Interannual-decadal variability of wintertime mixed layer depths in the North Pacific detected by an ensemble of ocean syntheses     

Toyoda  Takahiro  Fujii  Yosuke  Kuragano  Tsurane  Kosugi  Naohiro  Sasano  Daisuke  Kamachi  Masafumi  Ishikawa  Yoichi  Masuda  Shuhei  Sato  Kanako  Awaji  Toshiyuki  Hernandez  Fabrice  Ferry  Nicolas  Guinehut  Stéphanie  Martin  Matthew  Andrew Peterson  K.  Good  Simon A.  Valdivieso  Maria  Haines  Keith  Storto  Andrea  Masina  Simona  Köhl  Armin  Yin  Yonghong  Shi  Li  Alves  Oscar  Smith  Gregory  Chang  You-Soon  Vernieres  Guillaume  Wang  Xiaochun  Forget  Gael  Heimbach  Patrick  Wang  Ou  Fukumori  Ichiro  Lee  Tong  Zuo  Hao  Balmaseda  Magdalena 《Climate Dynamics》2017,49(3):891-907

Climate Dynamics - The interannual-decadal variability of the wintertime mixed layer depths (MLDs) over the North Pacific is investigated from an empirical orthogonal function (EOF) analysis of an...  相似文献   

Sr isotope excursion across the Precambrian–Cambrian boundary in the Three Gorges area, South China     

Yusuke Sawaki  Takeshi Ohno  Yusuke Fukushi  Tsuyoshi Komiya  Tomoko Ishikawa  Takafumi Hirata  Shigenori Maruyama 《Gondwana Research》2008,14(1-2):134

The Precambrian/Cambrian (PC/C) boundary is one of the most important intervals for the evolution of life. However, the scarcity of well-preserved outcrops across the boundary leaves an obstacle in decoding surface environmental changes and patterns of biological evolution.In south China, strata through the PC/C boundary are almost continuously exposed and contain many fossils, suitable for study of environmental and biological change across the PC/C boundary. We undertook deep drilling at four sites in the Three Gorges area to obtain continuous and fresh samples without surface alteration and oxidation. ⁸⁷Sr/⁸⁶Sr ratios of the fresh carbonate rocks, selected based on microscopic observation and geochemical signatures of Mn/Sr and Rb/Sr ratios, aluminum and silica contents, and δ¹³C and δ¹⁸O values, were measured with multiple collector-inductively coupled plasma–mass spectrometric techniques.The chemostratigraphy of ⁸⁷Sr/⁸⁶Sr ratios of the drilled samples displays a smooth curve and a large positive anomaly just below the PC/C boundary between the upper part of Baimatuo Member of the Dengying Formation and the lower part of the Yanjiahe Formation. The combination of chemostratigraphies of δ¹³C and ⁸⁷Sr/⁸⁶Sr indicates that the ⁸⁷Sr/⁸⁶Sr excursions preceded the δ¹³C negative excursion, and suggests that global regression or formation of the Gondwana supercontinent, possibly together with a high atmospheric pCO₂, caused biological depression.  相似文献   

Carbon isotope chemostratigraphy of a Precambrian/Cambrian boundary section in the Three Gorge area, South China: Prominent global-scale isotope excursions just before the Cambrian Explosion     

Tomoko Ishikawa  Yuichiro Ueno  Tsuyoshi Komiya  Yusuke Sawaki  Jian Han  Degan Shu  Yong Li  Shigenori Maruyama  Naohiro Yoshida   《Gondwana Research》2008,14(1-2):193

Carbon isotope chemostratigraphy has been used for worldwide correlation of Precambrian/Cambrian (Pc/C) boundary sections, and has elucidated significant change of the carbon cycle during the rapid diversification of skeletal metazoa (i.e. the Cambrian Explosion). Nevertheless, the standard δ¹³C curve of the Early Cambrian has been poorly established mainly due to the lack of a continuous stratigraphic record. Here we report high-resolution δ¹³C chemostratigraphy of a drill core sample across the Pc/C boundary in the Three Gorge area, South China. This section extends from an uppermost Ediacaran dolostone (Dengying Fm.), through a lowermost Early Cambrian muddy limestone (Yanjiahe Fm.) to a middle Early Cambrian calcareous black shale (Shuijingtuo Fm.). As a result, we have identified two positive and two negative isotope excursions within this interval. Near the Pc/C boundary, the δ¹³C_carb increases moderately from 0 to + 2‰ (positive excursion 1: P1), and then drops dramatically down to − 7‰ (negative excursion 1: N1). Subsequently, the δ¹³C_carb increases continuously up to about + 5‰ at the upper part of the Nemakit–Daldynian stage. After this positive excursion, δ¹³C_carb sharply decreases down to about − 9‰ (N2) just below the basal Tommotian unconformity. These continuous patterns of the δ¹³C shift are irrespective of lithotype, suggesting a primary origin of the record. Moreover, the obtained δ¹³C profile, except for the sharp excursion N2, is comparable to records of other sections within and outside of the Yangtze Platform. Hence, we conclude that the general feature of our δ¹³C profile best represents the global change in seawater chemistry. The minimum δ¹³C of the N1 (− 7‰) is slightly lower than carbon input from the mantle, thus implying an enhanced flux of ¹³C-depleted carbon just across the Pc/C boundary. Hence, the ocean at that time probably became anoxic, which may have affected the survival of sessile or benthic Ediacaran biota. The subsequent δ¹³C rise up to + 5‰ (P2) indicates an increase of primary productivity or an enhanced rate of organic carbon burial, which should have resulted in lowering pCO₂ and following global cooling. This scenario accounts for the cause of the global-scale sea-level fall at the base of the Tommotian stage. The subsequent, very short-term, and exceptionally low δ¹³C (− 9‰) in N2 could have been associated with the release of methane from gas hydrates due to the sea-level fall. The inferred dramatic environmental changes (i.e., ocean anoxia, increasing productivity, global cooling and subsequent sea-level fall with methane release) appear to coincide with or occur just before the Cambrian Explosion. This may indicate synchronism between the environmental changes and rapid diversification of skeletal metazoa.  相似文献   

Meridional distribution and carbon biomass of autotrophic picoplankton in the Central North Pacific Ocean during late northern summer 1990     

Joji Ishizaka  Hiroshi Kiyosawa  Kazunori Ishida  Kimitoshi Ishikawa  Masayuki Takahashi 《Deep Sea Research Part I: Oceanographic Research Papers》1994,41(11-12)

The meridional distribution of autotrophic picoplankton groups in the central north Pacific was studied during the late northern summer of 1990. Sampling was along a section at 175°N which extended from 45°N to 8°S. The section is far from coastal regions and included subarctic, central gyre, and equatorial areas. Five autotrophic picoplankton groups, autotrophic microflagellate, red-fluorescing picoplankton,Synechococcus, prochlorophyte, and orange-fluorescing picoplankton, were identified from samples taken at stations distributed along this section. These five groups showed distinctive differences in their meridional and vertical distributions. The autotrophic microflagellates and red-fluorescing picoplankton showed distributions that were similar to that of chlorophyll a, which was dominated by the <3 μm size fraction. However, the vertical distribution of these groups was different.Synechococcus was found mostly in surface waters (PAR<10%) and was particularly abundant in the Kuroshio Extension and south of the equatorial region where the nitracline was shallow (50–75 m). Prochlorophytes were abundant in the deep euphotic layer (PAR 1-0.1%) from the south of the Kuroshio Extension to the south of the equatorial area. Orange-fluorescing picoplankton, which may be one kind of cyanobacteria but is larger than typical Synechococcus, were mostly distributed in the oligotrophic surface waters of the central gyre. The carbon biomass estimates for these organisms showed that these five groups dominated in different areas. The vertical distribution of carbon biomass did not correspond to that of chlorophyll a in the central gyre and south of the equator because of the larger carbon/ chlorophyll a ratio of Synechococcus and orange-fluorescing picoplankton relative to that of the other picoplankton.  相似文献   

A new method of evaluating the mineralization of particulate and dissolved photoassimilated organic matter     

Masanobu Ishikawa  Hajime Nishimura 《Journal of Oceanography》1983,39(2):29-42

A new method of evaluating the rate of mineralization of photoassimilated organic matter is described. This method enables us to compare the rate of direct mineralization of particulate organic carbon (POC) to CO₂ with the rate of solubilization of photoassimilated organic carbon followed by the mineralization of the resultant dissolved organic carbon (DOC) under the same conditions. The direct mineralization of photoassimilated carbon from POC to CO₂ is a more significant process compared with the mineralization of extracellular released organic carbon. The first-order rate coefficients range from 0.132 to 0.434 day^–1 for direct mineralization and 0.034 to 0.189 day^–1 for solubilization.  相似文献   

Size and taxonomic plankton community structure and carbon flow at the equator, 175‡E during 1990–1994     

J. Ishizaka  K. Harada  K. Ishikawa  H. Kiyosawa  H. Furusawa  Y. Watanabe  H. Ishida  K. Suzuki  N. Handa  M. Takahashi 《Deep Sea Research Part II: Topical Studies in Oceanography》1997,44(9-10)

Size and taxonomic structure of plankton community carbon biomass for the 0.2–2000 μm equivalent spherical diameter range were determined at the equator at 175°E in September 1990–1993 and April 1994. Total biomass of the plankton community ranged from 1944 to 3448 mg C m⁻². Phytoplankton, zooplankton and bacteria carbon biomasses were 604–1669 mg C m^-2, 300–797 mg C m², and 968–1200 mg C m^-2, and the percentages were 31–54%, 15–26%, and 29–54%, respectively. Biomass of heterotrophic bacteria was always the largest fraction andProchlorococcus biomass was second. Heterotrophic and autotrophic flagellates and dinoflagellates in the nanoplankton size range and copepods (adults and copepodites) in the mesoplankton range were also high. Relatively small biomass was observed in the microplankton size range. The differences in integrated biomass of plankton community for El Nin˜o type oligotrophic conditions of September 1990–1993 and non-El Nifio type mesotrophic conditions of April 1994 were generally small compared with the interannual difference during 1990–1993. However, the percentage ofProchlorococcus in phytoplankton carbon biomass was larger in non-El Nin˜o year. Biomasses of cyanobacteria, diatom, dinoflagellates, nauplii of copepods, and crustaceans other than copepods were larger in the non-El Nin˜o year. Primary production increased significantly from El Nin˜o to non-El Nin˜o years. Carbon flow through the plankton food chain was estimated using the plankton carbon biomass data, primary production measurements, and published empirical relationships.  相似文献   

Verification of Net Primary Production Estimation Method in the Mongolian Plateau Using Landsat ETM＋ Data     

XIONGYan KanakoMuramatsu MasahiroHirata KazatoOishi IchirowKaihotsu TamioTakamura ShinobuFurumi NoboruFujiwara 《地球空间信息科学学报》2004,7(2):117-122

We plan to estimate global net primary production (NPP) of vegetation using the Advanced Earth Observing Satellite-Ⅱ (ADEOS-Ⅱ) Global Imager (GLI) multi-spectral data. We derive an NPP estimation algorithm from ground measurement data on temperate plants in Japan. By the algorithm, we estimate NPP using a vegetation index based on pattern decomposition (VIPD) for the Mongolian Plateau. The VIPD is derived from Landsat ETM multi-spectral data, and the resulting NPP estimation is compared with ground data measured in a semi-arid area of Mongolia. The NPP estimation derived from satellite remote sensing data agrees with the ground measurement data within the error range of 15% when all above-ground vegetation NPP is calculated for different vegetation classifications.  相似文献   

Transfer coefficients of sensible heat on a snowmelt surface     

N. Ishikawa  Y. Kodama 《Meteorology and Atmospheric Physics》1994,53(3-4):233-240

Summary Field observations were carried out in order to determine the transfer coefficeient of sensible heat flux above a melting snow surface at the Moshiri experimental site. The coefficient is calculated as the ratio of the sensible heat flux determined by the eddy correlation method using a sonic anemometer to the product of the wind speed and the temperature difference between the air and snow surface. The sensible heat fluxes are also compared with the result of the precise heat balance observations. The nondimensional transfer coefficienth shows a good correlation with the atmospheric stability,Ri. The value ofh=2.3×10^–3 is obtained in the range of 0<Ri<0.1, however, it is smaller and scattered under stronger stable condition (Ri>0.1). The dimensional transfer coefficent for sensible heat flux is calculated, and a linear relationship is obtained as a function of the logarithm of atmospheric stability.With 11 Figures  相似文献   

Field experiments constraining the probability distribution of particle travel distances during natural rainstorms on different slope gradients     

Afshin Ghahramani  Ishikawa Yoshiharu  Simon M. Mudd 《地球表面变化过程与地形》2012,37(5):473-485

Rain splash erosion is an important soil transport mechanism on steep hillslopes. The rain splash process is highly stochastic; here we seek to constrain the probability distribution of splash transport distances on natural hillslopes as a function of hillslope gradient and total precipitation depth. Field experiments were conducted under natural precipitation events to observe splash travel on varying slope gradients. The downslope fraction of splash transport on 15°, 25° and 33° gradients were 85%, 96% and 96%, respectively. Maximum splash transport (L_max) was related to the rain splash detachment of soil particles and slope gradient. An empirical relationship of L_max to the precipitation depth and gradient was obtained; it is linearly proportional to hillslope gradient and logarithmically related to precipitation depth. Measured splash distances were calibrated to the fully two‐dimensional (2D) model of splash transport of Furbish et al. (Journal of Geophysical Research 112 : F01001, 2007) that is based on the assumption that radial splash distances are exponentially distributed; calibrated values of mean splash transport distances are an order of magnitude greater than those previously determined in a controlled laboratory setting. We also compared measured data with several one‐dimensional (1D) probability distributions to asses if splash transport distances could be better explained by a heavy‐tailed probability distribution rather than an exponential probability distribution. We find that for hillslopes of 15° and 25°, although a log‐normal probability distribution best describes the data, we find its likelihood is nearly indistinguishable from an exponential distribution based on computing maximum likelihood estimators for all 1D distributions (exponential, log‐normal and Weibull). At 33°, however, we find stronger evidence that measured travel distances are heavy‐tailed. Copyright © 2011 John Wiley & Sons, Ltd.  相似文献   

The role of meso-scale eddies in mixed layer deepening and mode water formation in the western North Pacific   总被引：3，自引：1，他引：2  

Shinya Kouketsu  Hiroyuki Tomita  Eitarou Oka  Shigeki Hosoda  Taiyo Kobayashi  Kanako Sato 《Journal of Oceanography》2012,68(1):63-77

Distributions of mixed layer depths around the centers of anti-cyclonic and cyclonic eddies in the North Pacific Ocean were composited by using satellite-derived sea surface height anomaly data and Argo profiling float data. The composite distributions showed that in late winter, deeper mixed layers were more (less) frequently observed inside the cores of the anti-cyclonic (cyclonic) eddies than outside. This relationship was the clearest in the region of 140°E–160°W and 35°N–40°N, where the temperature and salinity of the deep mixed layers were similar to those of the lighter variety of central mode water (L-CMW). A simple one-dimensional bulk mixed layer model showed that both strong sea-surface heat and momentum fluxes and weak preexisting stratification contributed to formation of the deep mixed layer. These conditions were associated with the anti-cyclonic eddies, suggesting that these eddies are important in the formation of mode waters, particularly L-CMW.  相似文献