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1.
Seawater samples from the Eastern Equatorial Pacific Ocean were analyzed for amino acids by a ligand-exchange chromatography technique. The results showed that dissolved free amino acids make up only 0.3% of DOC, much less than has been previously reported for open ocean waters. Substantially larger amounts of combined amino acids are present, however. Concentration variations of the combined amino acid fraction in the water column suggest their potential use as a water mass indicator.  相似文献   

2.
New data for the direct measurement of the isotopic composition of neodymium in Atlantic Ocean seawater are compared with previous measurements of Pacific Ocean seawater and ferromanganese sediments from major ocean basins. Data for Atlantic seawater are in excellent agreement with Nd isotopic measurements made on Atlantic ferromanganese sediments and are distinctly different from the observed compositions of Pacific samples. These results clearly demonstrate the existence of distinctive differences in the isotopic composition of Nd in the waters of the major ocean basins and are characteristic of the ocean basin sampled. The average εNd(0) values for the major oceans as determined by data from seawater and ferromanganese sediments are as follows: Atlantic Ocean,εNd(0) ? ?12 ± 2; Indian Ocean,εNd(0) ? ?8 ± 2; Pacific Ocean,εNd(0) ? ?3 ± 2. These values are considerably less than εNd(0) value sources with oceanic mantle affinities indicating that the REE in the oceans are dominated by continental sources. The difference in the absolute abundance of143Nd between the Pacific and Atlantic Oceans corresponds to ～106 atoms143Nd per gram of seawater. The correspondence between the143Nd/144Nd in seawater and in the associated sediments suggests the possible application of this approach to paleo-oceanography.Distinctive differences in εNd(0) values are observed in the Atlantic Ocean between deep-ocean water associated with North Atlantic Deep Water and near-surface water. This suggests that North Atlantic Deep Water may be relatively well mixed with respect to Nd isotopic composition whereas near-surface water may be quite heterogeneous, reflecting different sources for surface waters relative to deep water. This suggests that it may be possible to distinguish the sources of water masses within an ocean basin on the basis of Nd isotopic composition.The Nd isotopic variations in seawater are used to relate the residence time of Nd and mixing rates between the oceans.  相似文献   

3.
Nutrient pollution from rivers, nonpoint source runoff, and nearly 100 wastewater discharges is a potential threat to the ecological health of Puget Sound with evidence of hypoxia in some basins. However, the relative contributions of loads entering Puget Sound from natural and anthropogenic sources, and the effects of exchange flow from the Pacific Ocean are not well understood. Development of a quantitative model of Puget Sound is thus presented to help improve our understanding of the annual biogeochemical cycles in this system using the unstructured grid Finite-Volume Coastal Ocean Model framework and the Integrated Compartment Model (CE-QUAL-ICM) water quality kinetics. Results based on 2006 data show that phytoplankton growth and die-off, succession between two species of algae, nutrient dynamics, and dissolved oxygen in Puget Sound are strongly tied to seasonal variation of temperature, solar radiation, and the annual exchange and flushing induced by upwelled Pacific Ocean waters. Concentrations in the mixed outflow surface layer occupying approximately 5–20?m of the upper water column show strong effects of eutrophication from natural and anthropogenic sources, spring and summer algae blooms, accompanied by depleted nutrients but high dissolved oxygen levels. The bottom layer reflects dissolved oxygen and nutrient concentrations of upwelled Pacific Ocean water modulated by mixing with biologically active surface outflow in the Strait of Juan de Fuca prior to entering Puget Sound over the Admiralty Inlet. The effect of reflux mixing at the Admiralty Inlet sill resulting in lower nutrient and higher dissolved oxygen levels in bottom waters of Puget Sound than the incoming upwelled Pacific Ocean water is reproduced. By late winter, with the reduction in algal activity, water column constituents of interest, were renewed and the system appeared to reset with cooler temperature, higher nutrient, and higher dissolved oxygen waters from the Pacific Ocean.  相似文献   

4.
The thorium isotope content of ocean water   总被引：1，自引：0，他引：1  
232Th concentrations of surface and deep Pacific Ocean waters are 0.01–0.02 dpm/1000 kg (60 pgm/kg). The230Th activity is 0.03–0.13 dpm/1000 kg in surface waters and 0.3–2.7 dpm/1000 kg in deep waters. Chemical residence times based on in situ production from parent isotopes are about the same for230Th and228Th in surface waters (1–5 years) but are ten times greater for230Th in deep waters (10–100 years). Apparently there are additional sources of230Th into deep waters. At MANOP site S manganese nodule tops are enriched in Th isotopes by adsorption of Th from seawater and not by incorporation of Th-rich particulates.  相似文献   

5.
The inter- and intra-crystalline fractions of Patella vulgata limpets recovered from archaeological sites in Northern Spain (covering Neolithic, Mesolithic, Magdalenian, Solutrean, and Aurignacian periods) were examined for amino acid composition and racemisation over time. The calcitic apex and rim areas of the shells were found to probably be composed of similar proteins, as the D/L values and amino acids were comparable and varied in the same way with increasing age; however, the mineral structures present in these areas differed. The aragonitic intermediate part of the shell showed a distinctly different amino acid composition and mineral structure. The main protein leaching from the inter-crystalline fraction occurred within the first 6000 yr after the death of the organism. In contrast, the intra-crystalline fraction — comprised of a different protein composition than the inter-crystalline fraction — appeared to behave as a closed system for at least 34 ka, as reflected by the lack of a significant decrease in the amino acid content; however, changes in the amino acid percentages occurred during this period. The concentration of aspartic acid remained almost constant with age both in inter- and intra-crystalline proteins, and its contribution to the total amino acid content increased with age at the expense of other amino acids such as glutamic acid, serine, glycine and alanine. Temperature is thought to play a key role in the amino acid racemisation of P. vulgata and could explain why in the localities belonging to the Gravettian and Solutrean period, which formed during relatively cold conditions, D/L values were similar to those detected in shells from sites formed during the Magdalenian.  相似文献   

6.
13C and ΣCO2 data from the North and South Atlantic, the Antarctic, and the North and South Pacific are given. The δ13C of the ΣCO2 in the deep water (～3000m) decreases from 1.7‰ in the North Atlantic to ?0.10‰ in the North Pacific. This change is attributed to the addition of about 158 μmoles of CO2 per kg of seawater. The in-situ oxidation of organic matter accounts for 83% of this increase in ΣCO2, while the remainder is attributed to dissolution of calcium carbonate.The δ13C of the dissolved CO2 in mid-latitude surface water samples is controlled by a quasi-steady-state equilibrium with atmospheric CO2 at a mean temperature of 16°C. The δ13C and ΣCO2 values of Antarctic surface water samples suggest that these waters are derived from a mixture of North Atlantic deep water and equilibrated surface water.  相似文献   

7.
The concentration ratio of the amino acids alanine and serine in calcite opercula of freshwater gastropods of genus Bithynia has been assessed as an age proxy for British Middle and Late Pleistocene sites. Due to decomposition of peptide-bound serine within intra-crystalline protein molecules, alanine/serine ratios increase with sample age, enabling resolution of the marine oxygen-isotope stage of almost all sites and substage resolution for some sites. However, slight overlaps are evident in alanine/serine ratios between some sites from late in one temperate stage and early in the next; this effect results from the low decomposition rates during cold stages, combined with an evident slight dependence of decomposition rates on site conditions. The technique, which can be extended to the Early Pleistocene without technical refinements, is amenable to quantitative calibration using a first-order rate equation, making it feasible in future to present results as numerical ages, subject to an assumed temperature history. Most Pleistocene sites investigated are shown using this technique to have the same ages as previously deduced using biostratigraphy. However, the serine–alanine ages obtained preclude glaciation of southeast England during MIS 16 or of central England during MIS 10.  相似文献   

8.
Oxygen isotope fractionation in dissolved oxygen in the deep sea   总被引：1，自引：0，他引：1  
18O variations in dissolved oxygen have been measured at five stations from the eastern equatorial Pacific, at the GEOSECS-I and -II intercalibration stations in the North Pacific and North Atlantic, and along an Antarctic-South Pacific section from MONSOON expedition. Relative to atmospheric oxygen, dissolved oxygen in the ocean is enriched in18O up to a maximum of 14‰, the extreme enrichments occurring in the oxygen-minimum region of the eastern Pacific. The vertical diffusion-advection model has been used to determine the isotopic fractionation of deep-water in-situ oxygen consumption ascribed to bacterial metabolism. The single-stage enrichment, ε, in Pacific Deep Water below 1 km is 10‰ (α = 0.99,16O consumed preferentially). The model calculations show that the isotopic data cannot be fit without the introduction of a fractionation factor, just as the dissolved oxygen data cannot be fit without an in-situ consumption parameter. The consistency of the positive sign for ε and the negative source term for O2, observed in all deep Pacific profiles analyzed to date, provide strong evidence that vertical transport and in-situ consumption terms dominate the horizontal tracer flux terms, and indicate the presence of a significant “deep metabolism” in abyssal ocean waters.  相似文献   

9.
Significant quantities of aerosol aluminum are transported from continental regions through the atmosphere to the oceans. Enrichments in the concentration of dissolved aluminum in open ocean surface seawater suggest that dissolution of aerosol aluminum is an important source of dissolved aluminum to these waters. Atmospheric aerosols collected at Enewetak Atoll were exposed to seawater and artificial rain water to determine directly the importance of atmospheric deposition as a source of marine dissolved aluminum.The results of these experiments indicate that 8–10% of the aluminum in atmospheric aerosols of crustal origin over the North Pacific is soluble in seawater. Approximately 5–6% dissolves very rapidly ( < 0.6 hr). An additional 3–4% dissolves within 60 hr. This bimodal dissolution of aerosol aluminum of crustal origin suggests that this aluminum is present in two forms. The rapidly dissolving fraction is likely aluminum already weathered from primary minerals, while the more slowly dissolving fraction is probably aluminum from the aluminosilicate matrix.Nearly the same amount of aerosol aluminum dissolved in artificial rain water (pH= 5.5) in 6 hr as dissolved in seawater (pH= 8) in 60 hr. The lower pH appears to not only increase the dissolution rate but may also increase the quantity of aerosol aluminum that dissolves. Dissolved organic matter in seawater appears to have relatively little effect on aerosol aluminum dissolution.Considering measured total aerosol aluminum fluxes, aluminum dissolution of 5–10% would constitute the major source for dissolved aluminum in surface waters of the open North Pacific. The calculated residence time of dissolved aluminum in the upper 100 m of the tropical North Pacific ranges from 2 to 6 years.  相似文献   

10.
On the biophilic nature of iodine in seawater   总被引：1，自引：0，他引：1  
Vertical profiles of concentrations of iodate- and total-iodine have been measured at thirty stations in the Pacific, Atlantic and Antarctic Oceans. The salinity-normalised iodine profiles are indicative of both iodine removal and iodate reduction in the euphotic zone. Thus, surface waters appear to be depleted in iodate-iodine (by 0.03?0.22 μM) but less so in total-iodine (by<0.01?0.06 μM) when compared with the near-constant iodine concentrations (～0.46 μM) at depth. Graphs of specific total-iodine versus specific phosphate fit a linear model well and lie within a narrow envelope for all stations, suggesting a direct coupling of iodine and nutrients during assimilation/regeneration. The I/C atom ratio calculated from these hydrographic data (1.0 × 10?4) agrees well with contemporary plankton compositions (I/C= 1.4 (±0.8) × 10?4). Similar graphs involving specific iodate also fit a linear model well. However, their gradients vary from station to station leading to a variability in I/C interconversion ratio, analogous to the variability of Redfield nutrient ratios for coastal waters. This variation is attributed to changes in both productivity and nitrate availability. Pacific deep waters contain anomalously high total-iodine concentrations which may reflect regional differences of I/P ratio in surface waters or else diffusion of iodine from bottom sediments.  相似文献   

11.
The diagenesis of the hydroxy amino acids serine and threonine in foraminiferal tests has been investigated. The decomposition pathways of these amino acids are complex; the principal reactions appear to be dehydration, aldol cleavage and decarboxylation. Stereochemical studies indicate that the α-amino-n-butyric acid (ABA) detected in foraminiferal tests is the end product of threonine dehydration pathway. Decomposition of serine and threonine in foraminiferal tests from two well-dated Caribbean deep-sea cores, P6304-8 and -9, has been found to follow irreversible first-order kinetics. Three empirical equations were derived for the disappearance of serine and threonine and the appearance of ABA. These equations can be used as a new geochronological method for dating foraminiferal tests from other deep-sea sediments. Preliminary results suggest that ages deduced from the ABA kinetics equation are most reliable because “species effect” and contamination problems are not important for this nonbiological amino acid. Because of the variable serine and threonine contents of modern foraminiferal species, it is likely that the accurate age estimates can be obtained from the serine and threonine decomposition equations only if a homogeneous species assemblage or single species sample isolated from mixed natural assemblages is used.  相似文献   

12.
Manganese in the North Pacific   总被引：1，自引：0，他引：1  
A quantitative and precise method for determination of dissolved Mn at the nanomole(nmol)/kg level in seawater has been developed and used to study the distribution of Mn in the northeast Pacific. Mn concentrations in the surface mixed layer decrease from 1.0 to 0.6 nmol/kg between the central gyre and the western boundary of the California Current, then increase to values from 2 to 6 nmol/kg near the coastal boundary (in contrast to the distribution of210Pb). Particulate Mn in the surface waters accounts for only about 1% of the total.Vertical distributions of Mn are characterized by surface maxima, minima near 300 m, maxima at mid-depth coinciding with the oxygen minimum and the labile nutrient maxima, and concentrations in Pacific bottom waters of approximately 0.2 nmol/kg. The oceanic distribution of Mn appears to be dominated by external inputs superimposed upon overall scavenging which can lead to Mn maxima in (1) the surface waters due to riverine and atmospheric sources; (2) the deep ocean as a result of hydrothermal injection and/or sediment resuspension; and (3) the oxygen minimum region resulting from in-situ breakdown of organic matter, in-situ MnO2 reduction, and/or advective-diffusive transport of dissolved Mn from anoxic slope sediments.  相似文献   

13.
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   

14.
Lead concentrations were determined by isotope dilution mass spectrometry in 34 surface- and deep-water samples collected in the northeast Pacific between Hawaii and California and off the California coast using a deep-water sampler protected against fouling by contamination from the ship and hydrowire. Measured concentrations lie more than one order of magnitude below previously published open ocean values and they show that in most cases 90% or more of the total lead is in a dissolved form. Lead concentrations are about 10-fold higher in surface and thermocline waters than in deep waters; values drop as low as 1 ng/kg (5 pmol/kg) below 3500 m depth. Lead profiles thus appear different compared to those of most trace metals, which show enrichment in deep waters compared to surface concentrations. Lead concentrations in surface waters increase from 5 to 15 ng/kg (25 to 75 pmol/kg) along a transect starting from a location 200 km off the California coast and continuing towards the center of the North Pacific Gyre. This increase is congruent with that observed for210Pb concentrations in the same waters sampled at the same time.Lead is supplied to the open North Pacific largely from the atmosphere, at a rate of about 60 ng/cm2 yr, which exceeds the prehistoric oceanic output flux of authigenic lead recorded in pelagic sediments about tenfold. This excess originates from emissions from smelters and combustion of leaded gasoline, overwhelming natural lead inputs that entered the ocean during prehistoric time probably largely through rivers. Vertical lead concentration profiles below the surface mixed layer are probably not in steady state. There, concentrations must be increasing in response to the increase of anthropogenic inputs because the estimated lead residence times are more than 20 years in the thermocline and about 80 years in deep waters. Based on an estimated 10-fold input and concentration increase since the mid-eighteenth century in the surface mixed layer in the central northeast Pacific, it is calculated that the 10 ng/kg average concentration between 100 and 900 m is 2 to 5 times larger, and the 1.8 ng/kg average concentration between 900 and 5000 m depth is about 2 times larger than it was in the mid-eighteenth century. Profiles of lead concentrations in the North Atlantic are expected to be shifted generally to larger values by a factor of 2 to 3 compared to those in the North Pacific because of the effects of greater industrial lead contamination, while lead concentration profiles in the South Pacific are expected to be shifted generally to lower values compared to the North Pacific by about this same factor because of the effects of lesser industrial lead contamination.  相似文献   

15.
The deep-sea environment is among the most stable on Earth, making it well suited for amino acid geochronology. Foraminifera with calcareous tests are distributed across the World Ocean and are often recovered in sufficient abundance from sediment cores to derive robust mean amino acid D/L values of multiple replicates from each stratigraphic level. The extent of racemization (D/L) can be compared with independent age control, which in most cases is based on correlation with global marine oxygen-isotope stages and radiocarbon ages from the same stratigraphic levels. In this study, we report the results of amino acid racemization analysis of multiple foraminifera species from well-dated sediment cores taken from the Pacific, Atlantic, and Arctic oceans. The composite of results analyzed to date (179 samples, each composed of an average of 8.6 subsamples = 1531 analyses) show that D/L values generally increase systematically down core, and are similar for samples of comparable ages from different deep-sea sites. Previously published equations that relate D/L values of aspartic and glutamic acids to post-depositional temperature and sample age for Pulleniatina obliquiloculata generally conform to the D/L trends for species analyzed in this study. Laboratory heating experiments were used to quantify the difference in the rate of racemization between P. obliquiloculata and other taxa. For example, aspartic acid in P. obliquiloculata racemizes an average of 12–16% faster than in the common high-latitude species, Neogloboquadrina pachyderma (s). Apparently, the unexpectedly high D/L values previously reported for N. pachyderma (s) older than 35 ka from the Arctic Ocean cannot be attributed to taxonomic effects.  相似文献   

16.
When mollusc shells are analysed conventionally for amino acid geochronology, the entire population of amino acids is included, both inter- and intra-crystalline. This study investigates the utility of removing the amino acids that are most susceptible to environmental effects by isolating the fraction of amino acids encapsulated within mineral crystals of mollusc shells (intra-crystalline fraction). Bleaching, heating and leaching (diffusive loss) experiments were undertaken on modern and fossil Corbicula fluminalis, Margaritifera falcata, Bithynia tentaculata and Valvata piscinalis shells. Exposure of powdered mollusc shells to concentrated NaOCl for 48 h effectively reduced the amino acid content of the four taxa to a residual level, assumed to represent the intra-crystalline fraction. When heated in water at 140 °C for 24 h, only 1% of amino acids were leached from the intra-crystalline fraction of modern shells compared with 40% from whole shell. Free amino acids were more effectively retained in the intra-crystalline fraction, comprising 55% (compared with 18%) of the whole shell after 24 h at 140 °C. For fossil gastropods, the inter-shell variability in D/L values for the intra-crystalline fraction of a single-age population was reduced by 50% compared with conventionally analysed shells. In contrast, analysis of the intra-crystalline fraction of C. fluminalis does not appear to improve the results for this taxon, possibly due to variability in shell ultrastructure. Nonetheless, the intra-crystalline fraction in gastropods approximates a closed system of amino acids and appears to provide a superior subset of amino acids for geochronological applications.  相似文献   

17.
We report here on particulate and dissolved210Pb profiles at 16 stations, and on total210Pb profiles at 3 stations, all occupied during the Pacific GEOSECS expedition. Comparison with measurements at Yale on GEOSECS library samples indicates that during separation of particulate lead from dissolved lead, our filtered water samples suffered some loss of210Pb in the filtration system; this effect appears to have reduced the dissolved210Pb activities by ～ 20% in stations where the water was filtered. However, for these first Pacific data on the210Pb distribution between the two phases, this effect does not significantly interfere with our recognition of the major features of both particulate and dissolved210Pb distributions.The dissolved210Pb profiles in general vary geographically, following the226Ra profiles. In deep water,226Ra increases northward and eastward from the southwest Pacific, from ～ 22dpm/100kg, to over 40 dpm/100 kg in the northeast Pacific. Our dissolved210Pb profiles show a similar increase in deep water, varying from about 10 to 20 dpm/100 kg along this line, and are commonly characterized by a mid-depth maximum. This210Pb maximum reflects the mid-depth226Ra maximum of the Pacific Deep Water observed along the western boundary current.In surface water at low latitudes there is a significant210Pb flux from the atmosphere, which produces a210Pb/226Ra activity ratio generally greater than unity. This flux penetrates as deep as 600 m, as indicated by an “induced”210Pb minimum caused by the surface maximum. The surface water210Pb excess decreases toward high southern latitudes and vanishes in the Circumpolar region.The particulate210Pb profiles show a general increase with depth, from ～ 0.3dpm/100kg in subsurface water to ～ 1.5dpm/100kg in bottom water, with or without a mid-depth maximum that reflects the226Ra or dissolved210Pb maximum. The particulate210Pb normally comprises about 2% of the total210Pb in subsurface water, and this fraction increases to about 10% near the bottom. As the filtration loss is not taken into account, the fraction of particulate210Pb quoted here is an upper limit. Since the particulate matter concentrations are quite uniform in the water column below a few hundred meters, the210Pb activity of the particulate matter also increases with depth. The particulate matter has a210Pb concentration of ～ 100dpm/g in subsurface water, but the concentration increases to ～ 500dpm/g or more toward the bottom. This indicates that there is a cumulative adsorption of Pb onto the suspended particles as they are sinking through the water column.  相似文献   

18.
Radium-barium-silica relationships are examined in various regions of the Pacific. Ra, Ba and Si are not linearly correlated except in the Circumpolar region. From surface water to the intermediate water, Ra usually increases linearly with Ba and Si. In the North Pacific where there is a Ra excess in the deep water, both the Ra-Ba and Ra-Si diagrams show curves concave upward with an increasing slope. The relationships are further complicated by a deep gentle Ba maximum and a broad mid-depth Si maximum.In the western boundary where the Antarctic Bottom Water and Pacific Deep Water are separated by the benthic front, the Ra-Ba and Ra-Si plots show “hooks” of various size and shape caused by a discordance in the depths of the Ra, Ba and Si maxima. The hook becomes smaller toward the south and flips from counterclockwise to clockwise in the southern basin.A two-dimensional horizontal model with a geostrophic circulation pattern is employed to calculate Ra distribution in the deep water with a constant upwelling rate but a variable mean input rate for Ra. The mean input rate or fluxF is the sum of the in-situ production rateJ by particulate dissolution in the water column and the bottom fluxQb. The global mean fluxF needed to balance the radiodecay in a steady-state distribution is used as a reference for discussion. It is found that anF value set at1.5 ×F fits the observed data in the deep Atlantic. TheF value needs to be about2.7 ×F in order to produce a comparable distribution in the deep Pacific. These model calculations indicate that a Ra source is required in the northeast Pacific. It appears that no uniqueF can produce a global Ra distribution in deep water comparable to both the Atlantic and Pacific observations. This is also true within the Pacific Ocean itself because of the large Ra excess observed in the northeast Pacific. Thus the Ra input rate is quite variable and increases by a factor of two from the Atlantic to the Pacific. This probably reflects the non-uniformity of the bottom fluxQb rather than that of the in-situ productionJ in the world oceans.  相似文献   

19.
Water sampling during the 1993 IV Russian–US Joint Expedition to the Bering and Chukchi Seas (BERPAC) indicates that Pacific Ocean burdens of the long-lived radionuclide 129I are relatively low in the Pacific-influenced Arctic, particularly compared to high latitude waters influenced by the North Atlantic. These low concentrations occur despite the presence of potential submerged anthropogenic sources in the East Sea (Sea of Japan), and in the northwest Pacific Ocean, east of the Kamchatka Peninsula. The concentration of 129I entering the Arctic Ocean through Bering Strait, 0.7×108 atoms kg−1, is only slightly higher than observed in deep Pacific waters. Similar concentrations (0.44–0.76×108 atoms kg−1) measured in Long Strait indicate no significant transfer of 129I eastward into the Chukchi Sea in the Siberian Coastal Current from the Siberian marginal seas to the west. However, the concentrations reported here are more than an order of magnitude higher than the Bering Strait input concentration estimated (1.0×106 atoms kg−1) from bomb fallout mass balances, which supports other existing evidence for a significant atmospheric deposition term for this radionuclide in surface ocean waters. Near-bottom water samples collected in productive waters of the Bering and Chukchi Seas also suggest that sediment regeneration may locally elevate 129I concentrations, and impact its utility as a water mass tracer. As part of this study, two deep 129I profiles were also measured in the East Sea in 1993–1994. The near-surface concentration of 129I ranged from 0.12 to 0.31×108 atoms kg−1. The 129I concentration showed a steady decrease with depth, although because of active deep water ventilation, the entire 3000 m water column exceeded natural concentrations of the radionuclide. Atom ratios of 129I/137Cs in the East Sea also suggest an excess of 129I above bomb fallout estimates, also possibly resulting from atmospheric deposition ultimately originating from nuclear facilities.  相似文献   

20.
By modelling the observed distribution of210Pb and210Po in surface waters of the Pacific, residence times relative to particulate removal are determined. For the center of the North Pacific gyre these are τPo = 0.6years andτPb = 1.7years. The surface ocean τPb is determined by particulate transport rather than plankton settling. The fact that it is about two orders of magnitude smaller than τPb for the deep ocean implies a sharp change in the adsorptive quality of particles during descent through the water column.  相似文献   

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