Accumulation and biological mixing of Peru margin sediments     

Kee Hyun Kim  William C Burnett 《Marine Geology》1988,80(3-4):181-194

Rates of sediment accumulation and biological particle mixing in eight cores from the Peru shelf have been estimated by application of uranium-series disequilibrium techniques and radiocarbon dating. Activities of ²¹⁰Pb, ²²⁶Ra, ²³⁴Th and ²³⁸U have been determined in closely spaced intervals in each sediment core. Biological particle mixing coefficients were determined via a two-box advection-diffusion steady-state mixing model based on the distribution profiles of excess ²¹⁰Pb and, in some cases, excess ²³⁴Th activities.

The sedimentation rates estimated were in the order of a few millimeters/yr except for cores enriched in phosphatic components which displayed rates a few orders of magnitude slower. Bioturbation was significant in most cores studied with the exception of one core collected from within the middle of the oxygen-minimum zone. Estimated biological mixing coefficients were in the order of 10⁰–10¹ cm² yr⁻¹ for the surface mixed layer and 10⁻¹–10⁰ cm² yr⁻¹ for the layer below. Sediment slumping appears to have affected the ²¹⁰Pb distribution of two or three of our cores.  相似文献   

Burial rates of organic matter along the eastern Canadian margin and stable isotope constraints on its origin and diagenetic evolution   总被引：3，自引：0，他引：3  

Alfred N. N. Muzuka  Claude Hillaire-Marcel 《Marine Geology》1999,160(3-4):251-270

Organic carbon (OC) and nitrogen (N) contents and δ¹³C and δ¹⁵N values in total organic matter (OM) were measured in sub-surface sediments (0–30 cm sub-bottom) from 21 cores raised from the Laurentian Channel of the Gulf of St. Lawrence and the Labrador Sea, to document OM fluxes and storage along the eastern Canadian margin. Storage rates as high as 2.5 g m⁻² yr⁻¹ for OC and 0.2 g m⁻² yr⁻¹ for N are observed in the Laurentian Channel, suggesting that the shelf plays a significant role in terms of OM storage (from 1 to 2% of the primary production). Based on the isotopic composition of the essentially marine OM of the Labrador Sea (δ¹³C/V-PDB=−21.9±0.4‰; δ¹⁵N/AIR=7.6±0.6‰; n=12), there is no isotopic evidence for a significant relative input of terrestrial OM along the Laurentian Channel (δ¹³C/V-PDB=−21.9±0.4‰; δ¹⁵N/AIR=8.0±0.9‰; n=10), either due to high relative fluxes of marine OM and/or to the trapping of continental OM in the estuary and upstream. High storage rates of OM are also observed on the continental rise of the Labrador Sea (as high as 1.1 g C m⁻² yr⁻¹ and 0.09 g N m⁻² yr⁻¹). They contrast with one order of magnitude lower rates on the slope, due to low sedimentation rates (SR) and sediment winnowing by the Western Boundary Undercurrent (WBUC). Reduced early diagenetic alteration of OM is observed, particularly in the Laurentian Channel. It results in discrete (i) losses of OC and N, (ii) shifts in C/N ratios, suggesting preferential removal of N-bearing OM also highlighted by losses in total hydrolysable amino acids (HAA). In the Labrador Sea slope records, due to low SR, OM concentration changes linked to long term temporal variations may superimpose on these diagenetic trends, and some influence of the WBUC is noticeable.  相似文献   

Carbon isotopic composition and lattice-bound carbonate of Peru-Chile margin phosphorites     

Craig R. Glenn  Michael A. Arthur  Hseuh-Wen Yeh  William C. Burnett 《Marine Geology》1988,80(3-4):287-307

New light-stable carbonate-carbon isotope and lattice-bound CO₂ data from Quaternary Peru-Chile margin phosphatic nodules, crusts and pelletal grains, and from associated dolomicritic concretions, are presented, which provide constraints on the timing and mechanisms of growth of these phases in organic carbon-rich sediments. Comparison of δ¹³C values from carbonate fluorapatite (CFA) nodules and pelletal grains (−4.8 to 0.0‰ and −2.9 to +1.0‰ PDB, respectively) with pore-water total dissolved δ¹³C values from these sediments suggests early authigenic CFA precipitation from pore waters within a few centimeters of the sediment-water interface in association with suboxic to perhaps anoxic microbial degradation of organic matter. In contrast, the dolomicritic cores of nodules recovered from about 12°S display both strongly negative to positive δ¹³C values (−10.8 to +6.1‰) characteristic of formation deeper in the sediments in association with methanogenic and perhaps sulfate reduction microbial processes.

The amount of structural carbonate in CFA suggests that carbonate substitution generally increases as δ¹³C in CFA decreases, a probable consequence of increasing carbonate and accompanying charge-balancing substitutions in the CFA lattice in response to increasing pore-water carbonate ion concentrations with depth below the sediment-water interface. In one buried upward-growing nodule, decreasing CFA δ¹³C and increasing structural CO₂ also correspond to decreasing CFA growth rates. These data suggest that in addition to other constraints such as pore-water phosphorus and fluoride availability, the lower limit of CFA precipitation in suboxic to anoxic sediments may be controlled by lattice poisoning due to excessive dissolved carbonate ion concentrations. In organic-rich Peru-Chile margin sediments this depth threshold appears to be at approximately 5–10 cm below the sediment-water interface where maximum CFA CO₂ contents of about 6 Wt.% occur; in less organic-rich settings, greater depths of precipitation of CFA may be anticipated. Below this relatively shallow depth of CFA precipitation on the Peru shelf, high pore-water alkalinity and associated elevated total dissolved carbon and carbonate ion concentration apparently favor the precipitation of authigenic carbonates.  相似文献   

Distribution, texture and composition of modern phosphate pellets in Peru shelf muds     

K. Bryan Baker  William C. Burnett 《Marine Geology》1988,80(3-4):195-213

Textural analysis, including estimates of concentrations of authigenic phosphate pellets, were made for eight sediment cores from the Peru continental margin. Phosphatic pellets separated from these modern organic-rich sediments are black, spherical-ovoidal in shape, and in thin section often display a concentric structure around a nucleus consisting of inorganic mineral grains. Some pellets have a gray-white exterior coating which appears to be secondary diagenetic calcite. Phosphatic pellets account for upwards of 80% of the sediment mass in some cores. Pellets concentrate in specific size classes, generally between 125 and 500 μm in diameter, and occur within a poorly sorted sediment.  相似文献   

Early diagenesis of organic matter in Peru continental margin sediments: Phosphorite precipitation     

P.N Froelich  M.A Arthur  W.C Burnett  M Deakin  V Hensley  R Jahnke  L Kaul  K.-H Kim  K Roe  A Soutar  C Vathakanon 《Marine Geology》1988,80(3-4):309-343

Pore water chemistry (total dissolved CO₂, NH₄, NO₃, NO₂, PO₄, Si(OH)₄, Ca, Mg, Fe, Mn, SO₄, H₂S and F, and titration alkalinity), solid phase chemistry (C_org, P_org, C_TOT, N_TOT, F, Si_OPAL and S_II), and sediment characteristics (porosity, dry bulk density and formation factors) were determined on a centimeter-scale spacing in the upper 20–40 cm of sediments under intense upwelling areas on the Peru continental shelf. These data demonstrate that carbonate fluorapatite (CFA) is precipitating from pore waters in the upper few centimeters of a gelatinous mud with high organic carbon content (up to 20% C_org), very high porosity ( > 0.96 ml cm⁻³) and very low dry bulk density (< 0.1 g cm⁻³). Dissolved phosphate concentrations at the sediment-water interface range from 20 to 100 μM, orders of magnitude higher than bottom-water concentrations, and much higher than predicted from regeneration of organic matter. The mechanism of this interfacial phosphate release is unclear, but is apparently uncoupled from carbon and nitrogen metabolism and thus may be linked either to dissolution of fish debris or to the presence of a microbial mat in surficial sediments. Fluoride is incorporated into CFA by diffusion from the overlying seawater, and carbonate ions are provided from pore-water alkalinity. Magnesium concentrations in this reaction zone are not significantly different from those of seawater, suggesting that magnesium depletion is not a necessary prerequisite for CFA precipitation.

The environment of precipitation is interface-linked rather than driven by organic diagenesis of phosphorus deeper in the sediment. Most of the cores display a wide range of diagenetic characteristics below the immediate interfacial region, but almost all show the precipitation signature near the interface. This interface-linked early diagenetic porewater environment for the precipitation of CFA explains many of the geochemical characteristics of phosphorites and provides a “testable” model to compare the modern phosphogenic analog with ancient phosphorite deposits. Two of the cores display very high solid phase phosphorus and fluoride contents reflecting the presence of apparently modern pelletal apatites.  相似文献   

A contemporary sediment and organic carbon budget for the Kara Sea shelf (Siberia)     

A.C. Gebhardt  B. Gaye-Haake  D. Unger  N. Lahajnar  V. Ittekkot 《Marine Geology》2005,220(1-4):83-100

It has recently been realized that the Arctic undergoes drastic changes, probably resulting from global change induced processes. This acts on the cycling of matter and on biogenic elements in the Arctic Ocean having feedback mechanisms with the global climate, for example by interacting with atmospheric trace gas concentration. A contemporary budget for biogenic elements as well as suspended matter for the Arctic Ocean as a baseline for comparison with effects of further global change is, thus, needed. Available budgets are based on the late Holocene sedimentary record and are therefore quiet different from the present which has already been affected by the intense anthropogenic activity of the last centuries.

We calculated a contemporary suspended matter and organic carbon budget for the Kara Sea utilizing the numerous available data from the recent literature as well as our own data from Russian-German SIRRO (Siberian River Run-off) expeditions. For calculation of the budgets we used a multi-box model to simplify the Kara Sea shelf and estuary system: input was assumed to comprise riverine and eolian input as well as coastal erosion, output was assumed to consist of sedimentation and export to the Arctic Ocean. Exchange with the adjacent seas was considered in our budget, and primary production as well as recycling of organic material was taken into account. According to our calculations, about 18.5 × 10⁶ t yr^− 1 of sediments and 0.37 × 10⁶ t yr^− 1 of organic carbon are buried in the estuaries, whereas 20.9 × 10⁶ t yr^− 1 sediment and 0.31 × 10⁶ t yr^− 1 organic carbon are buried on the shelf. Most sources and sinks of our organic carbon budget of the Kara Sea are in the same order of magnitude, making it a region very sensitive to further changes.  相似文献   

Glacial–interglacial variations in Quaternary production of marine organic matter at DSDP Site 594, Chatham Rise, southeastern New Zealand margin     

Elizabeth A. Kowalski  Philip A. Meyers 《Marine Geology》1997,140(3-4):249-263

CaCO₃ and total organic carbon concentrations, organic matter C/N and carbon isotope ratios, and sediment accumulation rates in late Quaternary sediments from DSDP Site 594 provide information about glacial–interglacial variations in the delivery of organic matter to the Chatham Rise offshore of southeastern New Zealand. Low C/N ratios and nearly constant organic δ¹³C values of −23‰ indicate that marine production dominates organic matter supply in both glacial and interglacial times during oxygen isotope stages 1 through 6 (0–140 ka) and 17 through 19 (660–790 ka). Increased organic carbon mass accumulation rates in isotope stages 2, 4, 6, and 18 record enhanced marine productivity during glacial maxima. Excursions of organic δ¹³C values to ca. −29‰ in portions of isotope stage 2 suggest that the local concentration of dissolved CO₂ was occasionally elevated during the last glacial maximum, probably as a result of short periods of lowered sea-surface temperature. Dilution of carbonates by clastic continental sediment generally increases at this location during glacial maxima, but enhanced delivery of land-derived organic matter does not accompany the increased accumulation of clastic sediments.  相似文献   

Across-shelf sediment dispersal, Hauraki Gulf, New Zealand     

B. Manighetti  L. Carter 《Marine Geology》1999,160(3-4):271-300

Side-scan, seismic and surficial sediment data accompanied by current meter records highlight across-shelf sediment transport in Hauraki Gulf, an island-studded embayment off northern New Zealand. Calm weather currents are locally dominated by the tides, with periodic incursions of oceanic water from detached meanders of the East Auckland Current. Under these conditions, bedload transport occurs mainly in three 15–20 km-wide channels, where bathymetric intensification of the flow brings about near-bottom speeds of up to 82 cm s⁻¹ for Colville Channel and 33–44 cm s⁻¹ in Jellicoe and Cradock Channels. Surficial sediments are gravelly to muddy sand, winnowed in places, leaving a lag deposit of mainly biogenic carbonate gravel. Modelling results suggest that in Colville Channel, dominant fine to medium sand modes are mobile for 20–60% of the time, with a net eastward movement for fine sand. In Jellicoe and Cradock Channels, the prevailing direction of transport is southwards across the shelf, with sand mobile for up to 33% of the time. Oceanic incursions have the potential to boost flow in the western Gulf, however such incursions are transitory, and there is no measurable expression of oceanic water in the sedimentary record. Because of their association with prolonged periods of calm weather, the incursions are unlikely to accompany storm events, where their cumulative effect might be important for sediment transport. Near-bottom currents resulting from oceanic incursion may reinforce peak tides inside the Gulf by up to 2–4 cm s⁻¹. Enhancement of prevailing water motions occurs during periods of extreme weather. During cyclone Drena (January 1997), measured flow speeds in Jellicoe Channel reached 48 cm s⁻¹. Furthermore, the disturbance generated large waves that stirred bottom sediments down to over 100 m water depth. Such events are probably the major agent of sediment redistribution in the Hauraki Gulf. The net effect of storm and calm weather currents is to move sediment across the outer to middle shelf where, in the western and central Gulf it accumulates, and in the eastern Gulf it escapes eastward via Colville Channel.  相似文献   

Age of settlement and accumulation rate of submarine “coralligène” (−10 to −60 m) of the northwestern Mediterranean Sea; relation to Holocene rise in sea level     

Stephane Sartoretto  Marc Verlaque  Jacques Laborel 《Marine Geology》1996,130(3-4):317-331

Morphological and chronological studies have been carried out on coralline algal buildups (“coralligène”) situated between 10 and 60 m depth near Marseilles, and in Corsica (France). Despite the presence of occasionally sizeable quantities of iron hydroxide, these constructions prove to be a reliable material for radiocarbon dating. Ages obtained using this method range from 640±120 yrs B.P. (Corsica, Scandola Natural Reserve, −15 m) to 7760±80 yrs B.P. (Marseilles, Grand Congloue, −52 m). Internal erosion surfaces within the buildups give evidence of discontinuous development. The accumulation rate of the coralligène constructions is very low (0.006–0.83 mm yr⁻¹ according to the depth and time period). The higher values (0.53–0.83 mm yr⁻¹) were recorded for the deeper constructions. They correspond to a period between 8000 and 6000 yrs B.P. After 6000 yrs B.P., the only appreciable accumulation rates (0.11–0.42 mm yr⁻¹) were recorded for constructions situated between 10 and 35 m depth, whereas the accumulation rates of deep coralligène (> 50 m) appear to be low or zero. The age of the large constructions (overhang: 80 cm in width) is positively correlated with depth (r = 0.95; p < 0.005). Their development occurred during the Flandrian transgression. The oldest structures, today situated at 50 to 60 m depth, started to develop when water depth was probably no greater than 10 to 15 m. Apart from in strongly shaded fissures on rocky coasts and areas subjected to heavy sedimentation, the main framework building algal species was initially Mesophyllum lichenoides (Ellis) Lemoine, a high tolerant species to light, hydrodynamic energy and temperature. With the rise in sea level, the coralligène structure gradually became available to other less tolerant algal species (Lithophyllum, Lithothamnion), and the crustforming population diversified. Because of the good preservation of coralligène structures, the reliability of radiocarbon dating and the correlation between the age and bathymetric position of the large coralligène structures (except in areas of heavy sedimentation and fissures in shallow rocky coasts), these buildups are considered to be of use as biological indicators of variations in sea level.  相似文献   

Carbon and nitrogen isotope excursions in mid-Pleistocene sapropels from the Tyrrhenian Basin: Evidence for climate-induced increases in microbial primary production     

Philip A. Meyers  Stefano M. Bernasconi 《Marine Geology》2005,220(1-4):41-58

The modern Mediterranean Sea is oligotrophic, yet its sediment record contains layers of organic-carbon-rich sapropels at 21 ky (precessional) spacing that imply periods of elevated paleoproductivity that approached the high productivities of modern upwelling systems. Resolution to this paradox is provided by lines of evidence suggesting that the mode of primary productivity changed from one dominated by algae to one during times of sapropel deposition in which photosynthetic bacteria were important. We have made a high-resolution comparison of the organic carbon and nitrogen isotopic compositions of three sapropels and their background sediments in a 3-m sequence that corresponds to 1001 to 946 ka. Organic δ¹³C values systematically increase from − 26‰ to − 21‰ and δ¹⁵N values systematically decrease from 4‰ to < 0‰ as organic carbon mass accumulation rates increase in the sapropel layers. The increase in carbon isotope values mirrors the increases in primary productivity and associated organic matter export indicated by the increased mass accumulation rates. The decrease in nitrogen isotope values implies major contributions of nitrogen-fixing cyanobacteria to the total marine productivity. The precessional minima with which sapropels coincide were times of wetter climate that stratified the surface Mediterranean Sea, increased delivery of soil-derived phosphorus, and evidently amplified microbial primary production. Our high-resolution study reveals several relatively rapid excursions into and out of the high-productivity mode that suggest that sapropel deposition was a climate-sensitive surface-driven phenomenon that was not accompanied by basin-wide stagnation.  相似文献   

Hardbottom development and significance to the sediment-starved west-central Florida inner continental shelf     

Stephen P. Obrochta  David S. Duncan  Gregg R. Brooks   《Marine Geology》2003,200(1-4):291-306

Hardbottoms are sequence boundaries and condensed sections that offer clues for the interpretation of the incomplete record of Tertiary continental shelf evolution. Seaward of 5 km, 50% of the inner west-central Florida shelf seafloor is flat hardbottom. These lithified surfaces are punctuated by shorefacing, scarped hardbottoms that trend shore-parallel (330°–0°) and vary in relief (up to 4 m). Scarped hardbottoms are the only natural relief on the inner shelf and support a diverse benthic community, the activities of which erode the outcrops, producing undercuts in excess of 1 m. Outcropping hardbottom strata are comprised of distinct, phosphate-rich, mixed carbonate–siliciclastic lithofacies, that range in age from Miocene to Quaternary. Miocene units are dolomite-rich and mark the upper surface of the inner shelf bedrock (Hawthorn Group). Dolomite within these beds (silt-sized, cloudy centered rhombs) fall into two age groups, correlating with highstands at 15 and 5 Ma. This lithofacies is consistent with models that indicate an increased flux of organic matter – resulting from topographically induced upwelling – promoting dolomitization during early burial diagenesis in the sulfate-reduction zone. Quaternary units are calcite-rich and perched atop the shelf bedrock. Samples of these units record a complex diagenetic history and multiple sea-level fluctuations. Based on evidence of primary marine cementation, they are interpreted to be hardground (non-deposition) surfaces, forming as a function of sediment starvation and minimal sediment movement. Decreased highstand magnitude or duration may have resulted in the absence of a significant organic component to Quaternary hardbottoms, which, in turn, may prevent subsequent dolomitization. These outcrops are a potential source for sediments to the inner shelf, not only as habitat for biological sediment production, but also through their destruction. The undercut, shorefacing, scarped hardbottom morphology displayed by west-central Florida hardbottoms is indicative of bio-erosion. Preliminary studies indicate a potential mass of 0.04 kg m⁻² yr⁻¹ of siliciclastic sediment is released to the inner shelf.  相似文献   

北部湾养殖牡蛎体内异养细菌数量及其耐药性研究     

李炳  王瑞旋  张立  罗帮  牟红莉  王江勇 《热带海洋学报》2021,40(4):70-83

为了探究北部湾养殖区域香港牡蛎(Crassostrea hongkongensis)体内的异养细菌和弧菌数量及其耐药概况变化, 对不同养殖场牡蛎体内的异养细菌进行分离培养, 并统计其数量, 通过药敏纸片扩散等方法研究了细菌的耐药状况。结果显示: 牡蛎在高死亡率养殖环境中体内的异养细菌[(8.6±0.4)×10⁶CFU·g^-1]和弧菌[(9.5±0.4)×10⁵CFU·g^-1]数量较高, 在中死亡率环境中体内的异养细菌[(6.9±0.2)×10⁶CFU·g^-1]和弧菌[(4.5±0.6)×10⁵CFU·g^-1]数量次之, 在低死亡率养殖环境中体内的异养细菌[(3.3±0.1)×10⁶CFU·g^-1]和弧菌[(2.5±0.6)×10⁵CFU·g^-1]数量最低。耐药细菌主要为革兰氏阴性菌, 对β-内酰胺类(青霉素)、糖肽类(万古霉素)的耐药率较高, 对四环素类(四环素、多西环素)的耐药率次之, 对氨基糖苷类(链霉素、庆大霉素、妥布霉素、新霉素)、大环内酯类(红霉素)、喹诺酮类(诺氟沙星、环丙沙星、氧氟沙星、恩诺沙星)的耐药率较低。在高死亡率环境中牡蛎体内的多重耐药菌占79.7%, 其耐药谱型(48种)较广; 在中度死亡率环境中牡蛎体内的多重耐药菌占66.2%, 其耐药谱型为30种; 在低死亡率环境中牡蛎体内的多重耐药菌占58.4%, 其耐药谱型为17种。本文探究了牡蛎死亡率与其体内异养细菌数量和细菌耐药性的关系, 结果显示牡蛎在高死亡率环境中体内的耐药细菌数量多、耐药谱型较广, 低死亡率环境中牡蛎体内的耐药细菌数量较少, 异养细菌数量与牡蛎死亡率呈正相关关系, 两者相关系数为0.996。  相似文献   

Sea State and Rain: A Second Take on Dual-Frequency Altimetry     

Graham D. Quartly 《Marine Geodesy》2004,27(1):133-152

TOPEX and Jason were the first two dual-frequency altimeters in space, with both operating at K_u- and C-band. Thus, each gives two measurements of the normalized backscatter, σ⁰, (from which wind speed is calculated) and two estimates of wave height. Departures from a well-defined relationship between the K_u- and C-band σ⁰ values give an indication of rain. This study investigates differences between the two instruments using data from Jason's verification phase. Jason's K_u-band estimates of wave height are ∼1.8% less than TOPEX's, whereas its σ⁰ values are higher. When these effects have been removed the root mean square (rms) mismatch between TOPEX and Jason's K_u-band observations is close to that for TOPEX's observations at its two frequencies, and the changes in σ⁰ with varying wave height conditions are the same for the two altimeters. Rain flagging and quantitative estimates of rain rate are both based on the atmospheric attenuation derived from the σ⁰ measurements at the two frequencies. The attenuation estimates of TOPEX and Jason agree very well, and a threshold of-0.5 dB is effective at removing the majority of spurious data records from the Jason GDRs. In the high σ⁰ regime, anomalous data can be caused by processes other than rain. Consequently, for these low wind conditions, neither can reliable rain detection be based on altimetry alone, nor can a generic rain flag be expected to remove all suspect data.  相似文献   

Nature and composition of shore-zone sediments between Jeddah and Yanbu, eastern Red Sea     

N.V.N. Durgaprasada Rao  A.K.A. Behairy 《Marine Geology》1986,70(3-4):287-305

The shore-zone sediments between Jeddah and Yanbu, west coast of Saudi Arabia, are composed mostly of skeletal carbonate sands. The nearshore sediments containing benthic foraminifera, algal fragments and molluscs are multimodal, the mean grain size varying between 0.76 and 2.35 ø. The beach sediments, except samples dominated by cerithid gastropods in some localities, are relatively finer than the nearshore sediments. Although the beaches to a great extent comprise sand-sized material, fine lime muds and coarse clastic gravels occur in certain areas. The dune sediments comprising mostly algal grains and ooids are very fine with 50 percent of the material in the 0.25–0.18 mm size grade. Except a general northward decrease in mean grain size, regional trends in the textural parameters of the sediments between Jeddah and Yanbu are not quite apparent. Lateral variations in the textural characteristics suggest a landward migration of the sediments in the shore zone under the influence of northerly and northwesterly winds. The carbon and oxygen (δ ¹³C + 4.80 to 4.84‰ PDB) (δ ¹³O − 0.04 to + 0.53‰ PDB) isotopic ratios of the lime muds occurring in certain shallow margins in the shore-zone, which are much higher than those of the green algae, indicate that the fine carbonates are at least in part inorganic in origin.

Like the shallow-water carbonates in tropical seas, aragonite and high Mg-calcite are the dominant carbonate minerals in the shore-zone sediments. There is a landward increase in aragonite contents caused by the landward migration of fine material from the nearshore. The dominant clay mineral in the nearshore sediments is kaolinite with subordinate swelling chlorite and little illite. Kaolinite is contributed by the coastal regions under the sub-tropical humid climate. Swelling chlorite is considered to have been formed in the nearshore by mechanical mixture of chlorite and montmorillonite derived from the metamorphic and igneous terrains of the Tertiary mountains bordering the coastal plain.  相似文献   

Benthic denitrification and nitrogen cycling at the slope and rise of the N.W. European Continental Margin (Goban Spur)     

W. Balzer  W. Helder  E. Epping  L. Lohse  S. Otto 《Progress in Oceanography》1998,42(1-4)

The rate of benthic denitrification in slope and rise sediments of a transect across the N.W. European Continental Margin (Goban Spur) was evaluated from 31 pore water nitrate profiles obtained during six cruises between May and October. All profiles had well separated zones of nitrification and denitrification. High near-surface nitrate concentrations prevented the influx of nitrate from the bottom water. The denitrification rates obtained from steady-state-modelling ranged from 0.13 to 2.56 μmol N cm⁻² y⁻¹ and showed an exponential increase both with decreasing water depth and with increasing rate of organic carbon degradation. Denitrification rates in a nearby canyon, which did not follow these relationships, were estimated to be much higher as a result of erosion and redistribution of organic matter. Denitrification at the Goban Spur slope and rise is much lower than previously reported for similar environments in the Pacific resulting predominantly from the different oxygen and nitrate concentrations in the bottom water. A weighted average for the whole slope and rise sediment system shows that 17% of the particulate organic nitrogen input (8.93 μmol N cm⁻² y⁻¹) is denitrified and only 1% is buried, the rest being released as nitrate. Although being ten times higher compared with basin sediments, denitrification on the slope and rise is several times lower than on the adjacent shelf.  相似文献   

Glacial deep-water properties in the west-equatorial Pacific: bathyal thermocline near a depth of 2000 m     

J. C. Herguera  L. D. Stott  W. H. Berger 《Marine Geology》1991,100(1-4):201-206

The stable isotope stratigraphy of Planulina wüllerstorfi in three box cores from Ontong Java Plateau in the western equatorial Pacific shows that there existed a bathyal thermocline near the depth of 2000 m during glacial time. Waters below the boundary were colder by about 1°C, those above were about the same as now. The deep waters were slightly enriched and the upper waters depleted in nutrients, compared with present values. The differences in δ¹³C to the present (after correcting for the global change) are of the order of 0.1‰ more positive (above 2000 m) and 0.1‰ more negative (below), corresponding to changes in phosphate of the order of 0.1 μmol/kg (less phosphate above, and more below the boundary).  相似文献   

珠江口异养细菌时空分布特征及其调控机制   总被引：2，自引：0，他引：2  

李祥付  徐杰  施震  李瑞环 《热带海洋学报》2018,37(1):27-36

河口是海陆相互作用的重要地带, 往往呈现出独特的生物地球化学过程, 是研究碳循环过程的重要场所。在春季(2015年5月)、夏季(2015年8月)和冬季(2016年1月)分别对珠江口海域异养附生细菌和游离细菌时空分布及其各自高核酸(HNA)、低核酸(LNA)类群的相对贡献进行了调查研究, 并对其调控因子进行了相应探讨。结果表明, 珠江口异养细菌分布具有明显的时空差异。空间分布上, 珠江口异养细菌丰度自河口上游至下游呈递减趋势, 主要与上游污水输入以及珠江径流与高盐外海水在河口内的混合有关; 在雨季, 河口中下游盐度锋面区出现异养细菌丰度和叶绿素a质量浓度的高值区, 锋面区使营养物质停留时间增加, 促进浮游生物生长。垂直方向上, 表层异养细菌丰度略高于底层。时间尺度上, 异养细菌总丰度在春季最高(表层均值为2.94±1.23×10⁹个 •L^-1, 底层为2.81±1.50×10⁹个 •L^-1), 夏季次之(表层均值为2.32±0.43×10⁹个 •L^-1, 底层为1.90±0.50×10⁹个 •L^-1), 冬季最低(表层均值为1.06±0.33×10⁹个 •L^-1, 底层为9.76± 3.44×10⁸个 •L^-1)。珠江口海域异养细菌以附生细菌为主, 占异养细菌总丰度的16.56%~96.19%, 整体分布较稳定, 冬季最高(平均78.65%)、夏季(70.32%)与春季相近(68.17%)。附生细菌以代谢活跃的HNA类群为主, 游离细菌则主要以LNA类群为主, 代谢活性整体相对较低。  相似文献   

Production, retention and export of zooplankton faecal pellets on and off the Iberian shelf, north-west Spain   总被引：1，自引：0，他引：1  

Christian Wexels Riser  Paul Wassmann  Kalle Olli  Elena Arashkevich 《Progress in Oceanography》2001,51(2-4)

Vertical distribution of faecal pellets (FP), their sedimentation and the production rates of FP by mesozooplankton were studied during a cruise on and off the Iberian shelf in August 1998. The cruise was divided into two legs, each of them a short-term Lagrangian drift experiment. FP were collected with water bottles, with drifting sediment traps and during experiments carried out onboard the ship. The pellets were enumerated and their biovolumes and carbon contents (FPC) were calculated.The standing stock of FP in the upper 50 m was on average three times higher during the first on-shelf experiment than during the second off-shelf experiment. There were large diurnal variations, but no clear pattern emerged between day and night sampling. The vertical export of FPC from the upper, productive layer was on average one order of magnitude greater on the shelf (range 6–160 mg.m⁻².d⁻¹) compared to the off-shelf experiment (range 1–30 mg.m⁻².d⁻¹). FPC sedimentation explained 20% of the total POC export from the euphotic layer on the shelf, but <5% off the shelf. FP sedimentation was dominated by medium-sized cylindrical pellets (40–60 μm in diameter), but larger cylindrical pellets (60–100 μm in diameter) also played an important role. The smaller FP size fractions were never of any significance, in spite of the high abundance of smaller calanoid and cyclopoid copepods. The community production of FPs by mesozooplankton were calculated for the off shelf stations, and the average retention potential of FP in the upper 200 m was estimated to be 98%. Thus retention processes are clearly important for cross-shelf advection of FPs, their injection into the deep ocean and in the regulation of pelagic benthic coupling.  相似文献   

Stable isotope evidence for a marine origin of ophicalcites from the north-central Apennines (Italy)   总被引：1，自引：0，他引：1  

M. Barbieri  U. Masi  L. Tolomeo 《Marine Geology》1979,30(3-4):193-204

Carbon and oxygen isotope ratios of 59 samples of Mesozoic ophicalcites from the north-central Apennines were measured. Strontium content and isotope ratios were only determined for selected samples.

The data obtained (−4.1 ≤ δ ¹³C ≤ + 3.0; 16.5 ≤ δ ¹⁸O ≤ 30.1; 0.7076 ≤ ⁸⁷Sr/⁸⁶Sr ≤ 0.7086; 60 ≤ Sr ppm ≤ 1140) suggest that the carbonate cement of the Apennines ophicalcites had a marine origin.

The ¹⁸O/¹⁶O values of most of the carbonates studied, however, indicate that the rocks have interacted with hydrothermal fluids, dominantly represented by sea water. In particular, the rocks from the northern section of the Apennines apparently reequilibrated their δ ¹⁸O content at higher temperature than those from the central zone.

Strontium isotope ratios, close to the Cretaceous—Cenozoic ocean water values, are well in agreement with such a kind of sea water/ophicalcites interaction, even if the carbonate cement formed earlier during the Jurassic period.  相似文献   

Rare earth elements in the phosphatic-enriched sediment of the Peru shelf   总被引：1，自引：0，他引：1  

David Z Piper  Philip A Baedecker  James G Crock  William C Burnett  Benny J Loebner 《Marine Geology》1988,80(3-4):269-285

Apatite-enriched materials from the Peru shelf have been analyzed for their major oxide and rare earth element (REE) concentrations. The samples consist of (1) the fine fraction of sediment, mostly clay material, (2) phosphatic pellets and fish debris, which are dispersed throughout the fine-grained sediment, (3) tabular-shaped phosphatic crusts, which occur within the uppermost few centimeters of sediment, and (4) phosphatic nodules, which occur on the seafloor. The bulk REE concentrations of the concretions suggest that these elements are partitioned between the enclosed detrital material and the apatite fraction. Analysis of the fine-grained sediment with which the samples are associated suggested that this detrital fraction in the concretions should have shale REE values; the analysis of the fish debris suggested that the apatite fraction might have seawater values. The seawater contribution of REE's is negligible in the nodules and crust, in which the apatite occurs as a fine-grained interstitial cement. That is, the concentration of REE's and the REE patterns are predominantly a function of the amount of enclosed fine-grained sediment. By contrast, the REE pattern of the pelletal apatite suggests a seawater source and the absolute REE concentrations are relatively high. The REE/P₂O₅ ratios of the apatite fraction of these samples thus vary from approximately zero (in the case of the crust and nodules) to as much as approximately 1.2 × 10⁻³ (in the case of the pellets). The range of this ratio suggests that rather subtle variations in the depositional environment might cause a significant variation in the REE content of this authigenic fraction of the sediment.

Pelletal glauconite was also recovered from one sediment core. Its REE concentrations closely resemble those of the fish debris.  相似文献