Salinity Variations Research Articles

Large-scale culturing of the subpolar foraminifera Globigerina bulloides reveals tolerance to a large range of environmental parameters associated to different life-strategies and an extended lifespan.

The subtropical to subpolar planktic foraminifera Globigerina bulloides is a calcifying marine protist, and one of the dominant foraminiferal species of the Nordic Seas. Previously, the relative abundance and shell geochemistry of fossil G. bulloides have been studied for palaeoceanographic reconstructions. There is however a lack of biological observations on the species and a poor understanding of its ecological tolerances, especially for high latitude genotypes. Here, we present observations from the first extensive culturing of G. bulloides under subpolar conditions, including the first low temperature (6-13°C) and variable salinity (30-38) experiments. Carbonate chemistry (pH and [CO3 2-]) was also manipulated. Experimental conditions were chosen to reflect a range of plausible past and future scenarios for the Nordic Seas. We found G. bulloides to be tolerant of environmental conditions well outside their optimal range (<10°C, salinity <33, pH <8). Observed life span was up to three months, which was attributed to a microalgal diet. Two alternative life strategies were employed, whereby individuals either experienced rapid growth and death, or a prolonged lifespan with minimal growth and death via slow decay. We posit this could help explain differences in geochemical signals recorded from different size fractions of fossil specimens used for palaeoceanographic reconstructions.

Characterizing Subsurface Oxygen Variability in the California Current System (CCS) and Its Links to Water Mass Distribution

AbstractThe california current system (CCS) supports a wide array of ecosystem services with hypoxia historically occurring in near‐bottom waters. Limited open ocean data coverage hinders the mechanistic understanding of CCS oxygen variability. By comparing three different models with varying horizontal resolutions, we found that dissolved oxygen (DO) anomalies in the CCS are propagated from shallower coastal areas to the deeper open ocean, where they are advected at a density and velocity consistent with basin‐scale circulation. Since DO decreases have been linked to water mass redistribution in the CCS, we conduct a water mass analysis on two of the models and on biogeochemical Argo floats that sampled multiple seasonal cycles. We found that high variability in biogeochemical variables (DO and nutrients) seen in regions of low variability of temperature and salinity could be linked to water mass mixing, as some of the water masses considered had higher gradients in biogeochemical variables compared to physical variables. Additional DO observations are needed, therefore, to further understand circulation changes in the CCS. We suggest that increased DO sampling north of 35˚N and near the shelf break would benefit model initialization and skill assessment, as well as allow for better assessment of the role of equatorial waters in driving DO in the northern CCS.

Modeling and characterization of shallow aquifer water based on ion concentrations to salinity variations using multivariate statistical approach

Water chemistry data (1965–2015) from the Chicot and Evangeline aquifers in Nueces and Kleberg counties of Texas were analyzed to assess the hydrogeochemical processes based on variations in ion concentrations affecting groundwater salinity levels in those coastal aquifers. A further aim of this study was to identify a proxy using major-ion concentrations to predict groundwater salinity. Correlation analysis suggests that the hydrogeochemical processes operating in these aquifers differ significantly. In principal component analyses, the first three principal components explain 91% and 94.8% of the total variabilities of the variation of groundwater chemistry in the Evangeline and Chicot aquifers, respectively. The rotated factors (factors 1, 2, and 3) using the varimax rotation method implied that depth control and salinity variations predominantly cause the highest variabilities in water chemistry in the Chicot and Evangeline aquifers in the study area. Results showed depth control on water quality parameters was more pronounced in the Evangeline aquifer compared to the Chicot aquifer. Stepwise elimination of the least significant predictors to identify the proxy for groundwater salinity revealed chloride (Cl) could be the most significant predictor to estimate groundwater salinity variations in both aquifers. However, regression models generated from 75% of the training datasets predicted total dissolved solid (TDS) variations with 78% and 43% accuracies in Chicot and Evangeline aquifers, indicating that Cl can be considered the proxy for the Chicot aquifer only but not suitable for the Evangeline aquifer in the study area.

Reconstructing salinity and redox variation of permian Lucaogou Formation in the Jimsar Sag, the Junggar Basin, China: Combining trace elements and biomarkers as proxies

The variation in paleosalinity and paleoredox affect the production and preservation of organic matter. The study of ancient salinity and redox conditions of source rocks is of great significance for the enrichment of organic matter and the exploration of petroleum resources. In this paper, the commonly proxies for paleosalinity and paleoredox are distinguished and discussed. The paleosalinity and paleoredox of the Lucaogou Formation in the Jimsar Sag of the Junggar Basin are reconstructed by combining the minerals, corrected elements, biomarkers and isotope indicators. Research suggests that the gammacerane index, carbon and oxygen isotopes, corrected Sr/Ba, and Mg/Al can be used to evaluate the paleosalinity of the Lucaogou Formation. Among the commonly used redox proxies, only V/Cr, U/Th, and VEF can be used to evaluate the redox conditions of the Lucaogou Formation, and their thresholds have been corrected. The paleo-sedimentary environment of the Lucaogou Formation has undergone frequent changes and is generally in a brackish and reductive environment. The paleo-sedimentary environment is an important influencing factor for the enrichment of organic matter of the study area. A relative higher salinity and reduction environment is conducive to the organic matter enrichment and high-quality source rocks formation in the Lucaogou Formation.

Atlantic Niño induced sea surface salinity variability as observed from the satellite

The Atlantic Niño exerts great impact on surrounding weather and climate anomalies, leading to anomalous wind, temperature, precipitation, etc. However, the impact of Atlantic Niño on ocean salinity in the tropical Atlantic has not been well disclosed. The present study examines the Atlantic Niño induced sea surface salinity (SSS) distribution in both boreal summer and winter seasons by using the satellite data as well as various reanalysis and objective analysis data sets. It concludes that the summer Atlantic Niño leads to large fresh SSS anomalies in the eastern equatorial basin, while the winter Atlantic Niño leads to a meridional dipole structure of SSS anomalies. The former is mostly controlled by the dynamical processes of ocean, while the latter is largely controlled by the atmospheric processes. Accordingly, two SSS indices are developed to describe the relationships in the two seasons. The present study advances our understanding of the Atlantic Niño and its associated SSS variability and reveals the possible deficiencies of current reanalysis and objective analysis data sets in the tropical Atlantic Ocean.

Variable salinity induced physio-chemical and chlorophyll a fluorescence responses in Kappaphycus alvarezii, a commercial carragenophyte

Variable salinity induced physio-chemical and chlorophyll a fluorescence responses in Kappaphycus alvarezii, a commercial carragenophyte

The bacterial influencing mechanisms of salinity fluctuations in a brackish-water lake on the dissolved organic matter characteristics of pore water

The dissolved organic matter (DOM) components in lake water have been widely studied; however, few previous studies have considered the growth of Phragmites australis in brackish lakes. It has not been well understood how salinity variations influence the DOM compositions in pore water and its bacterial mechanisms in lakes with Phragmites australis. This experiment included three salinity groups (1,200 mg/L, 3,600 mg/L, and 6,000 mg/L) to study the interactions between bacteria and DOM in pore water under a salinity gradient. The results showed that the maximum fluorescence intensity (Fmax) of DOM measured by excitation-emission fluorescence spectroscopy decreased with increasing salinity. Higher salinity reduced the Fmax of protein-like substances and resulted in DOM becoming more aromatic. Salinity affected DOM composition due to the responses of functional bacterial communities. Thiobacillus was salt-tolerant and dominated in the sediments, and its relative abundance was negatively correlated with the Fmax of protein-like components. The relative abundance of Flavobacterium showed a positive correlation with salinity and a negative correlation with the Fmax of the fulvic acid-like component. Pseudomonas, Brevundimonas, and Polaromonas were negatively correlated with salinity and the Fmax of the fulvic acid-like component, while being positively correlated with the Fmax of tyrosine-like and aromatic protein substances. Higher salinity inhibited the metabolism gene modules of tryptophan and tyrosine. The results of this study may offer a novel perspective on comprehending the biochemical cycling of fluorescent DOM, encompassing tryptophan-like, tyrosine-like, and fulvic acid-like components in brackish lakes with fluctuating salinity.

Effect of salinity on fads2 and elovl gene expression and fatty acid profile of the euryhaline flatfish Paralichthys orbignyanus

Paralichthys orbignyanus, a commercially important flatfish, presents in its natural environment, significant variations in salinity and fatty acid composition of its diet. In this work, we aimed to study the impact of salinity on the genetic expression of fads2 and elovl and its reflection in the muscle fatty acid profile of the fish. Since genetic resources for this species are absent, we performed hepatic transcriptome sequencing (mRNA-Seq) and conducted de novo assembly to obtain the novel transcripts of fads2 and elovl. The sequences obtained were used to analyze possible changes in the genetic expression of these enzymes in juvenile P. orbignyanus when cultured at four salinities (2, 10, 18 and 26 ppt) fed on a diet rich in 18:3n-3 and 18:2n-6 but poor in LC-PUFA. Results showed that salinity has a significant modulatory effect on fads2 gene expression, with an increase at 2 ppt salinity. Total lipid content in fish muscle decreased when moving away from the isosmotic point (10.9 ppt) suggesting higher energetic demands at 2, 18 and 26 ppt. This effect was also evident for specific fatty acids, such as 16:1n-7, 16:2n-3, 18:4n-3, 20:1n-9, 20:4n-3 and 20:5n-3. Interestingly, some fatty acids, particularly total MUFA, 18:2n-6 and 22:6n-3 presented a dichotomous profile between lower and higher salinities, suggesting the adaptation of P. orbignyanus to different environmental salinities. This study highlights the remarkable ability of P. orbignyanus to adapt to a wide range of salinities demonstrating the strong euryhalinity of this species. The observed salinity effects hold potential significance for its application in aquaculture.

Variations of salinity during reproduction and development affect ontogenetic trajectories in a coastal amphibian.

Although coastal ecosystems are naturally submitted to temporal variations of salinity, salinization has been increasing over time threatening coastal biodiversity. Species that exploit such habitats can thus be exposed to brackish water at different life stages. However, the impacts of variations of salinity on wildlife remain poorly understood. This is particularly true for coastal amphibians, due to the strong dependency of early life stages (embryos and larvae) on aquatic environments. In order to investigate the effect of salinity during egg laying and embryonic and larval development of coastal amphibians, we used a full-factorial design to expose reproductive adults, eggs, and larvae of coastal spined toads (Bufo spinosus) to fresh (0 g.l-1) or brackish water (4 g.l-1). At egg laying, we evaluated parental investment in reproduction. During embryonic and larval development, we assessed effects on survival, development, and growth. We highlighted strong effects of environmental salinity on reproduction (reduced egg laying time, marginally reduced egg size, and reduced investment in reproduction). Responses to salinity were highly dependent on the developmental stages of exposure (stronger effects when individuals were exposed during embryonic development). These effects carried over when exposure occurred at egg laying or during embryonic development, highlighting the importance of the environmental conditions during early life on ontogenetic trajectories. We also highlighted partial compensation when individuals were transferred back to freshwater. Whether the magnitude of these responses can allow coastal biodiversity to overcome the observed detrimental effects of salinization remain to be assessed.

A generalized and comprehensive slant channel modeling method for underwater wireless optical communication and its system performance analysis

The underwater wireless slant optical link is a more generalized type of communication links compared with vertical and horizontal links. Since several oceanic factors including temperature and salinity variations with the seawater depth, the performance of the slant link for the underwater wireless optical communication (UWOC) will be overestimated under the assumptions of constant temperature and salinity. To this end, this paper proposes a model of slant link considering the depth-dependent and inclination-angle-dependent turbulence and scattering that are the main causes of multipath fading for UWOC. Specifically, to model the turbulence-induced fluctuations of light fields, the random phase screen method is exploited, where the power spectrum of refractive index is calculated using the oceanic turbulence optical power spectrum (OTOPS) model and the light fields at the receivers are derived by the angular spectrum method. To emulate the scattering-induced divergence, the scattering phase function is applied, where the motion directions and coordinates of light spots propagating among phase screens are deduced using Rodrigues’ Rotation Formula. Simulation results demonstrate the effects of the depths and inclination angles of transmitters on the performance of UWOC by analyzing the scintillation index, channel impulse response, and BER (bit error rate).

The Dynamics of Soil Mesofauna Communities in a Tropical Urban Coastal Wetland: Responses to Spatiotemporal Fluctuations in Phreatic Level and Salinity

Coastal wetlands, vital for ecological diversity, have been significantly altered by anthropogenic activities, particularly in the Caribbean. These changes have created a complex mosaic of habitats and physicochemical conditions, further stressed by climate variability and sea-level rise. This study, conducted in Las Cucharillas Natural Reserve, a tropical urban coastal wetland in Puerto Rico, aimed to determine the effects of spatiotemporal variations in phreatic levels and salinity on soil mesofauna assemblages, crucial bio-indicators of environmental change. In 2020 and 2021, soil samples were collected from five diverse habitat types during different hydroperiods. Each sample was taken under four randomly selected plant types and processed using lighted Tullgren–Berlese extractors. Phreatic level and salinity were also measured. A total of 43 families were quantified, underscoring distinct habitat differences, similarities, and overall ecosystem diversity. Moderate correlations between phreatic levels, salinity, and mesofauna richness and abundance were determined. Peak richness and abundance were quantified at shallow (−0.03 to −0.07 m) and slightly moderate (−0.12 to −0.17 m) phreatic levels where oligohaline salinity (&gt;0.5 to 5.0 ppt) prevails. The study highlights the adaptability of mesofauna to environmental shifts and their potential as biosensors for effective coastal wetland management amid climatic and anthropogenic pressures.

Observations of river-wave interactions at a small-scale river mouth

Small coastal rivers often discharge directly into the surfzone, where the fate of freshwater and river-borne materials (e.g., sediment, nutrients and contaminants) is primarily determined by interactions between buoyant plume processes and the nearshore wave forcing. Understanding river-wave interactions in the surfzone is essential to assess coastal water quality and impacts on ecosystem health along adjacent shorelines. These interactions are modulated by the variability in river discharge, offshore wave climate, tidal forcing, and surfzone dynamics, and therefore occur over a wide range of timescales. However, the different timescales at which river-wave interactions occur have not been fully investigated. Here we use in-situ and remote (drone-based) observations collected at the mouth of the Maipo River, a small-scale river system in central Chile, to investigate interactions between the river outflow and the incident wave forcing that may influence the distribution of freshwater along the coast. We focus on interactions occurring at infragravity (wave groups), tidal, and synoptic (offshore wave climate) timescales. The observations included inlet and surfzone deployments, and documented low river discharge conditions (QR∼ 20–27 m3s−1) with variable wave forcing (Hs∼ 1–3 m). We observed that the salinity signal at the river mouth is strongly modulated by the tide, with a freshwater plume forming solely during the ebb. Large oscillations associated to infragravity (IG) motions are continuously observed on top of the tidal variability. These oscillations are evidenced in surfzone salinity, inlet water levels, and inlet velocity during the early ebb when the freshwater plume starts to develop. As the plume evolves into a strong outflow jet during the late ebb, they are not observed in the inlet and become restricted to the surfzone. The combined analysis of drone imagery and in-situ observations suggests that the observed variability in surfzone salinity at IG frequencies is associated with the arrival of wave groups and the propagation of wave fronts in the plume area. In particular, during the late ebb, the large oscillations in surfzone salinity (amplitude of 15–20 psu) are explained by a contraction and expansion of the outflow plume in response to the variability in the onshore wave forcing at the timescale of wave groups. On synoptic timescales (hours to days), the surfzone salinity responded to the intensity of the offshore wave forcing (∼ 20 m depth), with higher waves promoting lower salinity as freshwater is mostly retained near the coast. A wave-river momentum comparison confirms that the wave forcing had the potential to trap freshwater in the surfzone. This study shows that nearshore waves may influence the dynamics of small river plumes and the fate of freshwater (and associated terrestrial materials) on a wide range of timescales, from infragravity (1–5 min) to hours and days.

Simulated ocean circulation and its variability in the Northern Banda Sea from CROCO model

A simulation of 1/24º resolution 3-dimension regional ocean circulation of CROCO was successfully performed from 2015 to 2022 (8 years), covering the ENSO year in El Niño 2015 and La Niña 2022 in the northern Banda Sea (NBS). The model and data comparison of sea surface temperature/height reproduced the observed satellite datasets well, with correlation coefficients above 0.9. It is shown that the mean circulation in the NBS is fed by two inflows from western Buru and the Manipa Strait, resulting in a meandering eastward mean circulation with warmer water accumulated in the eastern NBS, associated with high current variance south of Buru and along the Manipa Strait. Seasonal variations in the oceanographic parameters were dominant in the study area. For example, during the southeast (northwest) monsoon period, the seawater temperature is minimum (maximum) and the salinity is maximum (minimum). Furthermore, the interannual timescale ENSO and IOD significantly modulated seawater temperature and salinity variation, particularly at the thermocline layer (110 m). Much cooler and saltier water is associated with El Niño 2015 and a positive IOD, in contrast to warmer and fresher water during La Niña 2022 and a negative IOD.

Estuarine Exchange Flow in the Salish Sea

AbstractThe Salish Sea is a large, fjordal estuarine system opening onto the northeast Pacific Ocean. It develops a strong estuarine exchange flow that draws in nutrients from the ocean and flushes the system on timescales of several months. It is difficult to apply existing dynamical theories of estuarine circulation there because of the extreme bathymetric complexity. A realistic numerical model of the system was manipulated to have stronger and weaker tides to explore the sensitivity of the exchange flow to tides. This sensitivity was explored over two timescales: annual means and the spring‐neap. Two theories for the estuarine exchange flow are: (a) “gravitational circulation” where exchange is driven by the baroclinic pressure gradient due to along‐channel salinity variation, and (b) “tidal pumping” where tidal advection combined with flow separation forces the exchange. Past observations suggested gravitational circulation was of leading importance in the Salish Sea. We find here that the exchange flow increases with stronger tides, particularly in annual averages, suggesting it is controlled by tidal pumping. However, the landward salt transport due to the exchange flow decreases with stronger tides because greater mixing decreases the salinity difference between incoming and outgoing water. These results may be characteristic of estuarine systems that have rough topography and strong tides.

A metabolomic snapshot through NMR revealed differences in phase transition during the induction of reproduction in Ulva ohnoi (Chlorophyta).

The present study deals with the metabolomic status of Ulva cells undergoing phase transition (vegetative, determination and differentiation) when exposed to different abiotic conditions. The objective was to study whether metabolite changes occurring during the phase transition reveal any commonality among differential abiotic conditions. The phase transition was followed through microscopic observations and 1H NMR characterization at 0 h, 24 h, and 48 h after the incubation of the thallus under abiotic conditions, such as different salinities (20-35 psu), temperatures (20-35 °C), photoperiods (18 : 6, 12 : 12, and 6 : 18 D/N), light intensities (220, 350, and 500 μmol photons m-2 s-1), nitrate (0.05-0.2 g L-1) and phosphate (0.05-0.2 g L-1) concentrations. Microscopic analysis revealed the role of all abiotic conditions except variable salinity and phosphate concentration in phase transition. NMR analysis revealed that glucose increased in the determination phase [7.58 to 9.62 normalized intensity (AU)] and differentiation phase (5.85 to 6.41 AU) from 20 °C to 25 °C temperature. Coniferyl aldehyde increased in vegetative (5.79 to 6.83 AU) and differentiation (6.66 to 7.40 AU) phases from 20 °C to 30 °C temperature. The highest average (22.97) was found in photoperiod (average range = 0-122.91) and the highest SD (24.73) in salinity (SD range = 1.86-57.04) in region 9 (creatinine and cysteine) of the differentiation phase. A total of 30 metabolites were identified under the categories of sugars, amino acids, and aromatic compounds. The present study will aid in understanding the mechanisms underlying cell differentiation during reproduction. The result may serve as an important reference point for future studies, besides helping in controlling seedling preparation for commercial farming as well as the management of rapid green tide formation.

Antibiotic Resistance in a Coastal River in Mississippi, USA – Potential Drivers

Wastewater treatment plants (WWTPs) are major sources of antibiotic resistant bacteria (ARB) and antibiotic resistance genes (ARGs) in water bodies. Most studies on the impact of WWTPs on antibiotic resistance have focused on freshwater systems, with little information on coastal and estuarine waters with variable salinity. This study monitored seasonal levels of ARGs at the effluent and downstream of the Pascagoula— Moss Point WWTP in the lower Pascagoula River, a coastal river in southeastern Mississippi, USA. Surface water samples were collected seasonally at upstream, outflow, and 3 downstream sites from February to November 2016. Bacterial resistance to sulfamethazine, tetracycline, and ciprofloxacin was quantified using selective culture and qPCR. Mixed—effects models were developed to identify potential driving factors of ARG concentrations related to the WWTP and local environmental conditions (salinity, water temperature, and pH). The best model was selected based on the lowest Akaike Information Criterion (AIC) corrected for small sample size. The results show that the genes sul1, sul2, and intI1 were detected, with intI1 having the highest relative concentration. The qPCR analysis suggests a negative relation between ARG levels and temperature and salinity. ARG concentrations peaked immediately downstream of the WWTP and decreased gradually further downstream in some months, but the spatial pattern varied widely between sampling months. The study highlights the complex patterns of environmental ARGs and the importance of accounting for the impact of WWTPs, local environmental factors, and other anthropogenic influences to understand their potential drivers.

Lake evolution and climate change in the South-West Siberia

A complex of mineralogical and geochemical data from the south of Western Siberia indicates that the middle Holocene warm and dry epoch ended 5.5–4 cal ka BP with the further onset of more humid and cold conditions in the region. Significant changes in the regional climate probably occurred about 3.6–3.1 cal ka BP that is marked by an increase in the content of carbonates in the sediments, and by changes in vegetation. A general trend in the content of Mg in the carbonate fraction of lake sediments clearly shows a variation in water salinity as a response to climate change. There was a cyclical change of periods of drying/humidification of the Holocene climate of southern Western Siberia.

Analysis of sea currents, sea temperature, and sea salinity variations in the malacca strait during january and july 2022 using vertical sections

This study analyzes the sea currents, temperature, and salinity in the Malacca Strait during the northeast (NE) and southwest (SW) monsoons of 2022, represented by monthly average data from the Copernicus Marine Service (CMEMS) data portal for January and July, respectively. Vertical sections are created to visualize the layer structure and variations of sea parameters within the water column. The findings reveal differences in sea currents, temperature, and salinity between the NE and SW monsoons. July (SW monsoon) records consistently warmer temperatures than January (NE monsoon), both at the sea surface and seabed. Surface salinity is higher in July than in January, while seabed salinity is greater in January than in July. In January, the salinity-influenced mixed layer depth (MLD) appears to be thicker than the temperature-influenced MLD. There are no significant differences in the thickness of the temperature- and salinity-influenced MLDs during July. These variations in sea currents, temperature, and salinity at different depths provide a comprehensive understanding of the marine environmental structure and dynamics of the Malacca Strait.

Variability in Quantity and Salinity of Produced Water from an Oil Production in South Kuwait

Variability in Quantity and Salinity of Produced Water from an Oil Production in South Kuwait

Observed Extreme Freshening in the Central Andaman Sea Induced by Strong Positive Indian Ocean Dipole

AbstractThe Indian Ocean Dipole (IOD) has been extensively studied for its significant impact on salinity distribution in tropical regions. However, its off‐equatorial influence in the northeastern Indian Ocean (IO) has received limited documentation thus far. In October 2019, a buoy in the central Andaman Sea (AS) observed an extreme freshening event that resulted in intensified upper‐ocean stratification and increased internal wave activities. The salt budget evaluation revealed the dominant role of horizontal advection. Interannual variability in autumn and winter sea surface salinity (SSS) showed a significant correlation with the IOD. Extreme freshening was observed exclusively during strong positive IOD (pIOD) years. This freshening primarily resulted from the outflow of low‐salinity water from the northeastern coast of the AS, driven by an anomalous anti‐cyclonic coastal‐trapped circulation exclusive to strong pIODs in the northeastern IO. This circulation tends to hinder southward freshwater transport in the western region while enhancing it in the eastern region. This circulation pattern is primarily influenced by Kelvin wave forcing, which is triggered by robust equatorial easterly anomalies that are typically more pronounced during strong pIOD events and weaker during weak pIOD events. The anticipated increase in the frequency of extreme freshening events due to the greenhouse warming has the potential to significantly modify the salinity distribution and freshwater transport in the future.