Frontal Zone Research Articles

Mineralogy, fluid regime and potential ore content of the post-accretion Ivdel gabbrodolerite-monzonite-granodiorite complex (Northern Urals)

Research subject. Hypabyssal intrusive bodies of a gabbro-dolerite-monzonite-granodiorite composition, common among the Devonian island-arc sequences of the East Tagil structural-formational zone in the Northern Urals. These bodies are dated as the Late Devonian-Early Carboniferous and attributed to the post-accretionary continuously differentiated Ivdel complex. Material and methods. The composition of rock-forming and accessory minerals of these intrusive bodies was studied using an SX-100 microanalyzer. This made it possible to obtain new data on the conditions of their formation, features of the fluid regime, and potential ore content. In addition, the geodynamic setting of this period was clarified, along with the composition, possible position of the primary mantle source, and the features of its fluid regime. Results. It was established that the mafic rocks (dolerites) in the Ivdel complex correspond to derivatives of the depleted mantle, with a primary source close to N-MORB basalts. The connection between the source and the separation of the slab and the “mantle window” located under the frontal zone of the former East Tagil island arc was substantiated. Such a position of the melting chamber determines the primary weak water saturation of dolerite magmas and their redox regime. According to mineralogical data, this feature is further manifested in the formation of the entire series of rocks of the Ivdel complex (with an increase in the iron index of clinopyroxenes and amphiboles, an increase in titanium contents in titanomagnetite, and other data). Further evolution of magmas (from dolerites to monzonites, quartz diorites, and granodiorites) occurred as they moved upward to the Earth’s surface and reflected the increasing contamination of differentiated melts by suprasubduction island-arc matter. Another important petrological feature of this complex is its formation with the participation of a chlorine-rich magmatogenic fluid. Depending on the composition of intruding melts, their contents of water, chlorine and oxygen activity, a number of autonomous degassing fluid-magmatic systems are formed. These systems are characterized by noticeable features in the processes of post-magmatic autometasomatosis, with the participation of an iron-chloride fluid. According to the regime of volatiles (halogens, water, and oxygen), the common affiliation of such autonomous fluid-magmatic systems to titanomagnetite ferrofacies (according to G.B. Fershtater), determines both their general metallogenic specialization and potential ore content. The removal of volatiles from such fluid-magmatic systems could be accompanied by extraction and transfer of chlorophyll ore elements from crystallizing melts to exocontacts of intrusive bodies. This, in the presence of migration zones favorable for fluids (faults, crushing zones, etc.) and geochemical barriers (especially in the presence of favorable enclosing sulfide-bearing island-arc strata), could have contributed to the formation of hydrothermal-metasomatic ore mineralization (Cu, Zn, Au, Mo and etc.). Such ore-bearing zones during erosion could be the primary source of gold for the known placers of this region. Large bodies of gabbrodolerites of the Ivdel complex may be promising for high-Ti magnetite-ilmenite mineralization.

Syn-tectonic fluid-flow and fault-fluid interaction along bedding-parallel thrust faults: Evidence from the frontal zone of the Chuandong-Xiangexi fold-and-thrust belt in central South China

Fluid-flow within tectonic belts and fault-fluid interaction are fundamental and controlling factors of large thrust belt evolutions, formation of mineral deposits in the upper crust and the ductile shear deformation in the middle crust. In central South China, a large Chuandong-Xiangexi fold-and-thrust belt and long-distance displaced thrust faulting are developed, but their formation mechanism is still in debate. In particular, the evolution of fluid-flow and fault-fluid interactions in this fold-and-thrust belt is still not well constrained. In this study, through detailed structural and microstructural observations together with stable isotope and fluid inclusion analyses, we aim to unravel the deformation characteristics and syn-tectonic fluid-flow along the detachment in the frontal zone of this fold-and-thrust belt. One approximately 30–60 m thick, NW-verging detachment thrust with brittle-ductile deformation and alternating the strongly and weakly deformed zones is identified in the Lower Permian bioclastic and argillaceous limestones. The strongly deformed zone is characterized by tectonic lenses, fault gouge, calcite veins, S–C fabric, and foliated fault rocks/gouge, while the weak deformation zone is marked by scattered fractures without calcite veins and weakly deformed tectonic lenses. The fluids within the thrust faults originate from formation waters (saline fluids or brines) in a closed system, evidenced by the δ18O values, the 87Sr/86Sr ratios, the hydrocarbon-bearing fluid inclusions characterized by moderate salinity (10–14 wt% NaClequiv.) and moderate-high homogenization temperatures (∼160–350 °C). In the hanging wall of the Huangyingshan fault, the fluids involved in the thrusting processes are most likely brines derived from Middle and Lower Triassic carbonate aquifers. While in the footwall, the fluids are likely brines derived from Cambrian evaporitic aquifers. These findings on the detachment thrust fault zone could provide valuable constraints on the conduit and distance of hydrocarbon secondary migration for exploring the potential of large-scale hydrocarbon accumulation in the Chuandong-Xiangexi fold-and-thrust belt.

The Structure and Dynamics of an Estuarine Tidal Intrusion Front

AbstractTidal intrusion fronts are surface convergences that occur at constrictions in estuaries during the flood tide, separating incoming higher‐salinity water from lower‐salinity, stratified estuarine water. Previous observations of tidal intrusion fronts describe a V‐shaped planform, with the apex of the V pointing into the estuary, however the significance of this structure has not been previously explained. Observations near the mouth of the James River estuary during the flood tide reveal the development of a quasi‐steady, V‐shaped front. Considering a reference frame oriented normal to the front, the velocity and density structure are consistent with gravity‐current dynamics, but the oblique orientation of the front relative to the impinging flow indicates strong, along‐front shear, which results from vorticity produced by flow separation at the lateral boundaries as well as topographic torque from upstream. The combination of convergence and along‐front shear leads to enhanced mixing, as revealed by acoustic backscatter images of shear instability and persistent subcritical gradient Richardson number in the frontal zone. Oblique fronts such as this tidal intrusion front are common features of estuaries, and they play an important role in vertical exchange due to subduction and mixing of surface water.

Proglacial lake evolution coincident with glacier dynamics in the frontal zone of Kvíárjökull, South‐East Iceland

AbstractThe termini of Icelandic glaciers are highly dynamic environments. Pronounced changes in frontal ablation in recent years have consequently changed ice dynamics. In this study, we reveal the inter‐seasonal dynamics of the Kvíárjökull ablation zone and proglacial zone using ArcticDEM and Sentinel‐2 images acquired between 2011 and 2021 and intra‐seasonal dynamics with repeated UAV surveys during summer 2021. Average glacier surface velocity in the ablation zone ranged from 51 m year−1 in 2015 up to 199 m year−1 in 2018, with maxima within the axial zone of the glacier and minima on the glacier edges. Coincidentally, and in accordance with glacier retreat/advance, the ice‐marginal proglacial lake fluctuated in its area, and we interpret that it was also a key factor in the development of the glacier terminus morphology. A complex spatial pattern of glacier surface elevation changes, including thickening in the frontal true left margin of the terminus, is interpreted to be due to variable subglacial topography, relatively fast ice flow from the accumulation zone and an insulating effect of glacier surface debris cover. In contrast, the true right (southern) part of the glacier terminus experienced thinning and retreat/disintegration also during the 2021 summer season, which we attribute to enhanced frontal ablation connected to the intrusion of lake water into the crevassed glacier terminus. Overall, this study suggests that where glaciers are developing ice‐marginal lakes complex patterns of glacier dynamics and mass loss can be expected, which will confound understanding of the short‐term evolution of these environments.

Impact of tidal shear fronts on terrigenous sediment transport in the Yellow River Mouth: Observations and a synthesis

A tidal shear front (TSF) can be defined as an obvious horizontal gradient of flow velocity formed by opposing tidal currents (reversed TSF) or same-direction tidal currents (homogenous TSF) on both sides of the front with limited impact by river runoff. Observational and modeling studies have been conducted to investigate the impact of a reversed TSF on the transport of freshwater and sediment in the Yellow River Mouth (YRM). The reversed TSF existence period is only about 40% of a tidal cycle (around slack of flood and ebb); however, when this front disappears (around maximum flood and ebb), sediment transport across the frontal zone is still rare. This suggests that the dynamic mechanism of cross-frontal sediment transport in a tidal cycle remains unclear. In this study, synchronous observations of sea current and suspended sediment concentrations along the river mouth profiles at the YRM in 1995, 2003, and 2019 were used to investigate the long-term variation characteristics, mechanisms, and impacts of the TSF on cross-frontal sediment transport. The results indicate that in addition to the reversed TSF, there are also homogenous TSF during flood and ebb tides, with the ebb homogenous TSF being more significant due to tidal asymmetry in the YRM. The ebb homogenous TSF is located between shallow shoals and the slopes of the subaqueous delta front and lasts for about 3 h around the maximum ebb. Its maximum shear strength is similar to that of the reversed TSF, and the formation mechanism is also similar. The presence of the ebb homogenous TSF reduces the efficiency of cross-frontal sediment transport during the ebb. The reversed and homogenous TSFs alternately block sediment moving towards the sea. Thus, terrigenous sediment is difficult to cross the frontal zone to the central Bohai Sea by tidal currents solely. Over the past two decades of low discharge, with the Yellow River implementing artificial water and sediment regulation, the homogenous TSF during the ebb tide has become more and more important and cannot be neglected for cross-frontal sediment transport under normal conditions. Furthermore, from a long-term perspective, the shear strength of the TSF is positively correlated with the distance of river mouth siltation into the sea. Additionally, salinity and turbidity gradients are also positively correlated with the shear strength in the estuary. This indicates that the blocking of cross-frontal sediment transport by the TSF is a key process in river-sea interaction in the YRM.

New data on the geological structure and zonality of the Vorontsovka gold field in the Northern Urals

Spatial distribution of gold, copper, and iron ore deposits in the Northern Urals with the largest Turya-Auerbakh ore region is controlled by north-west trending linear zones of a probably fault nature. The influence has been demonstrated of regional factors (including the tectonic, magmatic, and geochemical ones) favoring formation of the large Au-As-Sb-Hg-Tl Vorontsovka deposit located within a volcanogenicsedimentary, substantially carbonate rock sequence. Closely spaced swarms of Devonian pre-ore and Carboniferous post-ore mafic dykes have been identified within the deposit. The primary geochemical halos of the Vorontsovka deposit have a multielement composition and, coupled with the ores, form a thick ore-halo zone confined to the gentle tectonic contact of sandstone-siltstone and limestone units. The main halo-forming elements are zonally distributed in the section. The footwall side of the gold deposit (rear zone) is dominated by Zn, Cd, Cu, Pb, Ag, and Bi; the axial zone, by Sb, Hg, Tl, and As; and the hanging side (frontal zone), by
 As, Zn, Hg, Pb, Ag, (Cu). In the east (closer to the Auerbakh granitoid massif), Ag, Zn, Pb, Mn, Y, Mo, and W relatively accumulate, while in the west (most remotely from the intrusive), Sb, Ba, As, Hg, Co, Ni, and Sn dominate. The 40Ar/39Ar age of ~391.1 million years, obtained for hydromica of the gold-arsenic ores, corresponds to the period of emplacement of granodiorite of the final Auerbakh massif intrusive phase. The conclusion is made on the crucial magmatic contribution to the formation of gold ores of the deposit.

High-Resolution Regional Ocean Climatologies with the Northwest Atlantic as an Example: A Review

The advantages of high-resolution oceanographic data analysis stems from an increased ability to capture sharp gradients in frontal zones and across mesoscale entities, especially in the coastal regions and along ocean jet-like currents, relative to coarser resolution analyses. In a sense, the finer-resolution analysis pursues the same goal as the usage of progressively reduced grid sizes in succeeding from coarse-resolution to eddy-permitting and then to eddy-resolving in numerical models of ocean circulation. Thus, the high-resolution regional climatologies are now closing the gaps existing between observations and model simulations allowing meaningful data-model comparisons in critical data-rich regions, such as the Northwestern Atlantic, Northeast Pacific Ocean, and several others. In this paper, we briefly review the locations, timing, purpose, and specificity of the regional ocean climatologies developed at the National Center for Environmental Information of the National Oceanic and Atmospheric Administration. We describe the Northwestern Atlantic Regional Climatology, version 2 in more details and demonstrate how this regional climatology contributes to a better understanding of the long-term climate state and variability

Lidar Research during the First Stage of the 89th Cruise of the R/V “Academic Mstislav Keldysh”

A lidar survey of the western part of the Kara Sea was carried out in September 2022. The shipborne radiometric (profiling) lidar PLD-1 was used. The lidar optical unit was located on the 8th deck of the R/V ‘Akademik Mstislav Keldysh’ at an altitude of 15 m above the water surface. Lidar sounding was carried out at stations and underway. The vessel route passed through water areas characterized by a wide range of changes in hydrooptical characteristics. Lidar measurements were accompanied by synchronized measurements of hydrooptical and hydrological characteristics. These measurements were carried out using submersible instruments at stations and using a flow-through measuring complex along the ship's route. The hydrooptical characteristics vertical distribution uniformity in the upper ten-meter layer was controlled remotely using underway lidar data.Good agreement between the spatial distributions of the lidar echo signals parameters, of the hydrooptical and of the hydrological characteristics (coincidence of the locations of various distribution features, local maxima, minima and frontal zones) was demonstrated. A large volume of measurement data has been obtained, which allows for further statistical processing in order to find relationships between the parameters of lidar echo signals and hydrooptical characteristics recorded by contact methods.

The Results of Oceanographic Studies in the Marginal Ice Zone of the Barents Sea in the Spring of 2023

The results of oceanographic research in the marginal ice zone of the Barents Sea near the ice cover boundary, carried out from the R/V Dalnie Zelentsy from April 27 to May 6, 2023, are presented. The position of the frontal zones recorded from contact observations on hydrological meridional transects along 33°30′, 40°, 45°, and 50° E are considered. The transects were made from the fields of finely broken annual ice southward towards the open water area of the Barents Sea. High-gradient zones expressed in the temperature and salinity fields at different distances from the ice field edge were detected on all transects. It was shown that during the research period the frontal zone was located at a distance from 25 to 180 km from the ice field edge, the temperature gradients varied from 0.021 to 0.067 °C/km, the salinity — from 0.002 to 0.012 psu/km, the width of the frontal zone did not exceed 28 km. The maximum values of chlorophyll-a and dissolved oxygen were observed in the area of the frontal zone boundary.

Histological alterations as a recommended biomarker in the mussel Mytilus platensis (Bivalvia, Mytilidae) to study anthropic impact on seaports

Toxic effects of trace metals on digestive gland and gill cytoarchitecture were studied in the mussel Mytilus platensis after metal detection in the environment. Mussels were collected from the Port of San Antonio Este and from a reference site called Isla Mejillón, both in Rio Negro province (Argentina). Histological techniques, morphometrical analysis and lipofuscin detection with Nile blue method were performed. Mussels from the seaport presented dilated hemolymphatic vessels with numerous hemocytes in the gill filaments and fused filaments in the frontal zone. Morphometric analysis of the gill filaments showed an increase in the epithelial thickness of the lateral zone that bears cilia, and we infer that water filtering might be affected. The sublateral zone was also thickened, probably interfering with gas exchange. A reduction in the abfrontal zone epithelial thickness was also noticed, so water pumping, lubrication and cleaning of the gills might be impaired. Digestive glands of seaport mussels accumulated lipofuscin granules within the digestive cells, accounting for lipid and protein peroxidation. The observed histological alterations in gill and digestive gland in mussels from North Patagonia seaport are relevant findings to be considered as biomarkers of effect after exposure to metals.

Analysis of wind pressure characteristics of typical agricultural greenhouse buildings on tropical islands

Existing studies about wind pressure on agricultural greenhouse buildings concentrate on the mean wind pressure while ignoring the systematic research on fluctuating wind pressure characteristics and the influence of roof shape on the wind pressure characteristics, which are closely associated with the wind-induced damage mechanism. In this study, two typical agricultural greenhouse buildings on tropical islands are selected as prototypes to conduct pressure measurement experiments in the wind tunnel. Based on the wind pressure time series for the two greenhouses, the mean and fluctuating wind pressure distribution pattern and the localized high-pressure generation mechanism are analyzed. Then, the shape coefficient of the two greenhouses is compared in depth to the standards from four countries. Besides, wind pressure non-Gaussian determination criteria for agricultural greenhouse buildings considering the roof shape and wind directions are proposed. Lastly, the differences in wind pressure spectra on the roofs and walls of the two greenhouses are summarized. The results indicate the roof shape has a significant influence on the wind pressure characteristics. Compared with the pitched roof, the vaulted roof will increase the suction effect on the windward front zone and the middle area, mitigate the suction impact on the leeward roof, and weaken the wind pressure non-Gaussian characteristics. The experimental shape coefficient of the pitched-roof greenhouse is basically consistent with the standard from the U.S., while that of the vaulted-roof greenhouse has some deviation from the existing standards. The results provide a theoretical basis for the wind-resistant design of agricultural greenhouse buildings on tropical islands.

Review of studies on the distribution of Antarctic krill accumulations in the Scotia Sea and analysis of mesoscale dynamics of its habitat

This article studies the mesoscale dynamics of the waters of the Scotia Sea, located at the northern tip of the Southern Ocean on its border with the Southern Atlantic Ocean. The Scotia Sea is one of the most promising fishing areas where the industrial catch of Antarctic krill (Euphausia superba) is produced. Since the distribution of commercial krill accumulations is largely determined by oceanological conditions, this paper analyzes mesoscale vortex dynamics, frontal zones, and topography in the Scotia Sea, affecting the creation of favorable oceanological conditions for the formation of commercial krill accumulations. The study is conducted using satellite and model data. It is shown that the distribution of sea level according to the GLORYS12v1 reanalysis data in the Scotia Sea has a zonal character. In winter and spring, sea level anomalies are positive (up to 20 cm), and in summer and autumn, they are negative (up to -180 cm). In the northwestern part of the Scotia Sea, according to the data of the GLORYS12v1 reanalysis for 1993-2020, thermal frontal zones with high repeatability (> 80%) are distinguished. Dynamic frontal zones are also distinguished in the northwestern part of the water area and have a repeatability reaching 100%. This area in the Scotia Sea is the most dynamically active: increased kinetic energy values are observed here. The increased dynamic activity in the northwestern part of the Scotia Sea, considered above by the average and average seasonal distributions of characteristics, is also confirmed in the synoptic range of periods. Spatial distributions of long-lived mesoscale vortices according to META 3.2 data for 1993-2021 show the localization areas of these vortices, with cyclones forming significantly more than anticyclones. Analysis of the trajectories of these vortices showed that the direction of their propagation is mainly eastern. The intense vortex dynamics in the Scotia Sea is also confirmed by reconstructed altimetric data for 1970-1992.

Structure and Characteristics of Synoptic-Scale Waves in the Northern Eurasian Storm Track during Summer

Abstract This study examined the dominant structure and characteristics of synoptic-scale (2–8-day periods) waves over northern Eurasia during 40 summer seasons (June–August, 1979–2018). The synoptic-scale wave patterns are isolated using an extended empirical orthogonal function (EEOF) analysis on the 300-hPa geopotential height anomalies, and a composite based on atmospheric circulation fields and gridded precipitation product. The wave patterns are classified into two types from two pairs of EEOF modes. These two different wave types are defined as the polar frontal (PF) mode and Arctic frontal (AF) mode, respectively. The PF-mode waves are initiated in the North Atlantic sector to the west of the British Isles. They propagate eastward across Siberia into the North Pacific, and produce precipitation mainly over the Eurasian polar frontal zone. The AF-mode wave train arcs along the climatological Arctic frontal zone (AFZ). The AF-mode waves originate near the Scandinavian Peninsula. Their eastward passage brings precipitation along the AFZ. The development of the synoptic-scale waves is reflected by unique background conditions over northern Eurasia. The lower-tropospheric baroclinicity in southern Siberia and central Asia favored the baroclinic growth of the PF-mode waves. The AF-mode waves are trapped in the well-organized baroclinic zone along the north coast of the Eurasian continent. The baroclinic zone is coupled with a band of large meridional gradient of potential vorticity in the upper troposphere, suggesting that this band acts as a waveguide for the AF-mode waves. Significance Statement This study examines the synoptic-scale waves in the 2–8-day range of time scales over northern Eurasia during summer. The synoptic-scale waves are categorized into two distinct types at different latitude bands by the EEOF analysis on the 300-hPa z anomalies. They are defined as polar frontal (PF) mode and Arctic frontal (AF) mode. Then the EEOF-based composite analysis is conducted to detect the large-scale circulation anomalies associated with the propagation of different types of synoptic-scale waves. The structure and characteristics are examined. The roles of the mean background conditions in the development and propagation of the respective types are discussed. The behavior of these wave disturbances as rain-producing weather systems is also examined.

Multi-scale Uncertainty of Mesoscale Convective Systems in the Baiu Frontal Zone: A Case Study from June 2022

Multi-scale Uncertainty of Mesoscale Convective Systems in the Baiu Frontal Zone: A Case Study from June 2022

The 1991–2020 sea surface temperature normals

AbstractThe 1991–2020 climate normals for sea surface temperature (SST) are computed based on the NOAA Daily Optimum Interpolation SST dataset. This is the first time that high‐resolution SST normals with global coverage can be achieved in the satellite SST era. Normals are one of the fundamental parameters in describing and understanding weather and climate and provide decision‐making information to industry, public, and scientific communities. This product suite includes SST mean, standard deviation, count and extreme parameters at daily, monthly, seasonal and annual time scales on 0.25° spatial grids. The main feature of the SST mean state revealed by the normals is that in the Tropics, the Indo‐Pacific Ocean is dominated by the warm pool (SST ≥ 28°C) while the eastern Pacific is characterized by the cold tongue (SST ≤ 24°C); in the midlatitudes, SSTs are in zonal patterns with high meridional gradients. Daily SST standard deviations are generally small (<1.0°C) except in frontal zones (>1.5°C) mostly associated with ocean currents such as the Gulf Stream, Kuroshio and Equatorial Currents. Compared to the 1982–2011 climatology, the 1991–2020 mean SSTs increased over most global areas but obvious cooling is seen in the Southern Ocean, eastern tropical South Pacific Ocean and North Atlantic warming hole. The Indo‐Pacific warm pool (IPWP) is found to have strengthened in both intensity and coverage since 1982–2011. By a count parameter criterion of ≥300 days annually with SST ≥ 28°C, the IPWP coverage increased 33% from 1982–2011 to 1991–2020. The global mean SST of 1991–2020 is warmer than that of 1982–2011, and the warming rate over 1991–2020 doubles that over 1901–2020.

Decisive role of atmospheric circulation in the troposphere on ozone pollution in the Beijing-Tianjin-Hebei region

Using ozone observations and the ERA5 reanalysis, general circulation conditions between high and low ozone periods in the Beijing-Tianjin-Hebei (BTH) region in June are compared. The atmospheric circulation pattern is contrastingly different in midlatitudes between high and low ozone concentration periods. During high ozone periods in the BTH region, the East Asia–Pacific jet center shifts further eastward in the upper troposphere. Additionally, positive geopotential height anomalies develop at 500 hPa over the BTH region, accompanied by anomalously warm near surface conditions. In contrast, during low ozone periods in BTH, a similar circulation pattern is observed but with the sign reversed. During high (low) ozone periods, the temperature in the lower troposphere usually rises (reduces), solar ultraviolet radiation increases (decreases), and cloud cover, precipitation, and humidity decreases (increases). Moreover, during high (low) ozone periods in BTH, warm (cold) anomalies develop in the low troposphere, extending from the surface upward. This meteorological condition is (not) conducive to photochemical reactions in the near surface layer. The tropopause over the BTH region is anomalously higher (lower) during high (low) ozone periods, and the upper tropospheric ozone is ∼20% less (∼17.5% higher) than the average. Ozone from the upper levels might not consistently contribute to an increase (decrease) in the near surface ozone concentration in BTH, while negative (positive) ozone concentration anomalies prevail in upper levels. Existing evidence suggests that the frontal zone in the troposphere offsets the dynamic contribution of stratospheric transport to changes in ozone content in BTH.

Machine-learning applications for differentiation across states/stages of creative thinking based on time-series and time-frequency features of EEG/ERP signals

BACKGROUND: The study presents machine-learning (ML) classification approaches for the state/stage differentiation of creative tasks using the “test-control” approach. The control tasks were considered as the initial stages of the creative activity. Time-series and time-frequency electroencephalography (EEG) data analyses were employed in three divergent thinking tasks: 1) creating endings to well-known proverbs (“PROVERBS”, event-related potential [ERP] paradigm); 2) creating stories (“STORIES”, continuous EEG); 3) free creative painting (“viART”, continuous EEG). AIM: To compare and select effective ML classification approaches for EEG signal separation at different stages or states of creative task performance. METHODS: In this study, 22 individuals participated in the “PROVERBS” (ERP paradigm), 15 in the “STORIES”, and 1 (a longitudinal case study) in the “viART” tasks. Linear and convolutional neural network (CNN) classifiers were used. EEG data were previous artifacts corrected and converted to current source density (CSD). Continuous EEGs were divided into 4-s intervals and 1500 ms after stimulus presentation, were used in ERPs. The EEG/ERP time-frequency maps (Morlet wavelet transformation) for 3–30 Hz were generated for 4-s intervals with 100 ms shift (continuous EEGs in “STORIES” and “viART”) or for 1500 ms after stimulus presentation (ERPs in “PROVERBS”) and consisted of combined images (224×224 px) for frontal (Fz) and parietal (Pz) brain zones. Image classification was carried out using the modified CNN (ResNet50, ResNet18 architectures). RESULTS: The offline classification accuracy of the four-class system (description of a picture, inventing a story plot, continuation of story’s plot, and background with open eyes) in the “STORY” creation task was up to 96.4% [±8.3 SD] with ResNet architectures (ResNet50 and ResNet18). The accuracy of the three states discrimination of the artists’ creative painting (resting state with open eyes, painting on canvas, and viewing the painting) was 86.94% for kernel naive bayes and 98.2% for CNN. For the trained and tested samples given for the CNN in consecutive order (neurointerface mode), the accuracy diminished to 70.0% [11% SD] on average. In the ERP paradigm “PROVERBS”, the classification accuracy of the three-class system (creation of “new” ending, naming of semantic synonym, and remembering of the known ending) was 80.5% [±8.7 SD] for the common spatial pattern, followed by rSVM (radial kernel basis support vector machine), compared with 43.2% [±8.8 SD] for CNN. CONCLUSION: The use of CNNs allowed better classifying of “continuous” long-term states of creative activity. In fast “transient processes” such as ERP, time-series classifiers with spatial filtering proved to be more efficient.

Seasonal and Interannual Variability of Fronts and Their Impact on Chlorophyll-a in the Indonesian Seas

Abstract The spatiotemporal variability of oceanic fronts in the Indonesian seas was investigated using high-resolution satellite observations. The study aimed to understand the underlying mechanism driving these fronts and their impact on chlorophyll-a variability. A high value of frontal probability was found near the coasts of major islands, exhibiting a distinct seasonal cycle with peaks occurrences during austral winter. The distribution variability of chlorophyll-a was generally consistent with the presence of active frontal zones, although a significantly positive relationship between fronts and chlorophyll-a was limited to only some specific areas, e.g., south Java Island and the Celebes Sea. Wind-driven upwelling played a major role in front generation in the Java upwelling region and enhanced frontal activity can promote the growth of phytoplankton, leading to higher chlorophyll-a. Furthermore, the study demonstrated that wind patterns preceded variations in front probability and chlorophyll-a by approximately two months. This lag suggests that the spatiotemporal variability of fronts and chlorophyll-a in this region is primarily influenced by the monsoon system. In addition, the sea surface temperature (SST) simultaneously modulated the chlorophyll-a variability. Negative SST anomalies were typically associated with positive anomalies in front probability the chlorophyll-a in most areas. Notably, the interannual variability of fronts and chlorophyll-a are prominent in the Java upwelling region. During El Niño years, this region experienced an enhanced monsoon, resulting in a negative SST anomaly alongside positive anomalies in front probability and chlorophyll-a. A comprehensive description and underlying dynamics of frontal activity in the Indonesian seas are provided by this study. The findings are helpful to delineate the variability in chlorophyll-a, thereby facilitating the future understanding of local primary production and the carbon cycle. Significance Statement As typical mesoscale processes, oceanic fronts have significant impacts on biological processes and fisheries in marginal seas. The complex spatiotemporal variability of fronts and their effects on biological processes in the Indonesian seas remain poorly understood. This study aimed to address this knowledge gap by investigating the seasonal and interannual variability of fronts and their influence on chlorophyll-a, a key indicator of phytoplankton biomass and primary productivity. The study identified a high frontal probability in south Java Island during austral winter and El Niño years. Wind-driven upwelling was found to be a major factor in front generation and promoting phytoplankton growth. The findings of this study will improve the theoretical knowledge of regional dynamics, local primary production, and the carbon cycle in the Indonesian seas, benefiting fisheries management and ecosystem conservation efforts.

Marine copepod assemblages in the Arctic: The effect of frontal zones on biomass and productivity

The Barents Sea, as the largest Arctic shelf region with high productivity, supports vital commercial fisheries. The region's ecosystem is significantly impacted by both warm Atlantic Water (AW) and cold Arctic Water (ARW), resulting in frontal zones that delineate differing water masses. Zooplankton populations serve as the primary link between primary producers and higher trophic levels. To evaluate the potential influence of frontal zones on copepods, we conducted a summer survey focusing on sites where diverse water masses interacted. Our findings revealed that species richness, diversity, biomass, and daily production of common copepods were highest in the Polar Front, separating AW and ARW, as well as in the eastern frontal zones (Barents Sea Water and Novaya Zemlya Coastal Water). Herbivorous copepods, such as Calanus spp. and Pseudocalanus spp., dominated in terms of total copepod biomass and production, whereas the small omnivore Oithona similis prevailed by abundance. Multivariate analysis demonstrated a strong correspondence between frontal zones and copepod assemblages. The primary factors explaining spatial variations in copepod biomass and production included the geographic positions of sampling stations, depth, and chlorophyll a concentration. Our research underscores the significance of oceanographic fronts as zones of critical importance for overall pelagic productivity in Arctic regions.

Ongoing India–Asia convergence controlled differential growth of the eastern Tibetan Plateau

The eastern Tibetan Plateau is known for its unique topography and active tectonics, serves as a crucial region for investigating geodynamics and lithosphere–atmosphere interaction. Despite its importance, the formation process and geodynamics of this region remain controversial. We integrated new and reported thermochronological data, and paleo-crustal thickness reconstruction to explore the tectonic deformation, climate–tectonic coupling, and geodynamics of the area. New apatite fission track data, collected from the upstream areas of major rivers in the eastern Tibetan Plateau, revealed multiple rapid river incision phases during the Eocene and Neogene–Quaternary. Apatite (U-Th)/He data obtained from a borehole near the Gaoligong shear zone indicates that the Yingjiang fault experienced two rapid exhumation phases, which initiated at ∼22 Ma and ∼18 Ma, respectively. Thermo-kinematic modeling (Pecube), based on multiple thermochronometers, predicted three phases of thrusting along the Longmenshan fault, which were initiated at ∼34 Ma, ∼17 Ma and ∼14 Ma, respectively. During the late Eocene period, Sr/Y and (La/Yb)n ratios suggest that the eastern Qiangtang and Songpan–Ganzi terranes underwent considerable uplift, followed by outward uplift in the collisional front zone and the southeastern margin of the plateau during the late Oligocene. Paleo-crustal thickness reconstruction also indicate another ∼1 km surface uplift during the Neogene–Quaternary. Our findings, when combined with reported thermochronological data, suggest that during the Neogene–Quaternary, the collisional front zone and the eastern margin of the plateau underwent greater exhumation compared to the eastern Qiangtang and Songpan–Ganzi terranes. The temporally and spatially varied exhumation shaped the landscape of the eastern Tibetan Plateau, driven mainly by precipitation-related erosion and promoted by fold-thrust and strike-slip thrust. This was controlled primarily by eastward lithosphere/asthenosphere extrusion associated with ongoing India–Asia convergence.