Spatial and Temporal Variability of the CO2 Fluxes in a Tropical, Highly Urbanized Estuary

The spatial and temporal variations of the flux of CO₂ were determined during 2007 in the Recife estuarine system (RES), a tropical estuary that receives anthropogenic loads from one of the most populated and industrialized areas of the Brazilian coast. The RES acts as a source of nutrients (N and P) for coastal waters. The calculated CO₂ fluxes indicate that the upstream inputs of CO₂ from the rivers are largely responsible for the net annual CO₂ emission to the atmosphere of +30 to +48 mmol m^?2 day^?1, depending on the CO₂ exchange calculation used, which mainly occurs during the late austral winter and early summer. The observed inverse relationship between the CO₂ flux and the net ecosystem production (NEP) indicates the high heterotrophy of the system (except for the months of November and December). The NEP varies between ?33 mmol m^?2 day^?1 in summer and ?246 mmol m^?2 day^?1 in winter. The pCO₂ values were permanently high during the study period (average ~4,700 μatm) showing a gradient between the inner (12,900 μatm) and lower (389 μatm) sections on a path of approximately 30 km. This reflects a state of permanent pollution in the basin due to the upstream loading of untreated domestic effluents (N/P?=?1,367:6 μmol kg^?1 and pH?=?6.9 in the inner section), resulting in the continuous mineralization of organic material by heterotrophic organisms and thereby increasing the dissolved CO₂ in estuarine waters.     

A thermochemical study of vaterite

Vaterite is shown to be unstable with respect to calcite at 25°C by measurements of the enthalpies of solution in 0·1 N HCl under 0·97 atm CO₂ and the solubilities in water under 0·97 atm CO₂ of the two polymorphs. For a pure, synthetic vaterite ΔH (tr) = ?1036 ±16 cal mol^?1 and ΔG(tr) = ?790 ± 25 cal mol^?1 for the transition to calcite. For other vaterites aged longer during preparation ΔH(tr) is smaller and shows a linear relationship with the X-ray line broadening which extrapolates to ΔH(tr) = ?545 ± 30 cal mo^?1 for zero broadening. The use of X-ray line broadening as a measure of crystal imperfection and stability is discussed for various synthetic and natural vaterites.     

CO2 Input Dynamics and Air–Sea Exchange in a Large New England Estuary

Repeated surveys of the Kennebec estuary, a macrotidal river estuary in Maine, USA, between 2004 and 2008 found spatial and temporal variability both in sources of carbon dioxide (CO₂) to the estuary and the air–sea flux of estuary CO₂. On an annual basis, the surveyed area of the Kennebec estuary had an area-weighted average partial pressure of CO₂ (pCO₂) of 559 μatm. The area-weighted average CO₂ flux to the atmosphere was 3.54 mol C m^?2 year^?1. Overall, the Kennebec estuary was an annual source of 7.2?×?10⁷ mol CO₂ to the atmosphere. Distinct seasonality in estuarine pCO₂ was observed, with shifts in the seasonal pattern evident between lower and higher salinities. Fluxes of CO₂ from the estuary were elevated following two summertime storms, and inputs of riverine CO₂ outweighed internal estuarine CO₂ inputs in nearly all months. River and estuarine inputs of CO₂ represented 68 and 32 % of the total CO₂ contributions to the estuary, respectively. This study examines the variability of CO₂ in a large New England estuary, and highlights the comparatively high contribution of CO₂ from riverine sources.     

Biogeochemical cycling in an organic-rich coastal marine basin 4. An organic carbon budget for sediments dominated by sulfate reduction and methanogenesis

In situ carbon flux measurements and calculated burial rates are utilized to construct an organic carbon budget for the upper meter of sediment at a single station in Cape Lookout Bight, a small marine basin located on the Outer Banks of North Carolina, U.S.A. (34°37′N, 76°33′W). Of 149 ± 20 mole · m^?2 · yr^?1 of total organic carbon deposited, 35.6 ± 5.2 mole · m^?2 · yr^?1 is recycled to overlying waters, 84 ± 18% as ∑CO₂ and 16 ± 8% as CH₄. Approximately 68 ± 20% of the upward carbon flux is supported by sulfate reduction while 32 ± 16% takes place as the result of underlying methanogenesis. Measured ∑CO₂ and CH₄ sediment-water fluxes range seasonally from 1900–6300 and 50–2500 μmole · m^?2 · hr^?1 respectively.The mean residence time of metabolizable organic carbon in the upper 80 cm of sediment is approximately four months with greater than 98% of the calculated total remineralization taking place within three years. In spite of large upward fluxes of methane, larger molecules derived from metabolizable sedimentary organic carbon appear to be the dominant reductants for dissolved sulfate.     

Solubilities of noble gases in magnetite: implications for planetary gases in meteorites

Solubilities of noble gases in magnetite were determined by growing magnetite in a noble-gas atmosphere between 450 and 700°K. Henry's law is obeyed at pressures up to 10^?2 atm for He, Ne, Ar and up to 10^?5 atm for Kr, Xe, with the following distribution coefficients at 500° (cc STP g^?1 atm^?5): He 0.042, Ne 0.016, Ar 3.6, Kr 1.3, Xe 0.88, some 10²–10⁵ times higher than previous determinations on silicate and fluoride melts. Apparent heats of solution in kcal/mole are: He ?2.42 ±0.12, Ne ?2.20 ±0.10, Ar ?15.25 ±0.25, Kr ?13.0 ±0.3, Xe ?12-5 ± 0.5. These values, too, stand in sharp contrast with earlier determinations on melts which were small and positive, but are comparable to the values for clathrates. Presumably the gases are held in anion vacancies.Extrapolation of the magnetite data to the formation temperature of C1 chondrites, 360°K, shows that the Ar_p³⁶ content of Orgueil magnetite could be acquired by equilibrium solubility at a total nebular pressure of 4 × 10^?6 atm. In the absence of data for silicates (the principal host phase of planetary gas), an attempt is made to estimate the solubilities required to account for planetary gases in meteorites. These values do not appear grossly unreasonable in the light of the magnetite data, when structural differences between the two minerals are taken into account. It seems that equilibrium solubility may be able to account for four features of planetary gas: elemental ratios, amounts, correlations with other volatiles and retentive siting. It cannot account for the isotopic fractionation of planetary gas, however.     

Carbon Dioxide and Methane Dynamics in Three Coastal Systems of Cadiz Bay (SW Spain)

The partial pressure of CO₂ (pCO₂) and concentration of dissolved CH₄ in surface waters have been studied in three coastal systems connected to Cadiz Bay (southwestern coast of Spain) over different time scales. The concentration of CH₄ varied from 1 to 4200 nmol kg^?1 (192.1 ± 463.6 nmol kg^?1) and the saturation percent from 19 to 159,577% (6645 ± 16,921%), and pCO₂ from 315 to 3240 μatm (841.9 ± 466.3 μatm), with saturation percent values varying between 72 and 981% (220 ± 133%). The seasonal variation of pCO₂ mainly depends on the temperature. On the contrary, the annual distribution of dissolved CH₄ is associated with the precipitation regime. In addition, pCO₂ and dissolved CH₄ showed spatial variation. pCO₂ increased toward the inner part of the systems, with the proximity to the discharge points from human activities. Dissolved CH₄ is influenced by both anthropogenic inputs and natural processes such as benthic supply and exchange with the adjacent salt marshes. pCO₂ and dissolved CH₄ also varied with the tides: The highest concentrations were measured during the ebb, which suggests that the systems export CO₂ and CH₄ to the Bay and adjacent Atlantic Ocean.     

The effect of composition on the ferric-ferrous ratio in basaltic liquids at atmospheric pressure

The effects on the ferric-ferrous ratio of varying individual components in a dry basaltic liquid have been determined at atmospheric pressure and constant oxygen fugacity (fO₂). Experiments were conducted by suspending 100 mg samples from pt loops at 1200°C (fO₂ = 10^?8atm) and 1360°C (fO₂ = 10^?6atm) in an atmosphere controlled by mixtures of CO₂ and H₂. A microanalytical wetchemical technique and the electron microprobe were used to determine the composition of the resulting basaltic glasses. In order of decreasing significance, the addition of oxides of K, Na, Si, Al, or Ca produces an increase in the ferric-ferrous ratio of the melt at 1200°C. The change in the ferric-ferrous ratio produced by component addition is less at 1360°C than at 1200°C.     

Diurnal variations of pCO2 in relation to environmental factors in the cascade reservoirs along the Wujiang River, China

We have investigated the diurnal variations of the pCO2 and related environmental factors in the cascade reservoirs with different trophic levels along Wujiang River. In surface water the pCO2 was 357±11 μatm in Hong-jiadu Reservoir, 338±48 μatm in Dongfeng Reservoir, 682±303 μatm in Wujiangdu Reservoir, and 1677±429 μatm in Liuguang, respectively. The results indicated that these cascade reservoirs had much lower pCO2 values in surface water than river did, and hypereutrophic reservoir showed larger diurnal variations of pCO2 than meso-eutrophic reservoir. In water column, pCO2 tended to increase with the depth. Phytoplankton and the environmental factors such as temperature and pH had different influences on pCO2 diurnal variations due to different trophic levels, and the effect of phytoplankton on pCO2 variation increased with the increase of trophic level in these reservoirs.     

A thermochemical study of monohydrocalcite

The thermodynamic properties of monohydrocalcite, CaCO₃ · H₂O, have been obtained using a well-characterized natural specimen. Equilibration of the solid with water at 25°C under 0.97 atm CO₂ led to an activity product [Ca²⁺][CO₃^2?] = 10^?7.60±0.03 and a free energy of formation ΔG_f^o = ?325,430 ± 270 calmol^?. The enthalpy of solution of monohydrocalcite in 0.1 N HCl at 25°C led to a standard enthalpy of formation ΔH_f^o = ?358,100 ± 280 cal mol^?1. Estimates of the variation of ΔG_f with temperature and pressure showed monohydrocalcite to be metastable with respect to calcite and aragonite.     

CO2 emission from Dianshan Lake in summer, East China

Shallow fresh water bodies in peat areas could be an important contributor to greenhouse gases in the atmosphere.In this study,the partial pressure of CO2 in the surface water of the Dianshan Lake was investigated insitu in August 2011.The average pCO2 in the study area was 2300μatm and fluctuated within the range of 989–5000μatm.pCO2 showed a reverse trend to the variations of pH and DO in the surface water of the Dianshan Lake.The water to air diffusion flux of CO2 of the upstream,middle lake and downstream were respectively 63,33 and 14mmol/m2/d.On average,the diffusion flux of CO2 of the whole lake was 31 mmol/m2/d.Consequently,our results show that during the sampling season,the Dianshan Lake appears to be a great source of CO2.It is also demonstrated that respiration could be the dominant biochemical reaction in the Dianshan Lake in summer.     

CO<Subscript>2</Subscript> content of andesitic melts at graphite-saturated upper mantle conditions with implications for redox state of oceanic basalt source regions and remobilization of reduced carbon from subducted eclogite

We have performed experiments to determine the effects of pressure, temperature and oxygen fugacity on the CO₂ contents in nominally anhydrous andesitic melts at graphite saturation. The andesite composition was specifically chosen to match a low-degree partial melt composition that is generated from MORB-like eclogite in the convective, oceanic upper mantle. Experiments were performed at 1–3 GPa, 1375–1550?°C, and fO₂ of FMQ ?3.2 to FMQ ?2.3 and the resulting experimental glasses were analyzed for CO₂ and H₂O contents using FTIR and SIMS. Experimental results were used to develop a thermodynamic model to predict CO₂ content of nominally anhydrous andesitic melts at graphite saturation. Fitting of experimental data returned thermodynamic parameters for dissolution of CO₂ as molecular CO₂: ln(K ⁰) = ?21.79?±?0.04, ΔV ⁰?=?32.91?±?0.65 cm³mol^?1, ΔH ⁰?=?107?±?21 kJ mol^?1, and dissolution of CO₂ as CO₃ ^2?: ln(K ⁰ ) = ?21.38?±?0.08, ΔV ⁰?=?30.66?±?1.33 cm³ mol^?1, ΔH ⁰?=?42?±?37 kJ mol^?1, where K ⁰ is the equilibrium constant at some reference pressure and temperature, ΔV ⁰ is the volume change of reaction, and ΔH ⁰ is the enthalpy change of reaction. The thermodynamic model was used along with trace element partition coefficients to calculate the CO₂ contents and CO₂/Nb ratios resulting from the mixing of a depleted MORB and the partial melt of a graphite-saturated eclogite. Comparison with natural MORB and OIB data suggests that the CO₂ contents and CO₂/Nb ratios of CO₂-enriched oceanic basalts cannot be produced by mixing with partial melts of graphite-saturated eclogite. Instead, they must be produced by melting of a source containing carbonate. This result places a lower bound on the oxygen fugacity for the source region of these CO₂-enriched basalts, and suggests that fO₂ measurements made on cratonic xenoliths may not be applicable to the convecting upper mantle. CO₂-depleted basalts, on the other hand, are consistent with mixing between depleted MORB and partial melts of a graphite-saturated eclogite. Furthermore, calculations suggest that eclogite can remain saturated in graphite in the convecting upper mantle, acting as a reservoir for C.     

Air–Water CO<Subscript>2</Subscript> Fluxes and Net Ecosystem Production Changes in a Baja California Coastal Lagoon During the Anomalous North Pacific Warm Condition

The present study examines the temporal variability of air–water CO₂ fluxes (FCO₂) and seawater carbonate chemistry in a Baja California coastal lagoon during an exceptionally warm anomaly that was developed in Northeast Pacific coasts during 2014. This oceanographic condition led to a summer-like season (weak upwelling condition) during the study period, which reached a maximum surface temperature anomaly of 2 °C in September 2014. San Quintín Bay acts as a source of CO₂ to the atmosphere in 2014 (3.3 ± 4.8 mmol C m^?2 day^?1) with the higher positive fluxes mainly observed in summer months (9.0 ± 5.3 mmol C m^?2 day^?1). Net ecosystem production (NEP) switched seasonally between net heterotrophy and net autotrophy during the study period, with an annual average of 2.2 ± 7.1 mmol C m^?2 day^?1, which indicates that San Quintín Bay was a net autotrophic system during the atypical warm oceanographic condition in 2014. This pattern of seasonal variations in the carbon balance at San Quintín Bay appears to be linked to the life cycle of benthic communities, which play an important role in the whole-ecosystem metabolism. Under the limited input from external sources coupled with an increase in seawater temperatures, the recycled benthic carbon and nutrient fluxes play a major role to sustain water-column processes within the bay. Since the upwelling condition may influence the magnitude of the air–water CO₂ fluxes, our results clearly indicated that San Quintín Bay is a net source of carbon to the atmosphere regardless of the adjacent oceanic conditions. Our study sheds light on the carbon dynamics and its metabolic implications in a shallow coastal ecosystem under a regional warm anomaly and contributes potentially relevant information in view of the likely future scenario of global climate change.     

Groundwater,Acid and Carbon Dioxide Dynamics Along a Coastal Wetland,Lake and Estuary Continuum

Coastal wetlands are hotspots for biodiversity and biological productivity, yet the hydrology and carbon cycling within these systems remains poorly understood due to their complex nature. By using a novel spatiotemporal approach, this study quantified groundwater discharge and the related inputs of acidity and CO₂ along a continuum of a modified coastal acid sulphate soil (CASS) wetland, a coastal lake and an estuary under highly contrasting hydrological conditions. To increase the resolution of spatiotemporal data and advance upon previous methodologies, we relied on automated observations from four simultaneous time-series stations to develop multiple radon mass balance models to estimate groundwater discharge and related groundwater inputs of acidity and dissolved inorganic carbon (DIC), along with surface water to atmosphere CO₂ fluxes. Spatial surveys indicated distinct acid hotspots with minimum surface water pH of 2.91 (dry conditions) and 2.67 (flood conditions) near a non-remediated (drained) CASS area. Under flood conditions, groundwater discharge accounted for ～14.5 % of surface water entering the lake. During the same period, acid discharge from the acid sulphate soil section of the continuum produced ～4.8 kg H₂SO₄?ha^?1 day^?1, a rate much higher than previous studies in similar systems. During baseflow conditions, the low pH water was rapidly buffered within the estuarine lake, with the pH increasing from 4.22 to 6.07 over a distance of ～250 m. The CO₂ evasion rates within the CASS were extremely high, averaging 2163?±?125 mmol m^?2 day^?1 in the dry period and 4061?±?259 mmol m^?2 day^?1 under flood conditions. Groundwater input of DIC could only account for 0.4 % of this evasion in the dry conditions and ～5 % during the flood conditions. We demonstrated that by utilising a spatiotemporal (multiple time-series stations) approach, the study was able to isolate distinct zones of differing hydrology and biogeochemistry, whilst providing more reasonable groundwater acid input estimates and air–water CO₂ flux estimates than some traditional sampling designs. This study highlights the notion that modified CASS wetlands can release large amounts of CO₂ to the atmosphere because of high groundwater acid inputs and extremely low surface water pH.     

An evaluation of rate equations for calcite precipitation kinetics at pCO2 less than 0.01 atm and pH greater than 8

We used a reproducible seeded growth technique with a pH-stat to study the kinetics of calcite precipitation at 25°C. We performed different experiments at initial Ca²⁺ and HCO₃^? concentrations ranging from 0.7–2 and 4–7 mmol L^?1, pH values ranging from 8.25 to 8.70, $\text{pCO}{}_2$ values ranging from 0.0006 to 0.01 atm, and ionic strengths ranging from 0.015 to 0.10 mol L^?1. With this experimental data set, we used initial rate measurements and integral methods to test several precipitation rate equations. Rate equations that possess a disequilibrium functional dependence, such as the BURTON et al. (1951) dislocation model, forms of the Davies and Jones (1955) model, and the model used by Reddy and Nancollas (1973), did not adequately describe the kinetics of calcite precipitation at pH greater than 8 and $\text{pCO}{}_2$ less than 0.01 atm. Rate equations that describe independent dissolution and precipitation mechanisms with elementary reactions, such as the equation presented by Plummeret al. (1978), and nancollas and Reddy (1971) were more successful. However, Plummer's model did not adequately describe the rate of all experiments due to the presence of an OH^? surface term in the precipitation rate equation. The elementary reaction of the Nancollas and Reddy model is written in terms of bulk Ca²⁺ and CO₃^? concentrations, and appears to be the most successful model which describes calcite precipitation at pH > 8 and $\text{pCO}{}_2\text{< 0.01}$ atm. The Nancollas and Reddy model, altered to account for varying ionic strengths, adequately described the rate of all experiments and yielded a precipitation rate constant of $\text{118.2 ± 13.9}$ dm⁶ mol^?1 m^?2 s^?1, with an apparent Arrhenius activation energy of 48.1 kJ mol^?1.     

Carbonate Chemistry and Air–Sea CO2 Flux in a NW Mediterranean Bay Over a Four-Year Period: 2007–2011

The Service d’Observation de la Rade de Villefranche-sur-Mer is designed to study the temporal variability of hydrological conditions as well as the abundance and composition of holo- and meroplankton at a fixed station in this bay of the northwest Mediterranean. The weekly data collected at this site, designated as “Point B” since 1957, represent a long-term time series of hydrological conditions in a coastal environment. Since 2007, the historical measurements of hydrological and biological conditions have been complemented by measurements of the CO₂–carbonic acid system parameters. In this contribution, CO₂–carbonic acid system parameters and ancillary data are presented for the period 2007–2011. The data are evaluated in the context of the physical and biogeochemical processes that contribute to variations in CO₂ in the water column and exchange of this gas between the ocean and atmosphere. Seasonal cycles of the partial pressure of CO₂ in seawater (pCO₂) are controlled principally by variations in temperature, showing maxima in the summer and minima during the winter. Normalization of pCO₂ to the mean seawater temperature (18.5 °C), however, reveals an apparent reversal of the seasonal cycle with maxima observed in the winter and minima in the summer, consistent with a biogeochemical control of pCO₂ by primary production. Calculations of fluxes of CO₂ show this area to be a weak source of CO₂ to the atmosphere during the summer and a weak sink during the winter but near neutral overall (range ?0.3 to +0.3 mmol CO₂ m^?2 h^?1, average 0.02 mmol CO₂ m^?2 h^?1). We also provide an assessment of errors incurred from the estimation of annual fluxes of CO₂ as a function of sampling frequency (3-hourly, daily, weekly), using data obtained at the Hawaii Kilo Nalu coastal time-series station, which shows similar behavior to the Point B location despite significant differences in climate and hydrological conditions and the proximity of a coral reef ecosystem.     

Variation characteristics of CO2 in a newly-excavated soil profile,Chinese Loess Plateau: Excavation-induced ancient soil organic carbon decomposition

Soils of the Chinese Loess Plateau(CLP)contain substantial amounts of soil inorganic carbon(SIC),as well as recent and ancient soil organic carbon(SOC).With the advent of the Anthropocene,human perturbation,including excavation,has increased soil CO₂ emission from the huge loess carbon pool.This study aims to determine the potential of loess CO₂ emission induced by excavation.Soil CO₂ were continuously monitored for seven years on a newly-excavated profile in the central CLP and the stable C isotope compositions of soil CO₂ and SOC were used to identify their sources.The results showed that the soil CO₂ concentrations ranged from 830μL·L^-1 to 11190μL·L^-1 with an annually reducing trend after excavation,indicating that the human excavation can induce CO₂ production in loess profile.Theδ¹³ C of CO₂ ranged from–21.27‰to–19.22‰(mean:–20.11‰),with positive deviation from top to bottom.The range of δ¹³CSOC was–24.0‰to–21.1‰with an average of–23.1‰.Theδ¹³ C-CO₂ in this study has a positive relationship with the reversed CO₂ concentration,and it is calculated that 80.22%of the soil CO₂ in this profile is from the microbial decomposition of SOC and 19.78%from the degasification during carbonate precipitation.We conclude that the human excavation can significantly enhance the decomposition of the ancient OC in loess during the first two years after perturbation,producing and releasing soil CO₂ to atmosphere.     

Dynamics of carbon fluxes with responses to vegetation,meteorological and terrain factors in the south-eastern Tibetan Plateau

Tibetan Plateau (TP) is the highest and most extensive plateau in the world and has been known as the roof of the world, and it is sensitive to climate change. The researches of CO₂ fluxes (F _C) in the TP region play a significant role in understanding regional and global carbon balance and climate change. Eddy covariance flux measurements were conducted at three sites of south-eastern TP comprising Dali (DL, cropland ecosystem), LinZhi (LZ, alpine meadow ecosystem) and Wenjiang (WJ, cropland ecosystem); amongst those DL and LZ are located in plateau region, while WJ is in plain region. Dynamics of F _C and influences of vegetation, meteorological (air temperature, photosynthetically active radiation, soil temperature and soil water content) and terrain factors (altitude) were analysed on the basis of data taken during 2008. The results showed that, in the cool sub-season (March, April, October and December), carbon sink appeared even in December with fluxes of (?0.021 to ?0.05) mg CO₂ m^?2 s^?1 and carbon source only in October (0.03 ± 0.0048) mg CO₂ m^?2 s^?1 in DL and WJ site. In LZ site, carbon sink was observed in April: (?0.036 ± 0.0023) mg CO₂ m^?2 s^?1 and carbon sources in December and March (0.008–0.010 mg CO₂ m^?2 s^?1). In the hot sub-season (May–August), carbon source was observed only in May with (0.011 ± 0.0022), (0.104 ± 0.0029) and (0.036 ± 0.0017) fluxes in LZ, DL and WJ site, respectively, while carbon sinks with (?0.021 ± 0.0041), (?0.213 ± 0.0007) and (?0.110 ± 0.0015) mg CO₂ m^?2 s^?1 fluxes in LZ, DL, and WJ, respectively. Comparing with plain region (WJ), carbon sinks in plateau region (DL and LZ) lasted for a longer time, and the absorption sum was large and up to (–357.718 ± 0.0054) and (?371.111 ± 0.0039) g C m^?2 year^?1, respectively. The LZ site had the weakest carbon sink with (?178.547 ± 0.0070) g C m^?2 year^?1. Multivariate analysis of covariance showed that altitude (AL) as an independent factor explained 39.5 % of F _C (P < 0.026). F _C had a quadratic relationship with Normalized difference vegetation index (NDVI) (R ² ranges from 0.485 to 0.640 for three sites), an exponential relationship with soil temperature at 5-cm depth (ST ₅) at night time and a quadratic relationship with air temperature (T _a) at day time. Path analysis indicated that photosynthetically active radiation (PAR), sensible heat fluxes (H) and other factors all had direct or indirect effects on F _C in all of the three tested sites around the south-eastern TP.     

Fluid infiltration during contact metamorphism of interbedded marble and calc-silicate hornfels, Twin Lakes area, central Sierra Nevada, California

Abstract In the Twin Lakes area, central Sierra Nevada, California, most contact metamorphosed marbles contain calcite + dolomite + forsterite ± diopside ± phlogopite ± tremolite, and most calc-silicate hornfelses contain calcite + diopside + wollastonite + quartz ± anorthite ± K-feldspar ± grossular ± titanite. Mineral-fluid equilibria involving calcite + dolomite + tremolite + diopside + forsterite in two marble samples and wollastonite + anorthite + quartz + grossular in three hornfels samples record P± 3 kbar and T± 630° C. Various isobaric univariant assemblages record CO₂-H₂O fluid compositions of χCO₂= 0.61–0.74 in the marbles and χCO₂= 0.11 in the hornfelses. Assuming a siliceous dolomitic limestone protolith consisting of dolomite + quartz ° Calcite ± K-feldspar ± muscovite ± rutile, all plausible prograde reaction pathways were deduced for marble and hornfels on isobaric T-XCO₂ diagrams in the model system K₂O-CaO-MgO-Al₂O₃-SiO₂-H₂O-CO₂. Progress of the prograde reactions was estimated from measured modes and mass-balance calculations. Time-integrated fluxes of reactive fluid which infiltrated samples were computed for a temperature gradient of 150 °C/km along the fluid flow path, calculated fluid compositions, and estimated reaction progress using the mass-continuity equation. Marbles and hornfelses record values in the range 0.1–3.6 × 10⁴ cm³/cm² and 4.8–12.9 × 10⁴ cm³/cm², respectively. For an estimated duration of metamorphism of 10⁵ years, average in situ metamorphic rock permeabilities, calculated from Darcy's Law, are 0.1–8 × 10^?6 D in the marbles and 10–27 × 10^?6 D in the hornfelses. Reactive metamorphic fluids flowed up-temperature, and were preferentially channellized in hornfelses relative to the marbles. These results appear to give a general characterization of hydrothermal activity during contact metamorphism of small pendants and screens (dimensions ± 1 km or less) associated with emplacement of the Sierra Nevada batholith.     

Evolution of the radio emission of the Crab nebula from long-term observations at 927 and 151.5 MHz

Radio flux measurements of the Crab nebula have been performed over many years relative to Orion A at 927 MHz and relative to Cygnus A and Virgo A at 151.5 MHz. The inferred average secular rates of decrease in the radio flux of the Crab nebula are d _{927 MHz} = ?0.18 ± 0.10% yr^?1 over 1977–2000 and d _{151.5 MHz} = ?0.3 ± 0.1% yr^?1 over 1980–2003. The weighted mean flux-decrease rate averaged over several years of relative measurements at 86, 151.5, 927, and 8000 MHz is d _mw = ?0.17 ± 0.02% yr^?1. The secular flux decrease is frequency independent, with an upper limit of |dα/dt| < 3 × 10^?4 yr^?1 for the absolute value of the rate of change of the spectral index, and remains constant in time when averaged over long time intervals. The results of our measurements at 151.5 and 927 MHz combined with published absolute measurements at 81.5 and 8250 MHz are used to determine the radio spectrum of the Crab nebula for epoch 2010.0.     

Air–water CO<Subscript>2</Subscript> flux in an algae bloom year for Lake Hongfeng,Southwest China: implications for the carbon cycle of global inland waters

The carbon cycle of global inland waters is quantitatively comparable to other components in the global carbon budget. Among inland waters, a significant part is man-made lakes formed by damming rivers. Man-made lakes are undergoing a rapid increase in number and size. Human impacts and frequent algae blooms lead to it necessary to make a better constraint on their carbon cycles. Here, we make a primary estimation on the air–water CO₂ transfer flux through an algae bloom year for a subtropical man-made lake—Hongfeng Lake, Southwest China. To do this a new type of glass bottles was designed for content and isotopic analysis of DIC and other environmental parameters. At the early stage of algae bloom, CO₂ was transferred from the atmosphere to the lake with a net flux of 1.770 g·C·m^?2. Later, the partial pressure (pCO₂) of the aqueous CO₂ increased rapidly and the lake outgassed to the atmosphere with a net flux of 95.727 g·C·m^?2. In the remaining days, the lake again took up CO₂ from the atmosphere with a net flux of 14.804 g·C·m^?2. As a whole, Lake Hongfeng released 4527 t C to the atmosphere, accounting for one-third of the atmosphere/soil CO₂ sequestered by chemical weathering in the whole drainage. With an empirical mode decomposition method, we found air temperature plays a major role in controlling water temperature, aqueous pCO₂ and hence CO₂ flux. This work indicates a necessity to make detailed and comprehensive carbon budgets in man-made lakes.