Integrated estimates of global terrestrial carbon sequestration

Assessing the contribution of terrestrial carbon sequestration to climate change mitigation requires integration across scientific and disciplinary boundaries. A comprehensive analysis incorporating ecologic, geographic and economic data was used to develop terrestrial carbon sequestration estimates for agricultural soil carbon, reforestation and pasture management. These estimates were applied in the MiniCAM integrated assessment model to evaluate mitigation strategies within policy and technology scenarios aimed at achieving atmospheric greenhouse gas stabilization by 2100. Terrestrial sequestration reaches a peak rate of 0.5–0.7 GtC yr⁻¹ in mid-century with contributions from agricultural soils (0.21 GtC yr⁻¹), reforestation (0.31 GtC yr⁻¹) and pasture (0.15 GtC yr⁻¹). Sequestration rates vary over time and with different technology and policy scenarios. The combined contribution of terrestrial sequestration over the next century ranges from 23 to 41 GtC.     

Discriminating between background and mine-impacted groundwater at the Phoenix mine,Nevada USA

Differentiating between mineralized and non-mineralized background groundwater chemistry at a mine site can be challenging if there is an overprint of past and/or current mining on naturally mineralized conditions. At the Phoenix mine in the Copper Canyon mining district of Nevada, quantile–quantile H⁺/SO₄ plots were used to segregate four wells clearly impacted by historical mining activity. The mineralogy of rock at the elevation of the well screen interval was used to partition the 53 remaining wells into mineralized and non-mineralized populations. For each class, groundwater chemistry was examined to identify if SO₄ and H⁺ trends were stable (unimpacted) or increasing (impacted). Then each well was mapped as one of four resulting groundwater types across the mine site, defining the spatial extent of the different groups. Several groundwater regions were identified. A group of mineralized, mine-impacted wells (Type II) are located in Philadelphia Canyon adjacent to the Cu leach facility, with the anthropogenically impacted area bounded by several hydrologically downgradient, mineralized, unimpacted wells (Type I) to the south and east. There is a set of non-mineralized, impacted wells (Type III) downgradient from the tailings pond facility, where a historical release of SO₄ is apparent in the well record. However, in some downgradient wells the tailings pond pump-back mitigation system has resulted in recovery of the groundwater quality to a non-mineralized background condition. Finally, in the vicinity of the Reona heap leach pad, there is a group of non-mineralized, unimpacted wells (Type IV). Not surprisingly, most mineralized wells (Types I and II) are located in or near mined areas, while non-mineralized wells (Types III and IV) tend to be in the southern portion of the facility in the alluvia of Buffalo and Reese River valleys.     

Transformation of two-pyroxene hornblende granulite to garnet granulite involving simultaneous melting and fracturing of the lower crust, Fiordland, New Zealand

Granulite facies gabbroic and dioritic gneisses in the Pembroke Valley, Milford Sound, New Zealand, are cut by vertical and planar garnet reaction zones in rectilinear patterns. In gabbroic gneiss, narrow dykes of anorthositic leucosome are surrounded by fine‐grained garnet granulite that replaced the host two‐pyroxene hornblende granulite at conditions of 750 °C and 14 kbar. Major and trace element whole‐rock geochemical data indicate that recrystallization was mostly isochemical. The anorthositic veins cut contacts between gabbroic gneiss and dioritic gneiss, but change in morphology at the contacts, from the anorthositic vein surrounded by a garnet granulite reaction zone in the gabbroic gneiss, to zones with a septum of coarse‐grained garnet surrounded by anorthositic leucosome in the dioritic gneiss. The dioritic gneiss also contains isolated garnet grains enclosed by leucosome, and short planar trains of garnet grains linked by leucosome. Partial melting of the dioritic gneiss, mostly controlled by hornblende breakdown at water‐undersaturated conditions, is inferred to have generated the leucosomes. The form of the leucosomes is consistent with melt segregation and transport aided by fracture propagation; limited retrogression suggests considerable melt escape. Dyking and melt escape from the dioritic gneiss are inferred to have propagated fractures into the gabbroic gneiss. The migrating melt scavenged water from the surrounding gabbroic gneiss and induced the limited replacement by garnet granulite.     

Relationships between higher moments of concentration and of dose in turbulent dispersion

Chatwin and Sullivan (1990) proposed simple results for the relationships between moments of scalar fluctuations in self-similar turbulent shear flows. They showed these relationships to be well satisfied by observations from a range of experiments. Here their theory is extended to the skewness, kurtosis and higher order equivalents. It is shown that the relationships between these normalised moments are parameter-free, and are identical to those for zero molecular diffusion. Experimental observations are presented which show a remarkable degree of collapse when these normalised moments are plotted against each other. The agreement with the theoretical results is reasonably good, and better than for some other standard statistical distributions which are commonly applied to such observations. This is true not only for the concentration, but also for generalised doses. It is concluded that the simple theory provides a satisfactory basis for a model of both the concentration and of dose. Furthermore, the results suggest that the concentration and the dose can be modelled through a perturbation to a two-state model.     

ExcessHe in the Atlantic Ocean

³/He⁴He measurements at two stations in the Atlantic show that the deep water (> 2 km) contains far less excess³He than our previous measurements have shown for the Pacific Ocean. The³/He⁴He ratio anomaly (relative to atmospheric³/He⁴He) is approximately 5% for the deep Atlantic compared to about 20% for the deep Pacific. The North Atlantic³He profile shows much more structure than the South Atlantic profile, with maxima observed at 500 m, 1900 m, and 3200 m. The maxima at 500 m and 1900 m are probably due to in situ tritium decay, whereas the 3200 m maximum cannot be due to tritium, and is probably due to leakage of³He into the Atlantic water from the mantle. It seems significant that maxima in the trace elements Cu, Zn and Fe have also been observed at 3200 m at this station by Brewer, Spencer and Robertson.