Vertical material flux under seasonal sea ice in the Okhotsk Sea north of Hokkaido, Japan     

Takehiko Hiwatari  Kunio Shirasawa  Yasushi Fukamachi  Ryuichi Nagata  Tomoyoshi Koizumi  Hiroshi Koshikawa  Kunio Kohata 《Polar Science》2008,2(1):41-54

Downward material fluxes under seasonal sea ice were measured using a time-series sediment trap installed at an offshore site in the Okhotsk Sea north of Hokkaido, Japan, from 13 January to 23 March 2005. The maximum fluxes of lithogenic material (753 mg m⁻² day⁻¹) and organic matter (mainly detritus; 333 mg m⁻² day⁻¹) were recorded during the period in which sea ice drifted ashore and increased in extent, from 13 January to 9 February. Organic matter as fecal pellets (81–93 mg m⁻² day⁻¹) and opal as biosilica (51–67 mg m⁻² day⁻¹), representing diatom fluxes, were abundant in sediment trap samples obtained during the period of full sea ice coverage from 10 February to 9 March. Microscopic observations revealed that fecal pellets were largely diatom frustules, suggesting that zooplankton actively grazed on ice algae during the period of full sea ice coverage. During the period of retreating sea ice, from 10 to 23 March, the phytoplankton flux showed a rapid increase (from 9.5 to 22.5 × 10⁶ cells m⁻² day⁻¹), reflecting their release into the water column as the sea ice melted. Our results demonstrate that the quantity and quality of sinking biogenic and lithogenic materials vary with the seasonal extent of sea ice in mid-winter.  相似文献   

Northward-propagating nighttime medium-scale traveling ionospheric disturbances observed with SuperDARN Hokkaido HF radar and GEONET     

Akimitsu Ichihara  Nozomu Nishitani  Tadahiko Ogawa  Takuya Tsugawa 《极地研究(英文版)》2013,24(1)

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近百年来中国东北与日本北海道地区气温变化对比     

董满宇  吴正方  江源 《地理科学》2009,29(5):684-689

利用东北及北海道地区7个气象站点1909~2003年逐月气温数据,建立两地区近百年来年、季气温序列,对近百年来两地区气温变化特征进行对比分析,结果表明:近百年来东北及北海道地区气温变化存在显著的增温趋势,前者进入显著升温期早于后者,其中对年均温上升趋势贡献较大的是冬、春两季,夏季升温幅度最小。两地区年均温表现出强的增温持续性,未来气候将继续变暖;两地区都存在9、28、40~42 a的变化周期,但两者主周期的次序所有不同;近百年来两地区气温变化在不同时间尺度上具有不同突变点。  相似文献   

多传感器不同分辨率遥感数字图像的尺度转换   总被引：14，自引：0，他引：14  

布和敖斯尔  马建文  王勤学  金子正美  福山龙次 《地理学报》2004,59(1):101-110

针对日益增多的多传感器不同分辨率的遥感数字图像数据,提出其综合利用和尺度转换的有效方法。其中,作为尺度上推 (scaling-up) 技术,本研究选择IHS和小波分解变换两种数据融合方法,应用Landsat ETM+数据和IRS-1C数据进行了实例研究。发现: IHS方法操作简单,对两种待融合的图像的像元大小和像元数 (bit数) 的依赖不是很高,而对原始图像光谱信息的依赖很高,因此适用于不同传感器之间的数据融合上,其缺点就是不能够更多的保留原始多光谱数据的光谱信息。小波分解变换 (WD) 方法可以很好地保留多光谱传感器的所有光谱信息,但是在重采样中对两种待融合的图像的像元配准的要求很高,因此比较适合于对同一传感器的多光谱数据与全色光谱数据的融合上。作为尺度下退 (scaling-down) 技术,通过探讨将札幌野外实验站点数据镶嵌到高时间分辨率遥感图像的问题,提出像元级尺度扩展的具体操作方法和对NDVI图像进行扩展时出现混合像元的识别方法。应用AVHRR, MODIS, ETM+和ASTER的NDVI图像数据进行了像元尺度的扩展研究。得出: 对不同传感器的不同分辨率的数据之间进行像元级的尺度扩展后,能够较好地识别出不同地物的分布边界,较好的分辨混合像元,因此其结果可用于对不同地物分布特征的分类研究或土地覆盖变化中的时间序列变化的研究中。  相似文献   

Stratigraphic records of tsunamis along the Japan Sea,southwest Hokkaido,northern Japan          下载免费PDF全文

Gentaro Kawakami  Kenji Nishina  Yoshihiro Kase  Jun Tajika  Keiichi Hayashi  Wataru Hirose  Tsumoru Sagayama  Tatsuya Watanabe  Satoshi Ishimaru  Ken'ichi Koshimizu  Ryo Takahashi  Kazuomi Hirakawa 《Island Arc》2017,26(4)

The stratigraphy of tsunami deposits along the Japan Sea, southwest Hokkaido, northern Japan, reveals tsunami recurrences in this particular area. Sandy tsunami deposits are preserved in small valley plains, whereas gravelly deposits of possible tsunami origin are identified in surficial soils covering a Holocene marine terrace and a slope talus. At least five horizons of tsunami events can be defined in the Okushiri Island, the youngest of which immediately overlies the Ko‐d tephra layer (1640 AD) and was likely formed by the historical Oshima‐Ohshima tsunami in 1741 AD. The four older tsunami deposits, dated using accelerator mass spectrometry ¹⁴C, were formed at around the 12th century, 1.5–1.6, 2.4–2.6, and 2.8–3.1 ka, respectively. Tsunami sand beds of the 1741 AD and circa 12th century events are recognized in the Hiyama District of Hokkaido Island, but the older tsunami deposits are missing. The deposits of these two tsunamis are found together at the same sites and distributed in regions where wave heights of the 1993 tsunami (Hokkaido Nansei‐oki earthquake, Mw = 7.7) were less than 3 m. Thus, the 12th century tsunami waves were possibly generated near the south of Okushiri Island, whereas the 1993 tsunami was generated towards the north of the island. The estimated recurrence intervals of paleotsunamis, 200–1100 years with an average of 500 years, likely represents the recurrence interval of large earthquakes which would have occurred along several active faults offshore of southwest Hokkaido.  相似文献   

Time series of carbonate system variables off Otaru coast in Hokkaido, Japan     

Ai Sakamoto  Yutaka W. Watanabe  Masato Osawa  KazuoKido  Shinichiro Noriki 《Estuarine, Coastal and Shelf Science》2008,79(3):377-386

We report several biogeochemical parameters (dissolved inorganic carbon (DIC), total alkalinity (TA), dissolved oxygen (DO), phosphate (PO₄), nitrate + nitrite (NO₃ + NO₂), silicate (Si(OH)₄)) in a region off Otaru coast in Hokkaido, Japan on a “weekly” basis during the period of April 2002–May 2003. To better understand the long-term temporal variations of the main factors affecting CO₂ flux in this coastal region and its role as a sink/source of atmospheric CO₂, we constructed an algorithm of DIC and TA using other hydrographic properties. We estimated the CO₂ flux across the air–sea interface by using the classical bulk method. During 1998–2003 in our study region, the estimated fCO_2sea ranged about 185–335 μatm. The maximum of fCO_2sea in the summer was primarily due to the change of water temperature. The minimum of fCO_2sea in the early spring can be explained not only by the change of water temperature but also the change of nutrients and chlorophyll-a. To clarify the factors affecting fCO_2sea (water temperature, salinity, and biological activity), we carried out a sensitivity analysis of these effects on the variation of fCO_2sea. In spring, the biological effect had the largest effect for the minimum of fCO_2sea (40%). In summer, the water temperature effect had the largest effect for the maximum of fCO_2sea (25%). In fall, the water temperature effect had the largest effect for the minimum of fCO_2sea (53%). In winter, the biological effect had the largest effect for the minimum of fCO_2sea (35%).We found that our study region was a sink region of CO₂ throughout a year (−0.78 mol/m²/yr). Furthermore, we estimated that the increase of fCO_2sea was about 0.56 μatm/yr under equilibrium with the atmospheric CO₂ content for the period 1998–2003, with the temporal changes in the variables (T, S, PO₄) on fCO_2sea, thus as the maximum trend of each variable on fCO_2sea was 0.22 μatm/yr, and the trend of residual fCO₂ including gas exchange was 0.34 μatm/yr. This result suggests that interaction among variables would affect gas exchange between air and sea effects on fCO_2sea. We conclude that this study region as a representative coastal region of marginal seas of the North Pacific is special because it was measured, but there is no particular significance in comparison to any other area.  相似文献   

Palaeotemperature curve for the Late Cretaceous of the northwestern circum-Pacific     

Yuri D. Zakharov  Nataliya G. Boriskina  Alexander V. Ignatyev  Kazushige Tanabe  Yasunari Shigeta  Alexander M. Popov  Tamara B. Afanasyeva  Haruyoshi Maeda 《Cretaceous Research》1999,20(6):685

In the northwestern circum-Pacific, two main trends in Late Cretaceous temperatures can be recognized. (1) In general, a recurrent warming trend is thought to have begun in the Turonian–Campanian, reaching temperature maxima in the early Late Santonian and early Late Campanian, and temperature minima in the earliest Santonian and perhaps early Campanian. (2) During the Maastrichtian, temperatures dropped sharply, with only a slight warming in the early Late Maastrichtian. The existence of a thermal maximum at the Coniacian–Santonian transition has previously been expected, but is not confirmed by new isotopic results.  相似文献   

Late Miocene Magmatic-Hydrothermal Systems in the Jozankei-Zenibako District, Southwest Hokkaido, Japan     

Yasushi WATANABE  Eijun OHTA 《Resource Geology》1999,49(2):59-74

Abstract: Hydrothermal systems related to magmatic intrusions in the Jozankei-Zenibako district, southwest Hokkaido are examined, based on field observations, K-Ar ages, and alteration mineral assemblages. The study reveals five major magmat–ic–hydrothermal systems of Late Miocene in age, comprising Ogawa (9. 7 Ma), Jozankei (9. 5–9. 0 Ma), Otarunaigawa (8. 7 Ma), Asarigawa (8. 8 and 6. 7 Ma) and Hariusu (6. 7 Ma). The Ogawa system is related to granodiorite, and the Jozankei, Otarunaigawa and Asarigawa systems are related to quartz porphyry.
The Ogawa system includes potassic, sericitic, propylitic and advanced argillic alteration as well as base-metal mineralization, represented by the Toyotomi deposit. The Jozankei and Otarunaigawa systems lack significant potassic alteration, and are accompanied by sericitic and propylitic alteration. The Otarunaigawa system is associated with base-metal mineralization at Toyohiro and Inatoyo. The Asarigawa and Hariusu systems include advanced argillic and argillic alteration, as well as iron sulfide deposits. The presence of potassic alteration only in the Ogawa system is ascribed to deeper emplacement (˜3 km from the surface) of the intrusive magma. These systems formed in terrestrial environments that existed from ca. 11 Ma to 8. 5 Ma and after 7. 5 Ma in the district.
Age–data compilation shows that the major advanced argillic alteration events in southwest Hokkaido, including those in the Jozankei-Zenibako district, formed during the periods from 9. 7–6. 5 Ma and 3. 5–1. 5 Ma. These periods correspond to the timing of normal subduction of the Pacific plate beneath the Northeast Japan arc. Normal, in contrast to oblique, plate subduction is characterized by andesitic, polygenetic volcanism and associated advanced argillic alteration.  相似文献   

Plio–Pleistocene Hydrothermal Activity Related to Gold Mineralization in the Seta Area, Northeastern Hokkaido, Japan     

Masahiro YAHATA  Hiroharu MATSUEDA 《Resource Geology》1999,49(3):131-145

Abstract: Plio–Pleistocene hydrothermal activity resulted in high grade low sulfidation epithermal gold mineralization in the Seta area, the southern end of the Monbetsu-Kamishihoro Graben of northeastern Hokkaido, Japan. Hydrothermal activity and accompanying hydrothermal eruptions began at approximately 2 Ma along NNW-SSE trending faults, the Tohbu-ko fault I and II. This activity resulted in two main zones of gold mineralization, the west quartz-adularia veins(QAV) and east stock-work zone(STZ), formed between 1. 8 and 1. 2 Ma. A smectite-chlorite alteration zone is observed at deeper levels, while kaolinite and kaolinite-smectite zones occur at shallower levels with an acid-leached zone present near the surface. The kaoli-nite and kaolinite-smectite zones are also distributed along faults and the STZ, to depths of several hundred meters. δ³⁴S values of pyrite and alunite from the kaolinite and silicified zones indicate alunite formed by the oxidation of sulfide, either H₂S(vapor) or mineral.
Formation of the STZ and the southern part of the QAV took place during lacustrine sedimentation, while formation of the northern part of the QAV took place after eruption of andesitic lava; the latter being associated with widespread alteration formed under neutral-pH conditions. δ¹⁸O values of quartz veins and silicified rocks indicate that the paleo-hydrothermal waters have a large meteoric component, increasing with decreasing depth in the STZ. Acid hydrothermal waters, resulting from near surface oxidation of H₂S were responsible for acid-leaching and kaolinization of surrounding rocks. Between 1. 4 and 0. 3 Ma, the acid hot waters drained back along the STZ to depths of at least 500m, as a result of a fall in the paleo-water table level.  相似文献   

Climate and vegetation in Hokkaido, northern Japan, since the LGM: Pollen records from core GH02-1030 off Tokachi in the northwestern Pacific     

Yaeko Igarashi  Masanobu Yamamoto  Ken Ikehara 《Journal of Asian Earth Sciences》2011,40(6):78-1110

Vegetation and climate since the LGM in eastern Hokkaido were investigated based on a pollen record from marine core GH02-1030 from off Tokachi in the northwestern Pacific. We also examined pollen spectra in surface samples from Sakhalin to compare and understand the climatic conditions of Hokkaido during the last glacial period. Vegetation in the Tokachi region in the LGM (22–17 ka) was an open boreal forest dominated by Picea and Larix. During the last deglaciation (17–10 ka), vegetation was characterized by abundant Betula. In the Kenbuchi Basin, central Hokkaido, a remarkable increase of Larix and Pinus occurred in the LGM and the last deglaciation, which was assigned as the “Kenbuchi Stadial.” Comparison of climatic data between the core GH02-1030 and that of Kenbuchi Basin demonstrates that variations in temperature and precipitation were larger in inland Hokkaido than in the maritime area of the Pacific coast. During the LGM in the Tokachi region, the August mean temperature was about 5 °C lower, and annual precipitation was about 40% lower than today. In the Kenbuchi Basin, central Hokkaido, the August mean temperature was about 8 °C lower, and annual precipitation was half that of today. During the last deglaciation, August mean temperatures were about 3 °C lower, and annual precipitation was about 30% lower than today in the Tokachi region. In the Kenbuchi Basin, August mean temperatures were about 5–8 °C lower, and annual precipitation was about 40–60% lower than today. Cold ocean water and a strengthened summer monsoon after 15 ka may have resulted in the formation of advection fogs, reduced summer temperatures, and a decrease in the seasonal temperature difference in the Tokachi district, which established favorable maritime conditions for Betula forests.  相似文献