Western Pacific Ocean Research Articles

The Role of Precipitation and Salinity Effect in Multidecadal Changes and Long-Term Trend of the Indonesian Throughflow

Abstract Multidecadal variability of the Indonesian Throughflow (ITF) is crucial for the Indo-Pacific and global climate due to significant interbasin exchanges of heat and freshwater. Previous studies suggest that both wind and buoyancy forcing may drive ITF variability, but the role of precipitation and salinity effect in the variability of ITF on multidecadal time scales remains largely unexplored. Here, we investigate the multidecadal changes and long-term trend of the ITF transport during the past six decades, with a focus on the role of precipitation and salinity effect. The diverse datasets consistently indicate a substantial upward trend in the halosteric component of geostrophic transport of ITF in the outflow region at 114°E during the six decades. We find that the meridional differences of the salinity trend in the outflow region explain the increasing trend of the halosteric component of ITF transport. On a larger scale, the tropical western Pacific Ocean and Indonesian seas have experienced significant freshening, which has strengthened the Indo-Pacific pressure gradient and thus enhanced the ITF. In contrast, the equatorial trade wind in the western Pacific Ocean has weakened over recent decades, implying that changes in wind forcing have contributed to weakening the ITF. The combined effect of strengthened halosteric and weakened thermosteric components has resulted in a weak strengthening for the total ITF with large uncertainties. Although both the thermosteric and halosteric components are associated with natural climate modes, our results suggest that the importance of salinity effect is likely increasing given the enhanced water cycle under global warming.

Early diagenetic control on the enrichment and mobilization of rare earth elements and transition metals in buried ferromanganese crust

Ferromanganese crusts on seamounts represent a major reservoir of various critical metal elements (e.g., rare earth elements and transition metals) and hold substantial economic value. However, current research primarily focuses on crusts that are exposed to seawater, and little is known about the resource potential of buried crusts in sediments and the impact of early diagenesis on buried crusts. Here, we present in-situ high-resolution major and trace element analyses of a buried crust from the western Pacific Ocean to unravel how rare earth elements and transition metals are enriched and mobilized as burial. The elemental profiles of the buried crust indicate that as the crust is buried, dissolved nickel (Ni) and copper (Cu) are gradually released from it into the porewater. Manganese and cobalt (Co) contents of the buried crust remain relatively constant, while rare earth elements are incorporated into the buried crust. Collectively, the early diagenesis leads to the release of Ni and Cu into the porewater, whereas it facilitates the fixation of rare earth elements within the buried crust. Given the widespread distribution of buried crusts in modern oceans, they represent a potential resource for future economic extraction of critical metals, particularly rare earth elements and Co.

Sea surface temperature reconstruction in the Pacific Ocean using multi-elemental proxy in Porites and Diploastrea corals: Application to Palau Archipelago

Massive reef-building Porites corals are commonly studied to obtain long-term reconstructions of past sea surface temperature (SST) using temperature-sensitive elemental proxies, such as Sr/Ca or Li/Mg ratios. Most recently, a multi-proxy approach combining these two ratios (e.g. D'Olivo et al., 2018) and the SrU method (DeCarlo et al., 2016) have proved to be more robust to reconstruct paleo-temperatures. To date, no study has been carried out on the application of these new approaches on the Diploastrea heliopora coral, another massive reef-building genus that can potentially provide longer temperature records. Moreover, only a few studies have assessed coral SST calibrations at the scale of the Indo-Pacific basin and compared SST reconstructions obtained from two massive coral genera from the same site.In this study, we investigated the elemental composition of the topmost portion of 34 modern tropical Porites and 6 Diploastrea colonies collected during the Tara Pacific expedition (2016–2018) from various hydrological contexts in the Pacific Ocean. We derived and discussed annual Sr/Ca, Li/Mg, combined Sr/Ca-Li/Mg and Sr/Ca-Li/Ca-Mg/Ca and SrU vs. SST calibrations as well as potential intra-colonial and genus specific effects and evaluated the use of these basin-wide calibration equations. Overall, multi-ratio and multi-genera SST calibrations perform better than single-ratio calibrations and seem to improve temperature reconstructions.These new SST calibrations were applied to two colonies of Porites and Diploastrea collected from the same site in the North-West of the Palau archipelago located in the western Pacific Ocean to evaluate the applicability of universal calibrations based on different proxies and their combination. Coral-based SST records spanning the last 141 years show decadal changes and recent warming episodes that are related to major El Niño Southern Oscillation events. However, differences in reconstruction remain between both genera in the long-term trends, amplitudes, and absolute temperatures, depending on which genus or temperature proxy is considered.

Expanding the simulation of East Asian super dust storms: physical transport mechanisms impacting the western Pacific

Abstract. Dust models are widely applied over the East Asian region for the simulation of dust emission, transport, and deposition. However, due to the uncertainties in estimates of dust transport, these methods still lack the necessary precision to capture the complexity of transboundary dust events. This study demonstrates an improvement in the Community Multiscale Air Quality (CMAQ) model dust treatment during long-range transport of dust from northwestern China to the South China Sea (SCS). To accomplish this, we considered a super dust storm (SDS) event in March 2010 and evaluated the dust scheme by including adjustments to the recent calibration (Dust_Refined_1) and bulk density (Dust_Refined_2) refinements individually and in combination (Dust_Refined_3). The Dust_Refined_3 normalized mean bias of PM10 was −30.65 % for the 2010 SDS event, which was lower in magnitude compared to Dust_Refined_1 (−41.18 %) and Dust_Refined_2 (−49.88 %). Indeed, Dust_Refined_3 improved the simulated aerosol optical depth (AOD) value during significant dust cases, e.g., in March 2005, March 2006, and April 2009. Dust_Refined_3 also showed more clearly that, in March 2010, a “double plume” (i.e., one plume originating from the Taiwan Strait and the other from the western Pacific) separated by the Central Mountain Range (CMR) of Taiwan affected dust transport on the island of Dongsha in the SCS. On 15–21 April 2021, both CMAQ simulations and satellite data highlighted the influence of Typhoon Surigae on dust transport to downwind Taiwan and the western Pacific Ocean (WPO). The CMAQ Dust_Refined_3 simulations further revealed that many dust aerosols were removed over the WPO due to Typhoon Surigae. Hence, the model indicated a near-zero dust particle concentration over the WPO, which was significantly different from previous dust transport episodes over the Taiwan region. Therefore, our study suggested an effective method to improve dust management of CMAQ under unique topographical and meteorological conditions.

Environmental characteristics and major factors controlling chlorophyll a in three seamounts in the Subtropical Western Pacific Ocean

Seamounts interacting with oceanic currents created “seamount effect”, which could enhance the primary productivity in the euphotic zone. However, a large number of seamounts have not been investigated. In this study, the sectional distributions of temperature, salinity, dissolved inorganic nutrients, dissolved oxygen (DO), pH and chlorophyll a (Chl a) in three seamounts in the Subtropical Western Pacific Ocean (SWPO), named NA, NLG and MP4, were investigated. Consistent with no uplifts of isotherms and isohalines above three seamounts, the uplifts of the concentrations of dissolved inorganic nutrients and Chl a were unobvious, indicating that there was no “seamount effect” in these seamounts. Comparing with NA and MP4 seamounts, NLG seamount had higher salinity and lower temperature. However, the concentrations of inorganic nutrients and Chl a from surface to the subsurface chlorophyll maximum layer of NA and MP4 seamount were higher than those of NLG seamount. Meanwhile, due to the presence of tropic storm and cold eddy during the investigated period, the hydrological conditions there became more complex. Furthermore, Generalized Additive Models (GAMs) were used to infer the underlying factors controlling bottom-up effect on phytoplankton biomass in three seamounts. This study investigated the mechanism about the bottom-up effect on phytoplankton in seamount environment and provided basic information for future research on seamount ecosystem.

Variations in isoprenoid tetraether lipids through the water column of the Western Pacific Ocean: Implications for sedimentary TEX86 records

The TetraEther indeX of 86 carbon atoms (TEX86) is widely used as a proxy to reconstruct past sea surface temperatures. Most current applications of TEX86 are primarily based on analyzing the composition of isoprenoid glycerol dialkyl glycerol tetraethers (isoGDGTs) that comprise TEX86 in sediments, with the assumption that the sedimentary isoGDGTs are mainly derived from the surface mixed layer. Here we report on the variations in the isoGDGT distribution, archaeal abundance and community through the water column of the Western Pacific Ocean, directly testing the export depth of isoGDGTs and constraining the temperature records of TEX86. Our data show that maximum isoGDGT concentrations occurred in subsurface waters (150–200 m) with maximum archaeal abundances. The ratio between isoGDGTs bearing 2 vs. 3 cyclopentane moieties, i.e. [2/3] ratio, increased with depth, which is likely related to the shift of the archaeal community from Ca. Nitrosopelagicus-dominance to norank_f__Nitrosopumilaceae-dominance. Models based on the [2/3] ratios in the water column predicted an average export depth of isoGDGTs to sediments of around 150–200 m, consistent with the robust relationship between the compiled sedimentary TEX86 and the annual mean subsurface temperature. Taken together, our findings support that TEX86 records subsurface rather than surface temperatures in the open ocean.

Evidence of a small, island-associated population of common bottlenose dolphins in the Mariana Islands

Small, island-associated populations of cetaceans have evolved around numerous oceanic islands, likely due to habitat discontinuities between nearshore and offshore waters. However, little is known about the ecology and structure of cetacean populations around the Mariana Islands, a remote archipelago in the western Pacific Ocean. We present sighting, photo-identification, and genetic data collected during twelve years of surveys around these islands that reveal the existence of a small, island-associated population of bottlenose dolphins. Nearly half of the photo-identified individuals were encountered in more than one year. Both haplotypic and nuclear genetic diversity among sampled individuals was low (haplotypic diversity = 0.701, nuclear heterozygosity = 0.658), suggesting low abundance. We used mark-recapture analysis of photo-identification data to estimate yearly abundance in the southern portion of the population’s range from 2011 to 2018. Each abundance estimate was less than 54 individuals, with each upper 95% confidence interval below 100. Additional survey effort is necessary to generate a full population abundance estimate. We found extensive introgression of Fraser’s dolphin DNA into both the mitochondrial and nuclear genomes of the population, suggesting at least two hybridization events more than two generations in the past. The Mariana Islands are used extensively by the U.S. military for land and sea training operations. Thus, this unique bottlenose dolphin population likely faces high exposure to multiple threats.

Redescription and first Japanese seamount record of Stethopristes eos (Zeiformes; Parazenidae).

During a biodiversity survey conducted in 2020, focusing on seamounts located in the southern region of Japan, specifically designated as marine protected areas, a single specimen of Stethopristes eos Gilbert, 1905 measuring 124.2 mm in standard length was obtained via the use of a remotely operated vehicle (ROV). The collection occurred at a depth of 519 meters on the Ritto Seamount, located along the western Mariana Ridge. However, this species is poorly known, with only a limited dataset available concerning its morphology. In this study, we present a comprehensive redescription of the species, utilizing information obtained from the type specimens and a newly discovered specimen from Japanese waters. The Japanese specimen constitutes the first recorded occurrence of this species within the western Pacific Ocean. As part of this redescription, we suggest new standard Japanese names for both the genus and species.

The MSC approach for developing harvest strategies and harvest control rules for Regional Fisheries Management Organisations (RFMOs)

Well-designed and robust harvest strategies are a key governance tool to achieve long term sustainability of target stocks. In some fisheries, however, such as those governed by Regional Fisheries Management Organisations (RFMOs), the development and adoption of harvest strategies can be challenging. Seafood eco-labelling programs, such as the Marine Stewardship Council (MSC), can be one way of incentivising fisheries to advocate for the adoption of harvest strategies and harvest control rules (HCRs). Here we illustrate the process through which the MSC Fisheries Standard was recently revised to guide the development and implementation of harvest strategies tested using management strategy evaluation, with particular focus on RFMOs. We identify three case studies that highlight the challenge of harvest strategy and HCR adoption: Indian Ocean skipjack tuna fisheries, Western and Central Pacific Ocean tuna fisheries, and North-East Atlantic mackerel fisheries. We discuss the problem statement that highlighted the challenges present when applying the previous MSC Fisheries Standard to stocks managed by RFMOs, and how the revised requirements within the MSC Fisheries Standard aim to overcome those challenges. These revised requirements provide an operational framework within the MSC Fisheries Standard for how RFMO-managed fisheries can implement ‘state-of-the-art' harvest strategies through management strategy evaluation. When applied by MSC certified fisheries, the new requirements are expected to contribute to delivering positive change with respect to implementing robust harvest strategies and HCRs across RFMOs, particularly in cases where there is a strong interest in the market benefits of certification.

Variability in the white spot: a new genus and species of Discodorididae (Nudibranchia) from the central and western Pacific Ocean

ABSTRACT In this paper, a new genus in the nudibranch family Discodorididae, Avaldesia n. gen., is established for Avaldesia albomacula (Chan & Gosliner, 2007) and Avaldesia tahala (Chan & Gosliner, 2007), originally assigned to the genus Thordisa Bergh, 1877, and a new species, Avaldesia tamatoa n. sp., described here from the central Pacific. To establish species relationships within Avaldesia, as well as the placement of Avaldesia within Discodorididae, we utilized four molecular markers (cytochrome c oxidase subunit I, 16S rRNA, histone H3 and 28S rRNA) in our Bayesian inference and maximum likelihood analyses. Four species delimitation methods were complemented by morphological dissections and scanning electron microscopy. Our results reveal a clear separation between Avaldesia and Thordisa and suggest that Avaldesia is more closely related to the genera Hoplodoris Bergh, 1880 and Asteronotus Ehrenberg, 1831. The most characteristic features of Avaldesia include a radula with increasing denticulation towards the fimbriate outermost laterals and a reproductive system with a lobate vestibular gland, occasional hollow vestibular spine and a penis armed with one or more penial spines. All species of Avaldesia are found in shallow water (5–10 m depth) on rocky reefs, sandy sediments and algal fields with distributions across the Indo-Pacific.

A new genus of soft coral (Octocorallia, Malacalcyonacea, Cladiellidae) and three new species from Indo-Pacific coral reefs.

Molecular systematic studies of the anthozoan class Octocorallia have revealed widespread incongruence between phylogenetic relationships and taxonomic classification at all levels of the Linnean hierarchy. Among the soft coral taxa in order Malacalcyonacea, the family Alcyoniidae and its type genus Alcyonium have both been recognised to be highly polyphyletic. A recent family-level revision of Octocorallia established a number of new families for genera formerly considered to belong to Alcyoniidae, but revision of Alcyonium is not yet complete. Previous molecular studies have supported the placement of Alcyoniumverseveldti (Benayahu, 1982) in family Cladiellidae rather than Alcyoniidae, phylogenetically distinct from the other three genera in that family. Here we describe a new genus, Ofwegenumgen. nov. to accommodate O.verseveldticomb. nov. and three new species of that genus, O.coronalucissp. nov., O.kloogisp. nov., and O.collisp. nov., bringing the total number of species in this genus to four. Ofwegenumgen. nov. is a rarely encountered genus so far known from only a few locations spanning the Indian and western Pacific Oceans. We present the morphological characters of each species and use molecular data from both DNA barcoding and target-enrichment of conserved elements to explore species boundaries and phylogenetic relationships within the genus.

Stratification of dissolved organic matter in the upper 5000 m water column in the western Pacific Ocean

Marine dissolved organic matter (DOM) is a principal reservoir involved in biogeochemical cycles and exerts a pivotal influence on global carbon flux dynamics. In this study, excitation-emission matrix fluorescence spectroscopy combined with parallel factor analysis (EEM-PARAFAC) was conducted on 230 DOM samples collected from 21 sites between February and April 2022 in the Western Pacific Ocean (WPO). We identified five distinct fluorescence peaks (peaks B, T, A, C, and M), predominantly protein-like and humic-like components. These findings, marked by significant differences (p < 0.01) in fluorescence intensities and spectral indices, characterized the transformation of DOM with ocean depth, illustrating a transition from active to recalcitrant forms. Additionally, random forest analysis (RFA) identified depth as a key factor influencing marine dissolved organic carbon (DOC), with a 32.59% importance value. Correlations between hydrological and fluorescent parameters underscored the complexity of DOM sources and influencing processes. Overall, this work broadens our understanding of DOM variability in the upper 5000 m of the WPO, enhancing our knowledge of the marine environment's role in the global carbon cycle.

The Influence of Seamounts on the Enrichment of Rare Earth Elements in Sediments—A Case Study of the Marcus-Wake Seamounts in the Western Pacific Ocean

Deep-sea sediments enriched in rare earth elements and yttrium (REY-rich sediments) are widely distributed on the deep-sea floor, and their formation mechanism remains elusive. Although studies have recognized the link between seamounts and REY-rich sediments, in-depth analysis of the specific roles and effects of seamounts in the formation of REY-rich sediments is lacking. In this study, we analyzed surface sediments from the Marcus-Wake Seamounts for grain size, geochemistry, and mineral composition and classified the samples into three types: samples with moderate REY content and dominated by terrestrial detritus; samples with high REY and authigenic mineral content; and samples rich in CaCO3 but poor in REY. The REY in the sediments of the study area partly originate from Asian dust input and partly from seawater and/or pore water, and are mainly enriched in REY carrier particles including bioapatite fossils and micronodules. The amount of REY carrier particles influences the REY content in the sediments. The current field, primary productivity, weathering process, and depositional environment around seamounts are different from those of abyssal plains, which are conducive to the formation of REY-rich sediments. Strong bottom currents may exist in the southeastern direction of some large seamounts (e.g., Niulang Guyot), leading to the selective accumulation of REY-rich bioapatite fossils and micronodules, resulting in the formation of REY-rich sediments.

Spatio-temporal variability of fishing habitat suitability to tuna purse seine fleet in the Western and Central Pacific Ocean

Understanding the spatial distribution of fishing activity is important for ecosystem-based fisheries management.The dynamic vessel trajectory information provided by Automatic Identification System (AIS) together with local remote ocean environment data, provide an opportunity for new technologies to enable improvements in fisheries management.The spatio-temporal and variability to tuna purse seine fleet suitable fishing were evaluated based on fishing effort from AIS by constructing an integrated habitat suitability index (HSI), which weight of variables were determined with boosted regression trees (BRT) model. The results show that the fishing activity tuna purse-seine fleet and catch data from the Western and Central Pacific Fisheries Commission (WCPFC) have the same spatial distribution.The tuna purse seine fleet operation concentrate in EEZ area of the Pacifc Island countries and has seasonal environmental preferences. The fishing habitat suitability can be characterized by a few environmental factors. The HSI model had good capacity to predict habitat suitability to tuna purse seine fleet for mostly catch and fishing effort located in the suitable area. The suitable fishing areas showed significant seasonal changes and low utilization of the available environmentally suitable fishing habitat in each month. The most stable suitable area located in the New Guinea Offshore latitudinal region, may be experiencing high tuna purse-seine fishing pressure throughout the year. The research could help to improve the scientific and effective management of distant water fisheries under limited regulatory capacity.

Atmosphere–Ocean Coupled Energy Budgets of Tropical Convective Discharge–Recharge Cycles

Abstract An energy budget combining atmospheric moist static energy (MSE) and upper ocean heat content (OHC) is used to examine the processes impacting day-to-day convective variability in the tropical Indian and western Pacific Oceans. Feedbacks arising from atmospheric and oceanic transport processes, surface fluxes, and radiation drive the cyclical amplification and decay of convection around suppressed and enhanced convective equilibrium states, referred to as shallow and deep convective discharge–recharge (D–R) cycles, respectively. The shallow convective D–R cycle is characterized by alternating enhancements of shallow cumulus and stratocumulus, often in the presence of extensive cirrus clouds. The deep convective D–R cycle is characterized by sequential increases in shallow cumulus, congestus, narrow deep precipitation, wide deep precipitation, a mix of detached anvil and altostratus and altocumulus, and once again shallow cumulus cloud types. Transitions from the shallow to deep D–R cycle are favored by a positive “column process” feedback, while discharge of convective instability and OHC by mesoscale convective systems (MCSs) contributes to transitions from the deep to shallow D–R cycle. Variability in the processes impacting MSE is comparable in magnitude to, but considerably more balanced than, variability in the processes impacting OHC. Variations in the quantity of atmosphere–ocean coupled static energy (MSE + OHC) result primarily from atmospheric and oceanic transport processes, but are mainly realized as changes in OHC. MCSs are unique in their ability to rapidly discharge both lower-tropospheric convective instability and OHC.

Nano-Mineralogy and Mineralization of the Polymetallic Nodules from the Interbasin of Seamounts, the Western Pacific Ocean

Ferromanganese (Fe-Mn) polymetallic nodules are significant marine mineral resources containing various metal elements of substantial economic and scientific research value. Previous studies have primarily focused on the mineralogy and geochemistry of the nodules, while research on their nano-mineralogy is still lacking. In this study, we conducted scanning electron microscopy (SEM), X-ray powder diffraction (XRD), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), Brunauer–Emmett–Teller (BET) porous structure gas adsorption/desorption, and specific surface area analysis to examine the nano-mineralogy and mineralization of the polymetallic nodules from the interbasin of seamounts in the western Pacific Ocean (IBSWP). The results indicate that the growth profiles of the IBSWP polymetallic nodules exhibit microstructural features such as laminated, stromatolithic, columnar, and mottled structures. The mineral compositions are primarily composed of Fe-Mn minerals and detritus, including quartz; minerals from the feldspar group; and minerals from the clay group. The Fe-Mn phase minerals are relatively poorly crystallized. The Mn-phase minerals contain vernadite and small amounts of todorokite, buserite, and birnessite, while the Fe-phase minerals are mainly comprised of amorphous FeOOH. The main ore-forming minerals consist of nano-minerals, and the nanostructures of the polymetallic nodules endow them with unusually large specific surface areas and pore volumes, resulting in strong adsorption properties. The unique nano-properties and surface/interface adsorption effects of Fe-Mn minerals play a crucial role in controlling the enrichment of ore-forming elements.

Climate and sea-level fluctuations on the western coast of Bohai Bay during the 4.2 ka event: Multi-proxy evidence from the Nandagang area of Cangzhou, China

The 4.2 ka event was an important climatic event during the mid–late Holocene, with significant effects on the ecological environment and climatic evolution of different regions. Coastal wetlands, as a transitional ecosystem between land and sea, are sensitive to changes in climate and sea level; hence, research on coastal wetlands is important for reconstructing past climate and sea-level changes and for predicting future changes. However, little research has been conducted on the characteristics of the 4.2 ka event on the western coast of Bohai Bay in China. We analyzed the pollen assemblages (214 samples), grain size, and geochemical element contents of a mid–late Holocene sedimentary sequence from the Nandagang (NDG) wetland on Bohai Bay, with the chronology based on 13 AMS 14C dates. The results revealed the history of climate and sea-level changes on the western coast of Bohai Bay during the interval of 5000–3600 cal yr BP. High sedimentary arboreal pollen concentrations indicated that the NDG area had a relatively dense cover and humid climate during 5000–4450 cal yr BP. During the 380-year interval of 4450–4070 cal yr BP, corresponding to the 4.2 ka event, the decreased representation of arboreal pollen indicated a decrease in the regional forest cover and an arid climate. The internal structure of the 4.2 ka event recorded in core NDG showed a dry-wet-dry temporal structure during the intervals of 4450–4290 cal yr BP, 4290–4170 cal yr BP, and 4170–4070 cal yr BP, respectively, together with a relatively low sea level. Comparison of the relative sea level (RSL) record of the NDG wetland with similar records from other coastal regions in East Asia during the 4.2 ka event revealed contrasting trends. During 4070–3600 cal yr BP, the tree pollen concentration increased again, indicating that the forest vegetation coverage increased and the climate became wetter. Overall, our results suggest that the 4.2 ka event, as recorded in Bohai Bay, was related to the reduced influence of the western Pacific Ocean Warm Pool and the more frequent occurrence of the El Niño–Southern Oscillation.

The accumulation characteristics and exploration potential of oil and gas in the back-arc basin of Japan under the background of high heat flow

The Sea of Japan is located in the southeast margin of Eurasia, in the triangle area of the western Pacific Ocean. Due to the interaction of the Pacific plate, Eurasian plate and Philippine plate, its tectonic environment is complex, forming a typical trench-arc-basin system. At present, 148 oil and gas fields have been discovered in Japan, with an oil and gas resource of 255.78×106 t, showing a good prospect for oil and gas exploration. Based on the previous research and the recently collected geological and geophysical data, the characteristics of tectonic-sedimentary evolution and geothermal field in the basins around the Sea of Japan are analyzed. The results show that the tectonic evolution of the basin is mainly controlled by plate subduction and back-arc oceanic crust expansion, and it mainly undergone four tectonic-sedimentary evolution stages: Subduction period, basin development period, subsidence period and compression deformation period. The overall heat flow value of Japan Sea is high, and it is distributed annularly along Yamato Ridge. The geothermal heat flow value is about 50–130 MW/m2, and the average heat flow is 75.9±19.8 MW/m2, which has a typical “hot basin”. The high heat flow background provides unique thermal evolution conditions for hydrocarbon generation, which leads to the high temperature and rapid evolution. The authors summarized as “early hydrocarbon generation, rapid maturity and shallow and narrow hydrocarbon generation window”. The type of oil and gas is mainly natural gas, and it mainly distributed in Neogene oil and gas reservoirs. The trap types are mainly structural traps, lithologic traps and composite traps. In addition, the pre-Neogene bedrock oil and gas reservoirs also show a good exploration prospect. The resource prospecting indicates that Niigata Basin, Ulleung Basin and kitakami Basin are the main target areas for future exploration and development.©2023 China Geology Editorial Office.

Observed Anomaly of Temperature and Mixed Layer Depth Associated with the Madden Julian Oscillation (MJO) Active Phase in the Banda Sea, Indonesia

The eastward propagation of atmospheric waves along the equatorial band from the central equatorial Indian Ocean to the western Pacific Ocean passing through the Indonesian Maritime Continent (IMC), known as the intraseasonal Madden Julian Oscillation (MJO) event, plays an important role on modulating both atmospheric and upper ocean dynamics along its path. This study aims to investigate the MJO active phase dynamics and its impact on changes in near-surface seawater temperature and mixed layer depth (MLD) anomaly in the Banda Sea Indonesia, using multi-datasets of atmospheric reanalysis, satellites derived sea surface temperature (SST), and Argo float between 2017 - 2018. This study revealed that the MJO waves propagate eastward along the southern equator-line over the IMC and pass through the Banda Sea, associated with significant decreased on Outgoing Longwave Radiation (OLR) and increased in zonal wind speed at 850hPa. The study result shows anomalous increased on surface wind speed and SST cooling during of MJO active phase. The amplitude peaks of filtered ocean-atmosphere variables range between 30 – 60 days. Argo float datasets in the Banda Sea for the first time captured upper ocean responses to the arrival of the MJO active phase, as characterized by a negative temperature anomaly of ~0.3°C in the surface mixed layer, large temperature anomaly of ~0.8°C in the thermocline layer and the deepening of the MLD of ~25 m. Hence, the MJO active phase impacts significantly on surface and vertical temperature cooling and regulate upper ocean mixing intensity in the Banda Sea.

Sample contamination explains evidence of close kin proximity in yellowfin tuna (Thunnus albacares) in the Western and Central Pacific Ocean

Anderson et al.’s 2019 paper ‘Close Kin Proximity in Yellowfin Tuna (Thunnus albacares) as a Driver of Population Genetic Structure in the Tropical Western and Central Pacific’ provided observations of genetically related individuals among sampled yellowfin tuna. Resampling of some individuals from the original study produced very different sequencing results when compared with the original dataset, one possible explanation of which is cross-contamination among the original samples. Re-analyses produced no indication of strong population structure, including a very slightly and consistent heterozygosity deficit with only one statistically significant pairwise FST value of 0.002. We identified only one pair of genetically similar individuals that could still be an artefact of lingering contamination. These new results therefore support a highly connected population of yellowfin tuna in the study area, although we do not rule out the potential for local adaptation driven by non-observed loci or genetic sub-structure operating at more contemporary scales.