Offshore Areas Research Articles

Sound Speed Prediction Equations for Seafloor Sediments in Offshore Area Southeast of Hainan Island

In this study, single- and double-parameter empirical equations were produced, and the influences of physical properties on sound speed were assessed, based on the measured data of seafloor sediments obtained in an area near southeastern Hainan Island. The correlation coefficients of the single-parameter empirical equations were found to be greater than 0.65, while those of the double-parameter empirical equations were found to be greater than 0.72, indicating that the double-parameter empirical equations have an advantage in predicting sound speed. According to the sensitivity analysis, mean grain size is the best predictor for sediment sound speed. Furthermore, the empirical equations constructed in this study are a significant addition to sound speed prediction equations and have important application potential in predicting sound speed in the studied area near southeastern Hainan Island.

A Raster-Based Multi-Objective Spatial Optimization Framework for Offshore Wind Farm Site-Prospecting

Siting an offshore wind project is considered a complex planning problem with multiple interrelated objectives and constraints. Hence, compactness and contiguity are indispensable properties in spatial modeling for Renewable Energy Sources (RES) planning processes. The proposed methodology demonstrates the development of a raster-based spatial optimization model for future Offshore Wind Farm (OWF) multi-objective site-prospecting in terms of the simulated Annual Energy Production (AEP), Wind Power Variability (WPV) and the Depth Profile (DP) towards an integer mathematical programming approach. Geographic Information Systems (GIS), statistical modeling, and spatial optimization techniques are fused as a unified framework that allows exploring rigorously and systematically multiple alternatives for OWF planning. The stochastic generation scheme uses a Generalized Hurst-Kolmogorov (GHK) process embedded in a Symmetric-Moving-Average (SMA) model, which is used for the simulation of a wind process, as extracted from the UERRA (MESCAN-SURFEX) reanalysis data. The generated AEP and WPV, along with the bathymetry raster surfaces, are then transferred into the multi-objective spatial optimization algorithm via the Gurobi optimizer. Using a weighted spatial optimization approach, considering and guaranteeing compactness and continuity of the optimal solutions, the final optimal areas (clusters) are extracted for the North and Central Aegean Sea. The optimal OWF clusters, show increased AEP and minimum WPV, particularly across offshore areas from the North-East Aegean (around Lemnos Island) to the Central Aegean Sea (Cyclades Islands). All areas have a Hurst parameter in the range of 0.55–0.63, indicating greater long-term positive autocorrelation in specific areas of the North Aegean Sea.

Insights on the structural framework of the Egyptian Eastern Desert derived from edge detectors of gravity data

Advanced geophysical techniques are used on Bouguer gravity data to unravel the structural complexity of the Eastern Desert. Using methods such as tilt angle (TA), enhanced horizontal gradient amplitude (EHGA), lineament analysis, and 2Dcrustal modeling, we are able to differentiate between deep and shallow gravity sources and delineate the area’s geologic features. Using fast Fourier transform, positive and negative anomalies are identified. The positive anomalies are interpreted as uplifted block, anticline features, or intrusive occurrences of denser rocks, whereas the negative anomalies are interpreted as downfaulted blocks, providing crucial insights. Lineament analysis suggests that the predominant tectonic force that shaped the area is in the northwest direction. Integration of TA and EHGA reveals nuanced structural patterns. The constructed structural map indicates a network of uplifted and downfaulted blocks intersected by strike-slip faults with a northeast trend. The 2D crustal modeling illustrates the diverse composition of granitic and basaltic rocks, with a discernible thinning of the continental crust toward the Red Sea offshore area. This significantly advances the understanding of the Eastern Desert’s geologic evolution, offering valuable insights into the tectonic processes and crustal dynamics.

Effect of ocean dynamic processes on the temporal-spatial pattern of persistent organic pollutants (PCB-153 and BDE-47) in the shelf seas

Field observations of persistent organic pollutants (POPs) in shelf seas presented abnormal phenomena such as high-concentration patches in offshore areas and different vertical profiles of POPs at the same location. We assumed that these phenomena were associated with the presence of bottom cold water mass (BCWM) in shelf seas and used a hydrodynamic-ecosystem-POP coupled model to confirm this hypothesis. Based on model results, with the formation of BCWM during summer, POPs accumulated inside BCWM due to their transport across the thermocline by the sorption to sinking particles. With the intensification of vertical mixing during winter, the release of POPs from BCWM induced high-concentration patches of POPs on the surface layer. Meanwhile, the low water temperature in winter was favorable for the gas deposition of POPs, which led to high surface concentrations of POPs. Because the accumulation of POPs in BCWM depended on the sorption of dissolved POPs by particles, not all types of POPs accumulated in BCWM. Some POPs even accumulated at the sea surface above the BCWM due to large gaseous deposition and weak sorption by particles. Using this feature, we proposed a prediction function for the accumulation of POPs in BCWM.

Restricted recovery of Eisenia bicyclis kelp forest following sea urchin removal on the Pacific coast of Tohoku, Japan

Little information is available on the destruction of Eisenia bicyclis kelp forests (Phaeophyceae: Laminariales) due to overgrazing by sea urchins. In Shizugawa Bay, on the northeastern Pacific coast of Japan, overgrazing by the sea urchin Mesocentrotus nudus caused the destruction of E. bicyclis forests between 2014 and 2015. This study investigated the recovery of an adult kelp forest in relation to sea urchin densities through the continuous removal of sea urchins at 3 permanent experimental transects spanning 100 m2 for 3.8 yr from September 2015 to June 2019. The relationship between the densities of sea urchins and kelp juveniles was also analyzed. Estimates of the threshold density and biomass of sea urchins required to trigger the phase shift from an E. bicyclis forest to a barren were 15.5 ind. m-2 and 712.0 g m-2, respectively. The removal of sea urchins expanded the offshore kelp growth area. However, an increase in adult kelp following the return of juveniles was restricted to the nearshore half of the transects. The successful recruitment of kelp juveniles, followed by the recovery of adult kelp forest, requires reduction of the density of M. nudus of 40-50 mm diameter to 0 or 1 ind. m-2. Reducing sea urchin densities in autumn, when many move from barrens to invade kelp forests, is crucial to ensure the survival of kelp juveniles. This study highlights the presence of an intensified positive feedback mechanism of the barren state due to high grazing intensity and a weakened Oyashio Current.

Weighted Fusion Method of Marine Gravity Field Model Based on Water Depth Segmentation

Among the marine gravity field models derived from satellite altimetry, the Scripps Institution of Oceanography (SIO) series and Denmark Technical University (DTU) series models are the most representative and are often used to integrate global gravity field models, which were inverted by the deflection of vertical method and sea surface height method, respectively. The fusion method based on the offshore distance used in the EGM2008 model is just model stitching, which cannot realize the true fusion of the two types of marine gravity field models. In the paper, a new fusion method based on water depth segmentation is proposed, which established the Precision–Depth relationship of each model in each water depth segment in the investigated area, then constructed the FUSION model by weighted fusion based on the precision predicted from the Precision–Depth relationship at each grid in the whole region. The application in the South China Sea shows that the FUSION model built by the new fusion method has better accuracy than SIO28 and DTU17, especially in shallow water and offshore areas. Within 20 km offshore, the RMS of the FUSION model is 5.10 mGal, which is 8% and 4% better than original models, respectively. Within 100 m of shallow water, the accuracy of the FUSION model is 4.01 mGal, which is 14% and 12% higher than the original models, respectively. A further analysis shows that the fusion model is in better agreement with the seabed topography than original models. The new fusion method can blend the effective information of original models to provide a higher-precision marine gravity field.

Analysis of Downstream Sediment Transport Trends Based on In Situ Data and Numerical Simulation

This study conducted an in-depth analysis of the sediment dynamics in the lower reaches of the Changhua River and its estuary on Hainan Island. Through field collection of topographic data and sediment sampling, combined with advanced computational techniques, the study explored the transport pathways and depositional patterns of sediments. The grain size trend analysis (GSTA) method was utilized, in conjunction with the Flemming triangle diagram method, to classify the dynamic environment of the sediments. Furthermore, hydrodynamic modeling results were integrated to further analyze the transport trends of the sediments. The study revealed that the sediment types in the research area are complex, primarily consisting of gravelly sand and sandy gravel, indicating a generally coarse sedimentary environment in the region. The sediments in the lower reaches of the Changhua River generally transport towards the south and southwest (in the direction of Beili Bay). The net sediment transport directions inferred from the GSTA model are largely consistent with the Eulerian residual flow patterns, especially in the offshore area, where discrepancies are observed in the nearshore zone. The nearshore transport is influenced by the combined effects of alongshore currents, residual flows, and river inputs, while the offshore transport exhibits a shift from the northwest to southwest directions, reflecting the regional circulation patterns.

Accuracy assessment of offshore wind measurements partially compensated by MCP method considering data availability

Abstract In Japan, most offshore promotion areas for bottom-fixed wind turbines are in near-shore areas, where offshore wind speeds are not uniform. The dual-scanning LiDAR system (DSL), which is a remote-sensing technology, is widely used to measure the mean wind speed, wind direction, and turbulence for resource and site assessments. However, the availability of DSL data tends to be lower than the key performance indicators proposed in the Carbon Trust in Offshore Wind Accelerator project owing to the characteristics of DSL. Missing observed data can be predicted using the measure–correlate–predict (MCP) method, and the uncertainty of the MCP method can be examined using a prediction function. However, a method to evaluate the accuracy of the final dataset comprising observed data and data predicted by the MCP method is yet to be devised. In this study, a set of formulas is proposed to evaluate the accuracy of indices, such as the coefficient of determination, slope, and offset of linear regression, for a partially complemented dataset using the MCP method. The proposed formulas are validated against on-site measurements.

Identification of Shale Layer in Offshore Field of North East Java Basin for Non-Conventional Oil and Gas Exploration

<p>Non-conventional hydrocarbon exploration is one way to develop shale potential to increase oil and gas reserves in Indonesia. Shale is a rock that is rich in organic material and is a target for non-conventional exploration, because it functions as a source and reservoir rock with a large shale volume and low permeability. Isopach maps can represent the thickness of shale layers and have the potential to become non-conventional exploration targets located in thick shale layers. Based on this background, this research will identify shale layers in the offshore fields of the North East Java Basin for non-conventional oil and gas exploration. The methods used are well logging and seismic methods. This research focuses on determining the location of shale layer depocenters based on isopach maps as a first step in localizing areas that will be targeted for the development of non-conventional hydrocarbon exploration. This research uses 29 2D seismic lines and 2 well data, namely NP-1 and NP-2 wells and the research target is the Kujung Formation and Ngimbang Formation in the offshore area of the North East Java Basin. The results obtained from the isopach map show that the depocenter location of the Kujung Formation is in the northwest direction with a shale thickness of 600-800 meters, while the Ngimbang Formation is in the east direction with a shale thickness of 1000-1300 meters. From the depocenter location, it can be seen that this location has a wealth of organic material so it has the potential to become a source rock and reservoir.</p>

Field geology under the sea with a remotely operated vehicle: Mona Rift, Puerto Rico

We implemented concepts of field geology at great ocean depths by constructing virtual outcrops from a string of overlapping video frames collected by remotely operated vehicles (ROVs). This lower-cost alternative to drilling boreholes allows stratigraphic extension into the offshore and regional interpretation of marine seismic profiles. The imagery was collected along a dive transect on the western wall of Mona Rift, a deep and narrow rift northwest of Puerto Rico, between water depths of 1560 m and 3927 m. The northern coast of Puerto Rico and its large offshore area are underlain by a mid-Eocene and younger forearc basin topped by a thick carbonate platform. There are no drill holes offshore, and tying seismic lines across the shoreline there is problematic. We describe our virtual outcrop and constrain its age and stratigraphy using seven rock samples collected by ROV and compare the outcrop’s stratigraphy to deep boreholes and outcrops on land. Our formation descriptions and ages agree, for the most part, with those on land, but we identified a 100-m-thick section that is represented on land by an unconformity. Our stratigraphic interpretation indicates lateral variations in formation thicknesses and establishes a cross-section for additional sampling of the Eocene–Pliocene geology. It also suggests that Mona Rift has formed since the mid-Pliocene. The presence or absence of ferromanganese (Fe-Mn) crust on rocks along the transect may be correlated with the smoothness of the rock surface.

A checklist of marine phytoplankton species of Northeast Brazil

The oceanic zone of Northeast Brazil in the southwestern tropical Atlantic Ocean is characterised by the presence of a variety of current systems. Thus, it has the potential to host a large diversity of phytoplankton species. In this context, we propose a comprehensive checklist of documented marine phytoplankton species in this region. To this end, we have compiled all the published material and supplemented it with original data from two comprehensive surveys, the ABRAÇOS surveys, covering the shelf, slope, and offshore areas of Northeast Brazil. Even if few articles were atrieved from our review research, a total of 719 phytoplankton taxa are reported, including 98 new records plus 45 potential new records from the ABRACOS data. Most taxa are accompanied by a comprehensive library of illustrations. The two major phytoplankton groups, dinoflagellates and diatoms, contributed similarly to the total checklist richness, which is consistent with the global phytoplankton diversity. The contribution of nano- and microphytoplankton varies between areas. The shelf displays a greater diversity of pennate and small/medium-sized diatoms. This may be attributed to the inputs from estuarine rivers as well as the resuspension of benthic diatoms. Conversely, dinoflagellates are more prevalent offshore, demonstrating their adaptability to changing nutritional conditions, by employing numerous metabolic and growth strategies to survive. This checklist, which reveals an remarkable diversity of nano- and microphytoplankton in Northeast Brazil, provides a valuable reference for scientists and managers to monitor community evolution under global change.

Spatial distribution and deposits of cliffs along the Brazilian semi-arid coast

Cliffed coasts are common landforms found worldwide, but their precise spatial distribution and the nature of associated deposits may present regional gaps. This works presents a geological and geomorphological study of the Brazilian semi-arid coast (∼900 km), which was carried out on coastal cliffs with the aim of addressing three important knowledge gaps: i) spatial distribution of coastal cliffs, analyzed using topographic data from SRTM, LiDAR and field surveys, ii) the lithology and ages of the deposits, investigated through sedimentological analysis and OSL dating, and iii) origin of the cliffs, explored through relations with global and regional sea-level curves. The supply of terrigenous sediments to the western equatorial Atlantic coast was also considered. Coastal cliffs were identified along 235 km of the coastline, represented mainly by inactive cliffs (∼170 km). These cliffed coasts are composed mainly by poorly sorted siliciclastic sandstones and conglomerates, deposited in the Late Pleistocene. The depositional phases correlate with abrupt climate changes, due to pulses of terrigenous supply to the continental margin during the Heinrich Events. The formation of marine cliffs in these deposits occurred in the mid-Holocene, as sea level reached current elevation (msl) in ∼7 ka and 2-4 m above in ∼5.5 ka. This previous higher sea-level supports the widespread occurrence of inactive cliffs. The findings in this work contribute to i) improved mapping of coastal landforms, with higher resolution data demonstrating that previous works underestimated the presence of coastal cliffs; ii) the coastal cliffs are cut in Pleistocene sediments instead of older, Miocene deposits of the Barreiras Formation as previously assumed; iii) cliff formation due to marine erosion occurred in the mid- to- late Holocene; iv) the siliciclastic sediments that compose the cliffs are correlatable to marine sediments found in adjacent offshore areas, highlighting the role of abrupt global climatic changes in the Pleistocene in shaping contemporary coastal landscapes.

Retrieval of total suspended matter concentration in the yellow river estuary offshore area based on QAA-RF model

ABSTRACT Total suspended matter is one of the crucial water quality parameters for both inland and marine environments, and a key role in evaluating the water quality of estuaries and offshore areas. Each year, the Yellow River carries a significant amount of sediment into the semi-enclosed Bohai Sea, results in a prolonged high concentration of total suspended matter in the offshore areas of the Yellow River Estuary. This study focuses on the offshore region of the Yellow River Estuary in China. Utilizing Sentinel-2 satellite imagery data from 2020 to 2023 and in-situ measured data from August 2020 to August 2022, to address the lack of physical mechanisms currently studied in machine learning retrieval methods, a model that integrates the physics-driven Quasi-Analytical Algorithm (QAA) and data-driven Random Forest (RF) is employed for the retrieval of total suspended matter concentration in the study area. The fused model (QAA-RF) is compared and analysed against regression models and standalone machine learning models. The results indicate that the accuracy of machine learning retrieval models is consistently higher than that regression models. The QAA-RF model demonstrates the highest accuracy (R 2 = 0.87, MAE = 5.01 mg L−1, RMSE = 6.39 mg L−1). Based on the QAA-RF model and the imagery data, monthly total suspended matter concentration is conducted in the study area. The retrieval results indicates that: (1) the total suspended matter concentrations is primarily concentrated in the near estuary region, with concentrations decreasing as distance from the estuary increases. (2) the total suspended matter concentration exhibits a distribution pattern with higher values in spring and winter, and lower values in summer and autumn. (3) the concentration of total suspended matter shows relatively small fluctuations at the annual scale from 2020 to 2023.

Investigation of submarine groundwater discharge into the Baltic Sea through varved glacial clays

Submarine groundwater discharge (SGD) is an important process responsible for transporting terrestrial dissolved chemical substances into the coastal ocean, thereby impacting the marine ecosystem. Despites its significance, there are few studies addressing SGD in the northern Baltic Sea. Here we investigate the potential occurrence of SGD in an area characterized by seafloor terraces formed in varved glacial clay located around Fifång Island, Southern Stockholm Archipelago. We analyzed 222Rn activity and porewater geochemistry in both marine and terrestrial sediment cores retrieved from Fifång Island and its surrounding offshore areas. Results from 222Rn mass-balance calculations, water isotopes, salinity, chloride concentration, and dating (including 14C and helium-tritium dating) indicate that modern groundwater flows through varved glacial clay layers and fractured rocks on Fifång Island and discharges into Fifång Bay. Additionally, the offshore cores reveal a saline groundwater source that, dating of the dissolved inorganic carbon, appears systematically younger than the hosting clay varves dated using the Swedish clay varve chronology. Acoustic blanking in our acquired sub-bottom profiles may be related to this fluid migration. The occurrence of this saline groundwater seems to be independent from the distance to the submarine terraces. Collectively, our study confirms the occurrence of submarine groundwater in the varved glacial clay close to Fifång Island and further offshore. Our findings help establish the significance of submarine groundwater discharge in influencing the past and present coastal environment in the Baltic Sea region.

Experimental study on the thixotropic strength of the marine soft clay from the Yangtze River estuary

Soft clay in the offshore area of the Yangtze River estuary has been investigated considering its basic physical properties. Forty-five unconfined compressive strength tests were conducted on the remolded marine soft clay to investigate the impacts of curing time T, water content w, plasticity index IP, and clay particle content ρc on the thixotropic static shear strength ratio As of the marine soft clay from the Yangtze River estuary. Results show that the stress–strain curves were primarily strain hardening and strain softening curve types. Unconfined compressive strength qu increased with an increase in T. All specimens with different basic physical properties were capable of thixotropic strength recovery. When T = 0–28 days, As increased rapidly, while for T > 28 days, As of most specimens increased slightly or tended to stabilize. The impacts of w, IP and ρc on As do not follow a consistent pattern, but there is a strong correlation between As and w/wL (wL is the liquid-limit water content). For w/wL < 0.75, As increased with increasing w/wL, whereas for w/wL ≥0.75, As decreased with increasing w/wL. We proposed a simple and widely applicable power function prediction model for the As of the soft clay from the Yangtze River estuary.

Tectonics of Cauvery basin (India) in onshore and offshore portions

Morphometric studies coupled with geophysical investigations from petroliferous basins provide valuable information about tectonics of the regions. We deduce six morphologic parameters from the River Cauvery's designated (sub)watersheds and perform dendrogram clustering analysis. The main channels of the (sub)watersheds showcase steeper gradient and meandering nature with less concavity. On the other hand, the distributaries portray lesser gradient and straight nature with greater concavity. From the offshore region of the Cauvery basin, we perform gravity modeling. The results show variations in gravity values from low to high, -150 to 50 mGal probably because of the basement ridge-depression features. This anomaly orientation indicates the extension of the sub-basin in the region. A strong NE-SW gravity trend possibly suggests a high-density plug at mid-crust. The low gravity values near the Vedaranyam region indicate low-density rocks within the basement. Places of high gravity anomaly show a decrease in bathymetry depth and vice versa. This indicates isostatic compensation of the Moho geometry, possibly due to crustal thinning in the offshore areas. Isostatic regional gravity fields are manifested by Moho relief and can have implications on the lithospheric mechanical strengths. Bathymetric studies indicate multi-directional slopes. Relatively flat areas can indicate depocenters. E-W trending lineaments mapped on the Precambrian basement from a portion of the study area is presumably a manifestation of Cauvery Shear zone, which also persists in the offshore region.

High-resolution oceanic anoxic event 2 (OAE2) records from the north of eastern Tethys and evidence for short-term sea regression and wildfire at its early phase

Oceanic Anoxic Event 2 (OAE2), occurring at the Cenomanian-Turonian boundary (CTB; 93.9 Ma), is a representative global event of carbon cycling fluctuations and transient climate anomalies. OAE2 was initially discovered and intensively studied in the trans-Atlantic and western Tethys Oceans; however, research on the eastern Tethys Ocean, especially the vast northern regions, is inadequate. Further, there is still considerable controversy regarding the triggering mechanisms and early environmental changes of OAE2. In this study, we present high-resolution carbonate carbon isotopes (δ13Ccarb), total organic carbon, and mercury (Hg) concentration records from the northern part of the eastern Tethys Ocean during the OAE2 interval, sampled at the ZK20-1 drillcore section of the Kukebai Formation in the western Tarim Basin, China. Following the global classification scheme for carbon isotope excursion (CIE) at the CTB, the carbon isotope change curve of this study is classified into six stages (C1-C6), and three substages (C3a, C3b, C3c) in the C3 stage. Sedimentary features reveal a short-term sea-level regression in the Tarim Basin during the onset stage (C2) of OAE2, which likely involved vast regions of the eastern Tethys Ocean and even the Pacific region. The mercury (Hg) concentration data reveal increasing Hg levels in the lower part of the Kukebai Formation, mainly corresponding to the onset stage (C3) of the OAE2, but it is significantly lower than that in other typical volcanogenic Hg anomalies. We preliminarily speculated that the intensified wildfire activity at the onset stage of OAE2 potentially accelerate the Hg extracted from the terrestrial soil or organic matter into the offshore area. This is also supported by the evidence of wildfire and Hg anomalies from the Western Interior Seaway (WIS) of North America.

Seascape Genetics and Distinct Intraspecific Diversification of the Decapod Nephrops norvegicus in the Adriatic Sea.

Norway lobster Nephrops norvegicus, a prized decapod crustacean species, is found at different depths across the East Atlantic Ocean and Mediterranean Sea. Despite management efforts, the stocks are globally characterised as overexploited. In the present study, the impact of biogeographical boundaries on the phylogeographical and demographic population status was investigated within the Adriatic Sea, addressing important genetic indices for decapod functional conservation management. Central Mediterranean, Adriatic Sea A total of 482 individuals of Nephrops divided into the 12 samples were collected across biogeographical range of the Adriatic Sea. Using the mtDNA D-loop and microsatellite markers, methods of phylogeography and seascape genetics were applied to infer offshore versus coastal population divergence, demography and structure. Significant findings include genetic differentiation between offshore and coastal samples, with higher diversity indices in open waters. The limited gene flow observed between these two areas emphasises the self-sustained nature of coastal populations. Recent demographic changes in coastal populations reflect geographical constraints, fishing pressures and fluctuations in self-recruitment success. Additionally, the study reveals historical biogeographic events shaping the Adriatic populations, with evidence suggesting lineage divergence during the upper Pleistocene and postglacial recolonisation from southern Adriatic refugia. The role of biogeographical conditions in shaping genetic structure and limited gene flow between inshore and offshore areas underscore the need for improved management strategies, emphasising the importance of marine protected areas in conserving coastal populations and maintaining overall genetic diversity of the Norway lobster in the Adriatic Sea. Genomic monitoring within current management practices is recommended.

Experimental investigation on the oil occurrence and mobility of lacustrine shales in offshore area of China using 1D/2D nuclear magnetic resonance and centrifugal techniques

Shale oil occurrence mechanism and mobility have significant influences on hydrocarbons extraction from shale systems. However, the effects of petrophysical and petroleum geochemical properties on oil mobility are not understood. In this study, shales with different lithofacies were investigated using thin sections, scanning electron microscopy, nuclear magnetic resonance (NMR), and organic geochemical analysis. Shales at original, extracted, oil-saturated, and centrifugal states were systematically scanned using 1D and 2D NMR technologies. The multi-scaled pores were obtained by comparing the T2 spectra of samples at different states. The 2D NMR identification spectra for hydrocarbon-bearing components were established. The free oil, adsorbed oil, mobile oil contents were quantitatively evaluated and the geological controls on oil mobility were discussed.Results show that the siliceous shales have the highest total oil and movable oil contents, while the argillaceous shales have the lowest values due to the limited pore space and poor connectivity. Mobile oil mainly stores in interparticle pores, dissolution-related pores and bedding fractures. Its content increases with the increasing felsic minerals. Oil in siliceous shales are rich in low carbon-chain hydrocarbons and has high mobility. Based on oil distribution in multi-scaled pores, a strategy about the mobile oil distribution were proposed: Ultramicropores region is the immobile oil zone; Micropores region is the oil difficult-to-flow zone; Transition pores region is the oil easy-to-flow zone; Macropores region is the completely mobile oil zone. The mobile oil mainly accommodates in transition pores and macropores (pore size >20 nm and mobile oil saturation exceeds 60 %).

Variability of marine heatwaves’ characteristics and assessment of their potential drivers in the Baltic Sea over the last 42 years

This study examined Baltic Sea Marine Heatwaves (MHWs) using 42 years of satellite-derived sea surface temperature (SST) data. We found that MHWs in warmer months are more intense but shorter compared to MHWs in cooler months. Also, MHWs predominantly affect offshore areas in warmer months, whereas MHWs predominantly impacting coastal seas in cooler months, especially along the eastern coast. Our analysis of interannual variability revealed that, unlike in many other basins worldwide, Baltic MHWs tend to maintain a constant intensity, while their spatial extent has significantly increased over the last few decades. Shortwave radiation notably influences MHW intensity and spatial extent, with additional impacts from longwave radiation in cooler months and latent heat flux in warmer months. Northern Hemisphere teleconnections exhibit stronger correlations with MHWs in the Baltic Sea compared to global-scale climate oscillations, with the Eastern Atlantic pattern having a particularly significant effect on MHW variability in the region.