Plume Water Research Articles

Sub-Micrometer Particles Remote Detection in Enceladus’ Plume Based on Cassini’s UV Spectrograph Data

Enceladus is the Saturnian satellite is known to have water vapor erupting from its south pole region called „Tiger Stripes”. Data collected by Cassini Ultraviolet Imaging Spectrograph during Enceladus transiting Saturn allow us to estimate water plume absorption from 1115.35–1912.50 Å and compare it to the Mie solutions of Maxwell equations for particles with a diameter in the range from 10 nm up to 2 µm. The best fit performed using Gradient Descent method indicates a presence of sub-micrometer particles of diameters: 120–180 nm and 240–320 nm consistent with Thermofilum sp., Thermoproteus sp., and Pyrobaculum sp. cell sizes present in hydrothermal vents on Earth.

Circum-Antarctic bottom water formation mediated by tides and topographic waves

The downslope plumes of dense shelf water (DSW) are critical for the formation of Antarctic Bottom Water (AABW), and thus to the exchange of heat and carbon between surface and abyssal ocean. Previous studies have shown that tides and overflow-forced topographic Rossby waves (TRWs) may have strong impact on the downslope transport of DSW, but it remains unclear how the combined action of these two processes influence the descent processes of DSW, and of the resulting AABW properties. Here, with a synthesis of historical in situ observations and a set of numerical model experiments, we show that tides and TRWs play comparable roles in AABW formation: they both act to accelerate DSW descent to the abyss, leading to the formation of colder and denser AABW. Yet, tides have little impact on AABW formation unless the continental slope is steep enough to suppress TRW generation. We further characterize the dynamical regimes of dense overflows around the entire Antarctic continent based on the relative importance of TRWs versus tides. These findings highlight the pervasive role of high-frequency processes, which are not well represented in the present climate models, in the formation of AABW, and thus in the global overturning circulation.

Plumes of Water Ice/Gas Mixtures Observed in the Lunar Polar Region

The presence of water condensation in the lunar polar region has been reported. However, the origin and amount of water remain unknown, and information on the migration mechanism of water is key for understanding the delivery of water to the Earth–Moon system. We herein report the first identification of the migration process observed as localized and condensed plumes of water ice/gas mixtures ejected from the lunar surface to space in the polar region based on spectral data derived by SELENE/Kaguya. We identified water and other volatile absorption in 10,200 spectra at the nonpermanent shadowed region during the nighttime when no illumination reached the lunar surface, while nearly horizontal solar light at these regions could illuminate the sky. Ray-tracing analyses suggested that the majority of the observed volatile signal did not come from the lunar surface but from the sky (space). The majority of the identified plumes were observed at or near the hydrogen distribution reported previously. Volatile materials were repeatedly identified in some locations and most of the plume events did not coincide with the major meteoroid streams. Rather, more signals were identified during the winter season in each pole. The timing, duration, location, and temperature simulations all suggest that impact events cannot be their main origin, but rather the volatile sublimation from the subsurface (∼10 cm depth). Overall, it was revealed that the lunar polar region is active in terms of volatile migration, which is significant for understanding water delivery to the Earth–Moon system.

Conductivity anomalies provide evidence of large scale hydrothermal venting in Lake Taupō

ABSTRACT Lake Taupō (Taupō moana) in the central North Island is the largest freshwater lake in Aotearoa/New Zealand. Taupō is also a frequently active and potentially hazardous caldera volcano. Water quality monitoring in Lake Taupō shows possible chemical linkages between the lake and hydrothermal systems under the lake around the Horomatangi Reef. We found that hydrothermal venting, discovered in Lake Taupō in 1998, is not a steady emission of bubbles and geothermal fluid but occasional larger fluid discharges also occur as pulses. These larger discharges contain sulphate and manifest in vertical water column profiles as conductivity anomalies. These appear to be linked to magmatic activity, which can cause earthquakes and other volcanic unrest under the lake. Rising plumes of warm water from these larger hydrothermal events can entrain sediment and other nutrients such as dissolved organic nitrogen up to the lake surface and they can continue for several months. Periods of volcanic unrest are well documented at Taupō volcano and have recently occurred in 2008–9, 2019 and 2022–23. Lake water quality data suggest that the conductivity anomalies may reflect a magmatic ‘pulse’ of this active volcano and provide evidence of large scale hydrothermal venting in Lake Taupō.

Dynamics of the surface carbonate system in oil fields with a high concentration of wells on the northwestern South China Sea shelf

Oil exploitation may pose adverse effects on marine ecosystems, but its impacts on surface carbonate dynamics remain unknown. In a carbonate system with low air-sea ∆pCO2, such as the South China Sea (SCS), human activities may affect the pCO2 distribution patterns and potentially alter CO2 sink or source at the surface. This study investigates the surface carbonate system in two oil fields, namely the Wenchang Oil Feld and Enping Oil Feld, located on the northwestern SCS (NWSCS) shelf. In Enping Oil Field, although there is a slight increase in surface pCO2 due to probable total alkalinity (TA) consumption from CaCO3 precipitation, strong biological production makes the plume water a strong CO2 sink. Similarly, the biological processes dominated the pCO2 variability in Wenchang Oil Feld, exhibiting high values in its central area. In NWSCS, the influence of shelf water was observed during both cruises. And the pCO2 drawdown caused by the decreased sea surface temperature (SST) and CO2 outgassing outweighed their increases via enhanced vertical mixing, leading to a pCO2 drawdown from September to October within this water mass. More importantly, there were no significant disparities observed in carbonate parameters at stations along transects with and without wells, and the observed parameter values in this study fell within the range reported previously on the nSCS shelf with similar controlling processes. Thus the impact of oil exploitation on carbonate dynamics is negligible, and the characteristics of the carbonate system in oil field are primarily governed by natural processes such as the mixing of plume water and basin water, CaCO3 precipitation and the changes in SST. The provided data establish a crucial baseline for detecting future alterations in carbonate chemistry within oil fields, and the rapid fluctuations in sea surface pCO2 highlight the need for higher spatiotemporal resolution observation.

Nutrient fluxes, budgets and net ecosystem metabolism in a Brazilian coastal system under drought conditions

Integrated dissolved inorganic nutrient fluxes (nitrite, nitrate, ammonium, phosphate and silicate) between Patos Lagoon estuary (PLE), Brazil, and the inner continental shelf of the southwest Atlantic Ocean, were estimated from averaged water column nutrient concentrations and water fluxes (method 1 – M1). Daily surveys were carried out for 30 days, spanning from Feb-22 to Mar-23 of 2021 during late austral summer drought, at two stations — one next to the estuary mouth, the other in the inner estuary, at the interface between the estuary main channel and a shallow embayment called the Arraial bight. On average, PLE delivered dissolved inorganic phosphorus (DIP), nitrogen (DIN) and silicate outfluxes to the adjacent continental shelf at rates of 22.4 ± 596.1, 89.8 ± 207.3 and 1715.9 ± 3283.2 × 103 mmol m−2 d−1, respectively. Budgets for DIP and DIN were computed by the LOICZ box model approach (method 2 – M2) considering Patos Lagoon divided into its limnic (fresh, mean salinity 2 psu) and estuarine (brackish, mean salinity 18.5 psu) regions. The residual fluxes for DIP and DIN from PLE to the inner continental shelf were similar to those of M1, but the complete budget (M2) revealed that PLE also imported DIP, at a positive exchange rate between PLE and coastal waters. There is evidence that DIP is supplied by Plata Plume Water. Net ecosystem metabolism (NEM) and N-fixation – denitrification were assessed through the LOICZ budgets for DIP and DIN, respectively. Denitrification prevailed in both limnic and estuarine regions. Estimated NEM indicated weak autotrophy in the limnic region, and net heterotrophy in the estuarine region. The net heterotrophy in the estuarine region was mainly attributed to nitrogen limitation due to low allochthonous supply by river discharge, and N-loss by denitrification during austral summer drought conditions.

Neogene evolution of the margin adjacent to the La Plata River Delta (Pelotas Basin): Sedimentary pathways and the origins of the Rio Grande Cone

AbstractContinental margins that exhibit high terrigenous input are generally located near deltas that are capable of transporting large quantities of sediments into the basin. However, in rare cases, high terrigenous sedimentation occurs in regions deprived of major riverine systems where the sedimentary pathway is enigmatic. One such case is the Neogene of the Pelotas Basin of Brazil and Uruguay, adjacent to the La Plata River mouth. Since the Miocene, anomalous sedimentation formed a giant progradational wedge, the Rio Grande Cone, one of the largest submarine fan‐like features on Earth. To understand the Neogene evolution of the margin and the origins of the Rio Grande Cone, here we present a seismic‐stratigraphic framework based on well‐logs and 2D seismic data. Three depositional environments are identified: (1) on the shelf, upper Miocene to Pliocene fluvial channels delivered sand deposits on the mud‐dominated shelf; (2) on the slope, sediment instability resulted in structural deformation and multiple phases of mass transport deposition and (3) on the lower slope and basin floor, large contourite drifts formed by sediment reworking. We classify the Rio Grande Cone as a megaslide complex, due to its depositional and structural setting. Local deltaic systems were active on the shelf in the Neogene, but the limited size of their paleo‐drainage systems in comparison to the volume of sedimentation in the margin suggests that an additional sedimentary pathway existed. In this sense, the demise of an epicontinental sea over the La Plata Basin during the Neogene likely enabled the input of large volumes of fine sediments into the margin, via the La Plata plume water. We suggest that the desiccation of this epicontinental sea and the intensification of ocean currents since the middle Miocene explains the anomalous Neogene terrigenous influx into the SW Atlantic margin.

Impact of a CO2 leak on the release of major and trace elements according to groundwater flow conditions in a shallow freshwater carbonate aquifer: In-situ experiments and modelling

To investigate the role of hydrogeological conditions on the release of major and trace elements during CO2 leakage occurring in shallow freshwater aquifers in a CO2 Capture and Storage context, this paper compares the results of two in-situ CO2 leakage experiments. These experiments were carried out in a shallow freshwater carbonated aquifer located in Saint-Emilion, France, during both low and high-water levels periods. In both experiments, 200 L of carbonated water were injected into a well and groundwater monitoring was carried out downstream.Due to the physical heterogeneity of the aquifer at a small scale, the CO2-rich water plume did not follow the same flow path between the two hydrogeological periods, thus highlighting preferential pathways. It was observed that geochemical changes were not of the same intensity. The concentrations of Ca2+, HCO3−, Mg2+, Fe, Mn, As, Co, Cu, Ba, Sr and V increased during the low-water level experiment while the measured concentrations only reflected the dilution of the gasified water injected during the high-water level period.

Characteristics of Black Sea dispersion of freshened and polluted transitional waters from the Dnipro-Bug estuary after destruction of the Kakhovka Reservoir dam

This study examines the characteristics of distribution of large volumes of freshened and polluted transitional waters from the Dnipro-Bug estuary across the northwestern part of the Black Sea (NWBS) that was caused by destruction of the Kakhovka HPP dam in June 2023. From June 6, 2023 to June 12, 2023 14.4 km³ of water were discharged from the Kakhovka Reservoir into the Dnipro-Bug estuary and subsequently into the sea. This volume constitutes 27% of the total annual average natural runoff of the Dnipro River (53.5 km³). During the initial days following the dam destruction water flow through the breach amounted to 40-50 thousand m³/s. The water carried a variety of pollutants into the sea that were present in the water of the Kakhovka Reservoir, in its bottom sediments, and also washed off from the flooded territories of the lower Dnipro area (more than 2000 hectares).
 The analysis of the distribution characteristics was conducted using satellite images of the sea surface color and chlorophyll a concentrations, as well as the results of hydrodynamic modeling with application of the 3-D variant of a numerical hydrodynamic model Delft3D-Flow Flexible Mesh. It was established that the plume of freshened and polluted water initially spread across the Dnipro-Bug estuarine region of the NWBS and then moved towards the sea coast of Odesa reaching it on June 9-10, 2023. Subsequently, the plume began to spread along the western sea coast and reached the Tuzlivski Limans area on June 14, 2023. After this the narrow plume of dispersed water along the sea coast began to dilute when moving towards the open sea in the form of "tongues" that had formed over the sea bottom elevations. The modeling of dispersion of a conservative neutral buoyancy admixture serving as a marker of pollution spread with the transitional waters from the Dnipro-Bug estuary showed that reduction in pollution levels took place solely due to hydrodynamic dilution (up to 60% in Odesa District of the NWBS and up to 30% in the Danube-Dniester interfluve area of the river water pollution level observed in Kherson).
 The identified characteristics were determined based on the water circulation process that formed in the Dnipro-Bug estuarine area under the influence of significant sea level gradients resulting from the inflow of large volumes of freshened transitional waters through the estuary and the Kinburn Strait during the first days, and then followed by the density currents formed at the hydrofront between the transformed river water and surrounding sea. The influence of wind conditions manifested itself in the form of spread across the NWBS of the plume of dispersed transitional water from the Dnipro-Bug estuary and the hydrofront's position and configuration. Though wind-induced currents were not dominant, they still influenced the water dynamics and distribution of concentrations of admixtures, for instance, chlorophyll a, within the freshened plume that was outlined by the hydrofront. They also promoted penetration along the coastal shallow area of transformed river water towards Odesa.

Holocene geochronology and sedimentation in the southern Brazil shelf depocenters

Latitudinal modulation of proxies for environmental changes over the mid to late-Holocene was analyzed in four cores retrieved along mud depocenters on the South Brazilian Shelf, between 33.8°S and 25.1°S. To the south, early to mid-Holocene northwards migrations of the Southern Westerly Wind Belt (SWWB) and the post-LGM sea level rise are expressed as an increase in sand content, while the low Ti/Ca and Ti/K ratios point to dry climatic conditions. During the mid-Holocene, the sea level highstand coincided with a period of stabilization in atmospheric conditions, which led to a pulse of coarser sediment deposition in the southern area. In 3000 cal yr BP, a rapid and latitudinally simultaneous increase of Ti/Ca and Ti/K mark the late-Holocene more humid and warmer onset linked to an intensification of the South American Monsoon System (SAMS). Across-shelf branches of the Brazil Current (BC) that mix with the Plata Plume Water (PPW) to flow northwards could be responsible for sediment remobilization leading to clay depletion in the south extreme of the study area. The amplitude of grain size changes gets lower as we go further north, suggesting a buffering effect exerted by the distance to the source.

Mercury fluxes from hydrothermal venting at mid-ocean ridges constrained by measurements

Methylmercury is a potent toxin threatening the global population mainly through the consumption of marine fish. Hydrothermal venting directly delivers natural mercury to the ocean, yet its global flux remains poorly constrained. To determine the extent to which anthropogenic inputs have increased oceanic mercury levels, it is crucial to estimate natural mercury levels. Here we combine observations of vent fluids, plume waters, seawater and rock samples to quantify the release of mercury from the Trans-Atlantic Geotraverse hydrothermal vent at the Mid-Atlantic Ridge. The majority (67–95%) of the mercury enriched in the vent fluids (4,966 ± 497 pmol l−1) is rapidly diluted to reach background seawater levels (0.80 pmol l−1). A small Hg fraction (2.6–10%) is scavenged to the Trans-Atlantic Geotraverse mound rocks. Scaling up our findings and previous work, we propose a mercury flux estimate of 1.5–64.7 t per year from mid-ocean ridges. This hydrothermal flux is small in comparison to anthropogenic inputs. This suggests that most of the mercury present in the ocean must be of anthropogenic origin and that the implementation of emissions reduction measures outlined in the Minamata Convention could effectively reduce mercury levels in the global ocean and subsequently in marine fish.

Laboratory investigation of the plume-to-plume interaction in a rotating tank

This paper aims to understand the characteristics and dynamical processes of two rotating buoyant fluids (two adjacent river plumes) under ideal geostrophic conditions and further reveal their interaction mechanism. Experimental studies were conducted on a rotating tank, where the discharge (Qup) and density anomaly (g′up) in the upstream inflow were modified to investigate the resultant dynamics over two plumes. Instantaneous velocity fields were measured using the particle image velocimetry to re-construct the 3D plume structure. Based on high-resolution velocity measurements, the upstream coastal current wraps around the downstream bulge and transports further downstream, in association with the downstream coastal current. An alongshore transport equilibrium theory applicable to the plume-to-plume system was proposed to classify the plume alignment types at the laboratory scale. We discover that the increasing Qup or g′up promotes the alongshore transport and inhibits the offshore extension of the downstream bulge. The g′up adjustment decides the alignment types of two interacting plumes, while the Qup adjustment determines the degree of the interaction effect. Coastal currents transform from parallel to vertical alignment as g′up decreases until they become weak coastal currents where the alignment cannot be recognized. The alignment types directly modify the mass and momentum dynamic balance and can further affect the mass exchange between plume water and ambient water. The mechanisms of two interacting plumes provide a comprehensive perspective on the multi-source river plume system in nature, such as adjacent mountainous rivers, delta estuaries, and buoyancy-driven coastal current systems.

Experimental investigation on diffusion and fountain behavior of bubble plumes in quiescent water

Bubble plumes are a common phenomenon, which are simultaneously hazardous and exploitable. Diffusion and fountain behavior, regarded as significant characteristics of bubble plumes, were investigated in this experiment utilizing high-speed photography and image processing techniques within a rectangular bubble column crafted from organic glass. The diffusion, coalescence, and collapse phenomena of bubble plumes were visualized during their ascent under varying gas flow rates in quiescent water. Furthermore, the influence of gas supply pressure, flow rate, and water depth on the fountain height was examined. The research findings demonstrate that an increase in gas supply pressure and flow rate leads to a subsequent rise in fountain height once the bubble plume reaches the surface. Conversely, a reduction in the fountain height is observed with an increase in the depth of gas release. Through the application of a dimensionless analysis method, the factors influencing the fountain height were correlated, resulting in the proposal of a relationship formula for predicting fountain height. The predicted outcomes exhibited good consistency with the data reported in this experiment.

Effects of Rapid Thermal Cycling (Cold Shock) on Fish Health: Evidence from Controlled Laboratory Experiments, Behavior, and Telemetry

Powerplants frequently use river water for cooling, subsequently discharging warm effluent. Some of these plants can cycle on and off rapidly based on electricity demand, resulting in dramatic temperature fluctuations in the receiving waters. To understand the impacts on resident fish populations in the Upper Mississippi River, we (i) assessed the effects of rapid water cooling on three native fish species; (ii) investigated whether smallmouth bass (Micropterus dolomieu) behavior favored movement into thermal plumes when given a choice of cooler or ambient water; and (iii) tracked native M. dolomieu with acoustic tags and recorded core body temperature during the thermal cycling process of a steam electric powerplant. In cold shock experiments, mortality was associated with rapid temperature declines and dependent on the final (cold) holding temperature. The species or developmental stage of the tested organism did not affect survival. When given a choice between warm and ambient waters, M. dolomieu exhibited little inclination to acclimate to the warmer water and instead “self-regulated” by moving in and out of the warm water plume. This finding was supported by telemetry data on M. dolomieu. The core temperature of the fish never increased more than 2 °C above the ambient (upstream) Mississippi River temperature, even during warm effluent discharge.

Surface microplastics in the Kara Sea: from the Kara Gate to the 83°N

Despite ongoing research into microplastics pollution in the Arctic Ocean, the region remains underexplored. In the Eurasian Arctic studies mainly focus on the Barents Sea, while there are only limited and variable data from few stations in the Kara Sea. The study aims to perform an extensive survey of microplastics floating on the sea surface in the Kara Sea. The sampling throughout the Kara Sea was carried out using a neuston net in the August 2021 starting from the Kara Gate strait, reaching 83N latitude and ending in the north-eastern part of the Barents Sea along the border with the Kara Sea. Average abundance of microplastics was 0.124 ± 0.383 items/m3 in the Kara Sea. The Kara Gate exhibited the highest abundance of microplastics (0.93 ± 0.73 items/m3), suggesting that it is an important source of the microplastics pollution of the Kara Sea. The results suggest that the Ob and Yenisey rivers do not substantially contribute to the microplastic pollution of the Kara Sea due to significantly lower concentrations in the river plume water (0.008 ± 0.009 items/m3) compared to the other regions of the Kara Sea. Further, the river plume differs in chemical composition of microplastics dominated by expanded polystyrene (EPS) particles (52%) in contrast to other regions where the predominant polymer is polyethylene (PE) (64-77%). The study highlights the potential of the Kara Sea to accumulate the microplastics due to its semi-enclosed nature and complex interaction between inflow of waters originating from the North Atlantic and Ob-Yenisey river plume.

An experimental study of steam turbulent jet condensation & upward propagation of thermal plume into sub-cooled water pool

Supersonic steam’s axial injection into water in a cylindrical vessel (1 m high and 24 cm in diameter) was achieved through a nozzle of 6 mm diameter, located at the center of the vessel. Optical examinations were determined through a steam jet to find out condensation rate, which was allied with the steam mass flux (295–672 kg/m2/s) while leaving the nozzle’s exit. The Reynolds number (i.e., 41,000–73,610) has been estimated based on most swollen section of the steam’s jet. Further beyond the condensation zone, the steam, that has been condensed, progresses into a condensed steam plume, which is surrounded by the sub-cooled water. Particle Image Velocimetry (PIV) has been applied to focus region through the mid axis of the heated water plume along a vertical plane of 100 mm × 100 mm cross sections till 400 mm from the nozzle. Central upward averaged velocity profile of the condensed water thermal plume has been evaluated at 295 and 672 kg/m2s, both have hinted the exponential decrease of mean axial velocity when the plume travels vertically upward. The radial velocity distribution of the mean axial velocity across the radial dispersal of the jet, has been obtained as self-preservable and the mean axial velocity attained the Gaussian profile by incorporating appropriate grading of axial distance and mean velocity. Other significant aspect of the current work is to apply the buoyant scaling evolved from the single-phase non-condensing upward thermal plumes to the condensed upward plume through the relations of volume flow, momentum and buoyant being computed from the steam jet operating conditions. The source values of physical dimensionless parameters such as Reynolds number (Reo), Plume Richardson number (Ripo), entrainment coefficient (αo), buoyant vertical scale (Bo) have been evaluated. Based on the radial spread of the velocity profiles along the vertical distance from the condensation region, the dynamics of the thermal and the jet propagation has been highlighted through the evaluation of the dimensionless buoyant parameters along the downstream of the plume. The present experimental measurements obtained for condensed single-phase plume are compared with the experimental results of the non-condensed single-phase thermal plume to signify the vitality of the dimensionless parameters derived from non-condensed plumes.

Analysis of plasma plume parameters in physio-chemical processes of RF plasma jet plume direct in water for the inactivation of Enterococcus bacteria

The contamination of Enterococcus bacterium is widely observed in the living environment and water. The decontamination of drinking water from the bacterial pollution is an important issue in water treatment. Here, the inactivation of Enterococcus bacteria is studied by placing the dielectric barrier discharge structure, with the RF discharge frequency of 13.56 MHz atmospheric pressure argon plasma jet, directly in water, whereas the water around the plasma plume was seething and the bubbles produced stirring all liquid volume. The ability to place a plasma jet nozzle directly in water for 10 min while maintaining a steady and uniform plasma plume, besides water temperature, provides the effectiveness enhancement in the inactivation of bacteria. The absorption of UV radiation in water is effective, and the role of UV radiation of plasma plume was mainly responsible for the destruction of peptidoglycan, which is the outer layer of Enterococcus. Then, the presence of electrons and plasma plume in water leads to the formation of hydroxyl, hydrogen peroxide, and other reactive radicals that are involved in chemical reactions, which lead to the inactivation of micro-organisms. The number of bacteria decreases from the initial value of 16 × 105 MPN/100 ml to less than 1.2 MPN/100 ml. The spectra of the plasma radiation, with the plume length 2 cm within the water, have been analyzed via the first nitrogen negative system N2+B−X. The plume temperature was calculated to be about 64 °C, which has a good agreement with water temperature measured by using a thermometer at about 67 °C after 15 min at maximum 200 W input power of the plasma jet.

Responses of Phytoplankton Communities to the Effect of Both River Plume and Coastal Upwelling

AbstractRiver plumes and coastal upwelling systems are both nutrient‐abundant habitats compared to the open ocean, and the mechanisms that structure the phytoplankton community when these occur together are unclear. In this study we investigated the dynamics and drivers of phytoplankton biomass and community composition in the Pearl River plume‐coastal upwelling system on the northern South China Sea shelf during summer. We found that phytoplankton biomass was lower in the plume than in upwelled water. Diatoms were the only dominant group in the upwelled water. In contrast, diatoms and Synechococcus were co‐dominant in the plume, and the negative correlation between the proportions of these two groups indicated that they occupied distinct niches. The lower phytoplankton biomass in plume waters was due to nutrient limitation, and there was a transition from limitation by phosphorus to limitation by nitrogen in the plume along its path. This bottom‐up control limited only diatoms, whereas Synechococcus was limited mainly by top‐down control via microzooplankton grazing. This difference led to niche differentiation of the dominant phytoplankton groups in the plume‐upwelling system. This discovery of niche differentiation enhances understanding of food web structure and will facilitate modeling of marine biogeochemical cycles.

Dynamic Characteristics of an Underwater Ventilated Vehicle Exiting Water in an Environment with Scattered Ice Floes

The presence of ice floes on the water surface has a significant impact on the complex hydrodynamic process of submersible ventilated vehicles exiting the water. In this paper, we propose numerical simulations based on computational fluid dynamics to investigate the process of a ventilated vehicle exiting water in an ice-water mixture. The Schnerr–Sauer model is used to describe the cavitation, while the turbulence is solved by using the k-ω shear stress transport (SST) model. We also introduce the contact coupling method to simulate the rigid collision between the vehicle and the ice floe. We calculated and analyzed the process of the vehicle exiting the water under three conditions: ice-free conditions and in the presence of regularly shaped and irregularly shaped ice floes. The findings indicate that the ice floes contributed to the rapid fragmentation of the water plume to induce the premature collapse of the ventilated cavity and alter its form of collapse. The presence of ice floes intensified the evolution of the flow field close to the vehicle, and their flipping led to a significant volume of splashing water that could have led to the localized secondary closure of the cavity. Moreover, the collision between the vehicle and the ice floes caused pressure pulsations on the surface of the former, with a more pronounced effect observed on the head compared with the cylindrical section. While crossing the ice-water mixture, the vehicle was exposed to water jets formed by the flipping ice floes, which might have led to localized high pressure.

Drifting in the deep: Metatranscriptomics and metabarcoding reveal sustained metabolic activity and community composition in hydrothermal vent plume microbial communities

The deep sea is the largest habitat on our planet, supporting a vast diversity of organisms which have yet to be fully described. This habitat is punctuated by hydrothermal vents in which energy derived from chemosynthesis drives carbon fixation, supporting a complex and rich food web. Connectivity between vent systems remains an active area of research, with questions as to how vent-influenced microbial function and diversity persists over space and time. In particular, the role hydrothermal vent plumes play as potential highways for connectivity and biogeography is not well understood. To add to the growing body of research, this study sampled plume waters above the Moytirra hydrothermal vent field, located just north of the Azores. We examined how hydrothermal vent plume community biodiversity and metabolic activities change with distance from the vent using a combination of metabarcoding and metatranscriptomic sequencing. We detected a rich diversity of both prokaryotic and eukaryotic organisms inhabiting the plume, which remained metabolically active for kilometers from the vent source. Enriched sulfur metabolism functional signals and relative abundance of sulfur oxidizing bacteria suggest reduced sulfur compounds are a fundamental energy source within plume waters. Additionally, we observed evidence of top-down controls on primary production through both known grazers and putative viral activity. Although community-level functional signals suggest active metabolic functions for over a kilometer north or south of the vent field, these functions grew increasingly dissimilar to those observed directly above the vent site, and bacterial communities displayed indications of entering quiescent stages, likely due to decreasing resources and reduced temperatures. These data provide a first glimpse of Moytirra’s microbial biodiversity, in addition to providing a high-resolution understanding of life on the drift within a hydrothermal plume, its persistence with distance, and implications for connectivity.