Transition Zone Waters Research Articles

РЕЗУЛЬТАТЫ НАУЧНЫХ ЭКСПЕДИЦИОННЫХ ГЕОЛОГО-ГЕОФИЗИЧЕСКИХ ИССЛЕДОВАНИЙ ПОЛЕЗНЫХ ИСКОПАЕМЫХ МОРЕЙ ДАЛЬНЕВОСТОЧНОГО РЕГИОНА РОССИЙСКОЙ ФЕДЕРАЦИИ И ТИХОГО ОКЕАНА (ПРОЕКТ «ГЕОМИР»)

The paper presents a brief overview of the results of integrated geological, geophysical and oceanographic studies for the period 2017–2023, for which interregional generalizations were made on some promising areas of study of underwater mineral resources and the environment. The data on geological underwater objects, in particular, manganese ores of the Sea of Japan and the Sea of Okhotsk and adjacent water areas; rare-earth ores of the Tomtor ore cluster, ancient and modern coastal-marine placers of the Laptev Sea coast are presented; barite ore occurrences “Barite Hills” (in the Sea of Okhotsk); ferromanganese formations of the Eastern Arctic shelf of Russia; coastal marine placers of the shelf and coast of the Far Eastern seas, including gold-bearing placers. including gold-bearing placers of the shelf zone of the south of Primorye and north of Sakhalin, titanomagnetite placers of the Kuril Islands, gold-bearing placers of the North Sakhalin Plain and others. Direct signs of hydrocarbons were obtained in areas previously considered unpromising (including the South China Sea), gas hydrate accumulations were mapped and studied in the Sea of Okhotsk and the Sea of Japan, prospecting for gas hydrates in the Bering Sea was prepared, and comparative studies of hydrate-bearing capacity of the marginal seas of the NW Pacific and the Indian Ocean were carried out. The main features of the distribution of lithologic and gas-geochemical indicators of hydrocarbon gases in bottom sediments of the southwestern sector of the East Siberian Sea, which is the least studied in terms of oil and gas content, were studied. Based on the data of gas-geochemical studies, the prospects of oil and gas content of the eastern shelf of the Arctic were assessed. The results of geomicrobiological studies in the seas of the Far East region are described. In some cases deepsea sediments themselves (peloid-like sediments, etc.) appear to be a separate huge mineral resource. At present, the “continent-ocean” transition zone and neutral waters can become the most important source of replenishing the mineral resource base of these mineral components. The presented research corresponds to the main objectives of the GEOMIR project of the national action plan within the UN Decade of Ocean Sciences for Sustainable Development (2021–2030) and was carried out mainly in accordance with the directions of the state assignment. Studies of gas hydrates were carried out within the framework of the WESTPAC working group “Gas hydrates and methane fluxes in the Indo-Pacific region” (CoSGas, 2021–2024), established on the initiative and under the leadership of Russia.

Hydrogeologic and Geochemical Distinctions in Freshwater‐Brine Systems of an Andean Salar

AbstractThe Salar de Atacama contains one of the world's most important lithium resources and hosts unique and fragile desert ecosystems. Water use issues of the hyper‐arid region have placed it at the center of global attention. This work combines geochemical and hydrogeologic data with remote sensing analysis to address differences in water zones in the marginal environments of the salar. Water samples from across the inflow to brine transition were collected over the period 2012–2016 and analyzed for ẟD, 3H, 87Sr/86Sr and major and minor elements. The ẟD values range from about −64‰ to +20‰, 3H as Rmod from 0.01 to 0.36 and the 87Sr/86Sr from 0.70750 to 0.70804 with highest ẟD and 3H occurring in the regions of open water. Geochemical modeling results indicate inflow and shallow transition zone waters are saturated with respect to calcite, whereas all others are saturated with respect to calcite, gypsum, and halite. Long‐term remote‐sensing of surface water body extents indicate that extreme precipitation events are the primary driver of surface area changes as exemplified by an increase in size of the lagoons by a factor of 2.7 after a storm. A new conceptual model of the freshwater to brine transition zone that incorporates variability in aquifer geology, hydrology and geochemistry to explain important marginal water bodies is presented. The subsurface brines in the transition zone and the halite nucleus are geochemically distinct compared to the groundwater discharge features (e.g., lagoons) over modern time scales which aids in conceptualizing the transition zone system.

Revisiting groundwater chemical processes in a rapidly urbanizing basin

Monterrey procures about 40% of its water supply from groundwater resources, considering several aquifers below and nearby. This city meets semiarid climate conditions with highly variable precipitation rates. The increasing demand for groundwater during drought conditions can deteriorate water quality, raising the energy consumption and costs of lifting, moving, distributing, and treating water. Thus, the major ion content of this resource was assessed, analyzing changes across the Monterrey Basin during the last 11 years to obtain a more robust geochemical concept of the study area. Waters from three wellfields (Buenos Aires, Santiago, Mina) with low mineralization were classified as recharge waters. Waters circulating across evaporite–silicate–carbonate sediments of the Monterrey Basin with gradually increasing salinity were classified as transition zone waters (Metropolitan area) and discharge zone waters (north and northeast of the city). According to this, it can be concluded that groundwater from the different Monterrey sources exhibits high-quality mineralized water, considering the analyzed parameters. Nevertheless, further attention must be paid on nitrate and sulfate occurrence and evolution in the transition and discharge zones.

Freshwater-seawater transition in coastal Todos Santos aquifer, Baja California Sur

Todos Santos is a coastal town located in Baja California Sur (Mexico), which has experienced an increase in tourist and agricultural activities during the last years. However, the Todos Santos aquifer is the sole source of freshwater supplied to populations. Therefore, the goal of this work is to investigate the processes that can cause groundwater salinity in this aquifer. The results of the chemical analysis performed in groundwater indicate 3 water groups: i) less mineralized waters of the recharge zones showing a strong interaction with silicate rocks; ii) transition-zone waters from alluvial sediments also reflecting silicate rock-water interaction; iii) the most mineralized waters located along the coastline reflecting seawater intrusion. Overall, the ionic composition and the salinity gradient of groundwater are in agreement with the topographic flow paths. Nevertheless, in wells located in the coastline, groundwater interacts with seawater and undergoes evaporation simultaneously, exponentially increasing the salinity beyond seawater composition.

Geochemical processes controlling groundwater quality under semi arid environment: A case study in central Morocco

Bahira plain is an important area for Morocco due to its agriculture and mining activities. Situated in a sub-arid to arid climate, this plain hosts an aquifer system that represents sequences of carbonates, phosphates, evaporates and alluvial deposits. Groundwater flows from Ganntour plateau (recharge area) to the basin-fill deposits and Zima Lake and Sed Elmejnoun where water evaporates. The objective of this study was to characterize the chemical properties of the groundwater and to assess the processes controlling the groundwater's chemistry. We can divide water samples into three hydrochemical water groups: recharge waters (Ca/Mg–HCO3), transition zone waters (Ca–HCO3–SO4/Cl) and discharge waters (Na-Cl/SO4). Accordingly, compositions of waters are determined by the availability of easily soluble minerals like calcite (Ca–HCO3 dominant), halite (Na–Cl dominant) and gypsum (Ca–SO4 dominant). Cl/Br ratios show that Cl concentration increases from dissolution of natural halite. When groundwater is affected by extreme evaporation Cl/Br ratios may increase up to 1900. High fluoride concentrations are associated with low Ca2+ concentrations (<100mg/L). That means when recharge waters enter the aquifer, it starts dissolving fluorite since the Ca2+ concentration is low. Once groundwater becomes saturated with Ca2+, the immobilization of fluoride is occurring by precipitation of fluoride-rich minerals like fluoro-apatite. According to the environmental isotope (18O and 2H) analyses, they are three potential processes affecting groundwater: 1. Evaporation as verified by low slope value, 2. Water-rock interaction, 3. admixture of waters showed different stable isotope compositions and salinities.

Assessment of major ions and trace elements in groundwater supplied to the Monterrey metropolitan area, Nuevo Le\xf3n, Mexico

The Monterrey metropolitan area (MMA) is the third greatest urban area and the second largest economic city of Mexico. More than four million people living in this megacity use groundwater for drinking, industrial and household purposes. Thus, major ion and trace element content were assessed in order to investigate the main hydrochemical properties of groundwater and determine if groundwater of the area poses a threat to the MMA population. Hierarchical cluster analysis using all the groundwater chemical data showed five groups of water. The first two groups were classified as recharge waters (Ca-HCO3) coming from the foothills of mountain belts. The third group was also of Ca-HCO3 water type flowing through lutites and limestones. Transition zone waters of group four (Ca-HCO3-SO4) flow through the valley of Monterrey, whereas discharge waters of group 5 (Ca-SO4) were found toward the north and northeast of the MMA. Principal component analysis performed in groundwater data indicates four principal components (PCs). PC1 included major ions Si, Co, Se, and Zn, suggesting that these are derived by rock weathering. Other trace elements such as As, Mo, Mn, and U are coupled in PC2 because they show redox-sensitive properties. PC3 indicates that Pb and Cu could be the less mobile elements in groundwater. Although groundwater supplied to MMA showed a high-quality, high mineralized waters of group 5 have NO3− concentrations higher than the maximum value proposed by international guidelines and SO42−, NO3−, and total dissolved solid concentrations higher than the maximum levels allowed by the Mexican normative.

Hydrogeochemistry of Groundwater Supplied to the City of Monterrey, Mexico

The Monterrey Metropolitan Area (MMA) is the third greatest urban area of Mexico. Owing to the rapid industrialization and urbanization of this city, more water resources are necessary in this semi-arid region. Thus, the objectives of this work were to characterize the chemical properties of groundwater supplied to MMA and to assess inter-annual variations in the water chemistry. Three groups of water were identified: recharge waters from mountain belts dominated by marine sedimentary rocks (Ca-HCO3 type), transition zone waters from alluvial sediments (Ca-HCO3-SO4 type) and waters flowing through conglomerates and alluvial sediments of the northeastern MMA (Ca-SO4 type). The ionic composition and the salinity gradient of each water group were in agreement with the topographic flow paths of the study area. The non-parametric Mann-Whitney U-test indicated that there have been no significant changes on the groundwater quality supplied to the MMA between the years 2006 and 2012.

Trends in landings and vulnerability to climate change in different fleet components in the Portuguese coast

Portugal is the third highest per capita consumer of fish in the world, with a fishing fleet consisting of trawlers, purse-seiners and multi-gear vessels, which use a wide variety of fishing gears, such as gillnets, trammel nets, longlines or traps. Climate change affects ocean conditions, impacting marine organisms and ecosystems, with consequences for marine fisheries. The consequences of climate change on fishing communities will depend on their exposure to this factor, the sensitivity of target species and ecosystems to climate change and fishermen’s ability to adapt to climate change. The Portuguese coast is mainly north-south oriented and located in a biogeographic transition zone, between temperate and subtropical waters, where the northern or southern distribution limits of several species can be found. Also, the Portuguese coast is expected to suffer changes in temperature and precipitation more accelerated than the global mean alteration rate, which makes it particularly adequate for studies of the effect of climate change on coastal communities and fisheries. The present study analysed trends in landings of the most important fishing métiers in the Portuguese coast and the vulnerability and adaptation capacity of Portuguese fisheries to climate change. Official Portuguese landings (1992–2012) were analysed and a survey was conducted to assess fishermen’s perception of landings and their potential behaviour in response to the effects of climate change on fisheries. Eighteen new species were landed in Portuguese fisheries over the past 5 years, of which 12 were tropical or subtropical and 5 had their distribution limit along the Portuguese coast. A latitudinal pattern in the number of new species in landings was found, agreeing with a northward shift of subtropical species. The south coast has shown a higher vulnerability to climate change, in terms of both exposure and sensitivity of target species and ecosystems to its effects. Trawlermen may be more adaptable and less vulnerable to climate change, given the high mobility of their fleet. Multi-gear fisheries may be more flexible in changing target species or fishing gear, which makes them potentially less vulnerable to climate change. On the other hand, the high sensitivity of sardine to the effects of climate change makes the purse-seine fisheries particularly vulnerable to climate change.

Investigation of the geochemical evolution of groundwater under agricultural land: A case study in northeastern Mexico

• A scheme of statistical methods was developed to define hydrochemical groups. • An inverse modeling approach considered geogenic and anthropogenic processes. • Weathering of evaporitic rocks represents the main contribution to groundwater chemistry. • A process takes place which converts dolomite into calcite (dedolomitization). • It may not be cost-effective to regulate manure application to mitigate groundwater pollution. Zona Citrícola is an important area for Mexico due to its citriculture activity. Situated in a sub-humid to humid climate adjacent to the Sierra Madre Oriental, this valley hosts an aquifer system that represents sequences of shales, marls, conglomerates, and alluvial deposits. Groundwater flows from mountainous recharge areas to the basin-fill deposits and provides base flows to supply drinking water to the adjacent metropolitan area of Monterrey. Recent studies examining the groundwater quality of the study area urge the mitigation of groundwater pollution. The objective of this study was to characterize the physical and chemical properties of the groundwater and to assess the processes controlling the groundwater’s chemistry. Correlation was used to identify associations among various geochemical constituents. Factor analysis was applied to identify the water’s chemical characteristics that were responsible for generating most of the variability within the dataset. Hierarchical cluster analysis was employed in combination with a post-hoc analysis of variance to partition the water samples into hydrochemical water groups: recharge waters (Ca–HCO 3 ), transition zone waters (Ca–HCO 3 –SO 4 to Ca–SO 4 –HCO 3 ) and discharge waters (Ca–SO 4 ). Inverse geochemical models of these groups were developed and constrained using PHREEQC to elucidate the chemical reactions controlling the water’s chemistry between an initial (recharge) and final water. The primary reactions contributing to salinity were the following: (1) water–rock interactions, including the weathering of evaporitic rocks and dedolomitization; (2) dissolution of soil gas carbon dioxide; and (3) input from animal/human wastewater and manure in combination with by denitrification processes. Contributions from silicate weathering to salinity ranged from less important to insignificant. The findings suggest that it may not be cost-effective to regulate manure application to mitigate groundwater pollution.

Are regional fisheries’ catches changing with climate?

Climate change affects ocean conditions, which will in turn impact marine organisms and ecosystems, with consequences for fisheries. The Iberian Peninsula has faced an increase in both air and sea surface temperature, and rainfall has decreased in intensity and frequency in Portugal. As Portugal is the third highest per capita consumer of fish in the world and its coast is located in a biogeographic transition zone, between temperate and subtropical waters, the study of the effects of climate change on Portuguese fisheries is of the utmost importance. The present work focused on Setúbal, an important fishing port in central Portugal. Landings Per Unit of Effort (LPUE) time series (1927–2012) of the most important species were analysed and their relationships with sea surface temperature (SST), rainfall and the winter North Atlantic Oscillation (NAO) index were investigated. Mean annual SST has increased 0.9°C from 1926 to 2012. The main target species in 2012 were the same as in 1927. However, their landings have changed and have responded to changes in environmental variables, particularly SST. LPUE of the European sardine has shown a decreasing trend and was negatively correlated with SST and NAO, whereas the LPUE of the Atlantic chub mackerel has been increasing since 2000. The LPUE of the common cuttlefish has kept more or less stable through the studied time series, but it was correlated with SST. The LPUE of soles has increased with time and SST. The LPUE of the common octopus was correlated with SST and NAO and has presented higher values since 1975. Further increases in sea temperature in the future will pose challenges for fisheries in Setúbal. Purse-seine fisheries may try to compensate the expected losses in sardine landings by targeting the chub mackerel. Although landings of the most important species in multi-gear fisheries seem to have been favoured by increases in temperature, further studies on the tolerance of each particular species to increases in temperature are needed. As a recent increase in the relative importance of subtropical species in Portuguese fisheries has already been previously detected, climate change may also bring new fishing opportunities for this region.

Holoplanktonic molluscs (Gastropoda: Pterotracheoidea, Thecosomata and Gymnosomata) from the southern Mexican Pacific

This is the first study of species composition of holoplanktonic molluscs of the Pacific coast of southern Mexico, focusing mainly on the Gulf of Tehuantepec. From two oceanographic surveys during summer 2007 and 2010, 40 zooplankton samples were obtained. A total of 40 species contained within 17 genera and 8 families was found. The results show 15 range extensions, including Atlanta californiensis and Carinaria japonica which were previously considered as endemic to the Transition Zone waters of the California Current, and Limacina helicina which was thought to only inhabit polar and subpolar waters. Atlanta gibbosa and Creseis chierchiae f. constricta are two new records for the American Pacific. The use of holoplanktonic molluscs as indicators of water masses is a common practice; however, these reported range extensions limit the validity of their use as indicators, at least within the environmental parameters established in previous studies. Although the 40 species found represent only 43% of the species recorded for the Pacific Ocean, it is noted that this species richness only represents summer conditions and an increase could be expected if sampling was extended to winter.

Assessment of Microcystis growth rate potential and nutrient status across a trophic gradient in western Lake Erie

Plankton tow samples collected from 2002 through 2009 indicate that Microcystis biovolume in western Lake Erie is often most dense in transition zone (TZ) waters between Maumee Bay and the center of the western basin. TZ waters are generally high in nutrients and turbidity, and concentrations of each decrease with distance from Maumee Bay. High Microcystis biovolume in the TZ suggests the possibility that the conditions in these waters support a greater Microcystis growth rate relative to the open lake. To test this hypothesis, during the 2008 bloom, Microcystis was collected from western Lake Erie for measurements of total protein content (TPC) as an indicator of growth rate potential and cellular nutrient content to indicate nutrient deficiencies. TPC results indicate that Microcystis in the TZ had a higher potential growth rate compared to offshore waters. TPC values in Maumee Bay were intermediate but not significantly different from the TZ and offshore. Nitrogen content of Microcystis remained high over the summer at all sites, despite very low dissolved nitrate concentrations and low total nitrogen-to-total phosphorus ratio in late summer in the lake. Ammonium level in the lake was constant during the summer, and likely provided the nitrogen source for Microcystis. Cellular phosphorus content varied between site and sample date suggesting that Microcystis was moderately phosphorus deficient. Quotas of micronutrient indicated that Microcystis was not deficient of micronutrients. Results of this study suggest the waters in and adjacent to Maumee Bay provide more favorable growth conditions for Microcystis than offshore waters.

Application of multivariate statistical methods and inverse geochemical modeling for characterization of groundwater — A case study: Ain Azel plain (Algeria)

Multivariate statistical methods and inverse geochemical modeling were jointly used to define the variation and the genetic origin of chemical parameters of groundwater in the Ain Azel plain, Algeria. Interpretation of analytical data shows that the abundance of the major ions is as follows: Ca ≥ Mg > Na > K and HCO 3 ≥ Cl > SO 4. Q-mode hierarchical cluster analysis (HCA) was employed for partitioning the water samples into hydrochemical facies, also known as water groups or water types. Three major water groups resulted from the HCA analysis. The samples from the area were classified as recharge area waters (Group 1: Ca–Mg–HCO 3 water), transition zone waters (Group 2: Ca–Mg–Cl–HCO 3 water), and discharge area waters (Group 3: Mg–Ca–HCO 3–Cl water). Inverse geochemical models of the statistical groups were developed using PHREEQC to elucidate the chemical reactions controlling water chemistry. The inverse geochemical modeling demonstrated that relatively few phases are required to derive water chemistry in the area. In a broad sense, the reactions responsible for the hydrochemical evolution in the area fall into three categories: (1) dissolution of evaporite minerals; (2) precipitation of carbonate minerals; and (3) weathering reactions of silicate minerals.

Measurements of foraging success in a highly pelagic marine predator, the northern elephant seal

1. Identification of foraging behaviour and the ability to assess foraging success is critical to understanding individual and between-species variation in habitat use and foraging ecology. For pelagic predators, behaviour-dependent foraging metrics are commonly used to identify important foraging areas, yet few of these metrics have been validated. 2. Using the northern elephant seal as a model species, we validated the use of a behaviour-independent measure of foraging success (changes in drift rate) at the scale of the entire foraging migration, and then used this to assess a variety of common foraging metrics that are based on movement patterns and dive behaviour. Transit rate consistently provided the best estimate of daily foraging success, although the addition of other metrics provides insight into different foraging behaviours or strategies. 3. While positive changes in buoyancy occurred throughout most of the migrations, implying successful feeding across much of the north Pacific, the areas of most rapid changes in buoyancy occurred along a latitudinal band (40-50° N) corresponding to a dynamic hydrographic region including Subarctic Gyre and Transition Zone waters. 4. These results support the use of transit rate as an index of foraging success: a metric that is easily derived from tracking measurements on a wide range of marine species.

Mesoscale structure of copepod assemblages in the coastal transition zone and oceanic waters off central-southern Chile

In the Humboldt Current System, the region off central-southern Chile has relatively high eddy kinetic energy, generating an extensive coastal transition zone (∼600 km offshore) in which coastally derived eddies are recurrent features. This energy might promote strong exchanges of water, biogeochemical properties, and plankton between the coastal upwelling band and the adjacent oceanic zone. In this study, the mesoscale structure of epipelagic copepod assemblages and its relationship to environmental variability and the eddy field in the coastal transition zone and oceanic areas off Concepción (34–39°S, 73–84°W) were investigated. Zooplankton samples were collected during cruises of opportunity carried out during the 2006 coastal upwelling season and the oceanographic conditions were derived from satellite data on sea surface height, temperature, and chlorophyll a. The use of cluster analyses and indicator species revealed two main copepod assemblages: (i) species with a mainly coastal distribution, the maximum in total abundance being found nearshore and (ii) species with a mainly oceanic distribution (beyond ∼500 km from the coast), where a secondary maximum was observed. Both types of assemblages, however, included species widely distributed in the coastal transition zone. An ordination analysis identified sea surface temperature and chlorophyll a as the main factors affecting the distribution of most species and the clustering of stations resembled the distribution of these variables. Some of the large calanoid species that are common in shelf waters were more abundant within nearshore eddies rich in chlorophyll a and other cyclonic eddies far offshore; however, the eddy field alone did not explain the copepod mesoscale distribution. Altogether, the wide distribution of shelf/slope copepod species in this region suggests that physical and biological mechanisms might be acting to extend the productive area of the coastal upwelling zone.

Hydrologic and geologic factors controlling surface and groundwater chemistry in Indian Wells-Owens Valley area, southeastern California, USA

The Indian Wells-Owens Valley area is located in the semi-arid Basin and Range province, which is characterized by alternating mountains and alluvial basins. Surface water resources are limited in this arid region and water demand is mainly met by groundwater pumpage. In a classic Basin and Range groundwater system, water flows from recharge areas in the mountains to discharge areas in adjacent valleys. Discharge areas are generally occupied by playas where large amounts of salt deposition occur due to evaporating groundwater. Hydrochemical data from a total of 1368 spring, surface, and well water samples collected over an 80-year period were used to evaluate water quality and to determine processes that control water chemistry. Q-mode hierarchical cluster analysis (HCA) was employed for partitioning the water samples into hydrochemical facies, also known as water groups or water types. Five major water groups resulted from the HCA analysis. The samples from the area were classified as recharge area waters (Ca–Na–HCO 3 water and Na–Ca–HCO 3 water), transition zone waters (Na–HCO 3–Cl water), and discharge area waters (Na–Cl water and more concentrated Na–Cl water). Spatial plots of the major statistical groups show that the samples that belong to the same group are located in close proximity to one another suggesting the same processes and/or flowpaths. Inverse geochemical models of the statistical groups were developed using PHREEQC to elucidate the chemical reactions controlling water chemistry. The inverse geochemical modeling demonstrated that relatively few phases are required to derive water chemistry in the area. In a broad sense, the reactions responsible for the hydrochemical evolution in the area fall into four categories: (1) silicate weathering reactions; (2) dissolution of salts; (3) precipitation of calcite, amorphous silica, and clay minerals; and (4) ion exchange.

Late Pleistocene-Holocene oceanographic changes in the Northeastern Pacific

The distributions of the radiolarian assemblages in the Northeastern Pacific Ocean were determined and correlated with the average summer temperature of the near surface waters of this region. These assemblages were compared with those in three sediment cores taken beneath the Transition Zone waters. This comparison indicates that the assemblage off Oregon at the last maximum cold interval (24,000 yr B.P.) was like that now found off southern Alaska. The correlation of the radiolarian assemblages with temperature gives an estimate of 11°C for the average summer temperature at that time. This is approximately 4°C cooler than present day conditions in the area. Superimposed on the general warming trend that began 24,000 y.a., there are minor oscillations in the assemblages which correspond to estimates of temperature change of about 2°C in the Pleistocene and about 1°C in the Holocene. In the Holocene, these minor warm intervals appear to be approximately synchronous with advances in mountain glaciers.