Plume Water Research Articles

Heat sink temperature modeling for reservoir source heat pumps with experimental validation

Heat-pump systems utilizing renewable resources can significantly enhance the energy efficiency of building air conditioning. This study focuses on a system that uses reservoir water as a renewable resource and develops a macroscopic numerical model to simulate heat sink temperatures, which critically influence the energy efficiency of heat pumps. Experiments were conducted to gather essential data for constructing this model. Heat was released, simulating the exhaust heat from a heat pump, from the bottom of an experimental tank filled with water. Initially, the water was thermally stratified, with the lower half at 15 °C and the upper half at 25 °C, mimicking summer conditions. The experimental results indicated that the heat release caused temperature increases exclusively in the lower layer, elevating the boundary between the layers by 0.2–0.4 m over 5 h. Consequently, we developed a heat sink temperature model by simulating the plume and entrainment of ambient water to replicate this phenomenon. The model accurately represented the increase in the boundary height across different scenarios, demonstrating a high level of agreement between the simulated heat sink temperature and the experimental values, with a deviation of <0.8 K.

Late-Holocene paleoreconstruction of the Southwestern Atlantic Ocean: A multiproxy understanding of the paleoclimatic, paleoproductivity and paleotemperature variability

A multiproxy evaluation focusing on sedimentological, molecular, and isotopic proxies was used to reconstruct the environmental changes on the SW Atlantic Ocean margin enabling an integrated assessment of this basin’s Late-Holocene oceanographic and climatic dynamics. Variations in paleoproductivity, climate, and sea surface temperature (SST) indicate three phases throughout the core. The first phase (2800–1600 cal yr BP) showed a generally low marine and terrigenous organic matter input, marked by terrigenous material input pulses transported by the Brazil Current (BC) from small rivers of the South Brazil Bight (SBB) and/or Paraiba do Sul River. The second interval (1600–1300 cal yr BP) registered the lowest levels of fine sediments, total organic carbon content, and concentrations of all analyzed lipid biomarkers, indicating the occurrence of a semi-stationary meander of the BC that hindered the sedimentation of fine sediments. This phase may indicate a varied timing and duration due to the sparsed radiocarbon data. The third interval (1300 cal yr BP to modern years) presented the highest levels of marine and terrigenous proxies and were influenced by the strengthening of the South America Monson System (SAMS), the El Niño Southern Oscillation (ENSO) events, and the NE winds, which caused higher precipitation in the La Plata River drainage basin. A northward displacement of the Brazil Coastal Current (BCC) and the transport of the Plata Plume Water (PPW) to the central regions of the SBB, as well as the occurrence of more regular upwelling events may also influence the sedimentary organic matter composition. SST showed a variation up to ~3.2°C through the core and was related to the influence of the BC current associated with the Tropical Water (TW) and the South Atlantic Central Water (SACW), and the PPW influence on the shelf.

Bifurcation Graphs for the CR3BP via Symplectic Methods

In this article, using the symplectic methods developed by Moreno and Frauenfelder (aimed at analyzing periodic orbits, their stability and their bifurcations), we will carry out numerical studies concerning periodic orbits in the Jupiter–Europa and Saturn–Enceladus systems. We will put emphasis on planar-to-spatial bifurcations, from deformation of the families in Hill’s lunar problem studied by Aydin. We will also provide an algorithm for the numerical computation of Conley–Zehnder indices, which are instrumental in practice for determining which families of orbits connect to which. As an application, we use our tools to analyze a well-known family of Halo orbits that approaches Enceladus at an altitude of 29 km, which bears interest for future space missions that visit the water plumes.

Sea-air CO2 exchanges, pCO2 drivers and phytoplankton communities in the southwestern South Atlantic Ocean during spring

Hydrographic properties and carbon dioxide partial pressure (pCO2) were measured through underway survey of surface waters during spring 2014, mainly along the Surface Haline Front in the continental shelf-break domain in the southwestern South Atlantic Ocean margin. Additionally, discrete seawater surface samples were collected along the ship track to identify the phytoplankton community and measure seawater chemical properties. This study aims to identify the drivers of the marine CO2‑carbonate chemistry and the role played by the phytoplankton composition on changes in the surface marine carbonate properties and the sea-air CO2 exchanges in two biogeochemical provinces (i.e., South Brazil Bight – SBB, and Southern Brazilian Shelf – SBS) governed by the dynamics of the Brazil Current system in the South Atlantic Ocean. The water masses identified on the surface of the region were Tropical Water (mostly present at offshore regions), Subtropical Shelf Water (mostly present over the continental shelf and slope), and Plata Plume Water (present in the south coastal domain of the SBS). On average, the study area behaved as a weak net CO2 outgassing zone of 1.2 ± 2.3 mmol m−2 d−1 during the spring, despite some subregions behaving as CO2 ingassing zones. The CO2 uptake verified in the SBB was related with mesoscale activity bringing cold waters in the region while CO2 uptake in the continental shelf domain of SBS was associated with the presence of cooler and fresher Plata Plume Water. Changes in total alkalinity and dissolved inorganic carbon at surface were mainly governed by CaCO3 production in SBB and seawater dilution in SBS, although other processes may also have influenced on their spatial variability. The dominant phytoplankton groups were haptophytes (31 %), Trichodesmium (21 %), and picocyanobateria (28 %), corresponding to Synechococcus (17 %) and Prochlorococcus (11 %). The dominance of the diatom group was associated with a decrease in sea surface pCO2 (mainly at coastal zones at southern areas), although the sea-air CO2 exchanges were regulated by cooling process due the presence of Plata Plume Water in that region. Changes in surface pH were related to high concentration of Trichodesmium slicks at offshore zones with the highest microalgae concentration, leading to pH drops of up to 0.4. Trichodesmium slicks likely allowed the development of haptophytes in offshore oligotrophic waters due to its role on N2 fixation. An increase of ∼20 % in the dominance of haptophytes contribution was verified in that situation, which was likely in a post-bloom development stage, since an increased dissolved inorganic carbon content was observed, associated with a prevalence of net respiration processes.

Microplastic fate in Arctic coastal waters: accumulation hotspots and role of rivers in Svalbard

Little is known about the role of remote and sparsely populated Arctic coastal zones in the microplastic cycle. Distribution of microplastics was studied in the Svalbard fjords in June – July 2022 with the main goal of assessing rivers’ role in the fate of microplastic in Arctic coastal waters. Surface microplastics (0 – 20 cm depth, 500 – 5000 µm size) were sampled with a neuston net in triplicate per study site in parallel with sampling of subsurface microplastics with a pump system (1.5 m depth, 100 – 5000 µm size). The central part of Isfjorden and its several branches covering populated and unpopulated fjords were studied; the sampling was conducted during an intense riverine discharge in all studied sites. Maximum abundance of surface microplastics (71,400 items/km2 or 0.19 iterms/m3, 0.19 mg/m3) was found along the river plume border in the middle of populated Adventfjorden indicating importance of both local sources and surface hydrodynamics in the formation of microplastics accumulation hotspots. All other unpopulated fjords were free of the floating on the sea surface microplastics as river discharge prevented transport of microplastics inside the fjords. The highest concentration of subsurface microplastics was found in the central part of Isfjorden and the lowest – in river plume waters, which also indicates the removal of microplastics from the inner part of fjords during an intensive river discharge. Our results may suggest that Arctic rivers flowing through unpopulated areas bring clean water and thereby reduce level of microplastic pollution in the coastal waters. In contrast to the rest of the world’s ocean, rivers are not the main source of microplastic pollution in the Arctic Ocean.

A search for water vapor plumes on Europa by spatially resolved spectroscopic observation using Subaru/IRCS

Abstract We present near-infrared high-dispersion spectroscopic observations of Europa using the Infrared Camera and Spectrograph (IRCS) onboard the Subaru Telescope, seeking direct evidence of water plumes on Europa and exploring spatial variations in plume activity. Using the high spectral/spatial resolution and sensitivity of Subaru/IRCS, our observations have enabled a spatially resolved search for water plumes on Europa. Within our detection limits and time of observation, we found no evidence for the presence of water emission. For a rotation temperature of 50 K, we derived an upper limit on the H$_{2}$O abundance of 9.46 $\times$ 10$^{19}$–5.92 $\times$ 10$^{20}$ m$^{-2}$ in each divided slit area and 4.61 $\times$ 10$^{19}$ m$^{-2}$ in the entire area covered by the slit. This upper limit lies below the inferred water abundance from previous UV observations by the Hubble Space Telescope, while being less sensitive by a factor of three compared to the Keck telescope and by one order of magnitude or more than the James Webb Space Telescope observations. Our results align with previous studies and demonstrate that using Subaru/IRCS is an effective strategy for searching for water plumes on Europa with high spatial resolution. Continued observations across different surface areas and orbital phases are essential to fully characterize Europa’s plume activity and complement upcoming space missions.

Monitoring the Amazon River plume from satellite observations

ABSTRACT Most of our knowledge about the Amazon River plume is limited from the field experiments or modeling due to various challenges for satellite remote sensing, i.e., constant cloud coverage, atmospheric correction, and difficulties to differentiate the Amazon River plume from normal Atlantic Ocean water. In this study, observations of ocean properties from the Visible Infrared Imaging Radiometer Suite (VIIRS) and sea surface salinity (SSS) from the Soil Moisture Active Passive (SMAP) missions in 2021 are used as an example to demonstrate the capability to monitor the Amazon River plume on daily basis and characterize the change of the ocean environment driven by the offshoots and migration of the plume in the western tropical Atlantic Ocean. The start, development, evolvement, dispersion, and dissipation of the Amazon River plume in 2021 in the western tropical Atlantic Ocean were effectively monitored. The extensive influence of the Amazon River runoff mostly occurred between June and November. The water diffuse attenuation coefficient at 490 nm (K d (490)) and SSS were significantly impacted by the Amazon River plume in the vast region of the western tropical Atlantic Ocean. The routes of the Amazon River plume that flowed into the Atlantic Ocean were highly variable. High turbidity, low salinity plume water with K d (490) reaching ~1.0 m−1 and SSS ~25 practical salinity unit (psu) was found in a region over 500 km from the Amazon River Estuary. The comparison of the Amazon River plume in 2020 and 2022 further shows the complication of the driving forcing and inter-annual variability of the Amazon River plume. The combination of gap-free satellite ocean color and SSS observations provided a new tool to monitor the short-term variability of the Amazon River plume and assess its seasonal and interannual impact on the ocean environment in the western tropical Atlantic Ocean.

LARGE-SCALE LANDSLIDES DUE TO SALINE WATER PLUME INTRUSION - AN EXAMPLE OF THE OKIMI LANDSLIDE IN NIIGATA PREFECTURE, JAPAN

Large-scale landslides with volumes ranging from tens to hundreds of millions of m3 are scattered throughout Niigata Prefecture, Japan. There is no accepted theory, although many researchers have argued about the mechanism of these landslides. Highly concentrated Na-Cl type groundwater (hereafter called "saline water") has often been found in large-scale landslides in Niigata Prefecture. In addition, the observation wells where saline water occurs are sometimes flowing wells. We also pay special attention to the distribution of landslide-prone areas and oil and gas fields in Niigata Prefecture, which generally overlap, and saline water from landslides is originally fossil seawater such as oil-brine based on geochemical characteristics. On the other hand, anomalous high-pressure reservoirs at depths of more than 1,000 m in oil and gas fields have been known since the 1960s and are possible saline water sources. We believe saline water's behavior is key to better understanding the mechanism of large-scale landslides. The Okimi landslide, this research area, is located in the Kamiya area, Joetsu City, western part of Niigata Prefecture, Japan. The aspect of the active body is about 500 m wide and 1,500 m long, with an area of about 70 ha. The bedrock geology is mainly Neogene unconsolidated mudstone. According to previous studies, saline water has been detected in observation wells at the head of this landslide. Since the geological formation containing saline water has a considerably low resistivity value (≤ 2.0 Ωm), the CSMT method is best suited for electromagnetic exploration to visualize the resistivity up to 1,000 m depth. The survey results confirm the existence of a saline water plume rising from a "saline water chamber" located 100 to 300 m below the western side of this landslide to the bottom of this landslide (at a depth of about 30 m). The presence of the saline water plume suggests that the upwelling of saline water from the anomalous high-pressure reservoir (saline water chamber) is closely related to several large-scale landslides.

Wind and river effects on a coastal current in Chatham Sound, British Columbia

Chatham Sound is an ecologically and economically important semi-enclosed basin in the northeast Pacific which has received only limited oceanographic attention. Here we investigate the surface circulation in the southern Sound by analyzing hourly current fields obtained from a high-frequency (HF) radar array, installed there in 2017 and still in operation, as well as other hydrographic and mooring measurements that allow us to characterize subsurface features at several specific locations during 2018 and 2019, and satellite imagery processed to obtain a measure of suspended particulate matter at high spatial resolution. We find that the surface circulation is dominated by the plume of the Skeena River, which flows into the southeast corner of the Sound. On average, this plume forms a northward flowing coastal current in the eastern half of the Sound, and is turbid during the freshet. The plume width changes only marginally even though the Skeena’s flow changes seasonally by a factor of about 7. However, the depth of the plume and its salinity is dramatically different during the early summer freshet compared to values in winter. Fastest plume currents appear near the offshore edges of the plume, even though the plume depth is greatest near the coast. We show that these features are consistent with those predicted from an analytical 1-1/2 layer buoyant coastal current model. Winds can accelerate or retard the coastal current; when strong enough the flow is arrested and turbid plume water fills the southern Sound.

The impact of the destruction of the Kakhovka reservoir dam on the oceanographic conditions in the north-western part of the Black Sea according to the results of modeling

Based on the results of numerical modelling, characteristic features of distribution of transformed and polluted waters of the Dnieper River in the water area of the north-western part of the Black Sea (NWBS) are determined and analyzed. This pollution of the marine environment resulted from the extremely large man-made flood caused by the destruction of the Kakhovka Reservoir dam by the Russian occupation forces in June 2023. Various types of pollutants, which contained in the Kakhovka Reservoir, in the lower Dnieper River and in the bottom sediments, were carried out into the sea by the flood discharge. A significant amount of pollutants was washed into the sea from the flooded areas of the lower Dnieper basin. Special attention is given to changes in oceanographic conditions in the Dnieper-Bug estuary region (DBR) of the Black Sea, which determine the extent of marine pollution. Sea water salinity was used as an indicator of the degree of infiltration of polluted seawater from the estuary into the sea. It was identified that the least transformed river waters with low salinity correspond to high pollution levels. Delft3D-Flow Flexible Mesh hydrodynamic model, developed by Deltares, was used in this study. The simulation was performed for the time period 01 to 30 June 2023. During the first days after the dam break the desalinated and polluted transitional waters, flowing from the Dnieper-Bug estuary, spread over the entire water column down to 15-20 m depth in the DBR area. In this case, the spreading of transitional waters was atypical, as it usually occurs only within the thin near-surface layer of the sea. By mid-June the flow of transitional water with a salinity of 4-6 ‰ covered the entire water column from surface to bottom near the northern coast of the NWBS and over the Odessa Bank. This was facilitated by the supermassive volumes of transformed Dnieper river waters flowing out over a short period of time due to dam break, as well as by the resulting intense gradient currents and mixing caused by spatial gradients in the velocity of the generated currents. The width of the desalinated water plume and its area in the bottom layer were smaller than in the surface layer. The largest vertical salinity gradients were formed to the south of the Odessa Bank, where salinity was 4-6 ‰ in the surface layer and 14-17 ‰ in the bottom. Dilution of the desalinated water plume in the bottom water layer was much more intensive than in the surface water. The character of water circulation pattern in the northern part of the NWBS in the first days after the inflow of transient waters from the Dnieper-Bug estuary was determined by the runoff gradient currents, which later were replaced by wind-driven currents in the Odessa area and over the Odessa Bank, and by the meandering flow of gradient density currents further south. The findings of this study contribute to a better understanding of the impact of the inflow of transformed river waters from the Dnieper-Bug estuary on the variability of oceanographic characteristics and the ecological state of marine waters in the Dnieper-Bug region of the northwestern Black Sea.

River water heat pumps to decarbonise district heating and promote the resilience of hydrosystems: Technico-economic, environmental and sociological challenges

The interdependence between water and energy (water-energy nexus) has been identified as one of the major challenges at European level, with roadmaps calling for the development of integrated approaches in this sector. The increase in river temperature is at the heart of this nexus, with anthropogenic thermal pollution adding to the effect of global warming. River Water Heat Pumps can play a major role by decarbonising district heating network (DHN) while actively cooling the aquatic resource. Hence, the objective of this short communication is to identify the scientific challenges to be met and the progress to be achieved considering the current state of the art. To illustrate the point, a rapid evaluation of the potential is performed for the city of Lyon in France resulting in an achievable cooling of ∼1.5 K which is above the minimum threshold to see an effect on aquatic ecosystem while the CO2 savings are significant for the DHN (∼ divided by a factor of 10). Because of its holistic nature, the impact assessment of such a system implies considering a wide diversity of indicators: energy, environmental, economics and sociological that need to be appropriately defined and quantified. In each field, progress beyond the state of the art to be performed has been identified, e.g. 4E analysis, cold water plume dispersion, integration of biodiversity in LCA.

Simple olfactory navigation in air and water

Two simple algorithms based on combining odor concentration differences across time and space along with information on the flow direction are tested for their ability to locate an odor source in four different odor landscapes. Image data taken from air plumes in three different regimes and a water plume are used as test environments for a bilateral (“stereo sampling”) algorithm using concentration differences across two sensors and a “casting” algorithm that uses successive samples to decide orientation. Agents are started at random locations and orientations in the landscape and allowed to move until they reach the source of the odor (success) or leave the imaged area (failure). Parameters for the algorithm are chosen to optimize success and to minimize path length to the source. Success rates over 90% are consistently obtained with path lengths that can be as low as twice the starting distance from the source in air and four times the distance in the highly turbulent water plumes. We find that parameters that optimize success often lead to more exploratory pathways to the source. Information about the direction from which the odor is coming is necessary for successful navigation in the water plume and reduces the path length in the three tested air plumes.

High-resolution UK’37 sea surface temperature reconstruction in the southwestern Atlantic Ocean during the Holocene

Modern sea surface temperatures (SST) were assessed using the alkenone calibration index (UK′37; SST-UK′37) values from twenty-one core-top sediment samples collected along the Southwestern Atlantic Ocean and validated by comparison with satellite-derived SSTs. The SST-UK′37 values revealed an annual signal between 28 and 30°S and a winter signal (83% of the region samples) between 30 and 34° S, with deviations falling within the UK′37 calibration error range. The paleotemperature (SST-UK′37) reconstruction through the Holocene was performed using two high-resolution marine sediment cores from 33 to 34°S latitude band. Millennial-scale variations dominate most of the SST-UK′37 results with changes up to ∼6 °C. Considering the modern ocean circulation dynamics, the SST-UK’37 in our records likely stems from the combined influence of the Subtropical Shelf Front (STSF) position and the interaction between the warm, salty, and nutrient-poor Subtropical Shelf Water (STSW) and the cold, fresh, and nutrient-rich Subantarctic Shelf Water (SASW). Our SST-UK’37 results also suggest that the northernmost position limit of the STSF reached around 33°S during the mid-to-late Holocene, while after ∼5500 cal yr BP the Plata Plume Water became the dominant influence on the regional SST-UK’37 signal. Spectral analyses revealed statistically significant oscillations of ∼8600 and ∼ 2250 years in record MDBT 557, and ∼ 5300 and ∼ 2600 years in record MDBT 561 which suggests the influence of Southern Westerly Winds (SWW) on the SST-UK’37, and therefore, on the STSF dynamic through the Holocene.

Impact of river-discharged freshwater on surface ocean environments revealed by synergistic use of satellite measurements in the East China Sea

River discharge forms a plume of low-salinity water that spreads offshore, delivering terrestrial substances into the ocean and thus plays a critical role in controlling marine environments as well as the carbon cycle. This study investigated how freshwater discharged from the Changjiang impacts the physical and biological responses and oceanic uptake of carbon dioxide (CO2) in the northern East China Sea (ECS) by combining the recently available sea surface salinity (SSS) product from the Soil Moisture Active Passive (SMAP) mission with other satellite measurements of sea surface temperature (SST) and chlorophyll-a (chl-a) concentration. The partial pressure of CO2 (pCO2) and its interannual variability were estimated using empirical regression with satellite-derived environmental variables. The bias-corrected SMAP SSS revealed that river discharge largely contributed to the distinct interannual SSS variations, with a seasonal cycle reaching a maximum in winter and a minimum in summer. Compared to the SST and chl-a anomalies, we observed an increase in SST and primary production in the region where sea surface freshening was robust. Freshwater from rivers contributes to sea surface warming by trapping heat from the atmosphere at the surface layer. Nutrient-enriched freshwater within the buoyant plume enhances phytoplankton production, which in turn enriches the ocean surface with chl-a. Simultaneously, the pCO2 was relatively low in the region where the SST and primary production were high, highlighting that the heat and riverine nutrients trapped within the buoyant plume contributed to the reduction in pCO2 by promoting the biological uptake of CO2. The estimates conducted here illustrate the synergistic utility of multiple satellite measurements for the evaluation of CO2 uptake capacity, complemented by in situ measurements of river-dominated marginal seas.

Hypoxia Triggered by Expanding River Plume on the East China Sea Inner Shelf During Flood Years

AbstractThe frequency of riverine floods is predicted to increase in East Asia. However, the response of coastal hypoxia (&lt;63 μmol L−1) to floods has not been well understood. In the summer of 2020, characterized by one of the most significant Changjiang water fluxes in three decades, we conducted a cruise during the flood period on the East China Sea inner shelf. Our observations revealed severe bottom hypoxia with a maximum spatial coverage of ∼11,600 km2 and a minimum dissolved oxygen concentration (DO) of 21 μmol L−1. In the surface layer, the relationships between salinity and nitrate, dissolved inorganic carbon (DIC) indicated significant organic matter production, validated by a high‐Chlorophyll‐a (Chl a) patch (&gt;5 μg L−1). Furthermore, the significant relationship between apparent oxygen utilization and DIC of deep waters reveals that the organic matter decomposition primarily drove the hypoxia during the flood period. Episodic wind events also influenced bottom DO and DIC, by transporting surface waters to the deep. Multiple‐years data set shows that the average Changjiang nitrate flux during flood years is about 1.4 times that during non‐flood years. The flood waters mix with estuarine waters, forming the high‐nutrient plume waters, which expanded farther offshore during the flood period. While high turbidity remained confined to the inner estuary. Consequently, the high‐Chl a area significantly expanded, which significantly exacerbated the hypoxia.

Trajectory, fate, and magnitude of continental microplastic loads to the inner shelf: A case study of the world's largest coastal shallow lagoon

The Patos Lagoon estuary is a highly significant ecosystem where freshwater from a vast and densely populated area continuously flows into the Atlantic Ocean by coastal plumes, exporting not only freshwater but also sediment, nutrients, plastics, and other contaminants. In this work, numerical modeling tools together with field data were used to assess for the first time the capacity of the coastal plume to export microplastics (MPs) to the inner shelf under different hydrodynamic conditions. Two field surveys were conducted during plume events to quantify MP concentrations and validate the model approach. A bottom-up approach was employed to estimate the potential MP export from the estuary's domain to the Atlantic Ocean. MP concentration in surface plume waters ranged from 0.20 items m−3 to 1.37 items m−3, confirmed by FTIR as synthetic polymers in a 90 %, being Polypropylene (PP) and Polyethylene (PE) the most abundant in a 73 %. The accumulation pattern was observed on the plume's frontal system, consistent with simulation results. The estimated average MP potential export rate attained 9.0 million items day−1 during moderate plume events and 47.5 million items day−1 during high discharge plume events. Strong discharge events, coupled with intense northeast winds, facilitated rapid southwestward export of MPs. Conversely, moderate to weak discharge events retained MPs closer to the estuary's mouth, enabling either longer trajectories or earlier deposition. Significant MP accumulation hotspots were identified in the gyre between the jetties and Cassino beach, as well as in the saline front within the plume boundaries. These accumulation zones may function as reservoirs for MP particles, potentially posing threats to local ecosystems. Understanding these dynamics is crucial for ongoing monitoring efforts to assess potential harmful interactions over time.

Continuity and Enhancements in Sea Surface Salinity Estimation in the East China Sea Using GOCI and GOCI-II: Challenges and Further Developments

During the summer, substantial freshwater discharge from the Changjiang River into the East China Sea (ECS) results in extensive low-salinity water (LSW) plumes that significantly affect regions along the southern Korean Peninsula and near Jeju Island. Previous research developed an empirical equation to estimate sea surface salinity (SSS) in the ECS during the summer season using remote-sensing reflectance (Rrs) data from bands 3–6 (490, 555, 660, and 680 nm) of the Geostationary Ocean Color Imager (GOCI). With the conclusion of the GOCI mission in March 2021, this study aims to ensure the continuity of SSS estimation in the ECS by transitioning to its successor, the GOCI-II. This transition was facilitated through two approaches: applying the existing GOCI-based equation and introducing a new machine learning method using a random forest model. Our analysis demonstrated a high correlation between SSS estimates derived from the GOCI and GOCI-II when applying the equation developed for the GOCI to both satellites, as indicated by a robust R2 value of 0.984 and a low RMSD of 0.8465 psu. This study successfully addressed the challenge of maintaining continuous SSS estimation in the ECS post-GOCI mission and evaluated the accuracy and limitations of the GOCI-II-derived SSS, proposing future strategies to enhance its effectiveness.

Characterizing dissolved inorganic and organic nutrients in the oligotrophic Kuroshio Current off eastern Taiwan during warm seasons

This study conducted sensitive and precise analyses of dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) concentrations and trace concentrations of nitrate and nitrite (N+N) and soluble reactive phosphorus (SRP) in seawater. The methods were applied to investigate the distributions and controls of N+N, SRP, DON, and DOP in the oligotrophic Kuroshio Current (KC) area off eastern Taiwan during warm seasons. The water in the studied area was classified into four major types: typical Kuroshio water (KW), KW influenced by the East China Sea water, KC influenced by the South China Sea (SCS) water, and KW influenced by the SCS water and river plumes, which is confined to the coastal zone. Nutrient distributions in KC revealed very low N+N (0.002−0.40 μM) and SRP (0.015−0.125 μM) concentrations but high DON (&amp;lt;8 μM) and DOP (&amp;lt;0.3 μM) concentrations above the nutricline depth, which accounted for &amp;gt;80% of TDN and TDP, respectively; theses concentrations can primarily be attributed to strong, permanent surface stratification. Among the water types, KW had the lowest N+N, SRP, DON, and DOP concentrations but greatest chlorophyll maximum depth and nutricline depth, except for in locations influenced by island-induced upwelling. The concentrations of all nutrients increased by various degrees in the other water types, which was attributed to the exchange and mixing of different water masses and coastal uplift of subsurface waters. KW was not only highly oligotrophic but also N+N-limited reflected from very low [N+N]/[SRP] ratio (0.02−0.15) in the mixed layer (ML). Overall, the N+N limitation and high nitrate anomaly value (N*: 2.47 ± 0.16 μM) above the nutricline depth strongly indicate prevailing N2 fixation at the surface of KW. Very high DON/DOP ratio in KW (16.9−69.1) probably resulted from the release of N-rich organic nutrients from phytoplankton including N2 fixers at the surface and faster recycling of DOP than DON in deep waters. Persistent coastal uplift of subsurface water occurs everywhere over the shore-side region of the KC, resulting in increasing surface concentrations of nutrients and chlorophyll a. Overall, the aforementioned physical and biogeochemical processes determined the upper-ocean distributions of nutrient species in warm seasons.

Glimpsing the 2020 spring bloom in the Strait of Georgia (Canada) with autonomous ferry-based sensors

Spatiotemporal observations are data rich and offer insights into links between ecological patterns and underlying processes. We present fine-scale autonomous observations from repeated ferry transects in the Strait of Georgia (British Columbia, Canada) during the 2020 spring bloom period using a FerryBox system (temperature, salinity, chlorophyll a fluorescence) and a digital inline holographic microscope. Despite instrument cleaning interruptions related to COVID-19 restrictions, 3 periods from late winter (February) to springtime (March and April) contained 14 days of high-quality holograms (&gt;70000) capturing &gt;10500 identifiable micro- to mesoplankton using automatic object detection. The ferry set-up provided automatic data storage through Ocean Networks Canada, which also automatized data flagging and guaranteed remote access. The highest-quality holograms repeatedly covered the central and eastern Strait and showed aspects of bloom succession. Fast-growing diatoms (Skeletonema sp.) emerged first, followed by a diverse assemblage including Chaetoceros spp., Ditylum spp., and Eucampia spp., and by April, larger centric cells prevailed. The combined approach captured local suppression of chlorophyll a fluorescence and diatom concentrations in Fraser River plume waters during the freshet, suggesting fine-scale spatial patterns in seasonal planktonic community composition. This work is among the first of its kind to autonomously generate in situ imaging and physicochemical data with spatiotemporal resolution.

The Plata plume water penetration into the southwestern Atlantic shelf during the Holocene

The Plata plume water penetration into the southwestern Atlantic shelf during the Holocene