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1.
Tritium and 14C data of the “GOGO I” station at 28.5°N, 121.6°W in November 1971 are reported. The tritium decline between 150 and 350 m depth is as pronounced as was observed on a previous occupation of the same position, station “Geosecs I” in September 1969, and the tritium concentrations below 200 m are unchanged. 14C data from the depth range of tritium decline are corrected for fallout 14C contribution. The correcting procedure requires simultaneous measurements of 14C, ΣCO 2, and tritium. It is concluded that the natural absolute 14C concentration attains a maximum near 400 m depth, of 7.5% excess over that of surface water. 相似文献
2.
A two-? ocean reservoir model is employed to examine the combined effects of vertical ocean circulation, organic matter extraction and cosmic ray production on the 14C/ 12C in the atmosphere, ocean and sediment. In this model, dissolution of deep-sea calcium carbonate sediment is assumed to respond to the supply of particulate carbonate from the surface ocean and to the dissolved carbonate-ion concentration of the deep-sea.If the vertical ocean circulation decreased by 50% during the maximum rate of deglaciation, the atmospheric 14C/ 12C would have increased concurrently by 10% relative to the pre-bomb present. Further, if cosmic ray production of 14C was 50% greater than present at about 7800 years B.P. as suggested by archeomagnetic measurements, a double maximum of 10% occurs. The first is at about 10.5 ka and the second at 6.5 ka. This result is similar to the variation of 14C/ 12C over the last 10,000 years calculated from the 14C dates measured by Stuiver on the varved Lake of the Clouds. The result is not sensibly altered if 10 17 moles of organic carbon is extracted from the ocean during sea-level rise.Reduction of the thermohaline ocean circulation by 50% over a one- to two-thousand-year interval would not be sensibly detected in the dating of deep-sea sediment. If Broecker's organic nutrient extraction occurs in conjunction with reduction of vertical circulation, a decrease in the atmospheric PCO2 will precede the eventual rise. 相似文献
3.
A high-precision tree-ring record of the atmospheric 14C levels between 1820 and 1954 is presented. Good agreement is obtained between measured and model calculated 19th and 20th century atmospheric Δ 14C levels when both fossil fuel CO 2 release and predicted natural variations in 14C production are taken into account. The best fit is obtained by using a ?-diffusion model with an oceanic eddy diffusion coefficient of 3 cm 2/s, a CO 2 atmosphere-ocean gas exchange rate of 21 moles m ?2 yr ?1 and biospheric residence time of 60 years.For trees in the state of Washington the measured 1949–1951 atmospheric Δ 14C level was 20.0±1.2%. below the 1855–1864 level. Model calculations indicate that in 1950 industrial CO 2 emissions are responsible for at least 85% of the Δ 14C decline, whereas natural variability accounts for the remaining 15%. 相似文献
4.
A 14C balance for the Eastern Caribbean deep water indicates the average inflow of Atlantic water into the basin to be 2.3 × 10 5 m 3/sec (±30%), or about 2–4 times the values estimated previously. The balance uses a model representation of the deep-water turnover, and is based on 14C concentrations at a station in the Venezuelan Basin which average Δ14C= 89‰ below 800 m depth with a total range of only 9‰, as well as on a 14C concentration of the Atlantic inflow of Δ14C= ?71%. as obtained from measurements outside the Antilles Arch. The turnover time of the basin water below 2500 m depth is 55 years, which corresponds to an average upwelling velocity at this depth of about 35 m/year. With such upwelling, the temperature profile below 1800 m (the depth of the sill determining the inflow of new water) requires a vertical eddy diffusivity of about 5 cm 2/sec. The oxygen consumption, and silica and CO 2 regeneration, rates below 2500 m depth are obtained as ?0.18, + 0.08, and + 0.2 μmole kg ?1 yr ?1, respectively. The CO 2 regeneration has but a negligible effect on the 14C balance. 相似文献
5.
Excess 210Pb measurements and varve chronology were used to establish a sediment accumulation rate of 0.19 cm/yr in a 95-cm-long box core raised from the Gulf of California. Varve thickness is unchanged over the entire length of the core, indicating a constant rate of sediment accumulation. The 32Si specific activity of biogenic silica shows an exponential decrease with depth in this core. The half life of 32Si, calculated from these data and the 0.19-cm/yr sediment accumulation rate, is 276 ± 32 years. As most of the silica and 32Si supplied to the Gulf of California is a result of upwelling of deep ocean water, this half life determination should be relatively insensitive to secular variations in the atmospheric supply of 32Si. 相似文献
6.
Data on the content of the 14C cosmogenic isotope in tree rings, which were obtained as a result of laboratory measurements, are often used when solar activity (SA) is reconstructed for previous epochs, in which direct observations are absent. However, these data contain information not only about SA variations but also about changes in the Earth climatic parameters, such as the global temperature and the CO 2 content in the Earth’s atmosphere. The effect of these variations on the 14C isotope content in different natural reservoirs after the last glacial termination to the middle of the Holocene is considered. The global temperature and the CO 2 content increased on this time interval. In this case the 14C absolute content in the atmosphere increased on this time interval, even though the 14С to 12С isotope concentration ratio (as described by the Δ 14С parameter) decreased. These variations in the radiocarbon absolute content can be caused by its redistribution between natural reservoirs. It has been indicated that such a redistribution is possible only when the rate of carbon exchange between the ocean and atmosphere depends on temperature. The values of the corresponding temperature coefficient for the 17–10 ka BC time interval, which make it possible to describe the carbon redistribution between the ocean and atmosphere, have been obtained. 相似文献
7.
Areal distributions and complete time histories since 1952 are presented of the tritium and 90Sr concentrations in North Atlantic surface water. The distributions are based on a compilation of measured North Atlantic surface water tritium concentrations which is part of this paper and includes hitherto unpublished measurements, and on available 90Sr compilations. To reconstruct the insufficiently represented early concentrations, a two-box North Atlantic mixing model with tropospheric input is employed, for which the input is specified (on relative scales), and which is fitted to the available surface water observations. This procedure gives a natural tritium concentration of 0.2 TU (±30%), and furthermore suggests that part of the old oceanic tritium and 90Sr measurements are high. The fit requires characteristic model mixing times of 2.5 years (exchange with an intermediate-depth reservoir about three times the size of the surface box) and 30 years (loss into the deep ocean), and a tritium/ 90Sr input ratio of 310 Ci/Ci. The areal distributions and time histories can serve as boundary value data for evaluations of subsurface tritium and 90Sr measurements. 相似文献
8.
Since 1957 the 14C/C ratio of the dissolved inorganic carbon in Mono Lake has risen by about 60‰. The magnitude of this increase is about four times larger than that expected from the invasion of bomb-produced 14C from the atmosphere. We have eliminated the following explanations: (1) measurement error, (2) an unusually high physical exchange rate for non-reactive gases, (3) inorganic enhancement of the CO 2 exchange rate, and (4) biological enhancement of the CO 2 exchange rate. Clandestine disposal of waste radiocarbon remains a dark-horse explanation.In the course of our investigations we have uncovered evidence for at least one episodic input of radiocarbon-free carbon to the lake over the last 1000 years. We speculate that this injection was related to a hydrothermal event resulting from sublacustrine volcanic activity. 相似文献
9.
The reaction of CO + OH ? in aqueous solution to give formate was studied as a carbon monoxide sink on the primitive earth and in the present ocean. The reaction is first order in OH ? and first order in the molar CO concentration. The second order rate constant is given by log k(M ?1hr ?1) = 15.83?4886/T between 25°C and 60°C. Using the solubility of CO in sea water, and assuming a pH of 8 for a primitive ocean of the present size, the halflife of CO in the atmosphere is calculated to be 12 × 10 6 yr at 0°C and 5.5 × 10 4 yr at 25°C.Three other CO sinks would have been important in the primitive atmosphere: CO + H 2 → H 2CO driven by various energy sources, CO + OH → CO 2 + H, and the Fischer-Tropsch reaction of CO + H 2 → hydrocarbons, etc. It is concluded that the lifetime of a CO atmosphere would have been very short on the geological time scale although the relative importance of these four CO sinks is difficult to estimate.The CO + OH ? reaction to give formate is a very minor CO sink on the earth at the present time. 相似文献
10.
Continental weathering plays a dominant role in regulating the global carbon cycle, soil chemistry and nutrient supply to oceans. The CO 2-mediated silicate weathering acts as a major CO 2 sink, whereas sulphuric acid-mediated carbonate dissolution releases CO 2 to the atmosphere–ocean system. In this study, dissolved major ions and silica concentrations of two tropical (Damodar and Subarnarekha) river systems from India have been measured to constrain the type and rate of chemical weathering for these basins. The total dissolved solids (TDS) of these rivers, a measure of total solute supply from all possible sources, are about 2–3 times higher than that of the global average for rivers. Mass balance calculations involving inverse modelling estimate that 63 ± 11% of total cations are derived from rock weathering, of which 27 ± 7% of cations are supplied through silicate weathering. The sulphide-S concentrations are estimated by comparing the water chemistry of these two rivers with that of a nearby river (Brahmani) with similar lithology but no signatures of sulphide oxidation. The outflows of Damodar and Subarnarekha rivers receive 17% and 55% of SO 4 through sulphide oxidation, respectively. The sulphide oxidation fluxes from the ore mining areas, such as upper Damodar (0.52 × 10 9 mol/yr) and lower Subarnarekha (0.66 × 10 9 mol/yr) basins, are disproportionally (~9 times) higher compared to their fractional areal coverage to the global drainage area. The corresponding CO 2 release rate (2.84 × 10 4 mol/km 2/yr) for the Damodar basin is lower by five times than its CO 2 uptake rate (1.38 × 10 5 mol/km 2/yr). The outcomes of this study underscore the dominance of sulphide oxidation in controlling the dissolved chemical (cationic and sulphur) fluxes. 相似文献
11.
In the summer of 2005, continuous surface water measurements of fugacity of CO 2 ( fCO 2sw), salinity and temperature were performed onboard the IB Oden along the Northwest Passage from Cape Farwell (South Greenland) to the Chukchi Sea. The aim was to investigate the importance of sea ice and river runoff on the spatial variability of fCO 2 and the sea–air CO 2 fluxes in the Arctic Ocean. Additional data was obtained from measurements of total alkalinity ( AT) by discrete surface water and water column sampling in the Canadian Arctic Archipelago (CAA), on the Mackenzie shelf, and in the Bering Strait. The linear relationship between AT and salinity was used to evaluate and calculate the relative fractions of sea ice melt water and river runoff along the cruise track. High-frequency fCO 2sw data showed rapid changes, due to variable sea ice conditions, freshwater addition, physical upwelling and biological processes. The fCO 2sw varied between 102 and 678 μatm. Under the sea ice in the CAA and the northern Chukchi Sea, fCO 2sw were largely CO 2 undersaturated of approximately 100 μatm lower than the atmospheric level. This suggested CO 2 uptake by biological production and limited sea–air CO 2 gas exchange due to the ice cover. In open areas, such as the relatively fresh water of the Mackenzie shelf and the Bering Strait, the fCO 2sw values were close to the atmospheric CO 2 level. Upwelling of saline and relatively warm water at the Cape Bathurst caused a dramatic fCO 2sw increase of about 100 μatm relative to the values in the CAA. At the southern part of the Chukchi Peninsula we found the highest fCO 2sw values and the water was CO 2 supersaturated, likely due to upwelling. In the study area, the calculated sea–air CO 2 flux varied between an oceanic CO 2 sink of 140 mmol m −2 d −1 and an oceanic source of 18 mmol m −2 d −1. However, in the CAA and the northern Chukchi Sea, the sea ice cover prevented gas exchange, and the CO 2 fluxes were probably negligible at this time of the year. Assuming that the water was exposed to the atmosphere by total melting and gas exchange would be the only process, the CO 2 undersaturated water in the ice-covered areas will not have the time to reach the atmospheric CO 2 value, before the formation of new sea ice. This study highlights the value of using high-frequency measurements to gain increased insight into the variable and complex conditions, encountered on the shelves in the Arctic Ocean. 相似文献
12.
22 annual layered samples of coral from 1977 to 1998 were collected from Daya Bay, South China Sea, their bomb- 14C (nuclear weapons testing 14C) concentrations were determined and studied, and the atmosphere-sea exchange rate and diffusion thickness were estimated
and found to be 17 mol · m −2 · a −1 and 32 μm, respectively. The interannual variation of coral Δ 14C is mainly controlled by oceanic factors. In ENSO years, the coastwise upwelling current of South China Sea gets intensified,
hence the coral Δ 14C displays its bottom value. The coral Δ 14C does no respond vividly to the variation of the solar radiation energy. In the past 20 years or so, the genera situation
and the oceanic thermal structure of South China Sea are still stable even though inter annual variation occurs in the atmosphere-sea
interaction and the upwelling current driven by the tropical energy. 相似文献
13.
13C and ΣCO 2 data from the North and South Atlantic, the Antarctic, and the North and South Pacific are given. The δ13C of the ΣCO 2 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 CO 2 per kg of seawater. The in-situ oxidation of organic matter accounts for 83% of this increase in ΣCO 2, while the remainder is attributed to dissolution of calcium carbonate.The δ13C of the dissolved CO 2 in mid-latitude surface water samples is controlled by a quasi-steady-state equilibrium with atmospheric CO 2 at a mean temperature of 16°C. The δ13C and ΣCO 2 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
14.
We present the distribution of 226Ra 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. Surface 226Ra 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 the 226Ra content, from about 26 to 41 dpm/100 kg near the bottom. Unlike in the Atlantic and Antarctic Oceans, the effect of 226Ra injection from bottom sediments is clearly discernible in the area. The presence of this primary 226Ra 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 oceanic 226Ra. 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( Vz) = 3.5m/yr, vertical eddy diffusivity( Kz) = 0.6cm 2/s, horizontal (north-south) eddy diffusivity( Ky) = 1 × 10 7cm 2/s, and water-column regeneration flux of 226Ra( 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 of 226Ra balance leads us to suspect the appropriateness of describing the vertical exchange processes in the eastern Pacific with constant Vz and Kz. 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
15.
Coastal upwelling events in the California Current System can transport subsurface waters with high levels of carbon dioxide (CO 2) to the sea surface near shore. As these waters age and are advected offshore, CO 2 levels decrease dramatically, falling well below the atmospheric concentration beyond the continental shelf break. In May 2007 we observed an upwelling event off the coast of northern California. During the upwelling event subsurface respiration along the upwelling path added ∼35 μmol kg −1 of dissolved inorganic carbon (DIC) to the water as it transited toward shore causing the waters to become undersaturated with respect to Aragonite. Within the mixed layer, pCO 2 levels were reduced by the biological uptake of DIC (up to 70%), gas exchange (up to 44%), and the addition of total alkalinity through CaCO 3 dissolution in the undersaturated waters (up to 23%). The percentage contribution of each of these processes was dependent on distance from shore. At the time of measurement, a phytoplankton bloom was just beginning to develop over the continental shelf. A box model was used to project the evolution of the water chemistry as the bloom developed. The biological utilization of available nitrate resulted in a DIC decrease of ∼200 μmol kg −1, sea surface pCO 2 near ∼200 ppm, and an aragonite saturation state of ∼3. These results suggest that respiration processes along the upwelling path generally increase the acidification of the waters that are being upwelled, but once the waters reach the surface biological productivity and gas exchange reduce that acidification over time. 相似文献
16.
We measured soil, stem and branch respiration of trees and shrubs, foliage photosynthesis and respiration in ecosystem of the needle and broad-leaved Korean pine forest in Changbai Mountain by LI-6400 CO 2 analysis system. Measurement of forest microclimate was conducted simultaneously and a model was found for the relationship of soil, stem, leaf and climate factors. CO 2 flux of different components in ecosystem of the broad-leaved Korean pine forest was estimated based on vegetation characteristics. The net ecosystem exchange was measured by eddy covariance technique. And we studied the effect of temperature and photosynthetic active radiation on ecosystem CO 2 flux. Through analysis we found that the net ecosystem exchange was affected mainly by soil respiration and leaf photosynthesis. Annual net ecosystem exchange ranged from a minimum of about ?4.671 μmol·m ?2·s ?1 to a maximum of 13.80 μmol·m ?2·s ?1, mean net ecosystem exchange of CO 2 flux was ?2.0 μmol·m ?2·s ?1 and 3.9 μmol·m ?2·s ?1 in winter and summer respectively (mean value during 24 h). Primary productivity of tree, shrub and herbage contributed about 89.7%, 3.5% and 6.8% to the gross primary productivity of the broad-leaved Korean pine forest respectively. Soil respiration contributed about 69.7% CO 2 to the broad-leaved Korean pine forest ecosystem, comprising about 15.2% from tree leaves and 15.1% from branches. The net ecosystem exchange in growing season and non-growing season contributed 56.8% and 43.2% to the annual CO 2 efflux respectively. The ratio of autotrophic respiration to gross primary productivity ( R a:GPP) was 0.52 (NPP:GPP=0.48). Annual carbon accumulation underground accounted for 52% of the gross primary productivity, and soil respiration contributed 60% to gross primary productivity. The NPP of the needle and broad-leaved Korean pine forest was 769.3 gC·m ?2·a ?1. The net ecosystem exchange of this forest ecosystem (NEE) was 229.51 gC·m ?2·a ?1. The NEE of this forest ecosystem acquired by eddy covariance technique was lower than chamber estimates by 19.8%. 相似文献
17.
The shelf-break acts as a separator between the coastal ocean and the open ocean. Circulation (particularly deep near-bottom flow) is restricted from crossing the bathymetry. Eddies become elongated in the region of the shelf-break restricting exchange. An estimate of the horizontal eddy diffusivity over the shelf-break of less than 10m 2s -1 is found from a numerical model. Various mechanisms are responsible for the weak cross-isobath flow that does occur. One is the increase of the Rossby number over small-scale topography such as submarine canyons. Along-shore flow (in the direction opposite to Kelvin wave propagation) generates upwelling through submarine canyons. A review of upwelling through submarine canyons is given. The deep cross-shelf flow generated by the canyons is shown to be as significant as the wind-driven upwelling in some regions. Examples for the reduction of flow across the shelf-break and for upwelling through canyons are taken from the West Coast of Vancouver Island. 相似文献
18.
The effect of light intensity on the release of dissolved organic carbon during photosynthesis on NaH 14CO 3 was investigated using the phytoplanktonic Cyanobacterium Oscillatoria rubescens. The released products were fractionated by molecular size and chemical identifications attempted using combined thin-layer electrophoresis and chromatography, and high pressure liquid chromatography.Within the range of irradiances tested (from 6 to 60 µmole m –2 sec –1), though the upper one inhibited photosynthesis of O. rubescens, light had little effect on the quantity and composition of the excreted products. The released carbon was always lower than 3% of the incorporated carbon, and mainly composed (62 to 86%) by small molecular weight compounds. The prevailing identified compounds were amino acids which represented more than 20% of the excreted carbon. Among organic acids, glycolic acid accounted for less than 2% of the recovered radioactivity. Glucose was the only identified sugar.Abbreviations EOC
excreted organic carbon
- DOC
dissolved organic carbon
- PER
percent extracellular release
- LMW
low molecular weight
- HMW
high molecular weight
- AA
amino acids
- µmoles
m –2 sec –1 = µEinsteins m –2 sec –1 相似文献
19.
Eddy covariance technique was used to measure carbon flux during two growing seasons in 2003 and 2004 over typical steppe in the Inner Mongolia Plateau, China. The results showed that there were two different CO2 flux diurnal patterns at the grassland ecosystem. One had a dual peak in diurnal course of CO2 fluxes with a depression of CO2 flux after noon, and the other had a single peak. In 2003, the maximum diurnal uptake and emitting value of CO2 were −7.4 and 5.4 g·m−2·d−1 respectively and both occurred in July. While in 2004, the maximum diurnal uptake and release of CO2 were −12.8 and 5.8 g·m−2·d−1 and occurred both in August. The grassland fixed 294.66 and 467.46 g CO2·m−2 in 2003 and 2004, and released 333.14 and 437.17 g CO2·m−2 in 2003 and 2004, respectively from May to September. Water availability and photosynthetic active radiation (PAR) are two important factors of controlling CO2 flux. Consecutive precipitation can cause reduction in the ability of ecosystem carbon exchange. Under favorable soil water conditions, daytime CO2 flux is dependent on PAR. CO2 flux, under soil water stress conditions, is obviously less than those under favorable soil water conditions, and there is a light saturation phenomena at PAR=1200 μmol·m−2·s−1. Soil respiration was temperature dependent when there was no soil water stress; otherwise, this response became accumulatively decoupled from soil temperature. 相似文献
20.
Surface partial pressure of CO 2 ( pCO 2), temperature, salinity, nutrients, and chlorophyll a were measured in the East China Sea (ECS; 31°30′–34°00′N to 124°00′–127°30′E) in August 2003 (summer), May 2004 (spring), October 2004 (early fall), and November 2005 (fall). The warm and saline Tsushima Warm Current was observed in the eastern part of the survey area during four cruises, and relatively low salinity waters due to outflow from the Changjiang (Yangtze River) were observed over the western part of the survey area. Surface pCO 2 ranged from 236 to 445 μatm in spring and summer, and from 326 to 517 μatm in fall. Large pCO 2 (values >400 μatm) occurred in the western part of the study area in spring and fall, and in the eastern part in summer. A positive linear correlation existed between surface pCO 2 and temperature in the eastern part of the study area, where the Tsushima Warm Current dominates; this correlation suggests that temperature is the major factor controlling surface pCO 2 distribution in that area. In the western part of the study area, however, the main controlling factor is different and seasonally complex. There is large transport in this region of Changjiang Diluted Water in summer, causing low salinity and low pCO 2 values. The relationship between surface pCO 2 and water stability suggests that the amount of mixing and/or upwelling of CO 2-rich water might be the important process controlling surface pCO 2 levels during spring and fall in this shallow region. Sea–air CO 2 flux, based on the application of a Wanninkhof [1992. Relationship between wind speed and gas exchange over the ocean. Journal of Geophysical Research 97, 7373–7382] formula for gas transfer velocity and a set of monthly averaged satellite wind data, were −5.04±1.59, −2.52±1.81, 1.71±2.87, and 0.39±0.18 mmol m −2 d −1 in spring, summer, early fall, and fall, respectively, in the northern ECS. The ocean in this study area is therefore a carbon sink in spring and summer, but a weak source or in equilibrium with the atmosphere in fall. If the winter flux value is assumed to have been the mean of autumnal and vernal values, then the northern ECS absorbs about 0.013 Pg C annually. That result suggests that the northern ECS is a net sink for atmospheric CO 2, a result consistent with previous studies. 相似文献
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