Water Circulation Patterns Research Articles

Microfacies and species richness analysis of upper Bartonian and Priabonian carbonate shelf deposits from the Thrace Basin (Tethyan Ocean, Greece): Paleoenvironmental evolution and species-richness hotspot revealed

Sediment, thin section, microfacies and foraminiferal analyses were conducted on middle-upper Eocene carbonate deposits to shed new light on the paleoenvironmental evolution and species richness of the Thrace Basin (Tethyan Ocean, Greece). Material from a total of 7 new sites, covering localities on the mainland and the north-eastern Aegean islands of Samothraki and Lemnos, was examined in order to analyze the general conditions and environmental evolution of the basin over as large a geographical area as possible. Analysis of the sedimentological and paleontological data allowed the identification of 5 microfacies types. These can be assigned to a sequence of interior to outer shelf environments and speak in favor of a model of a rimmed carbonate shelf with isolated platforms. Both open and restricted water circulation patterns have prevailed on and between the platforms. Triggered and driven by dynamic syn-rifting, topographic highs have developed in this area on which productive and species-rich reef structures could thrive. In the late Eocene carbonate deposits we found the highest documented species richness of larger symbiont-bearing foraminifers (LBF) to date, characterizing the Thrace Basin not only as a particularly species-rich and diverse area, but also as a LBF hotspot of diversity.

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.

Reconstructing Redox Landscape With Coupled Nitrogen‐Sulfur Isotopes: A Case Study From Middle‐Late Triassic Chang 7 Member of the Yanchang Formation in the Ordos Basin (North China)

AbstractEuxinia, a crucial geological condition, usually signifies more severe extinction events attributed to deoxygenation in Earth's history. Despite extensive exploration of various proxies in paleoredox studies, most are primarily utilized to reconstruct atmospheric pO2, the proportion of anoxic water relative to the entire basin, and broader trends in redox states. Few, however, hold the capacity to precisely delineate local euxinia within confined areas. To address this gap and gain insights into the temporal and spatial extent of benthic euxinia, we propose leveraging the synergistic analysis of total nitrogen isotopes (δ15NTN) and pyrite sulfur isotopes (δ34Spy). Our study focuses on the Triassic Chang 7 Member from the Yanchang Formation, Ordos Basin, North China. Through coupling the δ15NTN and δ34Spy systematics on 11 drill cores within the Ordos Basin, we reconstruct the temporal and spatial distribution of the benthic euxinia zone during the Chang‐7 period. Our results suggest strong spatial heterogeneity of benthic redox conditions, with the euxinia boundary shifting from the central lake to the southwestern sections. Moreover, we identify redox‐controlling factors, including organic carbon loading, water depth, and potential water circulation, and evaluate their interplay with benthic euxinia. Furthermore, the discernment of water circulation patterns may provide an innovative approach to restore the paleowind direction. These findings highlight the effectiveness of coupling δ15NTN and δ34Spy in reconstructing the local benthic redox landscape of benthic environments, and enrich our understanding of biogeochemical processes.

The causes of algal blooms exist significant scale effect in tributary of the Three Gorges Reservoir

Algal blooms of rivers becomes a global issue, while there is controversy over the attribution of blooms due to the differences of research scales. This study utilized random forest and spatiotemporal geographically weighted models to explore the triggers and mechanisms of blooms from the different spatial resolutions (river, local and grid scales) in tributary bay of the Three Gorges reservoir based on Sentinel-2 data and Environmental Fluid Dynamics Code model. The results indicated that blooms in the Daning River were more severe during the spring and summer, with the average chlorophyll about 10.15 ug/L and 9.55 ug/L. The high-risk areas primarily located in the middle reaches (10.65 ug/L). The causes of blooms existed significant scaling effect. The water temperature recognized at the river scale was not a sufficient condition for blooms in the early stage of drainage. Compared with temperature, the relative importance of Zme ranked in the top three, which highlighted the influences of Zme at the local and grid scales. The macro-analysis identified the importance of water level fluctuations during drainage stage and the low level period, with ranking in the top two. The effects indirectly altered Zme and Zm, thus highlighting triggering effect of Zme and Zm at local scales. During the stage, thermal stratification and water circulation patterns determined the heterogeneity of blooms. The lag time between chlorophyll and these key factors ranged from 1 to 5 days. This diagnostic to the spatiotemporal scale contributes to understand of the formation mechanism of algal blooms in the tributary bay of the Three Gorges reservoir, providing reference for early warning and prevention strategy.

Net Transport Patterns of Surficial Marine Sediments in the North Aegean Sea, Greece

The spatial distribution of sediments on the seafloor reflects the various dynamic processes involved in the marine realm. To analyze sediment transport patterns in the North Aegean Sea, 323 surficial samples were obtained and studied. The granulometry data revealed a diverse range of grain sizes of surficial sediments, ranging from purely sandy to clay. The predominant size classes were silt and muddy sand, followed by sandy silt and mud. However, there were very few samples that fell within the clay classes. The sorting coefficient ranged from 0.21 to 5.48, while skewness ranged from −1.09 to 1.29. The sediment transport patterns were analyzed based on the grain-size parameters (mean, sorting, and skewness). The results showed the variability of flow parameters involved in sediment distribution. River influx and longshore drift near the shoreline are the most significant factors affecting sediment transport. At the open sea, sediment distribution is mainly controlled by general water circulation patterns, especially by the outflow of low-salinity waters from the Black Sea through the Dardanelles and the Marmara Sea. The heterogeneity of sediment textural parameters across the study area suggests that seafloor sediments are further reworked in areas where water masses are highly energetic. It can be concluded that open sea water circulation controls sediment distribution patterns at the open shelf, while close to the coast, river discharge plays a key role.

Evolution of ocean circulation and water masses in the Guaymas Basin (Gulf of California) during the last 31,000 years revealed by radiolarians and silicoflagellates in IODP expedition 385 sediment cores

The high-resolution analysis of radiolarians and silicoflagellates in sediments from Holes U1545A and U1549A drilled during IODP Expedition 385 in the Guaymas Basin, in the Gulf of California provides detailed insights into the evolution of ocean circulation and water masses, and its relation to Eastern Tropical Pacific Ocean climate conditions, over the past 31,000 cal years BP (based on AMS radiocarbon dates). In the pre-Last Glacial Maximum, the Guaymas Basin experienced alternating circulation patterns of California Current Water (CCW) and Gulf of California Water (GCW), with an extended presence of the Pacific Intermediate Water (PIW) owing to: amplified jet streams; southern movement of the California Current System (CCS) and the incursion of CCW into the gulf; and increased North Pacific Intermediate Water (NPIW) formation. The Last Glacial Maximum witnessed the incursion of CCW due to the stronger CCS. The dominance of the PIW indicates the expansion and formation of NPIW. The Heinrich-I event as manifested in the core record, displays two distinct patterns, one suggesting GCW-like dominance and the other, the occurrence of CCW. The Bølling-Ållerød interstadial featured the entry of Tropical Surface Water (TSW), GCW, and CCW, linked with the northward migration of the Intertropical Convergence Zone. In the Younger Dryas, CCW dominated, transitioning to GCW as colder climatic conditions and more intense CCS. The Holocene displayed alternating periods of TSW and GCW, with a modern monsoon regime from 7,600 to 1,000 cal years BP. From 1,000 cal years BP to the present the ITCZ shifted to the south.

Post-Mining Risk Management and multi-hazard approaches, methodology and application

After intensively exploiting the mineral resources of its subsoil for several centuries, French mining sites have gradually closed. The “post-mining” of a site mine is concerned by many hazards which can occur such as: ground movement phenomena (subsidence, collapses), rising gas, irreversible disruptions in underground water circulation induced by mining can potentially cause disturbances, both in terms of water circulation patterns (Flooding in low areas, disruption of waterway flows) and water quality (pollution). The multi-hazards assessment methodology consists of four steps: the identification and the assessment of the singles hazards, the identification of the potential hazard interactions, the identification of the level and the consequences of the interactions and the finally the adjustment and the mapping of the hazard interaction. The matrix tool and interaction organigrams are used to identify the potential interactions. The paper presents the methodology for the interaction between two main hazards: flooding and ground movement. The interaction methodology was applied on two case studies: shallow chalk mine and deep coal mine (France). The results demonstrate the importance of multi-hazard assessment. This analysis depends on the quality and the quantity of existing data for carrying out the multi-hazard assessment.

Microorganisms and dissolved metabolites distinguish Florida's Coral Reef habitats.

As coral reef ecosystems experience unprecedented change, effective monitoring of reef features supports management, conservation, and intervention efforts. Omic techniques show promise in quantifying key components of reef ecosystems including dissolved metabolites and microorganisms that may serve as invisible sensors for reef ecosystem dynamics. Dissolved metabolites are released by reef organisms and transferred among microorganisms, acting as chemical currencies and contributing to nutrient cycling and signaling on reefs. Here, we applied four omic techniques (taxonomic microbiome via amplicon sequencing, functional microbiome via shotgun metagenomics, targeted metabolomics, and untargeted metabolomics) to waters overlying Florida's Coral Reef, as well as microbiome profiling on individual coral colonies from these reefs to understand how microbes and dissolved metabolites reflect biogeographical, benthic, and nutrient properties of this 500-km barrier reef. We show that the microbial and metabolite omic approaches each differentiated reef habitats based on geographic zone. Further, seawater microbiome profiling and targeted metabolomics were significantly related to more reef habitat characteristics, such as amount of hard and soft coral, compared to metagenomic sequencing and untargeted metabolomics. Across five coral species, microbiomes were also significantly related to reef zone, followed by species and disease status, suggesting that the geographic water circulation patterns in Florida also impact the microbiomes of reef builders. A combination of differential abundance and indicator species analyses revealed metabolite and microbial signatures of specific reef zones, which demonstrates the utility of these techniques to provide new insights into reef microbial and metabolite features that reflect broader ecosystem processes.

Human Impact on Water Circulation Patterns in Raised Bogs of the Baltic Type, Northern Poland

Raised bogs of the Baltic type are unique because of their geomorphologic structure and hydrologic conditions. There are about 80 bogs of this type in Poland. All are affected by human impact, and their water circulation patterns are disrupted by artificial outflows. The aim of the study was to show the effects of human impact on water circulation patterns in raised bog on an example of the Wielkie Bagno peat bog. The main work consisted of field studies, during which measurements of groundwater fluctuations, flows at main outflows, and hydrographic mapping were performed. Data on precipitation and evaporation were also obtained from state institutions. Research has shown that fluctuations in groundwater levels in the Wielkie Bagno bog average 78 cm per year (hydrological years 2018–2019) and the bog is in poor condition. This is mainly due to climate change, which manifests itself in too little precipitation in summer and an increase in evaporation, a too dense drainage network causing the lowering of the groundwater level in the peat bog, and the close proximity of a peat mine causing significant drainage of water from the examined peat bog, as well as too large fluctuations of groundwater during the year and in individual months. In some areas, a near-surface layer of the bog was also detected, about 30 cm thick, which is a sign of bog desiccation (especially in summer). Water balance data were used to show that the quantity of water available in the bog is determined by atmospheric precipitation, which is too small in the warm period. As a consequence, there are months with a negative climatic balance. It was also observed that factors such as physical location in different parts of the bog and the degree of degradation also affect water circulation patterns in the study area. At the moment, the most important task in the peat bog is to raise the groundwater level, reduce its fluctuations, and reduce human pressure on the bog.

Keragaman Genetik Penyu Lekang (Lepidochelys olivacea) Dan Kaitannya Dengan Pola Arus Di Perairan Samudera Hindia Dan Perairan Tengah Indonesia

Indonesia is an important habitat for olive ridley (Lepidochelys olivacea) that it is necessary for sustainable management with respect to biological and ecological aspects as well as its environment. Genetic diversity and connectivity of L. olivacea can be calculated by using mitochondrial DNA analysis approach. The water circulation pattern are greatly affects to the distribution of L. olivacea that can be a transport medium for its migrations. This study aims to determined the genetic diversity of L. olivacea and its relation to water circulation across western and center of Indonesian waters. Samples of L. olivacea were collected in 6 locations across western and center of Indonesian waters from August 2015 to December 2016. The molecular analysis was conducted on control region gen based on 791-bp fragment. The water circulation analysis was performed through INDESO data and visualized by using Ferret software. Phylogenetic analysis showed that there are population connectivity of L. olivacea between western and central Indonesian waters. While population of L. olivacea in Kapoposang Island tend to be different compared to other populations. Genetic diversity analysis showed that L. olivacea from western Indonesia are more higher than center Indonesia. The water circulation analysis suggests that there is an established connection between western and center indonesian waters that connected by Northwest and Southeast seasons current, which the current vector indicates the movement of alternating water throughout Aceh, Pariaman, Panggul, Serangan, Kapoposang Island and Tuafanu populations.

Revealing karst water circulation based on the GIS and environmental isotopes methods—A case study in eastern Sichuan, southwestern China

Jura-type folds in eastern Sichuan Basin have created unique multi-type karst water circulation patterns. Understanding the karst water circulation features is helpful to the protection and management of water resources in this area. In this study, a typical Jura-type fold Mingyueshan in eastern Sichuan, Southwestern China is taken as an example. The geological conditions, natural geographical factors, and environmental isotopes data (δ2H, δ18O, δ3H) are analyzed, the GIS method was used to construct the groundwater flow system. The results reveal the karst water circulation patterns under the control of multiple drainage base levels. Finally, it comes to the conclusion that the north, middle and south sections of Mingyueshan present three water circulation patterns: unidirectional shallow circulation system, bidirectional shallow circulation system and unidirectional shallow-deep nested circulation system, respectively. These results are essentially qualitative, some numerical simulations of groundwater flow can be considered in future work, which will help to determine the groundwater flow system quantitatively. The research results can provide reference for the studies of karst aquifers in eastern Sichuan Jura-type folds area and other areas with similar characteristics.

Study of geometric shape and water circulation pattern in fish tanks using computational fluid dynamics

Study of geometric shape and water circulation pattern in fish tanks using computational fluid dynamics

SEASONAL VARIATION IN WATER CIRCULATIONS AND ITS IMPACT ON THERMAL ENVIRONMENT IN A CORAL REEF AREA OF SOUTHWEST JAPAN

Summer and wintertime observations were conducted through deploying horizontal oceanographic time series sensors in a coral reef region of Southwest Japan to assess the existing hydrodynamic and thermal environments in relation to seasonal changes. A significant variation in water circulation and temperature distribution pattern was recorded in Shiraho reef area between two different seasons. During winter, a strong inflow of oceanic water was recorded inside the reef on a semidiurnal pattern that led to significant water temperature rising while in summer, considerable amount of sea water entered the reef area with a diurnal frequency causing water temperature slightly lower. Outside the reef, current was found to flow nearly parallel in direction to the north-south stretch of the reef.

Studying the tidal-induced water circulation pattern within EL-Burullus fishing harbor, Egypt, using CMS-PTM numerical modeling

Protection from waves and providing an appropriate calmness ratio are vital requirements in the designing phase of a harbor. Another crucial issue is guaranteeing sufficient water circulation as a key indicator for water quality and avoiding the associated environmental problems of poor water quality conditions. In a coastal harbor, the interior basin's water quality largely depends on the harbor's natural/self-ability to flush out different existing pollutants. El-Burullus fishing harbors is one of the Egyptian coastal fishing harbors that suffer from environmental issues such as accumulated pollutants, particularly in stagnant areas, and deterioration of water quality within the harbor's basin. Investigating water quality status within the coastal harbors necessitates knowledge about the mechanism of water circulation patterns within the harbor. The most common indicator for the water renewal and circulation pattern evaluation is the flushing time. Therefore, a coupled coastal hydrodynamic modeling system and particle tracking model (CMS-PTM) are utilized to investigate the tidal-induced circulation pattern within the El-Burullus fishing harbor, considering two tide scenarios (best and worst). Three locations (where most operational fishing facilities exist) were selected as point sources (instantaneous mass) for particle release. The results highlight the role of tidal actions on the water circulation within El-Burullus harbor and how the residence time varies based on the source release location.

Effects of morphology and sediment permeability on coastal lagoons’ hydrological patterns

Mediterranean coastal lagoons are influenced from a wide variety of external factors such as surface and groundwater flows and climate dynamics. They are also vulnerable to human activities, which have caused a significant loss of these types of habitats. As a result, the EU habitat management have now prioritized restoration of natural wetlands. However, there is a lack of systemic studies on the mechanisms of coastal wetland degradation and ecohydrological processes that determine restored ecological functioning as an end goal, as well as a lack of reference sites to make comparisons. Furthermore, while lagoon morphometry and underlying sediment permeability have been studied extensively, combining these disciplines to evaluate lagoon hydrology and salinity dynamics is yet to be fully explored. The aim of this study was to analyze the hydrological dynamics of 4 newly constructed lagoons and compare them with 2 natural lagoons in the La Pletera salt marshes and evaluate the restoration and conservation efforts. We use the General Lake Model (GLM) to assess water volume fluctuations, salinity variability and lagoon water circulation (groundwater and surface water inflows, outflows and evaporation). We also combine data of the underlying lithological characteristics and lagoon morphometry, to compare and better understand the interplay of these parameters on the hydrological behavior of each lagoon. Results indicated that the older and natural lagoons exhibited more consistent patterns of confinement; with deeper morphologies, lower evaporation effect, lower water circulation, and more annual patterns of salinity fluctuation. The presence of low-permeability layers also resulted in less fluctuation of higher salinity levels. Conversely, three of the four new lagoons had similar, shallower morphologies and higher evaporation fluxes, but exhibited different water circulation patterns due to the presence or absence of low permeability layers. Also, their salinity fluctuations were more influenced by seasonal mixing than by evaporation, indicating more susceptibility to climatic influence in their annual hydrological pattern than in the natural lagoons. This could prove important when constructing and restoring lagoons according to predetermined morphology and underlying sediment patterns, as it could ultimately limit or enhance the success of set objectives and overall ecological functioning in a flooding – confinement driven lagoon ecosystem conditioned by irregular and unpredictable climatic events.

Transport and deposition processes of the sediment depocenter off the Shandong Peninsula: An observational study

The long-distance transport of Yellow River sediments has formed an omega-shaped (‘Ω’) distal muddy deposit in the Yellow Sea. Numerous studies have investigated the sediment dynamics and sedimentary evolution of the deposit, but several key questions remain unanswered due to insufficient observations. To reveal the mechanisms of sediment dynamics and quantify sediment transport and deposition processes, this study collected field datasets in the depocenter of the muddy deposit off the Shandong Peninsula. Bottom mounted tripods were deployed from August 18 to 27, 2017, and from February 23 to March 2, 2018, during which two strong wind events with speeds of over 10.8 m/s occurred. The results showed that near-bed suspended sediment concentration responded directly to varying hydrodynamic conditions, and significant differences in suspended sediment concentration between two wind events could be ascribed to a number of factors (e.g., tidal current, wave periods, wind stress, turbulence). The harmonic analysis demonstrated that suspended sediment variations during the spring tide were directed mainly by resuspension, while resuspension and advection contributed equally at neap tide. The variations in background suspended sediment concentration can be ascribed to the residual current. Furthermore, the sediment transport pattern is similar to the pattern of water circulation. Generally, the along-shore suspended sediment flux is about one order of magnitude higher than the cross-shore flux. In summer, the suspended sediment was transported mainly downcoast. In winter, sediment was transported downcoast during wavy periods and upcoast during calm periods. Advection dominated sediment flux in most cases, except during wavy periods when local resuspension increased significantly, and the contribution of resuspension term to along-shore flux was up to 87%. Meanwhile, cross-shore flux also increased significantly under strong winds, which was simultaneously modulated by downcoast and offshore winds. After statistical analysis, we found that offshore winds controlled the cross-shore sediment transport in winter. Using parameterized calculation and statistical analysis, the average accumulation rate of the study site was estimated to be 0.6 cm/yr. During calm periods, lower background sediment concentration in summer led to lower deposition rates than in winter. In addition, the frequent strong wind events in winter cause extremely high erosion rates. This study provides new perspectives on quantitative variations in suspended sediment transport and regional erosion/deposition from synoptic to seasonal variations in the distal mud deposit.

Evolutionary mechanisms and shifting trends in water circulation patterns in a tributary of the Three Gorges Reservoir, China

Abstract A 2-D CE-QUAL-W2 hydrodynamic model was established to simulate evolutionary mechanisms and shifting trends of flow patterns per annum and over seasons from 2008 to 2018 in a reflective tributary Xiangxi Bay (XXB) of the Three Gorges Reservoir, China. Reasons behind shifting trends of flow patterns were also investigated. Model performance was validated and simulated data was synchronous to observed data. In general, percentage of Pattern (6) was 14%, 20%, 17%, 12% and 11% per annum and in spring, summer, autumn and winter respectively by 2013. It was increased by 26%, 30%, 22%, 25% and 35% per annum and in spring, summer, autumn and winter respectively since 2014. Increased temperature and flow dynamics (such as 10,000 m3 s−1 in spring) in Three Gorges Resevoir (TGR) since 2014 were underlying shifting trends of density current patterns. Correlation among patterns prior to and after newly built upstream reservoirs was novel and innovative in finding hydrodynamic thresholds to increase effectivity. Particulars elaboated and associated with respective density current patterns indicate increased surface velocity and water exchange with increased overflows. This could help understanding hydrodynamics and ecological variations in TGR and XXB. Thermal establishment and flow dynamics in TGR triggering overflow intrusion in XXB are required to be achieved. A hydrodynamic and water quality model of XXB coupled with TGR mainstream is recommended to correlate additive impacts of advantageous and disadvantageous patterns and to evaluate hydrodynamical thresholds triggering advantageous patterns in XXB.

Geochemical and Isotopic Characteristics of Two Geothermal Systems at the Nanpu Sag, Northern Bohai Bay Basin

The utilization of geothermal energy has gradually increased in northern China because of its unique advantages as a heating supply. However, the sustainable exploitation of geothermal energy usually requires a comprehensive investigation of the geothermal water circulation pattern prevailing at a proposed site. During the exploitation of geothermal energy resources at Nanpu Sag in northern China, thermal anomalies were found to exist in two adjacent regions: the Caofeidian and the Matouying. To reconcile the anomalies and to examine both the source of recharge water and the geothermal systems’ circulation dynamics, a comprehensive investigation was performed using multiple chemical and isotopic tracers (δ2H, δ18O, 87Sr/86Sr, δ13C, and 14C). The total dissolved solids (TDS) of the geothermal water are approximately 750 mg/L and 1,250 mg/L, respectively. The geothermal water isotopes at the two sites are also different, with average values of -9.3‰ and -8.2‰ for δ18O and -73.4‰ and -71‰ for δ2H, respectively. Moreover, the 87Sr/86Sr ratio of geothermal water at Matouying is 0.7185, which is much greater than that of Caofeidian, with an average value of 0.7088. All the results confirm the difference between the two geothermal systems and may explain the two circulation patterns of deep groundwater at Caofeidian and Matouying. The reservoir temperature obtained from theoretical chemical geothermometers is estimated to be 83–92°C at the Caofeidian and 107–137°C at the Matouying, respectively. The corrected 14C age implies a low circulation rate that would allow sufficient time to heat the water at Caofeidian. In addition, we propose a geothermal conceptual model in our study area. This model could provide key information regarding the geothermal sustainable exploitation and the effective management of geothermal resources.

Harmful Algal Blooms and their impacts on shellfish mariculture follow regionally distinct patterns of water circulation in the western English Channel during the 2018 heatwave

Harmful algal blooms (HABs) can have severe ecological, societal and economic impacts upon marine ecosystems, human health and the seafood industry. We evaluated changes in marine plankton communities with prevailing physico-chemical conditions throughout an exceptionally warm summer (2018), to elucidate key factors governing HABs and their impacts on shellfish mariculture in the western English Channel. Despite warm, stable weather conditions and widespread seasonal stratification throughout the summer, divergent plankton community compositions were observed at two rope-grown mussel (Mytilus edulis) farms (St Austell Bay and Lyme Bay) and a long-term ecological research LTER site (Plymouth L4). There were significant differences between sites in the abundances of HAB species, including Dinophysis spp. and Karenia mikimotoi, whose cell counts bloomed in excess of UK Food Standards Agency (FSA) advisory 'trigger' levels at Plymouth L4 and St Austell Bay, but not at the Lyme Bay site. The K. mikimotoi bloom occurred over two weeks in August and comprised up to 88% of the standing phytoplankton biomass in St Austell Bay. Dinophysis spp. also bloomed here from May to September, constituting up to 28% of phytoplankton biomass. This protracted bloom resulted in concentrations of Dinophysis toxins 1 & 2 and pectenotoxins and okadaic acid in shellfish, which closed shellfish harvesting operations on farms located in St Austell Bay, and other shellfish sites in the west of the western English Channel (but not in the east of the region). Inter-site differences in the abundances of these and other HAB species were associated with variations in water circulation and co-occurring phytoplankton and zooplankton communities. Furthermore, plankton monitoring data obtained from the L4 site over the past 3 decades showed HAB species (including Dinophysis spp.) with abundances commonly occurring above advisory trigger levels during warmer periods, such as that coinciding with our study. Under projected climate warming these blooms are likely to continue to be governed by regionally distinct patterns of water circulation, which need to be taken into account in marine spatial planning, when assessing the suitability of new shellfish mariculture sites.

Persistent deep water anoxia in the eastern South Atlantic during the last ice age

During the last glacial interval, marine sediments recorded reduced current ventilation within the ocean interior below water depths of approximately >1,500 m [B. A. Hoogakker etal., Nat. Geosci. 8, 40-43 (2015)]. The degree of the associated oxygen depletion in the different ocean basins, however, is still poorly constrained. Here, we present sedimentary records of redox-sensitive metals from the southwest African margin. These records show evidence of continuous bottom water anoxia in the eastern South Atlantic during the last glaciation that led to enhanced carbon burial over a prolonged period of time. Our geochemical data indicate that upwelling-related productivity and the associated oxygen minimum zone in the eastern South Atlantic shifted far seaward during the last glacial period and only slowly retreated during deglaciation times. While increased productivity during the last ice age may have contributed to oxygen depletion in bottom waters, especially on the upper slope, slow-down of the Late Quaternary deep water circulation pattern [Rutberg etal., Nature 405, 935-938 (2000)] appears to be the ultimate driver of anoxic conditions in deep waters.