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1.
Seasonal and spatial variations of particulate organic carbon (POC) flux were observed with sediment traps at three sites in the Japan Sea (western and eastern Japan Basin and Yamato Basin). In order to investigate the transport processes of POC, radiocarbon (14C) measurements were also carried out. Annual mean POC flux at 1 km depth was 30.7 mg m−2day−1 in the western Japan Basin, 12.0 mg m−2day−1 in the eastern Japan Basin and 23.8 mg m−2day−1 in the Yamato Basin. At all stations, notably higher POC flux was observed in spring (March–May), indicating biological production and rapid sinking of POC in this season. Sinking POC in the high flux season showed modern Δ14C values (>0‰) and aged POC (Δ14C < −40‰) was observed in winter (December–January). The Δ14C values in sinking POC were negatively correlated with aluminum concentration, indicating that Δ14C is strongly related to the lateral supply of lithogenic materials. The Δ14C values also showed correlations with excess manganese (Mnxs) concentrations in sinking particles. The Δ14C-Mnxs relationship suggested that (1) the majority of the aged POC was advected by bottom currents and incorporated into sinking particles, and (2) some of the aged POC might be supplied from the sea surface at the trap site as part of terrestrial POC. From the difference in the Δ14C-Mnxs relationships between the Japan Basin and the Yamato Basin, we consider that basin-scale transport processes of POC occur in the Japan Sea.  相似文献   

2.
Intermediate Waters in the East/Japan Sea   总被引：4，自引：0，他引：4  
Properties of the intermediate layer in the East/Japan Sea are examined by using CREAMS data taken mainly in summer of 1995. Vertical profiles of potential temperature, salinity and dissolved oxygen and relationships between these physical and chemical properties show that the dissolved oxygen concentration of 250 μmol/l, roughly corresponding to 0.6°C at the depth of about 400 db, makes a boundary between intermediate and deep waters. Water colder than 0.6°C has a very stable relationship between potential temperature and salinity while salinity of the water warmer than 0.6°C is lower in the western Japan Basin than that in the eastern Japan Basin. The low salinity water with high oxygen corresponds to the East Sea Intermediate Water (ESIW; <34.06 psu, >250 μmol/l and >1.0°C) which was previously identified by Kim and Chung (1984) and the high salinity water with high oxygen found in eastern Japan Basin is named as the High Salinity Intermediate Water (HSIW; >34.07 psu, >250 μmol/l and >0.6°C). Spatial distribution of salinity and acceleration potential on the surface of σϑ = 27.2 kg/m3 shows that the ESIW prevailing in the western Japan Basin is transported eastward by a zonal flow along the polar front near 40°N and a cyclonic gyre in the eastern Japan Basin is closely related to the HSIW. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

3.
Tritium (3H or T) has been produced mostly by atmospheric nuclear weapon tests, and entered the ocean in the form of water (HTO). As tritium exists as water itself, it has been regarded as an ideal tool to study the transport of water masses. In April 2001 we collected water samples in the western Japan Basin (WJB) for tritium and helium measurement. The timely sampling provided direct evidence of the bottom water formation, resulting in the drastic increase in tritium concentration from 0.3 TU in 2000 to 0.67 TU in 2001. Considering that the new bottom waters were found mostly in the WJB, it implies that maximum 1% of the whole bottom layer below 2600 m should be replaced with the surface water during the severely cold winter 2000—2001.3H-3He age, showing the elapsed time since the water left from the surface, can be used to calculate oxygen utilization rate by dividing AOU by the age. Under the condition of 90% oxygen saturation in the surface water, the integration of OUR in the water column below 200 m yields net oxygen consumption of 12 mol (O2) m-2 yr-1, which corresponds to the export production of 99 g C m-2 yr-1 . This estimate is comparable to a previous estimate based on satellite data and implies that the ratio of export to primary production (f -ratio) is as high as 0.5 in the WJB.  相似文献   

4.
Water masses in the East Sea are newly defined based upon vertical structure and analysis of CTD data collected in 1993–1999 during Circulation Research of the East Asian Marginal Seas (CREAMS). A distinct salinity minimum layer was found at 1500 m for the first time in the East Sea, which divides the East Sea Central Water (ESCW) above the minimum layer and the East Sea Deep Water (ESDW) below the minimum layer. ESCW is characterized by a tight temperature–salinity relationship in the temperature range of 0.6–0.12 °C, occupying 400–1500 m. It is also high in dissolved oxygen, which has been increasing since 1969, unlike the decrease in the ESDW and East Sea Bottom Water (ESBW). In the eastern Japan Basin a new water with high salinity in the temperature range of 1–5 °C was found in the upper layer and named the High Salinity Intermediate Water (HSIW). The origin of the East Sea Intermediate Water (ESIW), whose characteristics were found near the Korea Strait in the southwestern part of the East Sea in 1981 [Kim, K., & Chung, J. Y. (1984) On the salinity-minimum and dissolved oxygen-maximum layer in the East Sea (Sea of Japan), In T. Ichiye (Ed.), Ocean Hydrodynamics of the Japan and East China Seas (pp. 55–65). Amsterdam: Elsevier Science Publishers], is traced by its low salinity and high dissolved oxygen in the western Japan Basin. CTD data collected in winters of 1995–1999 confirmed that the HSIW and ESIW are formed locally in the Eastern and Western Japan Basin. CREAMS CTD data reveal that overall structure and characteristics of water masses in the East Sea are as complicated as those of the open oceans, where minute variations of salinity in deep waters are carefully magnified to the limit of CTD resolution. Since the 1960s water mass characteristics in the East Sea have changed, as bottom water formation has stopped or slowed down and production of the ESCW has increased recently.  相似文献   

5.
The East/Japan Sea is a mid-latitude marginal sea that has undergone dramatic changes during the last 50–60 years. One of the most prominent characteristics of these changes is a rapid decrease in the amount of dissolved oxygen in deep waters. As a consequence of these changes, some investigators have even argued that the East/Japan Sea might become an anoxic sea in the next 200 years. While the causes of these changes are still under investigation, it has been shown that they are mainly due to modifications in the mode of the deep water ventilation system in the East/Japan Sea: a slowdown and complete cessation of bottom water formation accompanied by an enhancement of upper water formation instead. A simple moving-boundary box model (MBBM) was developed in order to analyze and quantify the processes involved in such changes over the last 50–60 years. Using a MBBM, we estimated the levels of several conservative chemical tracers (CFCs, Tritium, SF6, 137Cs) and bioactive tracers (oxygen and phosphate) in the deep water masses of the East/Japan Sea, comparing these with the historical data available, and making predictions for the near future. The model predicts that the East/Japan Sea should remain well-oxygenated, despite recent rapid oxygen decreases in its deep waters, accompanied by such structural changes as a shrinking of its oxygen-depleted deeper waters and an expansion of its oxygen-rich upper waters over the next few decades.  相似文献   

6.
We investigated the biogenic components (biogenic opal, calcium carbonate, and organic carbon) of the marine sediments in core TY99PC18 recovered from the southeastern part of the Ulleung Basin, East Sea (Japan Sea). Our results indicate that primary productivity by diatoms increased after the last glaciation (15,000 14C years b.p.) probably because of the onset of vertical mixing of seawater and nutrient supply from the deep water. Between 5,000 and 10,000 14C years b.p. a shift in the dominant primary producer, i.e. from diatoms to coccolithophores, coincides with decreased productivity, which could be related to the influx of warm, low-nutrient waters at that time. During the late Holocene (after 5,000 14C years b.p.) the productivity of diatoms increased once more probably due to renewed ventilation and vertical mixing.  相似文献   

7.
Natural marine gas hydrate was discovered in Korean territorial waters during a 2007 KIGAM cruise to the central/southwestern Ulleung Basin, East Sea. The first data on the geochemical characterization of hydrate-bound water and gas are presented here for cold seep site 07GHP-10 in the central basin sector, together with analogous data for four sites (07GHP-01, 07GHP-02, 07GHP-03, and 07GHP-14) where no hydrates were detected in other cores from the central/southwestern sectors. Hydrate-bound water displayed very low concentrations of major ions (Cl−, SO42−, Na+, Mg2+, K+, and Ca2+), and more positive δD (15.5‰) and δ18O (2.3‰) signatures compared to seawater. Cl– freshening and more positive isotopic values were also observed in the pore water at gas hydrate site 07GHP-10. The inferred sulfate–methane interface (SMI) was very shallow (<5 mbsf) at least at four sites, suggesting the widespread occurrence of anaerobic oxidation of methane (AOM) at shallow sediment depths, and possibly high methane flux. Around the SMI, pore water alkalinity was very high (>40 mM), but the carbon isotopic ratios of dissolved inorganic carbon (δ13CDIC) did not show minimum values typical of AOM. Moreover, macroscopic authigenic carbonates were not observed at any of the core sites. This can plausibly be explained by carbon with high δ13C values diffusing upward from below the SMI, increasing alkalinity via deep methanogenesis and eventually escaping as alkalinity into the water column, with minor precipitation as solid phase. This contrasts, but is not inconsistent with recent reports of methane-fuelled carbonate formation at other sites in the southwestern basin sector. Methane was the main hydrocarbon component (>99.85%) of headspace, void, and hydrate-bound gases, C1/C2+ ratios were at least 1,000, and δ13CCH4 and δDCH4 values were in the typical range of methane generated by microbial reduction of CO2. This is supported by the δ13CC2H6 signatures of void and hydrate-bound gases, and helps clarify some contradictory interpretations existing for the Ulleung Basin as a whole. In combination, these findings suggest that deep biogenic gas and pore waters migrate upward through pathways such as hydrofractures, and measurably influence the shallow carbon cycle. As a result, cation-adjusted alkalinity/removed sulfate diagrams cannot always serve to estimate the degree of alkalinity produced by sulfate reduction and AOM in high methane flux areas.  相似文献   

8.
Hydrographic observations have revealed detailed structure of the Bottom Water in the Japan Sea. The Yamato Basin Bottom Water (YBBW) exhibits higher temperatures and lower dissolved oxygen concentrations than those found in the Japan Basin Bottom Water (JBBW). Both Bottom Waters meet around the boundary region between the Yamato and the Japan Basins, forming a clear benthic front. The structure of the benthic front suggests an estuary-like water exchange between both Basins, with the inflow from the Japan Basin passing under the outflow from the Yamato Basin. It is inferred from the property distributions that the JBBW flowing into the Yamato Basin is entrained by the cyclonic circulation in the basin, and modified to become the YBBW. Vertical diffusion and thermal balance in the YBBW are examined using a box model. The results show that the effect of geothermal heating has about 70% of the magnitude of the vertical thermal diffusion and both terms cancel the advection term of the cold JBBW from the Japan Basin. The box model also estimates the turnover time and vertical diffusivity for the YBBW as 9.1 years and 3.4 × 10−3 m2s− 1, respectively.  相似文献   

9.
The long-term variation of water properties in the upper portion of the Japan Sea Proper Water (UJSPW) is examined on the basis of hydrographic data at PM10, located on the northwestern Japan Sea, and at PM05, in the Yamato Basin, taken from 1965 through 1982. At PM10, located at the southern boundary of the UJSPW formation region, dissolved oxygen fluctuations on the UJSPW core showed negative correlation with phosphate variations, but showed no signficant correlation with salinity variations. At PM05 water properties fluctuated with smaller amplitudes than those at PM10 except for salinity. Dissolved oxygen variations at PM10 lead those at PM05 by 12–15 months, suggesting that the UJSPW near PM10 circulates into the Yamato Basin spending 12–15 months. Increases of dissolved oxygen contents in summer on relevant isopycnal surfaces at PM10 occurred after cold and/or windy winters except for two of eight; this suggests that larger volume of the UJSPW is formed in severa winter. Rough estimations of the formation rate and existing volume of the UJSPW are made on the basis of a climatological dataset; 1.5×104 km3 yr–1 and 27.3×104 km3, respectively. The ventilation time of the UJSPW, 18.2 years, is about one tenth or less of residence time for the entire Japan Sea Proper Water. This indicates that the UJSPW is renewed about ten times as quick as the deeper water.  相似文献   

10.
The water under the main thermocline in the Japan Sea is a single water mass referred to as the Japan Sea Proper Water. It can be defined as having temperature below 2.0°C, salinity above 34.00%, and dissolved oxygen below 7.0 ml 1−1. In the north most of the water above the potential temperature 0.1°C depth (about 800–1000 m) is a mode water, with σθ of 27.32 to 27.34 kg m−3. North of 40°N it has high oxygen (more than 6.00 ml 1−1) with a distinct discontinuity (oxygen-cline) at the bottom of the mode water. The most probable region for the formation of the water is the area north of 41°N between 132° and 134°E. The deeper water probably is formed in the norther area of 43°N, and directly fills the main part of the Japan Basin north of 41°N and east of 134°E.  相似文献   

11.
This paper reports all available geochemical data on sediments and pore waters from the Xisha Trough on the northern continental margin of the South China Sea. The methane concentrations in marine sediments display a downhole increasing trend and their carbon isotopic compositions (δ 13C = −25 to −51‰) indicate a thermogenic origin. Pore water Cl− concentrations show a range from 537 to 730 mM, and the high Cl− samples also have higher concentrations of Br−, Na+, K+, and Mg2+, implying mixing between normal seawater and brine in the basin. The SO4 2− concentrations of pore waters vary from 19.9 to 36.8 mM, and show a downhole decreasing trend. Calculated SMI (sulfate-methane interfaces) depths and sulfate gradients are between 21 and 47 mbsf, and between −0.7 and −1.7 mM/m, respectively, which are similar to values in gas hydrate locations worldwide and suggest a high methane flux in the basin. Overall, the geochemical data, together with geological and geophysical evidence, such as the high sedimentation rates, high organic carbon contents, thick sediment piles, salt and mud diapirs, active faulting, abundant thermogenic gases, and occurrence of huge bottom simulating reflector (BSR), are suggestive of a favorable condition for occurrence of gas hydrates in this region.  相似文献   

12.
The δ18O, δ13C and trace element composition of pearls collected from Ago Bay, Japan, were investigated in order to evaluate biomineralization in the cultured pearl oyster (Pinctada fucata martensii). The oxygen isotopic data suggest that the pearls were produced around 23–24°C, mainly in June to early July, which is consistent with their occurrence in the field. Therefore the pearls were produced under or close to isotopic equilibrium conditions, although they showed high calcification rates (higher than 0.2–1.0 g cm− 2yr−1) under which, for example, coral skeletons (calcification rate ∼0.28 g cm− 2yr−1) often show non-equilibrium isotope partitioning. The δ13C values were ∼− 2.9‰ lower than those calculated for offshore waters under equilibrium conditions. This may be due to low-δ13C bottom waters resulting from the degradation of organic matter (OM) or to a contribution of low-δ 13C food. In the latter case, a simple mass balance calculation gives a respiration component of 14%. Twelve trace elements of bulk pearl samples were classified into four groups on the basis of their enrichment/depletion patterns relative to seawater and inter-element relationships: group 1, Co, Cr, Pb; group 2, Ba, Cs, U; group 3, Cu, Sn, V, and group 4, Mn, Rb, Mo. Comparison with coral skeletons suggests that Ba and Mn (groups 2 and 4) were definitely much enriched in proteinaceous OM relative to aragonite crystals in pearls and that V (group 3) in pearls showed only slight enrichment in the organicrich layer. By contrast, the other elements showed small differences between both layers (enrichment factor of <3), suggesting that these elements occur largely in aragonite crystals.  相似文献   

13.
Temporal changes in nitrogen isotopic composition (δ15N) of the NO3 − pool in the water column below the pycnocline in Ise Bay, Japan were investigated to evaluate the effect of nitrification on the change in the δ15N in the water column. The δ15N of NO3 − in the lower layers varied from −8.5‰ in May to +8.4‰ in July in response to the development of seasonal hypoxia and conversion from NH4 + to NO3 −. The significantly 15N-depleted NO3 − in May most likely arose from nitrification in the water column. The calculated apparent isotopic discrimination for water column nitrification (ɛnit = δ15Nsubstrate − δ15Nproduct) was 24.5‰, which lies within the range of previous laboratory-based estimates. Though prominent deficits of NO3 − from hypoxic bottom waters due to denitrification were revealed in July, the isotopic discrimination of denitrification in the sediments was low (ɛdenit = ∼1‰). δ15NNO3 in the hypoxic lower layer mainly reflects the isotopic effect of water column nitrification, given that water column nitrification is not directly linked with sedimentary denitrification and the effect of sedimentary denitrification on the change in δ15NNO3 is relatively small.  相似文献   

14.
Sediment cores collected in 1990 from the Gulf of California have been studied using stable isotope and radiocarbon techniques to reconstruct the climate and ventilation histories since the last glacial maximum. Benthic foraminiferal δ18O from core tops in a water depth range of 145 to 1442 m increases by about 2% with increasing depth. This is consistent with a composite temperature profile constructed from several hydrocasts in the various gulf basins. However, the δ18O water/salinity relationship is not sufficiently linear in gulf locations or in nearby open Pacific Geochemical Ocean Sections Study (GEOSECS) stations to be useful in solving paleotemperature equations. Of the most common benthic foraminifera, only Planulina ariminensis has δ13C that is consistent with the measured δ13C of ΣCO2. Several cores in the depth range 500 to 900 m have the laminated Holocene and Bolling/Allerod sediments, and the nonlaminated glacial age and Younger Dryas sediments that are typical of the gulf and other locations such as Santa Barbara Basin. The best of those, Jumbo Piston Core (JPC) 56 from 818 m water depth on the western margin of Guaymas Basin, was sampled for intensive study. Oxygen isotope ratios in benthic and planktonic foraminifera show little evidence for deglacial temperature oscillations. Carbon isotope ratios are generally lower during warm epochs, but the most striking result is strongly lowered benthic and planktonic δ13C about 9500 years ago. This may reflect water column oxidation of locally released methane. Neither benthic δ13C in depth section nor paired benthic and planktonic 14C data in JPC56 are consistent with increased intermediate water ventilation during the glacial maximum and Younger Dryas. Likewise, 14C data from 5 pairs of foraminifera from the Okhotsk Sea fail to support better ventilation in that basin during the last glacial maximum. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

15.
The data of meteorological and oceanographic observations on the northwest shelf of the Black Sea for 1973–2000 are used to compute the characteristics of the entire area in the presence of hypoxia of waters under the pycnocline in the summer–autumn period and the area of surface waters with a level of salinity lower than 17.5‰ in May. The time of onset of the spring warming of air (stable transition through a temperature of 5°) is determined. A statistically significant positive trend of the air temperature (0.8° per 100 yr) is revealed in Odessa. The process of warming was observed mainly for the winter (1.5° per 100 yr) and spring (0.8° per 100 yr) periods and became especially intense since the beginning of the 1990s. On the basis of the data of correlation analyses, we establish a statistically significant relationship between the large-scale atmospheric processes [the index of North Atlantic Oscillation (NAO) and the wind conditions], the area of surface waters whose salinity is lower than 17.5‰, and the total area with hypoxia in the summer–autumn periods. For positive mean values of the NAO index (in January–March), we most often observe early spring with elevated repetition of the south and west winds with subsequent development of hypoxia in large areas of the northwest shelf. We propose an empirical regression model for the prediction of the total area of summer–autumn hypoxia of waters with predictors: the onset of the spring warming of air and the area of propagation of waters whose salinity is lower than 17.5‰ in May. The maximum error of prediction of the area with hypoxia does not exceed 5.5 ⋅ 103 km2, i.e., less than 2% of the total area of the northwest shelf in the Black Sea (to the north of 45°N).  相似文献   

16.
 Recent sediment accumulation rates are 18–230 mg cm-2 yr-1 (0.02–0.2 cm yr-1) based on excess 210Pb activity profiles in the southwestern part of the East Sea (Sea of Japan). Assuming no mixing beneath surface mixed layers, 210Pb-derived sediment accumulation rates are 18–32 mg cm-2 yr-1 in the northern part of the Yamato Ridge and the Ulleung Basin, 29–136 mg cm-2 yr-1 in the Korea Plateau, and 230 mg cm-2 yr-1 in the southern shelf. These values generally agree with long-term sedimentation rates estimated from dated ash layers. Received: 6 October 1995 / Revision received: 31 May 1996  相似文献   

17.
Since 1960 when I was a senior student, I have studied natural phenomena observed in the hydrosphere and atmosphere by means of chemical elements. Each of the phenomena is, in general, very complicated and so I have attempted to depict the whole picture of material circulation in the marine environment by studying its various aspects at the same time. My chief strategy has been to use natural radio-nuclides as clocks of various phenomena, and to use sediment traps for the determination of vertical fluxes in the ocean. The many results I have obtained can be summarized as follows. 1. I have found that several sporadic events control the material exchange through the atmosphere. These include the strong winter monsoon and typhoons that transport sea-salt particles to the Japanese Islands, theKosa episodes that transport soil dust to the ocean, and storms that result in exchange of sparingly soluble gases such as oxygen and carbon dioxide at the air-sea interface. I have also proved quantitatively that the source of aluminosilicate material in pelagic sediments is air-borne dust. 2. I have proposed a model,Settling model, for the removal of chemical substances from the ocean and found various lines of evidence supporting the model. This model predicts the reversibility in the existing state of insoluble chemical elements in seawater among large settling particles, small suspended particles and colloidal particles that pass through a membrane filter and explains well their behavior in the ocean. I have first precisely measured calcium and iodine in the ocean and have explained their distributions on the basis of the solution and redox equilibria. 3. Using chemical tracers, I have estimated the vertical eddy diffusion coefficients to be 1.2 cm2sec−1 for the Pacific deep water, 0.5 cm2sec−1 for the deep Bering Sea water and 3–80 cm2sec−1 for the Pacific surface water, and have studied the structure of water masses in the western North Pacific and the Sea of Japan. I have also invented and applied a method for the calculation of the age of deep waters using radiocarbon. 4. I have calculated the rates of decomposition of organic matter and the regeneration rates of chemical components in the deep and bottom waters as well as coastal waters by modelling water circulation and mixing. Particulate fluxes and regeneration rates are larger in the deep waters beneath the more biologically productive surface waters. I have stressed the role of silicate in the marine ecosystem, especially in the succession of phytoplankton species. 5. I have quantitatively studied the migration of chemical elements during the early diagenesis of bottom sediments especially manganese using chemical and radiochemical techniques. Manganese is being actively recycled not only in coastal seas but also in pelagic sediments except in the highly oligotrophic subtropical ocean. This recycling can explain the formation of manganese nodules and enables us to balance the manganese budget in the ocean.  相似文献   

18.
According to the results of the international expedition aboard the R/Vs Roger Revelle and Professor Khromov in the summer 1999, areas with low oxygen contents (below 210 μM/kg) and those with increased contents of dissolved inorganic carbon and phosphates were found that roughly coincided with one another. These areas are located near the bottom on the southwestern slope of the Tsushima Basin in the region of the Korea Strait and on the continental slope in the region of the Tatar Strait in the northern part of the sea at about 46° N. The set of hydrochemical data points to a high geochemical activity in the near-bottom layer of the areas noted. This activity is confirmed by direct observations of the composition of the interstitial water in the sediments collected in the northern part of the sea during the expedition of R/V Akademik M.A. Lavrent’ev in 2003. It was supposed that the main cause of the increased geochemical activity is the runoff of suspended and dissolved matter from the Korea and Tatar straits. In the areas mentioned, the near-bottom waters are characterized by low values of the nitrogen-phosphorus ratio (below 10), which is geochemical proof of the denitrification process occurring under the conditions of high oxygen concentrations characteristic of the Sea of Japan. Based on the value of the annual production in the Sea of Japan, a rate of denitrification equal to 3.4 × 1012 gN/year was calculated. Hence, it is confirmed that the geochemical processes in the near-bottom layer have a direct influence on the spatiotemporal characteristics of the hydrochemical properties of the waters of the Sea of Japan.  相似文献   

19.
The importance of the North Pacific Intermediate Water as a sink for the anthropogenic carbon dioxide has been examined by mapping chemical and radiochemical properties at two isopycnal surfaces of of 26.6 ad 27.2 obtained in 1970's. Its radiocarbon contents in 1980's were determined for comparison. The isopleths of depth and salinity at the two isopycnal surfaces obviously show that the intermediate layer of the entire mid-latitudes of the North Pacific is occupied by a similar water mass. The distributions of dissolved oxygen contents and Si/N ratios in the intermediate water indicate its source in the northwestern North Pacific and its sink in the eastern Pacific. The 14C values clearly designate the intrusion of the artificial radiocarbon of mostly 1960's origin into the upper intermediate water of the western North Pacific having its maximum in the subarctic zone of 40–45°N and 160–180°E in 1973. The maximum region for tritium is much broader extending to the north. These suggest that the subboreal region is active in the gas exchange and/or the warm water residing for a long time at the surface and flowing into the region across the subarctic front sinks quickly in winter. At the lower isopycnal surface, the increase 14C value for 14±4 years was around 27, which is smaller than that expected from the total carbonate increase, indicating an active isopycnal mixing.  相似文献   

20.
Dissolved and total dissolvable manganese concentrations have been measured at four stations in the western North Atlantic Ocean. Total dissolvable manganese concentrations are high in surface waters, decrease to uniformly low levels throughout the bulk of the water column, and increase in the bottom nepheloid layer. Dissolved Mn (Mnd) concentrations follow the total dissolvable concentrations throughout the surface and deep waters but do not increase in the near-bottom waters.Deep water concentrations of Mnd decrease from 30 ng l?1 in the Newfoundland Basin to 20 ng l?1 in the Sargasso Sea. This change and other features of the deep water distribution of dissolved manganese could be associated with the slow oxidation of Mn2+ to MnO2. There is also evidence at one station of scavenging of manganese from the dissolved phase in the near-bottom layer which may again be related to the kinetics of manganese oxidation.  相似文献   

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