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1.
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
2.
The purposes of this study were to assess if Lake Apopka (FL, USA) was autotrophic or heterotrophic based on the partial pressure
of dissolved carbon dioxide ( pCO 2) in the surface water and to evaluate factors that influence the long-term changes in pCO 2. Monthly average pH, alkalinity and other limnological variables collected between 1987 and 2006 were used to estimate dissolved
inorganic carbon (DIC), pCO 2 and CO 2 flux between surface water and atmosphere. Results indicated that average pCO 2 in the surface water was 196 μatm, well below the atmospheric pCO 2. Direct measurements of DIC concentration on three sampling dates in 2009 also supported pCO 2 undersaturation in Lake Apopka. Supersaturation in CO 2 occurred in this lake in only 13% of the samples from the 20-year record. The surface-water pCO 2 was inversely related to Chl a concentrations. Average annual CO 2 flux was 28.2 g C m −2 year −1 from the atmosphere to the lake water and correlated significantly with Chl a concentration, indicating that biological carbon sequestration led to the low dissolved CO 2 concentration. Low pCO 2 and high invasion rates of atmospheric CO 2 in Lake Apopka indicated persistent autotrophy. High rates of nutrient loading and primary production, a high buffering capacity,
a lack of allochthonous loading of organic matter, and the dominance of a planktivorous–benthivorous fish food web have supported
long-term net autotrophy in this shallow subtropical eutrophic lake. Our results also showed that lake restoration by the
means of nutrient reduction resulted in significantly lower total phosphorus (TP) and Chl a concentrations, and higher pCO 2. 相似文献
3.
This study investigated CO 2 degassing and related carbon isotope fractionation effects in the Wiesent River that drains a catchment in the karst terrain of the Franconian Alb, Southern Germany. The river was investigated by physico‐chemical and stable isotope analyses of water and dissolved inorganic carbon during all seasons along 65‐km long downstream transects between source and mouth. Calculated pCO 2 values at the source were 21 400 ± 2400 µatm. The pCO 2 rapidly decreased in the river water and dropped to an average of 1240 ± 330 µatm near the mouth. About 90% of this decrease occurred within the first 6 km of the river. The river was supersaturated with respect to CO 2 over its entire course and must have acted as a continuous year‐round CO 2 source to the atmosphere. The average CO 2 flux from the karst river was estimated with 450 mmol m ?2 day ?1 with higher fluxes up to 5680 mmol m ?2 day ?1 at the source. At the source, δ13C DIC values showed no seasonal variations with an average of ?14.2 ± 0.2‰. This indicated that groundwater retained high pCO 2 mainly from soil CO 2. The contribution of soil CO 2 to dissolved inorganic carbon was estimated at 65% to 72%. The downstream CO 2 loss caused a positive shift in δ13C DIC values of 2‰ between source and mouth because of the preferential loss of the 12C isotope during degassing. Considering the findings of this study and the fact that carbonate lithology covers a significant part of the earth's surface, CO 2 evasion from karst regions might contribute notably to the annual carbon dioxide release from global freshwater systems. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
4.
We present an uncertainty analysis of ecological process parameters and CO 2 flux components ( R
eco, NEE and gross ecosystem exchange ( GEE)) derived from 3 years’ continuous eddy covariance measurements of CO 2 fluxes at subtropical evergreen coniferous plantation, Qianyanzhou of ChinaFlux. Daily-differencing approach was used to
analyze the random error of CO 2 fluxes measurements and bootstrapping method was used to quantify the uncertainties of three CO 2 flux components. In addition, we evaluated different models and optimization methods in influencing estimation of key parameters
and CO 2 flux components. The results show that: (1) Random flux error more closely follows a double-exponential (Laplace), rather
than a normal (Gaussian) distribution. (2) Different optimization methods result in different estimates of model parameters.
Uncertainties of parameters estimated by the maximum likelihood estimation (MLE) are lower than those derived from ordinary
least square method (OLS). (3) The differences between simulated R eco, NEE and GEE derived from MLE and those derived from OLS are 12.18% (176 g C·m −2·a −1), 34.33% (79 g C·m −2·a −1) and 5.4% (92 g C·m −2·a −1). However, for a given parameter optimization method, a temperature-dependent model (T_model) and the models derived from
a temperature and water-dependent model (TW_model) are 1.31% (17.8 g C·m −2·a −1), 2.1% (5.7 g C·m −2·a −1), and 0.26% (4.3 g C·m −2·a −1), respectively, which suggested that the optimization methods are more important than the ecological models in influencing
uncertainty in estimated carbon fluxes. (4) The relative uncertainty of CO 2 flux derived from OLS is higher than that from MLE, and the uncertainty is related to timescale, that is, the larger the
timescale, the smaller the uncertainty. The relative uncertainties of R eco, NEE and GEE are 4%−8%, 7%−22% and 2%−4% respectively at annual timescale.
Supported by the National Natural Science Foundation of China (Grant No. 30570347), Innovative Research International Partnership
Project of the Chinese Academy of Sciences (Grant No. CXTD-Z2005-1) and National Basic Research Program of China (Grant No.
2002CB412502) 相似文献
5.
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
6.
Seasonal metrics and environmental responses to forestry soil surface CO2 emission effluxes among three types of lower subtropical forests were consistently monitored over two years with static chamber-gas chromatograph techniques among three types of lower subtropical forests. Results showed that annual CO2 effluxes (S+L) reached 3942.20, 3422.36 and 2163.02 CO2 g·m−2·a−1, respectively in the monsoon evergreen broadleaf forest, mixed broadleaf-coniferous forest and coniferous forest. All the three types of forests revealed the same characteristics of seasonal changes with the CO2 effluxes peaking throughout June to August. During this peaking period, the effluxes were 35.9%, 38.1% and 40.2% of the total annual effluxes, respectively. The CO2 emission process responding to the environmental factors displayed significantly different patterns in forestry soils of the three types of forests. The coniferous forest (CF) was more sensitive to temperature than the other two types. The Q
10 values were higher, along with greater seasonal variations of the CO2 efflux, indicating that the structurally unique forestry ecosystem has disadvantage against interferences. All the three types of forestry CO2 effluxes showed significant correlation with the soil temperature (T
s), soil water content (M
s) and air pressure (P
a). However, stepwise regression analysis indicated no significant correlation between air pressure and the soil CO2 efflux. With an empirical model to measure soil temperature and water content in 5 cm beneath the soil surface, the CO2 effluxes accounting for 75.7%, 77.8% and 86.5% of the efflux variability respectively in soils of BF, MF and PF were calculated. This model can be better used to evaluate the CO2 emission of soils under water stress and arid or semi-arid conditions. 相似文献
7.
Long-term measurement of carbon metabolism of old-growth forests is critical to predict their behaviors and to reduce the uncertainties of carbon accounting under changing climate. Eddy covariance technology was applied to investigate the long-term carbon exchange over a 200 year-old Chinese broad-leaved Korean pine mixed forest in the Changbai Mountains (128°28′E and 42°24′N, Jilin Province, P. R. China) since August 2002. On the data obtained with open-path eddy covariance system and CO2 profile measurement system from Jan. 2003 to Dec. 2004, this paper reports (i) annual and seasonal variation of F
NEE, F
GPP and R
E; (ii) regulation of environmental factors on phase and amplitude of ecosystem CO2 uptake and release Corrections due to storage and friction velocity were applied to the eddy carbon flux. LAI and soil temperature determined the seasonal and annual dynamics of FGPP and RE separately. VPD and air temperature regulated ecosystem photosynthesis at finer scales in growing seasons. Water condition at the root zone exerted a significant influence on ecosystem maintenance carbon metabolism of this forest in winter. The forest was a net sink of atmospheric CO2 and sequestered −449 g C·m−2 during the study period; −278 and −171 gC·m−2 for 2003 and 2004 respectively. F
GPP and F
RE over 2003 and 2004 were −1332, −1294 g C·m−2. and 1054, 1124 g C·m−2 respectively. This study shows that old-growth forest can be a strong net carbon sink of atmospheric CO2. There was significant seasonal and annual variation in carbon metabolism. In winter, there was weak photosynthesis while the ecosystem emitted CO2. Carbon exchanges were active in spring and fall but contributed little to carbon sequestration on an annual scale. The summer is the most significant season as far as ecosystem carbon balance is concerned. The 90 days of summer contributed 66.9, 68.9% of F
GPP, and 60.4, 62.1% of R
E of the entire year. 相似文献
8.
Seasonal metrics and environmental responses to forestry soil surface CO 2 emission effluxes among three types of lower subtropical forests were consistently monitored over two years with static chamber-gas chromatograph techniques among three types of lower subtropical forests. Results showed that annual CO 2 effluxes (S+L) reached 3942.20, 3422.36 and 2163.02 CO 2 g·m ?2·a ?1, respectively in the monsoon evergreen broadleaf forest, mixed broadleaf-coniferous forest and coniferous forest. All the three types of forests revealed the same characteristics of seasonal changes with the CO 2 effluxes peaking throughout June to August. During this peaking period, the effluxes were 35.9%, 38.1% and 40.2% of the total annual effluxes, respectively. The CO 2 emission process responding to the environmental factors displayed significantly different patterns in forestry soils of the three types of forests. The coniferous forest (CF) was more sensitive to temperature than the other two types. The Q 10 values were higher, along with greater seasonal variations of the CO 2 efflux, indicating that the structurally unique forestry ecosystem has disadvantage against interferences. All the three types of forestry CO 2 effluxes showed significant correlation with the soil temperature ( T s), soil water content ( M s) and air pressure ( P a). However, stepwise regression analysis indicated no significant correlation between air pressure and the soil CO 2 efflux. With an empirical model to measure soil temperature and water content in 5 cm beneath the soil surface, the CO 2 effluxes accounting for 75.7%, 77.8% and 86.5% of the efflux variability respectively in soils of BF, MF and PF were calculated. This model can be better used to evaluate the CO 2 emission of soils under water stress and arid or semi-arid conditions. 相似文献
9.
Long-term measurement of carbon metabolism of old-growth forests is critical to predict their behaviors and to reduce the uncertainties of carbon accounting under changing climate. Eddy covariance technology was applied to investigate the long-term carbon exchange over a 200 year-old Chinese broad-leaved Korean pine mixed forest in the Changbai Mountains (128°28′E and 42°24′N, Jilin Province, P. R. China) since August 2002. On the data obtained with open-path eddy covariance system and CO 2 profile measurement system from Jan. 2003 to Dec. 2004, this paper reports (i) annual and seasonal variation of F NEE, F GPP and R E; (ii) regulation of environmental factors on phase and amplitude of ecosystem CO 2 uptake and release Corrections due to storage and friction velocity were applied to the eddy carbon flux. LAI and soil temperature determined the seasonal and annual dynamics of FGPP and RE separately. VPD and air temperature regulated ecosystem photosynthesis at finer scales in growing seasons. Water condition at the root zone exerted a significant influence on ecosystem maintenance carbon metabolism of this forest in winter.The forest was a net sink of atmospheric CO 2 and sequestered ?449 g C·m ?2 during the study period; ?278 and ?171 gC·m ?2 for 2003 and 2004 respectively. F GPP and F RE over 2003 and 2004 were ?1332, ?1294 g C·m ?2. and 1054, 1124 g C·m ?2 respectively. This study shows that old-growth forest can be a strong net carbon sink of atmospheric CO 2.There was significant seasonal and annual variation in carbon metabolism. In winter, there was weak photosynthesis while the ecosystem emitted CO 2. Carbon exchanges were active in spring and fall but contributed little to carbon sequestration on an annual scale. The summer is the most significant season as far as ecosystem carbon balance is concerned. The 90 days of summer contributed 66.9, 68.9% of F GPP, and 60.4, 62.1% of R E of the entire year. 相似文献
10.
Surface partial pressure of CO 2 ( pCO 2), dissolved inorganic carbon (DIC), temperature, salinity and chlorophyll a (Chl a) at grid stations were measured in the southern Yellow Sea (SYS; 32–37°N to 120–125°E) during four cruises conducted in March 2005 (winter), April 2006 (spring), May 2005 (late spring), and July 2001 (summer). Factors influencing pCO 2 spatial and seasonal variations are explored.Surface seawater pCO 2 during winter was oversaturated with respect to the atmosphere in the entire study area (380–606 μatm), primarily due to the complete mixing of the water column in winter which brought CO 2-enriched bottom water to the surface. However, during spring, surface pCO 2 in the central SYS was undersaturated relative to the atmosphere with a low range between 274 and 408 μatm. The net CO 2 sink in the central SYS was mainly due to the consumption of CO 2 by the strong phytoplankton activity and to the weak water stratification, whereas surface pCO 2 in the nearshore area was oversaturated for the atmosphere owing to vertical mixing and terrestrial inputs. During summer, surface pCO 2 varied between 125 and 599 μatm over the entire sampling area. In the Changjiang (Yangtze River) Diluted Water (CDW) area, surface pCO 2 was undersaturated because of the nutrient inputs via the Changjiang, triggering strong phytoplankton activity, whereas surface pCO 2 was oversaturated in other areas. We conclude that the nearshore area behaves as a source of atmospheric CO 2 during the entire investigated periods owing to vertical mixing and terrestrial inputs as well as upwelling, whereas the central region generally shifts from a source of CO 2 in March to a sink in the remaining time of the investigation. 相似文献
11.
The study by the eddy covariance technique in the alpine shrub meadow of the Qinghai-Tibet Plateau in 2003 and 2004 showed that the net ecosystem carbon dioxide exchange (NEE) exhibited noticeable diurnal and annual variations, with more distinct daily changes during the warmer seasons. The CO2 emission of the shrub ecosystem culminated in April and September while the CO2 absorption capacity reached a maximum in July and August. The absorbed carbon dioxide during the two consecutive years was 231.4 and 274.8 g CO2·m−2 respectively, yielding an average of 253.1 gCO2·m−2 per year: that accounts for a large proportion of absorbed CO2 in the region. Obviously, the diurnal carbon flux was negatively related to temperature, radiation and other atmospheric factors. Still, minute discrepancies in kurtosis and duration of carbon emission/absorption were detected between 2003 and 2004. It was found that the CO2 flux in the daytime was similarly affected by photosynthetic photon flux density in both years. Temperature appears to be the most important determinant of CO2 flux: specifically, the high temperature during the plant growing season inhibits the carbon absorption capacity. One potential explanation is that soil respiration is enhanced under such condition. Analysis of biomass revealed that the annual net carbon fixed capacity of aboveground and belowground biomass was 544.0 in 2003 and 559.4 g C·m−2 in 2004, which coincided with the NEE absorption capacity (63.1 g C·m−2 in 2003 and 74.9 g C·m−2 in 2004) in the corresponding plant growing season. 相似文献
12.
The southern Yellow Sea (SYS), located to the north of the East China Sea (ECS), was considered part of the ECS when Tsunogai et al. (1999) proposed the “continental shelf pump” (CSP) hypothesis. However, the original CSP carbon dioxide (CO 2) uptake flux (2.9 mol C m −2 yr −1) appears to have been overestimated, primarily due to the differences between the SYS and the ECS in terms of their CO 2 system. In this paper, we estimated air-sea CO 2 fluxes in the SYS using the surface water partial pressure of CO 2 ( pCO 2) measured in winter, spring, and summer, as well as that estimated in fall via the relationship of pCO 2 with salinity, temperature, and chlorophyll a. The results indicate that overall, the entire investigated area was a net source of atmospheric CO 2 during summer, winter, and fall, whereas it was a net sink during spring. Spatially, the nearshore area was almost a permanent CO 2 source, while the central SYS shifted from being a CO 2 sink in spring to a source in the other seasons of the year. Overall, the SYS is a net source of atmospheric CO 2 on an annual scale, releasing ∼7.38 Tg C (1 Tg=10 12 g) to the atmosphere annually. Thus, the updated CO 2 uptake flux in the combined SYS and ECS is reduced to ∼0.86 mol C m −2 yr −1. If this value is extrapolated globally following Tsunogai et al. (1999), the global continental shelf would be a sink of ∼0.29 Pg C yr −1, instead of 1 Pg C yr −1 (1 Pg=10 15 g).The SYS as a net annual source of atmospheric CO 2 is in sharp contrast to most mid- and high-latitude continental shelves, which are CO 2 sinks. We argue that unlike the ECS and the North Sea where carbon on the shelf could be exported to the open ocean, the SYS lacks the physical conditions required by the CSP to transport carbon off the shelf effectively. The global validity of the CSP theory is thus questionable. 相似文献
13.
The study by the eddy covariance technique in the alpine shrub meadow of the Qinghai-Tibet Plateau in 2003 and 2004 showed that the net ecosystem carbon dioxide exchange (NEE) exhibited noticeable diurnal and annual variations, with more distinct daily changes during the warmer seasons. The CO 2 emission of the shrub ecosystem culminated in April and September while the CO 2 absorption capacity reached a maximum in July and August. The absorbed carbon dioxide during the two consecutive years was 231.4 and 274.8 g CO 2·m ?2 respectively, yielding an average of 253.1 gCO 2·m ?2 per year: that accounts for a large proportion of absorbed CO 2 in the region. Obviously, the diurnal carbon flux was negatively related to temperature, radiation and other atmospheric factors. Still, minute discrepancies in kurtosis and duration of carbon emission/absorption were detected between 2003 and 2004. It was found that the CO 2 flux in the daytime was similarly affected by photosynthetic photon flux density in both years. Temperature appears to be the most important determinant of CO 2 flux: specifically, the high temperature during the plant growing season inhibits the carbon absorption capacity. One potential explanation is that soil respiration is enhanced under such condition. Analysis of biomass revealed that the annual net carbon fixed capacity of aboveground and belowground biomass was 544.0 in 2003 and 559.4 g C·m ?2 in 2004, which coincided with the NEE absorption capacity (63.1 g C·m ?2 in 2003 and 74.9 g C·m ?2 in 2004) in the corresponding plant growing season. 相似文献
14.
The Bay of Biscay is part of the North Atlantic Ocean, the most important sink of CO 2, and a subduction zone of mode waters that favours the entry of carbon to the ocean interior. To investigate the seasonal and interannual variability of CO 2 uptake, continuous underway measurements of the partial pressure of CO 2 at sea surface were performed along a commercial route between Vigo (Spain) and St. Nazaire (France). An unattended measuring system of CO 2 fugacity ( fCO 2), with meteorological station, and temperature, salinity, oxygen and fluorescence sensors, was installed on board of ships of opportunity ( RO-RO L’ Audace and RO-RO Surprise). 相似文献
15.
High-resolution sampling, measurements of organic carbon contents and 14C signatures of selected four soil profiles in the Haibei Station situated on the northeast Tibetan Plateau, and application
of 14C tracing technology were conducted in an attempt to investigate the turnover times of soil organic carbon and the soil-CO 2 flux in the alpine meadow ecosystem. The results show that the organic carbon stored in the soils varies from 22.12×10 4 kg C hm −2 to 30.75×10 4 kg C hm −2 in the alpine meadow ecosystems, with an average of 26.86×10 4 kg C hm −2. Turnover times of organic carbon pools increase with depth from 45 a to 73 a in the surface soil horizon to hundreds of
years or millennia or even longer at the deep soil horizons in the alpine meadow ecosystems. The soil-CO 2 flux ranges from 103.24 g C m −2 a −1 to 254.93 gC m −2 a −1, with an average of 191.23 g C m −2 a −1. The CO 2 efflux produced from microbial decomposition of organic matter varies from 73.3 g C m −2 a −1 to 181 g C m −2 a −1. More than 30% of total soil organic carbon resides in the active carbon pool and 72.8%281.23% of total CO 2 emitted from organic matter decomposition results from the topsoil horizon (from 0 cm to 10 cm) for the Kobresia meadow. Responding to global warming, the storage, volume of flow and fate of the soil organic carbon in the alpine meadow
ecosystem of the Tibetan Plateau will be changed, which needs further research.
Supported by the National Natural Science Foundation of China (Grant Nos. 40231015, 40471120 and 40473002) and the Guangdong
Provincial Natural Science Foundation of China (Grant No. 06300102) 相似文献
17.
A critical factor controlling changes in the acidity of coastal waters is the alkalinity of the water. Concentrations of alkalinity
are determined by supply from rivers and by in situ processes such as biological production and denitrification. A 2-year
study based on 15 cruises in Liverpool Bay followed the seasonal cycles of changing concentrations of total alkalinity (TA)
and total dissolved inorganic carbon (DIC) in relation to changes caused by the annual cycle of biological production during
the mixing of river water into the Bay. Consistent annual cycles in concentrations of nutrients, TA and DIC were observed
in both years. At a salinity of 31.5, the locus of primary production during the spring bloom, concentrations of NO
x
decreased by 25 ± 4 μmol kg −1 and DIC by 106 ± 16 μmol kg −1. Observed changes in TA were consistent with the uptake of protons during primary biological production. Concentrations of
TA increased by 33 ± 8 μmol kg −1 (2009) and 33 ± 15 μmol kg −1 (2010). The impact of changes in organic matter on the measured TA appears likely to be small in this area. Thomas et al.
( 2009) suggested that denitrification may enhance the CO 2 uptake of the North Sea by 25%, in contrast we find that although denitrification is a significant process in itself, it
does not increase concentrations of TA relative to those of DIC and so does not increase buffer capacity and potential uptake
of CO 2 into shelf seawaters. For Liverpool Bay historical data suggest that higher concentrations of TA during periods of low flow
are likely to contribute in part to the observed change in TA between winter and summer but the appropriate pattern cannot
be identified in recent low-frequency river data. On a wider scale, data for the rivers Mersey, Rhine, Elbe and Weser show
that patterns of seasonal change in concentrations of TA in river inputs differ between river systems. 相似文献
18.
The belowground part of terrestrial ecosystem is a huge carbon pool. It is believed that of the total 2500Gt carbon stored in global terrestrial ecosystem, soil carbon storage within the 1 m surface layer ac- counts for 2000Gt, which is 4-fold of vegetation car- bon storage[1,2]. Compared with the carbon in the vegetation, carbon in the deep soil layers is much more stable, and it will stay in soil profile permanentlyunless geological vicissitude occurs. Essentially, forest restoration is the… 相似文献
19.
In the Jungwon area, South Korea, two contrasting types of deep thermal groundwater (around 20–33 °C) occur together in granite. Compared to shallow groundwater and surface water, thermal groundwaters have significantly lower δ18O and δD values (> 1‰ lower in δ18O) and negligible tritium content (mostly < 2 TU), suggesting a relatively high age of these waters (at least pre-thermonuclear period) and relatively long subsurface circulation. However, the hydrochemical evolution yielded two distinct water types. CO 2-rich water ( PCO2 = 0.1 to 2 atm) is characterized by lower pH (5.7–6.4) and higher TDS content (up to 3300 mg/L), whereas alkaline water ( PCO2 = 10 − 4.1–10 − 4.6 atm) has higher pH (9.1–9.5) and lower TDS (< 254 mg/L). Carbon isotope data indicate that the CO 2-rich water is influenced by a local supply of deep CO 2 (potentially, magmatic), which enhanced dissolution of silicate minerals in surrounding rocks and resulted in elevated concentrations of Ca 2+, Na +, Mg 2+, K +, HCO 3− and silica under lower pH conditions. In contrast, the evolution of the alkaline water was characterized by a lesser degree of water–rock (granite) interaction under the negligible inflow of CO 2. The application of chemical thermometers indicates that the alkaline water represents partially equilibrated waters coming from a geothermal reservoir with a temperature of about 40 °C, while the immature characteristics of the CO 2-rich water resulted from the input of CO 2 in Na–HCO 3 waters and subsequent rock leaching. 相似文献
20.
Cave air PCO2 at two Irish sites varied dramatically on daily to seasonal timescales, potentially affecting the timing of calcite deposition and consequently climate proxy records derived from stalagmites collected at the same sites. Temperature-dependent biochemical processes in the soil control CO 2 production, resulting in high summer PCO2 values and low winter values at both sites. Large Large-amplitude, high-frequency variations superimposed on this seasonal cycle reflect cave air circulation. Here we model stalagmite growth rates, which are controlled partly by CO 2 degassing rates from drip water, by considering both the seasonal and high-frequency cave air PCO2 variations. Modeled hourly growth rates for stalagmite CC-Bil from Crag Cave in SW Ireland reach maxima in late December (0.063 μm h − 1) and minima in late June/early July (0.033 μm h − 1). For well-mixed ‘diffuse flow’ cave drips such as those that feed CC-Bil, high summer cave air PCO2 depresses summer calcite deposition, while low winter PCO2 promotes degassing and enhances deposition rates. In stalagmites fed by well-mixed drips lacking seasonal variations in δ18O, integrated annual stalagmite calcite δ18O is unaffected; however, seasonality in cave air PCO2 may influence non-conservative geochemical climate proxies (e.g., δ13C, Sr/Ca). Stalagmites fed by ‘seasonal’ drips whose hydrochemical properties vary in response to seasonality may have higher growth rates in summer because soil air PCO2 may increase relative to cave air PCO2 due to higher soil temperatures. This in turn may bias stalagmite calcite δ18O records towards isotopically heavier summer drip water δ18O values, resulting in elevated calcite δ18O values compared to the ‘equilibrium’ values predicted by calcite–water isotope fractionation equations. Interpretations of stalagmite-based paleoclimate proxies should therefore consider the consequences of cave air PCO2 variability and the resulting intra-annual variability in calcite deposition rates. 相似文献
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