Freshwater Inflow Research Articles

Ultra-deep carbonate basement reservoirs formed by polyphase fracture-related karstification in the Offshore Bohai Bay Basin, China

The Palaeozoic carbonate basement of the Offshore Bohai Bay Basin (OBBB) presents considerable potential for hydrocarbon exploration. However, the multistage tectonism and complex superimposed palaeo-karstification in the area are unclear, which leads to a lack of understanding on the formation mechanism and distribution of the deep carbonate basement reservoirs. In this study, the occurrence of a fracture-vug network and its fillings in carbonate reservoirs were investigated based on borehole cores, thin sections, and image logs from the southwestern slope of the OBBB's Bozhong Sag. Then the diagenetic fluid properties of the carbonate matrix and fillings were analysed via the data of carbon, oxygen, and strontium isotopes, and major, rare elements from coring intervals. The results revealed that fracture-related karst reservoirs have lithologic selectivity inclined toward dolomite strata. The intersecting relationships, widths, and strikes of the fractures and the regional tectonic background indicate three structural fracture families: NW-, NNE-, and NNW- trending, related to the Indosinian, middle Yanshanian, and late Yanshanian orogeny, respectively. The Indosinian NW- and end-Mesozoic NNE-trending fractures produced by compressional tectonic stress mainly contributed to the formation of the basement reservoirs. The geochemistry of the calcite veins filling these fractures suggests two main types of diagenetic fluids. The fluid of autogenic recharge related to the earlier fills is karstification diffuse flow dominated by internal runoff from rainfall in the highland setting of the Indosinian thrusting orogenic belt. The other fluid of allogenic recharge related to the later fills is the main lateral freshwater flow dominated by external runoff from the catchment in the setting of the horst-lowland within the rifting basin, induced by the Yanshanian destruction of the North China Craton. Finally, the relationship between the three fracture families and two kinds of related fluids is revealed. This allows us to propose a model to understand the polyphase-superimposed fracture-related karst reservoir complexes within the deep carbonate basement of tilting fault blocks that neighbour the Bozhong hydrocarbon kitchen and predict the formation of potential plays with high accuracy.

Radial growth in mangrove Xylocarpus granatum J. Koenig is driven by salinity in the Sundarbans, Bangladesh

Albeit the Sundarbans provides protection and livelihood supports to ∼ 7.5 million climate vulnerable coastal people in Bangladesh and India, this sentinel mangrove ecosystem has been threatened by anthropogenic disturbances and rapid environmental changes including sea level rise (SLR). In this context, long-term tree growth data are increasingly essential to understand the effects of environmental changes on mangroves and also to formulate their management plans. In this study, we evaluate the nature and periodicity of growth rings in Xylocarpus granatum, an ecologically important mangrove tree species growing in the Bangladesh Sundarbans. In addition, we analyze the influences of climatic variables (i.e., precipitation and temperature) and river discharge on its radial growth. The results reveal that X. granatum forms distinct growth rings which are marked by a layer of parenchyma band consisting of 1–4 cells. The visual crossdating and the quality of chronology statistics indicate that the growth rings are crossdatable. A site-specific chronology was developed spanning from 1973 to 2020 based on the crossdated samples. The annual nature of X. granatum’s growth rings offer an opportunity to estimate tree age and growth rate. The ring width is influenced by salinity which is regulated mainly by freshwater influx through annual precipitation along with river discharge, particularly in July. This study suggests that growth rings could be used as a proxy in exploring X. granatum’s growth dynamics, especially in relation to environmental changes.

A coherent status of summer monsoon phytoplankton communities (2017–2018) along the Western Indian continental shelf: Implications for fisheries

The western Indian continental shelf is characterized by contrasting biogeochemical features from south to north mostly governed by monsoon wind forcing. Here we present the first detailed study on the phytoplankton community (analyzed by marker pigments and microscopy) during the summer monsoon addressing the interannual variability (Aug 2017 and 2018) along the Western Indian Continental Shelf waters (8° N-21° N, at 200 m isobaths). A distinct interannual variability in monsoon impacted the hydrography and nutrient stoichiometry that was further cascaded to the phytoplankton community structure. The timing of the monsoon onset, wind speeds, and the strength of the alongshore wind component were the major factors that governed the interannual variability in the development and progression of the upwelling as well as phytoplankton bloom. The upwelling-dominated southwestern shelf was characterized by cold, nutrient-rich waters dominated by the marker pigment of diatoms, fucoxanthin, and microscopy also revealed the presence of large, chain-forming diatoms (Chaetoceros sp.; Dactyliosolen fragilissimus). In contrast, low nutrient warm waters in the northern shelf housed nanophytoplankton and picophytoplankton along with small diatoms (Thalassiosira sp.) and dinoflagellates (Gymnodinium sp.). Interestingly, in a few stations in the southern shelf, the surface waters were low saline that was intensified in 2018 compared to 2017 inhibiting upwelled water from reaching the surface. Consequently, due to low nutrient levels caused by reduced upwelling and low salinity, picoplanktonic cyanobacteria dominated replacing the larger diatoms that were found plenty in 2017. Likely, such a niche shift adversely impacted the planktivorous fish catch (Indian Oil Sardine) that was seen to be less in 2018 relative to 2017. Any further changes in monsoon variability and freshwater flow to this region may have direct consequences on the phytoplankton community as well as fisheries.

Microbial methane cycling in sediments of Arctic thermokarst lagoons.

Thermokarst lagoons represent the transition state from a freshwater lacustrine to a marine environment, and receive little attention regarding their role for greenhouse gas production and release in Arctic permafrost landscapes. We studied the fate of methane (CH4 ) in sediments of a thermokarst lagoon in comparison to two thermokarst lakes on the Bykovsky Peninsula in northeastern Siberia through the analysis of sediment CH4 concentrations and isotopic signature, methane-cycling microbial taxa, sediment geochemistry, lipid biomarkers, and network analysis. We assessed how differences in geochemistry between thermokarst lakes and thermokarst lagoons, caused by the infiltration of sulfate-rich marine water, altered the microbial methane-cycling community. Anaerobic sulfate-reducing ANME-2a/2b methanotrophs dominated the sulfate-rich sediments of the lagoon despite its known seasonal alternation between brackish and freshwater inflow and low sulfate concentrations compared to the usual marine ANME habitat. Non-competitive methylotrophic methanogens dominated the methanogenic community of the lakes and the lagoon, independent of differences in porewater chemistry and depth. This potentially contributed to the high CH4 concentrations observed in all sulfate-poor sediments. CH4 concentrations in the freshwater-influenced sediments averaged 1.34 ± 0.98 μmol g-1 , with highly depleted δ13 C-CH4 values ranging from -89‰ to -70‰. In contrast, the sulfate-affected upper 300 cm of the lagoon exhibited low average CH4 concentrations of 0.011 ± 0.005 μmol g-1 with comparatively enriched δ13 C-CH4 values of -54‰ to -37‰ pointing to substantial methane oxidation. Our study shows that lagoon formation specifically supports methane oxidizers and methane oxidation through changes in pore water chemistry, especially sulfate, while methanogens are similar to lake conditions.

Sedimentary response and restoration of paleoshoreline of Taiyuan-Shanxi Formations in North China basin

The Permian Taiyuan-Shanxi Formations in the North China Basin are a series of terrestrial-marine strata whose depositional evolution exhibits unique particularities. Current studies involving the paleoenvironment of the Taiyuan and Shanxi Formations are mainly supported by sedimentary facies or geochemical analysis, yet studies on the sedimentary and geochemical responses of the paleoshoreline remain inadequate, which leads to the inconsistency of the concluded paleoshoreline distribution. Based on outcrop data, well data and major and trace element analysis, sedimentary and geochemical features of the paleoshoreline in both formations are identified. Combining sedimentary facies and geochemical analysis, this study aims to restore the distribution of the paleoshoreline in the Taiyuan and Shanxi Formations as well as its migrations.The outcrop and well data show that the paleoshoreline of the Taiyuan and Shanxi Formations features 3 types of sedimentary responses: (1) distributary channel deposits of the delta plain + argillaceous deposits of the delta front; (2) peat mire of the delta plain + argillaceous deposits of the delta front; and (3) distributary channel deposits of the delta plain + tidal flat-lagoon deposits. Based on major and trace element results, Sr/Ba, m = 100 × (MgO/Al2O3), Mn/Fe, f = (Rb/K)/(Zr/Al), CIA, Sr/Cu, V/(V + Ni), and V/Cr are selected as proxies for paleosalinity, paleowater depth, paleoclimate and paleo-redox conditions. The results show that transitional-brackish water was dominant during the transgression period of the Taiyuan Formation with mild changes in paleowater depth, while fresh water primarily covered the North China Basin during regression during the Shanxi Period, which was a time when paleo-water depth exhibited evident fluctuation in the northern region. Generally, the paleoclimate during the Taiyuan-Shanxi Period was warm and moist to hot and humid, and the paleo-redox conditions were anoxic to reductive.Under the influence of transgression during the Taiyuan Period, the boundary of the freshwater zone closely matches the maximum range of marine deposition, indicating a generally steady transgression background; additionally, the paleoshoreline was distributed in the vicinity of Yulin - Shijiazhuang - Baoding. During the regression event of the Shanxi Period, the paleoshoreline migrated southeast to the south of ZK03-2 and southeast of Yu88, extending southward along Sanmenxia - Luoyang - Zhengzhou - Yuzhou, and the freshwater zone extended southward and covered a considerable range of marine deposition, indicating a strong flux of terrestrial freshwater with periodic transgression. The analysis and conclusions in this paper would hopefully provide insights and a reference for the paleoenvironmental evolution and shoreline changes in the Taiyuan - Shanxi Formations of the North China Basin.

Terrestrial Carbon Additions to Zooplankton Prey Influence Juvenile Estuarine Fish Growth

Freshwater inflows are linked to the abundance and catch rates of fish in estuaries. The role of terrestrial carbon resources brought into estuaries after inflows may be important, but this is currently not well understood. Therefore, we performed a study examining the effect of terrestrial dissolved organic matter (tDOM) dietary additions on the growth of food-limited juvenile Australian bass (Macquaria novemculeata). Crustaceous zooplankton Artemia franciscana (Artemia) were reared for two days under control conditions (no addition) or with additions of tDOM leachate at dissolved organic carbon (DOC) concentrations of 5 mg/L or 10 mg/L. Artemia were fed to juvenile bass in their treatment tanks over 42 days at feeding rates reduced by 65–75% of ad libitum. Juvenile fish from the 5 mg/L treatment exhibited no statistical difference in weight or standard, fork and total lengths compared to the control treatment. In contrast, the fish in the 10 mg/L tDOM treatment had significant increases (p < 0.05) in all length parameters after 42 days compared to the other treatments. The greater lengths of fish where tDOM is available indicate that tDOM can contribute to improved growth and development in juvenile Australian bass. While stable isotope analysis of fish tissue showed only minor changes toward terrestrial carbon signatures, increased terrestrial resource availability in the juvenile fish diets may have subsidised energetic needs, facilitating the greater utilisation of endogenous resources. Overall, the results indicate that freshwater inflows that deliver terrestrial resources may be important for the growth and development of estuarine fish.

Olfactory cueing responses in the early stages of a marine estuarine-dependent fish species in South Africa

Many marine fish species depend on estuaries as nurseries for their vulnerable life stages. Consequently, successful recruitment into estuaries by the larvae and juveniles of marine estuarine-dependant fish such as Rhabdosargus holubi (Sparidae) is vital to completing their lifecycles and thus maintaining populations. This species is known to be attracted to the water of riverine and estuarine origin, potentially via olfaction of chemical cues. However, the specific cues and cueing mechanisms involved in these recruitment responses have yet to be fully elucidated for many species utilising estuaries as nursery areas. In this study, choice chamber flume experiments were used to test the chemical attraction of fish to water from different sources to understand further the mechanisms and cues involved. Rhabdosargus holubi juveniles were attracted to the water of riverine and estuarine origin, as the larvae were previously shown to do. These fish were also attracted to exudates from seagrass that occur naturally in their preferred estuarine habitats. The results of the study highlight both the importance of conserving vegetated habitats and managing adequate freshwater flow into estuaries, as well as the need for more research on fish cueing into nursery areas.

Repulsion driven by groundwater level difference around cutoff walls on seawater intrusion in unconfined aquifers

Cutoff walls have been widely used to prevent seawater intrusion (SWI) in coastal regions. Previous studies generally concluded that the ability of cutoff walls to prevent seawater intrusion depends on the higher flow velocity at the wall opening, which we have shown is not the most critical mechanism. In this work, we implemented numerical simulations to explore the driving force of cutoff walls on the repulsion of SWI in both homogeneous and stratified unconfined aquifers. The results delineated that the inland groundwater level was raised by cutoff walls, which generated a significant groundwater level difference beside two sides of the wall and thus provided a large hydraulic gradient to repel SWI. We further concluded that by increasing inland freshwater influx, the construction of cutoff wall could result in a high inland freshwater hydraulic head and fast freshwater velocity. The high inland freshwater hydraulic head posed a large hydraulic pressure to push the saltwater wedge seawards. Meanwhile, the fast freshwater flow could rapidly carry the salt from the mixing zone to the ocean and induce a narrow mixing zone. This conclusion explained the reason that the cutoff wall can improve the efficiency of SWI prevention through recharging freshwater upstream. With a defined freshwater influx, the mixing zone width and saltwater pollution area mitigated with the increase of the ratio between high and low hydraulic conductivity values (KH/KL) of the two layers. This was because the increase of KH/KL caused a higher freshwater hydraulic head, a faster freshwater velocity in the high-permeability layer, and the prominent change of flow direction at the interface between the two layers. According to the above findings, we deduced that any way to increase the inland hydraulic head upstream of the wall would improve the efficiency of cutoff walls, such as the freshwater recharge, the air injection, and the subsurface dam.

Observations of River Plume Mixing in the Surf Zone

Abstract We use salinity observations from drifters and moorings at the Quinault River mouth to investigate mixing and stratification in a surf-zone-trapped river plume. We quantify mixing based on the rate of change of salinity DS/Dt in the drifters’ quasi-Lagrangian reference frame. We estimate a constant value of the vertical eddy diffusivity of salt of Kz = (2.2 ± 0.6) × 10−3 m2 s−1, based on the relationship between vertically integrated DS/Dt and stratification, with values as high as 1 × 10−2 m2 s−1 when stratification is low. Mixing, quantified as DS/Dt, is directly correlated to surf-zone stratification, and is therefore modulated by changes in stratification caused by tidal variability in freshwater volume flux. High DS/Dt is observed when the near-surface stratification is high and salinity gradients are collocated with wave-breaking turbulence. We observe a transition from low stratification and low DS/Dt at low tidal stage to high stratification and high DS/Dt at high tidal stage. Observed wave-breaking turbulence does not change significantly with stratification, tidal stage, or offshore wave height; as a result, we observe no relationship between plume mixing and offshore wave height for the range of conditions sampled. Thus, plume mixing in the surf zone is altered by changes in stratification; these are due to tidal variability in freshwater flux from the river and not wave conditions, presumably because depth-limited wave breaking causes sufficient turbulence for mixing to occur during all observed conditions. Significance Statement River outflows are important sources of pollutants, sediment, and nutrients to the coastal ocean. Small rivers often meet large breaking waves in the surf zone close to shore, trapping river water and river-borne material near the beach. Such trapped material can influence coastal public health, beach morphology, and nearshore ecology. This study investigates how trapped fresh river water mixes with salty ocean water in the presence of large breaking waves by using high-resolution measurements of waves, salinity, and turbulence. We find that the surf zone is often fresh and stratified, which could have significant implications for the fate of riverine material. Wave breaking provides a constant source of turbulence, and the amount of mixing is limited by the degree of vertical salt stratification; more mixing occurs when stratification is higher.

Wind‐Forced Upwelling Along the West Greenland Shelfbreak: Implications for Labrador Sea Water Formation

AbstractArctic‐origin and Greenland meltwaters circulate cyclonically in the boundary current system encircling the Labrador Sea. The ability of this freshwater to penetrate the interior basin has important consequences for dense water formation and the lower limb of the Atlantic Meridional Overturning Circulation. However, the precise mechanisms by which the freshwater is transported offshore, and the magnitude of this flux, remain uncertain. Here, we investigate wind‐driven upwelling northwest of Cape Farewell using 4 years of high‐resolution data from the Overturning in the Subpolar North Atlantic Program west Greenland mooring array, deployed from September 2014–2018, along with Argo, shipboard, and atmospheric reanalysis data. A total of 49 upwelling events were identified corresponding to enhanced northwesterly winds, followed by reduced along‐stream flow of the boundary current and anomalously dense water present on the outer shelf. The events occur during the development stage of forward Greenland tip jets. During the storms, a cross‐stream Ekman cell develops that transports freshwater offshore in the surface layer and warm, saline, Atlantic‐origin waters onshore at depth. The net fluxes of heat and freshwater for a representative storm are computed. Using a one‐dimensional mixing model, it is shown that the freshwater input resulting from the locus of winter storms could significantly limit the wintertime development of the mixed layer and hence the production of Labrador Sea Water in the southeastern part of the basin.

Streamflow characteristics of Sangu-Matamuhuri watershed in the southeastern part of Bangladesh

Quantification of streamflow chatacteristics is considered crucial for designing effective management practices in a watershed. Sangu and Matamuhuri are two major rivers of Chittagong Hill Tracts (CHT's) and main sources of upland freshwater inflows to the south-eastern part of Bangladesh. This study was performed to evaluate the streamflow characteristics of Sangu-Matamuhuri watershed based on 25 years historical observed streamflow and rainfall records. Mean daily discharge data recorded by Bangladesh Water Development Board were collected and analyzed for the period of 1995–2019. Stream flow characteristics were determined in terms of different parameters including mean annual runoff discharge, specific water yield, run-off ratio, peak flow, seasonal flow and flow duration. Various statistical measures including mean, standard deviation, co-efficient of variation, lag-1 serial correlation, Mann Kendall test and Sen's slope estimator were applied to justify these parameters. The mean annual runoff discharges of 2167.77 and 1490.61 million cubic meters (mcm) were measured at the gaging stations at Sangu and Matamuhuri watershed, respectively. Matamuhuri basin showed higher value of specific water yield (1.52 mcm/sq. km) compared to the Sangu basin (1.02 mcm/sq. km). The average annual runoff coefficient value of Sangu watershed was found 0.36 while in case of Matamuhuri watershed it was about 0.49. The mean annual peak discharges of 25 years were found 607.63 m3s-1 and 628.42 m3 s-1 at Sangu and Matamuhuri watershed, respectively. Mann-Kendall Test (MK) and Sen's Slope Estimator method were applied for temporal trend analysis. An increasing trend in runoff observed during wet season which may cause flash floods and a decreasing trend observed during dry season that may cause water scarcity in Sangu-Matamuhuri watershed area. Flow duration curves based on 25 years' hydrological data were developed which showed progressive reduction in flows over time in both the watersheds for three periods 1995–2002, 2003–2010 and 2011–2019 with major changes occurred in Matamuhuri watershed during 2011–2020 which might be due to the impact of land use and land cover changes as well as changes in precipitation pattern. Implications of these findings indicate baseline information that can be used to evaluate the impacts of land use changes and climate change, and thereby may facilitate the planning and local management of water resources in the long term.

Fresh Water availability and It’s Global challenge

Water is prime natural resources fulfilling our needs in a precisious assets. We must acts to preserve and utilize every drop of water. Water resources can be assessed on the basis of surface and subsurface water bodies. Climate change impact on ground Water the impact of climate change on ground water has been studied much less than the impact on surface waters. Ground water reacts to climate change mainly due to change in ground water recharge, but also change in river level in response to increase in mean Temperature, precipitation ,variability and sea level as mean precipitations. Changing land use pattern due to increasing, urbanization, industrialization and agriculture activities are serious issues that causing increase ground water with drawal resulting in depletion of ground water resources and mining of ground water resources, along with deterioration of water quality. Rainfall is highly irregular and erratic and declining year to year due to change climatic conditions as result of serious deforestation global warming etc. Human health is affected by change in biodiversity and ecosystem. Climate change will affect the quality of drinking water and impact of fresh water availability and impact on public health. About 70% of Earth’s surface is water of which 97.5% is salty water and 2.5% is fresh water. Less than 1% of this 2.5% amount of freshwater is accessible. As sea water rise’s, salt water of ocean in filtrate as coastal fresh water due heavy rainfall and flooding waste more fertilizer and municipal sewage mixed with coastal fresh water and change alter into more oxygen dead zone. Weather extreme and climate variability is main driver of food production in recent global challenge. Recent global challenge food security, fresh water availability, increase incidence of extreme high sea level. Loss of agriculture reproduction and increase in food prices and changes in weather patterns and alter availability and quality of water in many part of world. Climate change is an on-going phenomenon. This will inevitably bring about numerous environmental problems, including alterations to the hydrological cycle, which is already heavily influenced by anthropogenic activity. Chemical fertlizer’s has been adversely affecting the flora, fauna as well as soil quality . more ever every year plant pathogen are causing loss of 10 to 20% of agricultural production world wide. Ground water will be vital to alleviate some of the worst drought situations. flooding and contaiminated water supplies, more intense weather events are likely to increase to risk of infectious disease epidemics and erosion of low-lying and costal land. Climate Chang will affect the quality of drinking Water and impact of fresh water availlablity and impact on public health it’s better to use UV Water purifiers. This paper will explore what climate change. Water is prime natural resources fulfilling our needs in a precisious assets.we must acts to preserve and utilize every drop of water. water resources can be assessed on the basis of surface and subsurface water bodies. Climate change imapact on ground Water the impact of climate change on ground water has been studied much less than the impact on surface waters. Ground water reacts to climate change mainly due to change in ground water recharge, but also change in river level in response to increase in mean Temperature, precipitation, variability and sea level as mean precipitations. Changing land use pattern due to increasing, urbanization, industrialization and agriculture activities are serious issues that causing increase ground water with drawal resulting in depletion of ground water resources and mining of ground water resources, along with deterioration of water quality. Rainfall is highly irregular and erratic and declining year to year due to change climatic conditions as result of serious global warming .Impacts of sea level rise on salinity intrusion global climate change has resulted in gradual sea level rise. sea level rise can cause saline water to migrate up stream in estuaries and rivers, thereby threating fresh water habitat and drinking- water supplies. Hydrology all the costal margin; fresh ground water flowing in land areas meets with saline ground water from the ocean. the fresh ground water flows from in land areas towards the coast where elevation and groundwater level are lower because salt water has higher content of dissolved salt and minerals. it denser the fresh water, causing it to have hydraulic head than freshwater. hydraulic head refers to the liquid pressure exerted by water column. the higher pressure density of salt water cause it to move into costal aquifiers in a wedge shape under the freshwater. the salt water and fresh water meets in a transition zone where mixing occurs through dispersion and diffusion.

Transboundary Waters and Their Status in Today’s Water-Scarce World

Approximately 40% of the world’s population lives in transboundary river and lake basins, accounting for an estimated 60% of global freshwater flow. These shared water resources support the livelihoods of more than 3 billion people. Today, with the decrease in the amount of water in the world, the dispute over transboundary waters has increased. In this research, using library studies (including articles, books, reliable reports from the United Nations and other relevant organizations, etc.), problems of the most important transboundary waters have been investigated. Because transboundary water problems are widespread all over the world, solutions by researchers, relevant organizations such as UN sub-organizations, and politicians have been suggested. In this research, emphasizing the cases of diplomacy and hydro-hegemony, risk, water–energy–food nexus, and 5P, this issue is investigated. Finally, by examining the most important problems of transboundary waters all over the world, as well as the most critical cases and using successful experiences in the world in solving transboundary water crises, peaceful proposals to solve such problems and reach sustainable solutions in order to reach the Sustainable Development Goals (SDGs) have been proposed depending on the regional and country conditions of each of these basins.

Estimation of 226Ra and 228Ra Content Using Various Types of Sorbents and Their Distribution in the Surface Layer of the Black Sea

Radium isotopes have traditionally been used as tracers of surface and underground fresh waters in land-ocean interactions. The concentration of these isotopes is most effective on sorbents containing mixed oxides of manganese. During the 116 RV Professor Vodyanitsky cruise (22 April-17 May 2021), a study about the possibility and efficiency of 226Ra and 228Ra recovery from seawater using various types of sorbents was conducted. The influence of seawater flow rate on the sorption of 226Ra and 228Ra isotopes was estimated. It was indicated that the Modix, DMM, PAN-MnO2, and CRM-Sr sorbents show the best sorption efficiency at a flow rate of 4-8 column volumes per minute. Additionally, the distribution of biogenic elements (dissolved inorganic phosphorus (DIP), silicic acid, and the sum of nitrates and nitrites), salinity, and 226Ra and 228Ra isotopes was studied in the surface layer of the Black Sea in April-May 2021. Correlation dependencies between the concentration of long-lived radium isotopes and salinity are defined for various areas of the Black Sea. Two processes control the dependence of radium isotope concentration on salinity: conservative mixing of riverine and marine end members and desorption of long-lived radium isotopes when river particulate matter meets saline seawater. Despite the high long-lived radium isotope concentration in freshwater in comparison with that in seawater, their content near the Caucasus shore is lower mainly because riverine waters meet with a great open seawater body with a low content of these radionuclides, and radium desorption processes take place in an offshore area. The 228Ra/226Ra ratio derived from our data displays freshwater inflow spreading over not only the coastal region, but also the deep-sea region. The lowered concentration of the main biogenic elements corresponds to high-temperature fields because of their intensive uptake by phytoplankton. Therefore, nutrients coupled with long-lived radium isotopes trace the hydrological and biogeochemical peculiarities of the studied region.

Observation-based estimates of volume, heat, and freshwater exchanges between the subpolar North Atlantic interior, its boundary currents, and the atmosphere

Abstract. The Atlantic Meridional Overturning Circulation (AMOC) transports heat and salt between the tropical Atlantic and Arctic oceans. The interior of the North Atlantic subpolar gyre (SPG) is responsible for the much of the water mass transformation in the AMOC, and the export of this water to intensified boundary currents is crucial for projecting air–sea interaction onto the strength of the AMOC. However, the magnitude and location of exchange between the SPG and the boundary remains unclear. We present a novel climatology of the SPG boundary using quality-controlled CTD (conductivity–temperature–depth) and Argo hydrography, defining the SPG interior as the oceanic region bounded by 47∘ N and the 1000 m isobath. From this hydrography we find geostrophic flow out of the SPG around much of the boundary with minimal seasonality. The horizontal density gradient is reversed around western Greenland, where the geostrophic flow is into the SPG. Surface Ekman forcing drives net flow out of the SPG in all seasons with pronounced seasonality, varying between 2.45 ± 0.73 Sv in the summer and 7.70 ± 2.90 Sv in the winter. We estimate heat advected into the SPG to be between 0.14 ± 0.05 PW in the winter and 0.23 ± 0.05 PW in the spring, and freshwater advected out of the SPG to be between 0.07 ± 0.02 Sv in the summer and 0.15 ± 0.02 Sv in the autumn. These estimates approximately balance the surface heat and freshwater fluxes over the SPG domain. Overturning in the SPG varies seasonally, with a minimum of 6.20 ± 1.40 Sv in the autumn and a maximum of 10.17 ± 1.91 Sv in the spring, with surface Ekman the most likely mediator of this variability. The density of maximum overturning is at 27.30 kg m−3, with a second, smaller maximum at 27.54 kg m−3. Upper waters (σ0<27.30 kg m−3) are transformed in the interior then exported as either intermediate water (27.30–27.54 kg m−3) in the North Atlantic Current (NAC) or as dense water (σ0>27.54 kg m−3) exiting to the south. Our results support the present consensus that the formation and pre-conditioning of Subpolar Mode Water in the north-eastern Atlantic is a key determinant of AMOC strength.

Bridging the Gap Between Conservation Paleobiology and Resource Management: Recognizing the Past is the Key to the Future

A persistent challenge for conservation paleobiologists is communication of information on past environmental changes to resource managers in a way that allows them to apply these data to current restoration efforts. USGS scientists have learned a few lessons over 25 years of conducting applied paleoecology research in collaboration with the Greater Everglades Ecosystem Restoration (GEER) project. The first step is to engage resource managers in conversations prior to beginning research. What are their goals and information needs? Participation in GEER with teams of scientists and decision-makers working together to develop measures of success for Everglades restoration allowed us to overcome this first hurdle. Our initial research showed changes in salinity and freshwater influx over time, but how to use this information was not immediately apparent to management, so continued communication was critical. Through participation in meetings and presentation of our preliminary findings, the management team provided feedback that led us to develop a modern analog-based method to estimate past salinity, which was then used to adjust system-wide hydrologic models to reflect past conditions. Recently, we realized another management information gap — a set of indicator species for nearshore estuarine zones to monitor the effectiveness of upstream changes in flow. Again, by working with managers to determine needs, we combined distribution data of mollusk species in nearshore cores with our modern analog dataset to develop a suite of indicator species. These are a few examples of positive impacts from our long-term collaboration. We believe the key to advancing the use of conservation paleobiologic research in resource management is to communicate frequently and often, listen closely to management, discuss how paleo data can be applied, and be persistent. It is essential that we bridge these gaps because the past is our window to anticipating and planning for future change.

Bajocian–Bathonian dinoflagellate cyst assemblages from the Middle Atlas, Morocco: Palynostratigraphic and paleoenvironmental implications

The Bajocian–Bathonian transition has been identified for the first time in the Skoura syncline of the folded Middle Atlas of Morocco based on dinoflagellate cyst and palynofacies analysis of the Ich Timellaline/Bou Akrabene Formation carbonates. This palynological study involved 109 samples of marls and limestones whose organic content yielded diverse and well-preserved dinoflagellate cyst assemblages comprising 68 taxa including stratigraphic marker taxa. Two association biozones have been defined for the late Bajocian–early Bathonian interval. The Cribroperidinium crispum-Ctenidodinium cornigerum (CC/CC) biozone is defined between the base of the Recifa Formation (Upper Bajocian) and the Ich-Timellaline / Bou Akrabene Formation (Upper Bajocian–Lower Bathonian). The second association biozone of Ctenidodinium combazii and Dichadogonyaulax sellwoodii (CC/DS) corresponds to the upper interval of the FD section (top of the Ich-Timellaline / Bou Akrabene Formation and the base of the El Mers I Formation). These two biozones were correlated with the late Bajocian–early Bathonian biozones defined in the Sub-Boreal (northwest Europe), Tethyan, and Australian domains. Close similarity between the Moroccan Middle Atlas, the Tethyan, and the Sub-Boreal domain associations has been noted. Quantitative analysis of organic matter constituents has allowed the paleoenvironmental reconstruction of the late Bajocian–early Bathonian. The organic residues of the studied samples recorded an increased land-derived phytoclasts dominance compared to amorphous organic matter and palynomorphs, indicating a proximal oxic shelf depositional environment with high terrestrial and freshwater influx during the late Bajocian–early Bathonian. During the Late Bajocian, the depositional environment corresponds to a proximal continental shelf with fluctuations from a distal to a marginal/stagnant environment.Below the Upper Bajocian–Lower Bathonian boundary, a significant marine incursion, or rather a transgression, is recorded in the studied sediments attested by an important marine fraction and dinoflagellate cysts abundance, which probably corresponds to the last Bajocian Maximum flooding surface (MFS).During the early Bathonian, the depositional environment evolved towards a distal continental shelf with an increasing marine fraction including dinoflagellate cysts and high species diversity. This may be related to the rising sea level which corresponds to the first Bathonian eustatic elevation. The proximal /marginal conditions are restored at the uppermost part of the section.

The Importance of Paleoecology in Everglades Restoration Science and Management

Paleoecology studies provide pre-instrument data from the Everglades painting an informative picture of physical, biological, and ecological conditions prior to human intervention. Because Florida’s development history is relatively recent, and because observational data span only the last half-century, managers rely on paleoecology data as the basis for important decisions regarding multi-decadal and expensive restoration. Effective restoration depends strongly on the establishment of restoration targets, especially pre-development vegetation and hydropatterns (flow, depth, timing, distribution). Coring data were instrumental in the reconstruction of paleo hydrologic and vegetation trends in the ARM Loxahatchee National Wildlife Refuge, helping managers understand the magnitude and causes of 20th century problems. Similarly, sediment cores from the Big Cypress National Preserve led managers to understand that the development of marl prairies in Everglades National Park – critical habitat for the endangered Cape Sable Seaside Sparrow – was a 20th century phenomenon resulting from past water management practices. Finally, paleoecological and modeling studies in Florida Bay and the Everglades for the $20B+ Comprehensive Everglades Restoration plan established freshwater flow targets now used by managers. Although restoration of historic freshwater flow is not feasible, knowledge about Everglades hydrology and ecology prior to human intervention plays a pivotal role in the design, selection, and construction of restoration projects. Paleoecological data, coupled with decadal-scale monitoring and other long-term studies, provide the long-term perspective necessary to understand decadal, to centennial, and to millennial time-scale processes. While these data are cost-effective to procure, a long-term commitment to funding these types of studies is essential to provide the scientific foundation for restoration.

In situ ecological quality status in the Kosterhavet National Park (Skagerrak, North Sea): a 100 year-perspective

The Koster Trench is the deepest part of the Kosterfjord located in the Skagerrak at the north-west coast of Sweden. In 2009 the Kosterfjord was included into the Marine Protected area Kosterhavet National Park characterized by high biodiversity and a presence of cold-water coral reefs dominated by Lophelia pertusa. The cold-water coral reefs show signs of deterioration and are known to have a much wider distribution during the past. In this study we investigate the temporal variability of the Ecological Quality Status (EcoQS) using benthic foraminifera and sediment geochemistry from a sediment core collected in the Koster Trench together with available hydrographic timeseries and meteorological data. We found that the EcoQS for TOC, metals, and foraminiferal indices suggest high to good ecological status close to natural background levels (reference conditions). However, arsenic (As) content in the sediment has been rising steadily over the period ∼ 1880–2009. Given this pollutant will continue to rise further, it may pass a threshold after which it becomes toxic to the benthic organisms, reaching intermediate EcoQS as it was shown by previous studies. Multivariate statistics performed on foraminiferal data identified three assemblages characterising the record: 1) Stainforthia fusiformis group at ∼ 1880–1940; 2) Bulimina marginata, Cassidulina laevigata and Hyalinea baltica group between ∼ 1940–1985, and, finally, 3) Stainforthia fusiformis and Textularia earlandi group at ∼ 1985–2009. The benthic foraminifera and sediment geochemistry suggests that a decrease in coastal upwelling due to positive NAO together with an increase in freshwater inflow from 1979/1980s; changes in phytoplankton community composition in late 2000s, and trawling activity shifted to the deepest fjord basin from 2009, all together likely have caused a shift towards more opportunistic foraminiferal species with an omnivorous feeding strategies and tolerance of physical disturbance.

Benchmarking water and salt dynamics at subterranean estuaries using TOUGHREACT

The interactions between saline seawater and fresh groundwater occurs in subterranean estuaries (STEs), triggering complex hydrological and geochemical processes. These processes are influenced by multiple hydrological factors including tidal amplitude (A), freshwater head (h), seawater diffusion coefficient (d), and slope ratio. Besides, accurate predictions of the geochemical processes in STEs require validating the hydrological estimations by the geochemical models against that by conventionally used hydrological models. TOUGHREACT is employed to numerically study the effects of these hydrological factors on groundwater flow and salt transport in STEs. At the quasi-static state, the spatiotemporal distributions of the upper saline plume (USP) and the saltwater wedge (SW), and the water fluxes at the surface water-groundwater interface agree with previous results, confirming the applicability of TOUGHREACT for submarine groundwater discharge (SGD) simulations. Increasing tidal amplitude, inland freshwater head, seawater diffusion coefficient, and beach slope ratio enhances the exchange of groundwater and surface water, strengthens the density-driven circulation (DDC) of seawater, and alleviates the saltwater intrusion (SI) by shrinking the SW. The rise of tidal amplitude and seawater diffusion coefficient, and the reduction of freshwater head and beach slope ratio intensify the seawater exchange across the beach mainly by increasing the flux of tide-driven circulation (TDC) of seawater, but reducing the freshwater flux. These findings are beneficial for better understanding the hydrological processes of SGD and serve as a benchmark for predicting the water and salt flow across STEs using TOUGHREACT. This validation expands the numerical toolsets used for quantifying the hydrological processes, and enables future analysis of the geochemical processes occurred in STEs.