Western Bohai Sea Research Articles

Pollen and spore records constrained by millennial prodelta evolution: a case study of the Huanghe (Yellow River) delta

Pollen and spore records in prodeltaic sediments hold significant potential for reconstructing paleoecologic and paleoclimatic evolution. However, uncertainties in these reconstructions arise from millennial-scale prodelta evolution, which dominates stratigraphic development and consequently influences sedimentary processes and/or pollen provenance. Here we explore the intricate relationship between pollen/spore records and prodelta stratigraphic evolution, using established seismic stratigraphy and ten sediment cores (five new, five from literature) within both the proximal and distal (mud belt) parts of the Huanghe (Yellow River) prodelta. In the proximal region, dominant lobate stratigraphic development, accompanied by shifts in river mouth and depocenter, leads to variations in pollen assemblages and contents within individual cores and differences in vertical pollen distribution across core sites. Transport distance appears to be a key factor, with arboreal pollens, particularly saccate ones (e.g., Pinus), positively correlating with the distance from the river mouth in their percentages within a single delta lobe, while non-arboreal and non-saccate arboreal pollens show higher percentages within shorter transport distances, despite longer distances leading to decreased total pollen concentrations. Likely due to the total pollen concentration after extended long-distance transport, this pattern is not observable in the distal mud belt. Subsurface stratigraphy in this mud belt reveals a complex pollen provenance characterized by Artemisia-Ulmus-Chenopodiaceae-Pinus, with non-arboreal pollens in dominance. Therein, non-arboreal pollens are not consistent with deposition from long-distance transport, and Ulmus pollens are uncommon in the western Bohai Sea. Interestingly, surface sediments in the mud belt display a different assemblage, characterized by Pinus-Artemisia-Quercus, consistent with the nearby Luanhe River prodelta, suggesting recent pollen supply from nearby sources, possibly due to the recent abandonment of the mud belt. Additionally, an energetic longshore transport/erosional regime reduces pollen content at the mud-belt margins and create pollen sinks (with the highest concentration) in the mud patch (accumulation area) within the erosion-dominated region adjacent to the mud belt. Our findings confirm that stratigraphic evolution, alongside hydrodynamic conditions and pollen provenance, governs pollen assemblages in deltaic/prodeltaic sediments. They can provide insights for palynological and pollen-based paleoclimatic and paleoecologic studies in other deltas.

Source identification of sedimentary organic carbon in coastal wetlands of the western Bohai Sea

Coastal wetlands play a vital role in mitigating climate change, yet the characteristics of buried organic carbon (OC) and carbon cycling are limited due to difficulties in assessing the composition of OC from different sources (allochthonous vs. autochthonous). In this study, we analyzed the total organic carbon (TOC) to total nitrogen (TN) ratio (C/N), stable carbon isotope (δ13C) composition, and n-alkane content to distinguish different sources of OC in the surface sediments of the coastal wetlands on the western coast of the Bohai Sea. The coupling of the C/N ratio with δ13C and n-alkane biomarkers has been proved to be an effective tool for revealing OC sources. The three end-member Bayesian mixing model based on coupling C/N ratios with δ13C showed that the sedimentary OC was dominated by the contribution of terrestrial particulate organic matter (POM), followed by freshwater algae and marine phytoplankton, with relative contributions of 47 ± 21 %, 41 ± 18 % and 12 ± 17 %, respectively. The relative contributions of terrestrial plants, aquatic macrophytes and marine phytoplankton assessed by n-alkanes were 56 ± 8 %, 35 ± 9 % and 9 ± 5 % in the study area, respectively. The relatively high salinity levels and strong hydrodynamic conditions of the Beidagang Reservoir led to higher terrestrial plants source and lower aquatic macrophytes source than these of Qilihai Reservoir based on the assessment of n-alkanes. Both methods showed that sedimentary OC was mainly derived from terrestrial sources (plant-dominated), suggesting that vegetation plays a crucial role in storing carbon in coastal wetlands, thus, the coastal vegetation management needs to be strengthened in the future. Our findings provide insights into the origins and dynamics of OC in coastal wetlands on the western coast of the Bohai Sea and a significant scientific basis for future monitoring of the blue carbon budget balance in coastal wetlands.

Identification of three stages of paleochannels and main source analysis beginning in the middle Pleistocene in the western Bohai sea in north China

Significant global sea transgressions–regressions have occurred under the influence of glacial–interglacial climatic change during the Quaternary period. Various types of paleochannels developed on the continental shelf of the western Bohai Sea as a result of sea level decline. Currently, the source of the paleochannels and the sedimentary environment and evolutionary pattern of the paleochannels are disputed. This study interprets high-resolution single-channel seismic data using a chronological framework based on accelerator mass spectrometry 14C (AMS14C) dating and optically stimulated luminescence (OSL) dating of core DZQ01. Furthermore, this research correlates this data with the cores of TJC-1 and H6 in the Western Bohai Sea and analyzes sedimentological characteristics based on grain size and clay mineral analyses. The results indicate that (1) three stages of paleochannels, namely Seismic Unit 6 (SU6), SU4, and SU2 are identified from bottom to top during Marine Isotope Stage 8 (MIS 8), MIS 6, and MIS 4, respectively; (2) from 300 to 243 cal. ka B.P., the SU6 paleochannel has four pathways, with the Yellow River serving as a primary source; from 191 to 130 cal ka B.P., the SU4 paleochannel has three pathways, and the main sources are the Yellow River, the Liao River, and the Luan River; from 74 to 14 cal. ka B.P., the SU2 paleochannels have two large tributaries, with the principal sources being the Yellow River and the Luan River. We, therefore, it can be inferred that the uplift of the Tibetan Plateau and glacial–interglacial climatic change constitute the formation mechanism for the paleochannels.

Observed current variations in the Bohai Sea in the winter of 2020/2021

Hydrodynamic conditions in the Bohai Sea (BS) play an important role in regulating variabilities in the regional climate and marine ecosystem. In the current study, wintertime current variations in the BS were investigated using continuous in situ observations at two sites in the western BS (S1) and southeastern BS (S2) from November/December 2020 to March 2021. The results indicated that residual currents and their variations were both stronger at S1 than at S2. Residual currents had notable vertical variations, with nearly opposite directions in the upper and lower layers. Upper layer residual currents were mostly southeastward at both sites, while lower layer residual currents were basically west-northwestward at S2 following the topography in the deep trough in the South BS but were north-northwestward at S1 up the slope to the coast. Upper layer residual currents were strongly subsurface-intensified and experienced significant intraseasonal variations. Subsurface currents in the upper layer shifted from being weak in December 2020 to strong in January–February 2021, especially in the western BS. Surface currents were directly driven by surface winds following the Ekman layer dynamics in shallow waters. Weak/strong subsurface currents occurred during/after sustained strong sea surface winds, implying that they experienced more complex dynamics than surface currents. This study provides new understanding to the wintertime circulation pattern in the BS. It is helpful for fully understanding the characteristics and underlying dynamics of the BS circulation variations in winter and their impacts on biogeochemical processes.

Increased discharge of Yellow River sediments into the western Bohai Sea since 0.71 Ma

AbstractThe Yellow River originates on the Tibetan Plateau and transports vast amounts of terrestrial sediment to the ocean. However, previous studies have not reached a consensus as to when and how the Yellow River first began to flow into the sea. Here we present Sr-Nd-Pb isotope data and a high-resolution clay mineral record of a 200-m-long sediment core recovered from the modern Yellow River delta. The changes in Sr-Nd-Pb isotopic compositions and clay minerals at 0.71 Ma suggest that a larger proportion of sediment was derived from the Yellow River after this time. We propose that the Yellow River has influenced the Bohai Sea since 1.9 Ma (or even earlier), which provides important evidence for an older Yellow River than 1.2 Ma. A significant increase in discharge of Yellow River sediments since 0.71 Ma is due to continuing subsidence of the eastern China coast, the large amplitude of Quaternary sea-level changes, and increased supply of eroded loess during the last 1.0 Ma. After this time, the contribution of local rivers surrounding the Bohai Sea became negligible due to dilution by the huge amounts of Yellow River sediments. These results provide improved constraints on the evolution of the Yellow River and subsequent land-sea fluxes.

Tar ball pollution under the influence of ocean circulation in the Bohai Sea, China

The deposition of tar balls of unknown sources on the coast poses a great threat to the fishery, tourism and coastal biodiversity in the Bohai Sea. This work aimed to identify the sources of tar balls by using oil fingerprint technique. Tar ball samples were collected from the seashore of two islands of the western Bohai Sea and divided into two groups (Group I and Group II). Principal component analysis showed that although Caofeidian oilfield was one of the closest oilfields to the sampling area it was not a source. Fingerprints of characteristic hopanes and steranes showed that samples of Group I were similar to the crude oils from the nearby Jidong oilfield, and samples of Group II were similar to the Penglai-19-3 crude oils. Combined with cross-plots of the samples and the reference oils, it indicated that Group I may come from Jidong and Group II may come from Penglai-19-3. The weathering characteristics of alkanes and polycyclic aromatic hydrocarbons showed that the samples were affected by natural weathering processes (e.g., evaporation, photooxidation and biodegradation). It revealed that oil pollution from the nearby oilfields can also affect other areas under the influence of ocean circulation. It is the first study on source identification of tar balls from the Bohai Sea and the effects of ocean circulation on the tar ball transport. This study can considerably help to further understand the evolution of tar balls and consequently determine their sources.

OSL and radiocarbon dating of a core from the Bohai Sea in China and implication for Late Quaternary transgression pattern

The Bohai Sea is a semi-enclosed continental shelf sea in northern China. Three transgression layers have been identified from the Late Quaternary strata in the western Bohai Sea and the coastal regions, which provide critical information on Late Quaternary sea-level fluctuations and landscape development. The three transgression layers were previously assigned to Marine Isotope Stage (MIS) 1 (transgression 1, T1), MIS 3 (T2) and MIS 5 (T3), respectively, mainly based on 14C dating. However, this chronological framework aroused an enigma that the regional sea level in MIS 3 was even higher than that of MIS 5, conflicting with the context of global sea-level pattern. In order to clarify this issue, here quartz optically stimulated luminescence (OSL) dating (four samples) was used to constrain the T2 chronology of borehole TJC-1 from the western Bohai Sea. Radiocarbon samples (eight) of peaty sediments were also measured for reference and comparison. All the four OSL samples showed saturation ages of >80 ka, suggesting that the T2 layer should have formed at least in MIS 5, instead of in MIS 3. Radiocarbon ages in T2 should have been severely underestimated, with a saturation age range of 22–30 cal ka BP, similar to all the previous published radiocarbon ages. The renewed OSL chronological framework for Late Quaternary transgressions in the western Bohai Sea is in better compliance with the history of global sea-level change.

Numerical Modeling of a Green Tide Migration Process with Multiple Artificial Structures in the Western Bohai Sea, China

Green tides have increasingly become a nuisance worldwide in recent years, and especially in China. Since 2015, green tides have started recurring in Jinmeng Bay, Qinhuangdao, western Bohai Sea of China, and have severely deteriorated the tourism environment there. In order to investigate the migration process of the green tides in Jinmeng Bay, a hydrodynamic model and a particle-tracking model were applied based on the latest green tide event in August 2021. The hydrodynamic model was applied with triple-level 2DH meshes with different refinements and scales, which provided the hydrodynamics to drive the green macroalgae into the particle-tracking model. From the model results, the semi-enclosed waters surrounded by multiple artificial structures are a low-energy hydrodynamic environment, which is not helpful for water exchange and thus the dispersal of nutrients. The green macroalgae are distributed substantially within the semi-enclosed waters, and few are transported out with low biomass. The effects of wind and artificial structures both increase the coverage of the green macroalgae trajectories; the effect of wind plays a more important role. A sensitivity analysis of the effect of wind showed that 6 m/s wind in ENE led to the maximum coverage of the green macroalgae trajectories in the cases of different magnitudes and directions of winds. This study can provide references for the pre-warning and mitigation of green tides in Jinmeng Bay and other similar places.

Sensitivity Analysis of Offshore Sandstone Reservoir—A Case Study of an Oilfield in the Western Bohai Sea

X oilfield is located in the Western Bohai Sea. During the water injection development process, the oil well productivity continued to decline. The effect of water injection and oil increase is poor. This time, by analyzing the sensitivity of the reservoir, the damage mode of the reservoir is analyzed, the reasons for the poor water injection effect are obtained, because of strong water sensitivity, medium to strong stress sensitivity, and the corresponding measures and suggestions are put forward, such as greater than 4500 mg/l of the salinity of injected water, timely supplement formation energy. Provide basis for the development of similar oil fields.

Stratigraphic and three-dimensional morphological evolution of the late Quaternary sequences in the western Bohai Sea, China: Controls related to eustasy, high sediment supplies and neotectonics

The Bohai Sea is a shallow, semi-closed gulf (basin) at the proximal position of the very wide (one to several thousand kilometers) eastern Chinese margin and was persistently impacted by tectonic frameworks. Its late Quaternary stratigraphy provides an excellent natural laboratory for research on the sedimentary processes and evolutionary patterns on flat proximal continental margins with high sediment inputs and how these processes respond to synsedimentary tectonic activity. However, due to the scarcity of comprehensive sequence stratigraphic studies, our understanding of the above processes is limited. Here, we conducted a high-resolution sequence stratigraphic study using boomer seismic data with pseudo-3D coverage. The seismic data revealed seven seismic units (SUs A-G) within the late Quaternary stratigraphy, including (1) three marine prodeltaic units (SUs A, C, G) characterized by dipping/oblique internal reflections and/or lobate structures, (2) two terrestrial (fluvial/lacustrine) units (SUs B and E) dominated by heterogeneous reflections, (3) an erosional remnant unit (SUs D) with semitransparent reflectors and a lenticular geometry, and (4) a ravinement-attributed aggradational unit (SU F). Based on the extrapolation between the seismic stratigraphy and the onshore sedimentary architecture and well-established sequence stratigraphic models, our preferential interpretation for the four sets of SUs is that they correspond to the highstand, lowstand, falling-stage and transgressive system tracts, respectively. The seismic geomorphology suggests that the bulk of the accommodation is dominated by the former two, which is consistent with the alternative terrestrial-and-marine succession revealed by previous borehole studies. At such a proximal gulf, although the accumulation of thick highstand units is not surprising, the two thick lowstand units that are bounded above and below by two different subaerial unconformities are exceptional. Our interpretation indicates that abnormally thick accumulation occurred under subaerial environments during the lowstand period, which most likely corresponds to alluvial/floodplain progradation/aggradation given the western Bohai Sea is connected to the alluvial North China Plain. The lower subaerial unconformities of the lowstand units are associated with intensive subaerial (most likely fluvial) excavation. Erosion under SU E leads to the formation of incised and eroded areas that can be tens of kilometers wide and tens of meters deep, cutting into SU A or even into SU B, which are several times greater than the last glacial maximum incised valley at the top of SU E. Such intensive erosion appears to be a crucial contributor to the thick lowstand units, as it created more accommodation. The great scale of the subaerial incisions is presumably attributed to the fact that the bulk of them evolved from tectonically triggered depressions because their locations are consistent with the NE-SW- and NW-SE-striking fault populations. The tectonic forces also controlled the accumulation by resulting in high-relief basement blocks for the pre-Holocene sedimentation. However, despite such strong tectonic controls, the subsequent deposition filled and leveled the areas between the high-relief, steep-sided basement blocks and eventually resulted in a relatively flat substratum for post-LGM deposition, suggesting that the geomorphic threshold for geological control at such a proximal gulf was passed because of the high-supply environment.

Magnetic fingerprints of surface sediment in the Bohai Sea, China

The understanding of the surrounding river impacts on the sediment supply to the Bohai Sea, northern China, is insufficient. In this study, magnetic measurements on surface sediment from the Bohai Sea and surrounding rivers were performed to interpret the distribution and origin of sediment in the Bohai Sea. Different magnetic properties in the analyzed material correspond to seven provenance areas. The magnetic mineral content decreases gradually toward the central Bohai Sea from its marginal areas. Sediment in the central and northern parts contains higher concentrations of finer magnetic minerals than the southern Bohai Sea. The western Bohai Sea (western Bohai and Liaodong bays) has high contents of magnetic minerals because its provenance areas contain abundant old metamorphic rocks with magnetite. The Yellow River, with the most elevated sediment flux, contributes with fine, high-corercivity magnetic minerals (e.g., hematite) to the southern Bohai Sea (mainly in the northwestern Laizhou Bay). Some local rivers (e.g., Fuzhou River) are also important contributors to the coastal waters, due to the magnetic similarities. Sediment from the north Yellow Sea is magnetically similar to the Yellow River detritus. The results highlight the use of the rapid magnetic method in provenance tracing.

Effect of Wave, Current, and Lutocline on Sediment Resuspension in Yellow River Delta-Front

Historically, the Yellow River in China discharges > 1 × 109 ton/yr sediment to the sea, and has formed a large delta in the western Bohai Sea. Its river mouth is characterized by an extremely high suspended sediment concentration (SSC), up to 50 g/L. However, the hydrodynamic factors controlling the high suspended sediments in the Yellow River estuary are not well understood. Here, we conducted two hydrodynamic observations and SSC measurements in the winter and spring low-flow seasons of 2014–2015 and 2016–2017 under five sea conditions, including calm-rippled, smooth-wavelet, slight, moderate, and rough, in the Yellow River Delta-front during the observation period. Under calm-rippled conditions, the contribution of currents to the total resuspended sediment concentration (RSC) was 77.7%–100.0%. During the smooth-wavelet and slight periods, the currents’ contribution decreased as low as 30% and 3.0% of the total RSC, respectively. Under moderate and rough-sea conditions, waves accounted for at least 70% and 85% of the total RSC, respectively. The results indicate that 20 cm-thick lutoclines were created after a significant increase in the wave height to a peak value followed by a decrease. When the SSC is over 3 g/L and hydrodynamic conditions could not break the lutoclines, the flocculent settling of suspended sediment changes to hindered settling in the Yellow River Delta. Under hindered settling, the settling velocity decreases, and the resuspended sediments remains in the lutoclines and their lower water layers. This study reveals different controlling factors for the high SSC near a river-influenced delta, and helps us get a better understanding of a delta’s resuspension and settling mechanisms.

Rapid consolidation characteristics of Yellow River-derived sediment: Geotechnical characterization and its implications for the deltaic geomorphic evolution

The Yellow River, which presently discharges into the western Bohai Sea, has been widely recognized as having one of the highest sediment loads on Earth. Understanding the consolidation characteristics of Yellow River-derived sediments is critical for improving our knowledge of the riverine sediment transport, depositional processes, and evolution of the Yellow River Delta morphology. In this study, we conducted in situ experiments from 2004 to 2008 at an abandoned subaqueous delta lobe (Diaokou lobe) in order to investigate the consolidation process of the sediments. Our results show that the initial consolidation of Yellow River-derived sediment is a rapid process when the excess pore-water pressure caused by sediment aggradation can completely dissipate in ~1500 min. The change in the physical and geotechnical properties during the consolidation endows the sediments with a certain shear strength. However, due to the hydrodynamic conditions, the distribution of the sediment strength is both temporally and spatially inhomogeneous. Furthermore, a hard layer can develop at the depths of 10–30 cm and the adjacent layer can become a potential sliding surface. This study offers some insight into the formation and evolution processes of the Yellow River Delta's sedimentary and geomorphic forms.

Seasonal variation of the principal tidal constituents in the Bohai Sea

Abstract. The seasonal variation of tides plays a significant role in water level changes in coastal regions. In this study, seasonal variations of four principal tidal constituents, M2, S2, K1, and O1, in the Bohai Sea, China, were studied by applying an enhanced harmonic analysis method to two time series: 1-year sea level observations at a mooring station (named E2) located in the western Bohai Sea and 17-year sea level observations at Dalian. At E2, the M2 amplitude and phase lag have annual frequencies, with large values in summer and small values in winter, while the frequencies of S2 and K1 amplitudes are also nearly annual. In contrast, the O1 amplitude increases constantly from winter to autumn. The maxima of phase lags appear twice in 1 year for S2, K1, and O1, taking place near winter and summer. The seasonal variation trends estimated by the enhanced harmonic analysis at Dalian are different from those at E2, except for the M2 phase lag. The M2 and S2 amplitudes show semi-annual and annual cycles, respectively, which are relatively significant at Dalian. The results of numerical experiments indicate that the seasonality of vertical eddy viscosity induces seasonal variations of the principal tidal constituents at E2. However, the tested mechanisms, including seasonally varying stratification, vertical eddy viscosity, and mean sea level, do not adequately explain the observed seasonal variations of tidal constituents at Dalian.

Vegetation history and environment changes since MIS 5 recorded by pollen assemblages in sediments from the western Bohai Sea, Northern China

Due to the lack of well-constrained chronology, the history of climate and vegetation associated with sea level changes during the late Quaternary has been poorly understood in the Bohai sea area. In this study, the upper 56.0 m-long sediment of the TJC-1 core in the western Bohai Sea was investigated using pollen and spore analyses, together with OSL, AMS 14C dating, grain size, and foraminifera data. The chronologically well -constrained core records show that varying pollen and spore assemblages reflect changes in vegetation on the adjacent land, climate and sediment settings since MIS 5 stage. Arboreal pollen dominated by Pinus and Quercus generally prevailed during the warm periods (MIS 5a, 5c, 5e, MIS 3 and MIS 1), corresponding to the sea level highstands, while dominance of terrestrial herbs such as Artemisia and Chenopodiaceae indicate presence of grasslands during cold periods such as MIS 4, MIS 5b and 5d when sea level dropped significantly. During the stadial periods such as MIS 5b and MIS 5d, herbaceous assemblages predominated in relatively cold conditions, in response to fluvial and coastal high energy sedimentary environments. The dominance of herbs especially Chenopodiaceae in the early-middle of MIS 5 and early Holocene was probably associated with huge amounts of sandy sediments input from the Yellow River caused by strong rainfall. Furthermore, pollen concentration is closely related to sediment grain size, arboreal pollen and fern spores are especially deposited in the fine sediment while herbaceous pollen dominates in coarser sediment.

A SCiForest based semi-supervised learning method for the seismic interpretation of channel sand-body

Machine learning technology has been widely applied in the field of seismic interpretation. In most cases, machine learning assisted seismic interpretation is calibrated or constrained by wells. However, due to the limitation of drilling cost, sometimes there are only a few samples can be obtained from the well-points for a specific layer, which is insufficient to guarantee the generalization ability of supervised learning. In this article, we propose a novelty semi-supervised method by combining the unsupervised isolation forest with split-selection criterion (SCiForest) algorithm and the supervised feature selection process together. The key of the proposed method is to be able to make full use of both the self-contained distribution information of multiple seismic attributes and the calibration information of limited well-points at the same time. To highlight the advantages of the proposed method referred to conventional supervised and unsupervised methods, we take the channel identification practice in the western Bohai Sea as a case study for comparison. Further discussion confirms that the proposed method can improve the visibility of channel effectively by fusing the relevant information in amplitude, frequency, and morphological attributes with limited calibration, which may provide a reliable alternative way for further machine learning assisted seismic interpretation.

Spatiotemporal variations in the summer hypoxia in the Bohai Sea (China) and controlling mechanisms

Based on field observations in the summer of 2006 and long-term series data, this paper investigates the spatiotemporal variations of hypoxia and associated physical-biogeochemical driving mechanisms in the Bohai Sea (BS), China. Results show that the benthic hypoxic zone is mainly distributed in the “V”-shaped trough region in the western BS, and it tends to form two hypoxic centers which generally correspond to the bottom cold-water core. The regional difference in the intensity of stratification has a significant impact on the spatial distribution of hypoxia. The relatively weak stratification and the mesoscale anticyclonic eddy in the central shoal of the BS weaken the connectivity between the southern and northern hypoxic zones. Organic matter decomposition contributes to hypoxia and results in corresponding nutrient pool with a “dual (southern and northern)-core” structure. Intensified eutrophication is the main drive for decreasing in bottom dissolved oxygen and expansion of hypoxic zone in the BS.

Identifying channel sand-body from multiple seismic attributes with an improved random forest algorithm

Machine learning provides numerous data-driven tools for automatic pattern recognition. Even though various algorithms such as neural networks and support vector machines have been widely applied, it is still necessary to explore new paradigms and algorithms to improve the machine learning assisted seismic interpretation. Random Forest (RF) is a widely used ensemble algorithm, however, only limited studies of random forest in the seismic application were published. In this article, the methodology of random forest is introduced systematically. Meanwhile, to solve the problem of hyper-parameter determination, we propose an improved algorithm named Pruning Random Forest (PRF). To reveal the advantages of PRF in terms of predictive performance, robustness, and feature selection compared with support vector machine, neural network, and decision tree, several well-designed experiments are executed based on the seismic data of the western Bohai Sea of China. The potential and advantages of random forest in the present case are confirmed by various experiments, which substantiates that the proposed pruning random forest algorithm provides a reliable alternative way for further machine learning assisted seismic interpretation.

Post-glacial sequence and sedimentation in the western Bohai Sea, China, and its linkage to global sea-level changes

Post-glacial sedimentary sequences provide a unique window for observing depositional and environmental responses to rapid changes in global climate and sea level. Here, we integrate seismic records and the lithological variations of sediment cores from western Bohai Bay, China, in order to reveal the history of sedimentation and its linkages to global sea-level changes since marine isotope stage 2 (MIS 2). The post-glacial succession consists of six seismic units (SU1–SU6, in descending order) which are bounded by six key reflection surfaces (T0, R1, R2, R3, T1 and T2), respectively corresponding to six depositional units (DU1–DU6) identified in sediment cores. Together they comprise the latest sequence of infilling of western Bohai Bay, where SU6 is associated with the Lowstand Systems Tract (LST), SU5 is associated with the Transgressive Systems Tract (TST), and the last four units of SU4–SU1 comprise the complex Highstand Systems Tract (HST). During the interval of the MIS 2 (22–11.6kyrBP) sea level lowstand, the LST was formed in a long-term environment of sub-aerial exposure or fluvial floodplain. The TST is composed of transgressive deposits formed during the interval of global sea-level rise, and is characterized by a retrogradational feature, from a swamp to a tidal flat environment, and then to an estuarine subtidal environment. A series of sedimentary facies transitions represent abrupt sea-level rises in the early Holocene, which may correspond to the events MWP-1C, “8.2-ka event” and MWP-2. Erosional trenches were well developed within SU5 in the central-eastern region, and were probably part of a transgressive waterway system rooted from Bohai Strait. They demonstrate that Bohai Bay experienced strong tidal erosion in the early Holocene, as a result of its morphology which consisted of a long narrow embayment. The complex HST was initially formed at ca. 7calkyrBP when sea-level essentially stabilized in a highstand, and developed rapidly after ca. 6calkyrBP when the Yellow River supplied large amounts of sediment to the western or southwestern margin of Bohai Bay. Its complex internal structure is related to the configuration of three flooding surfaces caused by changes in sediment supply, and which in historical times separated four stages of river discharge, mainly from the Yellow River. During ca. 7.0–3.4calkyrBP, the Yellow River at one time emptied into the southwestern margin of Bohai Bay, forcing its subaqueous delta to extend over the southern area of western Bohai Bay, while open shelf sedimentation in the central and northern area of Bohai Bay consisted of the accumulation of a shelly layer subject to intensive storm-reworking. During ca. 3.4–1calkyrBP, the Yellow River once discharged into the central and northern parts of western Bohai Bay, forming two detached subaqueous deltas. During ca. 1–0.8calkyrBP, the Yellow River discharged into the central region, stacking a subaqueous delta confined by the two older underlying subaqueous deltas. During the last ~800years, the discharge of the Yellow River out of Bohai Bay has dominated coastal marine sedimentation which has a complex provenance.

Circulations associated with cold pools in the Bohai Sea on the Chinese continental shelf

Circulations associated with cold pools in the Bohai Sea were investigated in the summers of 1959 and 2006 using observations and numerical simulations. The climatological forcing was incorporated to drive a model based on the Regional Ocean Modeling Systems (ROMS) to reconstruct the monthly evolution of flow structure. Cold pools were found to be separated into two parts by an undersea ridge in the central Bohai Sea. A set of numerical experiments were conducted to evaluate the relative contributions from the exchange across the strait, heat flux, wind, and tides. Baroclinic circulation was the dominant component of the circulation. A basin-scale cyclonic gyre was the main feature during the stratified seasons from May through August. Cyclonic and anticyclonic sub-basin scale gyres emerged in late spring and peaked during July and early August, accompanied by intensifying frontal jets along the west and south coasts of the Bohai Sea. The cyclonic frontal jet in the model was responsible for rapid reduction of particles released from the surface layer of the Bohai Sea in summer; and 2) Experiments using Lagrangian particle tracking also showed that particles released in Liaodong and Bohai bays were retained longer than those released in the other regions as the surface convergence in the western Bohai Sea resulted in an intense concentration of particles.