Phytoplankton growth response to wind induced regional upwelling occurring around the Izu Islands off Japan     

Masayuki Takahashi  Michio J. Kishi 《Journal of Oceanography》1984,40(3):221-229

From frequent field observations performed in coastal waters around the Izu Islands, Japan, a clear regional upwelling associated with the wind was detected baside Niijima Island. Nutrient supply by the upwelling into the euphotic zone was confirmed, and the subsequent phytoplankton growth supported by the upwelled nutrients was evaluated. The upwelling and the nutrient supply occurred within a day over an area ofca. 400 km², and phytoplankton growth response occurred only a few days after the upwelling. Such regional upwelling is considered to be one of the major mechanisms supporting the high productivity of coastal waters.Contribution number 423 from the Shimoda Marine Research Center, University of Tsukuba.  相似文献   

Detection of nonlinear waves and their contribution to ocean wave spectra Part II: Observation     

Yukiharu Hisaki  Masayuki Tokuda 《Journal of Oceanography》1995,51(4):407-419

This is a Part II of a paper of nonlinearities of wind waves in the deep open ocean. As shown in Part I, bound waves in deep sea are detectable by extracting secondorder Doppler spectra from the Doppler spectra of HF (high-frequency) radio waves scattered from the sea surface. There is a remarkable agreement between the calculated and measured Doppler spectra, considering the noise levels in measured Doppler spectra and the uncertainties in directional properties. The theoretical expression for bound waves is thus verified. Furthermore, the upper limit in calculating the Doppler spectra for the second-order approximation is presented from field observations, although we cannot conclude that it is equivalent to the limitation of the second-order bound wave theory. It is shown that analysis of radio wave scattering by the sea surface is one useful means of understanding the nonlinear properties of ocean waves.  相似文献   

Preface     

Masayuki M. Takahashi  Shiro Imawaki 《Journal of Oceanography》2002,58(1):1-1

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Chlorophyll a Biomass of Netplankton in Surface Waters in the Pacific Sector of the Southern Ocean in Austral Summer     

Dong-Hoon Han  Masayuki Mac Takahashi 《Journal of Oceanography》2001,57(5):581-592

Chlorophyll a of total and particles retained on 30 μm mesh plankton net were both determined in surface waters along two cruise tracks ranging from the Subtropical water to the marginal ice zone in the Pacific sector of the Southern Ocean in austral summer. Total surface chlorophyll a in the study area was mostly less than 1 μg chl a 1⁻¹, and showed distributions with no obvious trend associated with different waters masses of the Antarctic and the Subantarctic, although total chlorophyll a concentrations changed greatly within each water mass. Particularly low concentrations of chlorophyll a were detected in the marginal ice zone. Chlorophyll a contained in 30 μm netplankton made up 5∼60% of total chlorophyll a: large near the marginal ice zone and becoming small with travel towards the north. High percentage shares of netplankton chlorophyll a were confirmed even in low total chlorophyll a concentrations in summer in the Southern Ocean. A positive relation was observed between the percentage of 30 μm netplankton and the “average total chlorophyll a”, although there was great scatter. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

40Ar/39Ar age of material returned from asteroid 25143 Itokawa          下载免费PDF全文

Jisun Park  Brent D. Turrin  Gregory F. Herzog  Fara N. Lindsay  Jeremy S. Delaney  Carl C. Swisher III  Masayuki Uesugi  Yuzuru Karouji  Toru Yada  Masanao Abe  Tatsuaki Okada  Yukihiro Ishibashi 《Meteoritics & planetary science》2015,50(12):2087-2098

The Hayabusa mission to asteroid 25143, Itokawa, brought back 2000 small particles, which most closely resemble material found in LL4‐6 chondrites. We report an ⁴⁰Ar/³⁹Ar age of 1.3 ± 0.3 Ga for a sample of Itokawa consisting of three grains with a total mass of ~2 μg. This age is lower than the >4.0 Ga ages measured for 75% of LL chondrites but close to one for Y‐790964 and its pairs. The flat ⁴⁰Ar/³⁹Ar release spectrum of the sample suggests complete degassing 1.3 Ga ago. Recent solar heating in Itokawa's current orbit does not appear likely to have reset that age. Solar or impact heating 1.3 Ga ago could have done so. If impact heating was responsible, then the 1.3 Ga age sets an upper bound on the time at which the Itokawa rubble pile was assembled and suggests that rubble pile creation was an ongoing process in the inner solar system for at least the first 3 billion years of solar system history.  相似文献   

Middle Permian cephalopods from central Peninsular Malaysia: implications for faunal migration through the southern Tethys     

Masatoshi Sone  Mohd Shafeea Leman  Masayuki Ehiro 《Journal of Asian Earth Sciences》2001,19(6)

A Wordian (Middle Permian) cephalopod fauna consisting of four ammonoid species, Tauroceras aff. scrobiculatum (Gemmellaro), Agathiceras sp., Bamyaniceras orientale n. sp. and Pronoritidae gen. and sp. indet., and two nautiloid species, Tainoceras sp. and Orthocerida fam. indet., were recovered from the Bera South area, southern Pahang, Peninsular Malaysia. The outcrop represents the southernmost extent of the Bera Formation. Bamyaniceras and Tainoceras are recorded in Malaysia for the first time. The presence of T. aff. scrobiculatum suggests a regional correlation with an ammonoid-bearing bed of Sungai Cheroh, western Pahang, and permits global correlations with strata of northeastern Iraq, northern Oman and Sicily (Italy). A possible eastwards faunal migration through the southern Tethys is suggested.  相似文献   

Diversity of Pliocene mysticetes from eastern Japan     

Masayuki  Oishi Yoshikazu  Hasegawa 《Island Arc》1994,3(4):436-452

Abstract Assemblages of Early Pliocene Mysticeti (Cetacea) from the Sendai-Iwate and Choshi areas in eastern Japan were examined. The early Early Pliocene Tatsunokuchi and Yushima formations of the Sendai-Iwate area have yielded many cetotheres assigned to Herpetocetus (Cetotheriidae) and some extinct rorquals assigned to Burtinopsis (Balaenopteridae) and other genera. The late Early Pliocene strata of the Na-arai Formation of the Choshi area has yielded more than 300 mysticete ear bones which fall into seven morphotypes. Assemblages from the two areas differ greatly in taxonomic composition. Archaic mysticetes are dominant in the Sendai-Iwate area, while modern mysticetes are dominant and diverse in the Choshi area. Based on the results of this study we conclude that the diversity of the Early Pliocene mysticetes in the western North Pacific is comparable to that of the Recent.  相似文献   

A list of fossil cetaceans in Japan     

Masayuki  Oishi Yoshikazu  Hasegawa 《Island Arc》1994,3(4):493-505

Abstract Fossil cetacea of Japan are abundant and diverse. Despite several summary articles, all the known taxa have not previously been compiled in one place. Here we present a list of the published fossil cetacean records from the Japanese archipelago. The record extends from Middle or Late Oligocene to the Holocene, and includes representatives of both the suborders Odontoceti and Mysticeti. No Eocene Cetacea or Archaeoceti are recorded from Japan. As is typical of the eastern North Pacific and the South Pacific, the Oligocene and Early Miocene assemblages are comprised of archaic and usually extinct families, and the younger assemblages are represented by modern groups comprised of extant genera and families.  相似文献   

PP-P differential traveltime measurement with crustal correction     

Masayuki Obayashi  Daisuke Suetsugu  Yoshio Fukao 《Geophysical Journal International》2004,157(3):1152-1162

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Early Permian ammonoids from the Kaeng Krachan Group of the Phatthalung-Hat Yai area, southern peninsular Thailand   总被引：1，自引：1，他引：1  

Masayuki Fujikawa  Katsumi Ueno  Apsorn Sardsud  Wirote Saengsrichan  Yoshihito Kamata  Ken-ichiro Hisada 《Journal of Asian Earth Sciences》2005,24(6):739

An Early Permian small ammonoid fauna consisting of Neocrimites sp., Agathiceras suessi Gemmellaro, A. girtyi Böse, Agathiceras? sp., and Miklukhoceras sp. was found in nodules of a fine sandstone bed exposed in the Phatthalung-Hat Yai area of southern peninsular Thailand. The ammonoid-bearing bed belongs stratigraphically to the uppermost part of the Kaeng Krachan Group, which is essentially a clastic-dominant, Late Carboniferous (?) to Early Permian stratigraphic unit, widely distributed in western and peninsular Thailand. This ammonoid fauna is considered to be of Bolorian (Kungurian) age and includes Agathiceras girtyi Böse, which is described for the first time from Thailand. The present discovery of Bolorian ammonoids suggests that the uppermost part of the Kaeng Krachan Group is slightly younger than previously considered and around the latest Early Permian. This further implies that the continental margin environment of the Sibumasu Block drastically changed at around Bolorian time from a cool, clastic-dominant shelf condition to a temperate to subtropical, carbonate platform due to rapid northward drift after middle Artinskian rifting.  相似文献