Bottom Conditions Research Articles

Coupling between Abyssal Boundary Layers and the Interior Ocean in the Absence of Along-Slope Variations

Abstract To close the overturning circulation, dense bottom water must upwell via turbulent mixing. Recent studies have identified thin bottom boundary layers (BLs) as locations of intense upwelling, yet it remains unclear how they interact with and shape the large-scale circulation of the abyssal ocean. The current understanding of this BL–interior coupling is shaped by 1D theory, suggesting that variations in locally produced BL transport generate exchange with the interior and thus a global circulation. Until now, however, this picture has been based on a 1D theory that fails to capture the local evolution in even highly idealized 2D geometries. The present work applies BL theory to revised 1D dynamics, which more naturally generalizes to two and three dimensions. The BL is assumed to be in quasi-equilibrium between the upwelling of dense water and the convergence of downward buoyancy fluxes. The BL transport, for which explicit formulas are presented, exerts an influence on the interior by modifying the bottom boundary condition. In 1D, this BL transport is independent of the interior evolution, but in 2D the BL and interior are fully coupled. Once interior variables and the bottom slope are allowed to vary in the horizontal, the resulting convergences and divergences in the BL transport exchange mass with the interior. This framework allows for the analysis of previously inaccessible problems such as the BL–interior coupling in the presence of an exponential interior stratification, laying the foundation for developing a full theory for the abyssal circulation.

Multi-proxy record of ocean-climate variability during the last two millennia on the Mackenzie Shelf, Beaufort Sea

A 2,000 year-long oceanographic history, in sub-centennial resolution, from a Canadian Beaufort Sea continental shelf site (60meters water depth) near the Mackenzie River outlet is reconstructed from ostracode and foraminifera faunal assemblages, shell stable isotopes (delta 18O, delta 13C) and sediment biogenic silica. The chronology of three sediment cores making up the composite section was established using 137Cs and 210Pb dating for the most recent 150 years and combined with linear interpolation of radiocarbon dates from bivalve shells and foraminifera tests.Continuous centimeter-sampling of the multicore and high-resolution sampling of a gravity and piston core yielded a time-averaged faunal record of every approximately 40 years from 0 to 1850 CE and every approximately 24 years from 1850 to 2013 CE. Proxy records were consistent with temperature oscillations and related changes in organic carbon cycling associated with the Medieval Climate Anomaly (MCA) and the Little Ice Age (LIA). Abundance changes in dominant microfossil species, such as the ostracode Paracyprideis pseudopunctillata and agglutinated foraminifers Spiroplectammina biformis and S. earlandi, are used as indicators of less saline, and possibly corrosive/turbid bottom conditions associated with the MCA (approximately 800 to 1200 CE) and the most recent approximately 60 years (1950–2013). During these periods, pronounced fluctuations in these species suggest that prolonged seasonal sea-ice melting, changes in riverine inputs and sediment dynamics affected the benthic environment. Taxa analyzed for stable oxygen isotope composition of carbonates show the lowest delta 18O values during intervals within the MCA and the highest during the late LIA, which is consistent with a 1 degree to 2 degree C cooling of bottom waters. Faunal and isotopic changes during the cooler LIA (1300 to 1850 CE) are most apparent at approximately 1500 to 1850 CE and are particularly pronounced during 1850 to approximately 1900 CE, with an approximate 0.5 per mil increase in delta 18O values of carbonates from median values in the analyzed taxa. This very cold 50-year period suggests that enhanced summer sea ice suppressed productivity,which is indicated by low sediment biogenic silica values and lower delta 13C values in analyzed species. From 1900CE to present, declines in calcareous faunal assemblages and changes in dominant species (Cassidulina reniforme and P. pseudopunctillata) are associated with less hospitable bottom waters, indicated by a peak in agglutinated foraminifera from 1950 to 1990 CE.

On the Construction of Traveling Water Waves with Constant Vorticity and Infinite Boundary

The issue of whether there is a closed orbit in the water waves in an infinite boundary condition is an outstanding open problem. In this work, we first discuss the various developments on the structure of water waves in the context of finite bottom conditions. We then focus on the behavior of water for the kinematic boundary for the infinite depth. We present some findings to address this issue by creating a water wave profile for the zero and constant vorticity conditions through the application of the Crandall–Rabinowitz theorem.

Limitations of the Yang’s breaking wave force formula and its improvement under a wider range of breaker conditions

Abstract Some commonly used empirical formulas (e.g., Soviet CHиПII57-75, Ikeno-Tanaka, Führböter-Sparboom, and Stanczak) for estimating plunging breaker wave slamming pressure on sea dike surface do not take into account the comprehensive influence of the wave steepness, slope angle, and breaker height and depth on the loads, and the Yang formula eliminates the drawback. The Yang formula is derived based on an analysis of the impulse in the breaking wave tongue and the kinetic and potential energy in the wave tongue. But the limited range of the Yang formula is 0.5 ≤ ξ ≤ 3.3 and 0.01 ≤ tan α ≤ 0.44; otherwise, its prediction error will greatly increase. In addition, some parameters in the Yang formula need to be optimized. The aim of this project is to revise the Yang formula for improving its performance and making it suitable for a wider range of hydraulic conditions and bottom slope conditions. A constant term in the Yang formula is replaced by the function obtained by analysis, and the calculation method of breaking wave height in the formula is also changed. The resulting formula is of interest because the comparison of the formula with some measurements is done well.

Environmental changes affect the microbial release of hydrogen sulfide and methane from sediments at Boknis Eck (SW Baltic Sea).

Anthropogenic activities are modifying the oceanic environment rapidly and are causing ocean warming and deoxygenation, affecting biodiversity, productivity, and biogeochemical cycling. In coastal sediments, anaerobic organic matter degradation essentially fuels the production of hydrogen sulfide and methane. The release of these compounds from sediments is detrimental for the (local) environment and entails socio-economic consequences. Therefore, it is vital to understand which microbes catalyze the re-oxidation of these compounds under environmental dynamics, thereby mitigating their release to the water column. Here we use the seasonally dynamic Boknis Eck study site (SW Baltic Sea), where bottom waters annually fall hypoxic or anoxic after the summer months, to extrapolate how the microbial community and its activity reflects rising temperatures and deoxygenation. During October 2018, hallmarked by warmer bottom water and following a hypoxic event, modeled sulfide and methane production and consumption rates are higher than in March at lower temperatures and under fully oxic bottom water conditions. The microbial populations catalyzing sulfide and methane metabolisms are found in shallower sediment zones in October 2018 than in March 2019. DNA-and RNA profiling of sediments indicate a shift from primarily organotrophic to (autotrophic) sulfide oxidizing Bacteria, respectively. Previous studies using data collected over decades demonstrate rising temperatures, decreasing eutrophication, lower primary production and thus less fresh organic matter transported to the Boknis Eck sediments. Elevated temperatures are known to stimulate methanogenesis, anaerobic oxidation of methane, sulfate reduction and essentially microbial sulfide consumption, likely explaining the shift to a phylogenetically more diverse sulfide oxidizing community based on RNA.

Using Fish as a Sentinel in Risk Management of Contaminated Sediments

Sediments polluted by historical emissions from anthropogenic point sources are common in industrialized parts of the world and pose a potential threat to the function of aquatic ecosystems. Gradient studies using fish as a bioindicator are an option to assess the ecological impact of locally polluted areas. This study investigates the remaining effects of historical emissions on sediments outside ten Swedish pulp and paper mills using perch (Perca fluviatilis). The aim has been to obtain a general picture of the impact area of local deposits of cellulose fiber-rich sediments containing elevated levels of trace metals, e.g., Hg, and organochlorines, e.g., dioxins. In addition to analyzing contaminant levels in muscle and liver tissue, morphological measures in the fish that constitute biomarkers for health and reproductivity were measured. Another aim was to augment existing historical data sets to observe possible signs of environmental recovery. Overall, the results indicate only a minor elevation in contaminant levels and a minor impact on the fish health status in the polluted areas, which in several cases is an improvement from historical conditions. However, exceptions exist. Differences in the ecosystems' responses to pollution loads are primarily explained by abiotic factors such as water turnover rate, bottom dynamic conditions, and water chemistry. Weaknesses in the sampling methodology and processing of data were identified. After minor modifications, the applied survey strategy has the potential to be a management tool for decision-makers working on the remediation of contaminated areas.

Geochemical Characteristics and Organic Matter Accumulation of Wufeng-Longmaxi Shales in the Southeast of the Sichuan Basin of South China

The Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation black shales are the critical targets for shale gas exploration in the Sichuan Basin of South China. The enrichment of organic matter (OM) in shale is the basis for the generation of large-scale shale gas; however, its controlling factors in Wufeng-Longmaxi shales are still under debate, and few studies have focused on the edge of the Sichuan Basin. Based on the mineral composition, total organic carbon (TOC), and systematic inorganic geochemistry analysis of 72 core samples from Wufeng and Longmaxi formations in Well Xike 1, southeastern Sichuan Basin, the sedimentary conditions (palaeoclimate, palaeoredox, and palaeoproductivity) were reconstructed, and the controlling factors of OM enrichment were identified. The mineral compositions are dominated by quartz, clay minerals, calcite, and feldspar, associated with minor dolomite, pyrite, and anhydrite. The TOC contents (0.31%-6.84%, avg. 2.22%) show an upward decreasing trend from the Wufeng Formation to Longmaxi Formation. The chemical index of alteration (CIA) ranges from 65 to 71 (avg. 69), indicating warm and humid climate with moderate weathering. The diagrams of Al2O3-TiO2, TiO2-Zr, Zr/Sc-Th/Sc, La/Th-Hf, and La-Th-Sc jointly indicate the contribution from felsic and intermediate rock weathering. The P/Al, Cu/Al, and Ni/Al ratios suggest that marine paleoproductivity was relatively high in the Wufeng Formation and relatively low to moderate in the Longmaxi Formation. The V/Cr, V/Sc, U/Th, MoEF/UEF, and Corg/P ratios indicate that the bottom water was anoxic during the Wufeng Formation deposition and then fluctuating dysoxic and/or oxic in the overlying Longmaxi Formation. The TOC content was positively correlated with productivity proxies (P/Al, Cu/Al, and Ni/Al) as well as redox proxies (U/Th, V/Cr, MoEF/UEF, and Corg/P), indicating that the OM accumulation in Wufeng-Longmaxi shales is mainly controlled by high productivity and anoxic bottom water conditions.

From biogenic silica and organic matter to authigenic clays and dolomite: Insights from Messinian (upper Miocene) sediments of the Northern Mediterranean

AbstractThe biogeochemical cycles of carbon and silicon are tightly coupled in modern marine environments due to the pivotal role of planktonic diatoms. Once diatoms are sedimented, the fate of organic matter and biogenic silica is initially governed by bottom water oxygen levels and bacterial communities involved in remineralization processes. The early diagenesis of biosiliceous sediments may result in drastic changes in composition, sometimes hampering palaeoenvironmental reconstruction. Sedimentary successions deposited in the Mediterranean region during the Messinian salinity crisis (5.97–5.33 Ma) allow to explore the early diagenetic transformation of organic matter and biogenic silica in a restricted basin experiencing a severe palaeoceanographic turnover. Sedimentological and petrographic observations coupled to elemental, mineralogical, inorganic and organic geochemical analyses were carried out on biosiliceous (diatomaceous shales and diatom‐bearing mudstones) and associated clay‐rich and dolomite‐rich sediments (dolomitic mudstones) interbedded with primary gypsum layers in the Piedmont Basin (north‐west Italy). The state of preservation of biogenic silica was governed by different pathways of organic matter remineralization, depending on bottom and pore water redox conditions, which were controlled by the structure of the water column. Aerobic respiration of organic matter in a mixed water column and an oxygenated seafloor promoted biogenic silica preservation. In contrast, bottom water anoxia induced by permanent stratification of the water column favoured the concomitant formation of dolomite and authigenic clays. In particular, organic matter degradation through bacterial sulphate reduction increased pore water alkalinity, promoting the precipitation of dolomite. At the same time, the rise in pH promoted the dissolution of biogenic silica which, reacting with pore water cations, ultimately caused the formation of authigenic clays. This study suggests that the apparent annihilation of Mediterranean marine biota during the Messinian salinity crisis partially reflects an early diagenetic bias produced by interactions of the carbon, silicon and sulphur biogeochemical cycles in a restricted basin.

Analytical solutions for heat conduction problems with three kinds of periodic boundary conditions and their applications

In the present study, a general analytic expression for solving heat conduction problem in finite domain under periodic boundary conditions was suggested by using the variable separation method. Heat conduction problems under three kinds of periodic upper boundary conditions and constant temperature or zero-flux as bottom boundary conditions were solved respectively. By applying the analytical solutions, an equivalent method for transferring the periodic heat flux and convection combination boundary condition to the Dirichlet boundary condition was proposed. In addition, the proposed solution was generalized to solve the heat conduction problem infinite domain with periodic sine-like law boundary conditions. The present study can provide references for investigating the evolution law of temperature field under complex periodic boundary conditions.

Sedimentary molybdenum and uranium: Improving proxies for deoxygenation in coastal depositional environments

Sedimentary molybdenum (Mo) and uranium (U) enrichments are widely used to reconstruct changes in bottom water oxygen conditions in aquatic environments. Until now, most studies using Mo and U have focused on restricted suboxic-euxinic basins and continental margin oxygen minimum zones (OMZs), leaving mildly reducing and oxic (but eutrophic) coastal depositional environments vastly understudied. Currently, it is unknown: (1) to what extent Mo and U enrichment factors (Mo- and U-EFs) can accurately reconstruct oxygen conditions in coastal sites experiencing mild deoxygenation, and (2) to what degree secondary (depositional environmental) factors impact Mo- and U-EFs. Here we investigate 18 coastal sites with varying bottom water redox conditions, which we define by means of five “redox bins”, ranging from persistently oxic to persistently euxinic, from a variety of depositional environments. Our results demonstrate that Mo- and U-EF-based redox proxies and sedimentary Mo and U contents can be used to differentiate bottom water oxygen concentration among a range of modern coastal depositional environments. This is underpinned by the contrasting EFs of Mo and U along the redox gradient, which shows a substantial difference of Mo-EFs between redox bins 3–5 (ir/regularly suboxic – ir/regularly dysoxic – persistently oxic) and of U-EFs between redox bins 1–2 (persistently euxinic – ir/regularly euxinic). Surprisingly, we observe comparatively low redox proxy potential for U in environments of mild deoxygenation (redox bins 3–5). Further, we found that secondary factors can bias Mo-and U-EFs to such an extent that EFs do not reliably reflect bottom water redox conditions. We investigate the impact of limited Mo sedimentary sequestration in sulfidic depositional environments (i.e., the “basin reservoir effect”, equilibrium with FeMoS4), Fe/Mn-(oxy)(hydr)oxide “shuttling”, oxidative dissolution, the sulfate methane transition zone in the sediment, sedimentation rate, and the local Al background on Mo- and U-EFs.

A computationally efficient hydrologic modeling framework to simulate surface-subsurface hydrological processes at the hillslope scale

Considering surface and subsurface interactions is imperative to predict water movement, water quantity and quality in the environment. However, substantial execution time and over-parameterization presently limit the applicability of integrated hydrologic models at larger scales. Herein, a new efficient coupling routine for one-dimensional (1D) surface–subsurface modeling was developed by externally coupling two widely used open-source codes. KINEROS2 (K2) solves the 1D kinematic wave equation for overland flow, and HYDRUS-1D (H1D) solves the Richards equation for subsurface flow. A novel approach, combined with water balance and boundary condition switching, is used to account for surface ponding and water exchange between the two model domains. A weighting factor related to the surface water depth is used to assign the time series of exchange fluxes in one H1D profile to multiple surface nodes in the K2 calculation. This novel approach enables us to represent the entire subsurface below each overland-flow plane by one vertical soil column with different soil layering. When soil properties vary horizontally, multiple soil columns can represent spatial heterogeneities. The performance of the coupled H1D-K2 model is examined by comparing simulation results with the HYDRUS-2D (H2D) model for six benchmark problems. The solution's robustness, stability, and accuracy are assessed for a wide variety of cases, including multiple rainstorms, different slopes, heterogeneous subsurface, and different bottom boundary conditions resulting in 41 cases. The simulated hydrographs, surface water levels, and water balance components are all in good agreement. Relative mass balance errors are very small, typically not exceeding 4.0% for the coupled H1D-K2 model. Compared with the H2D model, the coupled model achieves a factor of 1.3–10 speedup by applying one H1D soil profile to an entire overland flow plane rather than to individual surface nodes.

Paleoenvironment-driven organic matter accumulation in lacustrine shale mixed with shell bioclasts: A case study from the Jurassic Da'anzhai member, Sichuan Basin (China)

The sedimentary environment governs the depositional processes, ecological environments, and hydrodynamics, which affect the accumulation of organic-rich sediments. Some particular issues are unsolved about the organic matter accumulations of lacustrine shale mixed with shell bioclasts due to their alternating deposition. Freshwater bivalve remains are a familiar constituent of the Da'anzhai lacustrine calcareous shale, which indicates enhanced activities of benthic organisms. Under this background, favorable environmental conditions for the deposition and preservation of abundant organic matter may be different from classical models. Total organic carbon and elemental concentration analyses of lacustrine calcareous shale samples from the Jurassic Da'anzhai Member in the Sichuan Basin were carried out to reconstruct the paleoenvironment and reveal the organic enrichment mechanism. Results show that the samples are notably enriched in strontium, phosphorus and biogenic calcium (indicated by excess calcium concentrations) and reveal the mass death event of benthic organisms (including freshwater mussels and gastropods) in paleolakes under the control of climatic transformation. Such enrichment strongly supports the hypothesis that CaO is considered to be a paleoproductivity proxy to some extent. The paleolake was dominated by a warm and humid climate and rapid sedimentation rates and experienced intense chemical weathering, which are characteristic of freshwater input and a high flux of detrital fractions. The variations in the redox state and paleoproductivity are due to climatic shifts, hydrographic restrictions and biological behavior. Furthermore, the organic matter was enriched during both oxygenated and oxygen-deficient conditions. The combination of high sedimentation rates and high sinking influxes of particulate organic carbon reduced the chances of decomposition and thereby facilitated the efficiency of organic matter accumulation in an oxic environment. The low degree of organic matter degradation, moderate sedimentation rates and enhanced phosphorus recycling were responsible for the organic carbon accumulation and preservation in sediments for dysoxic bottom conditions.

Influence of Geotextile Materials on the Fractal Characteristics of Desiccation Cracking of Soil

In recent years, the irregular cracks formed during the damage evolution of civil engineering materials have been able to be quantitatively described by using fractals. In this study, the fractal characteristics of the desiccation cracking of soil were investigated under different substrate contact and permeability conditions through a natural drying test in the laboratory. Three kinds of base contact conditions of soil, namely, grease, geomembrane, and geotextile, were designed, and two samples for each contact condition, including one parallel sample, were used. The continuous drying experiment was carried out at a constant ambient temperature. The crack morphology under different spacings was analyzed quantitatively using digital image processing technology. The fractal dimensions of three soil substrate contact conditions (grease, geomembranes, and geotextiles) were between 1.238 and 1.93. When the crack network on the soil surface stops developing, the fractal dimensions under the three experimental conditions are 1.88, 1.93 and 1.79, respectively. In the final state of crack development, the crack intensity factor of the sample with grease at the bottom is 2.99% and 4.02% higher than that of the sample with geomembranes and geotextiles at the bottom, respectively. The residual water contents of the samples with bottom contact conditions of grease, geomembrane, and geotextile increase successively, which are 3.12%, 5.76% and 9.71%, respectively. The effects of interface friction and permeability on soil cracking behavior are analyzed, and the evolution characteristics and formation mechanisms of cracks in soil are revealed.

Palaeoceanographic and palaeoenvironmental controls on late Quaternary benthic foraminifera of the western continental slope of South Africa

Benthic foraminifera from two gravity cores recovered on the western continental slope (3522 and 3631 m water depth) of South Africa were studied to determine bottom water conditions and benthic environments over late Quaternary glacial-interglacial cycles. Benthic foraminifera assemblages and the carbon isotopic composition (δ13C) of Cibicidoides wuellerstorfi and Globoconella inflata were used to reconstruct palaeoenvironmental conditions. The assemblages reflect influences from substrate, productivity (seasonal and annual variations in the flux of organic matter, such as phytodetritus to the seafloor) and bottom water oxygenation. Uvigerinid forms were found to be distributed along bathymetric depths that also reflect oxygenation of bottom waters, where hispid and hispidocostate forms were more abundant at depths of oxygen-enriched bottom waters on the lower slope. These uvigerinids and other benthic species such as Epistominella exigua were also found to benefit from periods of high productivity. Palaeoproductivity increased during glacial periods but decreased sharply by a difference of ∼1‰ in δ13C during glacial terminations, reflecting a less nutrient-rich bottom water signal. During interglacial periods, epifaunal foraminifera and taxa adapted to oxygen-enriched environments, such as Cibicidoides spp. and high oxygen assemblages increased in abundance and were correlated to the less radiogenic regional εNd signals, while the abundance of high-productivity fauna and assemblages, associated with the nutrient-rich Southern Component Water, and that are adapted to a high organic matter flux and low oxygen conditions, decreased. Interglacial periods were reflected to exhibit benthic environments that are more oligotrophic, while glacial periods were interpreted to reflect more eutrophic conditions.

Development of irrigation schedule and management model for sustaining optimal crop production under agricultural drought

Agriculture is vulnerable to drought indicating that the increasing climate crisis requires the necessity of sustainable crop production. In this study, we developed the Irrigation Schedule and Management (ISM) model based on a simulation–optimization (Soil Water Atmosphere Plant-SWAP model with Genetic Algorithm-GA) framework. The ISM model finds an optimal combination of Irrigation Water Amount (IWA) and Irrigation Interval (II) by adjusting Water Stress (WS) responding to environmental conditions (weather, soils, crops and bottom boundary conditions) throughout growing periods. By conditioning the crop (WS) and water management (IWA and II) variables, ISM improves the sustainability of optimal crop productions under different climatic-land surface conditions. The Regional Agromet Center (RAC) site in Faisalabad (at Punjab, Pakistan) was selected to test the proposed ISM model for the field validation/synthetic numerical experiments with various crops (Wheat, Corn and Potato) and soils. We demonstrated that the ISM model that reflects the relationship between crop and water management variables improved the sustainability of crop productions and Water Productivity (WP) compared to those of the conventional irrigation method at the RAC site under various environment conditions. Additionally, the ISM-based long-term crop productions showed the variations along the yearly precipitation changes indicating that optimal combinations of the crop and water management variables are considerably influenced by environmental conditions. Although uncertainties exist, our proposed ISM model can contribute to the establishment of efficient irrigation schedule/management plans under agricultural drought.

Porewater geochemistry indicates methane seepage in the Okinawa Trough and its implications for the carbon cycle of the subtropical West Pacific

The Kuroshio Current, originating from the West Pacific Warm Pool and flowing through the Okinawa Trough, connects the equator and the subtropical West Pacific and plays an important role in the carbon cycle in the West Pacific Ocean. Previous studies have focused on the effects of surface export productivity and bottom redox conditions on the carbon cycle in the late Quaternary. Recent studies have demonstrated that methane seepages are very common in the Okinawa Trough, however, their significance for the carbon cycle remains not well understood. Here, methane seepages and sulfate-driven anaerobic oxidation of methane (SD-AOM) are constrained by the geochemical characteristics of porewater at site CSHC-4 (Length: 1555 cm) derived from the water depth of 934 m on the western continental slope of the Okinawa Trough. Using the △(DIC+ Ca2++ Mg2+)/△SO42− ratio, it is suggested that the sulfate reduction in the upper part of site CSHC-4 is dominated by organoclastic sulfate reduction (OSR), while that between 655 and 1055 cm is gradually dominated by SD-AOM with deepening depth. However, with the depletion of sulfate, the methanogenesis process predominates at the bottom of site CSHC-4. The depth of the sulfate-methane interface (SMI) and the methane diffusive flux of site CSHC-4 is calculated to be ∼1156 cm and ∼ 63 mmol m−2 yr−1, respectively. Near the SMI, the changes in concentrations of Ca2+, Mg2+, Sr2+ and ratios of Mg/Ca and Sr/Ca in the porewater indicate the possibility of the precipitation of authigenic high-Mg calcite in the sediments. In contrast, the increase in the concentration of Ba2+ in porewater below the SMI may imply the dissolution of barite (BaSO4). In addition, redox-sensitive elements in porewater exhibit various geochemical behaviours due to changes in redox conditions caused by SD-AOM. The above SD-AOM processes will affect the reconstruction of surface productivity and redox conditions of bottom water in the Okinawa Trough since the late Quaternary based on biogenic elements (e.g., Ca and Ba) and redox-sensitive elements (e.g., U and Cr), which requires careful evaluation. Therefore, our new findings illustrate the modern methane seepage in the Okinawa Trough and provide a reference for calculating the ancient carbon cycle in the subtropical West Pacific.

Palynomorphs Content and Paleodepositional Environments of Mamu Formation in Okpekpe-1, Imiegba-1 and Imiegba-2, Benin Flank of Anambra Basin, Nigeria

Twenty surface samples were taken from road cuttings along Okpekpe and Imiegba areas located in Benin Flank of Anambra Basin, Nigeria with an aim to establish the biozones, age and paleodepositional environments of the Mamu Formation. Using palynological laboratory standard procedures, the shale surface samples collected from the Mamu Formation in the study area were prepared and analyzed. The recovered marker pollens, spores and dinoflagellate cysts from the study area are Milforadia jardinei, Milforadia sp., Longapertites marginatus, Longapertites sp., Retidiporites sp., Monocolpites marginatus,Cyathidites minor, Cyathidites spp., Cingulatisporites ornatus, Distaverrusporites simplex, Laevigatosporites spp., Foveotriletes margaritae, Subtilisphaera sp., Andalusiella sp., Paleocystodinium australinium and microforaminiferal wall linings. Four biozones were erected for the shale intervals in the study area, namely: Longapertites sp., Monocolpites marginatus, Cyathidites minor, and Paleocystodinium australinium biozone, respectively, dated to Upper Maastrichtian to Early Paleocene age, which are lateral equivalents to Spinizonocolpites baculatus biozone of the Upper Benue Trough. The presence of the dinoflagellates cysts such as Paleocystodinium australinium, Subtilisphaera sp. and Andalusiella sp., microforaminiferal wall linings, pollens and spores established that the shales were deposited in nearshore to shallow marine environments. The presence of Cingulatisporites ornatus and Distaverrusporites simplex are indicative of marine regression that was followed by fluvial continental influence in anoxic bottom conditions that in turn favored the formation of coal seams in shales in the study area. The paucity of palynomorphs in the study area is inferred to have occurred because of the dry climatic condition that prevailed during the Upper Maastrichtian to Early Paleocene.

Towards a convection‐permitting regional reanalysis over the Italian domain

AbstractA new convection‐permitting regional reanalysis, SPHERA (High Resolution REAnalysis over Italy), has been developed over Italy and the surrounding seas using the COSMO model at 2.2 km horizontal resolution. The reanalysis system is nested in the global reanalysis ERA5; upper‐air and surface observations are assimilated at the convection‐permitting scale by the COSMO nudging scheme. Before the complete production of the hourly three‐dimensional fields and surface/soil parameters over the period 1995–2020, general issues regarding the reanalysis set‐up needed to be addressed over a shorter test period. These include the identification of the best approach to downscale the lateral boundary conditions from the global driver, and the definition of the bottom boundary condition related to deep soil temperature. With respect to the downscaling methodology, the results show a clear benefit in using lateral boundary conditions directly from the global ERA5, despite the large resolution difference between the two modes (1:15), instead of providing them from an intermediate resolution COSMO‐based reanalysis. Moreover, the soil bottom boundary condition for temperature is reconstructed from the shallower ERA5 soil, using a site‐dependent method based on a delayed running mean of the ERA5 temperature at the deepest soil level. Finally, an evaluation of SPHERA has been performed with respect to the skill in simulating daily precipitation over 2 years. Compared with ERA5, SPHERA shows a higher ability in simulating moderate and intense events, markedly during summer, in terms of skill scores, frequency of occurrence and bias.

Forward and inverse modeling of water flow in unsaturated soils with discontinuous hydraulic conductivities using physics-informed neural networks with domain decomposition

Abstract. Modeling water flow in unsaturated soils is vital for describing various hydrological and ecological phenomena. Soil water dynamics is described by well-established physical laws (Richardson–Richards equation – RRE). Solving the RRE is difficult due to the inherent nonlinearity of the processes, and various numerical methods have been proposed to solve the issue. However, applying the methods to practical situations is very challenging because they require well-defined initial and boundary conditions. Recent advances in machine learning and the growing availability of soil moisture data provide new opportunities for addressing the lingering challenges. Specifically, physics-informed machine learning allows both the known physics and data-driven modeling to be taken advantage of. Here, we present a physics-informed neural network (PINN) method that approximates the solution to the RRE using neural networks while concurrently matching available soil moisture data. Although the ability of PINNs to solve partial differential equations, including the RRE, has been demonstrated previously, its potential applications and limitations are not fully known. This study conducted a comprehensive analysis of PINNs and carefully tested the accuracy of the solutions by comparing them with analytical solutions and accepted traditional numerical solutions. We demonstrated that the solutions by PINNs with adaptive activation functions are comparable with those by traditional methods. Furthermore, while a single neural network (NN) is adequate to represent a homogeneous soil, we showed that soil moisture dynamics in layered soils with discontinuous hydraulic conductivities are correctly simulated by PINNs with domain decomposition (using separate NNs for each unique layer). A key advantage of PINNs is the absence of the strict requirement for precisely prescribed initial and boundary conditions. In addition, unlike traditional numerical methods, PINNs provide an inverse solution without repeatedly solving the forward problem. We demonstrated the application of these advantages by successfully simulating infiltration and redistribution constrained by sparse soil moisture measurements. As a free by-product, we gain knowledge of the water flux over the entire flow domain, including the unspecified upper and bottom boundary conditions. Nevertheless, there remain challenges that require further development. Chiefly, PINNs are sensitive to the initialization of NNs and are significantly slower than traditional numerical methods.

Paleoenvironmental changes recorded at a late Maastrichtian marine succession of northern South America

One of the major environmental and biotic turnovers of the Phanerozoic occurred at the Cretaceous-Paleogene (K-Pg) boundary, being the focus of countless scientific studies that addressed the timing, causes and consequences of this global event. Paleoenvironmental conditions that preceded the K-Pg boundary, however, have been less studied, especially at low latitudes. In order to help reconstructing late Maastrichtian marine environments along the equatorial South American margin, we apply micropaleontological and geochemical techniques to a stratigraphic core that recovered the Colón Formation in northern Colombia. Low abundance foraminiferal assemblages were overall dominated by benthic taxa (Maastrichtian local biozones Siphogenerinoides bramletti and Ammobaculites colombiana), and the planktonic species Guembelitria cretacea. Ostracod assemblages were mainly composed of the genera Veenia, Cytherella, Paracypris, and Cythereis. Calcareous nannofossils were typical of Upper Cretaceous low-latitude successions, with low abundance and diversity assemblages dominated by Micula staurophora, Kamptnerius magnificus and Cervisiella operculata. Sediment elemental ratios (Zr/Rb, Fe/Ca and Sr/Ba), as well foraminiferal, ostracod and nannofossils assemblages, indicate a shallowing upward trend, characterized by a transition from inner platform settings to sublittoral conditions. Input of terrigenous sediments and weathering intensity also increased upward in the section, probably related to the uplift pulses of the Andean orogeny. Proportions of benthic infauna, as well the V/Cr ratio and the distribution of redox-sensitive trace metals (Ni, Cu) along the core, mostly indicate suboxic bottom water conditions in the Colón Formation.