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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.
《Marine Chemistry》2002,80(1):11-26
Profiles of particulate and dissolved 234Th (t1/2=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.  相似文献   

3.
To study biological effects on the particulate removal of chemical elements from seawater, sediment trap experiments were carried out successively ten times throughout the spring phytoplankton bloom in Funka Bay. Sediment traps were deployed every one to two weeks at 1, 40 and 80 m depths. The settling particles obtained were analyzed for trace metals, phosphate and silicate. The propagation of diatoms in spring results in larger particulate fluxes than that of dinoflagellates. The biogenic silicate concentration is higher in the earlier period, when diatoms are predominant, than in the subsequent period, when dinoflagellates are predominant. The concentrations of aluminum, iron, manganese and cobalt in the settling particles comprising largely biogenic particles are lower during phytoplankton bloom. The concentration of copper is not reduced by the addition of biogenic particles, and its vertical flux is approximately proportional to the total flux, indicating that its concentration in the biogenic particles is nearly equal to that in the non-biogenic particles. The results for nickel and lead show the same tendency as for copper. Cadmium is more concentrated in biogenic particles than in non-biogenic particles, and the concentration of cadmium in the settling particles decreases with depth, similarly to phosphate and organic matter. Thus, metals in seawater are segregated by biological affinities, and the degree of incorporation into biogenic particles is in the order Cd > Pb, Ni, Cu > Co > Mn, Fe, Al. Biogenic particles are the most important agent controlling the vertical distribution of metals in the ocean. They remove the metals from the surface water, transport them through the water column, and regenerate them in the deep.  相似文献   

4.
In order to better understand the relationship between the natural radionuclide 234Th and particulate organic carbon (POC), marine particles were collected in the northwestern Mediterranean Sea (spring/summer, 2003 and 2005) by sediment traps that separated them according to their in situ settling velocities. Particles also were collected in time-series sediment traps. Particles settling at rates of >100 m d−1 carried 50% and 60% of the POC and 234Th fluxes, respectively, in both sampling years. The POC flux decreased with depth for all particle settling velocity intervals, with the greatest decrease (factor of 2.3) in the slowly settling intervals (0.68–49 m d−1) over trap depths of 524–1918 m, likely due to dissolution and decomposition of material. In contrast the flux of 234Th associated with the slowly settling particles remained constant with depth, while 234Th fluxes on the rapidly settling particles increased. Taking into account decay of 234Th on the settling particles, the patterns of 234Th flux with depth suggest that either both slow and fast settling particles scavenge additional 234Th during their descent or there is significant exchange between the particle classes. The observed changes in POC and 234Th flux produce a general decrease in POC/234Th of the settling particles with depth. There is no consistent trend in POC/234Th with settling velocity, such as might be expected from surface area and volume considerations. Good correlations are observed between 234Th and POC, lithogenic material and CaCO3 for all settling velocity intervals. Pseudo-Kds calculated for 234Th in the shallow traps (2005) are ranked as lithogenic material opal <calcium carbonate <organic carbon. Organic carbon contributes 33% to the bulk Kd, and for lithogenic material, opal and CaCO3, the fraction is 22% each. Decreases in POC/234Th with depth are accompanied by increases in the ratio of 234Th to lithogenic material and opal. No change in the relationship between 234Th and CaCO3 was evident with depth. These patterns are consistent with loss of POC through decomposition, opal through dissolution and additional scavenging of 234Th onto lithogenic material as the particles sink.  相似文献   

5.
Thorium-234 is increasingly used as a tracer of ocean particle flux, primarily as a means to estimate particulate organic carbon export from the surface ocean. This requires determination of both the 234Th activity distribution (in order to calculate 234Th fluxes) and an estimate of the C / 234Th ratio on sinking particles, to empirically derive C fluxes. In reviewing C / 234Th variability, results obtained using a single sampling method show the most predictable behavior. For example, in most studies that employ in situ pumps to collect size fractionated particles, C / 234Th either increases or is relatively invariant with increasing particle size (size classes > 1 to 100s μm). Observations also suggest that C / 234Th decreases with depth and can vary significantly between regions (highest in blooms of large diatoms and highly productive coastal settings). Comparisons of C fluxes derived from 234Th show good agreement with independent estimates of C flux, including mass balances of C and nutrients over appropriate space and time scales (within factors of 2–3). We recommend sampling for C / 234Th from a standard depth of 100 m, or at least one depth below the mixed layer using either large volume size fractionated filtration to capture the rarer large particles, or a sediment trap or other device to collect sinking particles. We also recommend collection of multiple 234Th profiles and C / 234Th samples during the course of longer observation periods to better sample temporal variations in both 234Th flux and the characteristic of sinking particles. We are encouraged by new technologies which are optimized to more reliably sample truly settling particles, and expect the utility of this tracer to increase, not just for upper ocean C fluxes but for other elements and processes deeper in the water column.  相似文献   

6.
Sediment trap experiments were carried out 39 times during the years from 1977 to 1981 in Funka Bay, Hokkaido, Japan. The observed total particulate flux varies seasonally, that is, the particulate fluxes in winter and spring are larger than those in summer. The fluxes in all seasons increased with depth. Major components of settling particles are aluminosilicate in winter, biogenic silicate in spring and organic matter and terrestrial material in summer, respectively. The fluxes of each chemical component observed with sediment traps are normalized to that of Al by assuming that the actual flux of Al is equal to the accumulation rate onto the sediment surface. Vertical changes of the normalized flux of each chemical component indicate the following: Fe was not regenerated from the settling particles in the water column. Mn was regenerated from the settling particles in the lower layer exclusively between 80 m depth and the sediment surface. Cd was actively regenerated in the upper layer above 80 m depth. Phosphate was regenerated in the upper layer, while biogenic silicate was in the lower layer. The silicate regeneration, therefore, occurs after phosphate regeneration. The material decomposing in the water column below 40 m has an atomic ratio of P ∶ Si ∶ C = 1 ∶ 52 ∶ 128.  相似文献   

7.
Sediment trap experiments were carried out ten times in one year (1977) at three depths in Funka Bay. The material obtained in the traps was analyzed for metals, organic elements and radionuclides, together with the suspended matter in the overlying water column. Two groups with extremely different downward fluxes were found, a group with a small flux increasing with depth, and another with a large flux that is rather constant with depth and is observed only in winter. The flux in winter, and sometimes in the bottom layer below the summer thermocline was larger than the net sedimentation rate for total dry matter or for each chemical constituent. The flux was also larger than the net removal flux for 234Th. A most striking fact is that the specific activity of short-lived 234Th did not decrease in winter, indicating that the large flux in winter was not caused by the re-suspension of old bottom sediments. The concentration of suspended matter in winter was not much greater than that in other seasons. These results suggest that the downward flux observed in sediment trap experiments is not a net removal rate and that there must be an upward particulate flux in the bay.  相似文献   

8.
Hydrophobic organic contaminants (HOCs) may be used as tracers of particle dynamics in aquatic systems. Internal cycling of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were studied in the mesohaline Chesapeake Bay to assess the role of resuspension in maintaining particle and contaminant inventories in the water column, and to compare settling and suspended particle characteristics. Direct measurements of sediment resuspension and settling conducted in conjunction with one of the sediment trap deployments indicate reasonable agreement between measurements of particle flux using the two different methods. Organic carbon and PCB concentrations in settling solids collected in near-surface sediment traps were remarkably lower than concentrations in suspended particles collected by filtration during the trap deployments, but higher PAH concentrations were found in the settling particles. The different behaviors of PAHs and PCBs in the settling particles are due to their different source types and association to different types of particles. Sediment trap collections in near bottom waters were dominated by resuspension. Resuspension fluxes of HOCs measured 2 m above the bay bottom were as high as 2.5 μg/m2 day for total PCBs and 15 μg/m2 day for fluoranthene, and were 25 and 10 times higher than their settling fluxes from surface waters, respectively. HOC concentrations in the near bottom traps varied much less between trap deployments than HOC concentrations in the surface traps, indicating that the chemical composition of the resuspended particles collected in the near bottom traps was more time-averaged by repeated resuspension than the surface particles.  相似文献   

9.
Disequilibrium between 234Th and 238U in water column profiles has been used to estimate the settling flux of Th (and, by proxy, of particulate organic carbon); yet potentially major non-steady-state influences on 234Th profiles are often not able to be considered in estimations of flux. We have compared temporal series of 234Th distributions in the upper water column at both coastal and deep-water sites in the northwestern Mediterranean Sea to coeval sediment trap records at the same sites. We have used sediment trap records of 234Th fluxes to predict temporal changes in water column 234Th deficits and have compared the predicted deficits to those measured to determine whether the time-evolution of the two coincide. At the coastal site (327 m water depth), trends in the two estimates of water column 234Th deficits are in fairly close agreement over the 1-month deployment during the spring bloom in 1999. In contrast, the pattern of water column 234Th deficits is poorly predicted by sediment trap records at the deep-water site (DYFAMED, 2300 m water depth) in both 2003 and 2005. In particular, the transition from a mesotrophic to an oligotrophic system, clearly seen in trap fluxes, is not evident in water column 234Th profiles, which show high-frequency variability. Allowing trapping efficiencies to vary from 100% does not reconcile the differences between trap and water column deficit observations; we conclude that substantial lateral and vertical advective influences must be invoked to account for the differences.Advective influences are potentially greater on 234Th fluxes derived from water column deficits relative to those obtained from traps because the calculation of deficits in open-ocean settings is dominated by the magnitude of the “dissolved” 234Th fraction. For observed current velocities of 5–20 cm s−1, in one radioactive mean-life of 234Th, the water column at the DYFAMED site can reflect 234Th scavenging produced tens to hundreds of kilometers away. In contrast, most of the 234Th flux collected in shallow sediment traps at the DFYFAMED site was in the fraction settling >200 m d−1; in effect the sediment trap can integrate the 234Th flux over distances 40-fold less than water column 234Th distributions. In some sense, sediment trap and water column sampling for 234Th provide complementary pictures of 234Th export. However, because the two methods can be dominated by different processes and are subject to different biases, their comparison must be treated with caution.  相似文献   

10.
The downward flux of Mn through the water column was directly measured using sediment traps. The Mn flux from the bottom sediment to the water column, and the removal rate of Mn in the bottom water were estimated from Mn gradients in the bottom water. The sediment traps were deployed more than ten times at the same station in Funka Bay, Japan. The trapped settling matter and filtered suspended matter samples were analyzed for Mn, Fe, Al and ignition loss. The observed downward flux of Mn through the water column in winter (1.3–2.8 μg/cm2 /day) was generally an order of magnitude larger than that in summer (0.13–0.45 μg/cm2 /day), and the Mn fluxes for both seasons were also greater than the accumulation rate of Mn in the bottom sediments (0.10 μg/cm 2/day). More Al was contained in the trapped settling matter than in the suspended matter, while Mn showed the opposite behavior. The Fe/Mn ratio of the residual fraction (obtained by subtracting the sediment component of the settling matter) was rather well correlated with the corresponding ratio in suspended matter. Settling particles are expected to scavenge suspended matter during their passage through the water column. The flux of Mn across the sediment—water interface was estimated from its vertical profiles in the water column to be 0.1–0.3 μg/cm2 day. The residence time of Mn in bottom water was about one to several months. These results suggest that Mn is actively recycled between the water column and the sediments of the coastal sea.  相似文献   

11.
We determined the sensitivity of the calculated sinking flux of 234Th in the central equatorial Pacific to physical processes and scavenging mechanisms by imposing a meridional and vertical advection and diffusion field on a simple dissolved and particulate 234Th cycle. We used the model to estimate the efficiency with which the 234Th deficiency relative to 238U reflected the predicted sinking flux of 234Th on particles and compared our results with 234Th data taken during the JGOFS-EqPac 1992 Survey II Cruise. 234Th deficiencies near the equator were strongly affected by both vertical advection and horizontal diffusion. The model 234Th deficiency at the equator underestimated the model 234Th sinking flux by 144% in neglecting advection and diffusion in the presence of strong upwelling at the equator. The model 234Th deficiency at the equator corrected for advection overestimated the sinking flux of 234Th by 33% in neglecting horizontal diffusion. Analysis of the scavenging mechanism suggests that, during situations of export governed by rapidly sinking particles, 234Th-based estimates of particle export are only half as sensitive to advection compared to situations of export governed by slowly sinking particles. Given that results using the mechanism of slowly sinking particles compare better with the observed 234Th deficiency and calculated meridional 234Th fluxes at the equator than the mechanism of rapidly sinking particles, we consider the mechanism of slowly sinking particle more appropriate for this region. In agreement with previous studies based on observed 234Th gradients, this study supports the incorporation of vertical advection terms in the 234Th balance to estimate particulate carbon export at the equator but suggests that this method may have overestimated the sinking flux at the equator during EqPac Survey II by 0–63% due to the role of horizontal diffusion.  相似文献   

12.
An analysis of the 234Th method for determining the export flux of particulate organic carbon (PPOC) from the upper ocean using in situ pumps or water bottles shows that the accuracy of the method (the ratio of the experimental value of PPOC divided by the true POC flux, FPOC), defined as the p-ratio, is equal to the mean settling velocity of particulate 234Th divided by that of POC. Therefore, PPOC is equivalent to the true POC flux (FPOC) and the p-ratio is equal to unity if, and only if, POC and particulate 234Th have the same mean sinking velocities. A simple particle settling model is discussed that invokes Stokes’ Law settling velocities, volume:surface area (V:SA) fractionation of C:234Th and two assemblages of particles having different sizes and densities. The model is used to illustrate the ranges of parameter values that conform to values of the p-ratio sufficiently close to unity that the experimentally determined POC flux can be considered to be an accurate representation of the true POC flux.Despite the over-simplification of real systems implicit in the model, the results suggest that p-ratios<1, equivalent to an under-estimate of the POC flux, are representative of single particle settling regimes in which the larger particles dominate the vertical flux. This follows from the assumption that the ratio of C/234Th on particles is governed by the volume to surface area (V:SA) ratio of the particles. This results in a greater proportion of 234Th compared to C being associated with the smaller, more slowly settling particles and, as a result, normalization of the POC flux to the 234Th flux provides an under-estimate of the former quantity. However, when the smaller particle assemblage dominates the vertical flux, as could occur in open ocean regimes having high aeolian inputs of dense, rapidly settling, inorganic particles, then the p-ratio could exceed unity (p-ratio >1) resulting in an over-estimate of the POC flux using the 234Th method. High levels of flocculation associated with phytoplankton blooms in productive regions of the ocean are likely to produce p-ratios approaching unity, because flocs would tend to preserve the V:SA partitioning of the original particle size distribution and thereby minimize differences in the mean settling speeds of POC and particulate 234Th (Waite, A.W., Hill, P.S., 2006. Flocculation, phytoplankton and the accuracy of 234Th-based estimates of the vertical flux of particulate organic carbon in the sea. Marine Chemistry in press). Selective sampling of the large particle fraction using, for example, 53-μm screens can produce a more accurate estimate of the true POC flux, but may not entirely shift the p-ratio to a value of unity.  相似文献   

13.
The characteristics of the ratios between cadmium (Cd) and phosphorus (P) in settling particles collected from the Okinawa Trough in the East China Sea were examined using a sediment trap, moored at a depth of 811 m for one year. The Cd/P ratios varied within a narrow range throughout the year, in spite of the large seasonal change in the total dry mass, Cd, and P fluxes. The average Cd/P ratio of settling particles was 0.062 (nmol/μmol), which was obviously lower than that of surface seawater around the study site (0.16). This lower ratio in the Okinawa Trough particles collected using the 811 m-moored trap certainly reflected the mixture of biologically produced organic matter around the study site and other components that were mainly transported as lateral flux from the shelf edge and slope area of the East China Sea.  相似文献   

14.
Downward fluxes of microbial assemblages associated with sinking particles sampled in sediment traps deployed at nominal depths of 1000 m (trap A), 3000 m (trap B) and 4700 m (trap C) were measured between October 1995 and August 1998 on the Porcupine Abyssal Plain (PAP, NE Atlantic). The goal of the study was to provide detailed information on the microbial contributions to the particulate organic carbon and DNA fluxes. Bacterial fluxes associated with settling particles in the PAP area were generally low and significantly lower than bacterial fluxes reported from the same area during 1989–90. Marked seasonal pulses in the microbial assemblages were observed in all years that were associated with particle flux maxima in April–June. No significant differences were found in microbial fluxes between 1000 and 4700 m depth, but both the bacterial biomass flux and the frequency of dividing bacteria increased with depth, suggesting that organic matter turnover and conversion into bacterial biomass increased in the deeper traps. The structure of microbial assemblages displayed clear changes with increasing depth; the ratios of bacteria to both flagellates and cyanobacteria increased up to 4-fold between 1000 and 4700 m, showing a marked increase in bacterial dominance in the deeper layers of the water column. A parallel increase of the bacterial contribution to particulate organic carbon (POC) and DNA fluxes was observed. Total microbial contribution to the POC flux in the PAP area was about 2%, whereas the contribution of cyanobacteria was negligible. Fluxes of microbial assemblages were significantly correlated with DNA fluxes and on average the bacteria accounted for 5% of DNA fluxes. Data reported here confirm that the “rain” of particulate bacterial DNA may represent an important source of nucleotides for deep-sea bacteria, but also suggests that a much larger pool of detrital DNA is potentially available to deep-sea micro-organisms.  相似文献   

15.
Mass, carbon, and nitrogen fluxes and carbon and nitrogen compositions were determined for particulate samples from plankton net tows, shallow floating sediment traps, intermediate and deep moored sediment traps, and sediment cores collected along 140°W in the central equatorial Pacific Ocean during the US JGOFS EqPac program. Mass, particulate organic carbon (POC), and particulate inorganic carbon (PIC) fluxes measured by the floating sediment traps during the Survey I (El Niño) and Survey II (non-El Niño) cruises follow essentially the same pattern as primary production: high near the equator and decreasing poleward. POC fluxes caught in free-floating traps were compared with alternative estimates of export fluxes, including 234Th models, new production, and other sediment trap studies, resulting in widely differing estimates. Applying 234Th corrections to the trap-based fluxes yielded more consistent results relative to primary production and new production. Despite factors of five differences in measured fluxes between different trap types, POC : 234Th ratios of trap material were generally within a factor of two and provided a robust means of converting modeled 234Th export fluxes to POC export fluxes. All measured fluxes decrease with depth. Trap compositional data suggest that mineral “ballasting” may be a prerequisite for POC settling. POC remineralization is most pronounced in the epipelagic zone and at the sediment–water interface, with two orders of magnitude loss at each level. Despite seawater supersaturation with respect to calcium carbonate in the upper ocean, 80% of PIC is dissolved in the epipelagic zone. Given the time-scale differences of processes throughout the water column, the contrasting environments, and the fact that only 0.01% of primary production is buried, sedimentary organic carbon accumulation rates along the transect are remarkably well correlated to primary production in the overlying surface waters. POC to particulate total nitrogen (PTN) ratios for all samples are close to Redfield values, indicating that POC and PTN are non-selectively remineralized. This constancy is somewhat surprising given conventional wisdom and previous equatorial Pacific results suggesting that particulate nitrogen is lost preferentially to organic carbon.  相似文献   

16.
Studying sedimentation and consolidation of dredged slurry has significant implications to the design of storage yard and subsequent ground improvement. In this study, settling velocity of soil particles in dredged slurry during sedimentation and consolidation processes was investigated using an improved multilayer extraction sampling (MES) method. A series of sedimentation column tests were performed on dredged slurry with three different initial water contents. Distributions of volume of soil particles and density of dredged slurry were first obtained by the MES method, settling velocity of soil particles was then calculated by volume flux function approach. It was found that the density and velocity inflection points can be used to distinguish the settling zone and the consolidation zone. The experimental results reveal that the velocity of soil particles was quite low and monotonically decreased with sedimentation height at low initial water content throughout the whole test period, whereas it was increased at 0–1 hours and almost remained constant at 1–7 hours in the settling zone at high initial water content. The effects of initial water content on sedimentation and consolidation mode of dredged slurry and the settling velocity of soil particles were discussed. The relationship between settling velocity of soil particles and particle diameter was also studied. It is indicated that the measured velocity of soil particles was much lower than that calculated by the Stokes equation, and it was related to 0.4881–0.5906 order of particle diameter at 0–1 hours and 0.1117–0.1825 order of particle diameter at 1–7 hours for the test slurries.  相似文献   

17.
利用高精度的电感耦合等离子体质谱仪对2014年1月长江口表层水中溶解铀浓度及其234U/238U比值、2013年3月长江口表层沉积物中各矿物组分的铀含量及其234U/238U比值进行了测定,研究了其空间分布特征和影响因素。结果表明:除了长江径流和海水之外,长江口还有其他的溶解铀来源。水体中过剩铀与悬浮颗粒物浓度呈现显著相关性（r2=0.96）。对长江口表层沉积物进行的序列提取实验进一步表明,水体中悬浮颗粒物或沉积物中可解吸态和碳酸钙结合态铀可以在河口区域释放进入水体,而铁锰氧化物和有机物结合铀比较稳定,不受河口区混合过程的影响。每千克颗粒物或沉积物能够释放约2 μmol颗粒态铀,使其转化为溶解态。然而,铁氢氧化物和细颗粒物的絮凝吸附作用也可使溶解铀同时从河口水体中清除。在低盐度区,铀的清除和添加过程速率相近,使溶解铀呈现暂时的"伪保守"现象:颗粒态释放的铀具有明显低的234U/238U比值,导致水体的234U/238U低于保守混合值。在中高盐度区域,溶解铀呈现明显的富集现象。但是由于水相和颗粒相中的铀交换,可释放颗粒态铀的234U/238U接近溶解铀的234U/238U比值,从而导致水体的234U/238U比值呈现出保守性。长江口颗粒物的铀释放通量为（3.48±0.41）×105 mol/a,约占输入的总颗粒态铀通量（1.80±0.17）×106 mol/a的19.3%。长江口输入东海的溶解铀总通量（河流溶解态铀与河口添加铀之和）为（2.68±0.13）×106 mol/a,约为世界河流入海铀通量的11.7%。  相似文献   

18.
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   

19.
Four year-long time-series sediment trap experiments were conducted along the equatorial Pacific Ocean in order to understand the biogeochemistry of particulate organic matter (POM) on the basis of amino acid (AA) and hexosamine (HA) compositions of the settling particles. Total mass flux in the study area varied over 4 orders of magnitude without a common seasonality among all trap sites. Planktonic blooms were apparent in terms of total mass and AA fluxes at the easternmost end of the Niño-4 region. AA fluxes closely followed the total mass flux profiles, suggesting that increased particle flux delivered a greater amount of labile OM to the deep ocean. A labile OM index (LI)-based classification showed that during the El Niño conditions in 2002, the eastern side of the equatorial Pacific transported relatively more labile OM than the western equatorial Pacific. An overall change in AA and HA composition of settling particles could be revealed with the help of discriminant analysis, suggesting that settling particles during El Niño were compositionally different from those settling during La Niña condition in the equatorial Pacific.  相似文献   

20.
The flux of settling particles in the ocean has been widely explored since 1980s due to its important role in biogenic elements cycling, especially in the transport of particulate organic carbon (POC) in the deep sea. However, research in the seamount area of the oligotrophic subtropical Northwest Pacific Ocean is lacking. In this work, two sediment traps were deployed at the foot and another two at the hillside of Niulang Guyot from August 2017 to July 2018. The magnitude and composition of particle fluxes were measured. The main factors influencing the spatial variations of the fluxes were evaluated. Our results indicated a low particulate flux from Niulang Guyot area in the Northwest Pacific Ocean, reflecting low primary productivity of the oligotrophic ocean. The total mass flux (TMF) decreased from 2.57 g/(m2·a) to 0.56 g/(m2·a) with increasing depth from 600 m to 4 850 m. A clear seasonal pattern of TMF was observed, with higher flux in summer than that in winter. The peak flux of 26.52 mg/(m2·d) occurred in August at 600 m, while the lowest value of 0.07 mg/(m2·d) was shown in February at 4 850 m. The settling particles at the deep layers had similar biochemical composition, with calcium carbonate (CaCO3) accounting for up to 90%, followed by organic matter and opal, characteristics of Carbonate Ocean. The POC flux decreased more rapidly in the twilight layer because of faster decomposition, remineralization, and higher temperature. A small fraction of POC was transported into the deep ocean by biological pump. Particle fluxes were mainly controlled by the calcareous ballasts besides the primary productivity of the surface water. The advection may be another important factor affecting the flux in the seamount area. The combination of settled matters rich in foraminiferal tests with topography and currents may be the reason for regulating the local abundance of benthos on seamounts. Our results will fill in the knowledge gap of sedimentation flux, improve the understanding of ecosystem in Niulang Guyot area, and eventually provide data support for the optimization of regional ecological modeling.  相似文献   

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