ALBERT

Description: Iron isotopes in ocean floor basalts (OFB) away from convergent margins comprising mid-ocean-ridge and ocean island lavas show significant variation of 〉0.4‰ (expressed in the delta notation δ57Fe relative to IRMM-014), but processes responsible for this variation remain elusive. Bond-valence theory predicts that valence states (Fe3+ vs. Fe2+) control Fe isotopes during partial melting and crystal fractionation along the liquid line of descent and thus contribute substantially to this variation. Memory of past melt extraction or metasomatic re-enrichment in the source of OFB may further add to the observed variability, but systematic investigations to elucidate the respective contributions of these effects have been lacking. Submarine ridges and rifts in the Lau back-arc basin offer a unique opportunity to compare Fe isotopes in OFB from different melting regimes and variably depleted mantle sources. New Fe isotope data is presented for submarine lavas from the Rochambeau Ridges (RR) and the Northwest Lau Spreading Centre (NWLSC), and is compared with published data from the Central Lau Spreading Centre (CLSC). In line with first principle calculations and observations from a range of natural systems, crystal fractionation is identified as the dominant, controlling process for elevating δ57Fe in the lavas with olivine tentatively identified as the key driver. To compensate for the effect of crystal fractionation, olivine is mathematically added towards calculated primitive melt compositions (δ57Feprim). For this, we used a constant Ol-melt isotope fractionation factor based on published equilibrium partition functions adapted to decreasing temperature in a cooling melt. The degree of calculated Fe isotope fractionation through olivine crystal fractionation (monitored as Δ57Fe = δ57Femeasured − δ57Feprim) is positively correlated with increasing S and decreasing Ni content in the cooling lavas, fortifying the validity of the approach. Primitive lavas from individual Lau spreading centres and ridges vary to 0.1‰ in δ57Feprim, similar to primitive open-ocean MORB. However, the entire spread in Fe isotope variability in the primitive melts remains at 0.3‰, which we propose to be the extent of isotope heterogeneity in Earth’s upper mantle, with few extreme exceptions. The largest variability in δ57Feprim is observed for RR intra-plate lavas, which have been associated with the Samoan mantle plume and melting in an edge-driven convection scenario. Low, mid-ocean ridge-like 87Sr/86Sr in RR lavas excludes significant influence of isotopically heavy Samoan EM2-type components. However, co-variations with rare earth element pattern in some RR intra-plate lavas indicate garnet plays a role in elevating δ57Feprim during deeper melting. Excluding these deep-seated melts uncovers systematically decreasing δ57Feprim coupled to the degree of mantle source depletion, as recorded in Lu/Hf and Sm/Nd, in the back-arc basin basalts. This, however, holds only true for a comparison between sources of individual ridges, whereas no co-variation is observed within ridge segment data. This suggests that a process other than source depletion and crystal fractionation further adds to Fe isotope variability in the order of 0.1‰ on scales of individual ridge segments. This either marks the degree of Fe isotope variability below ridge segments, or is caused by secondary processes, such as melt-wallrock interaction or RTX (recharge and crystal fractionation) magma chambers.

Description: The transition from the Proterozoic to the Phanerozoic Eon was accompanied by the rise of metazoan life, a key and unique biogeochemical milestone in Earth's history. Concomitant continental re-organization and collision were associated with enhanced continental reworking and changes in global ocean currents, with profound impacts on continental weathering rates, riverine run-off and associated changes in the ocean nutrient budget. The causal relationship between the geological re-organisation of continents and the biologic evolution of marine life, however, remains elusive. In this study, we investigate phosphatic shallow-water sedimentary successions from Kazakhstan, which host key marker horizons from the Precambrian-Cambrian (Pc-C) boundary. We show that a rapid change (over ca. 3 Myrs) towards heavier stable Mg isotope compositions of the phosphatic sedimentary deposits in Kazakhstan, which we consider representative for contemporaneous ocean chemistry, co-varies with changes in radiogenic Sr isotope signatures. We propose that ocean chemistry at the Pc-C boundary, represented through this co-variation, was strongly affected by continental re-organization and associated weathering, which, in analogy, would have affected ocean nutrient levels. A rapid reversal of isotope compositions towards signatures similar to those prior to the isotope excursion likely reflects the fading influence of weathering and a buffering of water-rock interactions during oceanic spreading. We conclude that, based on the positive, coupled 87Sr/86Sr- δ26Mg isotope spike in ocean water chemistry, a link between Gondwana re-organization at the Pc-C boundary and the marked change in marine fauna seems plausible.

Description: Monazite has the ability to incorporate a broad range of trace elements (TE), including Smsingle bondNd, in addition to being a reliable Usingle bondPb geochronometer. Nonetheless, many current isotopic tracer studies mostly focus on laser ablation-multicollector-inductively coupled plasma mass spectrometry (LA-MC-ICPMS) Hf-in-zircon or whole rock isotope dilution Smsingle bondNd. The conditions necessary to produce reliable Nd-isotopic data from whole rock analyses (i.e. absence of weathering and alteration) restricts the number of samples suitable for this type of study. Conversely, accessory phases such as monazite, apatite, allanite, epidote and titanite are more resistant to weathering and alteration and have a greater chance of preserving their original Nd-isotopic signature. The Archean Penzance granite, in the Yilgarn Craton, Western Australia, is a relatively unweathered high field strength elements (HFSE)-enriched granite that is associated with the Teutonic Bore volcanic-hosted massive sulfide (VHMS) Camp. Here we compare newly acquired LA split-stream (SS)-MC-ICPMS analyses in monazite from the Penzance granite to previously collected whole rock Nd-isotopes, SHRIMP ages in zircon and monazite and Hf-in-zircon of a specific outcrop. The ƐNd0 of monazite from the Penzance granite have a weighted mean value of +1.6 ± 0.2 both for the values calculated from the SHRIMP single population age and from individual LASS dates. This value is the same within uncertainty to the whole-rock ƐNd0 value of +1.99 ± 0.39, whereas ƐHf0 show similar juvenile values with mean value of +2.2 ± 0.5 (2 SE). These findings complement previous studies that argue that monazite has the potential to provide reliable time constrained isotopic and chemical data, which are comparable to, and at times superior than, Hf-in-zircon and whole-rock Nd-isotopes. Additionally, because monazite can record TE signatures that can be used to retrieve petrological information, this study proposes a LASS-MC-ICPMS routine that achieves simultaneous Smsingle bondNd isotopes, U/Th-Pb dating and TE analyses in monazite, allowing for further petrological information to be obtained from a single analytical routine. This study also assesses the precision and accuracy in Usingle bondPb ages in monazite reference materials, when additional masses are measured in the same routine. The application of the routine presented here facilitates the use of monazite as isotopic tracer in petrological and sedimentary studies.

Description: The global energy system is undergoing a major transition, and in energy planning and decision-making across governments, industry and academia, models play a crucial role. Because of their policy relevance and contested nature, the transparency and open availability of energy models and data are of particular importance. Here we provide a practical how-to guide based on the collective experience of members of the Open Energy Modelling Initiative (Openmod). We discuss key steps to consider when opening code and data, including determining intellectual property ownership, choosing a licence and appropriate modelling languages, distributing code and data, and providing support and building communities. After illustrating these decisions with examples and lessons learned from the community, we conclude that even though individual researchers' choices are important, institutional changes are still also necessary for more openness and transparency in energy research.

Description: In order to ensure security of supply in a future energy system with a high share of volatile electricity generation, flexibility technologies are needed. Industrial demand-side management ranks as one of the most efficient flexibility options. This paper analyses the effect of the integration of industrial demand-side management through the flexibilisation of aluminium electrolysis and other flexibilities of the electricity system and adjacent sectors. The additional flexibility options include electricity storage, heat storage in district heating networks, controlled charging of electric vehicles, and buffer storage in hydrogen electrolysis. The utilisation of the flexibilities is modelled in different settings with an increasing share of renewable energies, applying a dispatch model. This paper compares which contributions the different flexibilities can make to emission reduction, avoidance of curtailment, and reduction of fuel and CO2 costs, and which circumstances contribute to a decrease or increase of overall emissions with additional flexibilities. The analysis stresses the rising importance of flexibilities in an energy system based on increasing shares of renewable electricity generation, and shows that flexibilities are generally suited to reduce carbon emissions. It is presented that the relative contribution towards the reduction of curtailment and costs of flexibilisation of aluminium electrolysis are high, whereby the absolute effect is small compared to the other options due to the limited number of available processes.

Description: Wind energy that can neither be fed into the grid nor be used regionally must be curtailed. This paper proposes different options to deal with such surplus wind energy amounts in a time horizon until 2020. It assesses their ability to handle the surplus energy in a sustainable way using a multi criteria analysis. The paper bases on a study that was prepared for the Ministry for Climate Protection, Environment, Agriculture, Nature Conservation and Consumer Protection of North Rhine-Westphalia between 2010 and 2012.