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1.
Nitrogen isotope compositions of particulate organic matter and nitrate were analyzed for seawater sampled at five stations at the Alaskan Gyre, Western Subarctic Gyre and East China Sea, focusing on the samples from the surface to 5000 m water to characterize the nitrogen cycling in the subarctic North Pacific Ocean and its marginal sea. The 15N of particulate organic matter showed little agreement with a conceptual closed model that interprets isotopic variation as being caused by isotope discrimination on nitrate utilization. The 15N and 13C of particulate organic matter varied with the water depth. A correlation between isotope compositions and C/N elemental ratio was found generally at all stations, although some irregular data were also found in deep layers. We developed a hypothetical nitrogen balance model based on N2 fixation and denitrification in seawater and attempted to apply it to distinguish nutrient cycling using both 15N-NO3 – and N* variation in seawater. This model was applied to the observed data set of 15N-NO3 – and N* in the North Pacific water and estimated the 15N-NO3 – of primordial nitrate in the North Pacific deep water as 4.8. The North Pacific intermediate water for all stations showed similar 15N-NO3 – and N* values of 6 and –3 µmol/kg, respectively, suggesting a similar nitrogen biogeochemistry. In the East China Sea, analysis showed evidence of water exchange with the North Pacific intermediate water but a significant influence of nitrogen from the river runoff was found in depths shallower than 400 m.  相似文献   

2.
Ishiwatari  R.  Hirakawa  Y.  Uzaki  M.  Yamada  K.  Yada  T. 《Journal of Oceanography》1994,50(2):179-195
Organic geochemical study of bulk organic matter (OM), hopanoid hydrocarbon and normal hydrocarbon (C23C35) was conducted for a 936-cm-long sediment core sample from the Oki Ridge of the Japan Sea (Core KH-79-3, C-3; 37°03.5 N, 134°42.6E, water depth 935 m). Stable carbon isotopic ratios were also measured for both bulk OM and individual hydrocarbons. The following results were obtained: (1) The weight ratios of total organic carbon to total nitrogen range from 6.2 to 9.4 in the core. The 13C values of bulk OM range from –25.1–20.7%.. The 13C values of OM in the sections of 140190 cm are lower (–25–24) than those in the other sections (–23–21). This result indicates that OM in the core except for the 140190 cm sections is essentially of marine origin. (2) The 13C value of diploptene (a hopanoid hydrocarbon) in the last glacial maximum (LGM), is –66.3 (vs. PDB), which indicates it originating in methanotrophic bacteria. This result provides evidence to support for the previous ideas (Oba et al., 1980, 1984; Masuzawa and Kitano, 1984) that the bottom waters in the Japan Sea were anoxic in LGM. (3) Long chain (C23C35) n-alkanes of higher-plant wax origin were found throughout the core. Their concentration is high in 140190 cm in depth, suggesting that eolian dust load was high in LGM. (4) The n-alkane/TOC ratio increases with decreasing 13C values of bulk OM. This result indicates that the load of terrestrial (probably eolian dust-derived) OM to the Japan Sea became higher in colder climates. (5) The CPI values of long-chain n-alkanes are different in different 13O stages of paleoclimate, probably reflecting variations in species of terrestrial higher plants as a result of climatological adaptations.  相似文献   

3.
Alkalinity, dissolved inorganic carbon (DIC), and 13C profiles from seep sites on the northwestern Gulf of Mexico upper slope show anomalously negative 13C values of up to –4.5 PDB, increased levels of DIC of up to 2.45 mmole/liter, and slight alkalinity rises of up to 2.54 meq/liter, relative to water column profiles from a seep-free site (0.63, 2.04 mmole/liter, and 2.39 meq/liter). The observed DIC enrichments coupled with the13C-depletions are attributed to the release of CO2 by microbial oxidation of crude oil in the seep environment, and its migration into the water column. The 13C composition of the migrating CO2 is estimated to be –26.0 on the basis of dissolved carbon inventory. Manifestation of DIC and 13C anomalies in the water column caused by hydrocarbon seepage holds promise to be useful for hydrocarbon reconnaissance surveys over large offshore tracts on account of the simplicity of sampling acquisition, and rapidity of analytical techniques in the laboratory.  相似文献   

4.
Hydrocarbon-derived and microbially mediated authigenic carbonates occur over the entire depth range of the northern Gulf of Mexico slope. These carbonates consist of nodules and incipient nodules in surface sediments, hardgrounds and isolated slabs, and moundlike buildups of up to 10–20 m relief above the surrounding seafloor. The authigenic carbonates are characterized by 13C negative values in the range –18 to –55 (PDB) suggesting mixing of seawater carbon with13C-depleted carbon sources ranging from crude oil to biogenic methane. Near the shelf edge, carbonates are diluted with biogenic material produced by reefs—bioherms developed at low sea level stands. Fossil-poor carbonates over salt diapirs of the upper and middle slope formed in the shallow subsurface and have been exhumed by the combined processes of uplift and physical erosion. Middle and lower slope carbonates are generally rich in fossil shells of chemosynthetic organisms. Mg calcite pelloidal matrix and acicular to botryoidal aragonitic void-filling cements are common petrographic features of these hydrocarbonderived carbonates. At two sites carbonates are mixed with barite.  相似文献   

5.
The 18O and 13C compositions of glacial- to Holocene-aged benthic foraminifera in a core collected from the eastern Arabian sea (water depth 1230 m) were determined to investigate glacial—interglacial variations in the intermediate depth water chemistry of the North Indian Ocean. In addition, we determined the 13C composition of Holocene benthic foraminifera from seven cores for which the 18O and 13C of benthic foraminifera from last glacial maximum (LGM) were reported by Kallel et al. (1988). The 13CDIC in the intermediate waters was generally depleted by 0.3–0.4 during the last glacial maximum compared to Holocene.  相似文献   

6.
Marine isotope stages (MISs) 1 to 5 were identified in the planktonic 18O record in sediment core DP00-02 just south of the Antarctic Polar Front in the Drake Passage, Antarctica. The oxygen isotope record, based on Neogloboquadrina pachyderma sinistral, is correlated with the contemporaneous global 18O stratigraphy. Marked deviations from the global climate curve suggest a local/regional overprint, particularly during MIS 3 which is considered a colder time period in the ocean record than MIS 1 and MIS 5 during the last interglacial. The comparison shows that negative 18O shifts in core DP00-02 during MIS 3 are larger than mean global changes which show a shift equal to or smaller than 0.5. The isotope shift, exceeding the glacial-interglacial ice volume effect, probably resulted from changes in the isotope composition of seawater, which is linearly related to decreases in salinity rather than to increases in sea-surface temperature. Increased ice-rafted debris (IRD) content during this interval indicates a strong influx of IRD from melting ice shelves and icebergs, which may be related to upwelling of warmer circumpolar deep water.  相似文献   

7.
Microbial Diversity in Nankai Trough Sediments at a Depth of 3,843 m   总被引：6，自引：0，他引：6  
Dense populations of bivalves, primarily Calyptogena sp., were observed at cold seeps of the Nankai Trough. Bacterial input to the sediment was estimated through determination of phospholipid ester-linked fatty acid (PLFA) and DNA profiles. Results indicated a bacterial biomass of 109 cells (g dry wt)-1 while individual fatty acid profiles revealed a predominance of monounsaturated fatty acids, mainly 18:1 isomers. The presence of these fatty acids can be interpreted to reflect a response to low temperature and a predominance of psychrophilic bacteria. DNA fragments encoding bacterial ribosomal RNA small-subunit sequences (16S rDNA) were amplified by the polymerase chain reaction method using DNA extracted directly from the sediment samples. From the sequencing results, at least 19 kinds of bacterial 16S rDNAs related to mostly the Proteobacteria and a few gram-positive bacteria were identified. These results suggest that the bacterial community in the Nankai Trough sediments consists of mainly bacteria belonging to the Proteobacteria , , and subdivisions. Bacteria belonging to the and subdivisions, which are known to include epibiont and sulfate reducing bacteria, respectively, were mostly detected in the sediment obtained from inside the area of the Calyptogena community, and the -Proteobacteria may function to supply reduced sulfur to bacterial endosymbionts of Calyptogena.  相似文献   

8.
In the southeastern Yellow Sea, active seepage of hydrocarbon gases has been observed by high-resolution (3.5 kHz) seismic profiling both in 1987 and 2001, occurring through a large number of plumes from the topmost pre-Holocene sedimentary layer. It is strong enough to compensate for current speed, extending vertically up to the sea surface. The gas seepage often appears to be explosive to form craters and diapirs, although pockmarks are rare due to the redistribution of mobile palimpsest sands. In core-top seawater and sediments, the gases are characterized by high amounts of C2, homogenous 13C1 values and a large difference (19.7 on average) between 13C1 (–55.2 to –53.6 PDB) and 13C2 (–36.8 to –32.5 PDB) values. The gases are considered to be generated with a smaller amount of C1 at the early thermal cracking stage of labile source materials, after which the C2 gas is enriched in 13C by diffusion or biological alternation at the generation or accumulation site. The homogenous 13C1 values may be one of the geochemical characteristics of gases acquired at depth which are less altered in the case of rapid diffusive gas migration to the seafloor.  相似文献   

9.
A high-resolution sediment core (sedimentation rate ~2 mm/year) from the German Bight was analysed for its foraminiferal stable oxygen isotope (18O) composition. These data were correlated with instrumental summer sea-surface temperature and salinity data from the nearby island of Helgoland, reaching back 100 years. Comparing the isotope data with the instrumental records reveals a distinct 18O–salinity relationship (18O=0.34×S–9.36; r=0.86) for the German Bight, where salinity is mainly driven by freshwater input from the Elbe River. Thus, these findings provide the possibility for future regional paleosalinity and paleodischarge reconstructions for times far beyond the instrumental timescale.  相似文献   

10.
The chemical states of iron in near-shore and deep-sea sediments were investigated by means of57Fe Mössbauer spectroscopy in combination with selective and nonselective chemical leachings. As far as a limited number of the sediments analyzed are concerned, Mössbauer spectra of near-shore sediments consist of high-spin paramgnetic ferrous (=1.13 mm/s, Eq=2.65 mm/s) and paramagnetic ferric (=0.35 mm/s, Eq=0.64 mm/s) components, while those of deep-sea sediments are composed of high-spin paramagnetic ferrous, paramagnetic ferrous, paramagnetic ferric and magnetic ferric (0.4 mm/s,H510 KG) components. The Fe2+/Fe3+ ratios of deepsea sediments are much smaller than those in near-shore sediments, while the total contents of iron in the former are much higher than those in the latter. This is principally due to the high contents of authigenic ferric oxides in deep-sea sediments. Further, in the aluminosilicate fraction, the Fe2+/Fe3+ ratios of deep-sea sediments are also smaller than those of near-shore sediments. This is probably attributed to high contents of clay minerals and authigenic aluminosilicates in deep-sea sediments relative to near-shore ones. The magnetic components in deepsea sediments are attributable to hematite, magnetite and/or maghemite.  相似文献   

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