首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
对基于梯形积分原理的集成采样法的可行性在理论上进行了阐述,并在厦门湾和南海北部的5个站位分别采集不同深度的水样和由这些水样按一定比例混合而成的集成水样进行了现场研究,结果表明两种采样方法经不可逆稳态清除模型得出的溶解态234Th的清除通量、颗粒态234Th的输出通量及溶解态、颗粒态234Th的停留时间基本一致,证实了垂直集成采样法的可行性与可靠性。这种新的采样方案为今后充分发挥234Th法的优势,在更大空间尺度上进行新生产力的研究提供了可靠的保证。  相似文献   

2.
１９９６年 ９～１０月在厦门湾上屿附近海域定点站连续６个航次测定了水柱中溶解态（ＤＴｈ）、颗粒态~(２３４)Ｔｈ（ＰＴｈ）和溶解态~２３８Ｕ,获得了~２３４Ｔｈ的时空分布图象。研究海域水柱中ＤＴｈ、ＰＴｈ和总~２３４Ｔｈ（ＴＴｈ）的放射性比度分别在０．８０～３．９５山／ｍ~３、１,９３～５．６５Ｂｑ／ ｍ~３和 ３．４７～９． １８Ｂｑ／ｍ~３之间,整个水柱中 ＤＴｈ、ＰＴｈ和ＴＴｈ均与~(２３８)Ｕ呈不平衡,其特征是~(２３４)Ｔｈ亏损,且亏损程度明显大于大洋水体。颗粒态~(２３４)Ｔｈ和总悬浮颗粒物（ＴＳＭ）在水体中的分布及其随时间的变化趋势相当一致,非生物过程可能对近岸海域水体中~(２３４)Ｔｈ的分布起着非常重要的作用。  相似文献   

3.
MnO2共沉淀直接β计数测定小体积海水中的234Th   总被引：2，自引：0，他引：2  
探讨了MnO2共沉淀直接β计数测定小体积海水中234Th方法在固体闪烁α/β计数仪上实现的可能性,对实验流程空白、流程化学回收率、仪器探测效率、MnO2共沉淀量对全程回收率的影响以及检测核素的特征性等进行了研究.结果表明,该方法具有稳定的流程空白和全程回收率、高的探测效率和化学回收率,且所检测核素与234Th的理论半衰期基本吻合.将该流程应用于亚热带北太平洋表层水中234Th的分析也得到了令人满意的结果.与传统方法相比,该方法具有流程简单、所用水样体积小、快速获得结果等特点,适合于船载分析,由此可实现高时空分辨率数据的获取,为海洋颗粒有机碳输出通量以及颗粒物迁移速率的研究提供了更好的分析手段.  相似文献   

4.
利用234Th－238U不平衡研究南海东北部海域3个站位上层水体中的颗粒动力学性质，测定了水往中溶解态及颗粒态234Th的比活度，具体讨论各相中234Th／238U）AR（放射性活度比）比值的垂直分布情况及其与水化学要素间的关系。运用稿态箱式模型计算出各站位不同水层中溶解态234Th相对于清除至颗粒物的平均停留时间和颗粒态234Th相对于迁出作用的停留时间。由模型得出的参数表明3个站位的真光层具有两种不同的层化图像，这一情形与我们在南沙群岛海域得到的结果相一致。结合POC／PTh比值，估算出3个站位从真光层输出的颗粒有机碳（POC）通量分别为4.025.0和5．4mmolC·m－3－d-1。文中进一步讨论了234Th与POC两者停留时间的关系。  相似文献   

5.
中国第22次南极科学考察(2005年11月至2006年3月)期间,测定了南极普里兹湾海域5个站位的从表层至150 m水深的不同层位水样中溶解态和颗粒态234Th,238U的放射性比活度以及颗粒有机碳.利用234Th/238U在上层水体中的不平衡,计算了南极普里兹湾上层水体中234Th的平均停留时间和输出通量.结果显示,随着纬度的增加,上层水体中颗粒态和溶解态234Th的平均停留时间总体趋向减小,并在中纬度站位出现了最低值,分别为1~8和29~48 d,而颗粒态和溶解态234Th的输出通量则在中纬度站位出现了最大值,分别为21~38和26~39 dpm/(m3·d).运用箱型清除模式,利用两种不同的方法估算了各水柱中从真光层底部输出的POC通量,平均值分别达到104.7 mmol/(m2·d)(E法)和120.6 mmol/(m2·d)(B法),表明南极普里兹湾夏季存在很高的新生产力,它将会对该海域碳的生物泵过程产生重要作用.  相似文献   

6.
1Introduction CarboncyclingintheArcticOceanplaysanim- portantroletoglobalchange.Traditionally,marine productivityintheArcticOceanisthoughttobevery low,andthussomebiogeochemicalprocessessuchas particleexportandcyclingofnutrientsarenotsoac- tivebecauseofthembeingcoveredperenniallybyice, lowtemperatureandshorttimeofphotosynthesis (PlattandRao,1975).Afewpreviousestimatesof particulateorganiccarbon(POC)exportindicateda neglectablemagnitudeinthecentralArcticOcean (Baconetal.,1989).However,recen…  相似文献   

7.
234 Th was utilized as a tracer of particulate organic carbon (POC) export in the northwestern South China Sea (SCS) on the basis of the data collected at four stations during a spring cruise.Depth profiles of dissolved and particulate 234 Th activities were measured in the upper 60 m,showing a significant deficit relative to 238 U over the investigated stations.A stratified structure of 234 Th-238 U disequilibrium was in general observed in the upper 60 m water column,indicating that the euphotic zone of t...  相似文献   

8.
对厦门湾塔角附近海域某站位叶绿素 a、POC、初级生产力、234Th/238U不平衡进行的周日变化研究表明,POC含量介于14.4～34.6 mmol/m3之间,其中碎屑有机碳与活体有机碳所占份额分别为74%～92%和8%～26%.POC垂直分布呈现由表及底降低的趋势,且白昼期间POC含量高于晚间,说明研究海域POC含量与生物过程具有密切联系.初级生产力水平在1d之中变化达5倍,垂直分布亦随深度增加而降低,与叶绿素a的变化相对应.短时间(2h)培养获得的初级生产力水平明显高于长时间培养(24 h)的结果,证实部分新固定的碳被优先呼吸排出.结合234Th/238U不平衡法获得的颗粒态234Th输出通量及输出界面颗粒物中的POC/PTh比值,可计算出真光层 POC的垂向输出通量为16.0mmol/(m2·d),其中碎屑有机碳与活体有机碳贡献的数量分别为13.3和2.7mmol/(m2·d).POC输出通量与初级生产力的比值(ThE比值)平均为0.31,真光层POC停留时间平均为11d.上述结果与Aksnes和Wassmann[1]的模型计算结果相吻合,但与其他大多数模型的结果仍存在一定的差异.  相似文献   

9.
讨论了1997年冬季在北太平洋西北海域7个站位的表层至200m水深水柱中溶解及颗粒态234Th,颗粒态有机碳(POC)、氮(PON)及叶绿素a浓度的垂直分布剖面.溶解态、颗粒态及总的234Th的放射性在真光层中显著低于母体238U的放射性,总的234Th放射性在水深大于100m时趋于平衡.利用234Th-238U在海洋表层海水中的放射性不平衡推导出了北太平洋西北海域冬季真光层海水中234Th的平均停留时间和输出通量以及颗粒态有机碳和有机氮的输出通量.在亚北极环流区溶解态234Th的停留时间为40~50d,而在黑潮-亲潮共同影响区为20d左右.颗粒态有机碳和有机氮从真光层的输出通量范围分别为3.8~8.2和0.50~0.98mmol/(m2·d),西部海区高于东部海区,南部海区高于北部海区.在黑潮-亲潮共同影响区较高的颗粒态有机碳输出通量表明光照量及陆源营养盐物质的提供是两个决定生产力的主要因素.叶绿素a的水深分布和POC/PON的值同Redfield的比值的一致性表明这个海区的冬季颗粒物主要由浮游植物构成.北太平洋西北海域在冬季的颗粒有机碳输出通量可高于世界大洋一些海区春、夏季的颗粒有机碳输出通量.  相似文献   

10.
234Th is widely used to quantify the magnitude of upper ocean particulate organic carbon(POC)export in oceans.In the present work,the rates of particulate organic carbon export were measured based on the distribution patterns of234Th/238U disequilibrium in the water column within the continental slope of the East China Sea(ECS)during May 2011.The profiles of particulate and dissolved234Th activities at all three stations showed a relative deficit with respect to238U in the upper 100 m of the water column.The dissolved234Th scavenging rates and the particulate234Th removal rates and their residence times were calculated by a one-dimensional steady state model.The results showed that the dissolved234Th scavenging rates and the particulate234Th removal rates ranged from 12.4–61.4 dpm/(m3·d)andfrom3.8–21.8 dpm/(m3·d),respectively.The residence times of dissolved and particulate234Th were in the range of 3.4–158 d and 63.7–96.5 d,respectively.Combined with the measurement of POC/234Th ratios of suspended particles,POC export flux(calculated by carbon)from the euphotic zone was estimated in the study region,which ranged from 4.14–14.7 mmol/(m2·d),withanaverageof8.21mmol/(m2·d),occupying35%oftheprimeproductivity in the study area.The results of this study can provide new information for better understanding the carbon biogeochemical cycle within the continental slope of the ECS.  相似文献   

11.
Export fluxes of particulate organic carbon (POC) were estimated from the 234Th/238U disequilibrium in the Ulleung Basin1 (UB) of the East/Japan Sea1 (EJS) over four seasons. The fluxes were calculated by multiplying the average POC/234Th ratio of sinking particles larger than 0.7 μm at 100- and 200-m water depths to 234Th fluxes by the integrated 234Th/238U disequilibrium from the surface to 100-m water depth. In spring, the 234Th profiles changed dramatically with sampling time, and hence a non-steady-state 234Th model was used to estimate the 234Th fluxes. The 234Th flux estimated from the non-steady-state model was an order of magnitude higher than that estimated from the steady-state model. The 234Th fluxes estimated using the steady-state model showed distinct seasonal variation, with high values in summer and winter and low values in autumn. In spring, the phytoplankton biomass had the highest value, and primary production was higher than in summer and autumn, but the 234Th fluxes were moderate. However, these values might have been significantly underestimated, as the 234Th fluxes were estimated using the steady-state model. The POC export fluxes estimated in autumn were about four times lower than those in other seasons when they were rather similar. The annually averaged POC flux was estimated to be 161 ± 76 mgC m−2 day−1, which was somewhat lower than that in highly productive coastal areas, and higher than that in oligotrophic regions. The export/primary production (ThE) ratios ranged from 7.0 to 56.1%, with higher values in spring and summer and lower values in autumn and winter. In summer, a high ThE ratio of 48.4 ± 7.0% was measured. This may be attributed to the mass diatom sinking event following nitrate depletion. In the UB1, the annually averaged ThE ratio was estimated to be 34.4 ± 12.9%, much higher than that in oligotrophic oceans. The high ThE ratio may have contributed to the high organic carbon accumulation in the UB1.  相似文献   

12.
厦门湾水体中2 3 4 Th 2 3 8U不平衡的时间序列数据表明 ,无论是溶解态、颗粒态2 3 4 Th还是总2 3 4 Th ,相对于母体2 3 8U均严重亏损 ,呈现出与开阔大洋水明显不同的特征。溶解态、颗粒态2 3 4 Th的停留时间介于 0 .5— 41d之间 ,其中低潮时停留时间比高潮时小 2— 4倍 ,证实近岸海域具有强烈的清除、迁出作用 ,且潮汐变化对海域颗粒动力学特征有重要影响。2 3 4 Th停留时间与总悬浮颗粒物浓度 (TSM)、Chl.a的关系则表明 ,近岸海域元素的清除、迁出作用主要受陆源颗粒物输送的影响 ,与生物活动关系并不密切。此外 ,非稳态与稳态清除模型结果的对比证明 ,稳态模型对于具有强烈清除、迁出作用的近岸海域是适用的  相似文献   

13.
A record of radionuclide fluxes at a deep marginal sea of the Northwest Pacific Ocean (39°40′N 132°24′ E, Japan Basin, East Sea/Sea of Japan) was obtained from analysis of a 1-year continuous collection of sediment-trap samples. The trap was placed at a depth of 2800 m, 500 m above the sea floor, and the samples were recovered at the end of one year. Concentrations of 238U, 234U, 232Th, 230Th and 228Th were measured in the trapped material. All of the radionuclide fluxes showed seasonal variations that were in phase with the variations in total particle flux, which were shown in earlier work to be closely tied to the primary production in the surface water. The formation of authigenic 238U appears to be less than in other open ocean regimes. The residence time of particulate thorium isotopes were of the order of a year, resulting in an average settling rate of a meter per day. Comparison of the measured 230Thex flux with that of the theoretical production in the overlying water column yielded about 40% surplus of 230Th, indicating that lateral advection contributes 230Th to this sampling site.  相似文献   

14.
1IntroductionThefluxesofcarbon,nutrients,andassoci-atedelementsinvolvedinthebiogeochemicalcyclesoutoftheeuphoticzoneareimportantinthestudyofglobalCO2 change.Someworkershaveproposedthatatthesteadystatethefluxofparticulateorganiccarbonoutoftheeuphoticzoneequalsthenewproduction(EppleyandPe-terson,1979;Eppley,1989).Generallytwometh-odscanbeemployedtoobtainthefluxdata.Oneistousesedimenttrapsintheupperocean(<200m)orfloatingsedimenttraps.Thoughthesedimenttraptechnologyhasshowntobeuse-fulfortimeser…  相似文献   

15.
234Th was used to quantify sinking fluxes and residence times of particles in surface waters of the north-western Mediterranean Sea. Measurements of dissolved and particulate 234Th were made at the DYFAMED station (43°25′N–7°51′E, JGOFS-France program). Sampling covered 1 year on four cruises in 1994 (February 9, April 29, June 3, October 1) and focused on a transition period in mid-spring with six repeated profiles collected during May 1995. 234Th was nearly in equilibrium with its parent 238U most of the year, except in spring. The intensive sampling in May shows a rapid evolution throughout the month from a moderate 234Th deficit to near-equilibrium values. The time-series of 234Th were treated with steady-state and non-steady-state models. 234Th particulate fluxes clearly indicate large variability in export, with the highest values observed in spring. Particle residence times in the upper 40 m range from <10 to >250 days, and could increase by a factor of 10 within 2 weeks. POC fluxes from the upper 40 m and export ratios (ThE: ratio of 234Th-derived POC export to primary production), derived from the 234Th/238U disequilibrium in the water column and POC/234Th ratio on trapped material, decrease from about 9.5 mmol C m−2 d−1 and >22% in early May to less than 5 mmol C m−2 d−1 and 15% after mid-May. The 234Th-derived information is in agreement with the annual variations in Mediterranean Sea productivity.  相似文献   

16.
Fate of particle-reactive pollutants in the Xiamen Bay   总被引：2，自引：0，他引：2  
INTRODUCTIONItiswel1knownthattheabilitytopredictthetransportationandfateofPOllutantsinthecoastalenvironmentsisimportanttothemanagementofmarineenvironments,toconservingma-rineorganismsandsafeguardinghumanhealth.ThegeochemicalbehaviourofPOllutantsinama-rineecosystemisgenerallygovernedbybiologicaldegradation,photodegradation,volatilization,waterexchange,incorPorationintosediments,etc.TheincorPOrationofPollutantsinestuarineorcoastalsediments,viaanassociationwithsettlingparticles,hasbeenrec…  相似文献   

17.
An extensive 234Th data set was collected at two sites in the North Pacific: ALOHA, an oligotrophic site near Hawaii, and K2, a mesotrophic HNLC site in the NW Pacific as part of the VERTIGO (VERtical Transport In the Global Ocean) study. Total 234Th:238U activity ratios near 1.0 indicated low particle fluxes at ALOHA, while 234Th:238U ～0.6 in the euphotic zone at K2 indicated higher particle export. However, spatial variability was large at both sites—even greater than seasonal variability as reported in prior studies. This variability in space and time confounds the use of single profiles of 234Th for sediment trap calibration purposes. At K2, there was a decrease in export flux and increase in 234Th activities over time associated with the declining phase of a summer diatom bloom, which required the use of non-steady state models for flux predictions. This variability in space and time confounds the use of single profiles of 234Th for sediment trap calibration purposes. High vertical resolution profiles show narrow layers (20–30 m) of excess 234Th below the deep chlorophyll maximum at K2 associated with particle remineralization resulting in a decrease in flux at depth that may be missed with standard sampling for 234Th and/or with sediment traps. Also, the application of 234Th as POC flux tracer relies on accurate sampling of particulate POC/234Th ratios and here the ratio is similar on sinking particles and mid-sized particles collected by in-situ filtration (>10–50 μm at ALOHA and >5–350 μm at K2). To further address variability in particle fluxes at K2, a simple model of the drawdown of 234Th and nutrients is used to demonstrate that while coupled during export, their ratios in the water column will vary with time and depth after export. Overall these 234Th data provide a detailed view into particle flux and remineralization in the North Pacific over time and space scales that are varying over days to weeks, and 10's–100's km at a resolution that is difficult to obtain with other methods.  相似文献   

18.
Measurements of particle size-fractionated POC/234Th ratios and 234Th and POC fluxes were conducted using surface-tethered, free-floating, sediment traps and large-volume in-situ pumps during four cruises in 2004 and 2005 to the oligotrophic eastern Mediterranean Sea and the seasonally productive western Mediterranean and northwest Atlantic. Analysis of POC/234Th ratios in sediment trap material and 10, 20, 53, 70, and 100 μm size-fractionated particles indicate, for most stations, decreasing ratios with depth, a weak dependence on particle size, and ratios that converge to ～1–5 μmol dpm?1 below the euphotic zone (～100–150 m) throughout the contrasting biogeochemical regimes. In the oligotrophic waters of the Aegean Sea, 234Th and POC fluxes estimated using sediment traps were consistently higher than respective fluxes estimated from water-column 234Th–238U disequilibrium, observations that are attributed to terrigenous particle scavenging of 234Th. In the more productive western Mediterranean and northwest Atlantic, 234Th and POC fluxes measured by sediment trap and 234Th–238U disequilibrium agreed within a factor of 2–4 throughout the water column. An implication of these results is that estimates of POC export by sediment traps and 234Th–238U disequilibrium can be biased differently because of differential settling speeds of POC and 234Th-carrying particles.  相似文献   

19.
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   

20.
The deficit of 234Th relative to its radioactive parent 238U in the surface ocean can yield reliable estimates of vertical Particulate Organic Carbon (POC) fluxes to deeper waters, but only when coupled with an accurate ratio of POC concentration to activity of 234Th on sinking matter. Assuming a simple partitioning of suspended phytoplankton mass between single cells and flocs, we calculate the ratio of the POC flux estimated from 234Th deficit to the actual POC flux (p ratio, Smith, J.N., Moran, S.B., Speicher, E.A., in press. The p-ratio: a new diagnostic for evaluating the accuracy of upper ocean particulate organic carbon export fluxes estimated from 234Th/238U disequilibrium. Deep-Sea Research I.). The p ratios are calculated under the assumption that particle surface area is correlated with 234Th activity and particle volume is correlated with POC concentration. The value of the p ratio depends on the relative contributions of single cells and flocs to the vertical flux. When large single cells make up a significant fraction of the vertical flux, p ratios are less than one, meaning POC fluxes estimated from 234Th deficits underestimate actual POC fluxes. When large single cells are abundant but do not sink fast enough to contribute to vertical POC flux, p ratios are greater than one (up to 3 × overestimate). Factor analysis of the model indicates that altering the extent of flocculation in suspension and changing the density and maximum size of phytoplankton cells have the greatest effects on the p ratio. Failure to measure the properties of flocs when characterizing the ratio of POC to thorium on sinking matter potentially leads to large overestimation of the POC flux (over 20 ×). Failure to characterize the POC to thorium ratio of large particles, by, for example, destruction of phytoplankton cells in pumps, can lead to underestimation of POC flux. Estimates of POC flux should be most reliable in highly flocculated suspensions populated by small cells and rapidly sinking flocs. These conditions are often associated with intense phytoplankton blooms.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号