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1.
东海陆架盆地南部及邻区陆域中生界对比   总被引：1，自引：0，他引：1  
为了探讨东海陆架盆地南部中生界油气勘探前景,在对现有的钻井资料、地震剖面和重磁资料处理的基础上,对东海陆架盆地南部及邻区陆域的中生界岩相组合和地层展布特征进行分析对比。综合研究认为：陆域中生界分布广,但发育不均,沉积类型多样,火山活动频繁;海域中生界分布广、厚度大,呈现“东厚西薄、南厚北薄”的特征。海陆中生界的差异主要表现在：陆域中生界受火山活动影响较大,以陆相火山岩沉积为主,而海域中生界受火山活动影响相对较小,主要为受海侵影响的湖相沉积。因此,由陆到海,中生界岩性变细、颜色变暗,海域的生烃潜力可能优于陆域。  相似文献   

2.
Downward particle fluxes and hydrodynamics in the northwestern Mediterranean basin were measured by a sediment trap and a current meter deployed at 2350 m depth, 250 m above bottom, from November 2003 to April 2005. During the winter of 2003–2004 there were high river discharges, two strong E–SE storms and several moderate storms and short periods of moderate dense shelf-water cascading during which dense shelf water did not reach the deep basin. Downward particle fluxes at the basin site were low during most of this winter but increased above one order of magnitude as a consequence of the strong storm and moderate cascading event that occurred in late February 2004. During the winter of 2004–2005, neither important river floods nor strong storms occurred but there were very intense and persistent dense shelf-water cascading events from February to April 2005. Dense shelf water, mixed with offshore convection water, reached the basin site in early March 2005, increasing downward particle fluxes by more than two orders of magnitude for more than 1 month. These observations indicate that events of significant sediment transport to the northwestern Mediterranean basin can be caused by severe winter E–SE storms associated with moderate cascading events or by exceptionally intense and persistent dense shelf-water cascading episodes alone. On the other hand, river floods, severe storms during water column stratification conditions (without cascading) and moderate storms concurrent with moderate dense shelf-water cascading did not generate sediment transport events able to reach the basin.  相似文献   

3.
The Omo basin in south western Ethiopia at the Kenyan boundary is a northern extension of the trans- boundary Turkana rift. It is an Early Pliocene north-south trending depression bounded on either side by normal faulting. The Omo river flows in the middle of the basin and empties itself at its southern end into Lake Turkana.The structural pattern of the Omo basin is determined from 2D and 3D analyses of the gravity field. The basin is an asymmetric half-graben formed by and localized within the NS/NNE trending Early Pliocene normal faults. It is built up on the older NW trending structures that were reactivated and affected the recent NS faults. Automatic depth determination techniques and 3D inversion are used to estimate depth to the basement and determine the sedimentary thickness. The results indicate over 4 km thick sediments were deposited over the graben.The Omo basin lies within the East African Rift system and appears to connect the generally NW trending oil-rich Muglad-Melut basins of south Sudan and the highly prospective and similarly trending Anza graben of Kenya. The Omo basin contains thick sequence of sediments and appears to be a promising future site of intensive hydrocarbon exploration.  相似文献   

4.
In order to assess the possible environmental impact of oily cuttings discharged during oil exploration activities, we studied the benthic foraminiferal faunas in a five-station, 4-km-long sampling transect around a cuttings disposal site at about 670 m depth offshore Angola (W Africa), where drilling activities started 1.5 years before sampling. Living (Rose Bengal stained) and dead foraminiferal faunas were sampled in March 2006. The faunal patterns mirror the spatial distribution of hydrocarbons, which are dispersed into a southeastern direction. Four different areas can be distinguished on the basis of the investigated faunal parameters (density, diversity and species composition of the living fauna, and comparison with subrecent dead faunas). The fauna at station S31, 300 m SE of the oil cuttings disposal site, appears to be clearly impacted: the faunal density and diversity are maximal, but evenness is minimal. Taxa sensitive to organic enrichment, such as Uvigerina peregrina, Cancris auriculus and Cribrostomoides subglobosus, have largely disappeared, whereas the low-oxygen-resistant taxon Chilostomella oolina and opportunistic buliminids and bolivinids attain relatively high densities. At station S32, 500 m SE of the disposal site, environmental impact is still perceptible. The faunal density is slightly increased, and U. peregrina, apparently the most sensitive species, is still almost absent. The faunas found at 1 and 1.8 km SE of the disposal site are apparently no longer impacted by the drill mud disposal. Faunal density and diversity are low, and the faunal composition is typical for a mesotrophic to eutrophic upper slope environment. Finally, Station S35, 2 km NW of the disposal site, contains an intermediate fauna, where both the low-oxygen-resistant C. oolina and the more sensitive taxa (U. peregrina, C. auriculus and C. subglobosus) are present. All taxa live close to the sediment–water interface here, indicating a reduced oxygen penetration into the sediment. Since the hydrocarbon concentration is low at this station, it appears that the faunal characteristics are the consequence of a slightly different environmental setting, and not due to a contamination with drill cuttings. Our data underline the large potential of benthic foraminifera as bio-indicators of anthropogenic enrichment in open marine settings, such as caused by the disposal of oily drill cuttings. The foraminiferal faunas react essentially by a density increase of a number of tolerant and/or opportunistic taxa, and a progressive disappearance of more sensitive taxa in the most impacted area. Rather surprisingly, large-sized taxa appear to be more sensitive than small-sized foraminiferal taxa.  相似文献   

5.
The Dniepr-Donets Basin (DDB) hosts a multi-source petroleum system with more than 200 oil and gas fields, mainly in Carboniferous clastic rocks. Main aim of the present study was to correlate accumulated hydrocarbons with the most important source rocks and to verify their potential to generate oil and gas. Therefore, molecular and isotopic composition as well as biomarker data obtained from 12 oil and condensate samples and 48 source rock extracts was used together with USGS data for a geological interpretation of hydrocarbon charging history.Within the central DDB, results point to a significant contribution from (Upper) Visean black shales, highly oil-prone as well as mixed oil- and gas-prone Serpukhovian rocks and minor contribution from an additional Tournaisian source. Devonian rocks, an important hydrocarbon source within the Pripyat Trough, have not been identified as a major source within the central DDB. Additional input from Bashkirian to Moscovian (?) (Shebelinka Field) as well as Tournaisian to Lower Visean rocks (e.g. Dovgal Field) with higher contents of terrestrial organic matter is indicated in the SE and NW part, respectively.Whereas oil–source correlation contradicts major hydrocarbon migration in many cases for Tournaisian to Middle Carboniferous reservoir horizons, accumulations within Upper Carboniferous to Permian reservoirs require vertical migration up to 4000 m along faults related to Devonian salt domes.1-D thermal models indicate hydrocarbon generation during Permo-Carboniferous time. However, generation in coal-bearing Middle Carboniferous horizons in the SE part of the basin may have occurred during the Mesozoic.  相似文献   

6.
Integration of 2-D seismic lines, well data and field studies allow us to determine the geometry variations of anticlines in the highly prolific Central Frontal Fars region in the SE Zagros fold belt. These variations are directly related to changes in thickness of the principal evaporitic intermediate detachment level, located along the Late Triassic Dashtak Formation. Anticlines of short wavelength contain a significant over-thickening of the evaporitic detachment level in their crestal domain that may reach 1900 m (from an original thickness of 550–800 m). Folds containing thick Dashtak evaporites show decoupling across the detachment level and, thus, a shift of the anticline crest in the underlying Permo-Triassic carbonates of the Dehram Group, which form the major gas reservoir in the Central Frontal Fars. Four main parameters control the extent and distribution of the decoupled anticlines in the study area: (a) original large thickness of the Late Triassic evaporitic basin; (b) coinciding larger amounts of anhydrites with increasing total thickness of formation; (c) parallel occurrences of abnormally high fluid pressures; and (d) shortening variations across, and along, the strike of specific folds. The present work relating the different parameters of the Dashtak evaporites with the anticline geometry allows a better understanding of the fold geometry variations with depth, which is applicable to oil and gas exploration in the SE Zagros and other similar hydrocarbon provinces characterised by intermediate detachment horizons.  相似文献   

7.
The North Yellow Sea Basin ( NYSB ), which was developed on the basement of North China (Huabei) continental block, is a typical continental Mesozoic Cenozoic sedimentary basin in the sea area. Its Mesozoic basin is a residual basin, below which there is probably a larger Paleozoic sedimentary basin. The North Yellow Sea Basin comprises four sags and three uplifts. Of them, the eastern sag is a Mesozoic Cenozoic sedimentary sag in NYSB and has the biggest sediment thickness; the current Korean drilling wells are concentrated in the eastern sag. This sag is comparatively rich in oil and gas resources and thus has a relatively good petroleum prospect in the sea. The central sag has also accommodated thick Mesozoic-Cenozoic sediments. The latest research results show that there are three series of hydrocarbon source rocks in the North Yellow Sea Basin, namely, black shales of the Paleogene, Jurassic and Cretaceous. The principal hydrocarbon source rocks in NYSB are the Mesozoic black shale. According to the drilling data of Korea, the black shales of the Paleogene, Jurassic and Cretaceous have all come up to the standards of good and mature source rocks. The NYSB owns an intact system of oil generation, reservoir and capping rocks that can help hydrocarbon to form in the basin and thus it has the great potential of oil and gas. The vertical distribution of the hydrocarbon resources is mainly considered to be in the Cretaceous and then in the Jurassic.  相似文献   

8.
During TAiwan Integrated GEodynamics Research of 2009, we investigated data from thirty-seven ocean-bottom seismometers (OBS) and three multi-channel seismic (MCS) profiles across the deformation front in the northernmost South China Sea (SCS) off SW Taiwan. Initial velocity-interface models were built from horizon velocity analysis and pre-stack depth migration of MCS data. Subsequently, we used refracted, head-wave and reflected arrivals from OBS data to forward model and then invert the velocity-interface structures layer-by-layer. Based on OBS velocity models west of the deformation front, possible Mesozoic sedimentary rocks, revealed by large variation of the lateral velocity (3.1–4.8 km/s) and the thickness (5.0–10.0 km), below the rift-onset unconformity and above the continental crust extended southward to the NW limit of the continent–ocean boundary (COB). The interpreted Mesozoic sedimentary rocks NW of the COB and the oceanic layer 2 SE of the COB imaged from OBS and gravity data were incorporated into the overriding wedge below the deformation front because the transitional crust subducted beneath the overriding wedge of the southern Taiwan. East of the deformation front, the thickness of the overriding wedge (1.7–5.0 km/s) from the sea floor to the décollement decreases toward the WSW direction from 20.0 km off SW Taiwan to 8.0 km at the deformation front. In particular, near a turn in the orientation of the deformation front, the crustal thickness (7.0–12.0 km) is abruptly thinner and the free-air (?20 to 10 mGal) and Bouguer (30–50 mGal) gravity anomalies are relatively low due to plate warping from an ongoing transition from subduction to collision. West of the deformation front, intra-crustal interfaces dipping landward were observed owing to subduction of the extended continent toward the deformation front. However, the intra-crustal interface near the turn in the orientation of the deformation front dipping seaward caused by the transition from subduction to collision. SE of the COB, the oceanic crust, with a crustal thickness of about 10.0–17.0 km, was thickened due to late magmatic underplating or partially serpentinized mantle after SCS seafloor spreading. The thick oceanic crust may have subducted beneath the overriding wedge observed from the low anomalies of the free-air (?50 to ?20 mGal) and Bouguer (40–80 mGal) gravities across the deformation front.  相似文献   

9.
The distribution of dissolved organic carbon (DOC) and nitrogen (DON) and particulate organic carbon (POC) and nitrogen (PON) was studied on a transect perpendicular to the Catalan coast in the NW Mediterranean in June 1995. The transect covered a hydrographically diverse zone, including coastal waters and two frontal structures (the Catalan and the Balear fronts). The cruise was conducted during the stratified period, characterized by inorganic nutrient depletion in the photic zone and a well established deep chlorophyll a maximum. DOC concentrations were measured using a high-temperature catalytic oxidation method, and DON was determined directly, with an update of the Kjeldahl method, after removal of inorganic nitrogen.The ranges of DOC and DON concentrations were 44–95 μM-C and 2.8–6.2 μM-N. The particulate organic matter ranged between 0.9 and 14.9 μM-C and from 0.1 to 1.7 μM-N. The DOC : DON molar ratio averaged 15.5±0.4, and the mean POC : PON ratio was 8.6±0.6. The distribution of dissolved organic matter (DOM) was inverse to that of the salinity. The highest concentrations of DOM were found in coastal waters and in the stations affected by the Catalan front, located at the continental shelf break.It was estimated that recalcitrant DOM constituted 67% of the DOM pool in the upper 50 m. The data suggest that accumulation of DOC due to the decoupling of production and consumption may occur in the NW Mediterranean during stratification and that the organic matter exported from the photic layer is dominated by C-rich material.  相似文献   

10.
Below the sill depth (at about 2400 m) of the Alpha-Mendeleyev ridge complex, the waters of the Canada Basin (CB) of the Arctic Ocean are isolated, with a 14C isolation age of about 500 yr. The potential temperature θ decreases with depth to a minimum θm≈−0.524°C near 2400 m, increases with depth through an approximately 300 m thick transition layer to θh≈−0.514°C, and then remains uniform from about 2700 m to the bottom at 3200–4000 m. The salinity increases monotonically with depth through the deep θm and transition layer from about 34.952 to about 34.956 and then remains uniform in the bottom layer. A striking staircase structure, suggestive of double-diffusive convection, is observed within the transition layer. The staircase structure is observed for about 1000 km across the basin and has been persistent for more than a decade. It is characterized by 2–3 mixed layers (10–60 m thick) separated by 2–16 m thick interfaces. Standard formulae, based on temperature and salinity jumps, suggest a double-diffusive heat flux through the staircase of about 40 mW m−2, consistent with the measured geothermal heat flux of 40–60 mW m−2. This is to be expected for a scenario with no deep-water renewal at present as we also show that changes in the bottom layer are too small to account for more than a small fraction of the geothermal heat flux. On the other hand, the observed interfaces between mixed layers in the staircase are too thick to support the required double-diffusive heat flux, either by molecular conduction or by turbulent mixing, as there is no evidence of sufficiently vigorous overturns within the interfaces. It therefore seems, that while the staircase structure may be maintained by a very weak heat flux, most of the geothermal heat flux is escaping through regions of the basin near lateral boundaries, where the staircase structure is not observed. The vertical eddy diffusivity required in these near-boundary regions is O(10−3) m2 s−1. This implies Thorpe scales of order 10 m. We observe what may be Thorpe scales of this magnitude in boundary-region potential temperature profiles, but cannot tell if they are compensated by salinity. The weak stratification of the transition layer means that the large vertical mixing rate implies a local dissipation rate of only O(10−10) W kg−1, which is not ruled out by plausible energy budgets. In addition, we discuss an alternative scenario of slow, continuous renewal of the CB deep water. In this scenario, we find that some of the geothermal heat flux is required to heat the new water and vertical fluxes through the transition layer are reduced.  相似文献   

11.
A quantitative study of metazoan meiofauna was carried out on bathyal sediments (305, 562, 830 and 1210 m) along a transect within and beneath the oxygen minimum zone (OMZ) in the southeastern Pacific off Callao, Peru (12°S). Meiobenthos densities ranged from 1517 (upper slope, middle of OMZ) to 440–548 ind. 10 cm−2 (lower slope stations, beneath the OMZ). Nematodes were the numerically dominant meiofaunal taxon at every station, followed by copepods and nauplii. Increasing bottom-water oxygen concentration and decreasing organic matter availability downslope were correlated with observed changes in meiofaunal abundance. The 300-m site, located in the middle of the OMZ, differed significantly in meiofaunal abundance, dominance, and in vertical distribution pattern from the deeper sites. At 305 m, nematodes amounted to over 99% of total meiofauna; about 70% of nematodes were found in the 2–5 cm interval. At the deeper sites, about 50% were restricted to the top 1 cm. The importance of copepods and nauplii increased consistently with depth, reaching ∼12% of the total meiofauna at the deepest site. The observation of high nematode abundances at oxygen concentrations <0.02 ml l−1 supports the hypothesis that densities are enhanced by an indirect positive effect of low oxygen involving (a) reduction of predators and competitors and (b) preservation of organic matter leading to high food availability and quality. Food input and quality, represented here by chloroplastic pigment equivalents (CPE) and sedimentary labile organic compounds (protein, carbohydrates and lipids), were strongly, positively correlated with nematode abundance. By way of contrast, oxygen exhibited a strong negative correlation, overriding food availability, with abundance of other meiofauna such as copepods and nauplii. These taxa were absent at the 300-m site. The high correlation of labile organic matter (C-LOM, sum of carbon contents in lipids, proteins and carbohydrates) with CPE (Pearson's r=0.99, p<0.01) suggests that most of the sedimentary organic material sampled was of phytodetrital origin. The fraction of sediment organic carbon potentially available to benthic heterotrophs, measured as C-LOM/Total organic carbon, was on average 17% at all stations. Thus, a residual, refractory fraction, constitutes the major portion of organic matter at the studied bathyal sites.  相似文献   

12.
Submarine channel deposits are recognised as the primary heterogeneity within the turbidite systems that host them, with channel fill heterogeneities being considered secondary. An investigation of channel fill heterogeneities was conducted on Oligocene turbidites of the Grès du Champsaur, Hautes Alpes, SE France, which was deposited in a sub-basin within the Alpine peripheral foreland basin. Here, a series of erosional channels are exposed in mountainous terrain. Maximum channel widths are in the order of 1000 m, and depths of the order of 100 m. The channels can be traced along axis for at least 6 km. Mapping of channel facies revealed three orientations of fill heterogeneity expressed as: (1) upward variations in the character of vertically stacked fill sequences, (2) lateral variability, and (3) the occurrence of downstream dipping and stacking units forming the uppermost parts of channel fill. Vertically expressed heterogeneities are thought to have developed via the gradual reduction in the efficiency of channelised flow, leading to a progressive reduction in scour and the deposition of overall thinning and fining upwards sequences. Lateral heterogeneity is related to the development of downstream-oriented elongated scour and fill facies. Downstream-dipping heterogeneity is represented by a series of several metre-scale downstream-dipping low-angle clinoforms thought to be related to final infill of the negative channel bathymetry by a migrating front of sand that would have formed part of a downstream-migrating sheet to channel transition in plan view. Both first and second orders of channel heterogeneity may control the reservoir performance of channel prone turbidite sequences. Preferred-orientation channel facies heterogeneities are thought to affect potential hydrocarbon recovery through their impact on permeability anisotropy within the confines of the channel.  相似文献   

13.
In order to study temporal variations of the genetic material in the continental shelf and deep-sea sediments of the extremely oligotrophic Cretan Sea, samples were collected on seasonal basis from August 1994 to September 1995, with a multiple corer, at seven stations (from 40 to 1540 m depth). Surface sediments (0–1 cm) were sub-sampled and analyzed for nucleic acid content (DNA, RNA) and bacterial density. DNA concentrations in the sediments were high (on annual average, 25.0 μg g-1) and declined with increasing water depth, ranging from 3.5 to 55.2 μg g-1. DNA concentrations displayed wide temporal changes also at bathyal depths confirming the recent view of the large variability of the deep-sea environments. Also RNA concentrations decreased with increasing water depth (range: 0.4–29.9 μg g-1). The ratio of RNA to DNA did not show a clear spatial pattern but was characterized by significant changes between sampling periods. DNA concentrations were significantly correlated with protein and phytopigment concentrations in the sediment, indicating a possible relationship with the inputs of primary organic matter from the photic layer. Bacterial densities were generally high (range: 0.9–4.6×108 cells g-1) compared to other deep-sea environments and decreased with increasing water depth. Estimates of the bacterial contribution to the sedimentary genetic material indicated that bacterial-DNA accounted, on annual average, for a small fraction of the total DNA pool (4.3%) but that bacterial-RNA represented a significant fraction of the total sedimentary RNA (26%). Bacterial contribution to nucleic acids increased, even though irregularly, with increasing depth. In deep-sea sediments, changes in RNA concentrations appear to be largely dependent upon bacterial dynamics. Estimates of the overall living contribution to the DNA pools (i.e. microbial plus meiofaunal DNA) indicated that the large majority (about 90%) of the DNA in continental and deep-sea sediments of the eastern Mediterranean was detrital. The non-living DNA pools reach extremely high concentrations up to 0.41 g DNA m-2 cm-1. Thus, especially in deep benthic habitats, characterized by low inputs of labile organic compounds, detrital DNA could represent a suitable and high quality food source or a significant reservoir of nucleic acid precursors for benthic metabolism.  相似文献   

14.
《Marine Geology》2001,172(3-4):331-358
Analyses of over 6600 km of reflection seismic profiles on the northern continental margin of the South China Sea permit the recognition of four Quaternary high-frequency type 1 sequences of the 4th order, deposited during the past ca. 690 kyr. At the present-day shelf edge, only lowstand systems tracts characterised by a prograding clinoformal internal reflection pattern are preserved. The prograding complexes can be considered as regressive units accumulated during relative sea-level falls. They exhibit internal discontinuities which might point to minor sea-level fluctuations of the 5th order. A preliminary regional relative sea-level curve for the past 630 kyr is established using the present positions of the delta fronts mapped. The neotectonics curve derived by subtracting eustatic sea-level changes from the relative sea-level curve shows that the depths of the delta fronts today are controlled primarily by regional tectonic movements and the global sea-level.Our seismo-stratigraphic interpretation documents that the area off Hong Kong and around the Dongsha Islands experienced two uplift episodes during the past 5 ma, namely at the Miocene/Pliocene boundary and at the end of the lower Middle Pleistocene, respectively. These uplift events which are centred on the Dongsha Rise led to its subaerial exposure and to the erosion of the Pliocene and most of the Pleistocene strata. The change from thermal subsidence of the continental margin initiated at the end of the drift phase to the phase of magmato-tectonic uplift was caused by a reorientation of the tectonic regime.The Recent depositional environment on the northern continental margin of the South China Sea is dominated by sediment accumulation within the inner shelf and the Zhujiang (Pearl River) estuary. The outer shelf and upper slope, especially around the Dongsha Islands, are characterised by bypass of terrigenous material.The sedimentary column in the deepsea basin has a thickness of more than 2 km and comprises 14 depositional units starting with terrestrial rift deposits. It overlies oceanic as well as transitional crust.  相似文献   

15.
The compaction of quartzose sandstones is described by a macroscopical visco–elasto–plastic model, derived from microscopical considerations. This model considers that the reduction of total porosity (the relative pore volume) is related to the changes in the relative cemented volume and the relative intergrain volume. Furthermore, we consider that the variations of these two petrophysical parameters result from two physical mechanisms, mechanical compaction and closed system chemical compaction.The model has been calibrated for the Middle Jurassic Garn Formation from the Haltenbanken area of the Mid-Norwegian Continental Shelf. Around 300 data points from 17 wells have been used in this study. The viscous parameters have been optimised against the present day data. With total porosity data the best fit is obtained for an activation energy between 14 and 16 kJ/mole and a macroscopical viscosity at 15°C between 39 and 46 GpaMa (1.21024–1.41024 Pa.s). If quartz cement data are used, the best fit is obtained for an activation energy between 16 and 18 kJ/mole and a macroscopical viscosity at 15°C between 47 and 56 GpaMa (1.51024–17.1024 Pa.s).The visco–elasto–plastic compaction model has been tested in the Haltenbanken area of Mid Norway, with the result that observed porosity trends and pore pressures can be modelled. Using multiple 2-D basin modelling simulations the results of this model and its implications for fluid flow and petroleum systems analysis can be seen. The compaction method has significant impact on the simulated fluid flow and petroleum migration pattern.  相似文献   

16.
The activities of two hydrolytic enzymes (leucine aminopeptidase and β glucosidase), belonging to the particle-bound enzymatic fraction, were measured in open-sea surface waters. Samples were collected along a transect crossing the Indian Ocean during the early NW monsoon period (November and December 2001). The latitudinal pattern of the ectoenzymatic activities highlighted a generally increasing trend of glycolysis approaching the equator, with significantly higher β glucosidase activity (0.79–3.00 nmol l−1 h−1) within the latitudinal range from 12°N to 16°S. In this area, the surface waters coming from the Indonesian Throughflow and the Bay of Bengal carry a considerable quantity of carbohydrates (38.9–41.9 μg l−1), which stimulated glycolytic activity and its cell-specific rates scaled to bacterial abundance. On the other hand, in the Central Indian Ocean, the proteolytic activity was considerable (0.91–2.03 nmol l−1 h−1), although the particulate proteins did not show significant increases and the dissolved proteinlike signal was one of the lowest of the entire transect (0.7 mg l−1 on average compared to the 1.4–1.6 mg l−1 of the adjacent areas). Therefore, in this area, the two ectoenzymes studied did not respond to the same stimulatory effect (namely the specific substrate concentrations). The time needed for the hydrolysis of macromolecules within the particulate and dissolved organic substrate fractions, although these measures are affected by a number of assumptions starting with the potential nature of the ectoenzymatic determinations, confirms these observations. The Central Indian Ocean displayed the lowest values, from 8 to 26 days for particulate and dissolved organic carbon, respectively. As observed in the equatorial areas of the Atlantic Ocean, the relevant degradation activity of the central area of the Indian Ocean Basin suggests a notable heterotrophy based on a faster turnover of organic substrates.  相似文献   

17.
Recent constructions of the global nitrogen budget estimate that at least half of the ocean's fixed nitrogen is lost by sedimentary denitrification, the majority of which occurs in continental shelves. The Arctic contains approximately 20% of the world's continental shelf, suggesting it is a substantial contributor to the global sedimentary denitrification rate. During two cruises in the summer and spring of 2002 and 2004, respectively, denitrification rates were calculated from the downward diffusive flux of nitrate in the shelf and slope sediments of the Chukchi Sea in the western Arctic. Additionally, in the spring of 2004, denitrification rates were determined by whole-core incubations in which the flux of nitrogen gas out of the sediments was measured. Measurements were made along three transects crossing the shelf and slope (50–3000 m), each transect having different overlying water characteristics. Denitrification rates generally decreased with increasing water depth: rates varied from about 1.6 mmol N m−2 d−1 for the shallow-water sediments to undetectable in deep-water sediments. Rates showed little variation between the two seasons. However, rates were found to correspond with differences in annual overlying primary productivities and particulate organic carbon export fluxes. An extrapolation to the whole Arctic yielded an average Arctic sedimentary denitrification rate of 13 Tg N yr−1. Taken in the context of the global nitrogen budget, it is about 4–13% of the total sink of fixed nitrogen in the ocean.  相似文献   

18.
The giant diatom Ethmodiscus was examined along an east–west transect at 28–30°N during 2002 and 2003 to determine if abundance, chemical composition or physiological status of this largest of diatoms varied on the scale of 100's–1000's of km in North Pacific gyre. Abundance ranged from <0.1–>2.0 cells m−3 and supported the notion of an abundance mosaic reported previously. However, there was only minimal support for the relationship between abundance and nutrient concentration at 125 m reported previously. Cellular chlorophyll varied little along the transect (7.3–10.9 ng chl cell−1) except at the westernmost station. Cellular N and P quotas co-varied 3–4.5 fold (mean=50.8±3.7 and 3.7±0.8 nmol N and P cell−1) and yielded N:P ratios that closely clustered around the Redfield ratio (average=14.6±1.1). Only low levels of chlorophyll-normalized alkaline phosphatase (APase) activity were observed (0.4–2.5 nmol P μg chl−1 h−1) with APase activity lower than that in either the bulk water, or co-occurring Trichodesmium spp. and Pyrocystis noctiluca. The active fluorescence parameter Fv:Fm, a property sensitive to Fe stress, was uniformly high at all stations (average=0.73±0.04 for 2003, and 0.69±0.05 for 2002), indicating sufficient Fe for optimum photosynthetic competence. These results contrasted sharply with results from Rhizosolenia mats reported along the same transect where there was a significant decline westward in Fv:Fm. Both ferredoxin (Fd) and flavodoxin accumulated in cells of Ethmodiscus, resulting in Fd Index values of<0.6. Iron cell quotas ranged from 0.7–5.1 pmol Fe cell−1. When normalized to cytoplasmic volume, the Fe μm−3 was comparable to that of Escherichia coli. We note that the disproportionate contribution of the vacuole (with its high organic content) to total volume typical of large diatoms is a potentially significant source of error in Fe:C ratios and suggest that Fe should be normalized to cytoplasmic volume whenever possible to permit valid intercomparisons between studies. The composition, Fv:Fm data and Fe:C ratio suggest a relatively uniform population experiencing little N, P or Fe stress. The uncoupling of the Fd Index from these measures is consistent with previous findings showing that the expression of flavodoxin can be characterized as an early stress response and that its accumulation is not necessarily correlated with physiological deficit. Ethmodiscus appears to be well adapted to some of the most oligotrophic waters in the ocean. Because it is an important sedimentary marker, the biology of living Ethmodiscus provides insights into the source of extensive Ethmodiscus oozes. Mass sedimentation after frontal accumulation has been suggested as a source for these oozes. Our data contain no evidence that the flux is linked directly to Fe, N or P stress.  相似文献   

19.
Measurements of the density of deep pelagic bioluminescent zooplankton (BL) were made with the Intensified Silicon Intensifier Target (ISIT) profiler in the Ligurian, Tyrrhenian, Adriatic, Ionian Seas and the Strait of Sicily from ～300 m to near seafloor. Mean BL densities ranged from 2.61 m?3 at 500–1000 m depth in the Adriatic Sea to 0.01 m?3 at 4000–5000 m depth in the E Ionian Sea. We investigated drivers of spatial variation of deep pelagic BL density. Linear regression was applied between surface chlorophyll a (Chl a) concentration and underlying BL density. Chl a values were determined from satellite derived 100 km radius composites (six 10-day means per ISIT deployment, over preceding 60 days). At 500–1000 m depth we found a significant positive relationship between mean BL density and mean Chl a in the period prior to 0–10 days (at 1% level) and prior to 10–40 days (at 5% level). Beyond 40 days no relationship between BL density and Chl a was found at this depth. At depths 1000–1500 m BL density values were low and no significant relationship with Chl a was detected. Generalised additive modelling (GAM) was used to assess the influence of benthic hotspots (seamount; cold water coral mound; mud volcano) on overlying BL density. A reduction in BL density was found downstream of the Palinuro seamount from 300 to 600 m. No effect on BL density in the overlying water column was detected from the presence of cold water corals. Higher BL densities were detected over the W Madonna dello Ionio mud volcano than at other sites sampled in the NW Ionian Sea. We find surface Chl a to be a good predictor of BL density in the mesopelagic zone; below this depth we hypothesise that processes affecting the efficiency of particle export to deep water may exert greater influence on BL density.  相似文献   

20.
The Zapiola Rise (ZR) is a singular sedimentary deposit about 1200 m in height and 1500 km in width located in the Argentine Basin. In situ and satellite observations have revealed the presence of an intense counterclockwise circulation around the feature, with a volume transport comparable to those of the major ocean currents. The existence of a very low-frequency variability of the transport associated with the anticyclonic circulation is documented for the first time. As the Zapiola anticyclonic circulation plays a significant role in the mixing of the strongly contrasted water masses of the South Atlantic, variations in the anticyclonic transport can have a major impact on the mixing, hence a role in global climate variability. The circulation was clearly anticyclonic in the periods 1993–1999 and 2002–2007. In contrast, the 1999–2001 period did not show evidence of an anticyclonic flow in the mean surface velocity field. Moreover, the analysis of the weekly fields during that period of time revealed a cyclonic pattern from time to time. Previous work has shown that the flow can be considered as purely barotropic over the ZR region. A 15-year time-series of the transport was produced using absolute altimeter-derived geostrophic velocities. The estimated transport presents high-frequency variability associated with mesoscale activity superimposed on a low-frequency signal. The amplitude of the estimated transport is in good agreement with the only in situ-derived estimation available (80 Sv, January 1993). The low-frequency signal presents a minimum during the period 1999–2001, further suggesting that at times the Zapiola anticyclonic flow may have significantly decreased in strength or even vanished. Possible causes of the low-frequency variability are discussed.  相似文献   

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