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1.
Sediment trap experiments were carried out in two oceans, the eastern Pacific Ocean and the Antarctic Ocean, which have very different biological productivities. The natural radionuclides,234Th,210Po and210Pb were used as tracers of reactive metals. Larger particulate fluxes of these radionuclides were found in the seas where total mass fluxes were larger, although the concentrations of these radionuclides in the settling particles were somewhat smaller. The concentrations of234Th in the settling particles varied widely and irregularly with depth, whereas the concentrations of210Po and210Pb in the settling particles steadily increased with increasing water depth. The ratios of210Po/210Pb in the settling particulates were larger than unity which the ratio of234Th/excess210Po as larger than234Th/210Po in the deep water. These results suggest that, when the particles sink through the water column, these radionuclides are being absorbed by settling particles in the order234Th>210Po>210Pb. The observed particulate fluxes of210Pb are about one eighth of those calculated from the disequilibria between226Ra and210Pb at the stations in the subtropical eastern Pacific, although the observed fluxes are the same as the calculated ones in the northern North Pacific and the Antarctic Ocean. Thus, there must be a horizontal flow carrying these reactive metals from the oligotorophic ocean to the biologically productive ocean where the metals are removed by settling particles even in deep water.  相似文献   

2.
Analysis of 210Pb, 226Ra, 137Cs and 134Cs in short sediment cores provide first estimates of deposition rates in some Clyde sea lochs. The radio-caesium nuclides originate mainly in the liquid effluent released at distance from the Clyde by the Windscale nuclear fuel reprocessing plant and their concentrations in Clyde sediments provide information on (a) enrichment factors onto particulate matter, (b) surficial mixing coefficients and (c) sedimentation rates. A radiocaesium residence time in coastal waters of ca. 103 years reflects the importance of scavenging by the high nearshore particulate flux. 210Pb levels in sediments are controlled, in the unsupported fraction, by a major input sorbed on catchment particulates and, in the supported component, by 226Ra activities occasionally perturbed by unusually high surface values probably of planktonic origin. In one loch, detectable levels of 134Cs and 60Co are attributed to their discharge by nuclear submarines.  相似文献   

3.
The plot of210Pb activity against depth in carbonate sands on the Virgin Island Bank is a negative asymmetric hyperbolic curve. As depth increases, an initial rapid decrease in210Pb activity caused by the decay of unsupported210Pb and226Ra is followed by increasing activity as a result of210Pb achieving equilibrium with ingrowing230Th. As this curve is time dependent, an estimate of the relative ages in carbonate sequences and the rates of net carbonate accumulation can be made. The ease of210Pb activity determinations makes this procedure an attractive method in obtaining carbonate sand accumulation rates.  相似文献   

4.
A practical method has been developed for the simultaneous determination of226Ra,234Th,210Pb and210Po in seawater. In the method, the samples are spiked with228Ra,230Th,208Po and common lead to determine chemical yield. These nuclides are coprecipitated with calcium carbonate and ferric hydroxide from 20 to 50 l of seawater and separated from one another by using coprecipitation and ion exchange techniques. Counting sources of Ra and the other nuclides are prepared by electrodeposition onto silver discs. Their radioactivities are counted with an-spectrometer and a low background-counter. This method gives a standard deviation of about 5% for replicate determination of226Ra and the other nuclides.  相似文献   

5.
Box cores were collected close to river mouths along the eastern Brazilian shelf at water depths of 10–30 m. One core was taken from more than 1000 m depth at the shelf slope. 210Pb and 226Ra activities were measured to establish sediment accumulation rates. Seven of the 10 cores exhibited an exponential decrease with depth of excess 210Pb activities. The sediments from the sheltered Sudeste Channel off Caravelas revealed the highest sediment accumulation rate of 0.81 cm yr−1. The sediments at the shelf slope seaward of the Rio Doce revealed the lowest accumulation rate of 0.13 cm yr−1. Sediment accumulation rates increased towards the Caravelas Bank. Current patterns and the morphology of the seabed favor sediment deposition in this area.  相似文献   

6.
Distribution of210Pb in sediments on the South Texas Continental Shelf is related to dynamics of the sedimentary transport processes. This radioisotope, whose concentration is time-dependent, defines three depocenters on the shelf. In addition, the variation of210Pb activity at the sediment/water interface delineates areas of terrigenous sedimentation from hemipelagic sedimentation.  相似文献   

7.
The concentrations of228Ra in surface waters of the Seto Inland Sea were determined. Surface waters from the central region of the Seto Inland Sea, Hiuchi Nada and Bingo Nada, contained concentrations of228Ra of 655–811 dpm/1000 l which were 100 times higher than those obtained in the Pacific Ocean. These high concentrations of228Ra must be supported by a228Ra flux from the bottom sediment. The lower limit of this flux was estimated to be more than 0.16 dpm cm–2 y–1. The228Ra concentrations decreased markedly from central regions of the Seto Inland Sea to about 18 dpm/1000 l in the Kii and the Bungo Channels as salinity increased. Using a box model and the228Ra data, the mean residence time of sea water in the Seto Inland Sea with respect to the exchange with the open ocean water was estimated to be less than 10 y, and the most probable value is the order of several years.  相似文献   

8.
226Ra and 228Ra have non-conservative excess concentrations in the mixing zones of the Pee Dee River-Winyah Bay estuary, the Yangtze River estuary, and the Delaware Bay estuary. Laboratory experiments, using Pee Dee River sediment, indicate desorption of 226Ra to increase with increasing salinities up to 20‰. In Winyah Bay desorption from river-borne sediments could contribute almost all of the increases for both isotopes. Desorption adds only a portion of the excess 228Ra measured in the Yangtse River and adjacent Shelf waters and Delaware Bay. In the Yangtze River the mixing zone extends over a considerable portion of the Continental Shelf where 228Ra is added to the water column by diffusion from bottom sediments, while 226Ra concentrations decrease from dilution. Diffusion of 228Ra from bottom sediments in Delaware Bay primarily occurs in the upper part of the bay (< 22‰ water) where fine grained sediments predominate. A diffusive flux for 228Ra of 0·33 dpm cm?2 year was determined for Delaware Bay.  相似文献   

9.
The role of the Setúbal–Lisbon canyon in accumulation and transport of labile organic matter from the coastal sea and ocean surface water towards the deep sea was assessed by investigating the distribution of organic matter of different quality in sedimentary aggregates and surface sediments of the canyon and adjacent slopes. Total hydrolysable amino acids (THAA) and organic carbon (Corg) were measured from aggregates, and contents of Corg, chlorophyll a (chl a), phaeopigments (phaeo), chloroplastic pigment equivalents (CPE) from sediments. As indices of organic matter (OM) quality THAA:Corg, degradation index (DI), chl a:phaeo, chl a:Corg and C:N ratio were determined. Sediment profiles of chl a and the isotope 210 of lead (210Pb) were used as tracers in a transport model to estimate deposition rates and background levels of the tracers, and sediment mixing rates (Db). Whereas bulk Corg contents of canyon and slope sediments were practically similar at all depths, higher contents of THAA, chl a and CPE, as well as higher THAA:Corg, DI and chl a:Corg, in aggregates and sediments from the upper reaches of the canyon indicate that labile organic matter accumulates in the upper canyon. This is confirmed by higher chl a and 210Pb deposition and Db calculated from the model. Hence, the Setúbal–Lisbon canyon, specially the upper region, acts as a natural trap of organic matter that is transported to the region via lateral transport and vertical settling from primary productivity. Organic matter might be further transported in downward canyon direction via rebound processes. The chl a and 210Pb profiles reveal active sediment mixing by physical processes and/or animal reworking.  相似文献   

10.
用γ谱方法测定了南极长城站附近特有生物群落栖息地沉积物中放射性核素含量,地表沉积物中40K,137Cs,210Pb,226Ra,228Ra,228Th.和238U平均比活度,分别为143,7.56,24.1,3.65,5.36,4.15和6.5Bq/kg.同时测试了阿德雷岛企鹅栖息地粪土沉积地层中放射性核素含量,利用其中的210Pb比活度,210Pbex垂向变化特征,推演沉积物的沉积速率和地质历史年代:其中AD1-a柱样时间跨度约为74a(1928~2002年),据此计算了沉积速率为0.063mm/a(r=0.794),并讨论了在南极特定条件下,放射性核素示踪对定年影响以及与区域现代气候环境变化的内在联系.  相似文献   

11.
226Ra and 228Ra have non-conservative excess concentrations in the mixing zones of the Pee Dee River-Winyah Bay estuary, the Yangtze River estuary, and the Delaware Bay estuary. Laboratory experiments, using Pee Dee River sediment, indicate desorption of 226Ra to increase with increasing salinities up to 20‰. In Winyah Bay desorption from river-borne sediments could contribute almost all of the increases for both isotopes. Desorption adds only a portion of the excess 228Ra measured in the Yangtse River and adjacent Shelf waters and Delaware Bay. In the Yangtze River the mixing zone extends over a considerable portion of the Continental Shelf where 228Ra is added to the water column by diffusion from bottom sediments, while 226Ra concentrations decrease from dilution. Diffusion of 228Ra from bottom sediments in Delaware Bay primarily occurs in the upper part of the bay (< 22‰ water) where fine grained sediments predominate. A diffusive flux for 228Ra of 0·33 dpm cm−2 year was determined for Delaware Bay.  相似文献   

12.
Studies on the biogeochemical cycling of organic contaminants in the Mediterranean have demonstrated the importance of polychlorinated biphenyls (PCBs) as relatively stable markers of recent anthropogenic influence in ocean systems. This paper presents results of hydrocarbon analyses of deep water profiles, sediments and their associated surface flocculent layers, and zooplankton samples collected in the western basin. Seawater concentrations were higher than those previously reported for the eastern basin and were consistent with the presence of industrial sources in the northwestern segment. In the water column, the percent of PCBs associated with filterable particles was related to the ambient concentrations of total suspended matter, distance from coastal input sources and on depth. The occurrence of deep water residues primarily in the dissolved phase and observations of subsurface maxima in seawater concentrations during a season of high surface productivity were consistent with the predictions of vertical transport models based on residues associated with sinking particles and equilibrium partitioning. Flocculent layers at the sea/sediment interface contained two and three orders of magnitude, respectively, more PCBs and petroleum hydrocarbons (PHCs) than their associated surface sediments. The flocculent particles also contained several biogenic hydrocarbons presumably originating from plankton and relatively soluble and labile contaminants such as hexachlorohexane isomers (HCH) and hexachlorobenzene (HCB), thus confirming that the majority of the flux of hydrocarbons to sediments is carried on rapidly settling large particles. By combining the sediment and flocculents data with published sedimentation rates for the deep basins of the Mediterranean, a yearly flux rate of PCBs to the open sea sediments was estimated as 13 μg m−2 yr−1 or less than half of the rate measured in a coastal sediment trap experiment. Analytical results are placed in the context of other distribution data for PCBs and long-term flux studies to construct a partial mass balance budget for this semi-enclosed sea. The computed coastal inventory showed that about 35% remains suspended in the water column while the majority of residues are deposited in coastal sediments. However in the open sea, the deep water column may contain up to 70% of the total inventory and may be a continually increasing reservoir of stable organic contaminants reaching the ocean. The budget shows that priority for improved research and monitoring efforts in ocean systems should be given to continued advancement in techniques for the precise measurement of deep water concentrations and for measuring current atmospheric inputs and sedimentation rates in order to develop more accurate ocean flux models.  相似文献   

13.
I am deeply honored to have been awarded the 1988 Okada Prize of the Oceanographical Society of Japan. The present paper reviews my previous works regarding the ecology of deep-sea meiobenthos in the western Pacific area. The outline cen be summarized as follows:
1)  On the basis of multivariate analyses, it was found that the rate of the organic-matter flux to the sea bed and the amount of the interstitial space within the sediment are the main factors regulating the abundance of meiofauna in the deep sea.
2)  Two indices were proposed to characterize the vertical distribution of meiofauna in the sediment profile,i.e. their maximum depth in the sediment and the degree of their concentration in the surface layer of the sediment. The index of maximum depth was closely related to the oxygen concentration in the interstitial water. On the other hand, the index of degree of concentration in the surface of the sediment tended to be higher where the supply of food seemed lower.
3)  Some taxonomically important species were found from the axis of the Izu-Ogasawara Trench. They arePliciloricus hadalis, the first species of the newest phylum Loricifera from the Pacific area, from the hadal deep sea and the fine clay sediment, andOccultammina profunda, the first infaunal species of Xenophyophorea, a group of rhizopod Protozoa.
4)  The vertical distribution ofOccultammina profunda coincided well with the unusual distribution of210Pb in the sediment profile. The organisms concentrated as high as 500 dpm g–1 of210Pb in their stercomare and granellare. The steady state model confirmed that the species made the peculiar subsurface peak of210Pb in the sediment.
5)  The depth in the sediment profile where the distinct peak of MnO2 can be seen showed strong correlation with the vertical distribution of meiofauna. This relationship suggests that oxygen concentration in the interstitial water regulates the structure of the characteristic three layers of the calcareous ooze in the deep sea. This idea was proven by the vertical distribution of free oxygen in the sediment calculated on the basis of respiration rate of deep-sea meiofauna measured using the cartesian diver technique.
6)  Radio-isotope techniques used to measure the rates at which particulated organic matter was ingested and dissolved organic matter was absorbed, suggested that deep-sea meiofauna obtained a significant fraction of their energy by absorption.
7)  The work carried out so far has revealed the important role of meiofauna in the benthic ecosystem, and emphasized the necessity for intensive research from various points of views on these microscopic organisms.
  相似文献   

14.
Using the moored MnO2-fiber method, we have obtained 38 determinations of Th and Pa isotope concentrations from 18 sites along the margin of the western North Pacific near Japan, from water depths of 1,330 to 5,873 m. From our data, we are able to show that (1)228Ra and227Ac are being supplied to the seawater from the slope sediments of Honshu, Japan, (2) our230Th and231Pa concentrations match those obtained byin situ pumping with a MnO2-fiber adsorber in the Japan and Izu-Ogasawara trenches but are significantly higher than those from the Panama and Guatemala basins, and (3) our232Th concentrations show a similar systematic decrease with depth as do those of trace metals like Mn, Al, Te and Bi whose concentrations are strongly controlled by particulate matter scavenging.In contrast, our data fail to show (1) that enhanced removal of230Th and231Pa by scavenging from the water column is taking place near the western margins and (2) that231Pa is being removed in preference to230Th from the water column to the marginal sediments. This is probably due to rapid mixing of the deep waters as compared to the scavenging rates of230Th and231Pa in the water column and at the sediment/seawater interface.  相似文献   

15.
Arctic sea ice can incorporate sediment and associated chemical species during its formation in shallow shelf environments and can also intercept atmospherically transported material during transit. Release of this material in ice ablation areas (e.g. the Fram Strait) enhances fluxes of both sediments and associated species in such areas. We have used a suite of natural (7Be, 210Pb) and anthropogenic (137Cs, 239Pu, 240Pu) radionuclides in sea ice, sea-ice sediments (SIS), sediment trap material and bottom sediments from the Fram Strait to estimate transit times of sea ice from source to ablation areas, calculate radionuclide fluxes to the Fram Strait and investigate the role of sea-ice entrained sediments in sedimentation processes. Sea ice intercepts and transports the atmospherically supplied radionuclides 7Be and 210Pb, which are carried in the ice and are scavenged by any entrained SIS. All of the 7Be and most of the excess 210Pb measured in SIS collected in the Fram Strait are added to the ice during transit through the Arctic Ocean, and we use these radionuclides as chronometers to calculate ice transit times for individual ice floes. Transit times estimated from the 210Pb inventories in two ice cores are 1–3 years. Values estimated from the 7Be/210Pbexcess activity ratio of SIS are about 3–5 years. Finally, equilibrium values of the activity ratio of 210Pb to its granddaughter 210Po in the ice cores indicate transit times of at least 2 years. These transit times are consistent with back-trajectory analyses of the ice floes. The latter, as well as the clay-mineral assemblage of the SIS (low smectite and high illite content), suggest that the sampled sea-ice floes originated from the eastern Siberian Arctic shelf seas such as the eastern Laptev Sea and the East Siberian Sea. This result is in agreement with the relatively low activities of 239,240Pu and 137Cs and the 240Pu/239Pu atom ratios (∼0.18, equivalent to that in global fallout) in SIS, indicating that prior global atmospheric fallout, rather than nuclear fuel reprocessing facilities, forms the main source of these anthropogenic radionuclides reaching the western Fram Strait at the time of sampling (1999). Transport of radionuclides by sea ice through the Arctic Ocean, either associated with entrained SIS or dissolved in the ice, accounts for a significant flux in ablation areas such as the Fram Strait, up to several times larger than the current atmospheric flux in the area. Calculated fluxes derived from sea-ice melting compare well to fluxes obtained from sediment traps deployed in the Fram Strait and are consistent with inventories in bottom sediments. 240Pu/239Pu atomic ratios lower than 0.18 in bottom sediments from the Fram Strait provide evidence that plutonium from a source other than atmospheric fallout has reached the area. Most likely sources of this Pu include tropospheric fallout from atomic weapons testing of the former Soviet Union prior to 1963 and Pu released from nuclear reprocessing facilities, intercepted and transported by sea ice to the ablation areas. Future work is envisaged to more thoroughly understand the actual mechanisms by which radionuclides are incorporated in sea ice, focusing on the quantification of the efficiency of scavenging by SIS and the effect of melting and refreezing processes over the course of several years during transit.  相似文献   

16.
《Oceanologica Acta》1998,21(4):521-532
A sediment trap experiment was carried out in the West Caroline Basin, located in the equatorial western Pacific between influences of the Asian monsoon and the open ocean. Annual mass flux at the shallow trap at Site 1 was 57.10 g m-2 yr-1. Generally, the higher flux of organic matter was associated with higher activities of biogenic opal-producing and carbonate-producing plankton communities. In addition, as the organic matter content increases, the organic carbon/carbonate carbon ratio shows a tendency to increase. Carbonate-producing plankton was predominant during periods 1 and 3 (May to July and November to the beginning of December), which could be due to limited silica supply to the euphotic zone. On the other hand, surface sea water was more nutrient-rich during periods 2 and 4 (August to October and the end of December to April) at Site 1. These high total mass fluxes could be stimulated by wind.The amount of biogenic components collected in the sediment traps and the accumulation in surface sediments at Site 1 could be compared with primary productivity values. Carbonate and biogenic opal fluxes were 99% and 90% less, respectively, in the surface sediments compared to those in the shallow sediment trap. This could be due to the reaction of sinking particles with undersaturated deep sea water just above the sea floor, rather than with the water column during sinking. About 20% of the organic matter was decomposed between the shallow and deep sediment traps and more than 98% between the deep sediment trap and final burial in the surface sediments. The relative amount of organic carbon preserved in surface sediments was about 0.10% of annual primary productivity.  相似文献   

17.
钦州湾河流沉积物中镭的解吸行为   总被引：1，自引：0，他引：1  
放射性镭同位素在海底地下水排放（SGD）等海洋物质变化过程的研究中具有优良的示踪作用，估算SGD通量时需要计算河流悬浮颗粒物的解吸通量。因此，对河流沉积物/悬浮颗粒物中镭同位素解吸行为的研究不可或缺，而目前对于粒度较小范围内镭同位素的解吸特征及其机理的研究依然不足。本文选用钦州湾河流沉积物，通过室内实验探究粒度和盐度对沉积物中镭同位素解吸行为的影响。结果表明，在沉积物平均粒径0.9~136.0 μm范围内，随着粒径增大，沉积物中镭同位素在海水（盐度为33.9）中解吸活度逐渐减小，且变化趋势也逐渐变缓，平均粒径大于43.7 μm后，解吸量几乎不变；在海水盐度4.9~33.9范围内，随着盐度增大，沉积物中镭同位素解吸活度逐渐增大，盐度大于24.9后，解吸量趋于不变。本文创新性地建立了沉积物表面分形结构的镭解吸理论模型，拟合得到钦州湾河流沉积物表面最大可交换态224Ra、226Ra和228Ra活度分别为1.13 dpm/g、0.17 dpm/g和0.85 dpm/g，以干重计；沉积物中224Ra、226Ra和228Ra最大解吸比分别为30%、7%和18%。钦州湾河流沉积物颗粒表面最大可交换态224Ra和226Ra活度分别处于全球中等水平和较低水平，而其最大解吸比分别处于全球较高水平和较低水平。本研究结果有助于更好地理解镭同位素的解吸行为，以帮助更准确地估算SGD通量。  相似文献   

18.
《Marine Chemistry》2001,74(4):227-243
The distribution of trace metals in sediments and their exchange between sediments and overlying water is governed by multiple processes including molecular diffusion, bioturbation (porewater advection, porewater mixing, and particle mixing), chemical reactions and adsorption–desorption. To understand these processes and their relative contributions, a one-dimensional model was built, which includes bioturbation and adsorption–desorption processes, to describe the transport of 224Ra. Because 224Ra is adsorbed on MnO2, 224Ra may serve as a proxy for trace metal transport. Three sites were sampled and both dissolved and adsorbed 224Ra were analyzed and modeled to understand the transport and exchange processes. It was found that particle transport of adsorbed 224Ra followed by desorption at the sediment/water interface typically represents the dominant flux. We have further been able to define conditions where the porewater transport for adsorption reactive metals like 224Ra (and other metals) may be out of the sediments whereas the active scavenging of 224Ra from the water column at the sediment water interface via adsorption reactions can result in a flux of 224Ra into the sediment. These processes are both predicted by the model and observed in sediment samples.  相似文献   

19.
The distribution of trace metals in sediments and their exchange between sediments and overlying water is governed by multiple processes including molecular diffusion, bioturbation (porewater advection, porewater mixing, and particle mixing), chemical reactions and adsorption–desorption. To understand these processes and their relative contributions, a one-dimensional model was built, which includes bioturbation and adsorption–desorption processes, to describe the transport of 224Ra. Because 224Ra is adsorbed on MnO2, 224Ra may serve as a proxy for trace metal transport. Three sites were sampled and both dissolved and adsorbed 224Ra were analyzed and modeled to understand the transport and exchange processes. It was found that particle transport of adsorbed 224Ra followed by desorption at the sediment/water interface typically represents the dominant flux. We have further been able to define conditions where the porewater transport for adsorption reactive metals like 224Ra (and other metals) may be out of the sediments whereas the active scavenging of 224Ra from the water column at the sediment water interface via adsorption reactions can result in a flux of 224Ra into the sediment. These processes are both predicted by the model and observed in sediment samples.  相似文献   

20.
陈进兴 《海洋科学》1989,13(4):28-29
本文利用放射化学分析法测定了长江口及其邻近陆架沉积物中~(226)Ra和~(210)Pb的含量。结果表明,在该海区的沉积物中,~(226)Ra含量的水平分布随经度增加而直线下降,而~(210)Pb含量的水平分布则随经度增加而直线上升,二者形成明显的同步反向分布。  相似文献   

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