Distribution and sources of organic carbon, nitrogen and their isotopes in sediments of the subtropical Pearl River estuary and adjacent shelf, Southern China   总被引：17，自引：1，他引：17  

Jianfang Hu  Ping'an Peng  Guodong Jia  Bixian Mai  Gan Zhang 《Marine Chemistry》2006,98(2-4):274-285

The isotopic composition (δ¹³C and δ¹⁵N) and organic carbon (OC) and total nitrogen (TN, organic plus inorganic) content of 37 carbonate-free surficial sediments of the subtropical Pearl River estuary and the adjacent shelf of South China Sea (SCS) was determined. The δ¹³C values indicate that the sediment organic material is a mixture from two sources, terrestrial and marine. Several of the sediments have extremely low (< 4) OC / TN ratios, which could be due to low OC contents and/or to a significant fraction of the TN present as inorganic nitrogen adsorbed on clays. In general, the spatial patterns of OC, TN, δ¹³C and δ¹⁵N are similar. Values are low at the river mouth and on the western coast, suggesting proportionally greater accumulation of terrestrial particulate organic matter relative to marine phytodetritus, which is limited by low productivity in the turbid plume of the Pearl River. Algal-derived organic carbon (al-OC) content is estimated to be low (≤ 0.06%) at the river mouth and higher (up to 0.57%) on the adjacent inner shelf based on a mixing model of end members.  相似文献   

Isotopic signatures of organic matter in sediments of the continental shelf facing the Orinoco Delta: Possible contribution of organic carbon from savannas     

Ernesto Medina  Marta Francisco  Leonel Sternberg  William T. Anderson 《Estuarine, Coastal and Shelf Science》2005,63(4):527-536

The ⁸⁷Sr, ¹³C, and ¹⁵N isotopic signatures of organic matter in sediments from the continental shelf facing the Orinoco Delta were measured to determine the contribution of sediments transported from the Amazon River by the coastal Guayana current and the sediments transported by the Orinoco River. Box core samples between 60 and 300 m water depth collected along 4 transects located eastwards to the Orinoco Delta were analyzed. Carbon and nitrogen concentrations decreased with depth under water on the shelf, and were strongly correlated indicating homogeneity of organic matter composition. Phosphorus content was also associated to organic matter in most samples, but some of them revealed deposition of P-enriched sediments. The ⁸⁷Sr/⁸⁶Sr ratios showed a strong continental signature averaging 0.7117, therefore, limiting the possible carbon and nitrogen sources associated with these sediments to C3 trees, C4 grasses, or freshwater phytoplankton. The δ¹³C values were relatively high averaging −21‰, above values reported for sediments on the Amapá shelf and the Amazon River in Brazil. Average δ¹³C values did not differ significantly among transects. High δ¹³C values point to the influence of organic matter transported from the C4-plants dominated savannas in the northern fringe of the Orinoco River. δ¹⁵N values were positive and averaged 5‰, being within the range of values measured in the Marajo island (Amazon River) and the estuary of the Pará River. The δ¹⁵N values differed significantly among transects (4.9–5.2‰), lowest values corresponding to the northernmost transect near the coast of Trinidad, and the highest values corresponding to the transect located at the southernmost position.  相似文献   

Tracing suspended organic nitrogen from the Yangtze River catchment into the East China Sea   总被引：2，自引：0，他引：2  

Ying Wu  Thorsten Dittmar  Kai-Uwe Ludwichowski  Gerhard Kattner  Jing Zhang  Zhuo Y. Zhu  Boris P. Koch 《Marine Chemistry》2007

Total suspended matter was collected along the Yangtze River (Changjiang) and in the East China Sea in April to May and in September 2003, respectively, to study origin and fate of particulate organic nitrogen. Concentrations of particulate organic carbon (POC), nitrogen (PN) and hydrolyzable particulate amino acids (PAA; d- and l-enantiomers) were higher in the Yangtze Estuary than in the river and decreased offshore towards the shelf edge. In the coastal area, higher values of PAA were observed in the surface layer than in the bottom water. Stable carbon isotope ratios (δ¹³C) of POC increased from − 24.4‰ in the river to values around − 21‰ on the East China Sea Shelf. Dominant amino acids were aspartic acid + aspartine (Asx), glutamic acid + glutamine (Glx), glycine, alanine and serine. The proportions of Asx, Glx and isoleucine were higher in the marine than in the riverine samples contrary to the distributions of glycine, alanine, threonine and arginine. The proportions of d-amino acids were highest in the riverine suspended organic matter (6% of PAA) decreasing towards the shelf edge (1.5% of PAA). d-arginine, not reported in natural aquatic samples so far, was the most abundant d-amino acid in the river. The amino acid composition of the particulate organic matter (POM) in the Yangtze River indicates an advanced stage of degradation of POM. Highly degraded organic matter from soils is probably a main source of POM in the Yangtze River, but the relatively high δ¹³C values and low C/N ratios (7.7 ± 1.6) also indicate contribution from anthropogenic sources. The degraded riverine material was a dominant organic matter source in the estuary, where aquatic primary production had only a small overall contribution. In the East China Sea, gradual settling of riverine organic matter and the addition of fresher phytoplankton impacted the amino acid composition and δ¹³C values, and on the outer shelf relatively fresh phytoplankton-derived organic matter dominated.  相似文献   

南海沉积物中U,Th分布特征及其古环境意义   总被引：1，自引：0，他引：1  

温孝胜  刘韶  张惠玲  秦佩玲  赵焕庭 《热带海洋学报》1997,(3)

对采自南海深海中的两个柱样进行了分析。沉积速率分别为6.2cm·ka－1（317－82－25柱）和4．2cm·ka-1（90－37柱），均明显大于其他深海沉积速率，说明了南海这个边缘海的“放大效应”。此外，还分析了采自珠江口至外陆架的表层样，总结出从几元素在平面上的分布规律：从河口一陆架边缘～半深海，U，几含量的变化趋势均为多～少一多，Th／U比为小→大→小；而碳酸盐含量则显示出少→多→少的分布规律，即U，Th的含量与碳酸盐含量成反比，这可能是碳酸盐的所谓“稀释效应”所致。铀含量随柱样深度的变化曲线基本上与氧同位素曲线相吻合，其相关系数达0．67,证明U含量变化可能具有气候意义。Th的高含量点亦落在冷期之内。文中还探讨了水中铀的来源去向，说明了它能反映气候变化的原因。  相似文献   

Organic carbon and nitrogen isotopes in surface sediments from the western Arctic Ocean and their implications for sedimentary environments   总被引：1，自引：1，他引：1  

CHEN Zhihu  SHI Xuef  CAI Deling  HAN Yibing  YANG Zuosheng 《海洋学报(英文版)》2006,25(5):39-54

1 IntroductionFor several reasons, the Arctic Ocean and itsmarginal seas are key areas for understanding ocean-ic circulation and global climate system ( Clark,1982; Hansen et al., 1983; Walsh et al., 1996;Overpeck et al., 1997). First, the Arctic Ocean i…  相似文献   

富Co铁锰结壳铂族元素与铼-锇同位素组成及其意义   总被引：13，自引：0，他引：13  

姚德  张丽洁  初凤友  杜安道  刘心中  杨富贵 《海洋地质与第四纪地质》2002,22(3):53-58

用ICP－MS测定了太平洋富Co铁锰结壳铂族元素和铼－锇同位素组成。富Co铁锰结壳不仅异常富集铂族元素，而且铂族元素及其它亲铁元素的配发与陨石特征非常相似。铁锰结壳的铼－锇同位素组成明显有别于大陆地壳岩石，和K－T界线沉积物相似，接近陨石值。世界大洋范围内的富Co铁锰结壳均产于远离海底构造热液活动区，几乎不可能受到地幔源热液作用的直接影响。因此，富Co铁锰结壳中的铂族元素可能部分来源于地外物质。  相似文献   

An Ecosystem Model Including Nitrogen Isotopes: Perspectives on a Study of the Marine Nitrogen Cycle     

Chisato?YoshikawaEmail author  Yasuhiro?Yamanaka  Takeshi?Nakatsuka 《Journal of Oceanography》2005,61(5):921-942

We have developed an ecosystem model including two nitrogen isotopes (¹⁴N and ¹⁵N), and validated this model using an actual data set. A study of nitrogen isotopic ratios (δ¹⁵N) using a marine ecosystem model is thought to be most helpful in quantitatively understanding the marine nitrogen cycle. Moreover, the model study may indicate a new potential of δ¹⁵N as a tracer. This model has six compartments: phytoplankton, zooplankton, particulate organic nitrogen, dissolved organic nitrogen, nitrate and ammonium in a two-box model, and has biological processes with/without isotopic fractionation. We have applied this model to the Sea of Okhotsk and successfully reproduced the δ¹⁵N of nitrate measured in seawater and the seasonal variations in δ¹⁵N of sinking particles obtained from sediment trap experiments. Simulated δ¹⁵N of phytoplankton are determined by δ ¹⁵N of nitrate and ammonium, and the nitrogen f-ratio, defined as the ratio of nitrate assimilation by phytoplankton to total nitrogenous nutrient assimilation. Detailed considerations of biological processes in the spring and autumn blooms have demonstrated that there is a significant difference between simulated δ¹⁵N values of phytoplankton, which assimilates only nitrate, and only ammonium, respectively. We suggest that observations of δ ¹⁵N values of phytoplankton, nitrate and ammonium in the spring and autumn blooms may indicate the ratios of nutrient selectivity by phytoplankton. In winter, most of the simulated biogeochemical fluxes decrease rapidly, but nitrification flux decreases much more slowly than the other biogeochemical fluxes. Therefore, simulated δ¹⁵N values and concentrations of ammonium reflect almost only nitrification. We suggest that the nitrification rate can be parameterized with observations of δ¹⁵N of ammonium in winter and a sensitive study varying the parameter of nitrification rate.  相似文献   

The distribution and δC of dissolved organic carbon and its humic fraction in estuaries of southeastern USA     

Ernesto Otero  Randolph Culp  John E. Noakes  Robert E. Hodson 《Estuarine, Coastal and Shelf Science》2003,56(5-6):1187-1194

In this study, we examine the distribution and carbon stable isotope signature of dissolved organic carbon (DOC) and humic substances (HS) along a salinity gradient in the Altamaha and Satilla River estuaries. The maximum DOC concentrations in the Altamaha and Satilla were 10 and 29 mg C l⁻¹, respectively, though concentrations were similar at the mouth of both estuaries. There was a decrease in HS content of DOC from 50 to 80% at the head of the estuaries to 10% at salinities higher than 30‰. The δ¹³C DOC varied between −25.5 and −19‰ and between −27 and −21‰ in the Altamaha and Satilla estuaries, respectively. The tendency towards more depleted δ¹³C DOC in the Satilla, especially in the lower salinity portion of this estuary, suggests greater terrestrial inputs in the Satilla than in the Altamaha. Seasonal fluctuations were observed in the form of increased (two to three times) range in DOC concentration, heavier δ¹³C DOC and increased proportion of estuarine–marine-derived DOC (average enrichment of δ¹³C DOC from +1 to +2) during low river flow (July–October). The δ¹³C HS in both rivers showed a similar trend, but was consistently more depleted than DOC, with an average range from −28 to −24.5‰. This suggests that HS have larger proportions of terrestrial components (a maximum of >60% at the mouth of the estuary) than DOC. The less depleted δ¹³C values of DOC in comparison with HS indicate a different source for the non-humic (non-HS) component of DOC (range in δ¹³C non-HS, −22 to −16‰). That source could either be the decomposition of detrital material derived from saltmarsh environments or microalgal-derived DOC of estuarine or marine origins.  相似文献   

Geochemistry and origin of hornblende‐bearing xenoliths in the I‐type Petford Granite,North‐East Queensland     

J. C. Bailey 《Australian Journal of Earth Sciences》2013,60(1):7-23

Hornblende‐bearing xenoliths in the I‐type Petford Granite, north‐east Queensland, show an abundance pattern suggesting redistribution in a convecting magma system and were probably carried up with the host magma. The Petford Granite and xenoliths are chemically cognate, but quartz monzodiorite‐granodiorite bodies (a potential source for the xenoliths) in the adjacent country rocks belong to an independent magma suite. The xenoliths are chemically similar to andesite lavas and dykes 90 km to the NW. They represent fragments of the parental andesite (diorite) of a calcalkaline suite, which fractionated to yield the Petford Granite. They are not source rocks for the granite melt, melt residua, or early cumulates. The fractionated granite melt broke through the earlier envelope of diorite and rose into the upper crust, carrying dioritic fragments with it. Interaction between magma and xenoliths was generally minimal.  相似文献   

Controls on Devonian–Carboniferous magmatism in Tasmania,based on inherited zircon age patterns,Sr, Nd and Pb isotopes,and major and trace element geochemistry     

L. P. Black  J. L. Everard  M. P. McClenaghan  C. R. Calver  A. M. Fioretti 《Australian Journal of Earth Sciences》2013,60(7):933-968

Devonian–Carboniferous granites are widespread in Tasmania. In eastern Tasmania, Devonian granites intrude Ordovician–Early Devonian quartz-rich turbidites of the Mathinna Supergroup. The earliest (～400 Ma) I-type granodiorites may be arc-related. Following the Tabberabberan Orogeny (～389 Ma), more felsic and, finally, strongly fractionated I- and S-type granites were emplaced until ～373 Ma. In contrast, western Tasmania granites intrude a more diverse terrane of predominantly marine shelf successions, with depositional ages as old as Late Mesoproterozoic. They are mostly felsic and fractionated I- and S-types emplaced from ～374–351 Ma, possibly in response to post-collisional crustal extension following juxtaposition of the eastern and western Tasmanian terranes. Granites from the two terranes are readily distinguishable by the age spectra of their inherited zircon, which are noticeably similar to those of the detrital zircon from sedimentary successions in their respective terranes. Furthermore, within each terrane, both I and S-types yield similar inheritance patterns. This suggests a pivotal role for the sedimentary successions in the petrogenesis of both types. Western Tasmanian granites are also enriched in ～1600 Ma zircon, which is essentially unrepresented in the exposed supracrustal succession. Subtle differences between the inheritance and detrital age spectra in eastern Tasmania probably relate to unrepresentative sampling of the supracrustal rocks. Nd, Sr and Pb isotopic characteristics of the granites are consistent with their derivation by mixing of magmas derived from the mantle, possibly the lower crust, and from supracrustal rocks. Systematic isotopic trends in some eastern Tasmanian I-types, particularly in the Scottsdale Batholith, correlate well with major and trace element geochemistry and age. The isotopes are inconsistent with simple restite unmixing or crystal fractionation in a closed magma chamber, and indicate progressive contamination by the Mathinna Supergroup, or similar rocks. The isotopic characteristics of late, strongly fractionated granites, although sometimes obscured by hydrothermal alteration, are also consistent with concurrent assimilation-fractional crystallisation processes. Together with the close association of some strongly fractionated I- and S-types, this suggests that such granites were generated directly in the lower crust, and were not derived from unfractionated parental granite magmas.  相似文献