Stratified Water Masses Research Articles

Nutrient Shift in the Yucatan Basin during the late Early Miocene: Evidence from calcareous nannofossils and stable isotopes at ODP Leg 165 Site 998 Hole A

Paleoceanographic reconstructions in the Caribbean Sea during past climate transitions, namely the Late Oligocene to Early Miocene (up to the Miocene Climatic Optimum and Monterey Excursion) are crucial to understanding the effects of the Eastern Pacific interchange with the Atlantic Ocean. Studies of the planktonic domain in the Yucatan Basin during the Early Miocene are limited, with most Caribbean research focused on reconstructing the series of events that precede the final closure of the Isthmus of Panama in the Early Pliocene. Furthermore, paleoceanography of the Yucatan Basin is largely unrefined during this time, even though it is an important transition for ocean gateways, and development of Atlantic deepwater and Atlantic Meridional Overturning Current (AMOC), driving global ocean circulation. Here we conduct a relative percent abundance analysis of calcareous nannofossils and stable isotopes from bulk sediment of drill cores spanning the Upper Oligocene to Lower Miocene in the central Yucatan Basin, collected by the Ocean Drilling Program Leg 165 at Site 998 Hole A. Nannofossil assemblage data record a shift from a eutrophic to oligotrophic system ∼19.2–17.65 Ma. Eutrophic taxa (Reticulofenestra spp. and Cyclicargolithus floridanus) decline at ∼20.23 Ma, while oligotrophic taxa (discoasters and sphenoliths) increase as stable carbon isotope values decline. The palaeoecological turnover coincides with a possible restriction in the Central American Seaway (CAS) ∼20.7–21 Ma. Population dynamics of the Hole 998 A nannofossil assemblage track with global declines in C. floridanus relative abundance between ∼20.2 to ∼20.5 Ma, followed by a subsequent decrease in Reticulofenestra spp. These data suggest water mass stratification in the Yucatan Basin during the Early Miocene ∼19.2–17.65 Ma, likely due to restriction of the CAS.

Paleoenvironment in the circum-arctic region from the Middle Jurassic to Early Cretaceous: Trace element and stable isotope geochemistry of the Agardhfjellet Formation, Svalbard

From the Middle Jurassic to Early Cretaceous, the mudstone-dominated Agardhfjellet Formation was deposited during the prolonged shelf dysoxic-anoxic event (SDAE) recorded predominantly in the circum-arctic polar regions. Commonly, oceanic anoxic events (OAEs) throughout Earth's history are linked to the emplacement of large igneous provinces (LIPs). OAEs and LIPs, alone or jointly, are inferred to be triggers for severe biotic crises in Earth's history. However, the causes for SDAEs remain uncertain. To elucidate these causes, we document the geochemical features of the Agardhfjellet Formation using trace element concentrations and stable isotope ratios. The Agardhfjellet Formation, which consists of the Oppdalen, Lardyfjellet, Oppdalssåta, and Slottsmøya members in ascending order, formed during ∼13 Myr of prolonged dysoxic, anoxic, and euxinic conditions. The onset of shelf anoxia took place between deposition of the Oppdalen and Lardyfjellet Members. The extent of sea floor anoxia in the basin varied within the Lardyfjellet Member but likely persisted throughout most of the Slottsmøya Member. Mo/TOC and MoEF/UEF ratios in the sedimentary rocks are consistent with the anoxic events. Enhanced continental runoff marked the Oppdalen, Oppdalssåta, and Slottsmøya members, contrasting with most of the Lardyfjellet Member, in which authigenic phases were widespread under anoxic conditions. Our results show that, compared to other OAEs, such as the Toarcian OAE (∼183 Ma) or the OAE2 (∼94 Ma), the Late Jurassic – Early Cretaceous SDAE recorded in the Agardhfjellet Formation is characterized by prolonged suboxic–anoxic condition, substantial water-mass stratification, and increased continental runoff.

Assessment of Environmental Risks of a Shallow Water Body during Dredging Works

Introduction. The increasing anthropogenic impact on water bodies necessitates integrated solutions to assess environmental risks. Literature describes the stages of risk assessment, the possibilities of environmental management, and expert analysis, while risk modeling in this field is being investigated. However, the potential for predicting risks to water quality and biodiversity during frequently performed hydraulic engineering works such as dredging has not been fully explored. The relevance and practical significance of such an approach are evident. This study aims to develop a mathematical model and software package that can assess risks to species diversity of the ecosystem of a shallow reservoir ecosystem during work in its water area.Materials and Methods. The starting point for the simulation was a description of the movement of water masses based on the Navier-Stokes equations and the continuity equation at variable density. We used the diffusion-convection equation to predict the transfer of suspended and dissolved particles, as well as to assess the impact of impurities during eutrophication. To create the algorithm, we utilized the terms and definitions defined by the state standard for risk management in emergency situations.Results. To test the solution, we took data on hydro-mechanical work in the port area of Arkhangelsk. We visualized the concentration fields of suspended particles 0, 15, 30 and 45 minutes after the soil was unloaded. It was found that during the settling of the suspension, the area of its distribution expanded significantly, and this was fully consistent with the data of field experiments during dredging. We calculated and tabulated the volumes of contaminated water at soil dumps in three sites (with a single discharge and in total). To assess the risks to the Sea of Azov, we used the maximum concentrations of pollutant (copper) obtained through measurements, modeling and remote sensing of the Earth. In tests to determine the potential danger of the substance, we assumed that its concentration caused a reaction in 50% of organisms. For fish, the potentially dangerous concentration was 4 mg/l with a duration of 96 hours of exposure. For zooplankton — 50 mg/l and 48 hours. For microalgae, 20 mg/l and 72 hours. The normalized risk value Rn ≈ 0.52 was obtained. The risk of copper concentration of 80 µg/l in the waters of the Azov Sea was recognized as significant. A tendency towards increasing salinity and stratification of water masses in terms of oxygen content has been identified, consistent with the findings of expeditionary research.Discussion and Conclusion. The developed approach has allowed us to assess the change in the quality of the waters of the Azov Sea and describe some transformations of the water area. Specifically, we are talking about the distribution of suspended particles and areas of their deposition. These processes can lead to changes in the bottom topography, which in turn can reduce the species diversity of the ecosystem.

Water masses stratification and circulation in the southern part of Banggai Upwelling Region in Maluku Sea

Banggai Waters is in the western Maluku Sea, where the secondary pathway of Indonesian Throughflow passes and seasonal coastal upwelling takes place in this region, providing a high marine productivity and potential fishing ground. This study aims to describe water mass stratification and circulation using CTD casts and SADCP section datasets from the BUDEE cruise in September 2022 onboard RV Baruna Jaya VIII. The results show that mixed layer depth varies between 43-112 m with a mean temperature of 25.82(± 0.88) ºC. North Pacific water origin (NPSW and NPIW) is present in this southern section. The depth of chlorophyll maximum is much shallower in the upwelling center. Furthermore, for the first time, we identified a strong northward flow from the Bote Strait, disrupting Banggai upwelling water with cooler and fresher Banda water. Estimates of northward transport volume through this strait is about 0.531 Sv.

ОСОБЕННОСТИ ВНУТРИСУТОЧНЫХ КОЛЕБАНИЙ ПОКАЗАТЕЛЕЙ КАЧЕСТВА ВОДЫ, НАБЛЮДАЕМЫХ В КАМСКОМ ВОДОХРАНИЛИЩЕ9

To solve a wide range of problems related to the protection and rational use of water bodies, it is fundamentallyimportant to assess fluctuations in the variability of indicators of their chemical composition. In this case, as a rule, seasonal and monthly fluctuations are considered and analyzed. This is due, most of all, to the features of the current monitoring system. The transition to automated measurement systems makes it possible to study and analyze much shorter-period processes, such as inter- andintra-day fluctuations.Currently, these fluctuations in water quality indicators in reservoirs are an insufficiently studied phenomenon, although theyplay an important role both in shaping the consumer properties of water and ensuring the environmental safety of water bodies. Thesefluctuations are especially relevant for water bodies located in zones of active technogenesis, which are the most important sources ofwater supply for the largest industrial complexes.The article examines the processes recorded in two sections of the Kama Reservoir: the lower one, directly adjacent to theKama Hydroelectric Power Station, and the upper one, located in the zone of pinching out of its backwater. In the lower section, thequality of water taken in winter is characterized by pronounced inter- and intra-day fluctuations caused by significant changes in waterdischarge rates in the lower pool. At the same time, in the upper section of the reservoir, located in the zone of backwater wedging out,these fluctuations are observed in the warm period, during the formation of vertical stratification of water masses. These phenomenaoccur with a significant decrease in the slopes of the water surface and, accordingly, a decrease in current speeds.

Stratification of Indonesian Throughflow Water and Its Circulation along 125E in the Banggai - Maluku Sea

secondary pathway of Indonesian Throughflow (ITF) that enters from its inflow portal of the northern Maluku Sea is assumed to recirculate in the Banggai - Maluku Sea, where its upper-layer circulation returns into the Pacific and deeper flows continue southward into Seram/Banda Sea via Lifamatola Strait. However, direct observation in this key region is still limited. Here, using direct CTD (Conductivity Temperature Depth) casts and shipboard ADCP (Acoustic Doppler Curent Profiler) measurement datasets from BUDEE (Banggai Upwelling Dynamics and Ecosystem Experiment) cruise in September 2023, we study stratification and structure of ITF water and its circulation in a meridional section along 125E. The results show the water mass stratification of the mixed layer having a depth of 0-75m with a temperature range of 26-29°C, while the thermocline layer has a depth of 28-407m with a temperature range of 23-26°C, and the deep layer has a depth of 407-1000m with a temperature value of 4-12°C. The current pattern of the Banggai Sea Maluku Sea at a depth of 52-400m is more dominantly influenced by non-tidal currents, the influence of tidal currents only covers a depth of 52m less than non-tidal currents.

Characteristics of North Pacific water masses in the Bali Sea

The Bali Sea is the trajectory of Indonesian Throughflow (ITF)’s water mass which originates from the North Pacific (NP) Ocean before exiting through Lombok Strait. Therefore, the NP water masses have an impact on the characteristics of the water mass in this area. The study aims to describe the stratification and structure of water masses and calculate the contribution of North Pacific Subtropical Water (NPSW) and North Pacific Intermediate Water (NPIW) using Optimum Multiparameter (OMP) analysis. Stratification of the Bali Sea consists of mixed, thermocline, and deep layers. There were found remnants of NPSW and NPIW inside the thermocline layer, deeper than their origin in the NP Ocean. The core layer of NPSW has an S-max value of 34,6 psu at 120-170m depth, while NPIW has an S-min value of 34,3 psu at the deeper layer, 260-280m depth. The NPIW more dominant presence in the Bali Sea with 80% contribution at a depth of 200-215 meters, while NPSW contribution is 70% at a depth of 110-130 meters. NPSW’s contribution decreases from east to west and vice versa the NPIW.

Spatial distributions, environmental drivers and co-existence patterns of key cold-water corals in the deep sea of the Azores (NE Atlantic)

Habitat-forming cold-water corals (CWCs) represent a key component of deep-sea benthic communities and a priority target for conservation. Although research efforts have been mounting to try and identify the drivers of CWC distributions, progress has been limited by the scarcity of ecological data. The present work employs habitat suitability models (HSMs) to estimate spatial distributions, environmental drivers and co-existence patterns of 14 habitat-forming CWCs in the Azores, an area considered a hotspot of coral diversity in the Atlantic. The modelled CWCs showed a strong bathymetric zonation, which seems to be determined by the vertical stratification of water masses in the region. In particular, the modelled CWCs can be clustered in four groups named after the isopycnal (vertical) layers in which Atlantic water masses are organized: species restricted to upper water masses, species extending down from upper water masses, species restricted to intermediate water masses and species extending up from deep water masses. Horizontal patterns further indicate that the Azores Current and different production regimes north and south of the archipelago likely influence the distribution of CWCs in sub-surface waters. Such results have important implications for the regional management of deep-sea benthic communities and, in particular, for the design of representative networks of protected areas. The combined habitat of all modelled species covered only 11%. Given that they all possess the characteristics of benthic foundation organisms and represent indicator taxa of vulnerable marine ecosystems all the modelled species should be viewed as important targets for conservation. The lace coral Errina dabneyi deserves particular attention since this species appears to be endemic to the Azores and has a very limited estimated distribution.

Seasonal variation of mixed layer depth and thermocline thickness from the ctd argo float data in the Southern Makassar Strait

The Makassar Strait (MS) is directly connected to the Sulawesi Sea in the north and the Java Sea and the Flores Sea in the south and is the main route of Indonesia Throughflow(ITF). Hence Stratification of water mass in the MS is influenced by the dynamics of these waters. This study aims to describe seasonal variations of the mixed layer depth and the thermocline thickness, identify ITF water masses, and the occurrence of coastal upwelling in the southern part of the MS. The results show that the North Pacific water origin of North Pacific Subtropical Water (NPSW) and North Pacific Intermediate Water (NPIW) are dominant, with a maximum salinity characteristic of 34.6-34.7 psu in the thermocline layer and a minimum salinity of 34.5 psu in the intermediate layer. However, near-surface fresh Java Seawater appears to be dominant during the northwest monsoon (NWM-DJF) period. Seasonal variation of the mixed layer depth is much deeper (93m) and vertical gradient of temperature and salinity are much stronger due to the presence of fresh Java Sea water advected by the eastward Java Monsoon Current. However, during the southeast monsoon (SEM-JJA) period the mixed layer depth is much shallower and the thermocline layer is much thicker (198 m), Associated with much stronger ITF and upwelled colder water from the upwelling area. The coastal upwelling event during the SEM period in the study are is characterized by an increase of isotherm of 25 °C, isohaline of 34.0 psu, and isopycnal of 22.0 kg/m3 from about 75 m depth to the sea surface layer.

Millennial‐scale oscillations and an environmental regime shift around the Middle to Late Holocene transition in the North Atlantic region based on a multiproxy record from Isfjorden, West Spitsbergen

Palynological and sedimentological analyses were performed on the sediment core HH16‐1205‐GC retrieved from the central Isfjorden, West Spitsbergen. The sequence, which spans the last 7000 years, revealed an overall cooling trend with an important climate shift between 4.4 and 3.8 cal. ka BP, in addition to millennial‐scale oscillations. Sea‐surface reconstruction from dinocyst assemblages indicates a decrease in summer sea‐surface temperature, from 2.5 to 1.5 °C, and primary productivity, from 750 to 650 gC m−2 a−1 over the last 7000 years. From around 6.8 to 5.8 cal. ka BP, the sedimentological and palynological data suggest a predominant sediment supply from the inner part of the fjord, ice rafting, dense sea ice cover, strongly stratified water masses and high primary productivity. The interval from 4.4 to 3.8 cal. ka BP is marked by a layer of coarser material and a significant decrease in the grain‐size mode. Our geochemical data show large‐amplitude fluctuations after 2.0 cal. ka BP, while an increase in the dinocysts Impagidinium pallidum and Spiniferites elongatus from 2.0 to 1.2 cal. ka BP suggests enhanced Atlantic Water inflow. The dinocyst‐based reconstructions also reveal large‐amplitude millennial fluctuations in sea ice cover, summer sea‐surface temperature and salinity. Wavelet analysis and cross‐wavelet analysis on K/Ti ratio coupled with sea‐ice estimates confirm a strong signal with a periodicity of 1200–1500 years.

Biotic and Paleoceanographic Changes Across the Late Cretaceous Oceanic Anoxic Event 2 in the Southern High Latitudes (IODP Sites U1513 and U1516, SE Indian Ocean).

Oceanic Anoxic Event 2, spanning the Cenomanian/Turonian boundary (93.9 Ma), was an episode of major perturbations in the global carbon cycle. To investigate the response of biota and the paleoceanographic conditions across this event, we present data from International Ocean Discovery Program sites U1513 and U1516 in the Mentelle Basin (offshore SW Australia; paleolatitude 59°–60°S in the mid‐Cretaceous) that register the first complete records of OAE 2 at southern high latitudes. Calcareous nannofossils provide a reliable bio‐chronostratigraphic framework. The distribution and abundance patterns of planktonic and benthic foraminifera, radiolaria, and calcispheres permit interpretation of the dynamics of the water mass stratification and provide support for the paleobathymetric reconstruction of the two sites, with Site U1513 located northwest of the Mentelle Basin depocenter and at a deeper depth than Site U1516. The lower OAE 2 interval is characterized by reduced water mass stratification with alternating episodes of enhanced surface water productivity and variations of the thickness of the mixed layer as indicated by the fluctuations in abundance of the intermediate dwelling planktonic foraminifera. The middle OAE 2 interval contains lithologies composed almost entirely of radiolaria reflecting extremely high marine productivity; the low CaCO3 content is consistent with marked shoaling of the Carbonate Compensation Depth and ocean acidification because of CaCO3 undersaturation. Conditions moderated after deposition of the silica‐rich, CaCO3‐poor rocks as reflected by the microfossil changes indicating a relatively stable water column although episodes of enhanced eutrophy did continue into the lower Turonian at Site U1516.

Reflooding and repopulation of the Mediterranean Sea after the Messinian Salinity Crisis: Benthic foraminifera assemblages and stable isotopes of Spanish basins

Benthic foraminiferal, sedimentological, and stable isotope analyses performed on early Zanclean sediments from Alboran Basin ODP Site 976 and southern Spanish land-based sections in the Malaga, Nijar and Sorbas basins have enabled the reconstruction of Mediterranean environmental conditions immediately after the Messinian Salinity Crisis. The presence at the Miocene – Pliocene boundary of dark layers, often enriched in organic matter, suggests that the Zanclean reflooding has created water column stratification, and reduced bottom-water oxygen levels. Considering that such dark layers are recorded at both deep and marginal settings far away from the Gibraltar gateway/s, a Mediterranean-scale water-mass stratification must have occurred. This stratification could be the result of saline Atlantic waters sinking into a less saline Mediterranean Basin still under the influence of the Paratethys. Our early Zanclean benthic δ18O data show that the Mediterranean water budget was indeed less negative than at present, explaining the lower salinity of the basin. However, the Atlantic values of the benthic δ13C registered in the Alboran basin suggest that bottom-water renewal rates were quite high during the early Zanclean, preventing the reduction of δ13C at the seafloor as observed in the Messinian records. Zanclean benthic foraminiferal repopulation sequences show similarities with recovery from low-oxic episodes during sapropel deposition. These observations, paired with the gradual deepening of the basins, suggests that the Zanclean reflooding led to a progressive shift from stressed and unstable environments towards benthic associations typical of efficient circulation and bottom water ventilation.

Physiological characterization of Typhlatya cave shrimps: linking habitat with aerobic metabolism

The anchialine environment is characterized by a vertical stratification of water masses with different salinities. Cave shrimps of the genus Typhlatya are widespread inhabitants of the aquifer in fresh, brackish, and marine groundwater. Here we describe physiological aspects of three of the most abundant and widespread Typhlatya species that thrive in the fresh and marine groundwater habitats of the anchialine ecosystem of the Yucatan Peninsula. The aerobic scope (AS) of Typhlatya mitchelli, Typhlatya pearsei and Typhlatya dzilamensis was estimated through induced physical activity, whilst monitoring protein carbonylation and lipid peroxidation (as indicators of cellular damage), lactate accumulation (as an indicator of anaerobic metabolism) and the antioxidant system response. The critical thermal limits (CTL) of all three species as an additional measure of physiological plasticity were also determined. Our results showed that metabolic rates, AS and CTL were similar amongst the two species that inhabit fresh groundwater habitats, and differed markedly from T. dzilamensis, a species typically found in marine groundwater. The antioxidant system response in all three Typhlatya species accompanied the levels of aerobic metabolism following physical activity. However, the large amount of GSH observed in T. dzilamensis may be indicative of an adaptive trait to a more heterogeneous environment. The differences observed among Typhlatya species reflect different physiological adaptations that correspond to the environmental heterogeneity of their natural habitats. Our results suggest that the marine groundwater species, T. dzilamensis, could be better prepared to respond to a naturally more heterogeneous environment, in contrast to Typhlatya mitchelli and Typhlatya pearsei which rarely face environmental clines in the fresh groundwater habitat. Our findings contribute to a better understanding of the consequences of environmental change on ecologically important species that are restricted to live in the aquifer.

Stratification and productivity in the Western Tethys (NW Algeria) during early Toarcian

Profound environmental changes punctuated the Early Jurassic period, as recorded by marked carbon and oxygen isotope anomalies and major biotic crises. The response of low-latitude regions of Northern Gondwana to such intense changes is not documented as well as that of other Tethys areas. We present new calcareous nannofossil assemblages from three sections located in NW Algeria, in the Sahara and Tlemcen Basins, respectively. New stable carbon and nitrogen isotope data are provided from the Tlemcen Basin to reconstruct local environmental conditions in the wider context of a Toarcian greenhouse climate. We first established a solid chemo- and biostratigraphic framework by integrating stable carbon isotope data and calcareous nannofossil events. Calcareous nannofossil assemblages show common trends in the two basins, such as the occurrence in high proportions of the deep-dweller species Mitrolithus jansae , likely indicating stratification of the water column with a deep nutricline. This taxon dominated the assemblage during the negative carbon isotope excursion (CIE) interval, often used to delineate the base of the Toarcian anoxic event (T-OAE). Such a nannofossil record is unique in the Western Tethys domain, as M. jansae is known to drastically decrease in abundance during the T-OAE until its disappearance in the aftermath of the event. The NW Algeria nannofossil record indicates prolonged thermal stratification of water-masses, finally triggering hyper-oligotrophy and low productivity in shallow waters during the Toarcian CIE. Such peculiar conditions are likely related to the combined effects of a warm and arid climate dominating along the northern Gondwana margin and the presence of a strong clockwise gyre over the epicontinental shelf, which brought warm equatorial waters from the Tethys Ocean to the NW Algeria shelf. • The NW Algeria nannofossil record suggests prolonged thermal stratification of water-masses. • Hyper-oligotrophy and low productivity in shallow-waters occurred during the Toarcian Event. • Such conditions are likely related to the effects of a warm and arid climate of the Northern Gondwana.

Eocene to Oligocene vegetation and climate in the Tasmanian Gateway region were controlled by changes in ocean currents and <i>p</i>CO<sub>2</sub>

Abstract. Considered one of the most significant climate reorganizations of the Cenozoic period, the Eocene–Oligocene Transition (EOT; ca. 34.44–33.65) is characterized by global cooling and the first major glacial advance on Antarctica. In the southern high latitudes, the EOT cooling is primarily recorded in the marine realm, and its extent and effect on the terrestrial climate and vegetation are poorly documented. Here, we present new, well-dated, continuous, high-resolution palynological (sporomorph) data and quantitative sporomorph-based climate estimates recovered from the East Tasman Plateau (ODP Site 1172) to reconstruct climate and vegetation dynamics from the late Eocene (37.97 Ma) to the early Oligocene (33.06 Ma). Our results indicate three major climate transitions and four vegetation communities occupying Tasmania under different precipitation and temperature regimes: (i) a warm-temperate Nothofagus–Podocarpaceae-dominated rainforest with paratropical elements from 37.97 to 37.52 Ma; (ii) a cool-temperate Nothofagus-dominated rainforest with secondary Podocarpaceae rapidly expanding and taking over regions previously occupied by the warmer taxa between 37.306 and 35.60 Ma; (iii) fluctuation between warm-temperate–paratropical taxa and cool temperate forest from 35.50 to 34.49 Ma, followed by a cool phase across the EOT (34.30–33.82 Ma); and (iv) a post-EOT (earliest Oligocene) recovery characterized by a warm-temperate forest association from 33.55 to 33.06 Ma. Coincident with changes in the stratification of water masses and sequestration of carbon from surface water in the Southern Ocean, our sporomorph-based temperature estimates between 37.52 and 35.60 Ma (phase ii) showed 2–3 ∘C terrestrial cooling. The unusual fluctuation between warm and cold temperate forest between 35.50 to 34.59 Ma is suggested to be linked to the initial deepening of the Tasmanian Gateway, allowing eastern Tasmania to come under the influence of warm water associated with the proto-Leeuwin Current (PLC). Further to the above, our terrestrial data show the mean annual temperature declining by about 2 ∘C across the EOT before recovering in the earliest Oligocene. This phenomenon is synchronous with regional and global cooling during the EOT and linked to declining pCO2. However, the earliest Oligocene climate rebound along eastern Tasmania is linked to a transient recovery of atmospheric pCO2 and sustained deepening of the Tasmanian Gateway, promoting PLC throughflow. The three main climate transitional events across the studied interval (late Eocene–earliest Oligocene) in the Tasmanian Gateway region suggest that changes in ocean circulation due to accelerated deepening of the Tasmanian Gateway may not have been solely responsible for the changes in terrestrial climate and vegetation dynamics; a series of regional and global events, including a change in the stratification of water masses, sequestration of carbon from surface waters, and changes in pCO2, may have also played vital roles.

Multi‐elemental chemostratigraphy of Triassic mudstones in eastern Svalbard: Implications for source rock formation in front of the World’s largest delta plain

AbstractThe Triassic Boreal Ocean was a shallow epicontinental basin and the sink of the World's largest delta plain known to date. Nutrient and freshwater supply from this delta have been regarded as important causes for high productivity and water mass stratification, forming Middle Triassic oil‐prone source rocks. Recent studies attribute upwelling and a productivity‐induced oxygen minimum zone as important factors. A multi‐elemental chemostratigraphic study of a Spathian–Carnian mudstone succession exposed in eastern Svalbard was performed to investigate their formation. This includes 89 samples from three localities, from which 34 elements were acquired using combustion and X‐ray fluorescence analyses. The goal is to provide a correlation framework and infer the role of productivity, redox and water mass restriction on organic matter accumulation and source rock formation. These processes had major impact on the source potential. The Spathian Vendomdalen Member suggests deposition during intermittent benthic euxinia and low productivity, corresponding with a reported deep thermocline that obstructed upwelling. The lower Anisian lower–middle Muen Member shows negligible enrichment in redox‐sensitive elements but in situ phosphate nodules, consistent with developing upwelling and moderate productivity. The middle Anisian upper Muen Member formed during high productivity and phosphogenesis and is linked with basin‐wide upwelling. Productivity, phosphate and redox proxies are all strongly enriched in the upper Anisian–Ladinian Blanknuten Member. In the south‐western Barents Sea, the pro‐deltaic environment of the emerging Triassic Boreal Ocean delta system had terminated these conditions. The upper Ladinian upper Blanknuten Member formed within intermittent euxinic bottom waters due to the shallowing sea level. The Carnian Tschermakfjellet Formation marks the dominance of the prograding delta system and the end of Triassic oil‐prone source rock formation in Svalbard.

The dire straits of Paratethys: gateways to the anoxic giant of Eurasia

Abstract A complex interplay of palaeoclimatic, eustatic and tectonic processes led to fragmentation and dissipation of the vast Tethys Ocean in Eocene–Oligocene times. The resulting Paratethys Sea occupied the northern Tethys region on Eurasia, grouping water masses of various sub-basins, separated from each other and from the open ocean through narrow and shallow gateways and land bridges. Changes in marine gateway configuration and internal connectivity affected regional hydrology, shifting most Paratethyan basins to extreme carbon-sink anoxic environments, anomalohaline evaporitic or brackish conditions, or even endorheic lakes. Paratethys gateway restriction triggered the onset of a long-lasting ( c. 20 myr) giant anoxic sea, characterized by stratified water masses and anoxic bottom-water conditions, resulting in thick hydrocarbon source rocks. Here, we review the geological evolution of the ‘dire straits’ of Paratethys that played a crucial role in the Eocene–Oligocene connectivity history of the Central Eurasian seas and we show that the main anoxic phases (Kuma and Maikop) correspond to restricted connectivity with the global ocean and a period of CO 2 depletion in the atmosphere. Paratethys represents one of the largest carbon sinks in Earth's history and may thus have played a prominent role in global climate change.

Changes in sulfur cycling in a large lake during the Paleocene-Eocene Thermal Maximum and implications for lake deoxygenation

Understanding the biogeochemical effects of global warming on large lakes is central to managing aquatic resources. The Paleocene-Eocene Thermal Maximum (PETM) presents an excellent paleo-analog for potential impacts arising from current global warming. Here, we reconstructed dynamic redox changes in a large lake located in modern Central China during the PETM, using carbonate-associated sulfate sulfur and oxygen isotopes. Three major anoxic episodes (AE) associated with intensive microbial sulfate reduction (MSR) were identified, as indicated by higher sulfur and oxygen isotope compositions, and/or decreased sulfate contents. Thermal stratification in the lake was the likely main cause of the anoxia and associated changes in sulfur geochemical cycles. The first two AEs occurred during the initial stage of PETM. They are characterized by low sulfate and total organic carbon-minus-black carbon (TOC-BC) contents, suggestive of low biological productivity related to limited nutrient cycling in a stratified and anoxic water mass. The third AE occurred during the peak of the PETM. It was characterized by extremely low sulfate and high TOC-BC contents, possibly the product of increased near-surface productivity coupled with anoxia in the lower water column. An intensified hydrological cycle triggered by severe warming may have enhanced terrestrial nutrient fluxes to the lake, leading to increased surficial lake productivity. Upward expansion of the anoxic/sulfidic zone, however, may have suppressed the lake ecosystem by contracting its livable space. Our results suggest that current global warming could trigger similar ecological stress in large lakes.

Influence of non-stationary river discharge on the quality of water withdrawal in the presence of density stratification

The paper presents the results of field measurements and numerical modeling of different aspects of water quality in the Kama River (Kama reservoir), which is the source of technical water supply of industrial enterprises of the city of Berezniki. During the summer season, there are significant risks related to sustainability of water supply. It is traditionally believed that, over the winter period of low water, these risks increase manyfold. However, the results of departmental monitoring and field studies performed in winter provide evidence of the performance stability of technical water intakes from the Kama river. It was found that, in summer, when this part of the Kama river is located in the backwater zone of the Kama hydroelectric power station and, respectively, the flow velocity decreases, vertical stratification of water masses is formed, which significantly reduces the stability of water use from the near-bottom area. In winter, with a decrease in the water level in the Kama reservoir, the typical river conditions characterized by increased flow velocities occur. Under these conditions, the intense vertical mixing of water masses is implemented, which improves the consumer properties of water for sustainable water supply. The numerical simulations carried out within the framework of a three-dimensional model confirmed this conclusion. It is shown that if the amplitude of the flow velocity at a point changes with time according to a harmonic law, then the value of the salt concentration at this point also changes harmonically, but in antiphase with the velocity.

Relationship of Spatial Phytoplankton Variability during Spring with Eutrophic Inshore and Oligotrophic Offshore Waters in the East Sea, Including Dokdo, Korea

The area near the subpolar front of the East Sea has high primary productivity during the spring season. We conducted two surveys, one in early spring and another in late spring, to assess environmental factors that influence phytoplankton community structure during these times. During early spring, vertical mixing supplied abundant nutrients to the surface. Due to the well-mixed water column, there were high nutrient levels, but total phytoplankton abundances and diversity were relatively low and were dominated by the diatom Chaetoceros spp. During late spring, the water column gradually stratified, with relatively high levels of nutrients in the surface layers near the coastal areas. Phytoplankton abundance and diversity at that time were higher, and there were diatoms (Pseudo-nitzschia spp. and Chaetoceros spp.), cryptophytes, and small flagellates. Pseudo-nitzschia spp. were especially abundant in re-sampled areas. The presence of a stratified and stable water mass and sufficient nitrate led to high phytoplankton growth, even in the open sea during late spring. These findings provide a better understanding of how phytoplankton population dynamics in the East Sea depend on water column stability during both early and late spring seasons.