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Various herbivorous invertebrates in seagrass beds are considered to be generalists in food use and their diets may temporally fluctuate according to the availability of food sources. We assessed whether food sources of herbivorous gastropods vary in a subtropical seagrass bed in Nagura Bay, Ishigaki Island, where coexisting seaweeds grow densely in spring but minimally in summer. Abundant gastropods and their possible food sources were collected in spring and summer of 2013 and 2015, and their stable carbon and nitrogen isotope ratios were measured. Between the two seasons, each possible food source had similar isotopic values, but all the herbivorous gastropod species in summer were more enriched in 13C than the gastropod samples in spring. The mixing models in SIAR (Stable Isotope Analysis in R) showed that the total contribution rates of seaweeds, i.e. rhodophytes, phaeophytes and chlorophytes, for all herbivorous gastropod species decreased from spring to summer; in contrast, the contribution rate of seagrasses increased. Linear Mixed Models showed that the seasonal variation in δ13C of the herbivorous gastropods was larger than that of the possible food sources, adding further evidence to the seasonal change in food sources of the herbivorous gastropods. This seasonal change in food use appears to correspond to the change in seaweed biomass, suggesting that herbivorous gastropods flexibly change their diets depending on food availability.
This study establishes the chronological framework of the sedimentary sequence deposited Dead Sea, ICDP 5017-1, Radiocarbon chronology during the past 50 ka at the deepest part of the Dead Sea (the ICDP 5017-1 site), which was recovered by the Dead Sea Deep Drilling Project (DSDDP) under the auspices of the International Continental Scientific Drilling Program (ICDP). The age-depth model is constructed using 38 14C dates of terrestrial plant remains in a composite 150-m-long profile, generated by anchoring 32 marker layers identified in five cores. The sedimentary records at the ICDP 5017-1 site fills gaps in those obtained from the exposed sections at the high margins of the lake, particularly in times of lake-level retreat, and allows for a high-resolution comparison between the lake’s margins and deepest floor.
The friction of pure ice against various materials was studied at the melting point by pulling plates of the materials of known roughness under a melting ice sample, which was loaded from above, and by maintaining a surrounding air temperature of +2°C (±1°C). Speed was varied over a wide range from 0.05 to 400 mm s−1.
Results for an aluminium sheet of roughness Ra = 0.84 μm, showed a maximum in friction coefficient of 0.04 at a speed of 16 mm s−1. Below this speed the friction coefficient dropped to 0.002 at 0.2 mm s −1 and results from different ice samples were very reproducible. Above 16 mm s−1, the friction coefficient initially dropped to about 0.002 at 100 mm s−1, and then increased again to 0.037 at 400 mm s−1. Results at speeds above 16 mm s−1 were much less reproducible than those at lower speeds. Results are given also for the friction of ice on Formica, acrylic, and copper plates.
The amount of meltwater produced during a test was measured by weighing an absorbent tissue before and after mopping-up the meltwater. The amount of meltwater was significantly more for aluminium than for Formica or acrylic, showing that the thermal conductivity of the slider was controlling the amount of meltwater. The amount was also a strong function of velocity.
The evolution of the outer lake of Hwajinpo Lagoon in Korea has been reconstructed using environmental proxies (lithologic, geochemical, and fossil data) with a chronology established using 7 accelerator mass spectrometry (AMS) radiocarbon dates. Grain size, water content, and X-ray analyses from the core of outer coastal lakes (HJ99) were used to reconstruct sedimentary environments by using total organic carbon, C/N, S, and C/S chemical proxies. Assemblages of mollusc remains also provided paleoenvironmental information. The environmental changes of the outer lake of Hwajinpo Lagoon can be divided into 6 depositional phases. The basin of the Hwajinpo was exposed and underwent a weathering process before the Holocene period. The muddy sand layer on the weathered bedrock indicated an estuarine system about 6000 BP. The laminated layer implies that the lagoonal system was anoxic between about 5500–2800 BP. The marl layer implies a relatively oxic lagoonal condition with mollusc presence about 2500 B P. The layer of very low sulfur content indicates a freshwater lake system isolated by a sand barrier about 1700 BP. Beginning about 1000 B P, the river system deposits progress progradation on the marl layer. Two erosional landforms could be related with a high standing sea level span during Holocene. These high-stands are dated at 5700 BP and 2200 BP and are supposed to have formed erosional landforms of about 1.6 amsl and 0.8 amsl, respectively. Environmental changes of the outer lake of Hwajinpo Lagoon are considered due mainly to the lake- and sea-level fluctuation during Holocene.
A surface-water Δ14C record of AD 1948–1999 in the tropical South China Sea (SCS) has been reconstructed from accelerator mass spectrometric radiocarbon measurements of annual bands of a Pontes coral collected from Con Dao Island, Vietnam. Results gave the following Δ14C time series: a steady state of −47.8 ± 2.8‰ (mean ± SD, n = 8) during 1948–1955 (i.e. in the pre-bomb period); a sharp increase during 1956–1966; a gradual increase during 1967–1973; a relatively high maximum value of ∼174‰ in 1973; and a gradual decrease for the following period to ∼86‰ in 1999. This Δ14C record having a sharp increase and a relatively high peak is similar to the records of subtropical corals (latitudes 21–27°) and is distinctly different from the records of equatorial/tropical corals (latitudes <10°), although our coral sample was collected from an equatorial/tropical region (8°39′N, 106°33′E). This can be explained by the geographic, oceanographic, and climatic setting of our study site. The SCS is a semi-enclosed marginal sea in the far western tropical Pacific and is little influenced by equatorial upwelling or related ocean currents. Our study site is located in the southwestern SCS, where an enormous submerged plain (the Sunda Shelf) spreads out with very shallow waters (mean depth <100 m). Furthermore, in the SCS, the East Asian monsoon (a strong, seasonally reversing wind system) enhances air-sea gas exchange especially in the mainland coastal waters, including our study site. Such semi-enclosed shallow waters with enhanced ventilation were probably very sensitive to the atmospheric nuclear explosions in the late 1950s and early 1960s and caused the sharp increase and high peak in the coral Δ14C record. Our coral Δ14C values in the southwestern SCS are significantly higher than the values in the northwestern SCS (Xisha Islands), which seems to suggest that meridional mixing of surface waters is not active in the SCS and that the open-ocean water intruding into the northern SCS (i.e. the Kuroshio intrusion) has only a limited influence on the southern SCS.
We assessed marine reservoir age R(t) for the costal area of the northwest Pacific using radiocarbon measurements of the annually banded coral core (Porites sp) collected on Ishigaki Island in southern Japan. Reservoir age R(t) during the early 1900s at the Pacific coast of Ishigaki Island ranged between 290 and 455 14C yr, with a weighted mean of 355 ± 25 14C yr (n=5, ±1 σ). The regional-specific ΔR, defined as 14C age difference of regional and world ocean surface layer, was 35 ± 25 14C yr (n=5, ±1σ) on average and increased between 1900 and 1950.
We collected pore waters using an in situ pore water-squeezer for a submersible Shinkai 2000 at six depths beneath the sediment surface within a deep-sea “cold seep” giant clam community off Hatsushima Island, Sagami Bay, Japan. A box core sample was also collected ca. 4.5 km east of the community and pore waters were separated. Dissolved inorganic carbon (DIC) was extracted and purified in a vacuum line and 14C concentration was determined with a Tandetron accelerator mass spectrometer at Nagoya University after conversion to graphite targets using a batch Fe-catalytic hydrogen reduction method. ∆14C values decreased with increasing depth to −938‰ at the sulfate concentration minimum. This indicates that methane used for the active reduction of sulfate and formation of hydrogen sulfide, which is used by symbiotic chemoautotrophic bacteria in gills of the giant clams, is almost dead and is likely supplied from the deep. ∆14C values of DIC vary linearly with δ13C values along a mixing line between that in the bottom water and that produced by the oxidation of dead methane. The δ13C value of DIC oxidized from dead methane is estimated to be ca. −45‰.
A coral radiocarbon (Δ14C) investigation with a high time-resolution is crucial for reconstructing secular and seasonal Δ14C changes in the surface seawater which potentially reflect ocean circulations and dynamic ocean-atmosphere interactions. The Δ14C values of a modern coral (Porites sp.) from Kikai Island, southern Japan, in the subtropical northwestern Pacific, were determined for the period of 1991-1998 at a monthly resolution. A coral Δ14C time series for the 8 yr indicated seasonal cycles superimposed on a secular decreasing trend of 3.8 per yr. The seasonal amplitude of the coral Δ14C was about 18 on the average, and the minimum Δ14C was observed in late spring and summer. The Δ14C changes were tentatively explained by horizontal oceanic advections around Kikai Island or over the wide range of the equatorial and sub-equatorial Pacific.
Air sample collections over the western Pacific have continued since 1992 as a part of Center for Global Environmental Research, National Institute for Environmental Studies (CGER-NIES) global environmental monitoring program. The air samples collected on the Japan-Australia transect made it possible to trace the seasonal and secular 14CO2 variations, as well as an increasing trend of greenhouse gases over the western Pacific. A subset of CO2 samples from latitudes of 10–15°N and 23–28°S were chosen for accelerator mass spectrometry (AMS) 14C analysis using a NIES-TERRA AMS with a 0.3–0.4% precision. These 14CO2 records in maritime air show seasonal variations superimposed on normal exponential decreasing trends with a time constant of about 16 yr. The Δ14C values in the Northern Hemisphere are lower those in the Southern Hemisphere by 3–4 during 1994–2002. The Northern Hemisphere record shows relatively high seasonality (2.3 ± 1.5) as compared with the Southern Hemisphere (1.3 ± 1.2). The maximum values of seasonal cycles appear in late autumn and early winter in the Northern and Southern Hemispheres, respectively. Oscillations of 1–10 yr over the western Pacific are found to correlate possibly with the El Niño/Southern Oscillation (ENSO) events.
In order to measure the concentrations of anthropogenically influenced gases in the stratosphere, we have collected air samples from the lower stratosphere since 1985, by a balloon-borne cryogenic sampling method, developed at the Institute of Space and Astronautical Science (ISAS). Air samples of ≃16 liters at STP were collected in the stratosphere at altitudes from 18.6 to 30.4 km, over the northeastern part of Japan (39.5°N, 139–142°E), on 1 September 1989. We conducted 14C analyses to study the vertical and horizontal air-mass movement in the stratosphere, and to investigate the air transport mechanism between troposphere and stratosphere. Carbon dioxide (containing a few mg carbon) was separated cryogenically from the air samples, and the 14C concentration of the CO2 was measured by a Tandetron accelerator mass spectrometer, using Fe-graphite targets prepared by reducing CO2 on Fe-powder with hydrogen in a Vycor tube at 650°. The 14C concentrations, expressed as Δ14C, of CO2 were 267–309‰ at altitudes of 21–30 km, and 134‰ at 19–20 km. The Δ14C values at 21–30 km were higher than those of the current tropospheric CO2, of around 80–200‰. The observed 14C concentrations, higher in the stratosphere than the troposphere, seem to be explained by large bomb-produced 14C inventories and/or high 14C production by cosmic rays, as well as weak vertical mixing of air masses in the stratosphere.
We have developed a method of graphitization from CO2 samples for accurate 14C measurements by accelerator mass spectrometry. Our batch method, using a sealed Vycor tube, reduces the risk of contamination during graphitization and makes it possible to prepare many samples in a short time (typically 20 samples per day).
A sequence of annually laminated sediments is a potential tool for calibrating the radiocarbon time scale beyond the range of the absolute tree-ring calibration (11 ka). We performed accelerator mass spectrometric (AMS) 14C measurements on >250 terrestrial macrofossil samples from a 40,000-yr varve sequence from Lake Suigetsu, Japan. The results yield the first calibration curve for the total range of the 14C dating method.
We measured radiocarbon in an annually-banded coral core collected from Con Dao Island, Vietnam, 90 km from the mouth of the Mekong River, and estimated the regional correction of the marine reservoir age (ΔR value). Twelve samples were continuously taken from the annual bands (AD 1949–1960) which were clearly identified under UV light (∼352 nm) as well as by X-radiography. The 14C content of the samples was determined using an accelerator mass spectrometer at the National Institute for Environmental Studies, Tsukuba, Japan. Results provide a Δ14C time series showing a relatively steady value of −48.6 ± 4.6‰ for the period of 1949–1955 and an abrupt increase starting from 1956 that indicates a quick response to the atmospheric testing of nuclear bombs. Using the prebomb 14C data, the ΔR value in the south of Vietnam is estimated to be −74 ± 39 yr.
We made accelerator mass spectrometry (AMS) 14C measurements on terrestrial macrofossils from the Late Pleistocene/Holocene of the annually laminated sediments of Lake Suigetsu (central Japan). The AMS 14C dates of terrestrial macrofossils showed agreement between varve counting years and calibrated ages (tree rings and U/Th on coral) in the interval of 10.5 and ca. 11.5 ka cal bp. Beyond 11.5 ka cal bp, the age difference between 14C and varve counting years gradually diminish, contradicting published data on corals dated by U/Th and 14C.
In comparison with windward coral reefs, the facies and evolution of leeward coral reefs has been discussed to a lesser extent. By accelerator mass spectrometry (AMS) carbon-14 dating of coral specimens collected from the trench excavated across a modern coral reef during a fishery port repair, we revealed the internal facies and Holocene evolution of a leeward reef in Ishigaki Island, Ryukyu Islands, southwest Japan. The reef facies can be split into three facies: the tabular Acropora framework facies, the tabular Acropora reworked facies, and the unconsolidated bioclast facies. The tabular Acropora reworked facies first formed a ridge by 3500 BR Then, the tabular Acropora framework facies grew both upward and seaward. The accumulation rates of the tabular Acropora framework facies ranged from 2.2 to 8.3 m/ka. Thus, the reef framework facies and accumulation rates of this leeward reef is similar to those of windward reefs, although the age of the reef top is younger than that of windward reefs.
This paper presents the variation of radiocarbon content in annual tree rings for the period AD 1413–1553, which includes the Spoerer Minimum period (AD 1415–1534). Since the variation of the production rate of 14C is strongly related to solar activity, the variation of 14C content in annual tree rings gives us information on the characteristics of variation of solar activity. We have studied solar activity during the grand solar minima, focusing especially on the stability of the 11-yr cycle. The minima are determined to have been almost free of sunspots. Our results, however, have revealed quite remarkably the existence of the 11-yr cycle for most of the time during the Spoerer Minimum. The 11-yr variation weakened around AD 1460–1510, suggesting that solar activity might have been strongly suppressed during these 50 yr.
This paper presents an updated atmospheric radiocarbon calibration from annually laminated (varved) sediments from Lake Suigetsu (LS), central Japan. As presented earlier, the LS varved sediments can be used to extend the radiocarbon time scale beyond the tree ring calibration range that reaches 11,900 cal BP. We have increased the density of 14C measurements for terrestrial macrofossils from the same core analyzed previously. The combined data set now consists of 333 measurements, and is compared with other calibration data.
The paper consists of three parts A, B and C. In part A, “A contribution to the methodology of biomathematics”, general considerations on mathematical analysis and automaton theory are given in order to show how and why new approaches for biomathematics are required from the standpoint of information science. In fact three requirements are mentioned: (1°) general system approach; (2°) historical approach; (3°) three indispensable constituent fields of biological science. Regarding (1°), the author refers to his work on the logic of information science explained in 1968 at the CAS Seminar in Dubrovnik and published in 1969 in a Japanese monograph. Regarding (2°), reference is made to his paper “A contribution to the methodology of futurology” published in International Conference on Futurology, April 1970, Kyoto. The three indispensable constitutent fields are given by (a) theoretical, (b) experimental and (c) engineering biologies. In view of these three requirements, characteristic features of biomathematics in connection with an information science approach are (1°) discrete, (2°) combinatorial, (3°) dynamical, (4°) evolutionary, and (5°) design mathematics.