A Preliminary Study of Oceanic Bomb Radiocarbon Inventory in the North Pacific during the Last Two Decades     

Yutaka W. Watanabe  Tsuneo Ono  Koh Harada  Masao Fukasawa 《Journal of Oceanography》1999,55(6):705-716

Radiocarbon and total carbonate data were obtained near the 1973 GEOSECS stations in the North Pacific along 30°N and along 175°E between 1993 and 1994. In these stations, we estimated radiocarbon originating from atomic bomb tests using tritium, trichlorofluoromethane and silicate contents. The average penetration depth of bomb radiocarbon during the two decades has deepened from 900 m to 1300 m. Bomb radiocarbon inventories above the average value for the whole North Pacific were found widely in the western subtropical region around 30°N both in the 1970s and 1990s, and its area in the 1990s was broader than that in the 1970s. In most of the North Pacific, while the bomb radiocarbon has decreased above 25.4, the bomb radiocarbon flux below 25.4 was over 1 × 10¹² atom m^-2yr^-1 in the subtropical region around 30°N. In the tropical area south of 20°N, the bomb radiocarbon inventory below 25.4 increased from zero to over 10 × 10¹² atom m^-2 during the last three decades. These distributions suggest that the bomb radiocarbon removed from the surface is currently accumulated with bomb ¹⁴C flux of over 1 × 10¹² atom m^-2yr^-1 below 25.4 in the subtropical region, mainly by advection from the higher latitude, and that part of the accumulated bomb ¹⁴C gradually spread southward with about 30 years.  相似文献   

Nitrogen forms and decomposition of organic carbon in the southern Bohai Sea core sediments   总被引：5，自引：0，他引：5  

Song Jinming  Ma Hongbo  L&#; Xiaoxia 《海洋学报(英文版)》2002,21(1):125-133

Study on form characteristics of nitrogen in marine sediments is the primary method to research its biogeochemical cycling and nitrogen form characteristics in core sediments can reflect the process and results of early diagenesis in a certain degree. In this paper, Sequential extraction process in natural grain size was used for studying the existent forms of nitrogen in five core sediments of the southern Bohai Sea for the first time. Nitrogen was divided into two parts -transferable and fixed based on whether it could be extracted by the reagent. Distributions and early diagenesis of transferable nitrogen forms in the southern Bohai Sea were researched integratedly. Results indicate that IEF - N and OSF-N are predominant forms in transferable part in the studied core sediments. Contents of different nitrogen forms vary differently with depth, and have different diagenesis process. Decomposition constant of organic nitrogen (ON) and OC are about 15.51 × 10~(-3)a~(-1)and 4.79× 10~(-3)a~(-1) respective  相似文献   

脱盐处理对钢样-砂浆界面微观结构的影响     

李森林朱雅仙  朱秀娟 《海洋工程》2004,22(2):75-78

运用扫描电镜(SEM)和X-射线衍射(XRD)技术研究了电化学脱盐处理对钢样-砂浆界面微观结构的影响。试验结果表明，经电化学脱盐处理后，钢样-砂浆界面的微观形貌特征与组成发生了明显的变化。  相似文献   

Sources and distribution of organic matter in a river-dominated estuary (Winyah Bay, SC, USA)   总被引：12，自引：0，他引：12  

Miguel A. Goi  Maria J. Teixeira  David W. Perkey 《Estuarine, Coastal and Shelf Science》2003,57(5-6):1023-1048

The sources and distribution of organic matter (OM) in surface waters and sediments from Winyah Bay (South Carolina, USA) were investigated using a variety of analytical techniques, including elemental, stable isotope and organic biomarker analyses. Several locations along the estuary salinity gradient were sampled during four different periods of contrasting river discharge and tidal range. The dissolved organic carbon (DOC) concentrations of surface waters ranged from 7 mg l⁻¹ in the lower bay stations closest to the ocean to 20 mg l⁻¹ in the river and upper bay samples. There was a general linear relationship between DOC concentrations and salinity in three of the four sampling periods. In contrast, particulate organic carbon (POC) concentrations were significantly lower (0.1–3 mg l⁻¹) and showed no relationship with salinity. The high molecular weight dissolved OM (HMW DOM) isolated from selected water samples collected along the bay displayed atomic carbon:nitrogen ratios ([C/N]a) and stable carbon isotopic compositions of organic carbon (δ¹³C_OC) that ranged from 10 to 30 and from −28 to −25‰, respectively. Combined, such compositions indicate that in most HMW DOM samples, the majority of the OM originates from terrigenous sources, with smaller contributions from riverine and estuarine phytoplankton. In contrast, the [C/N]a ratios of particulate OM (POM) samples varied significantly among the collection periods, ranging from low values of 5 to high values of >20. Overall, the trends in [C/N]a ratios indicated that algal sources of POM were most important during the early and late summer, whereas terrigenous sources dominated in the winter and early spring.In Winyah Bay bottom sediments, the concentrations of the mineral-associated OM were positively correlated with sediment surface area. The [C/N]a ratios and δ¹³C_OC compositions of the bulk sedimentary OM ranged from 5 to 45 and from −28 to −23‰, respectively. These compositions were consistent with predominant contributions of terrigenous sources and lesser (but significant) inputs of freshwater, estuarine and marine phytoplankton. The highest terrigenous contents were found in sediments from the river and upper bay sites, with smaller contributions to the lower parts of the estuary. The yields of lignin-derived CuO oxidation products from Winyah Bay sediments indicated that the terrigenous OM in these samples was composed of variable mixtures of relatively fresh vascular plant detritus and moderately altered soil OM. Based on the lignin phenol compositions, most of this material appeared to be derived from angiosperm and gymnosperm vascular plant sources similar to those found in the upland coastal forests in this region. A few samples displayed lignin compositions that suggested a more significant contribution from marsh C₃ grasses. However, there was no evidence of inputs of Spartina alterniflora (a C₄ grass) remains from the salt marshes that surround the lower sections of Winyah Bay.  相似文献   

Upstream dams and downstream clams: growth rates of bivalve mollusks unveil impact of river management on estuarine ecosystems (Colorado River Delta, Mexico)     

B. R. Schne  K. W. Flessa  D. L. Dettman  D. H. Goodwin 《Estuarine, Coastal and Shelf Science》2003,58(4):715-726

We studied how the extensive diversion of Colorado River water, induced by dams and agricultural activities of the last 70 years, affected the growth rates of two abundant bivalve mollusk species (Chione cortezi and Chione fluctifraga) in the northern Gulf of California. Shells alive on the delta today (‘Post-dam’ shells) grow 5.8–27.9% faster than shells alive prior to the construction of dams (‘Pre-dam’ shells). This increase in annual shell production is linked to the currently sharply reduced freshwater influx to the Colorado River estuary. Before the upstream river management, lower salinity retarded growth rates in these bivalves. Intra-annual growth rates were 50% lower during spring and early summer, when river flow was at its maximum. Growth rates in Chione today are largely controlled by temperature and nutrients; prior to the construction of dams and the diversion of the Colorado River flow, seasonal changes in salinity played an important role in regulating calcification rates.Our study employs sclerochronological (growth increment analysis) and geochemical techniques to assess the impact of reduced freshwater influx on bivalve growth rates in the Colorado River estuary. A combination of both techniques provides an excellent tool to evaluate the impact of river management in areas where no pre-impact studies were made.  相似文献   

扇贝肝胰腺化学成分的初步研究     

秦学祥  张振生 《海洋科学进展》2001,19(1):70-73

通过多种化学分析方法 ,初步探讨了扇贝肝胰腺组织的化学成分。结果表明 :该组织中含有较丰富的营养物质 ,并含有重要生理活性的 EPA和 DHA,微量元素含量也很丰富。这些结果为扇贝加工后下脚料的利用 ,提供了基础资料  相似文献   

A fuzzy distinguishability on species composition similarities of pelagic fishes in different years in the southern Taiwan Strait     

Zhang Chengmao  Fang Shuimei  Yang Shengyun 《海洋学报(英文版)》2001,20(4):575-583

I\rnooUcrIoxThe drpdric fish species cor-npositlon is an imPOrtant element 1n the study of fish ecologyand plays an important guiding role ln fishery preduction and roouLrces rnanagement. Lin(l988) and Zhang (1994 and l995) have studied the simi1drities of mpulation COtwsition ofame s1ngle species of different yea-rs including hairtail Trichuras haumee and yellDw cndertwinena cmi. But no rePOrt is available on the discridrination of the sidrildrities amongmuLlt1ple sPecies composition of…  相似文献   

Deposition Rates of Terrestrial and Marine Organic Carbon in the Osaka Bay, Seto Inland Sea, Japan, Determined Using Carbon and Nitrogen Stable Isotope Ratios in the Sediment   总被引：1，自引：0，他引：1  

Yasufumi Mishima  Akira Hoshika  Terumi Tanimoto 《Journal of Oceanography》1999,55(1):1-11

Carbon and nitrogen stable isotope ratios (¹³C and ¹⁵N) of surface sediments were measured within Osaka Bay, in the Seto Inland Sea in Japan, in order to better understand the sedimentation processes operating on both terrestrial and marine organic matter in the Bay. The ¹³C and ¹⁵N of surface sediments in the estuary of the Yodo River were less than –23 and 5 respectively, but increased in the area up to about 10 km from the river mouth. At greater distances they became constant (giving ¹³C of about –20 and ¹⁵N about 6). It can be concluded that large amounts of terrestrial organic matter exist near the mouth of the Yodo River. Stable isotope ratios in the estuary of the Yodo River within 10 km of the river mouth were useful indicators allowing study of the movement of terrestrial organic matter. Deposition rates for total organic carbon (TOC) and total nitrogen (TN) over the whole of the Bay were estimated to be 63,100 ton C/year and 7,590 ton N/year, respectively. The deposition rate of terrestrial organic carbon was estimated to be 13,200 (range 2,000–21,500) ton C/year for the whole of Osaka Bay, and terrestrial organic carbon was estimated to be about 21% (range 3–34) of the TOC deposition rate. The ratio of the deposition rate of terrestrial organic carbon to the rate inflow of riverine TOC and particulate organic carbon (POC) were estimated to be 19% (range 3–31) and 76% (range 12–100), respectively.  相似文献   

Seasonal and annual variations of marine sinking particulate flux during 1993~1996 in the central South China Sea   总被引：1，自引：0，他引：1  

CHEN Ronghu  WIESNER M G  ZHENG Yulong  CHENG Xinrong  JIN Haiyan  ZHAO Qingying  ZHENG Lianfu 《海洋学报(英文版)》2007,26(3):33-43

A total of 67 samples from the upper and lower sediment traps in the central South China Sea were analyzed, which were collected during 1993~1996. It is indicated that the distribution of stable isotope values, surface primary productivity, fluxes of total particulate matter, carbonate, biogenic opal, organic carbon, planktonic foraminiferal species and their total amount exhibit obviously seasonal and annual fluctuations. High values of the fluxes occurred in the prevailing periods of the northeastern and southwestern monsoons, and the low values occurred during the periods between the two monsoons. The fluxes of some planktonic foraminiferal species (Globigerinoides sacculifer, G. ruber, Globigerinita glutinata, Neogloboquadrina dutertrei) and their percentages also exhibit two prominent peaks during the prevailing periods of the northeastern and southwestern monsoons respectively, while those of Globigerina bulloides, Globorotalia menardii and Pulleniatina obliquiloculata only exhibit one peak in the prevailing periods of the northeastern monsoon. In addition, fluxes and percentages of Globigerinoides sacculifer and Globorotalia menardii as well as the fluxes of carbonate and total amount of planktonic foraminifera decrease gradually from 1993 to 1996, and those of Globigerina bulloides, Globigerinita glutinata and biogenic opal increase gradually from 1993 to 1996. The fluxes of carbonate and organic carbon in the upper trap are higher than those in the lower one. The study indicates that the seasonal and annual variations of the sediment fluxes and planktonic foraminiferal species are mainly controlled by the changes of surface primary productivity and hydrological conditions related to the East Asian monsoon. The lower carbonate and organic carbon fluxes in the lower trap are related to the dissolution.  相似文献   

Assessment of spatial variation in carbon utilization by benthic and pelagic invertebrates in a temperate South African estuary using stable isotope signatures     

Nicole B. Richoux  P. William Froneman 《Estuarine, Coastal and Shelf Science》2007,71(3-4):545-558

Stable isotope analyses (δ¹³C and δ¹⁵N) were used to evaluate the spatial variations in carbon flow from primary producers to consumers at two sites in the temperate and permanently open Kariega Estuary on the southeastern coast of South Africa during October 2005 and February 2006. One site was located opposite a salt marsh while the second was upstream of the marsh. Except for significantly enriched δ¹³C values of Zostera capensis and surface sediments near the salt marsh, the δ¹³C and δ¹⁵N signatures of the producers were similar between sites. The invertebrates were clustered into groups roughly corresponding to the predominant feeding modes. The suspension feeders showed δ¹³C values closest to the seston, whereas the deposit feeders, detritivores and scavengers/predators had more enriched δ¹³C values reflecting primary carbon sources that were likely a combination of seston, Spartina maritima and Z. capensis at the upstream site, with an increased influence of benthic algae and Z. capensis at the salt marsh site. The δ¹⁵N signatures of the consumers showed a stepwise continuum rather than distinct levels of fractionation, indicating highly complex trophic linkages and significant dietary overlap among the species. Consumers exhibited significantly enriched δ¹³C values at the salt marsh site, an effect that was attributed to enriched Z. capensis detritus in this region in addition to increased phytoplankton biomass in their diets compared with invertebrates living upstream. The data reinforce the concept that between-site variations in the stable isotope ratios of consumers can result not only from dietary shifts, but also from alterations in the isotope ratios of primary producers.  相似文献