Development of a thin diatom layer observed in a stratified embayment in Japan     

Goh Onitsuka  Yutaka Yoshikawa  Tomoyuki Shikata  Kei Yufu  Kazuo Abe  Takahisa Tokunaga  Katsunori Kimoto  Takeshi Matsuno 《Journal of Oceanography》2018,74(4):351-365

The temporal evolution of a thin phytoplankton layer was observed by field measurements using a research vessel and mooring instruments in the Yatsushiro Sea, a semi-enclosed narrow embayment in Japan, in early August 2013. The subsurface chlorophyll maximum developed into a thin layer within 2 days just below the pycnocline at around 10-m depth, where turbulent mixing (the dissipation rate of turbulent kinetic energy) was weak (low). The layer persisted for 1.5 to 2 days and declined after irradiance drastically decreased at the sea surface. At the peak period, the layer thickness, which is defined as the full-width at half-maximum of the peak in chlorophyll a concentration, ranged from 0.6 to 1.4 m, and the maximum concentration reached 42.3 mg m^?3. The horizontal extent of the layer was approximately 10 km along the longitudinal axis of the bay. The phytoplankton population characterized by the layer was dominated by a chain-forming centric diatom, Chaetoceros spp. The formation mechanisms of the thin diatom layer were investigated using the observed data and a vertical one-dimensional model that includes physical and biological processes. The results suggest that the development of the thin layer was caused by in situ growth and aggregation due to nutrient-dependent sinking of the species under weak turbulence. The study highlights that continuous multidisciplinary observations and understanding species-specific physiological responses to environmental variations are necessary to elucidate drastically fluctuating phytoplankton dynamics in a coastal water.  相似文献   

霞浦湖沉积物需氧速率的研究   总被引：5，自引：1，他引：5  

范成新  相崎守弘  福岛武彦  松重一夫 《海洋与湖沼》1998,29(5):508-513

１９９５年２月,用大口径采样器采集日本霞浦湖土浦湾和湖心柱状沉积物样品,在２０℃恒温蔽光封闭条件下,研究了该湖泊沉积物需氧（ＳＯＤ）速率及实验前后上覆水和间隙水中形态营养物浓度变化,结果表明,实验初期（０－５ｈ）ＳＯＤ速率随时间呈线性上升,大于５ｈ后呈非线性下降,对线性部分计算的ＳＯＤ速率约在０．６－１．８ｍｇ／（ｍ＾２．ｄ）之间,实验发现,上覆水和表层间隙水中形态营养物Ｆｅ（Ⅱ）,ＮＨ＾＋４－Ｎ  相似文献   

Estimation of urban heat island intensity using biases in surface air temperature simulated by a nonhydrostatic regional climate model     

Akihiko Murata  Hidetaka Sasaki  Mizuki Hanafusa  Kazuo Kurihara 《Theoretical and Applied Climatology》2013,112(1-2):351-361

This study demonstrates that urban heat island (UHI) intensity can be estimated by comparing observational data and the outputs of a well-developed high-resolution regional climate model. Such an estimate is possible because the observations include the effects of UHI, whereas the model used does not include urban effects. Therefore, the errors in the simulated surface air temperature, defined as the difference between simulated and observed temperatures (simulated minus observed), are negative in urban areas but 0 in rural areas. UHI intensity is estimated by calculating the difference in temperature error between urban and rural areas. Our results indicate that overall UHI intensity in Japan is 1.5 K and that the intensity is greater in nighttime than in daytime, consistent with the previous studies. This study also shows that root mean square error and the magnitude of systematic error for the annual mean temperature are small (within 1.0 K).  相似文献   

Comparison of four ensemble methods combining regional climate simulations over Asia     

Jinming Feng  Dong-Kyou Lee  Congbin Fu  Jianping Tang  Yasuo Sato  Hisashi Kato  John L. Mcgregor  Kazuo Mabuchi 《Meteorology and Atmospheric Physics》2011,111(1-2):41-53

A number of uncertainties exist in climate simulation because the results of climate models are influenced by factors such as their dynamic framework, physical processes, initial and driving fields, and horizontal and vertical resolution. The uncertainties of the model results may be reduced, and the credibility can be improved by employing multi-model ensembles. In this paper, multi-model ensemble results using 10-year simulations of five regional climate models (RCMs) from December 1988 to November 1998 over Asia are presented and compared. The simulation results are derived from phase II of the Regional Climate Model Inter-comparison Project (RMIP) for Asia. Using the methods of the arithmetic mean, the weighted mean, multivariate linear regression, and singular value decomposition, the ensembles for temperature, precipitation, and sea level pressure are carried out. The results show that the multi-RCM ensembles outperform the single RCMs in many aspects. Among the four ensemble methods used, the multivariate linear regression, based on the minimization of the root mean square errors, significantly improved the ensemble results. With regard to the spatial distribution of the mean climate, the ensemble result for temperature was better than that for precipitation. With an increasing number of models used in the ensembles, the ensemble results were more accurate. Therefore, a multi-model ensemble is an efficient approach to improve the results of regional climate simulations.  相似文献   

中部冲绳海沟及伊豆,小笠原伴随海底热水活动的碳素起源     

酒井均  角皆润 《矿物岩石》1995,15(1):63-71

本文对日本中部冲绳海沟，小笠原弧的水了海山、爱丽斯泉与太平洋中央海岭威玛斯海盆等不同大地构造单元中的热水系，运用Ｃ，Ｎｅ，Ｎ等元素－同位素地球化学方法进行分析，对比和研究，并探讨了热水系中碳氮的来源，为大地构造单元的划分对比，提供了新的地球化学依据。  相似文献   

Geochemistry of hydroxy acids in sediments—I. Some freshwater and brackish water lakes in Japan     

Kazuo Fukushima  Hiroshi Kondo  Susumu Sakata 《Organic Geochemistry》1992,18(6)

Series of α, β, ω and (ω-1) hydroxy fatty acids (FAOHs) were determined in several freshwater and brackish water lacustrine sediments in Japan. Analytical procedure used was digestion of the solvent-extracted sediment with HF/HCl followed by solvent and saponification extraction of the residue. Abundances of α/β and ω-FAOH determined by this procedure were 2–3 times higher than those obtained by single alkaline saponification and of the same order with those provided by HCl hydrolysis. Major portion of α/β-FAOH was obtained by solvent extraction of the acid-treated sediments, while subsequent alkaline saponification was needed for the majority of ω-FAOH to be recovered. Thus determined FAOHs comprised 33–61% (Av. = 42%) of the “bound” acid constituents in the lacustrine surface sediments. The α/β and ω-FAOH composition was principally the same among the samples examined, except for relative proportions of the iso to anteiso C₁₅ and C₁₇ ß(α)-FAOH, which showed significant variations in the ranges of 0.30–1.1 and 0.46–1.5, respectively. In the holomictic lakes, the ratios together with the same ratios of the “bound” branched monocarboxylic acids tended to decrease with increasing water depth of the lakes, suggesting that the ratios may indicate an extent of the early diagenetic alteration of the bacteria-derived lipids either in water column or in surface sediment.  相似文献   

A simulation of continental basin margin sedimentation in response to crustal movements, eustatic sea level change, and sediment accumulation rates   总被引：1，自引：0，他引：1  

William Helland-Hansen  Christopher GSt C. Kendall  Ian Lerche  Kazuo Nakayama 《Mathematical Geology》1988,20(7):777-802

As eustasy, subsidence, and sediment accumulation vary, a 2D computer-based graphical simulation generates on-lapping and off-lapping geometries of both marine and near coastal alluvial deposits, reproducing timelines within sediment-bodies at basin margins. In the simulation, deposition is expressed by creation of new surfaces above previous ones. Thicknesses of layers are reduced by both erosion and compaction while their surfaces move vertically in response to tectonic change and loading. Simulation is divided into a series of equal time steps in which sediment is deposited as an array of en-echelon columns that mark the top of the previous depositional surface. The volume of sediment deposited in each time step is expressed as a 2D cross section and is derived from two right-angle triangles (sand and shale), whose areas are a 2D expression of the quantity of sediment deposited at that time step and whose length matches the width of the offshore sediment wedge seaward of the shoreline. Each column in the array is filled by both marine sediments up to sea level, and alluvial sediments to a surface determined by an alluvial angle that is projected landward from the shore to its intersection with the previous surface. Each time the area representing the sediment column is subtracted from the triangles, the triangle heights are reduced correspondingly. This process is repeated until the triangle heights match the position of sea level above the sediment surface, at which time the remaining area of the sediment triangle is deposited seaward as a single wedge of offshore sediments. This simulation is designed to aid interpretation of stratigraphic sequences. It can be used as a complement to seismic stratigraphy or can be used alone as an inexpensive test of stratigraphic models.  相似文献   

Gravity measurements with a portable absolute gravimeter A10 in Syowa Station and Langhovde,East Antarctica     

Takahito Kazama  Hideaki Hayakawa  Toshihiro Higashi  Shingo Ohsono  Shunsuke Iwanami  Tomoko Hanyu  Harumi Ohta  Koichiro Doi  Yuichi Aoyama  Yoichi Fukuda  Jun Nishijima  Kazuo Shibuya 《Polar Science》2013,7(3-4):260-277

Absolute gravity values were measured with a portable absolute gravimeter A10 in East Antarctica, for the first time by the Japanese Antarctic Research Expedition. This study aims to investigate regional spatiotemporal variations of ice mass distributions and associated crustal deformations around Syowa Station by means of repeated absolute gravity measurements, and we obtained the first absolute gravity value in Southern Langhovde on the Antarctic Continent. The average absolute gravity value at the newly installed benchmark AGS01 in Langhovde (obtained on 3 February 2012) was 982535584.2 ± 0.7 μgal (1 [μgal] = 1 × 10^?8 [m/s²]), which was in agreement with the gravity values obtained by the past relative gravity measurements within 1 mgal. In addition, the average absolute gravity value obtained at AGSaux in Syowa Station was consistent with both previous absolute gravity values and those obtained by simultaneous measurements using an FG5 gravimeter, owing to adequate data corrections associated with tidal effects and time variations in atomic clock frequencies. In order to detect the gravity changes associated with the ice mass changes and other tectonic phenomena, we plan to conduct absolute gravity measurements at AGS01 again and at other campaign sites around Syowa Station as well in the near future, with careful attention paid to the impacts of severe environmental conditions in Antarctica on gravity data collection.  相似文献   

Genetic constraints from paleomagnetic dating for the Aliva zinc–lead deposit,Picos de Europa Unit,northern Spain     

David T. A. Symons  Fernando Tornos  Kazuo Kawasaki  Francisco Velasco  Idoia Rosales 《Mineralium Deposita》2015,50(8):953-966

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Effects of the copepod community structure on fecal pellet flux in Kagoshima bay,a deep,semi-enclosed embayment     

Toru Kobari  Hiroyasu Akamatsu  Masato Minowa  Toshihiro Ichikawa  Kazuo Iseki  Ryuji Fukuda  Masataka Higashi 《Journal of Oceanography》2010,66(5):673-684

Seasonal changes in the shape and size composition of fecal pellets were investigated with sediment trap samples from 50 and 150 m in Kagoshima Bay to evaluate how the mesozooplankton community affects fecal pellet flux. Deep vertical mixing was evident in March, and thermal stratification was developed above 50 m in June, August and November. Chlorophyll a, suspended particulate organic carbon (POC) and copepod abundance were uniform throughout the water column during the seasonal mixing and concentrated above 50 m in the stratified seasons. Calanoids were the most predominant copepods in March and poecilostomatoids composed more than 45% of the copepod community in June, August and November. Fecal pellet fluxes at 50 and 150 m were the highest in March, nearly half of POC flux. The relative contribution declined considerably in the other months, especially for less than 4% of POC flux in August. The decline was corresponded to the predominance of cyclopoids and poecilostomatoids. Cylindrical pellets dominated the fecal matters at both depths throughout the study period, while larger cylindrical pellets nearly disappeared at 150 m in June, August and November. Copepod incubation revealed that cylindrical and oval pellets were egested by calanoids and the other copepods, respectively. We suggest that cylindrical fecal pellets produced by calanoid copepods contribute to feces flux but the predominance of poecilostomatoids and/or cyclopoids decreases feces flux via the increase of oval pellets and fragmentation of larger cylindrical pellets.  相似文献