Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.dsr2.2005.07.003

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/S0377-8398(03)00037-9

Publishing type：Research paper (scientific journal)   Publisher：Progress in Earth and Planetary Science  

Calcium carbonate (CaCO3) dissolution at the Southern Ocean seafloor has hypothetically contributed to lowering the atmospheric carbon dioxide concentration by increasing ocean alkalinity during glacial periods. We present new CaCO3 burial and dissolution records from two sediment cores obtained off the Chilean margin in the subantarctic SE Pacific and covering the past 140 kyr since Marine Isotope Stage (MIS) 6. These records include CaCO3 contents and mass accumulation rates, and microfossil-based analysis results, including fragmentation ratios, sieve-based weights (SBWs), and ultrastructural observations of planktic foraminiferal tests. Our bulk CaCO3-based analyses and Globorotalia inflata SBWs revealed three major CaCO3 dissolution events during colder stages of MIS 5d and 5b and at the MIS 5/4 boundary that are traceable events in the eastern South Pacific along the Chilean margin and in the Drake Passage. Furthermore, CaCO3 burial exhibited pronounced glacial/interglacial fluctuations, with almost no burial during glacials (MIS 6, 4, 3, and 2) and recovery during interglacials (MIS 5e and 1) and early glacials (MIS 5d–a). This pattern agrees with previous observations over a wide area of the Southern Ocean, except in the deep Cape Basin > 4600 m in the South Atlantic Ocean. Considering that our sites were located upstream of the Drake Passage, the Circumpolar Deep Water, which was influenced by carbon-rich Pacific Deep Water, likely propagated from the subantarctic eastern Pacific to the South Atlantic at least at depths of ~ 3000 to ~ 4000 m and decreased CaCO3 burial during glacials. These findings supported the importance of carbonate compensation in the Southern Ocean for the carbon cycle on the glacial/interglacial timescale. (Figure presented.)

DOI： 10.1186/s40645-024-00657-4

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Publishing type：Research paper (scientific journal)   Publisher：Wiley  

ABSTRACT

Hydroclimate variation and vegetation changes of the Nile River watershed area in northeast Africa since the Last Glacial Maximum (LGM) were reconstructed based on n‐alkanes, their carbon isotope ratios (δ¹³C_n‐alkanes), and their hydrogen isotope ratios (δ²H_n‐alkanes) in sediments from ODP Site 967 in the Eastern Mediterranean Sea. The results were compared with the present vegetation cover in the watershed areas using ArcGIS. The average proportion of current grassland in the Equatorial Lake and Ethiopian Highland Plateaus watershed areas was 45.8 and 64.7%, respectively. δ²H_n‐alkanes ranged from −199 to −127‰ and co‐varied with insolation change response to orbital forcing. Depleted δ²H_n‐alkanes were found from deglaciation to the middle Holocene, suggesting increased precipitation during the African Humid Period (AHP) from 15 to 5 ka caused by northward migration of the Intertropical Convergence Zone. However, lower precipitation was inferred by enriched δ²H_n‐alkanes during the LGM and late Holocene. δ¹³C_n‐alkanes at Site 967 did not show a trend in harmony with δ²H_n‐alkanes and instead exhibited millennial‐scale variations ranging from –25.9 to –33.2‰. These δ¹³C_n‐alkanes values consistently indicated a C4 grass‐dominated environment in the watershed areas of the River Nile since the LGM, persisting through the AHP and into the present. Reconstructions demonstrated orbital and abrupt forcing of hydroclimate variability while maintaining generally grass‐dominated vegetation with weak precipitation feedback over the late Quaternary.

DOI： 10.1002/jqs.3649

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

We investigated diatom-valve fragmentation and frustule separation in surface sediments in Lake Kitaura, a shallow lake in Japan, to clarify how sedimentation processes affect diatom assemblages. Twenty-two surface-sediment samples were collected from Lake Kitaura in 2014. Aulacoseira spp. were characteristic planktonic taxa, and Cocconeis placentula and Planothidium lanceolatum were characteristic benthic taxa, both with monoraphid valves. The fragmentation ratios of Aulacoseira spp., the most abundant taxon, were higher nearshore than in the central part of the lake. Cocconeis placentula, an epiphytic species, was widely distributed in Lake Kitaura, and its fragmentation ratios increased with distance from the lakeshore. The coexistence ratios of the two valve types of this species decreased with distance from the lakeshore and from macrophytic vegetation. Planothidium lanceolatum, a fluvial benthic species, was abundant at the three northernmost sites near a river mouth, and the frustules of this species were seldom separated. These results suggest that long-distance transport promotes fragmentation and separation of benthic diatom valves in shallow lakes.

DOI： 10.1007/s10933-024-00332-0

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Other Link： https://link.springer.com/article/10.1007/s10933-024-00332-0/fulltext.html

DOI： 10.14943/lowtemsci.82.119

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The Japan Sea is a semi-closed marginal sea that has been significantly affected by fluctuations of the East Asian monsoon. Due to its geographic setting, the influence of the monsoon is significant especially during the last glacial period, when the low sea level stand restricted surface water exchange with adjacent seas. Millennial-scale change in the summer monsoon controlled the input of freshwater and nutrients into the Japan Sea during Marine Isotope Stage (MIS) 3, resulting in the deposition of alternating dark- and light-colored sedimentary layers. However, the relationships between the sediment color alternations and winter sea surface conditions, such as temperature and salinity, are not understood. Here, we provide high-resolution Mg/Ca-based winter sea surface temperature (SST) records during MIS3 from two sediment cores from the southern Japan Sea. The SSTs at both sites showed millennial-scale fluctuations with significantly different amplitudes. The southern site had a larger SST amplitude with warmer in dark- and cooler in light-colored intervals. The SST difference between the two cores was greater in dark-colored intervals. The millennial-scale changes in SST difference are probably attributable to meridional migration of the subpolar front, induced by winter monsoons and inflow of the Tsushima Warm Current, which had a northerly (southerly) position during interstadials (stadials). The results suggest that the millennial-scale winter monsoon variability contributed to sediment color alternation via greater cooling during stadials, which enhanced ventilation, in conjunction with the summer monsoon-induced productivity change. Therefore, both the winter and summer monsoons are key drivers of the oceanographic condition in the Japan Sea.

DOI： 10.1016/j.palaeo.2023.111713

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1016/j.palaeo.2023.111713

Publishing type：Part of collection (book)   Publisher：International Ocean Discovery Program  

DOI： 10.14379/iodp.proc.383.201.2023

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Other Link： http://publications.iodp.org/proceedings/383/201/383_201.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Abstract

We present the first version of the Ocean Circulation and Carbon Cycling (OC3) working group database, of oxygen and carbon stable isotope ratios from benthic foraminifera in deep ocean sediment cores from the Last Glacial Maximum (LGM, 23-19 ky) to the Holocene (<10 ky) with a particular focus on the early last deglaciation (19-15 ky BP). It includes 287 globally distributed coring sites, with metadata, isotopic and chronostratigraphic information, and age models. A quality check was performed for all data and age models, and sites with at least millennial resolution were preferred. Deep water mass structure as well as differences between the early deglaciation and LGM are captured by the data, even though its coverage is still sparse in many regions. We find high correlations among time series calculated with different age models at sites that allow such analysis. The database provides a useful dynamical approach to map physical and biogeochemical changes of the ocean throughout the last deglaciation.

DOI： 10.1038/s41597-023-02024-2

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PubMed

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Other Link： https://www.nature.com/articles/s41597-023-02024-2

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1038/s41597-023-02024-2

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.pocean.2021.102687

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2021PA004312

Language：English   Publishing type：Research paper (scientific journal)  

Evaluation of foraminiferal test dissolution in deep-sea sediments facilitates reconstruction of seawater chemistry. Here we observed test dissolution processes of the planktic foraminifera Trilobatus sacculifer, Globigerinoides ruber, and Neogloboquadrina dutertrei from midlatitudes of the western North Pacific; in these three species, we tested the ability of a new dissolution index using data from X-ray micro-computed tomography scanning. Although the dissolution process of foraminiferal tests differed slightly among species, dissolution of all species was equally assessed by the calcite density distribution (%Low-CT-number calcite volume) calculated from the CT number histogram. In T. sacculifer and G. ruber, the test area density, a conventional proxy for assessing test condition based on weight measurement, is affected by variations in the thickness of the outermost chamber wall; thus, this conventional proxy can be affected by sea surface conditions during test calcification. In contrast, the relationship between the %Low-CT-number calcite volume of tests and the deep seawater calcite saturation state suggests that X-ray micro-computed tomography scanning is applicable for evaluating the intensity of foraminiferal test dissolution at the undersaturated deep seafloor in this area and is an invaluable proxy for detecting deep seawater carbonate ion concentration changes on glacial-interglacial timescales.

DOI： 10.1029/2019GC008456

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2019GC008456

Language：English   Publishing type：Research paper (scientific journal)  

We revisited the stratigraphy at Deep Sea Drilling Project (DSDP) Site 296, which has promise as a reference sequence for the mid-latitude northwestern Pacific. We constructed the biostratigraphy (calcareous nannofossils, planktic foraminifera, and radiolaria) and chemostratigraphy (strontium isotope ratios, and stable carbon and oxygen isotope ratios) to reveal continuous sedimentation at Site 296 through the past 20 million years (Myr). The biostratigraphy of calcareous nannofossils comprised 27 biohorizons from biozones NN2 to NN21 (early Miocene to Pleistocene), which are consistent with the biohorizons of planktic foraminifera and radiolaria. The uninterrupted sedimentation throughout the past 20 Myr was further supported by strontium isotope stratigraphy aligned tuned to nannofossil datums and by correlation of stable isotope data from benthic foraminifera with an isotopic compilation from the Pacific Ocean. The refined age–depth model showed low sedimentation rates (<2 cm/kyr) through most of the Miocene and higher sedimentation rates (2–4 cm/kyr) during the Plio–Pleistocene, and potentially identified the “biogenic bloom” event from the late Miocene to early Pliocene. The continuity of sedimentation through the middle Miocene contrasts with the shipboard biostratigraphy, which inferred a hiatus (erosion or non-deposition) during the middle Miocene. Thus, the revised stratigraphy at Site 296 provides a key to correlation with other deep-sea sites in the North Pacific. Our revised age–depth model provides a framework for future studies of important climatic events during the Miocene, including the Miocene Climatic Optimum, the middle Miocene Climatic Transition, and the late Miocene global cooling under the influence of the past Kuroshio Current.

DOI： 10.1127/nos/2019/0549

Language：English   Publishing type：Research paper (scientific journal)  

Phaeodaria, which comprise one group of large, single-celled eukaryotic zooplankton, have been largely ignored by past marine biological studies because Phaeodaria and their delicate skeletons are liable to collapse. As a result, collection and quantification of specimens are difficult, and seasonal changes of phaeodarian abundance have not been thoroughly studied. The transport of biogenic elements by sinking phaeodarians has been estimated for only a few representative species. Sinking particles >1 mm in size and swimmers have traditionally been excluded when estimating sinking particle fluxes. The focus of this study is the large number of phaeodarians among the >1-mm sinking particles collected in the western North Pacific from June 2014 to July 2015. Careful sorting by microscopic examination and chemical analyses revealed that phaeodarians accounted for up to about 10% of the organic carbon in all sinking particles and accounted for a mean of 33% of the organic carbon in the >1-mm sinking particles. The high-standing stocks of phaeodarians at depths of 150–1,000 m in the mesopelagic twilight zone suggested that particles sinking from the euphotic zone as aggregates and fecal pellets can be efficiently exported to the deep sea by the ballasting effect of large phaeodarian particles rich in organic carbon.

DOI： 10.1029/2019GB006258

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1130/G45033.1

Language：English   Publishing type：Research paper (scientific journal)  

The Japan Sea in the western North Pacific was connected to the deep Pacific via deep seaways before it became a semi-closed marginal sea. However, the timing of the semi-closure and its cause(s) remain debatable. To further constrain the timing, for the first time we analyzed Nd isotopic compositions of fossil fish teeth and fish debris deposited in the Japan Sea (Integrated Ocean Drilling Program [IODP] Site U1425, ~2000 m water depth) over the past 10 m.y. Neodymium isotope values (-4.5 to -3.2 ε_Nd) in the Japan Sea prior to 4.5 Ma illustrate that the deep Japan Sea was composed of an admixture of less-radiogenic Lower Circumpolar Deep Water (avg. -4.3 ε_Nd) and more-radiogenic North Pacific Deep Water (avg. -2.2 ε_Nd), potentially with inflow from the Okhotsk Sea. At 4.5 Ma, ε_Nd values fell to -5.5 ε_Nd within a span of 140 k.y., suggesting that the deep-water communication between the Japan Sea and the North Pacific rapidly declined. We argue that active mountain building in the northern Japan arc, initiated by accelerated Pacific plate motion from the late Miocene to mid-Pliocene, caused the shallowing/narrowing of the Japan Sea- Pacific seaways and rapidly made the Japan Sea semi-closed at 4.5 Ma. As a result, the Japan Sea circulation patterns were realigned; a cyclonic circulation was developed and drew less-radiogenic Amur River-influenced Okhotsk Sea water into the Japan Sea.

DOI： 10.1130/G45033.1

Language：Japanese   Publishing type：Research paper (scientific journal)  

DOI： 10.5575/geosoc.2017.0066

Language：English   Publishing type：Research paper (scientific journal)  

High resolution paleoceanography of the Pliocene-Pleistocene is important in understanding climate forcing mechanisms and associated environmental changes during this major transition from global warmth to the Ice Ages. This is particularly true in high latitude marginal seas such as the Bering Sea. The Bering Sea has been very sensitive to changes in global climate during interglacial and glacial, or Milankovitch, time scales. This is due to significant changes in water circulation, land-ocean interaction, and sea-ice formation. With the aim to reveal the climate and oceanographic history of the Bering Sea over the past 5 My, IODP Expedition 323 cored a total of 5741 m of sediment (97.4% recovery) at seven sites in 2009 on D/V JOIDES Resolution covering three regions: the Umnak Plateau, the Bowers Ridge, and the Bering Slope. The water depths of the drill sites range from 818 m to 3174 m, allowing for the characterization of past vertical water mass distribution including changes in the oxygen minimum zone. The four deepest holes range from 600 m to 745 m below the seafloor, and resulted in the recovery of long sediment sequences ranging from 1.9 My to 5 My in age. Following the expedition, two sampling parties at Kochi Core Center (for acquisition of ca. 58,000 subsamples) and two scientific meetings were conducted in order to proceed with the analyses of sediment core samples and discussions. Here, pertinent results, primarily from IODP Expedition 323, are consolidated as a single special volume of Deep-Sea Research Part II Topical Studies in Oceanography.

DOI： 10.1016/j.dsr2.2016.03.001

Language：English   Publishing type：Research paper (scientific journal)  

Radiolarian assemblages in sediment cores were investigated at the Integrated Ocean Drilling Program Site U1341 on Bowers Ridge in the southern Bering Sea. Radiolarian biozones at Site U1341 spanned the last 4 My from the youngest Amphimelissa setosa Zone (late Quaternary), via the Stylatractus universes Zone, the Eucyrtidium matuyamai Zone and a part of the Cycladophora sakaii Zone (middle to late Pliocene). The A. setosa Zone, newly proposed in this paper, is well correlated with the Botryostrobus aquilonaris Zone in the North Pacific Ocean. The bottom of the S. universus and top of the E. matuyamai Zones are emended in this paper by using the first common occurrence of A. setosa. Seventeen radiolarian datum points were identified at Site U1341 and tied to the geomagnetic and oxygen isotope stratigraphy. Radiolarian assemblages during the last 4 My showed a turnover from subarctic-transitional species (Spongopyle osculosa and Larcopyle buetschlii) to subarctic species (Ceratospyris borealis) between 3.6 and 2.4 Ma, corresponding to the intensification of the Northern Hemisphere Glaciation (NHG). Recent polar species (A. setosa and Actinomma boreale) appeared abundantly after the Mid-Pleistocene Transition (MPT, 1.2-0.8 Ma). Repeated numbers of individual peaks of the abundances of Cycladophora davisiana, dwelling in cold and well-ventilated intermediate water, suggest intermediate to deep water formation in the Bering Sea during the last 1 My.

DOI： 10.1016/j.dsr2.2015.03.004

Language：English   Publishing type：Research paper (scientific journal)  

High resolution paleoceanography of the Pliocene-Pleistocene is important in understanding climate forcing mechanisms and associated environmental changes during this major transition from global warmth to the Ice Ages. This is particularly true in high latitude marginal seas such as the Bering Sea. The Bering Sea has been very sensitive to changes in global climate during interglacial and glacial, or Milankovitch, time scales. This is due to significant changes in water circulation, land-ocean interaction, and sea-ice formation. With the aim to reveal the climate and oceanographic history of the Bering Sea over the past 5 My, IODP Expedition 323 cored a total of 5741 m of sediment (97.4% recovery) at seven sites in 2009 on D/V JOIDES Resolution covering three regions: the Umnak Plateau, the Bowers Ridge, and the Bering Slope. The water depths of the drill sites range from 818 m to 3174 m, allowing for the characterization of past vertical water mass distribution including changes in the oxygen minimum zone. The four deepest holes range from 600 m to 745 m below the seafloor, and resulted in the recovery of long sediment sequences ranging from 1.9 My to 5 My in age. Following the expedition, two sampling parties at Kochi Core Center (for acquisition of ca. 58,000 subsamples) and two scientific meetings were conducted in order to proceed with the analyses of sediment core samples and discussions. Here, pertinent results, primarily from IODP Expedition 323, are consolidated as a single special volume of Deep-Sea Research Part II Topical Studies in Oceanography.

DOI： 10.1016/j.dsr2.2016.03.001

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1016/j.dsr2.2016.03.001

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.dsr2.2015.03.004

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2015PA002801

Language：English   Publishing type：Research paper (scientific journal)  

We evaluated a 10 year time series of δ¹⁸O and δ¹³C records from three planktic foraminifers (Neogloboquadrina pachyderma, Globigerina umbilicata, and Globigerinita glutinata) in the Bering Sea and central subarctic Pacific with a focus on their responses to environmental changes. Foraminiferal δ¹⁸O followed the equilibrium equation for inorganic calcite, with species-specific equilibrium offsets ranging from nearly zero (-0.02‰ for N. pachyderma and -0.01‰ for G. umbilicata) to -0.16‰ (G. glutinata). Equilibrium offsets in our sediment trap samples were smaller than those from plankton tow studies, implying that foraminiferal δ¹⁸O was modified by encrustation during settling. Habitat/calcification depths varied from 35-55 m (N. pachyderma and G. umbilicata) or 25-45 m (G. glutinata) during warm, stratified seasons to around 100 m during winter, when the mixed layer depth increases. Unlike δ¹⁸O, foraminiferal δ¹³C showed species-specific responses to environmental changes. We found a dependency of δ¹³C in G. umbilicata on CO₃^2- concentrations in ambient seawater that agreed reasonably well with published laboratory results, suggesting that δ¹³C of G. umbilicata is subject to vital effects. In contrast, δ¹³C of N. pachyderma and G. glutinata are likely affected by other species-specific biological activities. Seasonal flux patterns reveal that fossil records of N. pachyderma and G. glutinata represent annual mean conditions, whereas that of G. umbilicata most likely indicates those of a specific season. Because none of these three taxa was abundant from December to February, their fossil records likely do not reflect isotope signals from cold seasons.

DOI： 10.1002/2015PA002801

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/2014PA002639

Language：English   Publishing type：Research paper (scientific journal)  

We performed a 9 day dissolution experiment with tests of the planktic foraminifer Globigerina bulloides at pH 6.7 ± 0.1 in water undersaturated with respect to calcite. The initial stage of the dissolution process, which is not recognizable from the surface structure of the tests, was quantitatively evaluated by X-ray microcomputed tomography (XMCT). XMCT revealed three distinct test structures: early-developed calcite formed during the juvenile stage of G. bulloides, an inner calcite layer, and an outer calcite layer. The test ultrastructure was observed by scanning electron microscopy, and CT number evaluated the density distribution in the test. The early-developed calcite and inner calcite layer had low CT numbers (500-1300; low density, porous) and were sensitive to dissolution, whereas the outer calcite layer had high CT numbers (<1300; high density) and resisted dissolution. Both the modes and the frequencies of the CT numbers decreased with progress of dissolution. Changes in the CT number histogram with progress of dissolution were quantified in terms of the percentage of calcite volume accounted for by low-density calcite (% Low-CT-number calcite). A clear linear relationship (R² = 0.87) between % Low-CT-number calcite and % Test weight loss was found. This relationship indicates that the amount of test dissolution can be estimated from the distribution of CT numbers. We propose that XMCT measurements will be useful for quantitatively estimating the amount of carbonate loss from foraminiferal tests by dissolution.

DOI： 10.1002/2014PA002639

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1002/jqs.2716

Language：English   Publishing type：Research paper (scientific journal)  

We present a method for determining sub-milligram quantities of biogenic opal. The method employs the inductive high-temperature carbon reduction method for dehydration of opal and reduction of silica, and a continuous-flow isotope ratio mass spectrometry system for direct analysis of the oxygen isotope ratio in the evolved carbon monoxide. The accuracy and precision of the online analytical system were evaluated by isotopic analysis of various quantities of standard SiO₂ in the range 40-538μg. The time required to analyse a single sample was relatively short (50min); hence, our method is suitable for routine analysis for paleoenvironmental studies that require large amounts of time-series data. The method was validated for samples in the sub-milligram range and can be applied to oxygen isotope analysis of various types of biogenic opal that have not been analysed because of their small amounts in natural samples. We successfully applied our method to (i) the first oxygen isotope analysis of monospecific radiolarian skeletons and (ii) high-resolution oxygen isotope analysis of Holocene diatom frustules from the Southern Ocean.

DOI： 10.1002/jqs.2716

Language：English   Publishing type：Research paper (scientific journal)  

As a source region of North Pacific Intermediate Water, the Okhotsk Sea plays an important role in the ventilation of the North Pacific. To understand the detailed oceanographic changes in this marginal sea since the last glaciation, we studied decadal to centennial scale proxy records from new sediment cores from the southwestern Okhotsk Sea. Glacial to Holocene δ¹⁴C records of benthic foraminiferal shells suggested enhanced ventilation in the Okhotsk Sea during the early deglacial period between 18 and 15ka, corresponding to Heinrich Event 1. Although the δ¹⁴C reconstruction has considerable uncertainties, the Okhotsk Sea may have acted as a source for vigorous ventilation of the subarctic Pacific during this period. CaCO₃ preservation events appear to be better explained by the ventilation history of the Okhotsk Sea than by coccolithophores and foraminifera production. CaCO₃ preservation started to improve during 18 to 15ka, and pronounced peaks in the CaCO₃ content corresponded to the Bølling-Allerød (15 to 13ka) and Preboreal (11.5 to 10ka) warm periods. Diatom and coccolithophore productivity remained low in the Okhotsk Sea throughout the glacial to deglacial periods, different from the situation in the open subarctic Pacific, where high productivity was observed during the Bølling-Allerød period. After the Preboreal period, biogenic opal gradually increased and δ¹⁵N decreased in the southern Okhotsk Sea, suggesting that productivity was enhanced by a relaxation of the nitrate limitation.

DOI： 10.1016/j.palaeo.2013.12.013

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.palaeo.2013.12.013

Language：English  

DOI： 10.1029/2011GB004177

Language：English   Publishing type：Research paper (scientific journal)  

Since 1997, ocean color satellite images have revealed large-scale blooms of the coccolithophorid Emiliania huxleyi in the eastern Bering Sea. The blooms are often sustained over several months and have caused ecosystem changes in the Arctic Ocean, as well as in the Bering Sea. We examined continental shelf sediment profiles of alkenone, a biomarker for E. huxleyi, covering the past ∼70 years. The alkenone records suggest that large E. huxleyi blooms are a novel feature in the Bering Sea as they have occurred only since the late 1970s. Recent changes in alkenone content were closely related to the 1976-77 climatic regime shift in the North Pacific, implying that warming and freshening of Bering Sea waters promoted E. huxleyi blooms. The production rate of diatoms (total valves in sediment samples), the dominant primary producers in the Bering Sea, also increased during the past several decades. However, the ratio of alkenone content to total diatom valves in the sediments increased as E. huxleyi production increased, suggesting that the increase in the E. huxleyi production rate frequently exceeded the increase in the diatom production rate. Overall, our results indicate a possible subarctic region ecosystem shift driven by climate change.

DOI： 10.1029/2011GB004177

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1029/2011GC004029

Language：English   Publishing type：Research paper (scientific journal)  

Optically stimulated luminescence (OSL) dating is now widely accepted as a chronometer for terrestrial sediment. More recently, it has been suggested that OSL may also be useful in the dating of deep-sea marine sediments. In this paper, we test the usefulness of high resolution quartz OSL dating in application to a 19 m marine sediment core (MR0604-PC04A) taken from the southwestern Sea of Okhotsk, immediately to the north of Hokkaido, Japan. Fine-grained quartz (4 to 11 μm) was chosen as the dosimeter, and a single-aliquot regenerative-dose protocol was used for the determination of equivalent dose (D_e), with stimulation by both infrared and blue light. The suitability of the measurement procedure was confirmed using dose recovery tests. A high resolution record (∼2 OSL ages/m) identified clear sedimentation rate changes down the core. The OSL ages are significantly dependent on the water content model chosen; two alternative interpretations are discussed, and the geologically preferred model identified. However, ages resulting from the observed (non-modeled) water content lie closest to the available radiocarbon ages (in the range back to 20 ka). Our OSL ages confirm the known high sedimentation rates in this locality, and for the first time demonstrate clear differences in sedimentation rate before, during and after deglaciation. Although the apparent accuracy of single sample ages is not always consistent with expectations, average ages are accurate, and our data show that OSL dating can be a powerful method for establishing high resolution marine chronologies.

DOI： 10.1029/2011GC004029

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.dsr2.2011.12.007

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.dsr2.2011.03.005

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.dsr2.2011.12.002

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2011GL050567

Language：English   Publishing type：Research paper (scientific journal)  

We reconstructed the ventilation record of deep water at 2100 m depth in the mid-latitude western North Pacific over the past 25 kyr from radiocarbon measurements of coexisting planktic and benthic foraminiferal shells in sediment with a high sedimentation rate. The ¹⁴C data on fragile and robust planktic foraminiferal shells were concordant with each other, ensuring high quality of the reconstructed ventilation record. The radiocarbon activity changes were consistent with the atmospheric record, suggesting that no massive mixing of old carbon from the abyssal reservoir occurred throughout the glacial to deglacial periods.

DOI： 10.5194/cp-8-17-2012

Language：English   Publishing type：Research paper (scientific journal)  

Several techniques have been introduced in the last decades for the dehydration and release of O₂ from biogenic silica (opal-A) for oxygen-isotope analysis. However, only one silica standard is universally available: a quartz standard (NBS28) distributed by the IAEA, Vienna. Hence, there is a need for biogenic silica working standards. This paper compares the existing methods of oxygen-isotope analyses of opal-A and aims to characterize additional possible working standards to calibrate the δ¹⁸O values of biogenic silica. For this purpose, an inter-laboratory comparison was organized. Six potential working standard materials were analysed repeatedly against NBS28 by eight participating laboratories using their specific analytical methods. The materials cover a wide range of δ¹⁸O values (+23 to +43‰) and include diatoms (marine, lacustrine), phytoliths and synthetically-produced hydrous silica. To characterize the proposed standards, chemical analyses and imaging by scanning electron microscopy (SEM) were also performed. Despite procedural differences at each laboratory, all methods are in reasonable agreement with a standard deviation (SD) for δ¹⁸O values between 0.3‰ and 0.9‰ (1σ). Based on the results, we propose four additional biogenic silica working standards (PS1772-8: 42.8‰; BFC: 29.0‰; MSG60: 37.0‰; G95-25-CL leaves: 36.6‰) for δ¹⁸O analyses, available on request through the relevant laboratories.

DOI： 10.1016/j.gca.2011.08.011

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1016/j.gca.2011.08.011

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.gloplacha.2009.12.005

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1130/G30225.1

Language：Japanese   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1177/0959683609105298

Language：English   Publishing type：Research paper (scientific journal)  

In this paper, we compile the plankton tow and sediment trap data previously obtained in the North Pacific and discuss the relevant results for ten representative radiolarian taxa. Didymocyrtis tetrathalamus and Tetrapyle octacantha group are controlled by warm water currents. Tetrapyle octacantha group is a Tropical-Subtropical indicator whose living zone is broader than that of D. tetrathalamus. Pseudocubus obeliscus is a productivity indicator. Spongotrochus glacialis appears to be advected from the Subarctic Current through the California Current into the central Equatorial Pacific. Pseudodictyophimus gracilipes, Stylochlamydium venustum, Larcopyle butschlii, and Litharachnium tentorium show distributions conformable with the "tropical submergence" hypothesis. Botryostrobus aquilonaris and Stylodictya aculeata seem to be associated with upwelling and we define them as "upwelling" taxa.

Language：English   Publishing type：Research paper (scientific journal)  

Coarse size (>63μm) radiolarian fluxes along the Equator in the central and western Pacific between 145°E and 160°W (Stations MT3, MT4, MT5, MT6 and MT7) were examined during January 1999 to January 2003 in order to evaluate how radiolarian assemblages respond to the El Niño Southern Oscillations (ENSO). Radiolarian fluxes were constrained by the water masses: the Western Pacific Warm Pool (WPWP) located in the west and the Equatorial Upwelling Region (EUR) east of the WPWP in the central equatorial Pacific. In general, radiolarian fluxes gradually increased from the western sites to the eastern sites, responding to the increases in nutrient supply and primary production in the euphotic layer. Notable annual cycles of radiolarian fluxes observed at the two Stations with nearly complete time series (MT3 and MT5) were likely corresponding to the rainy seasons of Papua New Guinea (MT3) and the extent of upwelling intensity in the equatorial Pacific (MT3 and MT5). With transition from La Niña to El Niño during 2001 to 2002, high radiolarian fluxes were coincident with cooler surface water. Among the radiolarian taxa, Lithomelissa sp. group and Pseudocubus obeliscus Haeckel 1887, which were mainly dwelling in the surface water in the EUR, responded distinctively to the WPWP excursion and decreased their fluxes as surface water temperature rose.

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Language：English   Publishing type：Research paper (scientific journal)  

Cycladophora davisiana, a radiolarian species dwelling at mesopelagic depths, is known as a representative glacial fauna due to its unique distribution during glacial periods. In the present ocean, abundant production of C. davisiana is only observed in the Okhotsk Sea, indicating an adaptation of C. davisiana for seasonal sea-ice covered conditions. We found pronounced abundant production of C. davisiana during the early to middle Holocene in the Okhotsk Sea, suggesting more favorable conditions for C. davisiana than the present Okhotsk Sea. In order to clarify the reason, oceanographic conditions during the Holocene were reconstructed based on biomarkers, lithogenic grains including ice-rafted debris (IRD), biogenic opal, and total organic carbon (TOC) in two sediment cores from the Okhotsk Sea. These indicators suggest that the pronounced C. davisiana production may be attributed to: 1) a supply to mesopelagic depths under intensified stratification of fine organic particles derived from coccolithophorids, bacteria, and detrital materials; and 2) cold, well-ventilated intermediate water formation.

DOI： 10.1007/s10872-006-0082-2

Language：English   Publishing type：Research paper (scientific journal)  

DOI： https://doi.org/10.1007/s10872-006-0082-2

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.dsr2.2005.07.007

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.dsr2.2005.07.006

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2004GL022260

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.marmicro.2004.01.003

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1029/2003GL018070

Event date： 2023.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：幕張メッセ+Online   Country：Japan  

Event date： 2023.5

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Venue：幕張メッセ+Online   Country：Japan  

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Venue：幕張メッセ+Online   Country：Japan  

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Venue：幕張メッセ+Online   Country：Japan  

Event date： 2022.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：高知大学   Country：Japan  

Event date： 2022.5

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Venue：幕張メッセ+Online   Country：Japan  

Event date： 2022.5

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Venue：幕張メッセ+Online   Country：Japan  

Event date： 2022.5

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Venue：幕張メッセ+Online   Country：Japan  

Event date： 2022.5

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Venue：幕張メッセ+Online   Country：Japan  

Event date： 2021.10

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.10

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Venue：Online   Country：Japan  

Event date： 2021.5

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2021.5

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Venue：Online   Country：Japan  

Event date： 2020.11

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Venue：Online   Country：Japan  

Event date： 2020.7

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Venue：Online   Country：Japan  

Event date： 2020.7

Language：English   Presentation type：Oral presentation (general)  

Venue：Online   Country：Japan  

Event date： 2020.7

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Venue：Online   Country：Japan  

Event date： 2019.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：産業技術総合研究所   Country：Japan  

Event date： 2019.11

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：産業技術総合研究所   Country：Japan  

Event date： 2019.9

Language：English  

Venue：University of New South Wales   Country：Australia  

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：幕張メッセ   Country：Japan  

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.6

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2019.6

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Country：Japan  

Event date： 2018.5

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Venue：幕張メッセ   Country：Japan  

Event date： 2018.5

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Venue：幕張メッセ   Country：Japan  

Event date： 2018.5

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Venue：幕張メッセ   Country：Japan  

Event date： 2018.5

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Venue：幕張メッセ   Country：Japan  

Event date： 2018.5

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Venue：幕張メッセ   Country：Japan  

Event date： 2017.11

Language：Japanese  

Venue：九州大学   Country：Japan  

Event date： 2017.11

Language：Japanese  

Venue：九州大学   Country：Japan  

Event date： 2017.11

Language：Japanese  

Venue：九州大学   Country：Japan  

Event date： 2017.11

Language：Japanese  

Venue：九州大学   Country：Japan  

Event date： 2017.11

Language：Japanese  

Venue：九州大学   Country：Japan  

Event date： 2017.11

Language：Japanese  

Venue：九州大学   Country：Japan  

Event date： 2017.11

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Venue：九州大学   Country：Japan  

Event date： 2017.11

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Venue：九州大学   Country：Japan  

Event date： 2017.10

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Venue：Niigata   Country：Japan  

Event date： 2017.10

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Venue：三方青年の家   Country：Japan  

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Event date： 2017.7

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Venue：幕張メッセ   Country：Japan  

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Venue：幕張メッセ   Country：Japan  

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Venue：幕張メッセ   Country：Japan  

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Venue：幕張メッセ   Country：Japan  

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Venue：鹿児島大学   Country：Japan  

Event date： 2016.8

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Venue：Utrecht   Country：Netherlands  

Event date： 2016.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：日光   Country：Japan  

Event date： 2016.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：日光   Country：Japan  

Event date： 2016.8

Language：Japanese   Presentation type：Oral presentation (general)  

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Event date： 2016.8

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Venue：Utrecht   Country：Netherlands  

Event date： 2016.7 - 2016.8

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Venue：Nagoya   Country：Japan  

Event date： 2016.6

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Venue：Yokohama   Country：Japan  

Event date： 2016.6

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Venue：Yokohama   Country：Japan  

Event date： 2016.5

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Venue：神戸大学   Country：Japan  

Event date： 2016.5

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Venue：幕張メッセ   Country：Japan  

Event date： 2016.5

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Venue：幕張メッセ   Country：Japan  

Event date： 2016.5

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Venue：幕張メッセ   Country：Japan  

Event date： 2016.5

Language：Japanese  

Venue：幕張メッセ   Country：Japan  

Event date： 2015.5 - 2016.5

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Event date： 2015.5

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Venue：幕張メッセ   Country：Japan  

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Venue：幕張メッセ   Country：Japan  

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Presentation type：Oral presentation (general)  

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Event date： 2008.10

Presentation type：Oral presentation (general)  

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Language：Japanese   Presentation type：Oral presentation (general)  

Venue：愛媛大学   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：幕張メッセ   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：九州大学   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京大学大気海洋研究所   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Irvine, California   Country：United States  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京大学大気海洋研究所   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：幕張メッセ   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Sitges   Country：Spain  

Language：English   Presentation type：Oral presentation (general)  

Venue：Sitges   Country：Spain  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：北海道大学   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京大学大気海洋研究所   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：海洋研究開発機構   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：パシフィコ横浜   Country：Japan  

Language：English  

Venue：Sapporo   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Bern   Country：Switzerland  

Language：English   Presentation type：Oral presentation (general)  

Venue：Bern   Country：Switzerland  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：東京大学大気海洋研究所   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：高知大学   Country：Japan  

Language：English   Presentation type：Oral presentation (general)  

Venue：Korea Institute of Geoscience and Mineral Resources   Country：Korea, Republic of  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Language：Japanese   Publishing type：Article, review, commentary, editorial, etc. (scientific journal)  

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：11

Number of peer-reviewed articles in Japanese journals：0

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：0

Type：Competition, symposium, etc. 

Type：Academic society, research group, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：5

Number of peer-reviewed articles in Japanese journals：2

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：3

Number of peer-reviewed articles in Japanese journals：2

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：5

Number of peer-reviewed articles in Japanese journals：0

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：0

Type：Competition, symposium, etc. 

Number of participants：60

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：4

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Number of participants：21

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：2

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Academic society, research group, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Academic society, research group, etc. 

Type：Competition, symposium, etc.