²²⁶Ra,²¹⁰Pb and²¹⁰Po in the Red Sea     

Y. Chung  R.C. Finkel  K. Kim 《Earth and Planetary Science Letters》1982,58(2):213-224

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   

²¹⁰Pb and²¹⁰Po during the destruction of stratification in the Dead Sea     

M. Stiller  A. Kaufman 《Earth and Planetary Science Letters》1984,71(2):390-404

The progressive weakening and final disappearance (in 1979) of the long-term meromictic structure of the Dead Sea are clearly reflected in the depth profiles of²¹⁰Pb and²¹⁰Po. In 1977/78, prior to overturn, dissolved²¹⁰Pb (35–50 dpm kg^?1) predominated over particulate²¹⁰Pb (1–2 dpm kg^?1) in the oxic upper waters, whereas the reverse was true in the anoxic deep waters (16–20 dpm kg^?1 particulate vs. 2–5 dpm kg^?1 dissolved). The exact extent of the disequilibrium between²¹⁰Pb and²²⁶Ra is hard to evaluate in the upper oxic layers, because the progressive deepenings resulted in mixing with deep waters. By contrast, one can estimate the residence time of dissolved²¹⁰Pb in the unperturbed anoxic deepest layers, because these remained isolated, at about 3 years. Following the overturn of 1979, dissolved²¹⁰Pb exceeded particulate²¹⁰Pb at all depths. The²¹⁰Po profiles of the stratified lake resembled in shape those of its grandparent²¹⁰Pb, but with distinct characteristics of their own in the oxic upper waters where particulate²¹⁰Po (8–12 dpm kg^?1) was greatly in excess over particulate²¹⁰Pb, while dissolved²¹⁰Po (25–40 dpm kg^?1) was slightly deficient. Immediately following the overturn, dissolved and particulate²¹⁰Po were similar (about 15 dpm kg^?1), at all depths. The destruction of the lake's meromictic structure was accompanied by a reduction of its²¹⁰Pb inventory, while that of²¹⁰Po was almost unaffected. Thus, at overturn a transient state was created with the inventory of²¹⁰Po exceeding that of²¹⁰Pb.  相似文献   

²²⁶Ra distribution in the Antarctic Ocean     

Teh-Lung Ku  Mu-Ching Lin 《Earth and Planetary Science Letters》1976,32(2):236-248

²²⁶Ra data on eleven vertical profiles taken during the GEOSECS program from the Antarctic Ocean and its vicinity in both the Atlantic and the Pacific are presented. Replicate measurements were made on each sample using the Rn-emanation method. The precision (1 σ) based on triplicate analyses averages about ±2.5%. Waters all around the Antarctic continent below 2 km depth appear to exhibit a uniform²²⁶Ra concentration of 21.5 ± 1dpm/100kg, except perhaps locally such as the Ross Sea and the Drake Passage where small variations may be present. Higher in the water column, the²²⁶Ra contents decrease toward the surface with gradients which vary as a function of the influence exerted by the Antarctic Convergence. Across this oceanic front, a north-to-south increase of²²⁶Ra occurs (the increase being the largest near the surface: from 8 to 18 dpm/100 kg), reflecting the combining effect of deep-water upwelling and meridional water mixing. The core layer of the Antarctic Intermediate Water contains about 14 dpm/100 kg of²²⁶Ra and that of the Circumpolar Intermediate Water (O₂ minimum and local T maximum) about 18 dpm/100 kg. To a first approximation,²²⁶Ra covaries with Si in the circumpolar waters.  相似文献   

²¹⁰Pb and²²⁶Ra distributions in the Circumpolar waters     

Y. Chung 《Earth and Planetary Science Letters》1981,55(2):205-216

²¹⁰Pb and²²⁶Ra profiles have been measured at five GEOSECS stations in the Circumpolar region. These profiles show that²²⁶Ra is quite uniformly distributed throughout the Circumpolar region, with slightly lower activities in surface waters, while²¹⁰Pb varies with depth as well as location or area. There is a subsurface²¹⁰Pb maximum which matches the oxygen minimum in depth and roughly correlates with the temperature and salinity maxima. This²¹⁰Pb maximum has its highest concentrations in the Atlantic sector and appears to originate near the South Sandwich Islands northeast of the Weddell Sea. Concentrations in this maximum decrease toward the Indian Ocean sector and then become fairly constant along the easterly Circumpolar Current.Relative to²²⁶Ra, the activity of²¹⁰Pb is deficient in the entire water column of the Circumpolar waters. The deficiency increases from the depth of the²¹⁰Pb maximum toward the bottom, and the²¹⁰Pb/²²⁶Ra activity ratio is lowest in the Antarctic Bottom Water, indicating a rapid removal of Pb by particulate scavenging in the bottom layer and/or a short mean residence time of the Antarctic Bottom Water in the Circumpolar region.²²⁶Ra is essentially linearly correlated with silica and barium in the Circumpolar waters. However, close examination of the vertical profiles reveals that Ba and Si are more variable than²²⁶Ra in this region.  相似文献   

²²⁶Ra and²¹⁰Pb in the Weddell Sea     

Y. Chung  M.D. Applequist 《Earth and Planetary Science Letters》1980,49(2):401-410

²²⁶Ra and²¹⁰Pb were measured in sections and profiles collected in the Weddell Sea during the International Weddell Sea Oceanographic Expedition in 1973. The results can be correlated with the circulation and mixing schemes deduced from hydrographic observations. Along the surface cyclonic gyre the Ra activities are fairly uniform at about 17 dpm/100 kg, quite similar to those of the Circumpolar surface water south of the Antarctic Convergence. The²¹⁰Pb activities in the northern flank of the gyre, probably influenced by the high²¹⁰Pb-bearing Circumpolar Deep Water in the north, are as high as 12 dpm/100 kg. At the central gyre and its southern flank, the surface water²¹⁰Pb activities are about 7 dpm/100 kg. The warmer surface water at the central gyre has a Ra activity of about 19 dpm/100 kg, slightly higher than the colder surface water at the flanks. Thus lower²¹⁰Pb/²²⁶Ra activity ratios are observed in the central gyre, and higher ratios in its flanks. Similar relationships between Ra and Pb are noted in the Weddell Sea Bottom Water (WSBW): lower Pb associated with higher Ra in the center; higher Pb with slightly lower Ra in the flanks.Vertical profiles along the cyclonic gyre show lower Ra and Pb activities in the southwestern Weddell Basin where lower temperature and lower silicate are observed. Similar to Ba, both Ra and Si are non-conservative in the Weddell Sea, with significant input from the bottom sediments and particulate dissolution during subsurface mixing.Each water mass or type in the Weddell Sea is well characterized by its Ra content, but not well by its Pb content. Ra and Si are crudely correlated with a slope of about 7 × 10^?4 dpm Ra per μmole of Si. The fact that the WSBW values fall on the slope suggests that the net input rate for Ra (corrected for the decay rate) is proportional to that of Si. The linear extrapolation to zero Si gives a Ra value of 13 dpm/100 kg. These relationships are quite similar to those observed in the Circumpolar waters.  相似文献   

²¹⁰Pb/²²⁶Ra and ²¹⁰Po/²¹⁰Pb disequilibria in seawater and suspended particulate matter   总被引：1，自引：0，他引：1  

M.P. Bacon  D.W. Spencer  P.G. Brewer 《Earth and Planetary Science Letters》1976,32(2):277-296

The distribution of²¹⁰Po and²¹⁰Po in dissolved (<0.4 μm) and particulate (>0.4 μm) phases has been measured at ten stations in the tropical and eastern North Atlantic and at two stations in the Pacific. Both radionuclides occur principally in the dissolved phase. Unsupported²¹⁰Pb activities, maintained by flux from the atmosphere, are present in the surface mixed layer and penetrate into the thermocline to depths of about 500 m. Dissolved²¹⁰Po is ordinarily present in the mixed layer at less than equilibrium concentrations, suggesting rapid biological removal of this nuclide. Particulate matter is enriched in²¹⁰Po, with²¹⁰Po/²¹⁰Pb activity ratios greater than 1.0, similar to those reported for phytoplankton. Box-model calculations yield a 2.5-year residence time for²¹⁰Pb and a 0.6-year residence time for²¹⁰Po in the mixed layer. These residence times are considerably longer than the time calculated for turnover of particles in the mixed layer (about 0.1 year). At depths of 100–300 m,²¹⁰Po maxima occur and unsupported²¹⁰Po is frequently present. Calculations indicate that at least 50% of the²¹⁰Po removed from the mixed layer is recycled within the thermocline. Similar calculations for²¹⁰Pb suggest much lower recycling efficiencies.Comparison of the²¹⁰Pb distribution with the reported distribution of²²⁶Ra at nearby GEOSECS stations has confirmed the widespread existence of a²¹⁰Pb/²²⁶Ra disequilibrium in the deep sea. Vertical profiles of particulate²¹⁰Pb were used to test the hypothesis that²¹⁰Pb is removed from deep water by in-situ scavenging. With the exception of one profile taken near the Mid-Atlantic Ridge, significant vertical gradients in particulate²¹⁰Pb concentration were not observed, and it is necessary to invoke exceptionally high particle sinking velocities to account for the inferred²¹⁰Pb flux. It is proposed instead that an additional sink for²¹⁰Pb in the deep sea must be sought. Estimates of the dissolved²¹⁰Pb/²²⁶Ra activity ratio at depths greater than 1000 m range from 0.2 to 0.8 and reveal a systematic increase, in both vertical and horizontal directions, with increasing distance from the sea floor. This observation implies rapid scavenging of²¹⁰Pb at the sediment-water interface and is consistent with a horizontal eddy diffusivity of 3?6 × 10⁷ cm²/sec. The more reactive element Po, on the other hand, shows evidence of rapid in-situ scavenging. In filtered seawater,²¹⁰Po is deficient, on the average, by ca. 10% relative to²¹⁰Pb; a corresponding enrichment is found in the particulate phase. Total inventories of²¹⁰Pb and²¹⁰Po over the entire water column, however, show no significant departure from secular equilibrium.  相似文献   

The distribution of ²²⁶Ra in the Atlantic Ocean     

W.S. Broecker  J. Goddard  J.L. Sarmiento 《Earth and Planetary Science Letters》1976,32(2):220-235

Based on results obtained during the GEOSECS program the primary features of the distribution of²²⁶Ra in the Atlantic Ocean can be defined. Outside the Antarctic no significant variation has been found in the²²⁶Ra content of surface waters. Eighty samples yield an average of 7.4 dpm/100 kg (normalized to a salinity of 35.00‰). Deep waters in the central Atlantic have²²⁶Ra contents several dpm/100 kg higher than expected from the mixing of Antarctic Bottom Water (21.3 dpm/100 kg) and basal North Atlantic Deep Water (10.3 dpm/100 kg). These excesses correlate well with deficiencies in O₂ and excesses in SiO₂. The intermediate water²²⁶Ra maximum in the South Atlantic is associated with the inflow of low-oxygen Circumpolar Intermediate Water beneath the Antarctic Intermediate Water.  相似文献   

Disequilibria betweenRa, Pb and Po in the Arctic Ocean and the implications for chemical modification of the Pacific water inflow     

R.M. Moore  J.N. Smith 《Earth and Planetary Science Letters》1986,77(3-4)

Measurements have been made of²²⁶Ra and both dissolved and particulate forms of²¹⁰Pb and²¹⁰Po in a vertical profile at 85°50′N, 108°50′W in the Arctic Ocean.In the upper water column²²⁶Ra shows a concentration maximum that is coincident with one in the nutrients, silicate, phosphate, and nitrate, while at the same depth, dissolved and particulate²¹⁰Pb and²¹⁰Po all show minimum concentrations. It is suggested that the concentration maxima are partly due to sources of the respective elements in the continental shelf sediments, the shelf waters being subsequently advected into the Arctic Ocean basins. The²¹⁰Pb and²¹⁰Po minima have similarly been explained by interaction between the shelf sediments and overlying waters. An estimate is made of the possible contributions of shelf sediments to the layer of silica-rich water which covers the Canada Basin at a depth of 100–150 m.Residence times have been calculated for dissolved²¹⁰Pb and²¹⁰Po at various depths in the water column. Surface water residence times of dissolved and particulate forms of these radionuclides are longer than in surface Atlantic waters, probably due to lower biological activity in the surface waters of the Canada Basin. An estimatee has been made of the average sinking velocity of particulate material.  相似文献   

²¹⁰Pb/²²⁶Ra disequilibrium in the Santa Barbara Basin     

S. Krishnaswami  B.L.K. Somayajulu  Y. Chung 《Earth and Planetary Science Letters》1975,27(3):388-392

The vertical distributions of²¹⁰Pb and²²⁶Ra in the Santa Barbara Basin have been measured. The²¹⁰Pb/²²⁶Ra activity ratio is close to unity in surface water, but ranges from 0.2 to 0.6 in deep water with a mean value of 0.3 (d > 250m), suggesting rapid removal of²¹⁰Pb from the water column. The²¹⁰Pb concentrations in the particulate phase at different water depths indicate that the removal of²¹⁰Pb is due to adsorption on settling particles.It is estimated that the particulate²¹⁰Pb contributes about 50–70% of the total²¹⁰Pb measured on unfiltered water samples of the Santa Barbara Basin. The fate of²¹⁰Pb (and Pb) in the water column is thus strongly controlled by the settling particles, which have a mean residence time of one year or less in the basin. Material balance calculation for²¹⁰Pb in the basin suggests that there is an external source supplying about 70–80% of the²¹⁰Pb observed in particulate material or sediments. This excess²¹⁰Pb is most likely provided by particles entering the basin loaded already with²¹⁰Pb.  相似文献   

Intercomparison of²¹⁰Pb measurements at GEOSECS station 500 in the northeast Pacific     

Y. Chung  R. Finkel  M.P. Bacon  J.K. Cochran  S. Krishnaswami 《Earth and Planetary Science Letters》1983,65(2):393-405

During reoccupation of the GEOSECS-I test station in May, 1979, more than eighty 30-liter Niskin samples were collected in profile, many as replicates, for²¹⁰Pb intercomparison measurements by the WHOI, SIO and Yale groups. In addition to the inter-laboratory comparisons, the SIO group also carried out extensive experiments to test the effect of sample scavenging method. Pb equilibration time (storage effect), and filtration process on the measured²¹⁰Pb results.The intercomparison measurements indicate that there is a general agreement between the various sets of data. The sample set which allows a direct comparison at the same depth was available in most cases only between two of the three groups. The direct paired comparison shows that (1) the WHOI data are systematically 3% lower than the SIO data; (2) there are no systematic differences observed between the SIO and Yale data although the scatter is rather large; (3) the Yale data are systematically higher than the WHOI data by about 8%.The SIO experiments show that (1) the two scavenging methods employed (Fe(OH)₃ and Co-APDC co-precipitation) yield identical²¹⁰Pb results; (2) variation of Pb carrier equilibration time or of storage time has no discernible effect; (3) the filtration apparatus and procedure employed at this station do not result in²¹⁰Pb loss or contamination.The²¹⁰Pb profile structure and absolute concentration measured earlier at the same location (GOGO-II test station and GEOSECS station 347) agree with those of station 500 within 10%. The present profile shows a minimum²¹⁰Pb concentration around 500 m depth, marking the penetration depth of the flux of excess²¹⁰Pb from the atmosphere. There is a mild mid-depth maximum around 2500–3000 m. The²¹⁰Pb/²²⁶Ra activity ratio decreases monotonically from about 1 at the²¹⁰Pb minimum to about 0.5 near the bottom. The particulate²¹⁰Pb profile shows a systematic increase from the subsurface water to the bottom water by a factor of 5. This feature has been observed in many GEOSECS particulate²¹⁰Pb profiles.  相似文献   

²¹⁰Po and²¹⁰Pb distributions in the central and eastern Indian Ocean     

J.K. Cochran  M.P. Bacon  S. Krishnaswami  K.K. Turekian 《Earth and Planetary Science Letters》1983,65(2):433-452

Disequilibrium between²¹⁰Po and²¹⁰Pb and between²¹⁰Pb and²²⁶Ra has been mapped in the eastern and central Indian Ocean based on stations from Legs 3 and 4 of the GEOSECS Indian Ocean expedition.²¹⁰Po/²¹⁰Pb activity ratios are less than 1.0 in the surface mixed layer and indicate a residence time for Po of 0.6 years.²¹⁰Po and²¹⁰Pb are generally in radioactive equilibrium elsewhere in the water column except at depths of 100–500 m, where Po may be returned to solution after removal from the surface water, and in samples taken near the bottom at a few stations.²¹⁰Pb excesses relative to²²⁶Ra are observed in the surface water but these excesses are not as pronounced as in the North Pacific and North Atlantic. The difference is attributable to a lower flux of²¹⁰Pb from the atmosphere to the Indian Ocean. Below the main thermocline,²¹⁰Pb activities increase with depth to a broad maximum before decreasing to lower values near the bottom. Departures from this pattern are especially evident at stations taken in the Bay of Bengal (where²¹⁰Pb/²²⁶Ra activity ratios as low as 0.16 are observed) and near the Mid-Indian Ridge. The data suggest that removal of²¹⁰Pb at oceanic boundaries, coupled with eddy diffusion along isopycnals, can explain gradients in²¹⁰Pb near the boundary. Application of a simple model including isopycnal diffusion, chemical removal, production and radioactive decay produces fits the observed²¹⁰Pb/²²⁶Ra gradients for eddy diffusion coeffients of ～ 10⁷ cm²/s. High productivity in surface waters of the Bay of Bengal makes this region a sink for reactive nuclides in the northern Indian Ocean.  相似文献   

²¹⁰Pb in GEOSECS water profiles from the North Pacific     

Y. Nozaki  K.K. Turekian  K. Von Damm 《Earth and Planetary Science Letters》1980,49(2):393-400

Ten GEOSECS profiles from the North Pacific have been analyzed for²¹⁰Pb. GEOSECS²²⁶Ra data on the same profiles are used to calculate²¹⁰Pb excess or deficiency relative to secular equilibrium. The resultant profiles are divisible into a thermocline zone (<2000m) showing an expected decrease with depth, a mid-water zone of about 2000 m showing small constant deficiencies with a zone of increasing deficiency to a bottom zone of about 1000 m having the highest deficiency virtually invariant with depth. The exponentially decreasing portion in the thermocline yields a “diffusion” coefficient of 3 cm²/s. The mid-water deficiencies yield ? model residence times of 400 years northeast of Hawaii decreasing to 100 years at the most marginal stations.  相似文献   

²¹⁰Po and ²¹⁰Pb distributions in ocean water profiles from the Eastern South Pacific     

John Thomson  Karl K. Turekian 《Earth and Planetary Science Letters》1976,32(2):297-303

Two ocean profiles from the Peru Basin from regions with different surface productivities were analyzed for total²¹⁰Pb and²⁰¹Po to evaluate the influence of particulates in the water column on their distribution. Comparison with a published²²⁶Ra profile for the region was made. The profile closest to the coast, where upwelling and productivity are high, shows depletion of²¹⁰Pb relative to²²⁶Ra at all depths, with particularly marked excursions from radioactive equilibrium at the surface and in the bottom water.²¹⁰Po appears to be deficient relative to²¹⁰Pb at depth as well. Mean residence times in the deep water, relative to particulate removal from the water column to the sediments, of about 100 years for²¹⁰Pb and about two years for²¹⁰Po are indicated. The profile northwest of the upwelling region shows the²²⁶Ra²¹⁰Pb²¹⁰Po system close to equilibrium at all depths to 1500 m (except for the effect of atmospheric²¹⁰Pb input seen at the surface.  相似文献   

Uranium and thorium series nuclides in oriented ferromanganese nodules: growth rates,turnover times and nuclide behavior     

S. Krishnaswami  J. Kirk Cochran 《Earth and Planetary Science Letters》1978,40(1):45-62

Three ferromanganese nodules handpicked from the tops of 2500 cm² area box cores taken from the north equatorial Pacific have been analysed for their U-Th series nuclides.²³⁰Th_exc concentrations in the surface 1–2 mm of the top side of the nodules indicate growth rates of 1.8–4.6 mm/10⁶ yr. In two of the nodules a significant discontinuity in the²³⁰Th_exc depth profile has been observed at ～0.3 m.y. ago, suggesting that the nodule growth has been episodic. The concentration profiles of²³¹Pa_exc (measured via²²⁷Th) yield growth rates similar to the²³⁰Th_exc data. The bottom sides of the nodules display exponential decrease of²³⁰Th_exc/²³²Th activity ratio with depth, yielding growth rates of 1.5–3.3 mm/10⁶ yr.The²³⁰Th_exc and²³¹Pa_exc concentrations in the outermost layer of the bottom face are significantly lower than in the outermost layer of the top face. Comparison of the extrapolated²³⁰Th_exc/²³²Th and²³⁰Th_exc/²³¹Pa_exc activity ratios for the top and bottom surfaces yields an “age” of (5?15) × 10⁴ yr for the bottom relative to the top. This “age” most probably represents the time elapsed since the nodules have attained the present orientation.The²¹⁰Pb concentration in the surface ～0.1 mm of the top side is in large excess over its parent²²⁶Ra. Elsewhere in the nodule, up to ～1 mm depth in both top and bottom sides,²¹⁰Pb is deficient relative to²²⁶Ra, probably due to²²²Rn loss. The absence of²¹⁰Pb_exc below the outermost layer of the top face rules out the possibility of a sampling artifact as the cause of the observed exponentially decreasing²³⁰Th_exc and²³¹Pa_exc concentration profiles. The flux of²¹⁰Pb_exc to the nodules ranges between 0.31 and 0.58 dpm/cm² yr. The exhalation rate of²²²Rn, estimated from the²²⁶Ra-²¹⁰Pb disequilibrium is ～570 dpm/cm² yr from the top side and >2000 dpm/cm² yr from the bottom side.²²⁶Ra is deficient in the top side relative to²³⁰Th up to ～0.5–1 mm and is in large excess throughout the bottom. The data indicate a net gain of²²⁶Ra into the nodule, corresponding to a flux of (24?46) × 10^?3 dpm/cm² yr. On a total area basis the gain of²²⁶Ra into the nodules is <20% of the²²⁶Ra escaping from the sediments. A similar gain of²²⁸Ra into the bottom side of the nodules is reflected by the high²²⁸Th/²³²Th activity ratios observed in the outermost layer in contact with sediments.  相似文献   

²²⁶Ra, ²¹⁰Pb and ²¹⁰Po disequilibria in the Western North Pacific     

Yoshiyuki Nozaki  Shizuo Tsunogai 《Earth and Planetary Science Letters》1976,32(2):313-321

²²⁶Ra,²¹⁰Pb and²¹⁰Po were measured in oceanic profiles at two stations near the Bonin and Kurile trenches.²¹⁰Po is depleted by 50% on average relative to²¹⁰Pb in the surface water. In the deep water,²¹⁰Pb is about 25% deficient relative to²²⁶Ra. Based on the deficiency,²¹⁰Pb residence time with respect to removal by particulate matter was estimated to be less than 96 years in the deep water.²¹⁰Pb deficiency in the bottom water was significantly greater than that of the adjacent deep water, indicating more effective removal near or at the bottom interface.²¹⁰Pb,²¹⁰Po and Th appear to have similar overall rate constants of particulate removal throughout the water column.  相似文献   

The flux of²²⁶Ra from deep-sea sediments     

J. Kirk Cochran 《Earth and Planetary Science Letters》1980,49(2):381-392

The flux of²²⁶Ra from bottom sediments has been determined from patterns of²²⁶Ra/²³⁰Th disequilibrium in ten deep-sea cores from the world oceans. Values range from ? 0.0015 dpm/cm² yr (in the Atlantic) to 0.21 dpm/cm² yr (in the north equatorial Pacific). The flux is poorly related to sediment type, but is inversely correlated in a non-linear fashion with sediment accumulation rate. There is a direct relationship between the production rate of²²⁶Ra near the sediment-water interface (i.e. the integrated²³⁰Th activity in the biologically mixed zone) and the²²⁶Ra flux. The²²⁶Ra concentration in near-bottom water follows the geographic variation in the²²⁶Ra flux. The high flux from north equatorial Pacific sediments especially is reflected in the high bottom water²²⁶Ra concentrations in that area. The data suggest that both rate of circulation and the magnitude of the radium flux influence the near-bottom²²⁶Ra concentration.  相似文献   

Particulate and soluble²¹⁰Pb activities in the deep sea     

B.L.K. Somayajulu  H. Craig 《Earth and Planetary Science Letters》1976,32(2):268-276

Particulate and soluble,²¹⁰Pb activities have been measured by filtration of large-volume water samples at two stations in the South Atlantic. Particulate phase²¹⁰Pb (caught by a 0.4-μm filter) varies from 0.3% of total²¹⁰Pb in equatorial surface water to 15% in the bottom water. The “absolute activity” of²¹⁰Pb per unit mass of particulate matter is about 10⁷ times the activity of soluble²¹⁰Pb per unit mass of water, but because the mass ratio of particulate matter to water is about 10^?8, the particulate phase carries only about 10% of the total activity. In Antarctic surface water the particulate phase carries 40% of the total²¹⁰Pb activity; the absolute activity of this material is about the same as in other water masses and the higher fraction is due to the much larger concentration of suspended matter in surface water in this region.In the equatorial Atlantic the particulate phase²¹⁰Pb activity increases with depth, by a factor of 40 from surface to bottom, and by a factor of 4 from the Antarctic Intermediate Water core to the Antarctic Bottom Water. This increase with depth is predicted by our previously proposed particulate scavenging model which indicated a scavenging residence time of 50 years for²¹⁰Pb in the deep sea. A scavenging experiment showed that red clay sediment removes all the²¹⁰Pb from seawater in less than a week. The Antarctic particulate profile shows little or no evidence of scavenging in this region, which may be due to the siliceous nature of the particulate phase in circumpolar waters. Our previous observation that the²¹⁰Pb/²²⁶Ra activity ratio is of the order of 0.5 in the deep water is further confirmed by the two South Atlantic profiles analyzed in the present work.  相似文献   

Meridional distribution of²²⁶Ra in the eastern Pacific along GEOSECS cruise tracks     

T.L. Ku  C.A. Huh  P.S. Chen 《Earth and Planetary Science Letters》1980,49(2):293-308

We present the distribution of²²⁶Ra in eight vertical profiles from the eastern Pacific. The profiles are located along a meridional trend near 125°W, from 43°S to 29°N. Surface²²⁶Ra concentrations are about 7 dpm/100 kg, except for the two stations south of 30°S where the higher values are due to the Antarctic influence. Deep waters show a distinctive south-to-north increase in the²²⁶Ra content, from about 26 to 41 dpm/100 kg near the bottom. Unlike in the Atlantic and Antarctic Oceans, the effect of²²⁶Ra injection from bottom sediments is clearly discernible in the area. The presence of this primary²²⁶Ra can be traced up to at least 1–1.5 km above the ocean floor, making this part of the sea bed among the strongest source regions for the oceanic²²⁶Ra. Numerical solutions of a two-dimensional vertical advection-diffusion model applied to the deep (1.2–4 km)²²⁶Ra data give the following set of best fits: upwelling velocity(V_z) = 3.5m/yr, vertical eddy diffusivity(K_z) = 0.6cm²/s, horizontal (north-south) eddy diffusivity(K_y) = 1 × 10⁷cm²/s, and water-column regeneration flux of²²⁶Ra(J) = 3.3 × 10^?5dpmkg^?1yr^?1 as an upper limit. These parametric values are in general agreement with one-dimensional (vertical) model fits for the Ra-Ba system. However, consideration of²²⁶Ra balance leads us to suspect the appropriateness of describing the vertical exchange processes in the eastern Pacific with constantV_z and K_z. If future modeling is attempted, it may be preferable to treat the area as a diffusion-dominant mixing regime with depth-dependent diffusivities.  相似文献   

Radium in the near-surface Caribbean Sea     

David F. Reid  William M. Sackett 《Earth and Planetary Science Letters》1982,60(1):17-26

Recent radium measurements from the near-surface Caribbean Sea are presented. The surface horizontal and vertical distributions of²²⁶Ra are essentially the same as reported by Szabo et al. (1967) for the early 1960's. The²²⁶Ra activity at the surface is relatively uniform across the Caribbean, with an average of8.2±0.4dpm/100kg. The subsurface distribution to ～200 m averages7.8±0.4dpm/100kg and increases slowly below 200 m. reaching ～9.5 dpm/100 kg at 560 m. In contrast to²²⁶Ra, the surface concentration of²²⁸Ra was much more variable in both time and space. An average increase of 33% was found between 1968 and 1976 in the western Caribbean and during both years an anomalously high²²⁸Ra activity was found in the eastern Caribbean. These data support previous hypotheses that water entering the eastern Caribbean has been enriched in²²⁸Ra prior to entry and that variable mixing of the Atlantic water masses found to the northeast and southeast of the Lesser Antilles may produce temporal variations in the near-surface²²⁸Ra activity. Scatter plots of²²⁸Ra vs. salinity and sigma-t indicate that the near-surface vertical distribution of²²⁸Ra in the Caribbean Sea is predominantly influenced by advection. Thus²²⁸Ra cannot be used to study near-surface vertical mixing rates in this region.  相似文献   

Lead-210 in the North Pacific and the transport of terrestrial material through the atmosphere     

Yoshiyuki Nozaki  Shizuo Tsunogai 《Earth and Planetary Science Letters》1973,20(1):88-92

²¹⁰Pb in the surface water of the North Pacific was extensively determined. The results showed that the highest concentrations of²¹⁰Pb of 19 ± 3dpm/100kg were found in the northern mid-latitudes around 30°N, but longitudinal variation across the North Pacific was not observed. The mean residence time of²¹⁰Pb in the surface water up to 100 m in depth is calculated to be 230 days. In the mid-latitudes of the northern hemisphere,²¹⁰Pb may be transported by the prevailing westerly wind of a higher speed than 15 m/sec, likely the jet stream.  相似文献