Carbon and its isotopes in mid-oceanic basaltic glasses

Three carbon components are evident in eleven analyzed mid-oceanic basalts: carbon on sample surfaces (resembling adsorbed gases, organic matter, or other non-magmatic carbon species acquired by the glasses subsequent to their eruption), mantle carbon dioxide in vesicles, and mantle carbon dissolved in the glasses. The combustion technique employed recovered only reduced sulfur, all of which appears to be indigenous to the glasses. The dissolved carbon concentration (measured in vesicle-free glass) increases with the eruption depth of the spreading ridge, and is consistent with earlier data which show that magma carbon solubility increases with pressure. The total glass carbon content (dissolved plus vesicular carbon) may be controlled by the depth of the shallowest ridge magma chamber. Carbon isotopic fractionation accompanies magma degassing; vesicle CO₂ is about 3.8‰ enriched in ¹³C, relative to dissolved carbon. Despite this fractionation, δ¹³C_PDB values for all spreading ridge glasses lie within the range ?5.6 and ?7.5, and the δ¹³C_PDB of mantle carbon likely lies between ?5 and ?7. The carbon abundances and δ¹³C_PDB values of Kilauea East Rift glasses apparently are influenced by the differentiation and movement of magma within that Hawaiian volcano. Using ³He and carbon data for submarine hydrothermal fluids, the present-day mid-oceanic ridge mantle carbon flux is estimated very roughly to be about 1.0 × 10¹³ g C/yr. Such a flux requires 8 Gyr to accumulate the earth's present crustal carbon inventory.     

Dissolved black carbon concentrations in suspended particulate matter from the Bohai Sea

Dissolved black carbon(DBC)includes the water-soluble component of black carbon and/or its degradation products.It is a hydrophobic organic compound due to its thick cyclic aromatic structure and can therefore be present as particulate DBC(PDBC)on suspended particulate matter or particulate organic matter.PDBC is not equivalent to particulate black carbon(PBC)and is thus often overlooked when researchers measure PBC in particulate matter using current conventional methods.Consequently,the amount...     

Nitrogen isotope geochemistry of basaltic glasses: implications for mantle degassing and structure?

The nitrogen isotope geochemistry of 15 basaltic glasses has been investigated using stepped heating and high sensitivity static vacuum mass spectrometry. At low temperature (< 600°C) the glasses release small amounts of nitrogen with δ¹⁵N_AIR, averaging −0.3‰, suggesting surficial adsorption of atmospheric nitrogen. At high temperature, usually with a maximum at 1000°C, indigenous nitrogen with a concentration ranging from 0.2 to 2.1 ppm is released. The δ¹⁵N values of this high temperature release show a wide range from −4.5‰ to +15.5‰. There is no correlation between N ppm and δ¹⁵N, and the samples apparently form 3 groups with distinctive δ¹⁵N. Six MORB glasses from the Mid-Atlantic Ridge, East Pacific Rise and Juan de Fuca Ridge define a group with δ¹⁵N = +7.5 ± 1.3‰. In contrast two Indian Ocean MORB glasses (Carlsberg Ridge and Gulf of Aden) gave negative δ¹⁵N averaging −3.2‰. Glasses from Loihi Seamount have high δ¹⁵N averaging +14.0 ± 1.0‰. Comparison of the δ¹⁵N data with the mantle models derived from helium and argon isotope studies suggests that the wide range in δ¹⁵N may reflect in part heterogeneities in the mantle related to its degassing history. It is possible, however, that magmatic degassing processes have also affected nitrogen isotopic compositions, and the data cannot yet be unambiguously interpreted in terms of source variations.     

Volatile and trace elements in basaltic glasses from Samoa: Implications for water distribution in the mantle

We report volatile (H₂O, CO₂, F, S, Cl) and trace element data for submarine alkalic basalt glasses from the three youngest Samoan volcanoes, Ta'u, Malumalu and Vailulu'u. Most samples are visibly sulfide saturated, so have likely lost some S during fractionation. Cl / K ratios (0.04–0.15) extend to higher values than pristine MORBs, but are suspected to be partly due to source differences since Cl / K roughly varies as a function of ⁸⁷Sr / ⁸⁶Sr. There are no resolvable differences in the relative enrichment of F among sources, and compatibility of F during mantle melting is established to be nearly identical to Nd. Shallow degassing has affected CO₂ in all samples, and H₂O only in the most shallowly erupted samples from Vailulu'u. Absolute water contents are high for Samoa (0.63–1.50 wt.%), but relative enrichment of water compared to equally incompatible trace elements (Ce, La) is low and falls entirely below normal MORB values. H₂O / Ce (58–157) and H₂O / La (120–350) correlate inversely with ⁸⁷Sr / ⁸⁶Sr compositions (0.7045–0.7089). This leads us to believe that, because of very fast diffusion of hydrogen in mantle minerals, recycled lithospheric material with high initial water and trace element content will lose water to the drier ambient mantle during storage within the inner Earth. The net result is the counter-intuitive appearance of greater dehydration with greater mantle enrichment. We expect that subducted slabs will experience a two-stage dehydration history, first within subduction zones and then in the ambient mantle during long-term convective mixing.     

Dissolved organic carbon in permafrost regions: A review

A large quantity of organic carbon(C) is stored in northern and elevational permafrost regions. A portion of this large terrestrial organic C pool will be transferred by water into soil solution(～0.4 Pg C yr~(-1))(1 Pg=10~(15) g), rivers (～0.06 Pg C yr~(-1)),wetlands, lakes, and oceans. The lateral transport of dissolved organic carbon(DOC) is the primary pathway, impacting river biogeochemistry and ecosystems. However, climate warming will substantially alter the lateral C shifts in permafrost regions.Vegetation, permafrost, precipitation, soil humidity and temperature, and microbial activities, among many other environmental factors, will shift substantially under a warming climate. It remains uncertain as to what extent the lateral C cycle is responding,and will respond, to climate change. This paper reviews recent studies on terrestrial origins of DOC, biodegradability, transfer pathways, and modelling, and on how to forecast of DOC fluxes in permafrost regions under a warming climate, as well as the potential anthropogenic impacts on DOC in permafrost regions. It is concluded that:(1) surface organic layer, permafrost soils,and vegetation leachates are the main DOC sources, with about 4.72 Pg C DOC stored in the topsoil at depths of 0–1 m in permafrost regions;(2) in-stream DOC concentrations vary spatially and temporally to a relatively small extent (1–60 mg C L~(-1)) and annual export varies from 0.1–10 g C m~(-2) yr~(-1);(3) biodegradability of DOC from the thawing permafrost can be as high as 71%, with a median at 52%;(4) DOC flux is controlled by multiple factors, mainly including vegetation, soil properties,permafrost occurrence, river discharge and other related environmental factors, and(5) many statistical and process-based models have been developed, but model predictions are inconsistent with observational results largely dependent on the individual watershed characteristics and future discharge trends. Thus, it is still difficult to predict how future lateral C flux will respond to climate change, but changes in the DOC regimes in individual catchments can be predicted with a reasonable reliability. It is advised that sampling protocols and preservation and analysis methods should be standardized, and analytical techniques at molecular scales and numerical modeling on thermokarsting processes should be prioritized.     

Dissolved inorganic carbon in the ocean and climate

Changes in the climate conditions in the recent decade arouse the heightened interest to the problem of the greenhouse effect and consequently to studying the dynamics of CO₂ concentration in the ocean-atmosphere system. The modern changes in CO₂ concentration and temperature can result both from the anthropogenic influence and from the rhythms of natural processes. The results of modelling carbon equilibrium in the World Ocean water for the Quaternary suggest that the modern climate change is a part of natural climate variations having taken place for at least more than 400 thousand years.     

The mechanism of Re enrichment in arc magmas: evidence from Lau Basin basaltic glasses and primitive melt inclusions

Rhenium and other trace element data were obtained in situ by laser ablation ICP-MS analysis of submarine-erupted volcanic glasses and olivine-hosted melt inclusions from the Valu Fa Ridge, the south tip of the Lau Basin, in the southwestern Pacific Ocean. The chemistry of the Lau Basin basaltic glasses changes systematically from compositions similar to MORB in the Lau Spreading Centers, to more arc-like compositions in the Valu Fa Ridge, providing geochemical profiles both along the Lau Spreading Centers (ridges) and across the Valu Fa Ridge. The east seamount samples of the Valu Fa Ridge have diagnostic trace element ratios (Ba/Nb, Nb/U, Ce/Pb) close to global arc averages, with high Ba/La, indicating addition of considerable amounts of subduction-released fluids. In contrast, samples from the west seamount and the Lau Spreading Centers show a smaller influence from subduction fluids. The variable degrees of subduction influences apparent in the chemistry of these suites provide an ideal means to explore the mechanisms of Re enrichment in undegassed arc magmas. All of the analyzed arc melts have significantly higher Re concentrations than previously published, largely subaerially erupted samples, confirming that high Re is a characteristic of undegassed arc magmas. The east seamount samples are characterized by higher Re and lower Yb/Re than the more MORB-like Lau Spreading Center lavas. The lack of correlation between Yb/Re and Fo of host olivine suggests that low Yb/Re is not due to magmatic differentiation. When the Lau Basin sample suite is plotted together with MORB data, Yb/Re is positively correlated with Ce/Pb and Nb/U, and negatively correlated with Ba/Nb, indicating that Re is much more mobile than Yb during dehydration of subducted slabs. Thus, Re enrichment in arc magmas is likely due to addition of Re via fluids released from subducted slabs; the recognition of high Re in arcs favors arguments for a slab origin of radiogenic ¹⁸⁷Os/¹⁸⁸Os components in arc rocks.     

Erratum to: Dissolved organic carbon in permafrost regions: A review

The article Dissolved organic carbon in pennafrost regions: A review, written by Qiang MA, Huijun JIN, Congrong YU, and Victor F. BENSE, was erroneously originally published online without open access. After publication in Vol 62 Issue 2 this was corrected and the article is now an open access publication.     

The carbon dioxide system in the oceans

A model of the carbon dioxide system in nature is derived and is used to further our understanding of the factors which control this system in the oceans, the atmosphere, and the sediments.     

Earthquakes produce carbon dioxide in crustal faults

Fourier transform infrared (FTIR) microanalysis of pseudotachylytes (i.e. friction-induced melts produced by seismic slip) from the Nojima fault (Japan) reveals that earthquakes almost instantaneously expel 99 wt.% of the wall rock CO₂ content. Carbon is exsolved because it is supersaturated in the friction melts. By extrapolation to a crustal-scale fault rupture, large events such as the M7.2 Kobe earthquake (1995) may yield a total production of 1.8 to 3.4 × 10³ tons CO₂ within a few seconds. This extraordinary release of CO₂ can cause a flash fluid pressure increase in the fault plane, and therefore enhance earthquake slip or trigger aftershocks; it may also explain the anomalous discharge of carbon monitored in nearby fault springs after large earthquakes. Because carbon saturation in silicate melts is pressure-dependent, FTIR can be used as a new tool to constrain the maximum depth of pseudotachylyte formation in exhumed faults.     

Dissolved organic carbon export from a cutover and restored peatland

High demand for horticultural peat has increased peatland drainage and peat extraction in Canada. The hydrology and carbon cycling of these cutover peatlands is greatly altered, necessitating active restoration efforts to permit the regeneration of Sphagnum mosses and the re‐establishment of natural peatland function. The effect of peatland extraction and restoration on the export of dissolved organic carbon (DOC) was examined for three successive seasons (May to October, 1999 to 2001) at two different sites (cutover and restored) in eastern Québec. A shift towards higher DOC concentrations was observed following peatland extraction (maximum: 182·6 mg L^?1) and concentrations remained high post‐restoration (maximum: 191·0 mg L^?1). The cutover site exported more DOC than the restored site in all three study seasons. The highest exports occurred during the wettest year (1999), with cutover and restored site export of 10·3 and 4·8 g m^?2, respectively. In 2000, 8·5 g C m^?2 was released from the cutover site, while the restored site released less than half that amount (3·4 g C m^?2). In 2001, the restored site released about the same amount of DOC as in the previous year (3·5 g C m^?2), while the cutover site load dropped to 6·2 g C m^?2. Both sites were net exporters of DOC in all years. Copyright © 2007 John Wiley & Sons, Ltd.     

Dissolved organic carbon transport in the Qilian mountainous areas of China

The Dissolved Organic Carbon (DOC) content of rivers is the most significant part of the carbon cycle migration in the basin under consideration, and it is the basis for a comprehensive understanding of the regional carbon cycle. In this study, we periodically collected samples from four monitoring stations in the Xiying River Basin of the Qilian Mountains in the northern Qinghai-Tibet Plateau. We calculated the fluxes of organic carbon in the rivers within the study area and have discussed the influencing factors of DOC concentration in these rivers. The results showed that: (a) The DOC concentration and transport flux of the Xiying river showed significant seasonal changes. The DOC concentration during summer and autumn was higher than that in winter and spring, and the output flux in summer and autumn accounted for approximately 88.3% of the total annual output. (b) Precipitation runoff has a higher DOC concentration than meltwater runoff. Climate factors, river-water chemical characteristics, and seasonal frozen-soil changes in the river basin have significant effects on the river DOC concentration and transport flux. (c) Larger runoff causes higher DOC concentrations in rivers. Runoff is the primary means of carbon migration in the inland river basin. Carbon migration is significant from the upstream to the middle and downstream sections of the inland river basin.     

Dissolved organic carbon in a eutrophic lake; dynamics,biodegradability and origin

The seasonal and spatial changes in dissolved organic carbon (DOC) in Lake Kasumigaura, a shallow, eutrophic lake, were analyzed and the lability of DOC was tested by long-term incubations. There was a nearly 1 mgCl^–1 downstream increase in refractory DOC in the lake; at the center it fluctuated little seasonally. The characteristic UV-absorbance: DOC ratios were determined for samples from the influent rivers (pedogenic: used interchangeably with allochthonous) and outdoor experimental ponds (autochthonous) during incubations. These ratios were then used to calculate the proportion of total measured lake water DOC in each of four components: pedogenic-refractory (PR), pedogenic-labile (PL), autochthonous-refractory (AR) and autochthonous-labile (AL). PR was uniform (around 1.5 mgCl^–1) or diminished very slightly over time. AR increased from nearly zero at the station closest to an influent river to 1 mgCl^–1 at the lake center. PL declined downstream from 0.3 mgCl^–1 to zero. AL was virtually constant at 0.8 mgCl^–1 except at the station closest to the influent river. The constancy of the UV-absorbance: DOC ratio during the biodegradation process was confirmed for Lake Kasumigaura; hence a two-component model (pedogenic-autochthonous) could be applied here without consideration of DOC lability. However, this assumption is not always met for other water bodies, and therefore it should be checked before applying a two-component model elsewhere.     

Dissolved inorganic carbon evolution in neutral discharge from mine tailings piles

We measured the concentrations of dissolved inorganic carbon (DIC) and major ions and the stable carbon isotope ratios of DIC (δ¹³C_DIC) in two creeks discharging from carbonate‐rich sulphide‐containing mine tailings piles. Our aim was to assess downstream carbon evolution of the tailings discharge as it interacted with the atmosphere. The discharge had pH of 6.5–8.1 and was saturated with respect to carbonates. Over the reach of one creek, the DIC concentrations decreased by 1.1 mmol C/l and δ¹³C_DIC increased by ~4.0‰ 200 m from the seep source. The decrease in the DIC concentrations was concomitant with decreases in the partial pressure of CO_2(aq) because of the loss of excess CO_2(aq) from the discharge. The corresponding enrichment in the δ¹³C_DIC is because of kinetic isotope fractionation accompanying the loss of CO_2(g). Over the reach of the other creek, there was no significant decrease in the DIC concentrations or notable changes in the δ¹³C_DIC. The insignificant change in the DIC concentrations and the δ¹³C_DIC is because the first water sample was collected 160 m away from the discharge seep, not accessible during this research. In this case, most of the excess CO_2(aq) was lost before our first sampling station. Our results indicate that neutral discharges from tailings piles quickly lose excess CO_2(aq) to the atmosphere and the DIC becomes enrich in ¹³C. We suggest that a significant amount of carbon cycling in neutral discharges from tailings piles occur close to the locations where the discharge seeps to the surface. Copyright © 2015 John Wiley & Sons, Ltd.     

Dissolved oxygen as an indicator of bioavailable dissolved organic carbon in groundwater

Concentrations of dissolved oxygen (DO) plotted vs. dissolved organic carbon (DOC) in groundwater samples taken from a coastal plain aquifer of South Carolina (SC) showed a statistically significant hyperbolic relationship. In contrast, DO-DOC plots of groundwater samples taken from the eastern San Joaquin Valley of California (CA) showed a random scatter. It was hypothesized that differences in the bioavailability of naturally occurring DOC might contribute to these observations. This hypothesis was examined by comparing nine different biochemical indicators of DOC bioavailability in groundwater sampled from these two systems. Concentrations of DOC, total hydrolysable neutral sugars (THNS), total hydrolysable amino acids (THAA), mole% glycine of THAA, initial bacterial cell counts, bacterial growth rates, and carbon dioxide production/consumption were greater in SC samples relative to CA samples. In contrast, the mole% glucose of THNS and the aromaticity (SUVA(254)) of DOC was greater in CA samples. Each of these indicator parameters were observed to change with depth in the SC system in a manner consistent with active biodegradation. These results are uniformly consistent with the hypothesis that the bioavailability of DOC is greater in SC relative to CA groundwater samples. This, in turn, suggests that the presence/absence of a hyperbolic DO-DOC relationship may be a qualitative indicator of relative DOC bioavailability in groundwater systems.