permeability increased from 10−4 mD to 0.1 mD, an increase of nearly 1000 times. Changes in the pore structure, pore distribution, porosity, and permeability of HDR are caused by multiple damage mechanisms related to high-temperature nonlinear expansion, thermal shock effects, chemical erosion, and fatigue. Additionally, the permeability of the HDR after seawater treatment at the same heat treatment temperature and number of thermal shocks was higher than that after freshwater treatment. At a temperature of approximately 500 °C and 20 thermal shocks, the permeability of HDR under the action of seawater was approximately seven times that of fresh water. Therefore, these results suggest that using seawater as a heat transfer fluid has more advantages in enhancing the permeability of reservoirs.

Lithium isotope systematics and water/rock interactions in a shallow-water hydrothermal system at Milos Island, Greece

The active venting fluids of Milos Island, located within the southern Aegean Sea, belong to a shallow-water hydrothermal system (< 200 m depth) that shows chemical compositions and evolution processes comparable to those of mid-ocean ridges (MOR). In this study, we analyze Li and δ7Li in 69 vent water samples, grouped into two types based on their salt content. The low-Cl end-member (EM) Cave fluids show a relatively high Li content (0.39–0.54 mM) with MORB-like δ7Li (∼4.5 ‰, MORB = 3.7 ‰) compared to that of seawater, and the high-Cl brine fluids contain remarkably high Li (6.14–10.6 mM) and variable δ7Li (1.4–8.7 ‰). The latter fluids may have derived from metamorphic basement modified by seawater interactions at ∼300 °C. A scenario using a steady-state dissolution/precipitation model can generate consistent Li and δ7Li patterns, where linear correlations of Cl and Li suggest phase separation occurred after water/rock interaction at depth. On the contrary, no significant δ7Li variation in most Milos fluids suggests limited isotopic fractionation occurred during phase separation. More importantly, the detected Li enrichment in the high-Cl fluids implies a large Li flux, ∼3.4 × 107 mol/yr, to the ocean from the Milos system. Assuming that 10% of the world's shallow-water systems discovered to date have similar Li outputs to those of Milos, this Li flux would represent ∼1.8% of MOR hydrothermal fluxes which is on the order of ∼13 × 109 mol/yr. These results emphasize the importance of Li flux derived from shallow-water hydrothermal systems, which should not be excluded from the calculation of the marine Li budget and its impact on the global silicate weathering cycles.

Groundwater chemistry and entropy weighted water quality index of tsunami affected and ecologically sensitive coastal region of India

Quality groundwater is the most essential prerequisite for the better livelihood of the coastal villages and a vital resource for a safe living. Seawater interaction and coastal inundation modify hydro geochemical cycles leading to gross utility as a challenge. Poor quality water intake causes diseases and seriously affects human health. In this study, the suitability of shallow drinking water sources (10–15 m) has been studied with a focus on coastal village in south west of India (Alappad coast, Kollam, Kerala) which is a host of huge placer mineral reserve of the country. This coastal stretch has good deposition of Late Quaternary sediments of heavy mineral placers subjected to severe seawater interactions. Mineralogically, garnet and heavy minerals comprises the beaches and most coastal plains of the Alappad. A concerted geological process where moving water and waves causes erosion, leads to lowering of the earth's surface -is prominent in this fragmented land. This study critically evaluates the temporal-spatial impact of these interactions in an age of varying climatic conditions and hence for reference beyond. Water quality index analysis has been attempted using the entropy weighted water quality index (EWQI) method for a total of 45 samples (15 samples season-wise). It aims to ascertain better choices of groundwater sources for domestic uses for isolated settlers endowed with estuaries, and old coastal plains with barrier beaches. Irrigation suitability was evaluated using sodium adsorption ratio (SAR) and Na%. Observed EWQ Indices (38.2 ± 14.5) for post-monsoon (80% samples), (66.1 ± 77.7) for monsoon (66% samples), and (71.4 ± 71.3) for pre-monsoon (53% samples) fall in excellent category. Post-monsoon is most favoured for a better quality groundwater as evidenced by WQI of 80% among the samples tested. Ca–HCO3 is the dominant hydrochemical type observed. The mean value of iron (0.9 ± 1.3 mg/L) exceeded the permissible limit of 0.3 mg/L during monsoon season due to mineral-water interactions. In pre-monsoon season the parameters Na+ (95.9 ± 200.7 mg/L), Cl− (173.4 ± 510.2 mg/L), EC (1559.3 ± 2510.6 μS/cm), and TDS (492.5 ± 629.7 mg/L) were observed in higher ranges. Significant correlation (p < 0.05) prevailed between EWQI, and parameters-conductivity (0.75), TDS (0.75), Iron (0.59), Ca2+ (0.66), and Mg2+ (0.74). Principal component analysis (PCA) on chemical parameters accounted for the total variance of 84.2% in pre-monsoon, 89.9% in monsoon and 82.9% in post-monsoon. Groundwater quality is influenced by geochemical processes, salt intrusion, and human activities like fertiliser application and domestic sewage discharge. Hierarchical cluster analysis (HCA) grouped the samples into three clusters. Cluster 3 represents poor quality water (13%) in pre-monsoon (EWQI ranged 32.2–192.7), and monsoon (EWQI ranged 171.8–309.7). Cluster 3 in post-monsoon (20%) indicating good water quality (EWQI ranged 51.4–72.6). Ultimate finding is that post-monsoon groundwater is more suitable for drinking and domestic purposes for the selected coastal area.

Groundwater hydrogeochemical assessment in and around the northern part of the Chennai city, South India

In the present study, 50 groundwater samples from the bore wells and tube wells, were collected in North Chennai, Tamil Nadu, India during the premonsoon (June 2021) and postmonsoon (January 2022) seasons and their physicochemical properties were assessed. The majority of the physicochemical characteristics with the exception of electrical conductivity (EC), total dissolved solids (TDS), sodium (Na+), chloride (Cl-) and sulphate (SO42-) were determined to be within the world health organization (WHO) standards for drinking water. The water quality index (WQI) was assessed and given one of six categories, from excellent to unfit for consumption. Gibb's plots showed that evaporation was the dominating type, while Piper and Chadha models predominantly showed sodium-chloride (Na-Cl) kinds. The interaction of freshwater and seawater has been observed through an ionic ratio analysis. In accordance to a groundwater quality research conducted in the study region, practically in all the sample locations, the levels of standard plate count (SPC) total coliforms (TC) bacterial contamination were higher than the acceptable guidelines (WHO). Water management and treatment policy decisions can be made with the support of water quality analysis which can also help to identify potential health issues.

Atmosphere injection of sea salts during large explosive submarine volcanic eruptions

The 15 January 2022 submarine eruption at Hunga volcano was the most explosive volcanic eruption in 140 years. It involved exceptional magma and seawater interaction throughout the entire submarine caldera collapse. The submarine volcanic jet breached the sea surface and formed a subaerial eruptive plume that transported volcanic ash, gas, sea salts and seawater up to ~ 57 km, reaching into the mesosphere. We document high concentrations of sea salts in tephra (volcanic ash) collected shortly after deposition. We also discuss the potential climatic consequences of large-scale injection of salts into the upper atmosphere during submarine eruptions. Sodium chloride in these volcanic plumes can reach extreme concentrations, and dehalogenation of chlorides and bromides poses the risk of long-term atmospheric and weather impact. Salt content in rapidly collected tephra samples may also be used as a proxy to estimate the water:magma ratio during eruption, with implications for quantification of fragmentation efficiency in submarine breaching events. The balance between salt loading into the atmosphere versus deposition in ash aggregates is a key factor in understanding the atmospheric and climatic consequences of submarine eruptions.

Shifts in bacterioplankton community structure between dry and wet seasons in a tropical estuary strongly affected by riverine discharge

Estuaries are among the most productive ecosystems in the world and are highly dynamic due to the interaction of freshwater and seawater, which results in strong spatial gradients in physico-chemical conditions. Bacterioplankton play a central role in these systems, driving the fluxes of carbon and energy, and being central for contaminant removal in human-impacted areas. Most studies on bacterioplankton dynamics have been carried out in temperate estuaries, and they show that salinity is a major factor driving bacterioplankton distribution. Tropical estuaries, although largely understudied, experience drastic variations in river discharge between the dry and the rainy seasons, influencing the spatial distribution of the salinity gradient and thus likely impacting bacterioplankton communities. Using Illumina sequencing of the 16S rRNA gene, here we studied bacterial communities from the Nicoya's Gulf (Costa Rica), a large tropical estuary characterized by high riverine discharge during the rainy season, to explore seasonal changes in the spatial distribution and connectivity of these communities along the Gulf. Our results show pronounced differences in bacterial diversity and community structure between seasons and zones within the estuary (the shallow upper Gulf, the middle zone and the lower zone, located in the marine end of the estuary). Bacterial communities from the different regions were more similar during the rainy season, suggesting a larger degree of microbial connectivity likely driven by the fast water circulation fueled by the riverine discharge. In the dry season, Enterobacteriales and Cyanobacteria dominated bacterial communities, whereas in the rainy season Alphaproteobacteria was the dominant group. These contrasting seasonal trends were consistent with the seasonal variations observed in bacterial assemblages during a year at a single station in the upper region of the Gulf. We conclude that the Gulf is highly dynamic in both the spatial and temporal scale and that bacterioplankton communities are strongly influenced by the riverine and tidal inputs during both seasons. This study sheds light on the sources of variability in the structure of bacterial communities in tropical estuarine systems, an understudied type of aquatic ecosystem, and sets the basis to design further comprehensive studies on their microbial diversity.

Interaction of seawater with (ultra)mafic alkaline rocks—Alternative process for the formation of aegirine

Abstract Submarine mafic and relatively Na-poor alkaline rocks in the Outer Carpathians often contain aegirine, a sodic pyroxene usually found in differentiated alkaline rocks. Its presence in rocks that are too basic and Na-poor for its conventional magmatic appearance is linked to sodic alteration of submarine alkaline rocks. Aegirine crystals grow on altered rims of diopside, commonly with crystal-lographic unconformity, suggesting that their growth was related to alteration and that aegirine does not represent a late stage of continuous clinopyroxene crystallization. The U-shaped REE patterns in the studied aegirine lack Eu anomaly, characteristic for aegirine from differentiated alkaline rocks. Therefore, the involvement of chemically more evolved magma is unlikely to have played any role in the formation of aegirine in ijolites and essexites. Formation of aegirine in submarine alkaline rocks may thus represent an alternative process to spilitization. However, this process is strongly limited by the availability of Fe3+ oxidized and mobilized by hydrothermal alteration, which may explain a relative scarcity of aegirine observed in submarine alkaline rocks compared to near-complete albitization of spilites, and its absence in high-MgO rocks (&amp;gt;10 wt%). Due to the blocking effect related to Fe3+ unavailability, ijolites, and essexites do not display significant Na enrichment. We posit that Na incorporated in aegirine was mainly sourced from the zeolitized interstitial glass.