Western Pacific Marginal Seas Research Articles

Rifting in the Western Pacific Marginal Seas

Rifting in the Western Pacific Marginal Seas

Effects of Late Pleistocene Climatic Fluctuations on the Phylogeographic and Demographic History of Japanese Scad (Decapterus maruadsi)

The Late Pleistocene-Holocene climate fluctuations have greatly influenced the phylogeographic structure and historical dynamics of many marine organisms in the western Pacific marginal seas. Here, we investigated the impact of Pleistocene glacial-interglacial cycles on the phylogeographic structure and demographic dynamics of Decapterus maruadsi, an economically important fish along the coast of the East China Sea (ECS) and northern South China Sea (NSCS). We obtained 430 concatenated sequences (Cyt b + control region, 1548–1554 bp) of D. maruadsi, including 246 newly sampled from the ECS and 184 previously determined from the NSCS. Genetic structure and phylogenetic analysis demonstrated a lack of significant population structure among 16 populations. Moreover, there was no significant differentiation among populations from Chinese coastal waters and northern Vietnam. Neutrality tests, unimodal mismatch distributions, Bayesian skyline plots, and the star-like haplotype networks all indicated a recent demographic expansion for D. maruadsi population during the Late Pleistocene-Holocene, explaining the low genetic diversity in D. maruadsi along the southeast coast of China. Notably, phylogenetic analyses and net genetic distances based on Cyt b jointly confirmed that 57 Cyt b haplotypes identified as D. maruadsi from the previously defined Sundaland-Rosario-Ranong clade actually represented D. russelli. These results not only reveal the complex effects of Pleistocene-Holocene climate fluctuations on the phylogeographic structure and demographic history of D. maruadsi but also provide useful genetic information for the management of genetic resources.

Role of Marginal Seas in Deep Ocean Regeneration of Dissolved Silica: A Case Study in the Marginal Seas of the Western Pacific

Deep ocean regeneration of dissolved silica (DSi) is an essential part of the ocean silica cycle and is driven by a complex series of biogeochemical processes. Here we compare the distributions of DSi and other environmental parameters in several western Pacific marginal seas to explore the role of marginal seas in deep ocean DSi regeneration. Results show that in oligotrophic marginal seas (such as the South China Sea), the DSi content in deep waters is similar to that of the adjacent Pacific waters. However, in productive marginal seas (such as the Bering Sea), the DSi content in deep waters is markedly higher than that in adjacent Pacific waters at the same depths. This is mainly due to deep ocean DSi regeneration in the marginal sea basin, which is fueled by the high biogenic particle flux from the productive surface waters. On a global scale, deep ocean DSi regeneration is accelerated in productive marginal seas, causing marginal seas such as the Bering Sea to have the highest DSi concentrations of all global waters.

On the sedimentary carbonate accumulation and dissolution in Western Pacific marginal basins

AbstractThe critical role of marginal seas in the global carbon cycle and their response to climate and circulation changes are not well understood. In this study, we used long‐term archives of sedimentary CaCO3 data and a conceptual model to systematically determine the spatial and vertical features of the sediment carbonate system in the marginal seas along the Western Pacific Ocean. Our results show that the northward‐flowing Antarctic Bottom Water and Lower Circumpolar Deep Water produced shallower calcium carbonate preservation depths as they moved north and became more carbonate‐undersaturated. This suggests that the carbonate chemistry in the deep Western Pacific marginal sea basins is mostly governed by the global ocean thermohaline circulation. In contrast, the carbonate system in the deep Japan/East Sea is unique, with limited sedimentary carbonate accumulation due to weak calcification and its internal overturning circulation. Despite differences in the hydrological and ecological settings, the sedimentary calcium carbonate profiles in the Tasman Sea and South Fiji Basin are comparable to those in the Atlantic and Pacific Oceans, reflecting the remarkable influence of open‐ocean carbonate chemistry.

Estimating Curie-point depths using both wavelet-based and Fourier spectral centroid methods in the western Pacific marginal seas

SUMMARY The Curie-point depth is an important magnetic parameter for studying the geological structure and thermal evolution of the lithosphere. In this study, we first apply wavelet transform to the centroid method, and compare it with the conventional Fourier spectral centroid method based on a 3-D fractal magnetization model. We find that the Fourier transform method is suitable for estimating smaller Curie-point depths (less than 20 km), whereas the wavelet transform method has better accuracy in estimating large Curie-point depths (more than 30 km). The application of both methods to the western Pacific magnetic anomalies from the Earth Magnetic Anomaly Grid of 2-arcmin resolution (EMAG2) proves their reliability and comparability. Our results show small Curie-point depths in areas with active magmatism and high heat flow, like mid-ocean ridges and island arcs of subduction zones, but large Curie-point depths in sedimentary basins and forearcs of subduction zones with low surface heat flow. We wrote our Curie-point depth inversion software CPDINV using FORTRAN language, which includes completed modules of minimum-curvature gridding, projection, wavelet and Fourier transforms, least-squares fitting and depth estimation.

Progress of micropaleontological research in the western Pacific marginal seas

Progress of micropaleontological research in the western Pacific marginal seas

Sea-level changes controlled detrital sediment inputs to the Bicol Shelf in the western Philippine Sea since 150 ka

Detrital sediments derived from the Philippine Islands are one of the main sources of deep-sea sediments in the western Philippine Sea. However, systematic research on their characteristics and transport mechanisms are lacking. We used parametric end-member analysis to quantitatively partition the grain size of detrital sediments in core MD06-3052 from the Bicol Shelf in the western Philippine Sea; three end-members EM1, EM2, and EM3, whose respective modes were at 2, 10, and 45 µm, were separated. We also measured the Sr and Nd isotopic compositions of different size fractions ( 20 µm) of the detrital sediments and the results showed that the detrital sediments mainly originate from the Philippine Islands. Components EM1 and EM2 are transported to the Bicol Shelf mainly by surface and bottom currents from the islands, and component EM3 is delivered by gravity flow from the exposed shelf during low sea-level stands. The content of the total detrital fraction and the three end-members, as well as the mass accumulation rates (MARs) of the coarse detritus (EM2 and EM3), were considerably higher during glacial periods (40–14 ka and 150–130 ka) than during other intervals; the glacials corresponded to a low sea level, while the MAR of the fine detritus (EM1) did not increase remarkably during 40–14 ka. We therefore concluded that the input of coarse detritus to the Bicol Shelf from the islands was mainly controlled by sea-level change. Variations of the input of fine-grained detritus (EM1) was influenced not only by sea level but also by ocean currents and regional precipitation. Overall, our results help understand “source-to-sink” processes in the western Pacific marginal seas and their response to global change.

Surface Ocean Hydrographic Changes in the Western Pacific Marginal Seas Since the Early Holocene

Climatic changes in the western Pacific marginal seas are influenced by global forcing and regional processes, including monsoons and ocean circulation. To better understand the process of hydrographic and temperature changes, we applied the UK’37 as our index of Sea Surface Temperature (SST) and TEX86 as the index of Subsurface Water Temperature (SWT) for the last 8400 years using the sediment core MZ01 from the continental shelf of the East China Sea (ECS). To focus on centennial and millennial variabilities, the original SST and SWT are filtered with the Ensemble Empirical Mode Decomposition (EEMD) of the Hilbert-Huang Transform (HHT), with the confidence defined by a new method, the Continuity Superposition Error Calculation Method (CSECM). The SST and SWT both have a quasi-period of 1000-2000 years, exhibiting some teleconnection with the north Atlantic climatic changes. The SWT decreased during approximately 6-4 ka and then increased by ~4°C to the late Holocene, almost anti-phase with the SST. The stronger Asian winter monsoon and China Coastal Current (CCC), are very likely responsible for the decreased SST in the late Holocene. In contrast, the increased SWT may imply that the stronger CCC has brought more Changjiang Diluted Water (CDW) southward and formed a thicker barrier layer in the ECS, which dampened bottom water heat loss that was transported from the Taiwan Warm Current (TWC) and Western Kuroshio Branch Current (WKBC). This process is tested by the hosing experiment that supports stronger stratification when the north Atlantic cooled. The combined results by UK’37 and TEX86 provide a new insight into the interaction mechanism among the winter monsoon, precipitation and the Kuroshio Current, and also raises caution to take more regional factors into account in the application of TEX86.

A new radiolarian transfer function for the Pacific Ocean and application to fossil records: Assessing potential and limitations for the last glacial-interglacial cycle

Abstract Climatic and oceanographic processes in the Pacific Ocean have global implications. Reliable sedimentary proxies in this region are thus necessary to understand the magnitude of past climate variability. Radiolarian assemblages are of particular relevance in some regions of the Pacific Ocean where other proxies are either poorly preserved or are biased towards a specific season. Previously published radiolarian-based transfer functions in the Pacific Ocean did not cover some regions, such as the Western Pacific marginal seas or high-latitude Southwestern Pacific. Filling these gaps in sample distribution and using a thorough methodology for finding the most important variable for radiolarian assemblages in surface sediment are both essential steps in quantitative studies. In this study, we use published radiolarian census counts from 801 core-tops distributed across the Pacific Ocean, to investigate which environmental factors drive the assemblages. We harmonized taxonomically the modern microfossil dataset, and using multivariate statistical analyses, we determined that sea surface temperature at 10 m (SST10) is the most important variable influencing the changes observed in the radiolarian assemblages. The calibration method weighted-mean modern analogue technique with five analogs (WMAT-K5) corrected for autocorrelation using a cut-off distance of 500 km, showed a performance of R2cv = 0.83; RMSEP = 3.8 °C. This calibration method was then applied to taxonomically harmonized radiolarian census counts from 31 cores located in the Bering Sea, Western Pacific marginal seas, and Southwest and Eastern Equatorial Pacific, with some of these records covering at least the last 165 ka. We assessed the analogue quality and significance of the downcore SST10 reconstructions in all of them. We found that temperatures at 10 and 200 m were the most significant variables for the fossil assemblages. Finally, we compare the temperature reconstructions to previously published radiolarian-based SST estimates for the same cores, or to other SST records based on other methodologies. We find some differences between our new temperature estimates compared to existing ones, in particular in the Eastern Equatorial Pacific. Comparison to other methods in the Japan and Bering Sea and Sea of Okhotsk show that radiolarian-based reconstructions provide robust temperature estimates compared to biogeochemical methods, which showed SST overestimation during glacial periods.

Sedimentary records of nitrogen isotope in the western tropical Pacific linked to the eastern tropical Pacific denitrification during the last deglacial time

The influence of past variations in water column denitrification (WCD) in the eastern tropical Pacific (ETP) on the western tropical Pacific (WTP) remains ambiguous, due to the deficiency of enough down-core records of nitrogen isotope (δ15N) in the WTP. In this study, sedimentary δ15N record down a core from the northern WTP is investigated to revisit this issue. After elucidating the potential presence of multiple forms of N by analyzing bulk parameters and the potential occurrence of alteration by examining amino acids, the bulk sedimentary δ15N can be accepted as an available indicator of nitrate δ15N. Further, a comprehensive comparison of δ15N records in the North Pacific reveals largely similar variations from the last glacial maximum to early Holocene, suggesting a common feature of WCD signals associated with basin-scale processes, likely as a consequence of basin-wide ocean circulations. Our result suggests that the signals of local N2 fixation in the western Pacific marginal seas would have been constrained by a synchronous glacial-interglacial change of the source WCD signals.

The Model of Formation of the Western Pacific Marginal Seas: Vortex Geodynamics, Seismicity, and Mantle Upwelling

An extended and improved model of the origin and evolution of marginal seas in the strike-slip megazone due to the lateral interaction of the Eurasian and Pacific lithospheric plates is proposed. In the megazone, fragmentation of continental and oceanic plates, mantle upwelling, and ascending and descending lithospheric seismic vortexes occur. As a proof of the validity of the proposed model, the paper presents data from factor analysis, results of gravity and termophysical modeling, an analysis of distributions of earthquake magnitudes in 3D space, and geochemical features of volcanism in the Sea of Japan and Sea of Okhotsk. Study of the variability of earthquake magnitudes for the Sea of Okhotsk region revealed traces of vortex processes in the circular orientation in the variability vectors of magnitudes in the subcrustal viscous layer and in the asthenosphere. The head of the mantle plume has a typical mushroom shape, and its central trunk extends into the mantle below a depth of 200 km. Studies of the isotopic age and geochemical features of volcanic rocks in the Sea of Okhotsk and Sea of Japan have allowed researchers to identify the magma sources—lithospheric, asthenospheric, and subasthenospheric (plume); to trace the geochronological sequence in the ascent of mantle substrate; and to determine the underlying formation mechanisms for the marine basins. The origin of marginal seas is discussed and compared to other geodynamic models with different geotectonic paradigms. The origin of marginal seas is discussed and compared with other geodynamic models of different geotectonic paradigms.

Evaluation of environmental proxies based on long chain alkyl diols in the East China Sea

Long chain alkyl diols (LCDs) in marine environments are useful indicators of source organisms, ambient temperature, upwelling and nutrient conditions. However, the distribution of LCDs in the western Pacific marginal seas has been rarely reported, where wide shallow continental shelves and huge freshwater input from many rivers occur. In this study, we analyzed LCDs in surface sediments distributed from the Changjiang River estuary (CRE) to the East China Sea shelf to evaluate their sources and associated environmental proxies. Our results showed that the fractional abundance of C32 1,15-diol (FC32 1,15-diol) was highest in coastal area close to the CRE, with FC32 1,15-diol > 15% implying significant freshwater input. The C28 and C30 1,13-diols showed a similar spatial distribution to the C32 1,15-diol, suggesting that the long chain diol index (LDI), a sea surface temperature (SST) proxy, may be biased by freshwater-derived diols. By excluding the freshwater-influenced samples (i.e., FC32 1,15-diol > 15%), LDI reflected the autumn SST, yielding minimum temperature residuals (0.2 ± 1.5 °C). The C28, C30 and C30:1 1,14-diols were abundant in the mid-depth (15–45 m) offshore environment that was affected only slightly by the Changjiang River plume, and decreased toward both the eutrophic estuarine and oligotrophic marine environments; whereas the C28:1 1,14-diol showed higher fractional abundances close to the CE. The spatial distribution of 1,14-diols is similar to that reported for Proboscia diatoms in this region, although the exact sources of 1,14-diol requires further study. Nutrient proxies based on 1,14-diols did not correlate well with nutrient concentrations in this river-dominated marginal sea, where nutrient supply is dominated by the Changjiang River input.

Preface to the special issue “Tectonics and depositional infilling of western Pacific marginal sea”

Preface to the special issue “Tectonics and depositional infilling of western Pacific marginal sea”

МОРФОСТРУКТУРНЫЙ АНАЛИЗ ПРИ РЕШЕНИИ ГЕОЛОГИЧЕСКИХ ПРОБЛЕМ ВОСТОКА АЗИИ, "Геоморфология"

Окраинные моря Западно-Тихоокеанской зоны перехода континент-океан рассматриваются как вихревые структуры. В Япономорском регионе (ЯР) применение линеаментного анализа (комплекса геоморфологических, геологических и геофизических методов) позволило выявить в континентальной части Япономорского региона рудоконтролирующие зоны (эндогенного оруденения, месторождений алмазов и др.), скрытых разломов фундамента и магматических очаговых структур, а на дне Японского моря разломных структур. В регионе: 1) выявлены три литосферные вихревые морфоструктуры - Япономорская (ЯМ), Нижнеамурская (НА) и Сунляо (СЛ), 2) выделены два структурных этажа: мантийный и литосферный, включающие, соответственно, тектонический каркас и вихревые структуры, тесно связанные с подстилающей астеносферой. ЯМ морфоструктура отражает процесс раскрытия Японского моря - как результат взаимодействия Евроазиатской и Тихоокеанской плит; НА - соответствует межгорная впадина, с которой на западе сочленяется нефтегазоносная депрессия Сунляо вихревого типа. В ЯР развиты нефтегазоносные мезокайнозойские осадочные бассейны, представляющие литосферные вихри. Линеаментный анализ позволит по-новому прогнозировать характер миграции углеводородов в земной коре и выявлять предполагаемые места их скопления. Этот метод может быть использован в процессе подготовительного этапа при исследовании нефтегазоносности Западно-Тихоокеанских окраинных морей, а также Арктических бассейнов.

Sources and accumulation of plutonium in a large Western Pacific marginal sea: The South China Sea

In order to examine the sources of plutonium (Pu) and elaborate its scavenging and accumulation processes, 240Pu/239Pu atom ratios and 239+240Pu activities in the water column of the South China Sea (SCS) were determined and compared with our previously reported data for the sediments. Consistently high 240Pu/239Pu atom ratios that ranged from 0.184–0.250 (average=0.228±0.015), indicative of non-global fallout Pu sources were observed both in the surface water and at depth during 2012–2014. The spatial distribution of the 240Pu/239Pu atom ratio in the SCS showed a decreasing trend away from the Luzon Strait, which was very consistent with the introduction pathway of the Kuroshio Current. The Kuroshio had an even heavier Pu isotopic ratio ranging from 0.250–0.263 (average=0.255±0.006), traceable to the non-global fallout Pu signature from the Pacific Proving Grounds (PPG). Using a simple two end-member mixing model, we further revealed that this PPG source contributed 41±17% of the Pu in the SCS water column. The 239+240Pu activities in the SCS surface seawater varied from 1.59 to 2.94mBqm−3, with an average of 2.34±0.38mBqm−3. Such an activity level was ~40% higher than that in the Kuroshio. The distribution of 239+240Pu in the surface seawater further showed a general trend of increase from the Kuroshio to the SCS basin, suggesting significant accumulation of Pu within the SCS. The 239+240Pu inventory of the water column in the SCS basin at the SEATS station with a total depth of ~3840m was estimated to be ~29Bqm−2, which was substantially higher than the sediment core estimates made for the SCS basin (3.75Bqm−2) but much lower than the sediment core estimates made for the shelf of the northern SCS (365.6Bqm−2). Such differences were determined by the lower scavenging efficiency of Pu in the SCS basin compared to the northern SCS shelf.

Global major events in Miocene and its significance: Revelation from data mining

The GEOROC (Geochemistry of Rocks of the Ocean-sand Continents) database is a comprehensive global petrological database and it is constantly updated and available online to users around the world. Based on this database, we analyze the age data of the global Cenozoic igneous rocks including convergent margin andesite and basalt, continental rift andesite and basalt, ocean island andesite and basalt, adakite, and so on. Statistical analysis reveals that the global magmatism either became active in the Miocene or peaked in the Miocene. Magmatic rocks formed in different tectonic settings represent different geological effects: convergent margin magmatic rock suggests the speed up of subduction; the huge eruption of rift andesite and basalt indicates the occurrence of plate extension; the sharp increase of ocean island andesite and basalt indicates an abnormally active lower mantle, which brings materials from the lower mantle into the crust; a large scale of medium-acid magmatic rock represents the lower crust at high temperature and the asthenosphere mantle strongly upwelling, which leads to the crust intensely reforming; adakite is usually related to strongly tectonic pressing and results in crustal thickening in these areas. In addition, there was a series of significant events in the Miocene. For instance, the Tibetan Plateau rapidly uplifted in the middle Miocene, leading to the formation of the Loess Plateau; the Andean Mountains rose abruptly probably during 8–3 Ma; Tethys dried up from 20–5 Ma, which may have been a cause of the global desertification; the development of the western Pacific marginal sea basins mainly occurred during the late Oligocene to early Miocene. We tried to explain the connection among all of these events as follows. Generally, magmatism usually goes with tectonic activities, and their interaction may change the paleogeography, paleoclimate, and paleoenvironment. The accelerated motion of the Pacific Plate in the Miocene could have thickened or raised the crust, resulting in the formation of the Andean mountains. The interaction between the Indian plate and Eurasian plate in the Miocene induced the speedy uplifting of the Tibetan Plateau. The new mountain and plateau reformed the original landscape and landform, which made these areas easily suffer weathering and erosion, and the resulting sediments were taken into global ocean basalts with ocean currents. As a result, the accumulation rate of oceanic sediments would have risen quickly. Furthermore, the upraising of the Andean and Tibetan Plateaus also influenced the general atmospheric circulation, which ultimately changed the environment; this might be an important reason why primitive man originated from the Miocene. In addition, as for China, the strike-slip fault in the Red River, the expansion of the South China Sea, and the formation of the Taklimakan Desert may be more or less related to the magmatism in the Miocene. There remain a number of problems to explore. Therefore, studying the interrelationship among magmatism, tectonic activity, climate, and environment in the Miocene should be a priority for geoscience workers in the present and future. Besides, scientific research is gradually entering the big data era, and geological science is no exception. The primary characteristic of big data research is not how big the data is but how creative the thought is. In this study, we took advantage of all available data to investigate the relationship among the data sets. The findings reveal that data mining with a global database can provide new insights and new lines of inquiry for scientific research in the future.

Origin of transform faults in back‐arc basins: examples from Western Pacific marginal seas

AbstractTransform faults in back‐arc basins are the key to revealing the evolution of marginal seas. Four marginal basins in the Western Pacific, i.e. the South China Sea (SCS), Okinawa Trough (OT), West Philippine Basin (WPB) and Shikoku‐Parece Vela Basin (SPVB), were studied to redefine the strikes and spatial distribution of transform faults or fracture zones. Based on high‐resolution tectonomorphology, gravity and magnetic anomalies, pattern of magnetic lineations, seismic profiles, geometry of basins and palaeomagnetic data, together with analyses of regional geological setting, plate reconstruction and geodynamic analysis, this paper suggests that all the transform faults in the four marginal basins are in general NNE‐trending. Moreover, by comparing with the contemporary structural framework of the East Asian Continental Margin, we propose new models concerning marginal seas spreading and have revised the previous Cenozoic plate reconstruction models related to the East Asian Continental Margin and the Western Pacific marginal seas. There are three possible origins of these NNE‐trending transform faults. 1. Inheriting the orientation of the strike‐slip faults at the rifting continental margin (e.g. the SCS and OT). The real strike of transform faults should not be NW but NNE. The large‐scale NNE‐trending dextral strike‐slip faults distributed in the continental shelf of the SCS control a series of pull‐apart basins of the SCS. Due to a higher degree of pull‐apart, oceanic crust began to open. Then they evolved into the NNE‐trending transform faults in the SCS and could also be regarded as a natural extension of the NNE‐trending strike‐slip faults in the South China Block (SCB). The geodynamic mechanism of the OT is similar to that of the SCS. Consequently, transform faults of the OT should also be NNE‐trending, which is not perpendicular to the spreading axis but instead displays oblique spreading. 2. Izu‐Bonin‐Mariana (IBM) Trench retreat to the NNE and NE. Subduction rollback to the NE and NNE produced the NE‐ and NNE‐striking horizontal tensile stress, resulting in the rifting of the Kyushu‐Palau Ridge (KPR), controlling the spreading of the SPVB and forming the NE‐ and NNE‐trending transform faults. This also involves oblique spreading. 3. The later overall rotation of the Philippine Sea Plate (PSP). Since 25 Ma, the WPB has rotated clockwise about 40°. Therefore the NW‐ and NNW‐trending transform faults that formed at the later spreading stage have rotated to be the near‐N–S‐ or NNE‐striking faults. These transform faults are almost perpendicular to the spreading axis. Copyright © 2016 John Wiley & Sons, Ltd.

Variations in Moho and Curie depths and heat flow in Eastern and Southeastern Asia

The Eastern and Southeastern Asian regions witness the strongest land–ocean and lithosphere–asthenosphere interactions. The extreme diversity of geological features warrants a unified study for a better understanding of their geodynamic uniqueness and/or ubiquity from a regional perspective. In this paper we have explored a large coverage of potential field data and have detected high resolution Moho and Curie depths in the aforementioned regions. The oldest continental and oceanic domains, i.e. the North China craton and the Pacific and Indian Ocean have been found thermally perturbed by events probably linked to small-scale convection or serpentinization in the mantle and to numerous volcanic seamounts and ridges. The thermal perturbation has also been observed in proximity of the fossil ridge of the western Philippine Sea Basin, which shows anomalously small Curie depths. The western Pacific marginal seas have the lowest Moho temperature, with Curie depths generally larger than Moho depths. The contrary is true in most parts of easternmost Eurasian continent. Magmatic processes feeding the Permian Emeishan large igneous province could have also been genetically linked to deep mantle/crustal processes beneath the Sichuan Basin. The regionally elongated magnetic features and small Curie depths along the Triassic Yangtze-Indochina plate boundary suggest that the igneous province could be caused by tectonic processes along plate margins, rather than by a deep mantle plume. At the same time, we interpret the Caroline Ridge, the boundary between the Pacific and the Caroline Sea, as a structure having a continental origin, rather than as hotspot or arc volcanism. The surface heat flow is primarily modulated by a deep isotherm through thermal conduction. This concordance is emphasized along many subduction trenches, where zones of large Curie depths often correspond with low heat flow. Local or regional surface heat flow variations cannot be faithfully used in inferring deep thermal structures, which can be better constrained overall through Curie depths detected from surface magnetic anomalies.

Ubiquity and diversity of heterotrophic bacterial nasA genes in diverse marine environments.

Nitrate uptake by heterotrophic bacteria plays an important role in marine N cycling. However, few studies have investigated the diversity of environmental nitrate assimilating bacteria (NAB). In this study, the diversity and biogeographical distribution of NAB in several global oceans and particularly in the western Pacific marginal seas were investigated using both cultivation and culture-independent molecular approaches. Phylogenetic analyses based on 16S rRNA and nasA (encoding the large subunit of the assimilatory nitrate reductase) gene sequences indicated that the cultivable NAB in South China Sea belonged to the α-Proteobacteria, γ-Proteobacteria and CFB (Cytophaga-Flavobacteria-Bacteroides) bacterial groups. In all the environmental samples of the present study, α-Proteobacteria, γ-Proteobacteria and Bacteroidetes were found to be the dominant nasA-harboring bacteria. Almost all of the α-Proteobacteria OTUs were classified into three Roseobacter-like groups (I to III). Clone library analysis revealed previously underestimated nasA diversity; e.g. the nasA gene sequences affiliated with β-Proteobacteria, ε-Proteobacteria and Lentisphaerae were observed in the field investigation for the first time, to the best of our knowledge. The geographical and vertical distributions of seawater nasA-harboring bacteria indicated that NAB were highly diverse and ubiquitously distributed in the studied marginal seas and world oceans. Niche adaptation and separation and/or limited dispersal might mediate the NAB composition and community structure in different water bodies. In the shallow-water Kueishantao hydrothermal vent environment, chemolithoautotrophic sulfur-oxidizing bacteria were the primary NAB, indicating a unique nitrate-assimilating community in this extreme environment. In the coastal water of the East China Sea, the relative abundance of Alteromonas and Roseobacter-like nasA gene sequences responded closely to algal blooms, indicating that NAB may be active participants contributing to the bloom dynamics. Our statistical results suggested that salinity, temperature and nitrate may be some of the key environmental factors controlling the composition and dynamics of the marine NAB communities.

Demographic response of cutlassfish (Trichiurus japonicus and T. nanhaiensis) to fluctuating palaeo-climate and regional oceanographic conditions in the China seas.

Glacial cycles of the Quaternary have heavily influenced the demographic history of various species. To test the evolutionary impact of palaeo-geologic and climatic events on the demographic history of marine taxa from the coastal Western Pacific, we investigated the population structure and demographic history of two economically important fish (Trichiurus japonicus and T. nanhaiensis) that inhabit the continental shelves of the East China and northern South China Seas using the mitochondrial cytochrome b sequences and Bayesian Skyline Plot analyses. A molecular rate of 2.03% per million years, calibrated to the earliest flooding of the East China Sea shelf (70–140 kya), revealed a strong correlation between population sizes and primary production. Furthermore, comparison of the demographic history of T. japonicus populations from the East China and South China Seas provided evidence of the postglacial development of the Changjiang (Yangtze River) Delta. In the South China Sea, interspecific comparisons between T. japonicus and T. nanhaiensis indicated possible evolutionary responses to changes in palaeo-productivity that were influenced by East Asian winter monsoons. This study not only provides insight into the demographic history of cutlassfish but also reveals potential clues regarding the historic productivity and regional oceanographic conditions of the Western Pacific marginal seas.