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141.
Undisturbed sediment cores were collected by a modified gravity corer from Funka Bay. The sedimentation rate is determined by both210Pb and pumice chronological methods. The sedimentation rates by210Pb method are concordant with those by pumice methods. The derived rate varies from 0.06 to 0.22 g cm–2 y–1, and an average is 0.09 g cm–2 y–1. 相似文献
142.
Kazuhiko Matsumoto Ken Furuya Takeshi Kawano 《Deep Sea Research Part I: Oceanographic Research Papers》2004,51(12):1319
Climatological variability of picophytoplankton populations that consisted of >64% of total chlorophyll a concentrations was investigated in the equatorial Pacific. Flow cytometric analysis was conducted along the equator between 145°E and 160°W during three cruises in November–December 1999, January 2001, and January–February 2002. Those cruises were covering the La Niña (1999, 2001) and the pre-El Niño (2002) periods. According to the sea surface temperature (SST) and nitrate concentrations in the surface water, three regions were distinguished spatially, viz., the warm-water region with >28 °C SST and nitrate depletion (<0.1 μmol kg−1), the upwelling region with <28 °C SST and high nitrate (>4 μmol kg−1) water, and the in-between frontal zone with low nitrate (0.1–4 μmol kg−1). Picophytoplankton identified as the groups of Prochlorococcus, Synechococcus and picoeukaryotes showed a distinct spatial heterogeneity in abundance corresponding to the watermass distribution. Prochlorococcus was most abundant in the warm-water region, especially in the nitrate-depleted water with >150×103 cells ml−1, Synechococcus in the frontal zone with >15×103 cells ml−1, and picoeukaryotes in the upwelling region with >8×103 cells ml−1. The warm-water region extended eastward with eastward shift of the frontal zone and the upwelling region during the pre-El Niño period. On the contrary, these regions distributed westward during the La Niña period. These climatological fluctuations of the watermass significantly influenced the distribution of picophytoplankton populations. The most abundant area of Prochlorococcus and Synechococcus extended eastward and picoeukaryotes developed westward during the pre-El Niño period. The spatial heterogeneity of each picophytoplankton group is discussed here in association with spatial variations in nitrate supply, ambient ammonium concentration, and light field. 相似文献
143.
A 3600 YEARS PALEOCLIMATIC CHANGE INFERRED FROM ORGANIC δ~(13)C AND TOC/TN OF THE GUCHENG LAKE SEDIMENTS, SOUTHEAST CHINA 总被引:1,自引:0,他引:1
Im0DUrmNItiswellknownthatpabodbotechangeamrdedbyisotopesinlakesedimentScanbeobtainedbymcasuringthebl0andb'3CofauthigeniccarbonateSpeudsonetal.,l989),orbyrmsuringtheblbandb'tofmoiluscanshellsopntZetal.,l987)togetpabolaketeInPeratme.ButitisdiffictiltsoInebotodistinguishthegenetictypeofthecarbonatesfoedinoroutSidethelake.Furthennre,thepaservationof6'Dasapaleotemeraturerecordcanbeahabypostdepositionisotopicexchangecausedbydi-agnosesandotherfactorssuchas"vitalefTtal'(Marshall,l992).Itisdimcul… 相似文献
144.
The aculeate and isopteran fauna was surveyed in 1982 on the Krakatau islands, all the biota of which had been exterminated by the great eruption in 1883.The pattern of colonization of these insects (wasps, bees and termites) and the present state of their faunas are discussed based upon our 1982 survey and those made earlier. Species numbers varied only slightly between the four islands in spite of their differing sizes. This may be because the islands are situated close to each other and most of the aculeates prefer open sites rather than forests.The species/time curve for the Aculeata as a whole was still rising in 1982. However, in some groups flattening of the curve had occurred, and a comparison of species number in social wasps and bees, for example, between Java, Krakatau and Sumatra suggested the occurrence of supersaturation. Cumulative species numbers was distinctly larger than actual number in the three most recent surveys showing that several species must have become extinct in each intersurvey period. Species turnover associated with habitat changes may have occurred for the whole island group and on particular islands.Analysis of the colour pattern of the Krakatau populations of certain species with different geographical races on Java and Sumatra showed that the Javan elements have a slight preponderance over the Sumatran ones on the Krakataus.Some examples of faunal disharmony were found; the most remarkable was the almost complete lack of species of swarm-founding social wasps and bees, and of ground-nesting termites probably reflecting their poor dispersal ability across the sea barrier. 相似文献
145.
146.
Takuya Iwamura Antoine Guisan Kerrie A. Wilson Hugh P. Possingham 《Global Environmental Change》2013,23(5):1277-1284
International conservation organisations have identified priority areas for biodiversity conservation. These global-scale prioritisations affect the distribution of funds for conservation interventions. As each organisation has a different focus, each prioritisation scheme is determined by different decision criteria and the resultant priority areas vary considerably. However, little is known about how the priority areas will respond to the impacts of climate change. In this paper, we examined the robustness of eight global-scale prioritisations to climate change under various climate predictions from seven global circulation models. We developed a novel metric of the climate stability for 803 ecoregions based on a recently introduced method to estimate the overlap of climate envelopes. The relationships between the decision criteria and the robustness of the global prioritisation schemes were statistically examined. We found that decision criteria related to level of endemism and landscape fragmentation were strongly correlated with areas predicted to be robust to a changing climate. Hence, policies that prioritise intact areas due to the likely cost efficiency, and assumptions related to the potential to mitigate the impacts of climate change, require further examination. Our findings will help determine where additional management is required to enable biodiversity to adapt to the impacts of climate change. 相似文献
147.
Anne Deschamps Ryuichi Shinjo Takeshi Matsumoto Chao‐Shing Lee Serge E. Lallemand Shiguo Wu Scientific party of KR‐ KR‐ cruises 《地学学报》2008,20(4):327-332
We explore the tectono‐magmatic processes in the western West Philippine Basin, Philippine Sea Plate, using bathymetric data acquired in 2003 and 2004. The northwestern part of the basin formed through a series of northwestward propagating rifts. We identify at least five sequences of propagating rifts, probably triggered by mantle flow away from the mantle thermal anomaly that is responsible for the origin of the Benham and Urdenata plateaus. Gravitational forces caused by along‐axis topographic gradient and a ~30° ridge reorientation appear to also be driving the rift propagations. The along‐axis mantle flow appears to be reduced and deflected along the Luzon‐Okinawa fracture zone, because the spreading system remained stable west of this major fault zone. North‐east of the Benham plateau, a left‐lateral fracture zone has turned into a NE–SW‐trending spreading axis. As a result, a microplate developed at the triple junction. 相似文献
148.
Jae Il Lee Ho Il Yoon Kyu-Cheul Yoo Hyoun Soo Lim Yong Il Lee Donghyun Kim Young-Suk Bak Takuya Itaki 《Quaternary Research》2012,78(1):119-129
Geochemical characteristics of marine sediment from the southern Drake Passage were analyzed to reconstruct variations in sediment provenance and transport paths during the late Quaternary. The 5.95 m gravity core used in this study records paleoenvironmental changes during the last approximately 600 ka. Down-core variations in trace element, rare earth element, and Nd and Sr isotopic compositions reveal that sediment provenance varied according to glacial cycles. During glacial periods, detrital sediments in the southern Drake Passage were mostly derived from the nearby South Shetland Islands and shelf sediments. In contrast, interglacial sediments are composed of mixed sediments, derived from both West Antarctica and East Antarctica. The East Antarctic provenance of the interglacial sediments was inferred to be the Weddell Sea region. Sediment input from the Weddell Sea was reduced during glacial periods by extensive ice sheets and weakened current from the Weddell Sea. Sediment supply from the Weddell Sea increased during interglacial periods, especially those with higher warmth such as MIS 5, 9, and 11. This suggests that the influence of deep water from the Weddell Sea increases during interglacial periods and decreases during glacial periods, with the degree of influence increasing as interglacial intensity increases. 相似文献
149.
Takuya Echigo Tamao Hatta Seiko Nemoto Shigeru Takizawa 《Physics and Chemistry of Minerals》2012,39(9):769-778
We examined the effects of crystallinity and crystal morphology on surface hydroxyl concentration of goethite using four kinds of goethite samples prepared by aging a hydrous ferric oxide (ferrihydrite) at different temperatures ranging from 4 to 70?°C. These samples were analyzed with the following methods: powder X-ray diffraction, Brunauer–Emmett–Teller surface area analyzer, atomic force microscopy, attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and high-resolution X-ray photoelectron spectroscopy (XPS). The first three analyses showed that the goethite aged at lower temperature has lower crystallinity, smaller particle size and lower aspect ratio. The ATR-FTIR analysis revealed that the OH-stretching band of goethite aged at 4?°C moves to slightly higher wavenumber than those of the samples aged at higher temperatures. Their XPS analyses demonstrated that variation in the concentration of surface hydroxyl group ranges from 6.6 (nm?2) for the sample aged at 4?°C to 7.7 (nm?2) for the sample aged at 70?°C. Considering the analytical depth of the XPS (~5?nm), photoelectrons are emitted from the uppermost layers of the analyte. Hence, XPS results are interpreted to reflect variations in the morphology of fine crystals (<100?nm thick). The morphology of the present goethites can be characterized by their aspect ratio, in other words, the degree of development of (110)–(110) intersection edges at which protons preferentially accumulate. This variation in the concentration of surface hydroxyl group revealed by XPS analysis offers experimental evidence for the effects of crystallinity and morphology on the surface chemical properties of goethite. 相似文献
150.
Makio C. Honda Kosei Sasaoka Hajime Kawakami Kazuhiko Matsumoto Shuichi Watanabe Tommy Dickey 《Deep Sea Research Part I: Oceanographic Research Papers》2009,56(12):2281-2292
We conducted time-series observations of optical fields near the base of the euphotic zone (approximately 40 m) using moored automatic optical sensors at a time-series station in the Western Pacific Subarctic Gyre from March 2005 to July 2006 (with some gaps). We used the ratio of photosynthetically available radiation at the surface (surface PAR) to in situ quantum irradiance (in situ QI) at about 40 m as an index of opacity (surface PAR/in situ QI), which began to increase in the middle of April and peaked between the end of June and the middle of July 2005. This ratio then decreased toward winter. The ratio increased again beginning in January 2006, and large peaks were observed in June and July 2006. As an index of chlorophyll abundance we used the ratio of spectral irradiance at wavelengths of 555 and 443 nm (Ed555/Ed443) at about 40 m; seasonal variability of this ratio synchronized well with the attenuation coefficient “k” estimated with surface PAR, in situ QI, and BLOOMS depth. We estimated primary productivity (PP) using Ed555/Ed443 and an empirical equation based on a previous model but improved on the basis of shipboard observations. Estimated PP agreed well with observed PP. Seasonal variability of estimated PP was synchronized with that of organic carbon flux observed by sediment traps from approximately 150, 540, 1000, and 5000 m. This study demonstrates that time-series observations of in situ optical fields could contribute to the estimation of primary productivity and the study of the biological pump in the ocean. 相似文献