Behaviors of 210Pb and 210Po around hydrothermal vents in the Okinawa Trough

Vertical profiles for the uranium-series radioisotopes 210Pb and 210Po were obtained at thetwo hydrothermal vent sites, the Iheya Ridge and the Minami-Ensei Knoll, in the Mid-Okinawa Trough in 1993 and 1994, respectively. In 1995, both radioisotopes were measured at the Minami-Ensei Knoll a-gain. At the Iheya Ridge, where the hydrothermal activity is not active as reflected by the CH_4, and 222Rn data, both the total 210Pb and 210Po activities show deficiency relative to their parents, and the mean residence time of 210Pb and 210Po is approximately equal to 20 and 2-5 a, respectively. At the Minami-Ensei Knoll, which is characterized by black smokers, the total 210Pb(0.167 × 10~(-3)-2.5 × 10~(-3)_ Bq/kg) around the plumes is deficient relative to 226Ra but the total 210Po activities (1.83 × 10 ~(-3) - 2.83 × 10~(-3) Bq/kg) are in excess relative to 210Pb. The 210Po activities are higher than those in the East China Sea and the Okinawa Trough and excess 210Po has been found. The 210Pb/226Ra and 210Po/     

冲绳海槽海底热液喷出口附近海水中210Pb和210Po的行为

讨论了在冲绳海槽伊平屋海岭和南奄西海丘两处海底热液喷出口附近海水中的铀系子体放射性核素210Pb和210Po浓度的垂直分布剖面.在伊平屋海岭,甲烷及222Rn的数据表明海底热液活动不强,总210Pb和210Po放射性均低于它们各自母体的放射性,210Pb和210Po在海水中的平均停留时间分别为20和2～5a,而在以“黑色烟雾”为特征的海底热液活动强烈的南奄西海丘,在”烟雾”中的总210Pb含量(0.167×10-3～2.50×10-3Bq/kg)相对其母体226Ra贫乏,而总210Po含量(1.83×10-3～2.83×10-3Bq/kg)则相对其母体210Pb过剩.该处海水中的210Po的放射性高于东海陆架区及冲绳海槽其他海区,并且显示了210Po过剩.210Pb/226Ra以及210Po/210Pb放射性比值的范围分别为0.1～0.4和1.1～7.8.在热液扩散带中210Pb被优先从海水中清除.控制南奄西海丘海水中210Pb浓度的可能机制涉及到210Pb通过扩散作用的横向输送.在热液扩散带中高210Po/210Pb放射性比值表明210Pb的耗尽及210Po从海底热液喷出口的加入.     

Fluxes of234Th,210Po and210Pb determined by sediment trap experiments in pelagic oceans

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.     

冬季台湾海峡210Po和210Pb的分布特征及颗粒物的输出

~(210) Po and ~(210) Pb are increasingly used to constrain particle dynamics in the open oceans, however they are less used in coastal waters. Here, distributions and partitions of ~(210) Po and ~(210) Pb were examined in the Taiwan Strait, as well as their application to quantify particle sinking. Activity concentrations of dissolved ~(210) Po and ~(210) Pb(0.6 μm)ranged from 1.21 to 7.63 dpm/(100 L) and from 1.07 to 6.33 dpm/(100 L), respectively. Activity concentrations of particulate ~(210) Po and ~(210) Pb varied from 1.96 to 36.74 dpm/(100 L) and from 3.11 to 38.06 dpm/(100 L). Overall,particulate ~(210) Po and ~(210) Pb accounted for the majority of the bulk ~(210) Po and ~(210) Pb. 210 Po either in dissolved or particulate phases showed similar spatial patterns to 210 Pb, indicating similar mechanisms for controlling the distributions of ~(210) Po and ~(210) Pb in the Taiwan Strait. The different fractionation coefficients indicated that particles in the Zhemin Coastal Current(ZCC) inclined to absorb 210 Po prior to 210 Pb while they showed an opposite effect in the Taiwan Warm Current(TWC). Based on the disequilibria between ~(210) Po and ~(210) Pb, the sinking fluxes of total particulate matter(TPM) were estimated to range from –0.22 to 3.84 g/(m2·d), showing an overall comparable spatial distribution to previous reported sediment accumulation rates. However, our sinking fluxes were lower than the sedimentation rates, indicating a sediment resuspension in winter and horizontal transport of particulate matter from the Taiwan Strait to the East China Sea.     

厦门近岸210Po和210Pb的大气沉降通量

为揭示中国东南沿海地区210Po和210Pb的大气沉降时空变化特征,探讨该地区气溶胶的停留时间,于2013年1月至2014年12月对厦门地区210Po和210Pb的大气沉降通量进行了时间序列研究。结果发现,210Po和210Pb的平均日沉降通量分别为（65.38±4.79） mBq/（m2·d）（n=54）和（0.78±0.09） Bq/（m2·d）（n=54）,表现出明显的周年变化。东北季风期间,210Po和210Pb的沉降通量较高,而西南季风期间其通量较低。2013年和2014年,210Po的年沉降通量分别为19.29 Bq/（m2·a）和9.25 Bq/（m2·a）,210Pb的年沉降通量分别为159.2 Bq/（m2·a）和189.6 Bq/（m2·a）。两核素的年沉降通量表现出不同程度的年际差异。210Po与210Pb沉降通量之间存在显著的线性正相关关系,揭示了大气中210Po和210Pb具有相同的迁出机制,降雨和大气中核素含量是影响210Po和210Pb沉降通量的主要因素。该研究结果可以为探求台湾海峡海水中210Po与210Pb的收支平衡提供大气来源项。     

北冰洋表层积雪中7Be、210Po和210Pb的分布特征

大气输送的放射性核素7Be、210Po和210Pb,可以作为研究北冰洋大气沉降通量、海洋现代沉积以及海冰中物质传输的重要示踪剂,已被广泛应用于包括气团运动、土壤侵蚀以及水系统中颗粒物循环过程的研究。本文报道了2018年北极高纬度浮冰区表层积雪中7Be、210Po和210Pb的活度特征。7Be、210Po和210Pb的比活度变化范围分别为33.6～632.68 mBq/L、36.2～87.5 mBq/L、30.9～194.49 mBq/L。本文的研究发现,北冰洋表层积雪中7Be和210Pb比活度小于中纬度大陆地区。研究区域表层积雪中7Be的比活度随着纬度的增加而增加。此外,表层积雪中210Po/210Pb活度比值范围为0.70～1.48 (平均为0.93),210Po与210Pb活度已基本达到平衡,表明积雪样品年龄可能较“老”。     

POC export from ocean surface waters by means of 234Th/238U and 210Po/210Pb disequilibria: A review of the use of two radiotracer pairs

²³⁴Th (T_1/2=24.1 d) and ²¹⁰Po (T_1/2=138.4 d) are particle reactive radioisotopes that are used as tracers for particle cycling in the upper ocean. Particulate organic carbon (POC) export has frequently been estimated using ²³⁴Th/²³⁸U disequilibrium. Recent evidence suggests that ²¹⁰Po/²¹⁰Pb disequilibrium may be used as an additional tool to examine particle export, given the direct biological uptake of ²¹⁰Po into cellular material. Differences in these two radioisotope pairs with regard to their half-lives, particle reactivity and scavenging affinity in seawater should provide complementary information to be obtained on the processes occurring in the water column. Here, we review eight different studies that have simultaneously used both approaches to estimate POC export fluxes from the surface ocean. Our aim is to provide a complete “dataset” of all the existing POC flux data derived from the coupled use of both ²³⁴Th and ²¹⁰Po and to evaluate the advantages and limitations of each tracer pair. Our analysis suggests that the simultaneous use of both radiotracers provides more useful comparative data than can be derived from the use of a single tracer alone. The difference in half-lives of ²³⁴Th and ²¹⁰Po enables the study of export production rates over different time scales. In addition, their different biogeochemical behaviour and preferred affinity for specific types of particles leads to the conclusion that ²³⁴Th is a better tracer of total mass flux, whereas ²¹⁰Po tracks POC export more specifically. The synthesis presented here is also intended to provide a basis for planning future sampling strategies and promoting further work in this field to help reveal the more specific application of each tracer under specific water column biogeochemistries.     

234Th/238U disequilibrium and particulate organic carbon export in the northwestern South China Sea

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...     

POC export from ocean surface waters by means of Th/U and Po/Pb disequilibria: A review of the use of two radiotracer pairs

²³⁴Th (T_1/2=24.1 d) and ²¹⁰Po (T_1/2=138.4 d) are particle reactive radioisotopes that are used as tracers for particle cycling in the upper ocean. Particulate organic carbon (POC) export has frequently been estimated using ²³⁴Th/²³⁸U disequilibrium. Recent evidence suggests that ²¹⁰Po/²¹⁰Pb disequilibrium may be used as an additional tool to examine particle export, given the direct biological uptake of ²¹⁰Po into cellular material. Differences in these two radioisotope pairs with regard to their half-lives, particle reactivity and scavenging affinity in seawater should provide complementary information to be obtained on the processes occurring in the water column. Here, we review eight different studies that have simultaneously used both approaches to estimate POC export fluxes from the surface ocean. Our aim is to provide a complete “dataset” of all the existing POC flux data derived from the coupled use of both ²³⁴Th and ²¹⁰Po and to evaluate the advantages and limitations of each tracer pair. Our analysis suggests that the simultaneous use of both radiotracers provides more useful comparative data than can be derived from the use of a single tracer alone. The difference in half-lives of ²³⁴Th and ²¹⁰Po enables the study of export production rates over different time scales. In addition, their different biogeochemical behaviour and preferred affinity for specific types of particles leads to the conclusion that ²³⁴Th is a better tracer of total mass flux, whereas ²¹⁰Po tracks POC export more specifically. The synthesis presented here is also intended to provide a basis for planning future sampling strategies and promoting further work in this field to help reveal the more specific application of each tracer under specific water column biogeochemistries.     

Exploring the connection between 210Po and organic matter in the northwestern Mediterranean

The disequilibrium between ²¹⁰Po and its grandparent ²¹⁰Pb has been proposed as a tracer of the vertical flux of sinking particulate organic matter in the ocean. The mechanism of association between ²¹⁰Po and organic matter is, however, still unclear. To investigate this association we measured trace metals, minerals, organic carbon, nitrogen, and the natural radioisotopes ²³⁴Th, ²²⁸Th, ²¹⁰Po, and ²¹⁰Pb in sinking particles collected in sediment traps at 200 m in the northwestern Mediterranean. Pigments, fatty acids, and amino acids were used to identify the types and sources of particulate organic matter. Multivariate analyses were used to determine which components of sinking particulate matter are traced by ²¹⁰Po and/or by the ²¹⁰Po/²¹⁰Pb ratio. Statistical analysis of the results indicates that the distribution of polonium in sinking marine particles is influenced by fresh phytoplankton-derived, nitrogen-rich organic matter as well as sulfur-containing amino acids. These findings are consistent with previous laboratory observations that the distribution of ²¹⁰Po in biota parallels the distributions of both sulfur and protein, and indicate that these associations persist as material sinks through the water column. While this research generally supports the use of ²¹⁰Po as a specific tracer of the flux of organic matter, the signals traced by ²¹⁰Po/²¹⁰Pb and ²³⁴Th/²³⁸U are not as distinct in the field as in laboratory experiments. Further work is needed to determine more precisely what ²¹⁰Po/²¹⁰Pb traces in order to increase the correspondence of ²¹⁰Po/²¹⁰Pb measurements to biogeochemically important rates and quantities.     

210Po-210Pb活度不平衡鉴年法测定北极冰区表层冰雪年龄

远离河流和大陆的北冰洋冰区,大气沉降是210Po、210Bi、210Pb和7Be核素等最重要的来源。降雪一旦形成即被标记具有特定的210Po/210Pb活度比值,并降落到海冰表面,进入封闭状态。在封闭体系的冰雪中,随着时间推移,210Po从相对于210Pb强烈亏损的状态逐渐达到210Po-210Pb平衡状态。因此可以通过分析北冰洋表层冰雪中210Po-210Pb活度不平衡特征,量化冰区表层冰雪的表观年龄。本文搜集整理了北极地区气溶胶的210Po/210Pb活度比值,结合2018年中国第9次北极科学考察航次和2015年美国GEOTRACES 北冰洋航次中若干冰站表层冰雪的210Po/210Pb活度比特征,估算了北冰洋表层冰雪的表观年龄。结果表明,2018年中国冰站采集的表层冰雪年龄变化范围为106～272 d,远大于2015年美国冰站采集的表层冰雪的年龄;而两国冰站表层冰雪的年龄都呈现一定的纬度效应,即随着采样站位越靠近北极点,总体上表层冰雪的年龄呈现越来越大的特点,表明北极冰区表层冰雪越靠近北极点,表层冰雪被保留的时间会越长。210Po-210Pb 活度不平衡定年法可以作为一种评估北冰洋冰雪年龄的方法并与遥感技术协同使用。     

Distribution of 210Po and export of organic carbon from the euphotic zone in the southwestern East Sea (Sea of Japan)

The distribution of the natural radionuclide ²¹⁰Po in the water column along a horizontal transect of the continental shelf, slope and deep basin regions of the East Sea (Sea of Japan), a marginal sea of the Northwest Pacific Ocean, was investigated, and its behavior is described here. The settling fluxes of particulate ²¹⁰Po in the deep basin along with ²¹⁰Pb, ²³⁴Th and biogenic matter were also determined. ²¹⁰Po inventories in the water column were observed to decrease from winter to summer in all stations, probably due to increased influx of ²¹⁰Po-poor Kuroshio Water of the Northwest Pacific Ocean during summer. Vertical profiles of dissolved and particulate ²¹⁰Po along with the settling fluxes of particulate ²¹⁰Po in the deep basin station have enabled us to evaluate temporal variations and residence times of ²¹⁰Po. In the slope and basin, activities of dissolved ²¹⁰Po generally decreased from the surface to the bottom water, with maximum activity just below the subsurface chlorophyll a maximum at 50–75 m depth in spring and summer. These subsurface peaks of dissolved ²¹⁰Po activity were attributed to the release of ²¹⁰Po from the decomposition of ²¹⁰Po-laden biogenic particulate organic matter. In the deep basin, despite the decrease in total mass flux, the sinking flux of particulate ²¹⁰Po was higher in the deeper trap (2000 m) than in the shallower one (1000 m), probably due to scavenging of dissolved ²¹⁰Po from the water column during particle descent and/or break-down of ²¹⁰Po-depleted particulate matter between 1,000 m and 2,000 m depths. In general, the ratios of the particulate phase to the dissolved phase of ²¹⁰Po (K_d) increased with depth in the slope and basin stations. ²¹⁰Po removal from the water column appears to depend on the primary productivity in the upper waters. There is an inverse relationship between K_d and suspended particulate matter (SPM) concentration in the water column. From the ²¹⁰Po activity/chlorophyll a concentration ratios, it appears that sinking particles arriving at 1000 m depth were similar to those in the surface waters.     

Particulate organic carbon export flux by 234Th/238U disequilibrium in the continental slope of the East China Sea

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.     

Controls of 234Th removal from the oligotrophic ocean by polyuronic acids and modification by microbial activity

To gain new insights into the variability of particulate organic carbon (POC) fluxes and to better understand the factors controlling the POC/²³⁴Th ratios in suspended and sinking particulate matter, we investigated the relationships between POC/²³⁴Th ratios and biochemical composition (uronic acids, URA; total carbohydrates, TCHO; acid polysaccharides, APS; and POC) of suspended and sinking matter from the Gulf of Mexico in 2005 and 2006. Our data show that URA/POC in sediment traps (STs), APS/POC in the suspended particles, and turnover times of particulate ²³⁴Th in the water column and those of bacteria in STs inside eddies usually increased with depth, whereas particulate POC/²³⁴Th (10–50 μm) and the sediment-trap parameters (POC flux, POC/²³⁴Th ratio, bacterial biomass, and bacterial production) decreased with depth. However, this trend was not the case for most biological parameters (e.g., phytoplankton and bacterial biomass) or for the other parameters at the edges of eddies or at coastal-upwelling sites.In general, the following relationships were observed: 1) ²³⁴Th/POC ratios in STs were correlated with APS flux, and these ratios in the 10–50 μm suspended particles also correlated with URA/POC ratios; 2) neither URA fluxes nor URA/POC ratios were significantly related to bacterial biomass; 3) the sum of two uronic acids (G2, glucuronic, and galacturonic acid, which composed most of the URA pool) was positively related to bacterial biomass; and 4) the POC/²³⁴Th ratios in intermediate-sized particles (10–50 μm) were close to those in sinking particles but much lower than those in > 50 μm particles. The results indicate that acid polysaccharides, though a minor fraction (~ 1%) of the organic carbon, act more likely as proxy compound classes that might contain the more refractory ²³⁴Th-binding biopolymer, rather than acting as the original ²³⁴Th “scavenger” compound. Moreover, these acid polysaccharides, which might first be produced by phytoplankton and then modified by bacteria, also influence the on-and-off “piggy-back” processes of organic matter and ²³⁴Th, thus causing additional variability of the POC/²³⁴Th in particles of different sizes.     

Calibration of sediment traps and particulate organic carbon export using 234Th in the Barents Sea

Profiles of particulate and dissolved ²³⁴Th (t_1/2=24.1 days) in seawater and particulate ²³⁴Th collected in drifting traps were analyzed in the Barents Sea at five stations during the ALV3 cruise (from June 28 to July 12, 1999) along a transect from 78°15′N–34°09′E to 73°49′N–31°43′E. ²³⁴Th/²³⁸U disequilibrium was observed at all locations. ²³⁴Th data measured in suspended and trapped particles were used to calibrate the catchment efficiency of the sediment traps. Model-derived ²³⁴Th fluxes were similar to ²³⁴Th fluxes measured in sediment traps based on a steady-state ²³⁴Th model. This suggests that the sediment traps were not subject to large trapping efficiency problems (collection efficiency ranges from 70% to 100% for four traps). The export flux of particulate organic carbon (POC) can be calculated from the model-derived export flux of ²³⁴Th and the POC/²³⁴Th ratio. POC/²³⁴Th ratios measured in suspended and trapped particles were very different (52.0±9.9 and 5.3±2.2 μmol dpm⁻¹, respectively). The agreement between calculated and measured POC fluxes when the POC/²³⁴Th ratio of trapped particles was used confirms that the POC/²³⁴Th ratio in trap particles is representative of sinking particles. Large discrepancies were observed between calculated and measured POC fluxes when the POC/²³⁴Th ratio of suspended particles was used. In the Barents Sea, vertical POC fluxes are higher than POC fluxes estimated in the central Arctic Ocean and the Beaufort Sea and lower than those calculated in the Northeast Water Polynya and the Chukchi Sea. We suggest that the latter fluxes may have been strongly overestimated, because they were based on high POC/²³⁴Th ratios measured on suspended particles. It seems that POC fluxes cannot be reliably derived from thorium budgets without measuring the POC/²³⁴Th ratio of sediment trap material or of large filtered particles.     

Pb and Po, manganese and iron cycling across the O2/H2S interface of a permanently anoxic fjord: Framvaren, Norway

Vertical profiles of dissolved and particulate ²¹⁰Po and ²¹⁰Pb were measured across the redox transition zone at Station F1 in Framvaren Fjord, Norway. In this fjord, a sharp decrease in pH above the O₂/H₂S interface facilitates the aerobic dissolution of MnO₂. In contrast, Fe(II) concentrations begin to increase only at the O₂/H₂S interface depth. Activity profiles reveal that dissolved ²¹⁰Po and ²¹⁰Pb are sequestered efficiently by particulates in surface waters. As polonium-210 and lead-210 activities descend down into the aerobic manganese reduction (AMR) zone, they are remobilized during the reductive dissolution of the carrier phase oxyhydroxides. Both ²¹⁰Po and ²¹⁰Pb are highly enriched at the O₂/H₂S interface where an active community of microbes, such as anoxygenic phototrophs (e.g., Chromatium, Chlorobium sp.), thrives. The coincident peaks in ²¹⁰Po, ²¹⁰Pb and microbial biomass suggest a strong biological influence on the behavior of these radionuclides. There is a strong covariance between the vertical distribution of Mn and Pb, indicating that their redox cycling is closely coupled and is likely microbially mediated.     

南极长城站附近企鹅栖息地粪土沉积地层放射性核素210Pb定年

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,210Pb_ex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.     

Seasonal POC fluxes at BATS estimated from 210Po deficits

In this study at the Bermuda Atlantic Time-series Study (BATS) site we demonstrate that the polonium–lead disequilibrium system may perform better as a tracer of organic carbon export under low-flux conditions (in this case, <2.5 mmol C m^?2 d^?1) than under bloom conditions in an oligotrophic setting. With very few exceptions, the POC flux predictions calculated from the water-column ²¹⁰Po deficit were within a factor of 2 of the POC flux caught in surface-tethered sediment traps. However, we found higher correlation between size-fractionated particulate ²¹⁰Po activity and POC concentration in November 2006 (r=0.93) than in January (r=0.79) and during the spring bloom in March 2007 (r=0.80). We suggest that this is due to the ability of polonium to distinguish between bulk mass flux and organic carbon export under oligotrophic and lithogenic-driven flux regimes. Further, we found that the POC/Po ratio on particles was largely independent of size class between 10 and 100 μm (P=0.13) during each season, supporting the notion that export in this oligotrophic system is driven by sinking aggregates of smaller cells and not by large, individual cells.     

Concentrations of the elements Ag,Al, Ca,Cd, Cu,Fe, Mg,Mn, Pb and Zn,and the radionuclides 210Pb and 210Po in the digestive gland of the squid Nototodarus gouldi

Ag, Al, Ca, Cd, Cu, Fe, Mg, Mn, Pb and Zn concentrations and ²¹⁰Po and ²¹⁰Pb activities were measured in 26 specimens of the squid Nototodarus gouldi taken from the waters of Bass Strait in one jigging operation. All the elements show wide ranges in concentrations in specimens apparently subject to the same environmental conditions. Copper concentration was 27-1 200 μg/g, and ²¹⁰Po activity 4·8–24·2 Bq/g. The animal wet weights, the elements Ag, Al, Cd, Fe and Zn, and the radionuclide ²¹⁰Po have coefficients of variation in the range 40–60%; Ca, Mg and Mn show the smallest variability (CV = < 30%), and Cu the greatest (CV = 12%). Significant correlations (p < 0·001) were found between the following pairs of elements: Cd-Zn, Cd-Cu, Zn-Cu, Mg-Mn, Fe-Mn, Ca-Mg and Fe-²¹⁰Po.     

厦门湾水体中颗粒有机碳的垂向输出通量:234Th/238U不平衡的应用

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/P_Th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.