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Marine oxygen production and open water supported an active nitrogen cycle during the Marinoan Snowball Earth
The Neoproterozoic Earth was punctuated by two low-latitude Snowball Earth glaciations. Models permit oceans with either total ice cover or substantial areas of open water. Total ice cover would make an anoxic ocean likely, and would be a formidable barrier to biologic survival. However, there are no direct data constraining either the redox state of the ocean or marine biological productivity during the glacials. Here we present iron-speciation, redox-sensitive trace element, and nitrogen isotope data from a Neoproterozoic (Marinoan) glacial episode. Iron-speciation indicates deeper waters were anoxic and Fe-rich, while trace element concentrations indicate surface waters were in contact with an oxygenated atmosphere. Furthermore, synglacial sedimentary nitrogen is isotopically heavier than the modern atmosphere, requiring a biologic cycle with nitrogen fixation, nitrification and denitrification. Our results indicate significant regions of open marine water and active biologic productivity throughout one of the harshest glaciations in Earth history
Fluxing of mantle carbon as a physical agent for metallogenic fertilization of the crust
Magmatic systems play a crucial role in enriching the crust with volatiles and elements that
reside primarily within the Earth’s mantle, including economically important metals like nickel,
copper and platinum-group elements. However, transport of these metals within silicate
magmas primarily occurs within dense sulfide liquids, which tend to coalesce, settle and not
be efficiently transported in ascending magmas. Here we show textural observations, backed
up with carbon and oxygen isotope data, which indicate an intimate association between
mantle-derived carbonates and sulfides in some mafic-ultramafic magmatic systems
emplaced at the base of the continental crust. We propose that carbon, as a buoyant
supercritical CO2 fluid, might be a covert agent aiding and promoting the physical transport of
sulfides across the mantle-crust transition. This may be a common but cryptic mechanism
that facilitates cycling of volatiles and metals from the mantle to the lower-to-mid continental
crust, which leaves little footprint behind by the time magmas reach the Earth’s surface.NERC Minerals Security of Supply (SOS)
NE/M010848/1Australian Research Council
CE11E0070Consolidated Nickel MinesUniversity of Leiceste
Persistence and changes in the peripheral Beles basin of Ethiopia
We have investigated the relevance of the notion of "peripheralism" in the Beles basin. In this lowland border area of Ethiopia, important investments require an evaluation of their socio-economic and ecological impacts in the light of Ethiopia's Climate-Resilient Green Economy (CRGE) strategy. We contrasted literature of different periods with field observations. In the middle and lower parts of the basin, the Gumuz people traditionally practised shifting cultivation. Resettlement of highlanders is particularly linked to water and land resources. A large irrigation project was initiated in the 1980s, but vegetables and fruits face post-harvest losses. Large water transfers from Lake Tana since 2010 affect the movement of people, the hydrogeomorphology, and ecology of the river. In several parts of the basin, the settlers' economy now dominates. Many Gumuz became sedentary but maintained their agricultural system, particularly in the south of the lower basin. Land titling allowed allocation of "vacant" areas to transnational or domestic investors. As a result, the semi-natural vegetation is frequently replaced by open cropland, leading to decreased carbon storage and increased soil erosion. This and water abstraction for irrigation jeopardise hydropower production, in contradiction with the CRGE objectives. Despite the recent developments, the contrasts in economic activity make the core-periphery dichotomy to remain actual in the Beles basin. The resettlements and permanent cropping tend to make the upper basin part of the core. However, the installation of a transit road and commercial farms in the lower basin do not allow to consider that a non-peripheral integration has taken place