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1.
The hydrography, circulation and distribution of particulate matter in Thermaikos Gulf (NW Aegean Sea) are described, for September 2001 and October 2001 and February 2002. The observations were obtained to assess the impact of anthropogenic and natural resuspension processes on the coastal ecosystem. The first two periods represent highly stratified conditions and mild weather conditions; in September trawling is prohibited, whilst the October cruise took place following the commencement of the activity. The sampling in February was undertaken to record the contribution of natural resuspension to the system, in a stormy period.The water circulation was mainly baroclinic during autumn and barotropic in winter; this was due to vertical homogenisation of the water column, during the latter period. The distribution of the bottom nepheloid layer (BNL) was very different in the winter than in the autumn.Microstructure measurements were undertaken, which allowed the vertical eddy diffusivity to be estimated, together with the near-bed shear stresses. Computation of the diffusive flux of particulate matter (PM), from the BNL into the intermediate water column in response to turbulent motions, reveals that the PM flux was much higher in October than in September; this is despite the fact that the friction velocities were similar. This observation could explain partly the observed higher PM concentrations (PMC) in the intermediate layer, in October. Likewise suggest that the higher PMC in October could be attributed to trawling. The limited shear stress and friction velocity values obtained during the September and October cruises were always low; these were possibly capable of resuspending only recently deposited, “fluffy” material. Thus, the observed nepheloid layers are likely to be maintained by advection from the shallow water regions and trawled areas.  相似文献   

2.
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3.
Four vertical profiles of230Th and228Th were determined using large volume water samples in the western North Pacific. An almost linear increase of230Th with depth was observed for all of the profiles for which the unidirectional first order scavenging model was difficult to explain. We developed a model which included a dissolved-particulate transformation as well as parameters of the scavenging model. Application of the model to the vertical distributions of total and the GEOSECS particulate Th isotopes (230Th and234Th) yielded the residence time of dissolved Th with respect to adsorption to particles and the turnover time of particulate Th to be 235 days and 57 days, respectively. The Th isotopes appeared to be carried down the water column by fine particles with a mean settling velocity of 1 m/day which continually release Th into sea water as well as pick up Th from the water along their journey to the bottom.For228Th, a large excess over232Th was observed throughout the water column with pronounced high concentrations in surface and bottom waters, suggesting that the228Th was derived from228Ra diffused out of sediments. The vertical distributions of228Th seemed to be significantly influenced by lateral mixing along isopycnals.  相似文献   

4.
The concentrations of radionuclides of the U-Th series (238U,234Th,234U,230Th,226Ra,210Pb,210Po, and232Th,228Ra,228Th) in the water of Narragansett Bay are reported. Analysis of the total, particulate, dissolved and colloidal forms of Th isotopes reveal a consistent removal behavior which is controlled mainly by the particulate matter concentration and the sediment resuspension rate. Half-removal times of Th from solution onto particles range from 1.5 to 15 days, and settling velocities of Th containing particles range generally between 1 and 11 m/day.210Pb and210Po concentrations are seasonally dependent, with higher concentrations and slower removal during the early summer (half-removal times from solution onto particles of 1–5 days in winter and up to 2 months in early summer).  相似文献   

5.
Dissolved and particulate Mn and Fe in the nearshore waters were determined at 27 stations along the west coast of Taiwan during 19-23 November 2004. The latitudinal distributions of Mn and Fe were very similar; however, the concentration in the dissolved phase was lower, whereas that in the particulate phase was higher in the northern regime. The higher percentage of Fe than Mn that was associated with particles resulted in a two-order of magnitude higher particle-water partition coefficient for Fe, Kd(Fe), than that for Mn, Kd(Mn). The removal fluxes of Mn and Fe could be estimated by multiplying the particulate 234Th removal flux with the Mn/234Th and Fe/234Th ratios in suspended particles, which ranged from 0.1 to 3.8 mmol m−2 d−1 for Mn, and from 3.4 to 194.5 mmol m−2 d−1 for Fe. Residence times ranged from 1 to 20 days for Mn and Fe were estimated in the nearshore.  相似文献   

6.
Vertical profiles of dissolved and particulate Mn, Fe, Ni, Cu, Zn, Cd, Pb, and (234)Th were determined in the Hung-Tsai Trough off southwestern Taiwan during 19-23 November, 2004. Except in the case of Cd, the distribution coefficient (K(d)) of the trace elements showed a negative correlation with the suspended particle concentration. Based on the average K(d) values, the general sequence of particle affinities for the eight trace elements is, from highest to lowest, Fe>Mn≈Pb>Zn≈Th>Cd≈Cu≈Ni. The trace metal data was coupled with the particle removal flux estimated from (234)Th/(238)U disequilibrium to investigate metal removal by particle sinking from the euphotic layer. The residence time of trace elements with respect to particle removal from the euphotic layer was estimated. A negative correlation between the residence time and the distribution coefficient for the trace metals was found.  相似文献   

7.
The objectives of this study were to examine both spatial and temporal changes of particulate major elements and minor metals, as well as dissolved Mn and Cd, in the waters of Thermaikos Gulf. Collections of water and suspended particulate matter (SPM), as depth profiles (5–8 depths), were undertaken at 10 principal stations, essentially on a N–S traverse of the western side of the Gulf.One of the principal aims of the study was to observe if there was any change in the patterning of the elements between the three occupations of the stations: (a) in September 2001, immediately before the commencement of trawling; (b) in October 2001, whilst fishing was active; and (c) in winter/early spring conditions (February 2002), when fishing was still active, but after a change of river/atmospheric conditions.Bottom (20 m) waters were dominated by sediment resuspension; this was identified by concentration changes in the aluminosilicate elements (e.g. Al, Ti, K, Fe) of the SPM. A two- to three-fold increase occurred between September and October, caused probably by trawling; this was sustained at the offshore stations, in February. During February, the western inshore stations showed little sediment resuspension, caused by extreme winter cooling and the sinking of water. Consequently, a N–S density discontinuity existed at all water depths, which prevented the thermohaline cyclonic circulation from penetrating into the western seaboard of the Gulf. The distribution of dissolved and particulate Mn in the lower waters was due to redox cycling of the element at the benthic boundary; this was more intense in the north, where the organic supply was higher.Biogenic element concentrations and Ca/Al, Si/Al ratios showed no evidence that trawling activity promoted higher biological production. Strong correlations of Co, Cr, Ni and V, with Al and K, showed that these elements were associated strongly with detrital aluminosilicates. However, the variable association of Cd, Pb and Zn, with K (and Al), especially in the upper waters, implied an anthropogenic source derived from the rivers and the city of Thessaloniki. Examination of the Kd's of Cd showed a two-order of magnitude decrease with depth, caused by resuspension and possible advection of relatively unpolluted sediments, into the western Gulf.  相似文献   

8.
In Funka Bay of Hokkaido, Japan, seawater, suspended matter and settling matter were collected once every month in the summer of 1974. These samples were analyzed for234Th, a short-lived daughter of dissolved238U. A pronounced disequilibrium between234Th and238U, and a highly variable concentration of234Th were found. Positive correlation, however, exist among the deficiency of234Th relative to238U in seawater, the concentration of particulate234Th, the fraction of particulate234Th to total234Th in seawater, the total dry weight of suspended matter, and the primary productivity during the month previous to sampling. The specific activity of234Th for the settling particles (620 ± 170 dpm/g) was nearly equal to that for suspended particles (720 ± 600 dpm/g) but much greater than that for plankton (47 ± 24 dpm/g). These facts suggest that suspended particles are somehow closely related to the removal of heavy metals from seawater, in spite of the negligibly small settling flux of suspended matter. The residence time of thorium in Funka Bay (mean depth: 60 m) is found to be about 60 days, which is nearly equal to those of210Pb and210Po.  相似文献   

9.
Two expeditions (October 1989 and May 1992) were carried out to two points of the main Amazon River channel and four tributaries. The Solimões and Madeira rivers, taking their origin in the Andes, are whitewater rivers. The Negro River is a typical acid, blackwater river. The Trombetas River flows through bauxite‐rich areas, and is characterized by low concentrations of dissolved humic substances. The 238U, 234U, 232Th and 230Th activities were recorded from dissolved, suspended particulate phases and river bank sediments. The latter were analysed for their 226Ra, 228Ra and 210Pb contents, and also subjected to leaching with 0·2 M hydroxylamine–hydrochloride solution to determine the concentrations of radionuclides bound to amorphous Fe hydroxides and Mn oxides and hydroxides. The dissolved U average concentration in the Amazon system is ten times lower than the mean world river concentration. The uranium concentration observed at Óbidos in the lower Amazon (0·095 µg L?1), where the U content in the river bank sediments and suspended matter is lowest, suggests U release from the solid phase during river transport. About 485 t of U are transported annually to the Amazon delta area in dissolved form, and 1943 t bound to suspended particulate matter. Total U and Th concentrations in the river bank sediments ranged from 1·59 to 7·14 µg g?1 and from 6·74 to 32 µg g?1, respectively. The highest concentrations were observed in the Trombetas River. The proportion extracted by means of the hydroxylamine solution (HL) was relatively high for U in the Trombetas river bank sediment (31%) and for Th in the Solimões sediment (30%). According to the alpha recoil effects, the 234U/238U activity ratios of the Andean river waters and downstream Amazon water (Óbidos) were >1, but were <1 in the Negro River (at Manaus). The activity ratios of dissolved U correlate with pH and also with the U activity ratios in the river bank sediment hydroxylamine extracts. As expected, the 234U/238U activity ratios in river bank sediments were <1 in the Andean rivers and in the downstream Amazon, but they were >1 in the Trombetas and Negro rivers. Such ratios probably result from the binding of dissolved uranium to solid sediment. The 228Th/232Th ratios of river bank sediments were close to unity (except for the Negro River, where it is lower), suggesting no significant Th exchanges between the river water and the sediment. The 226Ra/232Th activity ratios were <1, and the 226Ra/228Ra activity ratios generally were significantly higher than the activity ratios of their respective parents. This perhaps is the result of easier leaching of the 226Ra parent, 230Th, from solid material (owing to the alpha recoil effect) than of the 228Ra parent. Uranium and thorium isotopes were used as tools to evaluate the chemical weathering rate of rocks in the Amazon system, which was estimated to be 2·7 cm 1000 year?1 s?1. Copyright © 2002 John Wiley & Sons, Ltd.  相似文献   

10.
Uranium isotopes were measured in waters and suspended particulate matters (SPM) of the main channel of Yellow River, China that were sampled during four field trips between August 2005 and July 2006. The results show that the concentration of dissolved U (2.04–7.83 μg/l) and the activity ratio of 234U/238U (1.36–1.67) are much higher than the average U concentrations and activity ratios of global major rivers. Mass balance calculations using the results of simulated experiments and measurement data show that the section of the Yellow River between Lanzhou and Sanmenxia has its dissolved U derived from two sources: suspended sediments (68%) and groundwater/runoff from loess deposits (32%). Both sources are related to the heavy erosion of the Chinese Loess Plateau.  相似文献   

11.
Concentrations of230Th and231Pa were measured in particulate matter collected by sediment traps deployed in the Sargasso Sea (Site S2), the north equatorial Atlantic (site E), and the north equatorial Pacific (Site P) as well as in particles collected by in situ filtration at Site E. Concentrations of dissolved Th and Pa were determined by extraction onto manganese dioxide adsorbers at Site P and at a second site in the Sargasso Sea (site D).Dissolved230Th/231Pa activity ratios were 3–6 at Sites P and D. In contrast, for all sediment trap samples from greater than 2000 m, unsupported230Th/231Pa ratios were 22–35 (average 29.7). Ratios were lower in particulate matter sampled at shallower depths. Particles filtered at 3600 m and 5000 m at Site E had ratios of 50 and 40. Results show that suspended particulate matter in the open ocean preferentially scavenges Th relative to Pa. Most of the230Th produced by decay of234U in the open ocean is removed by adsorption to settling particulate matter. In contrast, less than 50% of the231Pa produced by decay of235U is removed from the water column by this mechanism. Mixing processes transport the remainder to other sinks.  相似文献   

12.
《Continental Shelf Research》2007,27(10-11):1600-1615
Multiple box cores were collected on the continental shelf in the Mississippi Deltaic Region adjacent to Southwest Pass and analyzed for particle reactive radionuclides 234Th and 7Be to examine seasonal sediment dynamics associated with variations of river discharge and hydrodynamics. Three stations located along a line west of Southwest Pass were cored and reoccupied in October, November, and December of 2003 and March, April, and May of 2004. High-frequency sampling (∼monthly) comparable to the short half-life of the radiotracers (234Th t1/2=24.1 d; 7Be t1/2=53.3) enabled us to isolate the relative influence that various forcing agents (river discharge, waves, currents) had on sediment inventories of 7Be and 234Th. In addition, the primary source of 7Be (fluvial) differs from 234Th (marine), providing further insight into processes affecting sediment transport and supply. Monthly 7Be inventories showed a significant positive relationship to river discharge (P=0.03) proximal to Southwest Pass. Sites further from Southwest Pass exhibited little to no relationship between 7Be inventories and river flow. At these sites, monthly 7Be inventories demonstrated a significant positive relationship with average wave orbital velocity (P<0.01). During our sampling period, the transport of 7Be-rich sediments to sites located on the middle to outer shelf were dependent on sea conditions not river discharge. Relatively high wave orbital velocities potentially allow particles to remain in suspension longer and travel further distances before initial deposition. In addition, 234Th inventories showed evidence of sediment focusing during periods of high wave orbital velocities.  相似文献   

13.
We have used in-situ pumps which filter large volumes of sea water through a 1 μm cartridge prefilter and two MnO2-coated cartridges to obtain information on dissolved and particulate radionuclide distributions in the oceans. Two sites in the northwest Atlantic show subsurface maxima of the fallout radionuclides137Cs,239,240Pu and241Am. Although the processes of scavenging onto sinking particles and release at depth may contribute to the tracer distributions, comparison of predicted and measured water column inventories suggests that at least 35–50% of the Pu and241Am are supplied to the deep water by advection.The depth distributions of the naturally occurring radionuclides232Th,228Th and230Th reflect their sources to the oceans.232Th shows high dissolved concentrations in surface waters, presumably as a result of atmospheric or riverine supply. Activities of232Th decrease with depth to values 0.01 dpm/1000 l.228Th shows high activities in near surface and near bottom water, due to the distribution of its parent,228Ra. Dissolved230Th, produced throughout the water column from234U decay, increases with depth to 3000 m. Values in the deep water (> 3000 m) are nearly constant ( 0.6–0.7 dpm/1000 l), and the distribution of this tracer (and perhaps other long-lived particle-reactive tracers as well) may be affected by the advection inferred from Pu and241Am data.The ratio of particulate to dissolved activity for both230Th and228Th is 0.15–0.20. This similarity precludes the calculation of sorption rate constants using a simple model of reversible sorption equilibrium. Moreover, in mid-depths228Th tends to have a higher particulate/dissolved ratio than230Th, suggesting uptake and release of230Th and228Th by different processes. This could occur if228Th, produced in surface water, were incorporated into biogenic particles formed there and released as those particles dissolved or decomposed during sinking.230Th, produced throughout the water column, may more closely approach a sorption equilibrium at all depths.230Th,241Am and239,240Pu are partitioned onto particles in the sequence Th > Am > Pu with 15% of the230Th on particles compared with 7% for Am and 1% for Pu. Distribution coefficients (Kd) are 1.3–1.6 × 107 for Th, 5–6 × 106 for Am and 7–10 × 105 for Pu. The lower reactivity for Pu is consistent with analyses of Pu oxidation states which show 85% oxidized (V + VI) Pu. However, theKd value for Pu may be an upper limit because Pu, like228Th, may be incorporated into particles in surface waters and released at depth only by destruction of the carrier phase.  相似文献   

14.
The mean residence time (τ) of thorium with respect to non-radioactive removal from water was determined as a function of location in three traverses of the New York Bight using both234Th/238U and228Th/228Ra. τ correlates well with salinity increasing from about ten days near shore to 70 days at the shelf break. It shows a much weaker correlation with suspended matter concentrations both because suspended matter varies in its scavenging efficiency and because salinity is a longer-term integrator of scavenging potential.τ's computed from228Th/228Ra were often higher than those computed from234Th/238U either because of the detrital matter present as reflected in the232Th concentrations or because the water parcels had recently arrived from environments of lower scavenging efficiency.Anomalous isotopic concentrations found in three adjacent samples can best be explained as the result of an episodic release of228Ra from bottom sediments at a rate 200 times the normal one.  相似文献   

15.
Profiles of226Ra and dissolved210Pb have been measured at several stations in the Red Sea. At one station in the central Red Sea an expanded profile was measured including226Ra and dissolved and particulate210Pb and210Po. These profiles show several distinct features: (1)226Ra displays a mid-depth maximum of about 13 dpm/100 kg at about 500 m; (2) dissolved210Pb concentrations are uniformly low at about 2 dpm/100 kg with little lateral or vertical variation; (3) the surface-water210Pb excess which is commonly observed in low-latitude open ocean regions is entirely lacking; (4)210Pb and210Po activities are essentially identical to each other in both particulate and dissolved phases although210Po activities appear somewhat lower; (5) about 20% of the210Pb and210Po in the water column residues on particulate matter.Assuming the atmospheric210Pb flux to be in the dissolved form and at the lower level of the normal range i.e. 0.5 dpm/cm2 yr, the residence time of the dissolved Pb is about 1.5 years. However, if the same atmospheric flux is entirely in particulate form, then the residence time of the dissolved Pb is about 5 years. The residence time of Pb in the particulate phase is less than 0.4 years if all the Pb is removed only by sinking particles.  相似文献   

16.
The concentrations of214Pb (half-life=26.4minutes) and22Rn (half-life=3.84days) have been measured in deep groundwaters of Gujarat, India. The results show that the abundance of214Pb in the water is only ～25% of that expected from its production through the radioactive decay of dissolved222Rn. This deficiency if modelled in terms of a first-order removal, yields a residence time of ～10 minutes for214Pb in these waters. The estimated residence time for214Pb is the shortest observed for any nuclide in natural water systems and suggests that reactive nuclides lead like could be removed from aqueous phases to adjoining solid surfaces on extremely short time scales. Results of laboratory experiments using the212Pb-224Ra pair are compatible with the observed fast removal of214Pb from groundwaters.Re-evaluation of234Th residence times in these waters using a model with a recoil flux of234Th into aqueous phase, the same as that of222Rn, yields values in the range of 23 to<176 minutes, very similar to that of214Pb. This “concordancy” in the residence times seems to suggest that the geochemical behaviour of234Th and214Pb in these waters is quite similar.  相似文献   

17.
Measurement of excess 234Th (t1/2 = 24.1 days) in surface sediment from 12 stations throughout Long Island Sound, U.S.A., demonstrates: (1) a mean (summer) sediment inventory of 3.6 dpm/cm2 consistent with complete, nearly instantaneous removal of 234Th from the overlying water and capture within the estuary, and (2) preferential association of excess 234Th with small particles and inventory build-ups in muddy bottom areas. There may also be a tendency for higher inventories in areas of high physical or biogenic reworking of surface sediments. A range of particle reworking rates (0–5 cm) from <0.01 × 10?6 to 1.6 × 10?6 cm2/s is found in the Sound with most values ～0.2?0.5 × 10?6 cm2/s. The inventory and reworking patterns demonstrate the high mobility, both horizontal and vertical, of particles in the estuary on 234Th decay time scales and are unequivocal evidence for control of reactive element distribution in the water column by the muddy regions of the basin.  相似文献   

18.
Manganese transport through a well-developed oxygen minimum was studied off central Mexico (18°N, 108°W) in October–November 1981 as part of the VERTEX (Vertical Transport and Exchange) research program. Refractory, leachable and dissolved Mn fractions associated with particulates caught in traps set at eight depths (120–1950 m) were analyzed. Particles entering the oxygen minimum had relatively large Mn loads; however, as the particulates sank further into the minimum, total Mn fluxes steadily decreased from 190 nmol m?2 day?1 at 120 m to 36 nmol m?2 day?1 at 400 m. Manganese fluxes then steadily increased in the remaining 800–1950 m, reaching rates of up to 230 nmol m?2 day?1 at 1950 m.Manganese concentrations were also measured in the water column. Dissolved Mn levels < 3.0 nmol kg?1 were consistently observed within the 150–600 m depth interval. In contrast, suspended particulate leachable Mn amounts were especially low at those depths, and never exceeded 0.04 nmol kg?1.The combined water column and particle trap data clearly indicate that Mn is released from particles as they sink through the oxygen minimum. Rate-of-change estimates based on trap flux data yield regeneration rates of up to 0.44 nmol kg?1 yr?1 in the upper oxygen minimum (120–200 m). However, only 30% of the dissolved Mn in the oxygen minimum appears to be from sinking particulate regeneration; the other 70% probably results from continental-slope-release-horizontal-transport processes.Dissolved Mn scavenges back onto particles as oxygen levels begin to increase with depth. Scavenging rates ranging from ?0.03 to ?0.09 nmol kg?1 yr?1 were observed at depths from 700 to 1950 m. These scavenging rates result in Mn residence times of 16–19 years, and scavenging rate constants on the order of 0.057 yr?1. Manganese removal via scavenging on sinking particles below the oxygen minimum is balanced by Mn released along continental boundaries and transported horizontally via advective-diffusive processes.Manganese appears to be very weakly associated with particulates. Nevertheless, the amounts of Mn involved with sinking biogenic particles are large, and the resulting fluxes are on the same order of magnitude as those necessary to explain the excess Mn accumulating on the sea floor. The overall behavior of Mn observed in this, and other, studies strongly suggests some type of equilibrium occurring between dissolved and particulate phases. This equilibrium appears to shift in direct or indirect response to dissolved oxygen levels.  相似文献   

19.
The distribution of “ash” (the non-combustible fraction of marine suspended matter) and concentrations of particulate Al, Ca, Fe, Cr, Ni, Cu, Sr and234Th in surface waters and of210Pb,230Th and234Th in two vertical profiles (385–4400 m) of the Indian Ocean are reported.The ash concentrations in surface waters follow the primary productivity pattern, with higher abundances in samples south of 40°S and lower concentrations in the equatorial and subtropical regions. Opaline silica and CaCO3 are the dominant components of the ash in samples from >40°S and from 7°N to 39°S, respectively. Aluminosilicates are only a minor constituent of the surface particulate matter. The metal/Al ratios in the surface particles are significantly higher compared to their corresponding crustal ratios for all the metals analyzed in this work. Comparison of enrichment factors between marine aerosols, plankton and surface oceanic particles, seem to indicate that this high metal/Al ratio in surface particles most likely arises from their involvement in marine biogeochemical cycles. Particulate234Th activity in surface waters parallels the ash abundance implying that its scavenging efficiency from surface waters depends on the particulate concentration.The particulate230Th and210Pb concentration profiles increase monotonously with depth. It is difficult to ascribe this increase to a process other than the in-situ vertical scavenging of230Th and210Pb from the water column by settling particles. The mean settling velocities of particles calculated from the particulate230Th data using a one-dimensional settling model is about 2 × 10?3 cm/s. The settling velocity computed from the particulate230Th profiles does not appear to be compatible with the particulate210Pb depth profiles; one possible explanation to account for the disparity would be that230Th and210Pb are scavenged by different size populations of particles.On the whole, the geographic distribution of particulate matter, their composition and settling velocities in the Atlantic, Pacific and Indian Oceans are similar indicating that they are controlled by quite similar processes in the marine hydrosphere.  相似文献   

20.
Because of high specific activities of excess234Th (t1/2 = 24.1 days) on suspended particles in the deep sea, this nuclide is potentially an extremely sensitive indicator of particle inputs and dynamics at the seafloor. Measurements were made at two deep-sea sites in order to examine this potential. Inventories of excess234Th at a low-current hemipelagic mud site (3990 m) in the Panama Basin were～ 1.5 (September, ′81) and～ 2.5 (June, ′82) dpm/cm2. The steady state fluxes to the seafloor calculated from these inventories are in rough agreement with radionuclide fluxes measured in sediment traps. Small-scale (～ 100m) spatial variability in inventories implies biologically significant heterogeneity in particle inputs. Sediment from the continental rise site in the northwest Atlantic (2800 m), a site with higher current velocities than the Panama Basin, had an inventory of～ 1.9dpm/cm2. This inventory is also in rough agreement with predictions made on the basis of nearby sediment trap data. Particle mixing coefficients of～ 30cm2/yr calculated at the Pacific and Atlantic sites are similar to those in shallow water deposits but could reflect disturbance during handling. Based on210Pb data from the Panama Basin, sediment from below～ 6cm is mixed at a rate～ 10 × slower than the near-surface sediment to a depth of at least 20 cm. Agreement between234Th predicted mixing rates at the Panama Basin site with210Pb profiles and in-situ experiments with glass bead tracers implies that these rates are real. Although the diffusion of dissolved234Th into deep-sea sediments complicates interpretations,234Thxs distributions in bottom sediments offer a useful adjunct to sediment traps for investigation of particle dynamics near the deep-sea floor.  相似文献   

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