ALBERT

Description: [1]  GLACE-CMIP5 is a multi-model experiment investigating the impact of soil moisture-climate feedbacks in CMIP5 projections. We present here first GLACE-CMIP5 results based on five Earth System Models, focusing on impacts of projected changes in regional soil moisture dryness (mostly increases) on late 21 st -century climate. Projected soil moisture changes substantially impact climate in several regions in both boreal and austral summer. Strong and consistent effects are found on temperature, especially for extremes (about 1–1.5 K for mean temperature and 2–2.5 K for extreme daytime temperature). In the Northern Hemisphere, effects on mean and heavy precipitation are also found in most models, but the results are less consistent than for temperature. A direct scaling between soil moisture-induced changes in evaporative cooling and resulting changes in temperature mean and extremes is found in the simulations. In the Mediterranean region, the projected soil moisture changes affect about 25% of the projected changes in extreme temperature.

Description: Background: A regional-scale sensitivity study has been carried out to investigate the climatic effects of forest cover change in Europe. Applying REMO (regional climate model of the Max Planck Institute for Meteorology), the projected temperature and precipitation tendencies have been analysed for summer, based on the results of the A2 IPCC-SRES emission scenario simulation. For the end of the 21st century it has been studied, whether the assumed forest cover increase could reduce the effects of the greenhouse gas concentration change. Results: Based on the simulation results, biogeophysical effects of the hypothetic potential afforestation may lead to cooler and moister conditions during summer in most parts of the temperate zone. The largest relative effects of forest cover increase can be expected in northern Germany, Poland and Ukraine, which is 15--20% of the climate change signal for temperature and more than 50% for precipitation. In northern Germany and France, potential afforestation may enhance the effects of emission change, resulting in more severe heavy precipitation events. The probability of dry days and warm temperature extremes would decrease. Conclusions: Large contiguous forest blocks can have distinctive biogeophysical effect on the climate on regional and local scale. In certain regions of the temperate zone, climate change signal due to greenhouse gas emission can be reduced by afforestation due to the dominant evaporative cooling effect during summer. Results of this case study with a hypothetical land cover change can contribute to the assessment of the role of forests in adapting to climate change. Thus they can build an important basis of the future forest policy.

Description: The Serra Norte Carajás banded iron-formation (BIF)-hosted iron ore deposits are located in the Carajás mineral province. The deposits are hosted in the ca. 2.7 Ga Grão Pará Group, a metamorphosed volcanic-sedimentary sequence where jaspilites are under- and overlain by basalts, both at greenschist facies conditions. They represent one of the largest high-grade (〉60 wt % Fe) BIF iron ore deposits and resources in the world, with hypogene iron mineralization considered to be Paleoproterozoic. Four main open pits have, to date, produced about 1.2 billion metric tons (Bt) of high-grade iron ore with additional resources of 10 Bt. Ore types at the Serra Norte deposits include soft and hard ore; the latter consists of banded, massive and/or brecciated ores and is mainly localized along the contact with the surrounding hydrothermally altered basalts. Distinct hydrothermal alteration zones consist of veins and breccias that surround the hard ores, including: (1) an early alteration zone (distal portion of orebodies), characterized by recrystallization of jasper, formation of magnetite (± martite), and the local introduction of quartz and carbonate-sulfide (±quartz) veins; (2) intermediate alteration, synchronous with the main iron ore-forming event, which is accompanied by widespread development of martite, quartz-hematite and hematite-quartz veins, and dissolution of carbonate; and (3) proximal alteration zone having various types of hard and hard-porous hematite ores containing microplaty, anhedral, euhedral, and tabular hematite species. Locally, high-grade breccia ores contain dolomite and kutnahorite matrices indicating carbonate introduction. High-grade ore zones contain quartz ± carbonate-hematite veins and breccias. Combined microthermometry, iron chromatography, and in situ laser ablation ICP-MS analyses on fluid inclusion assemblages from five vein types reveal that (1) early alteration vein-breccia quartz-carbonate contains high-salinity (up to 30 equiv wt % NaCl) fluid inclusions, with Ca, besides Na, K, and Mg, which were trapped at temperatures of 220° to 320°C. The quartz-hosted fluid inclusions have a wide range of Cl/Br ratios, presence of Li, base metals Cu-Pb-Zn, and Fe; (2) intermediate alteration vein quartz contains both low-salinity (Na-Fe-Mg-rich) and high-salinity (Ca-Mg-Fe-rich) fluid inclusions, with trapping temperatures of 210° to 290°C; (3) advanced alteration vein and breccia quartz-carbonate has low- to high-salinity fluid inclusions and trapping temperatures between 240° to 310°C, with the low-salinity inclusions being much more abundant in quartz. There is a gradual dilution of the metals signature in fluid inclusions from early to late- and/or advanced-stage veins and breccias. The large amount of Ca in the fluid inclusions is compatible with extensive exchange of the hydrothermal fluids with the surrounding chloritized-hematitized metabasaltic wall rock. Oxygen isotope analyses on different oxide species reveal that the heaviest 18 O SMOW values, up to 15.2, are recorded for jaspilites, followed by magnetite, between –0.4 to +4.3, and then by different hematite species such as microplaty, anhedral and tabular, which fall in the range of –9.5 to –2.4. These results show a progressive depletion in 18 O values from the earliest introduced hydrothermal oxide magnetite toward the latest tabular hematite. The advanced alteration stage in high-grade ore displays the most depleted 18 O values and represents the highest fluid/rock ratio during hydrothermal alteration. This depletion is interpreted to result from the progressive mixture of descending, heated meteoric water with ascending modified magmatic fluids. Sulfides from the distal zone of metabasaltic rocks have 34 S values close to 0, consistent with a magmatic origin for the sulfur. Heavier 34 S values, of up to 10.8, in vein sulfides hosted in jaspilite, may reflect interaction with meteoric waters or, alternatively, variations in f O 2 and pH conditions during evolution of the hydrothermal fluid. Calcite-kutnahorite 13 C and 18 O values from the distal alteration zones show a large 13 C range of –5.5 to –2.4 and a relatively narrow 18 O range of 9.3 to 11.7. However, dolomite matrix breccias from the advanced hydrothermal zone, i.e., ore, exhibit a wider 18 O range from 15.1 to 21.8 and a more restricted 13 C range from –5.0 to –3.9. This latter range points to a single carbon source, of possible magmatic nature, whereas the larger 18 O range suggests multiple carbon and oxygen sources. The 87 Sr/ 86 Sr ratios for carbonates from the distal and advanced hydrothermal zones range between 0.7116 to 0.7460, suggesting incorporation of strontium from multiple crustal sources, including magmatic-hydrothermal fluids. A dual magmatic-meteoric hydrothermal fluid-flow model is proposed for the hematite ores in which an early, low Cl/Br ratio, saline, ascending modified magmatic fluid, caused widespread oxidation of magnetite to hematite. Progressive influx of light 18 O meteoric water, mixing with the ascending magmatic fluids, is interpreted to have been initiated during the intermediate stage of alteration. The advanced and final hydrothermal stage was dominated by a massive influx of low-salinity meteoric water, which maintained intermediate temperatures of 240° to 310°C, and concomitant formation of the paragenetically latest tabular hematite. The giant Carajás iron deposits are unique in their setting within an Archean granite-greenstone belt and their modified magmatic-meteoric hydrothermal system, compared to the other two end-member BIF iron deposit types, namely the basin-related Hamersley type and the metamorphosed metasedimentary- basin-related Iron-Quadrangle-type. The distinct hydrothermal alteration signature present in both wall-rock basalts and jaspilites, in combination with distinct fluid chemistry signatures, particularly the low 18 O values of paragenetically late oxides indicative of massive influx of meteoric water into the high-grade orebodies, provide distinctive parameters for defining the Carajás end-member type BIF deposit class.

Description: [1]  To assess the robustness of projected changes of the hydrological cycle simulated by an Earth system model (ESM), it is fundamental to validate the ESM and to characterize its major deficits. As the hydrological cycle is closely coupled to the energy cycle, a common large-scale evaluation of these fundamental components of the Earth system is highly beneficial, even though this has been rarely done up to now. Consequently, the purpose of the present study is the combined evaluation of land surface water and energy fluxes from the newest ESM version of the Max Planck Institute for Meteorology (MPI-ESM), which was used to produce an ensemble of Coupled Model Intercomparison Project Phase 5 (CMIP5) simulations. With regard to energy fluxes, we especially make use of recent satellite data sets. Additionally, MPI-ESM results are compared with CMIP3 results from the predecessor of MPI-ESM, ECHAM5/MPIOM, as well as to results from the atmosphere/land part of MPI-ESM (ECHAM6/JSBACH) forced by observed sea surface temperature (SST). Analyses focus on regions where notable differences occur between the two ESM versions as well as between the fully coupled and the uncoupled SST-driven simulations. In general, our results show a considerable improvement of MPI-ESM in simulating surface shortwave radiation fluxes. The precipitation of the fully coupled simulations notably differs from those of the SST-forced simulations over a few river catchments. Over the Amazon catchment, the coupling to the ocean leads to a large negative precipitation bias, while for the Ganges/Brahmaputra, the coupling significantly improves the simulated precipitation.

Description: Banded iron formations (BIF) are the protolith to most of the world’s largest iron ore deposits. Previous hypogene genetic models for Paleoproterozoic "Lake Superior" BIF-hosted deposits invoke upwards, down-temperature flow of basinal brines via complex silica and carbonate precipitation/dissolution processes. Such models are challenged by the necessary SiO 2 removal. Thermodynamic and mass balance constraints are used to refine conceptual models of the formation of BIF-hosted iron ore. These constraints, plus existing isotope and halogen ratio evidence, are consistent with removal of silica by down- or up-directed infiltration of high-pH hypersaline brines, with or without a contribution from basinal brines. The proposed link to surface environments suggest that Paleoproterozoic BIF-ore upgrade may provide a record of a critical time in the evolution of the Earth’s biosphere and hydrosphere.

Description: We investigate the reasons for the opposite climate change signals in precipitation between the regional climate model REMO and its driving earth system model MPI-ESM over the greater Congo region. Three REMO simulations following three RCP scenarios (RCP 2.6, RCP 4.5 and RCP 8.5) are conducted, and it is found that the opposite signals, with REMO showing a decrease and MPI-ESM an increase in the future precipitation, diverge strongly as we move from a less extreme to a more extreme scenario. It has been shown that REMO simulates a much higher number of extreme rainfall events than MPI-ESM. This results in higher surface runoff and thus less soil infiltration, which leads to lower amounts of soil moisture in REMO. This further leads to less moisture recycling via evapotranspiration, which in turn results in less precipitation over the region. In the presence of a strong radiative forcing, the hydrological cycle becomes less intense in REMO and a downward trend in hydrological variables is observed. Contrary to this, the higher amounts of soil-moisture due to the lack of extreme rainfall events in MPI-ESM enhance the hydrological cycle. In the presence of strong radiative forcing, higher amounts of soil moisture result in increased evapotranspiration which in turn results in the higher amount of precipitation. It is concluded that the land-atmosphere coupling over the Congo region is very sensitive to the change in soil moisture amounts, which is likely to play a major role in global warming conditions. Therefore, adequate and improved representation of soil processes in climate models is essential to study the effects of climate change. However, the better representation of extreme rainfall events in REMO compared to MPI-ESM can be regarded as an added value of the model.