Western Pacific Research Articles

New species and genus of Columbellidae (Gastropoda: Buccinoidea) from the Western Pacific

Ten new species and one new genus of Columbellidae from several Pacific Islands are introduced as new to science. The following species originating from Saipan, Northern Marianas are described: Ascalista saipanensis sp. nov., Mitrella harryleei sp. nov., Mitropsis noduliferus sp. nov., Retizafra praefulgida sp. nov. and Zafra spadicea sp. nov. Euspiralta okinawaensis sp. nov. originates from Okinawa, Japan. Zafra fijiensis sp. nov. originates from Fiji. From Wake Atoll the species Mokumea gracilicostata sp. nov., Speirazafra wakensis gen. nov. et sp. nov. and Zafra thaanumi sp. nov..

Harnessing the power of mobile and messaging apps for risk communication and intervention during the COVID-19 pandemic: lessons from the Western Pacific.

The spread of mis- and disinformation on mobile and messaging apps during the COVID-19 pandemic not only fuelled anxieties and mistrust in health authorities but also undermined the effectiveness of the overall public health response. Mobile and messaging apps help users stay informed and connected to their families, friends, colleagues and communities. However, during the COVID-19 pandemic, these apps were also one of the primary channels where mis- and disinformation were circulated. Recognizing the importance of including mobile and messaging apps in risk communication and emergency response strategies, the World Health Organization (WHO) and some countries in the WHO Western Pacific Region independently piloted initiatives to reach messaging app users, meet their evolving information needs, and streamline health ministry communication. The enhanced use of mobile and messaging apps enabled consistent and timely communication and improved coordination during the COVID-19 pandemic. Leveraging their features also helped identify and potentially fill crucial information gaps, mitigating the harms of mis- and disinformation and fostering stronger trust in health authorities. The findings from the work carried out by WHO and countries in the Western Pacific Region identified some promising innovative communication interventions using mobile and messaging apps. While these interventions should be further explored and evaluated, they have demonstrated that interventions need to be proactive, flexible, and able to adapt to changes in mis- and disinformation content being shared through messaging apps.

Современные российско-филиппинские отношения: вызовы и возможности

This article is devoted to the main areas of cooperation between Russia and the Philippines in the present.It discusses the prerequisites for the development of bilateral relations along with the results of interaction in the spheres of interstate relations, economy, security, culture over the past decade and a half. The article also examines the problematic aspects of bilateral relations, reflects the impact of the American factor on the nature of Russian Philippine interaction, primarily in the context of strengthening of the US military and political presence in the Western Pacific and the involvement of the Philippines in the policy of containing China. The paper presents proposals and arguments regarding the rapprochement between Russia and the Philippines, indicating the reasons that may affect the establishment of stable relations between the two countries. The methodological basis of the work is the analysis ofthe research findings of both Russian and international scholars, as well as materials and documents that are available on the topic of research.

The relative contributions of internal variability and external forcing to Pacific Walker Circulation over the last millennium

Abstract Pacific Walker Circulation (PWC) is an important component of tropical atmospheric circulation. Current studies have mainly focused on PWC changes over recent decades and the near future, while less effort has been devoted to long-term PWC variations. In this study, we investigate PWC changes over the last millennium (LM) based on the Community Earth System Model Last Millennium Ensemble (CESM-LME). The simulated PWC variations show no significant trend but do reveal decadal fluctuations during the LM, which underestimate the strengthened LIA-MCA PWC differences indicated by proxy-based reconstructions. A quantitative estimation of the contributions made to PWC variability from internal variability and external forcing is conducted by using multiple linear regression (MLR) analysis. The internal variabilities contribute approximately 80% to the changes of PWC during the LM, among which the Interdecadal Pacific Oscillation (IPO) has the largest contribution. In the positive phase of the IPO, the Indo-Pacific sea-level pressure (SLP) gradient decreases, and anomalous westerlies occur in the tropical western Pacific, corresponding to a weakened PWC. The relationships between the IPO and PWC show multidecadal to centennial fluctuations, suggesting that other internal modes or external forcings may have modulated the IPO-PWC relationship. Volcanic forcing is also an important contributor to PWC variability during the LM. The simulated PWC significantly weakens and lasts for 1-2 years after large volcanic eruptions. The El Niño-like SST pattern and the corresponding zonal SLP gradient lead to the PWC weakening following large volcanic eruptions.

Variation in the Local Grey Mullet Populations (Mugil cephalus) on the Western Pacific Fringe

Background: Understanding population genetic structures is crucial for planning and implementing conservation programmes to preserve species’ adaptive and evolutionary potential and thus ensure their long-term persistence. The grey mullet (Mugil cephalus) is a globally distributed coastal fish. Its populations in waters surrounding Taiwan on the western Pacific fringe are divided into at least two stocks (migratory and residential), but questions remain regarding their genetic divergence and gene flow. Methods and Results: To cast more light on this, allozyme variations at 21 presumptive gene loci of 1217 adult grey mullets from 15 localities in Japan, Taiwan and mainland China, and four gene loci from 1470 juveniles from three localities in Taiwan were used to investigate patterns of genetic variation. The mean expected heterozygosity (He) was 0.128—ranging from 0.031 (Matsu) to 0.442 (Kaoping)—and the mean observed heterozygosity (Ho) was 0.086—ranging from 0.017 (Kaohsiung) to 0.215 (Kaoping). Both AMOVA and the high overall mean FST of 0.252 indicated enormous genetic differentiation among populations and the positive mean value of FIS was 0.328, indicating a deficiency of heterozygotes. PCoA indicated that the samples of M. cephalus could be split into three groups and STRUCTURE analysis showed that all individuals were grouped into three genetic clusters. The results of mutation-drift equilibrium tests did not suggest that the populations experienced any recent genetic bottleneck. The results from all localities in the present investigation showed significant change in the GPI-A genotype frequencies with latitudes—e.g., increases in GPI-A*135/135 homozygote frequencies and GPI-A*100/100 frequencies were highly correlated with latitudinal cline. All migratory populations with the GPI-A genotype were almost exclusively the GPI-A*100/100 homozygote. During the life history of M. cephalus, the GPI-A*100/135 heterozygote frequency significantly decreases with age. Conclusions: Based on these data, we suggest that each GPI-A genotype represents trait combinations of higher fitness in some portions of the environment. Furthermore, the genotypic frequencies change in accordance with life stages, suggesting that selection occurs throughout the life span.

Evaluation of five global AI models for predicting weather in Eastern Asia and Western Pacific

Recent development of artificial intelligence (AI) technology has resulted in the fruition of machine learning-based weather prediction (MLWP) systems. Five prominent global MLWP model, Pangu-Weather, FourCastNet v2 (FCN2), GraphCast, FuXi, and FengWu, emerged. This study conducts a homogeneous comparison of these models utilizing identical initial conditions from ERA5. The performance is evaluated in the Eastern Asia and Western Pacific from June to November 2023. The evaluation comprises Root Mean Square Error and Anomaly Correlation Coefficients within the designated region, typhoon track and intensity predictions, and a case study for Typhoon Haikui. Results indicate that FengWu emerges as the best-performing model, followed by FuXi and GraphCast, with FCN2 and Pangu-Weather ranking lower. A multi-model ensemble, constructed by averaging predictions from the five models, demonstrates superior performance, rivaling that of FengWu. For the 11 typhoons in 2023, FengWu demonstrates the most accurate track prediction; however, it also has the largest intensity errors.

The role of family doctors in developing primary care systems in Asia: a systematic review of qualitative research conducted in middle-income countries 2010-2020.

The Asia Pacific Region's middle-income countries (MICs) face unique challenges in the ongoing development of primary care (PC) systems. This development is complicated by systemic factors, including rapid policy changes and the introduction of private healthcare services, as well as the mounting challenges associated with ageing populations and increasing rates of chronic diseases. Despite the widespread acknowledgement of the importance of family doctors in the development of PC services, relatively little is known about how these roles have developed in Asian MICs. To address this gap, this systematic review presents a synthesis of recent research focused on the role of family doctors within the PC systems of MICs in the Asia Pacific Region. We searched six electronic databases (CINAHL Complete, Embase, PsycINFO, PubMed, Web of Science, and Index Medicus for the South-East Asia Region and Western Pacific) for peer-reviewed qualitative literature published between January 2010 and December 2020. The quality of the studies was evaluated using the Critical Appraisal Skills Programme tool. Eighteen articles were included in the analysis. Findings from these articles were extracted and synthesised using qualitative thematic synthesis. We used the Rainbow Framework to analyse the interconnections within health systems at the macro, meso and micro levels. Our analysis of the included articles showed that family doctors play a crucial role in bridging the gap between hospitals and communities. They are essential in adopting holistic approaches to health and wellbeing and are in a unique position to try and address social, psychological, and biological aspects of health. Our findings also highlight the influence of policy changes at the macro level on the role and responsibilities of family doctors at the meso (organisational) and micro (interpersonal) levels. Limited research has explored the role of family doctors in the ongoing development of primary care systems in MICs in the Asia Pacific Region. The findings of this review have significant implications for policymakers and healthcare administrators involved in ongoing improvements to and strengthening of PC systems. Areas of particular concern relate to policy linked with training and workforce development, insurance systems and public awareness of what primary care services are.

Miocene Petit-Spot Basanitic Volcanoes on Cretaceous Alba Guyot (Magellan Seamount Trail, Pacific Ocean)

New data obtained from core samples of two boreholes and dredged samples from the Alba Guyot in the Magellan Seamount Trail (MST), Western Pacific, including the 40Ar/39Ar age determinations of basanite, and the mineralogy of basanite, tuff, tuffite, mantle-derived inclusions in basanite and tuff (lherzolite xenolith and Ol, Cpx, and Opx xenocrysts), and calcareous nannofossil biostratigraphy, have implications for the guyot′s development and history. Volcanic units in the upper part of the Alba Guyot main edifice and its Oma Vlinder satellite, at sea depths between 3600 and 2200 m, were deposited during the Cretaceous 112 to 86 Ma interval. In the following ~60 myr, the Alba Guyot became partly submerged and denuded with the formation of a flat summit platform while the respective fragment of the Pacific Plate was moving to the Northern Hemisphere. Volcanic activity in the northeastern part of the guyot summit platform was rejuvenated in the Miocene (24–15 Ma) and produced onshore basanitic volcanoes and layers of tuff in subaerial and tuffite in shallow-water near-shore conditions. In the Middle-Late Miocene (10–6 Ma), after the guyot had submerged, carbonates containing calcareous nannofossils were deposited on the porous surfaces of tuff and tuffite. Precipitation of the Fe-Mn crust (Unit III) recommenced during the Pliocene–Pleistocene (<1.8 Ma) when the guyot summit reached favorable sea depths. The location of the MST guyots in the northwestern segment of the Pacific Plate near the Mariana Trench, along with the Miocene age and alkali-basaltic signatures of basanite, provide first evidence for petit-spot volcanism on the Alba Guyot. This inference agrees with the geochemistry of Cenozoic petit-spot basaltic rocks from the Pacific and Miocene basanite on the Alba Guyot. Petit-spot volcanics presumably originated from alkali-basaltic melts produced by decompression partial melting of carbonatized peridotite in the metasomatized oceanic lithosphere at the Lithosphere–Asthenosphere Boundary level. The numerous volcanic cones with elevations of up to 750 m high and 5.1 km in basal diameter, discovered on the Alba summit platform, provide the first evidence of voluminous Miocene petit-spot basanitic volcanism upon the Cretaceous guyots and seamounts of the Pacific.

Thermochemistry of the Mantle Transition Zone Beneath the Western Pacific

AbstractThe Earth's mantle transition zone has significant control on material flux between upper and lower mantle, thus constraining its properties is imperative to understand dynamic processes and circulation patterns. Global seismic data sets to study the transition zone typically display highly uneven spatial distribution. Therefore, complementary geometries are essential to improve knowledge of physical structures, thermochemistry, and impact on convection. Here, we present a new automated approach utilizing machine learning to analyze large seismic data sets, and derive high‐resolution maps of transition zone discontinuity properties. Seismic measurements from ScSScS precursors are integrated with mineralogical modeling to constrain thermochemistry of the western Pacific subduction zone. Our models map recent subduction patterns through the transition zone, indicating stagnation of slabs and accumulation of basalt at its base, and interaction between stagnant slabs and plumes. These results suggest that the thermochemical properties of upper mantle discontinuities can provide high‐resolution images of mantle circulation patterns.

Photophysiological status of phytoplankton communities in different types of eddies during winter in the western Pacific Ocean

The Western Pacific Ocean (WPO) is one of the most active eddy regions in the world, where a variety of ocean processes are frequently observed, but little research has been conducted on the phytoplankton communities and their photosynthetic physiological status within the eddies in this region. The bio-optical parameters of phytoplankton communities and their physiological status within the warm core and cold core eddies of the WPO during the winter of 2021 were investigated based on fast repetition rate fluorometry (FRRF). In this paper, environmental factors, phytoplankton community parameters, chlorophyll a (Chl a), and various bio-optical parameters were investigated for two opposite types of eddies at the WPO. The results show the maximum [Fv/Fm, 0.18 to 0.26 (warm eddy), 0.14 to 0.28 (cold eddy)] and effective photosynthetic efficiency [Fq'/Fm', 0.11 to 0.23 (warm eddy), 0.10 to 0.27 (cold eddy)] of the DCM for both warm and cold eddies, the electron transport rates ETRRCII [0.002–6.18 mol e− mol RCII−1 s−1 (warm eddy), 0.002–4.94 mol e− mol RCII−1 s−1 (cold eddy)] and the primary production potential PPmax [0.68–118.19 mg C (mg Chl a)−1 day−1 (warm eddy), 2.47–243.49 mg C (mg Chl a)−1 day−1 (cold eddy)] for different types eddies. In warm eddy, temperature and Chl a concentrations had significant effects on Fv/Fm and Fq'/Fm', while in cold eddy the correlation of Fv/Fm and Fq'/Fm' with temperature was not significant, and Fv/Fm was significantly negatively correlated with DIP only. Light was the main variable affecting the electron transport capacity and primary production potential of the phytoplankton community in the eddies, while larger cyanobacteria and dinoflagellates contributed significantly to the primary production potential of the cold eddy. In addition, both eddies centers had higher primary production potentials, with the cold eddy had a higher primary production potential than the warm eddy, based on microscopic analysis this phenomenon may be due to differences in electron transfer rates between phytoplankton communities.

Adolescent Suicides in the Western Pacific Region Have Become a More Serious Public Health Problem than in Other Regions

Adolescent Suicides in the Western Pacific Region Have Become a More Serious Public Health Problem than in Other Regions

Process-based evaluation of intraseasonal oceanic Kelvin waves in the Pacific Ocean in CMIP6 models

Abstract Oceanic intraseasonal Kelvin waves (KWs) help modulate upper-ocean thermal characteristics, providing feedbacks to important coupled air-sea phenomena in the tropics. The recent availability of daily thermocline depth fields from several CMIP6 models makes it possible to evaluate the performance of KWs and identify potential sources of bias. Most models fail to simulate a realistic spatial distribution of KW variability. Models simulate large variability of KWs in the western or eastern Pacific rather than in the central Pacific as observed. The modeled KWs propagate slowly (about 1.5 m/s) compared to observations (about 2.5 m/s). This slow propagation is also identified in wavenumber-frequency spectra for KWs and meridional KW structures, which is more consistent with a second baroclinic mode structure in models compared to the first baroclinic mode structure in observations. An analysis of the relative contributions of vertical wavenumber and background ocean stability to KW phase speeds indicates that the high vertical wavenumber bias in models contributes most to the slow propagation, in which the higher-than-observed vertical wavenumbers implying the biased incorporation of higher baroclinic modes in model KW structure. This finding is further supported by the results of vertical mode decomposition that incorporates background density profiles. These results indicate that a realistic representation of the KW vertical structure is essential to produce realistic KW propagations in models.

Heterogeneity of the East Asian rainfall influenced by solar-forced western Pacific subtropical high

The existence and causes of the recently observed rainfall heterogeneity over monsoonal east Asia in historical periods remain unclear. Here we show that such rainfall heterogeneity has been present at least in the last millennium, with decadal to centennial precipitation variations over southeast Asia and north China being broadly synchronous, while central to southwest China’s variations are generally out-of-phase with those in southeast Asia and north China. We propose that the western Pacific subtropical high, which reduces decadal to centennial precipitation over central to southwest China due to its anticyclonic feature, could be responsible for the observed rainfall heterogeneity over subtropical East Asia. Further analyses suggest that intensified decadal to centennial solar activity can lead to enhanced and northward and westward extension of the western Pacific subtropical high, resulting in tripolar rainfall heterogenous patterns over monsoonal East Asia.

A new discovery of cryptic species in barred sand burrower Limnichthys fasciatus (Pisces: Creediidae) from the western Pacific, with evolutionary perspectives of anti-equatorial species.

Although the barred sand burrower, Limnichthys fasciatus, is widely distributed throughout the western Pacific, including Japan, Taiwan, and Australia, its morphology and genetics are poorly known. We discovered four cryptic species of Limnichthys from the western Pacific based on mtDNA cytochrome c oxidase subunit I (COI) and 16S ribosomal RNA (rRNA) sequences. Genetic distances showed remarkably large differences (12.7%-24.3% in COI and 7.9%-19.6% in 16S rRNA) between true L. fasciatus (type locality: southeastern Australia) and the others. A relaxed clock model with optimized selected substitution models showed that their deep divergence began in the middle Miocene epoch and subsequently diverged into the current cryptic species in the Plio-Pleistocene. A eurythermal common ancestor may have evolved independently in each region due to geographical events and paleoclimatic fluctuations, which made it possible for L. fasciatus complex to be an anti-equatorial species. Despite their deep genetic divergence, they showed marked phenotypic similarity, suggesting that they have experienced similar selective pressures related to their specific behavior.

Air-sea CO2 exchange in the western Pacific influenced by monsoon and giant diatom (Ethmodiscus rex) blooms during the last deglaciation

The concentration of atmospheric CO2 increased rapidly during the last deglaciation due to CO2 outgassing from oceans. However, records of deglacial surface seawater pCO2-sw are sparse, hindering our understanding of the process and mechanism of air-sea CO2 exchange and its influence on glacial-interglacial climate change. Here we reconstructed surface seawater pCO2-sw for the last deglacial period using carbon isotope composition (δ13C) of giant diatom (Ethmodiscus rex) frustules from deep-sea sedimentary core collected in the Philippine Sea, western Pacific. Results showed that air-sea CO2 was fluctuating in the western Pacific during the last deglaciation. The gradients of air-sea CO2 are dominated by monsoon and biological productivity. The enhanced East Asian winter Monsoon and shallow thermocline during late Heinrich Stadial 1 maintained equilibrium in the air-sea CO2 exchange balance. During the Bølling period, enhanced East Asian Summer Monsoon has been observed to accelerate the dissolution of eolian-dust and promoted the growth of Ethmodiscus rex, which has been linked to increased primary productivity and, consequently, the uptake of atmospheric CO2 in the western Pacific. During the Allerød period, continued enhancement of EASM allowed the Philippine Sea to act as a weak CO2 source releasing CO2 to the atmosphere. During the Younger Dryas period, as the EASM weaken and the EAWM strengthen, ΔpCO2(sw-atm) decreased. Our findings highlight the tropical ocean’s role in deglacial air-sea CO2 exchange and provide insights into the monsoonal and biological drivers of the processes.

A Physics-Informed Auto-Learning Framework for Developing Stochastic Conceptual Models for ENSO Diversity

Abstract Understanding ENSO dynamics has tremendously improved over past decades. The ENSO diversity in spatial pattern, peak intensity, and temporal evolution is however still poorly represented in conceptual ENSO models. In this paper, a physics-informed auto-learning framework is applied to derive ENSO stochastic conceptual models with varying degrees of freedom. The framework is computationally efficient and easy to apply. Once the state vector of the target model is set, causal inference is exploited to build the right-hand side of the equations based on a mathematical function library. Fundamentally different from standard nonlinear regression, the auto-learning framework provides a parsimonious model by retaining only terms that improve the dynamical consistency with observations. It can also identify crucial latent variables and provide physical explanations. This methodology successfully reconstructs the equations of a realistic six-dimensional reference ENSO model based on the recharge oscillator theory from its data. A hierarchy of lower-dimensional models is derived and their representation of ENSO (including its diversity) systematically assessed. The minimum model that represents ENSO diversity is four-dimensional, with three interannual variables describing the western Pacific thermocline depth, the eastern and central Pacific sea surface temperatures (SSTs), and one intraseasonal variable for westerly wind events. Without the intraseasonal variable, the resulting three-dimensional model underestimates extreme events and is too regular. The limited number of weak nonlinearities in the model are essential in reproducing the observed extreme El Niño events and the observed nonlinear relationship between eastern and western Pacific SSTs.

MJO Diversity in CMIP6 Models

Abstract Recent studies have shown that individual Madden–Julian oscillation (MJO) events can be categorized into four types based on their propagation characteristics: standing, jumping, slow-propagating, and fast-propagating MJOs. While their structures and impacts are well documented in observations, their representation in state-of-the-art climate models has not been investigated. This study evaluates the four types of MJOs in phase 6 of Coupled Model Intercomparison Project (CMIP6) models. While most models show reasonable MJO propagation characteristics, their performance varies among MJO types, with better performance for the propagating MJO types. To identify the factors that drive each MJO type, background conditions at the surface, troposphere, and stratosphere are examined. We found that the standing and fast MJOs are closely associated with sea surface temperature (SST) and precipitable water (PW) distributions. Specifically, negative and positive SST and PW anomalies are observed over the equatorial Pacific during the standing and fast-propagating MJOs, respectively. In contrast, the jumping and slow-propagating MJOs do not show noticeable SST and PW distributions, suggesting that they may be more strongly influenced by the internal dynamics than by the background conditions. It is further found that the models with more frequent standing MJO than fast MJO generally have stronger negative biases in both SST and PW over the equatorial western Pacific. Although the standing MJO is also preferred when the stratospheric wind at 50 hPa is westerly, such a relationship is absent in the models. These results suggest that MJO diversity in climate models could be improved by better simulation of the mean state, especially for the standing and fast-propagating MJOs.

Characteristics of Water Vapor Transport during the “7·20” Extraordinary Heavy Rain Process in Zhengzhou City Simulated by the HYSPLIT Model

Water vapor transport is an important foundation and prerequisite for the occurrence of rainstorms. Consequently, the understanding of water vapor transport as well as the sources of water vapor during rainstorm processes should be considered as essential to study the formation mechanism of rainstorms. In this study, the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model is adopted for backward tracking of water vapor transport trajectories and sources during the “7·20” extraordinary heavy rain process in Zhengzhou City of China that occurred on 20 July 2021. On this basis, the trajectory clustering method is applied to quantitatively analyze the contributions of water vapor sources, aiming to provide a basis for exploring the maintenance mechanism of this extreme rainstorm event. The spatio-temporal characteristics of this rainstorm event show that there are 4 consecutive days with the precipitation reaching or exceeding the rainstorm level across the whole Zhengzhou City, with the daily rainfall amounts at eight national meteorological stations all breaking their respective historical extreme values. The regional-averaged rainfall amount in Zhengzhou City is 527.4 mm, while the maximum accumulated rainfall amount reaches 985.2 mm at Xinmi station and the maximum hourly rainfall amount at Zhengzhou national meteorological station reaches 201.9 mm h−1. The water vapor sources for this rainfall process, ranked in descending order of contribution, are the Western Pacific, inland areas of Northwest China and South China, and South China Sea. The water vapor at lower levels is mainly transported from the Western Pacific and the South China Sea, while those from the inland areas of Northwest China and South China provide a supply of water vapor at upper levels to a certain extent. The water vapor at 950 hPa is mainly sourced from the Western Pacific and South China Sea, accounting for 56% and 44%, respectively. The water vapor at 850 hPa mainly derives from the Western Pacific and the inland areas of South China, contributing 58% and 34% of the total, respectively. The water vapor at 700 hPa mainly comes from the inland areas of Northwest China and South China Sea. Specifically, the water vapor from inland Northwest China contributes 44% of the total, acting as the primary source. The water vapor at 500 hPa is mainly transported from the inland areas of South China and Northwest China, with that from the inland South China (56%) being more prominent. The water vapor at all levels is mainly transported to the rainstorm region through the eastern and southern regions of China from the source areas. Additionally, there are some differences in the water vapor trajectories at a 6 h interval.

Unusual cobalt behaviors and enrichment in cobalt-rich crust from the Magellan seamounts in the Western Pacific

Marine cobalt-rich (Co-rich) crusts are submarine critical metal resources with high economic value. In this study, detailed in-situ fine-scale morphological, mineralogical, and geochemical analyses were conducted on Co-rich crust from the Western Pacific. The Co-rich crust can be divided into three layers: (1) Layer 1 is the oldest anthracite layer and contacts with the substrate, showing a very dense laminated/columnar texture. Layer 1 can be further divided into two distinct sublayers: a lower black, massive, dense sublayer (Layer 1–1) and an upper black-to-brown sublayer (Layer 1–2). (2) Layer 2 is porous and locally vuggy, and its pore space is filled with a large amount of silicate detrital minerals and clay minerals. (3) Layer 3, on the top, is black and dense, with a dendritic, columnar/laminated texture. Co is very unevenly distributed throughout the whole crust, with three distinct Co-rich areas. Layer 3 is a typical hydrogenetic crust and has not undergone late alteration. The main processes for Co enrichment are specific adsorption-oxidation on Mn-oxides and the structural incorporation of Co3+ into Mn-oxide phases. The average Co content of the Layer 3 is much higher than that of the other two layers. The presence of abundant detrital and clay minerals, along with high levels of Al, Si, and Ti in Layer 2, indicates the incorporation of terrigenous material, resulting in a high average growth rate. However, these processes are not conducive to Co enrichment. In the phosphatized Layer 1, fluctuations in element content are significantly greater than in the upper, non-phosphatized layers. Phosphatization has resulted in the partial decomposition of the initial Co-rich micro-layers, which may have reactivated and migrated Co, contributing to secondary Co enrichment.

Unraveling the Extensive Impact of Subthermocline Eddies on the Western Pacific Undercurrent System

Unraveling the Extensive Impact of Subthermocline Eddies on the Western Pacific Undercurrent System