Surface Seawater Research Articles

OTEC Systems’ Heat Losses in Pipes

Ocean Thermal Energy Conversion (OTEC) systems utilize the temperature difference between surface seawater and deep seawater to produce electricity through a heat engine. A major disadvantage of the OTEC systems is that seawater temperature on the surface and on the seabed varies with the geographical location. This difference is also dependent on the depth and the distance from the coastline, where there are cases with the required temperature difference size to be found at a high distance from shore. This study evaluates the heat losses of the cold water pipe, where such long distances occur, and the subsequent effects for such cases. The current investigation is performed computationally and is based on the accurate estimation of the temperature difference between the deep seawater temperature and the inlet to the condenser temperature. Most literature studies do not consider any heat losses due to the transfer of the seawater when evaluating the performance of the CWP; however, in some cases, even a small temperature change can have a major effect on the output of the system.

Complete genome sequence of Algoriphagus halophilus strain SOCE 003, a marine bacterium isolated from the surface seawater of Dapeng Bay.

Algoriphagus is a heterotrophic bacterium commonly found in diverse marine environments. Here, we report the complete genome sequence of Algoriphagus halophilus strain SOCE 003, which is 5,154,101 bp long, encoding 5,524 annotated protein-coding genes, 39 tRNAs, and 8 rRNAs. This genome information will help us understand the ecology of Algoriphagus.

Groundwater releases CO2 to diverse global coastal ecosystems.

Coastal ecosystems play a major role in marine carbon budgets, but substantial uncertainties remain in the sources and fluxes of coastal carbon dioxide (CO2). Here, we assess when, where, and how submarine groundwater discharge (SGD) releases CO2 to shallow coastal ecosystems. Time-series observations of dissolved CO2 and radon (222Rn, a natural groundwater tracer) across 40 coastal systems from 14 countries revealed large SGD-derived CO2 fluxes. The mean groundwater partial pressure of CO2 was 35 times higher than surface seawater. The mean SGD-derived CO2 flux was 148 ± 226 millimoles per square meter per day (mmol m-2 day-1), resulting in a mean water-air CO2 flux of 80 ± 133 mmol m-2 day-1. Tidal rather than diel cycles drove CO2 enrichment in most ecosystems. Tidally driven SGD was the primary CO2 source in mangroves, salt marshes, tidal flats, estuaries, and canals. Overall, we expand current knowledge of marine carbon cycles by demonstrating SGD as an important source of CO2 that requires inclusion in coastal carbon budgets.

Influence of mesh selectivity on risk assessment of marine microplastics.

In this study, environmental microplastic samples (>30μm) were collected from surface seawater and the water column, characterized, and used to assess ecological risks. The influence of mesh selectivity on ecological risks was also evaluated through subsampling. Results show that surface microplastic concentrations (>30μm) range from 92 to 3306 pieces/m3 along Japan's southwest coast, with significant increases at Stas. 2 and 1. Subsurface vertical concentration near Okinawa ranges from 991 to 1992 pieces/m3, with denser, more toxic polymers more frequently observed in deeper waters, suggesting that polymer types may be sorted by marine structure. Risk assessments revealed very high risks near main islands and populated regions, while remote regions had lower risks. Further analysis revealed that ecological risk estimates are significantly influenced by mesh selectivity, with variations in particle size distribution and polymer type composition resulting in changes of up to 100-fold at the same location when different mesh sizes were used, suggesting that current framework is not ideal for risk assessment of microplastics. This study is the first to demonstrate that samplers with different mesh sizes can lead to substantial differences in risk assessments, even at the same location. These findings underscore the critical impact of mesh selectivity on ecological risk estimates and highlight the need for standardized sampling protocols in microplastic research.

Evaluation of spatial variation and nutritional status of environmental quality in the surface seawater from fishing harbours of Hainan island

To investigate the nutrient distribution characteristics and the eutrophication status of the main fishing ports in Hainan Province, this study analyzed the 2021 seawater quality indicators, including biochemical oxygen demand (BOD5), chemical oxygen demand (COD), chlorophyll a (Chl a), ammonia nitrogen (NH4-N), nitrite nitrogen (NO2-N), nitrate nitrogen (NO3-N), and soluble active phosphate (DIP). The single-factor contaminant index method was employed to evaluate the water quality, revealing that the levels of COD, BOD5, and DIP surpass the national seawater quality standards for Type IV. The eutrophication index (EI) of the different fishing ports ranges from 2.38 to 56.29, indicating a high level of eutrophication.

Tidal currents and atmospheric inorganic nitrogen contribute to diurnal variation of dissolved nutrients and chlorophyll a concentrations in Mirs Bay, Hong Kong

The surface layer of central Mirs Bay exhibits high chlorophyll a concentrations despite having lower dissolved nitrate levels than other parts of Hong Kong. It is hypothesised that tidal currents and atmospheric inorganic nitrogen bring in nutrients that could be rapidly consumed by primary producers. We conducted fieldwork campaigns in September and December 2022 to test these hypotheses. Surface seawater was obtained hourly in September and half-hourly in December, and concentrations of chlorophyll a and dissolved nutrients were determined. Nitrogen content of aerosols was measured by a newly-developed online analyser. In September, we observed peaks in dissolved nutrients and chlorophyll a occurred after receding tides, which may have transported nutrients from the surrounding land. In December, there were anomalous nutrient and chlorophyll peaks that could not be attributed to low tides. These peaks may be responses to the overnight deposition of atmospheric nitrogen. Our dataset thus supports our hypothesis and highlights the need for further investigation to quantify the impact of both tidal currents and atmospheric deposition on carbon export to and oxygen consumption in bottom waters. The rapid changes observed could also be due to tidal currents transporting nutrients and chlorophyll a. Follow-up studies can repeat the fieldwork using Lagrangian (i.e. following tidal currents) instead of Eulerian (i.e. static sampling points) sampling. Moreover, current results indicate strong diurnal variability in chlorophyll a and suggest that existing monitoring efforts may be biased, depending on their timing during the day and/or the season.

Distribution of Heavy Metals in Surface Seawater and Sediment of Cirebon Coastal Area, West Java

Distribution of Heavy Metals in Surface Seawater and Sediment of Cirebon Coastal Area, West Java

Modeling the global ocean distribution of dissolved cadmium based on machine learning-SHAP algorithm.

Cadmium (Cd) is a bio-essential trace metal in the ocean that can be toxic at high concentrations, significantly impacting the marine environment and phytoplankton growth. Its distribution pattern is closely proportional to that of phosphate (PO4), although the mechanism is not fully understood. At low concentrations, evidence indicates Cd is able to act as an enzyme cofactor in biological processes. An understanding of the spatial distribution of dissolved cadmium (dCd) remains lacking and is constrained by the limitations of current observational data. Based on the observational data, this study applied advanced machine learning methods to reconstruct a global dataset of dCd, aiming to improve the accuracy and comprehensiveness of dCd cycling analyses. A comparison of five machine learning algorithms (artificial neural network, support vector machine, Lasso regression, k-nearest neighbors, and random forest) found that the random forest model showed the best performance (Rsq=0.99, RMSE=0.035nmolkg-1, MAE=0.019nmolkg-1, MAPE=0.345), reducing bias by 25% compared to previous studies. Using SHapley Additive exPlanations approach (SHAP), this study explored the factors influencing the dCd distribution at various depths and discussed the potential causes of changes in the Cd-PO4 relationship. The results showed that the temporal and spatial variability of Cd was influenced by surface biological processes, deep-sea mineralization, and seawater stratification. Variations in the Cd-PO4 relationship were linked to differences in biological fractionation inside and outside high-nutrient, low-chlorophyll (HNLC) regions, as well as the mixing of water masses with different Cd:PO4 ratios. Further analysis indicated that >80% of particles degraded into Cd and PO4 were produced in HNLC regions. This study highlights the broad potential of machine learning in oceanography, offering a global perspective on Cd cycling and new insights into the mechanisms driving element cycling.

Sea surface water isotope changes recorded by alkenone δ2H from the northern South China Sea over the last 260 kyrs

Sea surface water isotope changes recorded by alkenone δ2H from the northern South China Sea over the last 260 kyrs

Summer profiles: Tracing currently used organophosphorus pollutants in the surface seawater of the Arctic Ocean.

We investigate the spatial distribution and potential ecological impact of Currently Used Organophosphorus Pollutants (CUOPPs) in the Arctic Ocean, focusing on the East Siberian Sea, Laptev Sea, and high Arctic regions. Analyzing surface water samples collected during a scientific expedition aboard the "Xuelong 2" in August and September 2021, we detected 38 out of 83 targeted CUOPPs, including Phorate, Paraoxon, and Azinphos-ethyl, with concentrations exhibiting significant geographical variance. The results reveal a pronounced increase in CUOPP concentrations towards the Arctic poles, diverging markedly from the patterns observed in the East China Sea, thereby highlighting distinct regional pollution profiles and environmental interactions. Our findings suggest various potential sources and transport mechanisms for CUOPPs, indicating complex pollutant dynamics. Furthermore, the study delves into the influence of Arctic sea ice dynamics on the distribution patterns of CUOPPs, underscoring the pivotal role of environmental factors such as surface currents. Ecological risk assessments conducted for essential Arctic species pose a high ecological risk in the Arctic Ocean, with a "Summer Alert" effect. This investigation elucidates the intricate relationship between CUOPPs dispersal in the Arctic and the broader implications of climate change, offering critical insights into the emerging environmental challenges in polar ecosystems.

Mapping the fine spatial distribution of global offshore surface seawater mariculture using remote sensing big data

ABSTRACT Against the backdrop of near-saturation in global marine capture fisheries, current mariculture production now exceeds one-third of capture production and continues to hold significant growth potential. However, the lack of spatially detailed global offshore surface seawater mariculture (OSSM) data hampers scientific understanding and management from a spatial perspective. In this study, utilizing multi-source remote sensing time-series imagery, we achieve the world’s first spatially detailed mapping of both raft and cage mariculture types. The results show that (1) in 2020, the total global OSSM area was 20,079.97 km², comprising 85.04% raft mariculture and 14.96% cage mariculture. 95.33% of the OSSM was concentrated in Asia. (2) The interpreted national OSSM areas align well with the FAO production statistics trends. Obtaining these areas using remote sensing offers greater timeliness compared to production statistics, which is advantageous for dynamic monitoring and production estimation. (3) Through analysis of global pond aquaculture data, it was found that most coastal areas worldwide had a single-type of aquaculture. However, in parts of Asia, regions with both OSSM and pond aquaculture coexisted. The data acquired in this study, characterized by detailed spatial information, provide significant insights for constructing spatial models of mariculture, researching resource-environment effects, and informing management practices.

Environmental Assessment Using Phytoplankton Diversity, Nutrients, Chlorophyll-a, and Trophic Status Along Southern Coast of Jeddah, Red Sea

The objective of this study is to better identify the state of eutrophication of coastal waters along the southern coast of the city of Jeddah in the Red Sea. Thirty-six samples from surface seawater were collected during the spring and autumn of 2021. Water temperature, pH, salinity, dissolved oxygen (DO), nutrients, and chlorophyll-a (Chl-a) content were examined as a guide of water quality indicators. The present data revealed low levels of Chl-a content (in the range of 0.11–0.24 µg L−1). The average concentrations of DIN (dissolved inorganic nitrogen) forms follow the order NO3-N > NH4-N ~ NO2-N (representing about 11.4–29.4% of the total nitrogen). To investigate the trophic status and water quality, numerical indicators were applied to the results of the analysis of chemical variables (NH4-N, NO3-N, and PO4-P) and the biological analysis (Chl-a) in the aqueous environment within the study area. These indicators are simplified based on the specialist, the non-specialist, the decision-maker, and the one responsible for managing the coastal areas. We also obtain through this method a single numerical value that expresses the state of the coastal waters. According to the analysis of phosphorus and nitrogen data and a trophic index (TRIX), the study area’s trophic status was determined as oligotrophic, due to low nutrient concentrations in the seawater. The current study identified a total of 58 species of phytoplankton comprised four classes in the investigated areas; Bacillariophyceae was the dominant algal class (Diatoms 30 species), followed by Chlorophyceae (9 species), Dinophyceae (11 species), and Cyanophyceae (8 species). Seasonally, spring recorded the highest value of total phytoplankton, recording a value of 251 × 103 cells/L with a percentage of 61%, while autumn recorded the lowest value of 186 × 103 cells/L with a percentage of 39%. Phytoplankton classes can be arranged in order of prevalence as follows: Bacillariophyceae >> Dinophyceae > Chlorophyceae > Cyanophyceae.

Stenotrophomonas strain DP30; a marine bacteria capable of precipitating calcium carbonate

This study aimed to evaluate the calcium carbonate precipitation potential of culturable bacteria found in sea surface water. Ureolytic strains were selected using Stuart’s broth. In the preliminary screening, strain DP30 was selected and used in further experiments. Based on the morphological, physiological, and biochemical characteristics with phylogenetic analysis of the 16S rRNA sequencing, the selected strain was identified as Stenotrophomonas maltophilia. DP30 showed the highest urease activity on the 7th day at 28 °C. In addition, it was found that the isolate can show urease activity in low pH environmental conditions such as pH 5. The strain DP30 precipitated CaCO3 on solid Urea-CaCl2 and B4 media but exhibited different crystal morphologies. Plate-like crystals appeared on solid Urea-CaCl2 media, while the strain produced dihydrate calcium oxalate and rhombohedral crystals on solid B4 media. EDS analysis confirmed that the precipitated minerals were composed solely of calcium, carbon, and oxygen. Furthermore, the study showed that S. maltophilia strain DP30 was able to precipitate calcium carbonate under aerobic conditions without urea hydrolysis. These findings suggest that the DP30 strain may have the potential for use in self-healing concrete applications. Moreover, calcium carbonate precipitation without urea hydrolysis where ammonia is produced will provide an environmentally friendly application.

Microplastic abundance in the surface water of tropical estuarine fronts.

Estuarine fronts are formed due to sharp density discontinuities resulting from the convergence of different water masses. This study, conducted in May and August of 2022 during the southwest monsoon season, focuses on assessing the role of estuarine fronts at Kuala Terengganu estuary in the accumulation of microplastics in surface seawater. The Terengganu River basin area covers approximately 4600 km2 and consists of two main tributaries that drain into the Kuala Terengganu estuary. Microplastic samples were collected from three areas, the plume, front, and shelf, utilizing two methods: manta net (> 350µm) and bucket-water sampling (> 20µm). Results indicate that the estuarine front consistently exhibited higher microplastic concentrations than the plume and shelf regions throughout the study period, with bucket-water sampling contributing significantly to the abundance. Specifically, peak concentrations occurred during the ebb tide at the frontal region in both months, reaching 5761.703 particles m-3 and 12,687.437 particles m-3, respectively. The microplastics, predominantly transparent fibers smaller than 1000µm, mostly showed signs of oxidative and mechanical weathering through SEM-EDS analysis, providing insights into their fate in estuarine surface waters. FTIR spectroscopy revealed polypropylene, polyethylene, and polyamide as the dominant polymers. These findings establish a baseline for microplastic abundance at the estuarine front of the Kuala Terengganu estuary and may inform future strategies for mitigating and recovering microplastic contamination in aquatic environments.

Observed features of stable surface seawater isotopes across the Pacific, Indian and Southern oceans

Observed features of stable surface seawater isotopes across the Pacific, Indian and Southern oceans

Organoclay flocculation as a pathway to export carbon from the sea surface

Marine microorganisms play a critical role in regulating atmospheric CO2 concentration via the biological carbon pump. Deposition of continental mineral dust on the sea surface increases carbon sequestration but the interaction between minerals and marine microorganisms is not well understood. We discovered that the interaction of clay minerals with dissolved organic matter and a γ-proteobacterium in seawater increases Transparent Exopolymer Particle (TEP) concentration, leading to organoclay floc formation. To explore this observation further, we conducted a microcosm experiment using surface seawater collected from the Spring 2023 phytoplankton bloom in the Gulf of Maine. Unfiltered (natural community) and filtered (200 μm and 3 μm) seawater was sprayed with clay (20 mg L− 1 and 60 mg L− 1) and incubated. All clay treatments led to a tenfold increase in TEP concentration. 16S rRNA gene amplicon sequence analyses of seawater and settled organoclay flocs showed the dominance of α-proteobacteria, γ-proteobacteria, and Bacteroidota. The initial seawater phytoplankton community was dominated by dinoflagellates followed by a haptophyte (Phaeocystis sp.) and diatoms. Following clay addition, dinoflagellate cell abundance declined sharply while diatom cell abundance increased. By analyzing organoclay flocs for 18S rRNA we confirmed that dinoflagellates were removed in the flocs. The clay amendment removed as much as 50% of phytoplankton organic carbon. We then explored the fate of organoclay flocs at the next trophic level by feeding clay and phytoplankton (Rhodomonas salina) to Calanus finmarchicus. The copepod ingested R. salina and organoclay flocs and egested denser fecal pellets with 1.8- to 3.6- fold higher sinking velocity compared to controls. Fecal pellet density enhancement could facilitate carbon sequestration through zooplankton diel vertical migration. These findings provide insights into how atmospheric dust-derived clay minerals interact with marine microorganisms to enhance the biological carbon pump, facilitating the burial of organic carbon at depths where it is less likely to exchange with the atmosphere.

Survey on the presence of floating microplastics, trace metals and metalloids in seawater from Southern Italy to the United States of America.

The presence of microplastics (MPs), trace metals (TM) and metalloids (Ms) in surface seawater is a severe emerging issue of global concern. Information about the distribution of these pollutants is often lacking, and large-scale studies come with uncertainties because of difficult comparisons of results obtained using different methods to collect and process data. This study presents a comprehensive investigation of microplastics (MPs), trace metals (TM) and metalloids (Ms) in surface seawater during two transatlantic sampling campaigns, covering approximately 17,000 nautical miles. The results reveal the presence of MPs in all the samples analyzed and a broad variation in microplastic concentration (230-3320 MPs/L), with filaments or fibers being the most abundant shape. Coastal waters generally exhibit higher MPs, TM and Ms concentrations than open sea waters. The results showed high concentrations of MPs, particularly in the waters near the Faroe Islands, in the Sea of Magdalena department and in the Strait of Gibraltar. The order of the overall metals and metalloids concentrations was: As>Cr>Pb>Cd. High concentrations of Pb and Cr were recorded in the Mediterranean waters whereas high Arsenic (As) were found in the Southern coasts of United States, with values that exceeded the limits considered hazardous for aquatic life (81.55-101.12 µg/L). No significant correlations were found between microplastics, and the heavy metals examined. Here, we emphasize the need for sustainable environmental management actions and policies in a global context to monitoring the growing problem of pollutants in our oceans.

HALOBATES: An Autonomous Surface Vehicle for High-Resolution Mapping of the Sea Surface Microlayer and Near-Surface Layer on Essential Climate Variables

Abstract Essential climate variables (ECVs) are physical, chemical, or biological parameters supporting the characterization of the climate system. The oceanic ECVs temperature and salinity have been defined for the sea surface (upper 1 mm) and bulk water (upper 2 m). Direct observation and sampling of the sea surface from ships and buoys are limited due to the potential loss of integrity of the sea surface and contamination by the research platform. The design, development, and operation of a research vehicle with autonomous capabilities based on commercially available components are described in this study. The autonomous operation and fully automated sampling enable high-resolution mapping of the sea surface microlayer (SML), i.e., the upper < 1-mm layer and the near-surface layer (<1.2 m). Sampling the SML is based on a rotating glass disk sampler. The autonomous surface vehicle HALOBATES has been equipped with multiple conductivity–temperature–depth (CTD) sensors in a flow-through system to measure both sea surface and bulk temperature and salinity. The performance of the autopilot under various scenarios is demonstrated. Typical anomalies of ECVs within the SML and near-surface layer are evident and forced by both atmospheric and oceanic processes. Data analyses reveal HALOBATES’ ability to resolve thermohaline structure on different spatial and temporal scales, for example, small-scale freshwater lenses and thermohaline changes across oceanic fronts. The integration of an acoustic Doppler current profiler supports the interpretation of thermohaline structures. HALOBATES is a platform with cutting-edge technology for understanding climate-related processes between the ocean and atmosphere and providing high-resolution sea surface data for validating satellite products of ECVs. Significance Statement An autonomous surface vehicle was developed to address the challenges in the in situ measurement of essential climate variables at the sea surface (upper 1 mm) and near-surface layer (upper 1 m) of the ocean. Autonomous operation for up to 12 h and fully automated sampling enable high-resolution mapping of the sea surface and near-surface layers. The ability of the vehicle to resolve thermohaline structures at various spatial and temporal scales is demonstrated, providing valuable data on freshwater fluxes (evaporation minus precipitation) between the ocean and the atmosphere. This cutting-edge technology enhances the understanding of climate-related processes, offering crucial “sea surface data” for validating satellite products of essential climate variables.

Enhanced crude oil degradation observed in sea ice following bioaugmentation with arctic bacteria.

Petroleum-derived contamination is a growing hazard for the Arctic Ocean and northern marine transportation corridors. In northern settings where the accessibility to oil spills can be limited, natural attenuation is the most promising remediation process. The goal of the presented research is to evaluate the impact of biodegradation on crude oil inside sea ice. To this end, a bioremediation experiment was conducted at the Sea-ice Environmental Research Facility, University of Manitoba. The experiment utilized two mesocosm tanks (Augmented and Native) filled with nutrient-enriched artificial seawater (i.e., biostimulation). The water in the Augmented tank also contained oil-acclimated bacteria enriched from Arctic surface seawater from Cambridge Bay, Canada (i.e., bioaugmentation). The Native tank was not inoculated, but both tanks contained a bacterial community originating with the artificial seawater preparation. Crude oil was added under the naturally formed ice cover within each tank, creating areas that contained different oil concentrations. The Augmented tank contained 22 distinct bacterial genera compared to the Native tank, presumably due to the inoculation. The abundance of distinct bacterial genera was maximal in the water column and in low-contaminated ice core samples (<0.21g oil/L). In these ice cores, bioaugmentation affected the concentration of low-molecular-weight aliphatic compounds (<C18) and naphthalenes (<C5). We also observed a 1% loss per day of n-nonadecane, n-docosane, methylphenanthrene, and tetramethylnaphthalene in the Augmented tank, which we attribute to bioaugmentation by the Arctic bacterial enrichment. In contrast, losses of these same compounds plateaued after day 15 in the Native tank.

Effects of heavy metal concentration on zooplankton community composition and abundance in the Yellow Sea coast

The coastal area of the Yellow Sea is a highly urbanized and industrialized region in China, which has been severely polluted because of intensive human activities. And the heavy metals (HMs) pollution has posed a serious threat to aquatic environments and ecosystem health. However, most studies have focused on the toxicity and bio-accumulation of HMs in zooplankton, while neglecting their effects on the overall community structure. To address the gap in this field, four research cruises was conducted in 2022 to analyze the concentrations of representative HMs (Hg, As, Cu, Zn, Pb, and Cd) in surface seawater along the Yellow Sea coast, as well as the composition and abundance of zooplankton communities, aiming to assess the potential ecological impacts in the region. The results indicated that the concentrations of the six HMs in the seawater were in the low to moderate range. Analytical results showed that Zn and As were key metals influencing the abundance and community composition of zooplankton along the Yellow Sea coast: an increase in Zn concentration, coupled with a decrease in As concentration, was associated with an increase in total zooplankton abundance and a more diverse community. The most frequently occurring zooplankton in the survey were copepods, which exhibited a higher tolerance to HMs. Additionally, the significant fluctuations of Zn, As, and Hg during spring and autumn led to explosive growth of Noctiluca scintillans. We observed that the influence of HMs on marine zooplankton was not isolated but rather interacts with multiple factors. Overall, this study highlights the possibility of alterations in marine ecological structures due to changes in HMs concentration levels. It underscores the importance of continuous monitoring of heavy metal concentrations in the Yellow Sea for the long-term protection of marine ecosystems.