Sea-level Changes Research Articles

The deep-water, high-diversity Edgewood-Cathay brachiopod Fauna and its Hirnantian counterpart

The last phase of the end-Ordovician extinction event involved substantial sea-level changes. The Oslo/Asker District in Norway is a rare place where the deeper-water early Hirnantian fauna is succeeded by the equivalent deeper-water Edgewood-Cathay Fauna. Both faunas are highly diverse, with the same small-shelled brachiopods, Onniella, Leangella, and Eoplectodonta, dominating. They also share a large number of long-ranging and eurytopic genera. Taxa from contemporary shallower-water environments are rare. Near a third of the brachiopod genera in the Norwegian deeper-water early Hirnantian Fauna went extinct, including seven genera that survived into the Ordovician/Silurian boundary strata. Deeper-water early Hirnatian and Edgewood-Cathay collections are not well-known worldwide. Global quantitative samples from low latitudes, including the Norwegian samples, were compared against each other using NMDS (Non-metric Multidimensional Scaling) with the Bray-Curtis index. Qualitative samples used NMDS with the Raup-Crick index and Network Analysis. The Raup-Crick index sharply differentiated the early Hirnantian and Edgewood-Cathay faunas, possibly due to sensitivity to extinction and origination data. In contrast, the paleogeographic affinity between collections of the two faunas is pronounced using the Bray-Curtis index. Network Analysis also demonstrates regionality; the Edgewood-Cathay Fauna is especially heterogeneous. This contrasts with the shallower-water Hirnantia Fauna, which is more cosmopolitan. Quiet waters below the storm-wave base possibly hindered the spread of larvae, and anoxic plumes of water may have caused further barriers to the lateral spreading of the Edgewood-Cathay Fauna. As in Norway, long-ranging, eurytopic taxa were shared between the two faunas with few typical shallow-water taxa.

Sediment provenance variations driven by sea level in the eastern Arabian Sea since the MIS 9 period: Evidence from geochemical proxies

Although the uplift of the Tibetan Plateau has led to strong land-sea interactions, the characteristics of sediment transport and their controlling factors in typical marine areas in the northern Indian Ocean since the Quaternary are not clear. This work aimed to reconstruct the pattern of change in the sources of sediments since the Marine Isotope Stage 9 (MIS 9) period and to explore the mechanism of their response to changes in the marine environment in the Arabian Sea. To this end, a comprehensive multi-indicator study of the chronology and geochemical elements was carried out in core AS05-7 from the eastern Arabian Sea. Major trace element factor analysis and rare earth element (La/Yb)N-δEuN mapping suggested that sediments in the eastern Arabian Sea were mainly derived from terrestrial inputs from the Indus River and the Deccan Plateau. The sediments showed a clear glacial-interglacial cycle of change, with the contribution of the Indus River increasing during the interglacial period and that of the Deccan Plateau increasing during the glacial period. On average, the Indus River and Deccan Plateau contributed 71 % and 29 %, respectively, to the total amount of sediment. Indicators such as mass accumulation rate and Ca/Ti showed that the inputs from the terrestrial sources showed clear glacial-interglacial characteristics, with inputs during the glacial period being higher than those during the interglacial period. The lowering of the sea level during the glacial period led to an increase in the exposed area of the shelf, the shifting of deposition centers closer to the core, an increase in the rate of mass accumulation, and an increase in riverine inputs to the sea when clastic sediments from the Deccan Plateau increased. The elevation of the sea level during the interglacial period led to the inundation of the shelf, the shifting of deposition centers away from the core, a decrease in the rate of mass accumulation, and a reduction in riverine inputs to the sea when detrital sediments from the Deccan Plateau decreased. Changes in terrestrial inputs and sources revealed the orbital-scale control of sea-level change on sedimentary processes in the Arabian Sea and provided direct evidence for the “source-sink” model of sedimentation in the tropical Indian Ocean.

Inferring Global Ocean Mass Increase From Tide Gauges Network With Climate Models

AbstractOcean mass increase contributes to global sea level rise, and plays an important role in understanding climate change. Here, we develop a data assimilation approach that enables the inference of ocean mass increase from global tide gauge network. This approach incorporates outputs from climate models and sea level fingerprints caused by water mass changes over land areas. The results suggest a trend of 2.15 ± 0.72 mm/yr for ocean mass increase over the period 1993–2022, which closes the global sea level budget with estimates of thermosteric sea level rise. Furthermore, the inferred ocean mass increase offers an insight into the causes of sea level rise since 1950. These findings emphasize the significance of climate models, in addition to simulating sea level changes, they contribute to understanding causes of sea level rise over the past decades.

Integrative taxonomic analyses reveal that rapid genetic divergence drives Acropora speciation

Reef-building corals provide the structural basis for one of Earth's most spectacular and diverse but increasingly threatened ecosystems. The reef-building coral genus Acropora may have undergone substantial speciation during the Pleistocene climate and sea-level changes. Here, we aimed to evaluate the speciation history of four morphologically similar tabular Acropora species (Acropora aff. hyacinthus, A. cf. bifurcata, A. cf. cytherea, and A. cf. subulata) using an integrative approach with morphology, genetic, and reproduction methodology. Extensive morphological analyses showed that these four species are distinct and exhibited high gamete incompatibility, preventing hybridization. Furthermore, population structure and principal component analyses with SNPs (>60,000) indicated that these species were genetically distinct, and the ABBA-BABA test did not support introgression among these species. Many of their coding and noncoding RNA sequences showed high genetic variance at loci with high Fst values along the genome. Comparison of these orthologs with those of other Acropora species suggested that many of these genes are under positive selection, which could be associated with spawning time, gamete, and morphological divergence. Our findings show that the speciation of tabular Acropora occurred without hybridization, and the divergence accompanying the rapid evolution of genes in species-rich Acropora could be associated with speciation.

Late Albian-Cenomanian paleoenvironmental and paleoclimatic reconstructions in northeastern Gondwana: Palynological perceptions

The late Albian-Cenomanian (100.5–93.9 Ma) is considered a greenhouse world without permanent ice caps and with high eustatic sea levels. The high sea-level led to the flooding of low-lying coastal plains and the formation of extensive shallow shelf seas. Depositional conditions and ecosystems at these marginal and shallow shelf settings were affected by changes in environmental conditions, such as climate and vegetational ecosystems in surrounding regions. This study conducts palynomorph and palynofacies and lithofacies analysis of fifty-nine cutting samples from the North Qarun-1x well in the Gindi Basin (North Western Desert, Egypt) to assess the evolution of depositional and paleoenvironmental conditions as well as paleo-vegetation pattern in response to changes in climate and sea level. The sediment succession comprises the upper Albian to Cenomanian upper Kharita and Bahariya formations and Abu Roash G Member. Biostratigraphic analysis of palynomorph composition led to define seven interval zones of upper Albian-Cenomanian. At this time, Egypt was inundated by the southern margin of the Tethys Ocean, which led to the deposition of thick siliciclastic and carbonate facies in a marginal marine depositional environment. Statistical cluster analysis of particulate organic matter (POM) allowed three palynofacies assemblages (PFA-1 to PFA-3) to be recognized, indicating oscillating depositional conditions that shifted between fluvio-deltaic to marginal shallow marine, proximal, and distal inner neritic shelf environments. PFA-1 comprises the highest proportions of total phytoclasts, indicating fluvio-deltaic to marginal shallow marine conditions. PFA-2 is dominated by moderate abundances of AOM and phytoclasts, characterizing a proximal inner neritic shelf environment. PFA-3 consists of a slightly higher concentration of AOM compared to phytoclasts, indicating a distal inner neritic shelf environment with diminished terrestrial input and increased abundances of marine microplankton. Organic palynomorphs are abundant in mid-Cretaceous strata of northern Egypt. Abundant records of humidity indicators, mainly fern spores, along with other gymnosperms (mainly Taxodiaceae and Araucariaceae) compared to low aridity indicators of gnetalean Elaterates and Ephedroids along with non-gnetalean Classopollis suggest predominantly warm and humid conditions. Two intervals in the lower part of the Bahariya Formation and in the middle part of the Abu Roash G Member showed moderate to high abundances of aridity indicators and thus, warm arid to semi-arid climate events during the early and late Cenomanian.

Uncertainties in the Projection of Dynamic Sea Level in CMIP6 and FGOALS-g3 Large Ensemble

Abstract Decision-makers need reliable projections of future sea level change for risk assessment. Untangling the sources of uncertainty in sea level projections will help narrow the projection uncertainty. Here, we separate and quantify the contributions of internal variability, intermodel uncertainty, and scenario uncertainty to the ensemble spread of dynamic sea level (DSL) at both the basin and regional scales using Coupled Model Intercomparison Project phase 6 (CMIP6) and FGOALS-g3 large ensemble (LEN) data. For basin-mean DSL projections, intermodel uncertainty is the dominant contributor (>55%) in the near term (2021–40), midterm (2041–60), and long term (2081–2100) relative to the climatology of 1995–2014. Internal variability is of secondary importance in the near- and midterm until scenario uncertainty exceeds it in all basins except the Indian Ocean in the long term. For regional-scale DSL projections, internal variability is the dominant contributor (60%–100%) in the Pacific Ocean, Indian Ocean, and western boundary of the Atlantic Ocean, while intermodel uncertainty is more important in other regions in the near term. The contribution of internal variability (intermodel uncertainty) decreases (increases) in most regions from midterm to long term. Scenario uncertainty becomes important after emerging in the Southern, Pacific, and Atlantic Oceans. The signal-to-noise ratio (S/N) maps for regional DSL projections show that anthropogenic DSL signals can only emerge from a few regions. Assuming that model differences are eliminated, the perfect CMIP6 ensemble can capture more anthropogenic regional DSL signals in advance. These findings will help establish future constraints on DSL projections and further improve the next generation of climate models. Significance Statement Clarifying the sources of uncertainty in DSL projections is fundamental for further improving projections. Hence, this study aims to separate and quantify the three uncertainties in both basin and regional scale DSL projections using CMIP6 models and a 110-member large-ensemble experiment: internal variability, intermodel, and scenario uncertainty. We show that intermodel uncertainty is the dominant contributor at both the basin and regional scale, even though internal variability plays an important role in most regions of the Indian Ocean, Pacific Ocean, and Atlantic Ocean. Scenario uncertainty is negligible before it emerges at both the basin and regional scale in the long term. This provides the direction for constraining uncertainty in DSL projections.

Characteristics and Geological Conditions of Coastal Zone Quaternary Sediment Formations in The Binh -Tri -Thien Area under The Context of Global Sea Level Change

Quaternary sediments in the Binh Tri Thien coastal zone are diverse in both material composition and development history. From land to sea, there are 4 structural regions: i) marginal plain region; ii) Coastal lagoon region; iii) Coastal sand dunes region; and iv) Monocline coastal subsidence region. In the vertical direction, all four regions have five sedimentary cycles as follows: a) Early Pleistocene (Q11); b) Early middle Pleistocene (Q12a); c) Late middle Pleistocene (Q12b); d) Early late Pleistocene (Q13a); e) Late late Pleistocene (Q13b-Q2). Four structural zones are characterized by different lithofacies complexes: 1) In the lowstand systems tract (LST) at the beginning of each cycle in all 4 structural zones, the SmaLST facies complex is present; 2) In the transgressive systems tract (TST), there are the following lithofacies complexes: a) region I: MsbTST; b) region II: MlgTST; c) region III: SmTST; d) region IV: Msam,mTST; 3) In the highstand systems tract (HST) there are the following facies complexes: a) Region I: (MsabHST); b) Region II: MslgHST; c) Region III: SmvHST; d) Region IV: SmmHST. The difference in sedimentary facies in the transgressive and highstand systems tract depends on the differentiation of four geological structure regions.

Changes in Sea Level along the South China Sea Coast Based on the Homogenized Tide Gauge Data

To estimate the changes in the annual mean sea level (MSL) and extreme sea levels (ESLs), the largest collection of tide gauge records from 10 tidal stations along the northern coast of the South China Sea (SCS) were analyzed in this study. Here, all the tide gauge records had been homogenized by a two-step process involving the detection of inhomogeneities, that is, breakpoints caused by non-climatic changes and the application of the adjustment. The study’s conclusions, based on the homogenized tide gauge records, can be summarized as follows: The instrument change and station relocation are the main causes for the identified inhomogeneities. From 1989 to 2018, the sea level along the SCS was at an average rate of 4.0 mm per year, as measured by the homogenized tide gauges. The ESLs from the nine tidal stations rose notably with interannual fluctuations, except for the XSA station. Additionally, the ESLs exhibited substantial decadal variations. The ESLs rose along the northern coast of the SCS and were accelerated at most stations throughout the whole study period, especially after the 1980s. There were significant positive correlations between the ESL and the annual MSL at most tide gauges. The MSL’s changes, especially long-term changes, play an important role in the change in ESLs.

Island-based GNSS-IR network for tsunami detecting and warning

Deep-sea tsunami detection relies on Deep-ocean Assessment and Reporting of Tsunamis (DART), GNSS buoys, and cabled Ocean-Bottom Pressure (OBP) gauges, which are very expensive and difficult to maintain, and often suffer from vandalism or negligent damage. Here, we exploit the potential of establishing a less expensive and more robust island-based geodetic network for tsunami detecting, source reconstruction and warning. The network locates at the coastline of islands and uses a new technique: GNSS Interferometric Reflectometry (GNSS-IR). GNSS-IR retrieves sea levels from combination of the direct and reflected signals from the sea surface sent by satellites. To test the feasibility and efficiency of such a new geodetic network, we use the South China Sea region as an example, and compare its performance in reconciling the variable slip distribution on the Manila megathrust with the previously designed deep-sea monitoring system, i.e., DARTs and planned cable-based OBP gauges. We find that the newly designed GNSS-IR network could work equally well as the cabled OBP network in detecting tsunamis if the stations are built in strategically chosen locations. Combining GNSS-IR with a Kalman filter approach, we demonstrate that carefully situated coastal GNSS stations at global remote deep-ocean islands could function similarly to conventional tide gauges but with advantages of simultaneously measuring relative sea-level and land-height changes, meanwhile suffering lower risk from damaging sea-level events and potential vandalism.

Records of deep-sea turbidity current activity in the Bengal Fan since the Last Glacial Maximum

The long-term evolution of deep-sea turbidity current activity is closely related to climate and sea level changes; however, the impact of abrupt climate change (e.g. millennial-scale events in high northern latitudes) is poorly known. In this paper, deep-sea turbidite records in the western part of the lower Bengal Fan were identified since the Last Glacial Maximum (LGM) to investigate the effects of abrupt climate change on the development of the Earth's largest deep-sea fan. Our records show a termination of turbidite activity in the western lower fan at 16.6 ka–15.4 ka almost contemporaneous with Heinrich 1 event (a cooling stadial in high northern latitudes). The trigger of this termination in turbidite activity may have been a sharp decrease in erosion rates during a time of relatively stable sea level and rapid source-sink processes. The subsequent episodes of the Bolling/Allerod warm interstadial and Younger Dryas cold stadial and the rapid sea level rise event that followed possibly induced adjustment of turbidity current activities in the Bengal Fan, as indicated by other published records. In summary, we show that close links exist between abrupt climate changes in the high-latitude Northern Hemisphere and deep-sea turbidity current activity in the low-latitude South Asia.

Geochemical behavior of C, N, and S in sediments of Hangzhou Bay, Southeastern China: implications for the study of paleoclimate and sea-level changes

The correlation between the amount of organic carbon (OC) and sulfur (S) in sediments has been widely used as a paleosalinity indicator to distinguish between marine and freshwater environments. However, whether the ratio of total OC to total S (TOC/TS) can be used to identify unsteady or dynamic marine environments across sedimentary strata is still contended. An HZW1907 sediment core of 80 m in length was successfully collected in the middle of Hangzhou Bay (HZB), serving as one of the few boreholes that are crucial for the study of geologic and geo-environment changes in the coastal regions of eastern China since the Last Glacial Maximum (LGM). Total OC (TOC), stable carbon isotope, and TS of 82 subsamples from the HZW1907 core were analyzed to reconstruct the history of the shallow water biological pump and sulfur preservation record in the bay since the Late Pleistocene. Our results indicate that the samples had low concentrations of TOC (0.21%) and total nitrogen (TN) (0.02%), high mass ratio of TOC/TN (10.8), low δ13C (−24.9‰), low TS content (0.06%), and a high ratio of TOC/TS (9.1) from 33.6 ka BP to 12.3 ka BP, implying that freshwater organic matter (OM), algae, and C3 plant fragments were the main sources of OM in a relatively cold environment. The abundances of TOC, TN, and TS increased to 0.56%, 0.07%, and 0.4%, respectively, while δ13C (−23.9‰) increased and TOC/TS (2.7) decreased in the Holocene sediments, suggesting that seawater began to influence the composition of the sediments of HZB. Climate warming, which is likely to have impacted the results, was experienced from 12.3 ka BP. An OC isotope mixing model indicated that since the Mid-late Holocene, more than 70% of riverine OM accounted for the total OM. The TOC/TS ratio was identified as an effective indicator of seawater intrusion, with C/S ratios of 1–6 being considered to indicate a “sea–land transitional zone” sedimentary environment, a C/S >6 indicating freshwater, and a C/S<1 indicating normal marine facies. These findings provide crucial evidence for using TOC/TS to distinguish freshwater from marine environments and enhance our understanding of past climate changes. Therefore, these geochemical indicators can be used in conjunction with other sedimentary records to obtain accurate results about sedimentary evolution.

Assessment of Porites microatolls for paleothermometry: Calibration for French Polynesia

Massive dome-shaped coral Porites are the predominant choice for paleoclimate studies due to their consistent and reliable growth. When growing close to sea level, they become limited in their vertical growth and form so-called ‘microatolls’. Microatolls have not yet been extensively explored for paleoclimate reconstruction. Here, we investigate how reliable modern Porites microatolls are against empirical sea-surface temperature using Sr/Ca, δ18O, Li/Mg and SrU paleothermometry methods on samples from the Society Islands, French Polynesia. Our results show Sr/Ca ratios have the lowest Standard Error of the Inverse Prediction (SEIP) at 0.415 °C (N = 41) with a calibration of Sr/Ca (mmol mol−1) = −0.082 ± 0.006 SST (°C) + 11.256 ± 0.170 and with high reproducibility across multiple corals. The reproducibility of δ18O was less good, with SEIP increasing to 0.829 °C (N = 41). Considering methods directly from the literature, Li/Mg ratio empirically corrected for Sr/Ca had the best balance between bias and precision where no local calibration could be available. This study independently evaluates and confirms the suitability of Porites microatolls from well-flushed environments for paleoclimate studies. Fossil dome-shaped Porites grow anywhere between near-surface and roughly 20 m depths which inherently incorporates uncertainty into any sea surface temperature reconstruction. This uncertainty is significantly reduced for microatolls due to their well-constrained bathymetry. The study represents a fundamental step in paleoclimate research targeting consistently near the water-air interface bringing reliability and, especially when combined with their ability to reconstruct past sea-level changes, microatolls have the potential to be central for future paleoenvironmental studies.

Taraxerol abundance as a proxy for in situ mangrove sediment

Mangrove sediments are valuable archives of relative sea-level change if they can be distinguished in the stratigraphic record from other organic-rich depositional environments (e.g., freshwater swamps). Proxies for establishing environment of deposition can be poorly preserved (e.g., foraminifera) in mangrove sediment. Consequently, differentiating mangrove and freshwater sediment in the stratigraphic record is often subjective. We explore if biomarkers can objectively identify mangrove sediment with emphasis on their utility for reconstructing relative sea level. Our approach is specific to identifying in situ sediment, which has received less attention than identifying allochthonous mangrove organic matter. To characterize mangrove and non-mangrove (freshwater) environments, we measured n-alkane, sterol, and triterpenoid abundances in surface sediments at three sites in the Federated States of Micronesia. Elevated taraxerol abundance is diagnostic of sediment accumulating in mangroves and taraxerol is particularly abundant beneath monospecific stands of Rhizophora spp. Taraxerol was undetectable in freshwater sediment. Other triterpenoids are more abundant in mangrove sediment than in freshwater sediment. Using cores from Micronesian mangroves, we examine if biomarkers in sediments are indicative of in situ deposition in a mangrove, and have utility as a relative sea-level proxy. Taraxerol concentrations in cores are comparable to surface mangrove sediments, which indicates deposition in a mangrove. This interpretation is supported by pollen assemblages. Downcore taraxerol variability may reflect changing inputs from Rhizophora spp. rather than diagenesis. We propose that taraxerol is a proxy that differentiates between organic sediment that accumulated in mangrove vs. freshwater environments, lending it utility for reconstructing relative sea level.

Interactions between local glaciers and adjacent grounded Ross Sea ice in the Royal Society Range, Antarctica

The Antarctic Ice Sheet (AIS) has the potential to exert a major control on future global sea level. Here, we gain insight into the response of the Antarctic Ice Sheet (AIS) to changing climate through assessment of ice-sheet behavior during and since the Last Glacial Maximum (LGM) along the western coast of McMurdo Sound. We examine whether expansion of grounded ice in this sector of the Ross Embayment during the last glaciation was caused by increased flux from East Antarctic outlets and local glaciers or was produced by marine influences, such as lowered sea level or reduced melting of submarine grounded ice. During the LGM, grounded ice derived from the Ross Sea deposited a well-defined drift sheet along the Royal Society headlands on the western coast of McMurdo Sound. Twenty-six new radiocarbon dates of subfossil algae within this drift sheet suggest that the ice sheet was at its maximum extent by at least ∼18.4 ka and maintained this position for about five thousand years. Cross-cutting relationships show that local alpine glaciers did not contribute to the grounded ice but rather fluctuated asynchronously. This same relationship held true during the penultimate glaciation, dated to roughly 137–191 ka with 10Be exposure ages. An explanation for this out-of-phase relationship is that different mechanisms controlled their respective extents. Because they lack significant surface melting ablation zones, the local alpine glaciers, which largely terminate on land, were driven by changes in accumulation. These glaciers likely expanded during warmer times when accumulation was higher. In contrast, marine factors, such as global sea-level change and/or subglacial melting, controlled ice fluctuations in the Ross Embayment, including McMurdo Sound, leading to advance during the LGM.

Geomorphologic and infilling characteristics of the shelf-incising submarine canyon in the eastern Makran accretionary prism, offshore Pakistan

Seven shelf-incising submarine canyon systems are developed in the Makran accretionary prism, offshore Pakistan. This paper uses multibeam bathymetric data and multichannel seismic profiles to study the geomorphologic and infilling characteristics of E Canyon in the east of accretionary prism. The E Canyon extends nearly north–south from the upper slope to lower slope, the bottom of the canyon is located in 1000 to 3000 m water depth, the main axis extends about 55 km, and the width varies from 5 to 9 km. The E Canyon shows U-shaped concave features in the northern cross-section view and V-shaped concave features in the southern cross-section view. Two continuous erosion pools are developed at the fifth and third ridges of the southern segment, respectively. The steepest sidewall (with slopes of 25.75° and 40.47°) of E Canyon was found near the third ridge. The filling sequence of coarse channel lags, slump debris flows, stacked channel sands and mass transported deposits and turbidite deposits from bottom to top is developed in the northern segment of the canyon. Strong erosion is developed in the southern part of the canyon and there is no sedimentation inside. On the abyssal plain, the continuation of the E Canyon is clearly erosive. Our preliminary analysis shows that the factors controlling the evolution of E Canyon may include sediment gravity flow, tectonic activity, sea-level change, climate and onshore rivers activity. The correlation between evolution of E Canyon and gas hydrates was explored, and it is believed that the erosion of E Canyon plays a destructive role in hydrate accumulation. At the same time, the destruction of hydrate-bearing layer induces the escape and leakage of hydrocarbon-bearing fluid, leading to the development of pockmark on the sidewalls of E Canyon. And the evolution model of gas hydrate accumulation in the development area of E Canyon was established.

Nodal modulation of M2 and N2 tides along the Norwegian coast

It is crucial to assess the nodal modulation for tides in high-latitude coast areas within the context of global warming. In this paper, five stations (Maloy, Rorvik, Andenes, Vardo, and Honningsvag) along the Norwegian coast are selected to analyze the nodal modulation using the S_TIDE toolbox, which is developed from the enhanced harmonic analysis method. Three criterions are proposed to determine the optimal number of independent points (IPs), a parameter in S_TIDE toolbox, and the decision steps are elaborated in detail. The optimal number of IPs is evaluated by comparing the primary and the hindcasts tidal amplitudes. The amplitudes of 18.61-year cycle and 4.42-year cycle show noticeable temporal and spatial variations, which can be attributed to the changes of sea levels, local topography, and the active and robust mesoscale activity in the Norwegian Sea. Moreover, the temporal and spatial variations in nodal modulation are quantitatively demonstrated at the Rorvik and Vardo stations, highlighting the importance of nodal modulation in assessing tides over interdecadal periods.

Reservoir identification of marine facies carbonate shoals in the Middle Permian in the Sichuan Basin

Controlled by the base level change cycle, the carbonates exposed from the periodically shallowed water body at the top of the high-frequency sequence develops multiple sets of thin reservoirs. Such reservoir identification has always been tricky in the prediction of carbonate reservoirs. Based on the Middle Permian strata from the Sichuan Basin, this paper established a forecasting approach of high-frequency-sequence-controlled carbonate thin reservoir. The steps are as follows: (1) Combine the measured results of samples from the typical outcrops with changes of carbon and oxygen isotopes, thus to construct a division program for the 3rd-order sequence of the Middle Permian strata. (2) Compare the carbon and oxygen isotope changes and the global sea level change trend, determine the controlling factors of the 3rd-order sequences. (3) Carry out spectrum analysis based on the natural gamma energy spectrum logging (ln (Th/K)) curves of Wells Long-17 and Anping-1 to establish a high-frequency sequence framework division program, and then apply the logging curve characteristics to correct the top interface positions of the high-frequency sequences, which is the potential location of carbonate reservoir. The research results suggest that the Middle Permian in the Sichuan Basin can be divided into three 3rd-order sequences, which are PSQ1, PSQ2 and PSQ3 from bottom to top. Among which, PSQ1 is mainly affected by global sea level (GSL) changes, and the changes originated from its tuning curve can be directly applied to the division of high-frequency sequences and reservoir prediction. PSQ2 and PSQ3 are jointly controlled by global sea level changes and regional tectonics. In cope with the influence of regional tectonics, the positions of the four-level sequence interface established according to the tuning curve need to be fully considered, and good results were achieved through systematical correction. This method can effectively reduce the risk of reservoir prediction caused by marine carbonate heterogeneity, and provide scientific foundation for the prediction of high-frequency cyclic reservoirs of platform facies and platform margin subfacies in other marine carbonate sedimentary basins.

Phylogeographic History of Endangered Hokuriku Salamander, Hynobius takedai (Amphibia: Caudata).

Knowledge of the phylogeographic history of organisms is valuable for understanding their evolutionary processes. To the best of our knowledge, the phylogeographic structure of Hokuriku salamander, Hynobius takedai, an endangered species, remains unclear. This study aimed to elucidate the phylogeographic history of H. takedai, which is expected to be strongly influenced by paleogeographic events. Phylogenetic analysis based on partial sequences of the mitochondrial DNA cytochrome b gene confirmed the genetic independence of H. takedai, and the divergence time with closely related species was estimated to be from the Late Pliocene to the Early Pleistocene. In the phylogenetic tree, two clades were identified within H. takedai, and their haplotypes were found in samples collected from the west and east of the distribution range. These intraspecific divergences were strongly influenced by geohistorical subdivisions of the current major distribution areas in the Middle Pleistocene. One clade was further subdivided and its formation may have been influenced by sea level changes in the Late Pleistocene.

The Role of Anthropogenic Forcings on Historical Sea‐Level Change in the Indo‐Pacific Warm Pool Region

AbstractDetecting and attributing sea‐level rise over different spatiotemporal scales is essential for low‐lying and highly populated coastal regions. Using the Detection and Attribution Model Intercomparison Project (DAMIP) from the Coupled Model Intercomparison Project Phase 6, we evaluate the role of anthropogenic forcing in sea‐level change in the historical (1950–2014) period in the Indo‐Pacific warm pool region. We use three models that have at least 10 ensemble members, corresponding to different DAMIP simulations. We determined the changes in regional sea level from both natural and anthropogenic forcings. Our results demonstrate: (a) the emergence of an anthropogenic footprint on regional sterodynamic sea‐level change has a large spatiotemporal diversity over the Indo‐Pacific warm pool region with the earliest emergence in the western Indian Ocean; (b) a significant rise in dynamic sea level (DSL) (up to 25 mm) and thermosteric (up to 40 mm) sea level over the western Indian Ocean due to greenhouse gas forcing; (c) a positive Indian Ocean Dipole‐like pattern in the DSL changes over the tropical Indian Ocean; (d) a significant increase in the halosteric contribution to sea‐level rise in the Indo‐Pacific warm pool region, and (e) a pronounced rise of manometric sea level (up to 20 mm) over shallow oceans and coastal regions in recent decades. These results provide a comprehensive spatiotemporal analysis of the attribution of anthropogenic factors to sea‐level changes in the Indo‐Pacific warm pool region.

Comparative analysis of PCS and ICA on trend estimation of sea-level change from tide gauge observations

Comparative analysis of PCS and ICA on trend estimation of sea-level change from tide gauge observations