Transparent Exopolymer Particles Concentrations Research Articles

Distribution of polysaccharidic and proteinaceous gel−like particles in three cyclonic eddies in the Eastern Tropical North Atlantic

Transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP), two prominent classes of gel−like particles in the ocean primarily produced by phytoplankton, play crucial roles in ecological and biogeochemical processes, influencing microbial nutrition, growth, and particle aggregation. The distribution of these particles is intricately linked to the spatiotemporal dynamics of phytoplankton. Mesoscale cyclonic eddies (CEs) are known to stimulate phytoplankton growth and influence particle transport, but their effects on TEP and CSP remain to be determined. In the Eastern Tropical North Atlantic (ETNA), we examined three CEs: one off the Mauritanian coast during summer (Mau), one offshore during winter (Sal), and another near Brava island during winter. Mau and Brava CEs were in their intensification/maturity phase, while the Sal CE was in its decay phase. Both TEP and CSP concentrations correlated with primary productivity, but TEP increased with chlorophyll−a concentration, whereas elevated CSP coincided also with the highest abundance of pico−nanophytoplankton (<20 µm), mainly Synechococcus. Both gels exhibited a positive correlation with bacterial biomass production, indicating their consumption by heterotrophic bacteria. TEP total area in the epipelagic waters of all CEs (Mau, Brava, and Sal) was elevated compared to surrounding waters, with on average 4, 2.5, and 1.6−fold higher values, respectively. However, no significant difference in TEP size distribution was observed within any CEs and their surroundings. Similarly, CSP total area increased in the epipelagic waters of Mau and Brava CEs, with on average 5 and 2.4−fold higher values, respectively, compared to surrounding waters. CSP particles were notably larger in these two eddies, while the Sal CE showed no significant difference from surrounding waters in CSP abundance and size. Overall, TEP and CSP exhibited distinct responses to CEs, with increased concentrations during their intensification/maturation stage and remineralization dominating during their decaying stage.

Effect of biopolymer concentration on the kinetics of marine snow formation

Marine snow floc refers to coagulation of microbes and marine debris in the upper ocean layers, bound together by bio-polymers such as transparent exopolymer particles (TEP) secreted by microbes. The stickiness of TEP plays a crucial role in determining the rate of marine snow floc formation. Additionally, the effect of TEP on the size distribution of marine snow influences the sinking velocity of the flocs. Using a surrogate material system, we study the kinetics of marine snow using a custom-built experimental setup, which allows direct measurement of floc size, floc number density, and floc sinking velocity as a function of TEP concentration. By comparing the experimental floc size with Smoluchowski coagulation theory, we obtain stickiness index, which increases with TEP concentration first, reaches maximum around 0.3 g/L of TEP and decreases upon further increase in TEP concentration. The experimental sinking velocity scales with floc size as ws=adb, with b ranging from 0.57 to 0.68. The exponent is slightly higher than that of 0.5 expected in the Stokes limit. This study establishes a clear link between stickiness index, sinking velocity, and polymer concentration, providing valuable insights for modelling of marine snow dynamics in deep ocean conditions. These findings contribute to a better understanding of the kinetics of marine snow formation, essential for predicting carbon sequestration within the biological carbon pump.

Mitigation of reverse osmosis membrane fouling by coagulation pretreatment to remove silica and transparent exopolymer particles

The dissolution of silica and transparent exopolymer particles (TEP) can deposit on the membrane surface and cause serious membrane fouling in reverse osmosis (RO) technology. Coagulation, as a common pretreatment process for RO, can effectively intercept pollutants and alleviate membrane fouling. In this study, FeCl3 and AlCl3 coagulants and polyacrylamide (PAM) flocculants were used to explore the optimal coagulation conditions to reduce the concentration of silica and TEP in the RO process. The results showed that the two coagulants had the best removal effect on pollutants when the pH was 7 and the dosage was 50 mg/L. Considering the proportion of reversible fouling after coagulation, the removal rate of pollutants, and the residual amount of coagulation metal ions, the best PAM dosage was 5 mg/L for FeCl3 and 1 mg/L for AlCl3. After coagulation pretreatment, the Zeta potential decreased, and the particle size distribution increased, making pollutants tend to aggregate, thus effectively removing foulants. The removal mechanisms of pollutants by coagulation pretreatment were determined to be adsorption, electric neutralization and co-precipitation. This study determined the best removal conditions of silica and TEP by coagulation and explored the removal mechanism.

Abundance, Distribution Patterns, and the Contribution of Transparent Exopolymer Particles and Dissolved Acidic Polysaccharides to Organic Carbon in Lake Taihu, China

Transparent exopolymer particles (TEP) are essential for the carbon cycle in aquatic environments. However, the distribution of TEP, its precursor, and the contribution to the organic carbon pool in the large freshwater lake remain inadequately understood. Here, we focused on the spatial distribution of TEP and dissolved acidic polysaccharides (dAPS) in four typical seasons in Lake Taihu, the third-largest lake in China. TEP concentrations in Lake Taihu ranged from 0.05 to 5.19 mg Xeq/L, with a mean value of 1.31 ± 1.08 mg Xeq/L. The concentration of dAPS in the lake averaged 3.7 ± 2.19 mg Xeq/L (range, 0.19–13.12 mg Xeq/L). Higher content of TEP and dAPS was found in summer, and their distributions appeared to be influenced by the cyanobacterial blooms, as they showed significant correlations with chlorophyll-a content in Lake Taihu in summer. In addition, TEP accounted for an average of 24.3% of particulate organic carbon, and dAPS represented 25.9% of dissolved organic carbon. These results provide valuable insights into the contribution of TEP to organic carbon pools in inland waters and highlight the role of TEP in the carbon cycling of large freshwater lakes.

Concentrations of transparent exopolymer particles (TEPs) and their role in the carbon export in the South China Sea and western tropical North Pacific

The role of TEPs in the carbon cycle remains inadequately understood in oligotrophic tropical oceans. This study investigates TEP concentrations, distributions, sinking behavior and fluxes in the oligotrophic South China Sea (SCS) and western tropical North Pacific (WTNP). The results suggested that TEPs levels were relatively low [< 60 μg Xeq. L−1 (μg xanthan gum equivalent per liter)] in both regions, and they were higher in the epipelagic layer than in deeper layers. TEP concentrations correlated significantly positively with Chl a and picophytoplankton biomass, and TEP-associated carbon contributed significantly to particulate organic carbon (POC) pool in the SCS and WTNP. The sinking flux of TEPs constituted a mean of 61% of the total POC flux in the SCS and 46% in the WTNP, highlighting their important role in carbon export in these areas. Generally, this study should provide good insight into the role TEPs play in the carbon cycle in oligotrophic tropical oceans.

High number concentrations of transparent exopolymer particles in ambient aerosol particles and cloud water – a case study at the tropical Atlantic Ocean

Abstract. Transparent exopolymer particles (TEPs) exhibit the properties of gels and are ubiquitously found in the world oceans. TEPs may enter the atmosphere as part of sea-spray aerosol. Here, we report number concentrations of TEPs with a diameter &gt; 4.5 µm, hence covering a part of the supermicron particle range, in ambient aerosol and cloud water samples from the tropical Atlantic Ocean as well as in generated aerosol particles using a plunging waterfall tank that was filled with the ambient seawater. The ambient TEP concentrations ranged between 7×102 and 3×104 #TEP m−3 in the aerosol particles and correlations with sodium (Na+) and calcium (Ca2+) (R2=0.5) suggested some contribution via bubble bursting. Cloud water TEP concentrations were between 4×106 and 9×106 #TEP L−1 and, according to the measured cloud liquid water content, corresponding to equivalent air concentrations of 2–4×103 #TEP m−3. Based on Na+ concentrations in seawater and in the atmosphere, the enrichment factors for TEPs in the atmosphere were calculated. The tank-generated TEPs were enriched by a factor of 50 compared with seawater and, therefore, in-line with published enrichment factors for supermicron organic matter in general and TEPs specifically. TEP enrichment in the ambient atmosphere was on average 1×103 in cloud water and 9×103 in ambient aerosol particles and therefore about two orders of magnitude higher than the corresponding enrichment from the tank study. Such high enrichment of supermicron particulate organic constituents in the atmosphere is uncommon and we propose that atmospheric TEP concentrations resulted from a combination of enrichment during bubble bursting transfer from the ocean and a secondary TEP in-situ formation in atmospheric phases. Abiotic in-situ formation might have occurred from aqueous reactions of dissolved organic precursors that were present in particle and cloud water samples, whereas biotic formation involves bacteria, which were abundant in the cloud water samples. The ambient TEP number concentrations were two orders of magnitude higher than recently reported ice nucleating particle (INP) concentrations measured at the same location. As TEPs likely possess good properties to act as INPs, in future experiments it is worth studying if a certain part of TEPs contributes a fraction of the biogenic INP population.

Organic Matter Composition of Biomineral Flocs and Its Influence on Suspended Particulate Matter Dynamics Along a Nearshore to Offshore Transect

AbstractThe seasonal variation in concentration of transparent exopolymer particles (TEPs), particulate organic carbon (POC) and particulate organic nitrogen (PON) were investigated together with floc size and the concentration of suspended particulate matter (SPM) along the cross‐shore gradient, from the high turbid nearshore toward the low‐turbid offshore waters in the Southern Bight of the North Sea. Our data demonstrate that biophysical flocculation cannot be explained by these heterogeneous parameters, but requires a distinction between a more reactive labile (“fresh”) and a less reactive refractory (“mineral‐associated”) fraction. Based on all data, we separated the labile and mineral‐associated POC, PON, and TEP using a semi‐empirical model approach. The model's estimates of fresh and mineral‐associated organic matter (OM) show that great parts of the POC, PON, and TEP are associated with suspended minerals, which are present in the water column throughout the year, whereas the occurrence of fresh TEP, POC, and PON is restricted to spring and summer months. In spite of a constantly high abundance of total TEP throughout the entire year, it is its fresh fraction that promotes the formation of larger and faster sinking biomineral flocs, thereby contributing to reducing the SPM concentration in the water column over spring and summer. Our results show that the different components of the SPM, such as minerals, extracellular OM and living organisms, form an integrated dynamic system with direct interactions and feedback controls.

Uncoupled seasonal variability of transparent exopolymer and Coomassie stainable particles in coastal Mediterranean waters

Transparent exopolymer particles (TEP) and Coomassie stainable particles (CSP) are gel-like particles, ubiquitous in the ocean, that affect important biogeochemical processes including organic carbon cycling by planktonic food webs. Despite much research on both groups of particles (especially TEP) over many years, whether they exist as distinctly stainable fractions of the same particles or as independent particles, each with different driving factors, remains unclear. To address this question, we examined the temporal dynamics of TEP and CSP over 2 complete seasonal cycles at 2 coastal sites in the Northwestern Mediterranean Sea, the Blanes Bay Microbial Observatory (BBMO) and the L’Estartit Oceanographic Station (EOS), as well as their spatial distribution along a coast-to-offshore transect. Biological, chemical, and physical variables were measured in parallel. Surface concentrations (mean ± standard deviation [SD]) of TEP were 36.7 ± 21.5 µg Xanthan Gum (XG) eq L–1 at BBMO and 36.6 ± 28.3 µg XG eq L–1 at EOS; for CSP, they were 11.9 ± 6.1 µg BSA eq L–1 at BBMO and 13.0 ± 5.9 µg BSA eq L–1 at EOS. Seasonal variability was more evident at EOS, where surface TEP and CSP concentrations peaked in summer and spring, respectively, and less predictable at the shore-most station, BBMO. Vertical distributions between surface and 80 m, monitored at EOS, showed highest TEP concentrations within the surface mixed layer during the stratification period, whereas CSP concentrations were highest before the onset of summer stratification. Phytoplankton were the main drivers of TEP and CSP distributions, although nutrient limitation and saturating irradiance also appeared to play important roles. The dynamics and distribution of TEP and CSP were uncoupled both in the coastal sites and along the transect, suggesting that they are different types of particles produced and consumed differently in response to environmental variability.

Impact of dust addition on the metabolism of Mediterranean plankton communities and carbon export under present and future conditions of pH and temperature

Abstract. Although atmospheric dust fluxes from arid as well as human-impacted areas represent a significant source of nutrients to surface waters of the Mediterranean Sea, studies focusing on the evolution of the metabolic balance of the plankton community following a dust deposition event are scarce, and none were conducted in the context of projected future levels of temperature and pH. Moreover, most of the experiments took place in coastal areas. In the framework of the PEACETIME project, three dust-addition perturbation experiments were conducted in 300 L tanks filled with surface seawater collected in the Tyrrhenian Sea (TYR), Ionian Sea (ION) and Algerian basin (FAST) on board the R/V Pourquoi Pas? in late spring 2017. For each experiment, six tanks were used to follow the evolution of chemical and biological stocks, biological activity and particle export. The impacts of a dust deposition event simulated at their surface were followed under present environmental conditions and under a realistic climate change scenario for 2100 (ca. +3 ∘C and −0.3 pH units). The tested waters were all typical of stratified oligotrophic conditions encountered in the open Mediterranean Sea at this period of the year, with low rates of primary production and a metabolic balance towards net heterotrophy. The release of nutrients after dust seeding had very contrasting impacts on the metabolism of the communities, depending on the station investigated. At TYR, the release of new nutrients was followed by a negative impact on both particulate and dissolved 14C-based production rates, while heterotrophic bacterial production strongly increased, driving the community to an even more heterotrophic state. At ION and FAST, the efficiency of organic matter export due to mineral/organic aggregation processes was lower than at TYR and likely related to a lower quantity/age of dissolved organic matter present at the time of the seeding and a smaller production of DOM following dust addition. This was also reflected by lower initial concentrations in transparent exopolymer particles (TEPs) and a lower increase in TEP concentrations following the dust addition, as compared to TYR. At ION and FAST, both the autotrophic and heterotrophic community benefited from dust addition, with a stronger relative increase in autotrophic processes observed at FAST. Our study showed that the potential positive impact of dust deposition on primary production depends on the initial composition and metabolic state of the investigated community. This impact is constrained by the quantity of nutrients added in order to sustain both the fast response of heterotrophic prokaryotes and the delayed one of primary producers. Finally, under future environmental conditions, heterotrophic metabolism was overall more impacted than primary production, with the consequence that all integrated net community production rates decreased with no detectable impact on carbon export, therefore reducing the capacity of surface waters to sequester anthropogenic CO2.

Seasonal Variations in the Biochemical Compositions of Phytoplankton and Transparent Exopolymer Particles (TEPs) at Jang Bogo Station (Terra Nova Bay, Ross Sea), 2017–2018

The biochemical composition of particulate organic matter (POM) mainly originates from phytoplankton. Transparent exopolymer particles (TEPs) depend on environmental conditions and play a role in the food web and biogeochemical cycle in marine ecosystems. However, little information on their characteristics in the Southern Ocean is available, particularly in winter. To investigate the seasonal characteristics of POM and TEPSs, seawater samples were collected once every two weeks from November 2017 to October 2018 at Jang Bogo Station (JBS) located on the coast of Terra Nova Bay in the Ross Sea. The total chlorophyll-a (Chl-a) concentrations increased from spring (0.08 ± 0.06 μg L−1) to summer (0.97 ± 0.95 μg L−1) with a highest Chl-a value of 2.15 μg L−1. After sea ice formation, Chl-a rapidly decreased in autumn (0.12 ± 0.10 μg L−1) and winter (0.01 ± 0.01 μg L−1). The low phytoplankton Chl-a measured in this study was related to a short ice-free period in summer. Strong seasonal variations were detected in the concentrations of proteins and lipids (one-way ANOVA test, p &lt; 0.05), whereas no significant difference in carbohydrate concentrations was observed among different seasons (one-way ANOVA test, p &gt; 0.05). The phytoplankton community was mostly composed of diatoms (88.8% ± 11.6%) with a large accumulation of lipids. During the summer, the POM primarily consisted of proteins. The composition being high in lipids and proteins and the high caloric content in summer indicated that the phytoplankton would make a good food source. In winter, the concentrations of proteins decreased sharply. In contrast, relatively stable concentrations of carbohydrates and lipids have been utilized for respiration and long-term energy storage in the survival of phytoplankton. The TEPS values were significantly correlated with variations in the biomass and species of the phytoplankton. Our study site was characterized by dominant diatoms and low Chl-a concentrations, which could have resulted in relatively low TEP concentrations compared to other areas. The average contributions of TEP-C to the total POC were relatively high in autumn (26.9% ± 6.1%), followed by those in summer (21.9% ± 7.1%), winter (13.0% ± 4.2%), and spring (9.8% ± 3.1%).

Transparent Exopolymer Particles (TEP), phytoplankton and picocyanobacteria a littoral-to-pelagic depth-gradient in a large subalpine lake

Transparent Exopolymer Particles (TEP) play an important role in the organic carbon cycle of many aquatic systems but the production and distribution of TEP have been studied mainly in the marine environment, neglecting the large oligotrophic lakes. We selected Lake Maggiore, one of the most important freshwater reserve in Northern Italy, to study the horizontal and vertical distribution of TEP and of its possible drivers. Samplings along a transect in the Borromeo basin were performed in May, July and September 2019. Total Organic Carbon (TOC), TEP, chlorophyll-a (Chl) of different algal groups, picocyanobacteria, bacteria and eukaryotes counting, were measured at six stations and five depths. Our study showed that TEP exhibited a clear vertical heterogeneity from surface to the bottom related to the autotrophic microorganisms that are the main source of TEP and are prevalent in the euphotic zone of the lake. On the other hand, TEP was fairly evenly distributed along the horizontal transect from littoral to pelagic zone, although patches were present in spring, when TEP concentrations were low. In contrast to TEP, TOC and to a lesser extent Chl and bacteria showed horizontal heterogeneity, in some months. In Lake Maggiore TEP indeed was an important fraction of Total Organic Carbon (TOC), making up to 54% of TOC (in carbon units: 910 µg C L-1) and it was significantly correlated with Chl. The highest TEP concentration (1.44 mg GX eq L-1) was measured in September 2019, in coincidence with an episode of superficial foam appearance. Considering the biomass as Chl concentrations, the algal group mostly related to TEP was that of brown algae, particularly diatoms; but considering the numbers, the picocyanobacteria and bacteria were more significantly correlated to TEP. The presence of pennate diatoms in May and July, with their TEP-related chlorophyll, did not produce TEP in as high concentration as that observed in September in the presence of centric diatoms and of very high numbers of picocyanobacteria and bacteria.

Environmental influences on sinking rates and distributions of transparent exopolymer particles after a typhoon surge at the Western Pacific

A multidisciplinary approach was used to investigate the causes of the distributions and sinking rates of transparent exopolymer particles (TEPs) during the period of September–October (2017) in the Western Pacific Ocean (WPO); the study period was closely dated to a northwest typhoon surge. The present study discussed the impact of biogeophysical features on TEPs and their sinking rates (sTEP) at depths of 0–150 m. During the study, the concentration of TEPs was found to be higher in areas adjacent to the Kuroshio current and in the bottom water layer of the Mindanao upwelling zone due to the widespread distribution of cyanobacteria, i.e., Trichodesmium hildebrandti and T. theibauti. The positive significant regressions of TEP concentrations with Chl-a contents in eddy-driven areas (R2 = 0.73, especially at 100 m (R2 = 0.75)) support this hypothesis. However, low TEP concentrations and TEPs were observed at mixed layer depths (MLDs) in the upwelling zone (Mindanao). Conversely, high TEP concentrations and high sTEP were found at the bottom of the downwelling zone (Halmahera). The geophysical directions of eddies may have caused these conditions. In demonstrating these relations, the average interpretation showed the negative linearity of TEP concentrations with TEPs (R2 = 0.41 ~ 0.65) at such eddies. Additionally, regression curves (R2 = 0.78) indicated that atmospheric pressure played a key role in the changes in TEPs throughout the study area. Diatoms and cyanobacteria also curved the TEPs significantly (R2 = 0.5, P < 0.05) at the surface of the WPO. This study also revealed that TEP concentration contributes less to the average particulate organic carbon in this oligotrophic WPO.

Distribution and Settling Regime of Transparent Exopolymer Particles (TEP) Potentially Associated With Bio‐Physical Processes in the Eastern Indian Ocean

AbstractThe detailed transparent exopolymer particles (TEP) distribution, sinking behavior and the potential mechanisms behind that were revealed in the upper 200 m water column of the eastern Indian Ocean (EIO). The biological process and nutrient limitation have proved to be non‐negligible, both of which possessed potential functions in controlling the TEP pool. TEP production and fate presented significant subregional variations in the study area. The vertical distributions of TEP displayed coherent declined patterns with depth between the marginal sea and pelagic ecosystems, but the concentration of TEP horizontally decreased from marginal sea to open ocean. Dissimilarly, variable distribution patterns and magnitudes were distinguished between stratified and active current zones with the conclusion that the stratified condition was in favor of downward remove of TEP pool but turbulence facilitated the accumulation of TEP especially in the deep chlorophyll maximum (DCM) layer. Distinct sinking regimes of TEP in the stratified zone were distinguishable between layers, with the regulatory mechanisms in the upper, DCM and lower layer of water column being physical diffusion of denser seawater and solutes, aggregation by biotic and abiotic processes and buoyancy effect by entrained lighter fluid, respectively. By comparing the theoretical and measured sinking rates of TEP‐formed aggregates and considering the complicated and uncontrollable situations in non‐culture scenarios, the coupling effects of physical and biological variables on TEP dynamics were elucidated, thus providing a compelling theory for predicting the downward fate of carbon flux in the field environments.

Spatio-temporal variation of transparent exopolymer particles (TEP) and their sinking flux in a temperate bay: Jiaozhou Bay, China

This study investigates transparent exopolymer particles (TEP) distribution, seasonal variability and its sinking flux in a shallow coastal sea, Jiaozhou Bay, China. The TEP concentrations in the bay ranged from 75 to 553 μg xanthum gum equivalents per liter (Xeq. L−1), which was within the range of values reported in other coastal seas. Spatially, high levels of TEP were always observed in the northern bay during all four seasons. In the southern and outer bay, TEP levels were relatively low. Significant positive correlations were observed between TEP and chlorophyll a during spring, summer and fall, suggesting that phytoplankton was the primary source of TEP during these three seasons. Seasonally, TEP concentrations were highest in summer (mean = 275 ± 142 μg Xeq. L−1), followed by winter (mean = 209 ± 53 μg Xeq. L−1), and lowest in spring (mean = 142 ± 43 μg Xeq. L−1) and fall (mean = 180 ± 49 μg Xeq. L−1). High phytoplankton biomass and temperature contributed to the high TEP levels in summer, while the relatively high amount of TEP in winter was most probably derived from re-suspension of sedimentary particles. For the whole year, TEP carbon (TEP-C) contributed to a mean of ~26% of POC in the bay, representing the second most important contributor to POC pool after phytoplankton (mean: 38%). Sinking flux of TEP was measured with sediment trap, and the results revealed that sinking TEP contributed to a mean of 20% of total POC flux for the four seasons in the bay. This study highlights the fact that TEP-C could represent a significant fraction of the POC pool in the coastal sea, and their sedimentation could play an important role in the carbon sedimentation in these areas.

Assessing the Temporal Variability and Drivers of Transparent Exopolymer Particle Concentrations and Production Rates in a Subtropical Estuary

Transparent exopolymer particles (TEP) are the central mechanism by which carbon is shuttled from the surface to the deep ocean. Despite the importance of these particles, the magnitude and drivers of temporal variability in the concentration and production rate of TEP in the ocean are not well resolved, especially in highly dynamic and productive regions like estuaries. Here, TEP dynamics were evaluated across weekly, tidal, and diel time scales within the Skidaway River Estuary (GA, USA) and adjacent coastal waters in the South Atlantic Bight. No significant trends in TEP concentration or production rates were observed over weekly time scales, though over tidal cycles, TEP concentration varied between tide stage and TEP:chlorophyll ratios were always lower at low relative to high tides. Over sequential diel cycles, TEP concentrations were two times higher at night relative to midday. Different biological and environmental variables were correlated with TEP dynamics (Spearman ρ) depending on the time scale considered, reinforcing the importance of time-specific drivers of TEP. These results emphasize the importance in considering the temporal variability of field-based TEP measurements, with implications for accurate assessments of carbon cycling in coastal ecosystems and the incorporation of TEP into carbon export models.

Concentrations and sinking rates of transparent exopolymer particles (TEPs) in a coastal sea: the Changjiang River (Yangtze River) Estuary

Transparent exopolymer particles (TEPs) are ubiquitous throughout the oceans, and their sedimentation is considered an efficient biological carbon sink pathway. To investigate the role of coastal TEPs in sinking carbon from the upper layer, samples were collected in the spring and summer of 2011 in the Changjiang River (Yangtze River) Estuary, a typical coastal water. The concentrations and sinking rates of TEPs were measured, and potential sedimentation flux of TEPs was estimated. TEPs concentrations ranged from 40.00 µg/L to 1 040.00 µg/L (mean=(209.70±240.93) µg/L) in spring and 56.67 µg/L to 1 423.33 µg/L (mean=(433.33±393.02) µg/L) in summer, and they were higher at bloom stations than at non-bloom stations during both cruises. A significant positive correlation between TEPs concentration and chlorophyll a (Chl a) concentration was detected, suggesting that phytoplankton was the primary source of TEPs in this area. TEPs sinking rates ranged from 0.08 m/d to 0.57 m/d with a mean of (0.28±0.14) m/d in spring and 0.10 m/d to 1.08 m/d with a mean of (0.34±0.31) m/d in summer. The potential sedimentation flux of TEP-C ranged from 4.95 mg/(m2·d) to 29.40 mg/(m2·d) with a mean of (14.66±8.83) mg/(m2·d) in spring and 6.80 mg/(m2·d) to 30.45 mg/(m2·d) with a mean of (15.71±8.73) mg/(m2·d) in summer, which was ∼17.81% to 138.27% (mean=65.15%±31.75%) of sedimentation flux of phytoplankton cells in the study area. Due to the increase of TEPs concentrations and their sinking rates, sedimentation fluxes of TEPs at the bloom station were obviously higher than at the non-bloom station during both cruises. This study indicates that TEPs serve as a carbon sink in the Changjiang River Estuary, especially during bloom events, and their sedimentation should be taken into account when we study the carbon sedimentation in the coastal sea.

Phaeocystis globosa Bloom Monitoring: Based on P. globosa Induced Seawater Viscosity Modification Adjacent to a Nuclear Power Plant in Qinzhou Bay, China

The mucus produced by the outbreak of Phaeocystis globosa in the adjacent waters of the Fangchenggang Nuclear Power Plant (FCGNPP) in China has blocked the entrance of the cooling water filtration system of the FCGNPP, and posed a threat to the safe operation of the FCGNPP. At present, there is no related research on whether the changes in seawater viscosity could be used as a new method for monitoring and providing early warning of P. globosa tide. During a complete red tide cycle, the temporal and spatial changes in the hydrological conditions (temperature, salinity, dissolved oxygen), chlorophyll-a (Chl-a), composition and abundance of phytoplankton, number and size of P. globose colonies, concentration of transparent exopolymer particles (TEP) and the seawater viscosity were measured in this study. The results indicate that there was an extremely significant negative correlation between the physical seawater viscosity ηT,S and temperature, and the correlation coefficient reached −0.998. The biological seawater viscosity ηBio was positively correlated with the number of P. globosa colonies, and the correlation coefficients is 0.747. Because the increase in phytoplankton abundance, especially during the outbreak of P. globosa and a large amount of mucus produced by the colonies could significantly increase seawater viscosity, we suggest that biological factors were the main reasons for the increase in seawater viscosity. The ηBio was completely consistent with the occurrence process of P. globosa bloom and could be used as a valuable index for P. globosa bloom monitoring.

Transparent Exopolymer Particle (TEPs) Dynamics and Contribution to Particulate Organic Carbon (POC) in Jaran Bay, Korea

Transparent exopolymer particles (TEPs) are defined as acidic polysaccharide particles and they are influenced by various biotic and abiotic processes that play significant roles in marine biogeochemical cycles. However, little information on their monthly variation, relationship and contribution to particulate organic carbon (POC) is currently available particularly in coastal regions. In this study, the water samples were collected monthly to determine TEP concentrations and POC concentrations in a southern coastal region of Korea, Jaran Bay from April 2016 to March 2017. The TEP concentrations varied from 26.5 to 1695.4 μg Xeq L−1 (mean ± standard deviation (S.D.) = 215.9 ± 172.2 μg Xeq L−1) and POC concentrations ranged from 109.9 to 1201.9 μg L−1 (mean ± S.D. = 399.1 ± 186.5 μg L−1) during our observation period. Based on the 13C stable isotope tracer technique, monthly carbon uptake rates of phytoplankton ranged from 3.0 to 274.1 mg C m−2 h−1 (mean ± S.D. = 34.5 ± 45.2 mg C m−2 h−1). The cross-correlation analysis showed a lag-time of 2 months between chlorophyll a and TEP concentrations (r = 0.86, p &lt; 0.01; Pearson’s correlation coefficient). In addition, we observed a 2 month lag-phased correlation between TEP concentrations and primary production (r = 0.73, p &lt; 0.05; Pearson’s correlation coefficient). In Jaran Bay, the TEP contribution was as high as 78.0% of the POC when the TEP-C content was high and declined to 2.4% of the POC when it was low. These results showed that TEP-C could be a significant contributor to the POC pool in Jaran Bay.

Depth is relative: the importance of depth for transparent exopolymer particles in the near-surface environment

Abstract. Transparent exopolymer particles (TEPs) are a major source for both organic matter (OM) and carbon transfer in the ocean and into the atmosphere. Consequently, understanding the vertical distribution of TEPs and the processes which impact their movement is important in understanding the OM and carbon pools on a larger scale. Additionally, most studies looking at the vertical profile of TEPs have focused on large depth scales from 5 to 1000 m and have omitted the near-surface environment. Results from a study of TEP enrichment in the sea surface microlayer (SML) in different regions (tropical, temperate) has shown that, while there is a correlation between TEP concentration and primary production (PP) on larger or seasonal scales, such relationships break down on shorter timescales and spatial scales. Using a novel small-scale vertical sampler, the vertical distribution of TEPs within the uppermost 2 m was investigated. For two regions with a total of 20 depth profiles, a maximum variance of TEP concentration of 1.39×106 µg XG eq2 L−2 between depths and a minimum variance of 6×102 µg XG eq2 L−2 was found. This shows that the vertical distribution of TEPs was both heterogeneous and homogeneous at times. Results from the enrichment of TEPs and Chl a between different regions have shown TEP enrichment in the SML to be greater in oligotrophic waters, when both Chl a and TEP concentrations were low, suggesting the importance of abiotic sources for the enrichment of TEPs in the SML. However, considering multiple additional parameters that were sampled, it is clear that no single parameter could be used as a proxy for TEP heterogeneity. Other probable biochemical drivers of TEP transport are discussed.

Effects of Phytoplankton Growth Phase on Settling Properties of Marine Aggregates

Marine snow aggregates often dominate carbon export from the surface layer to the deep ocean. Therefore, understanding the formation and properties of aggregates is essential to the study of the biological pump. Previous studies have observed a relationship between phytoplankton growth phase and the production of transparent exopolymer particles (TEP), the sticky particles secreted by phytoplankton that act as the glue during aggregate formation. In this experimental study, we aim to determine the effect of phytoplankton growth phase on properties related to aggregate settling. Cultures of the diatom Thalassiosira weissflogii were grown to four different growth phases and incubated in rotating cylindrical tanks to form aggregates. Aggregate excess density and delayed settling time through a sharp density gradient were quantified for the aggregates that were formed, and relative TEP concentration was measured for cultures before aggregate formation. Compared to the first growth phase, later phytoplankton growth phases were found to have higher relative TEP concentration and aggregates with lower excess densities and longer delayed settling times. These findings may suggest that, although particle concentrations are higher at later stages of phytoplankton blooms, aggregates may be less dense and sink slower, thus affecting carbon export.