analytical methods were used to obtain a large spectrum of major and trace element data, in particular, EPMA, SIMS, LA-ICPMS, and isotope dilution by TIMS and ICPMS. Altogether, more than 60 qualified geochemical laboratories worldwide contributed to the analyses, allowing us to present new reference and information values and their uncertainties (at 95% confidence level) for up to 74 elements. We complied with the recommendations for the certification of geological reference materials by the International Association of Geoanalysts (IAG). The reference values were derived from the results of 16 independent techniques, including definitive (isotope dilution) and comparative bulk (e.g., INAA, ICPMS, SSMS) and microanalytical (e.g., LA-ICPMS, SIMS, EPMA) methods. Agreement between two or more independent methods and the use of definitive methods provided traceability to the fullest extent possible. We also present new and recently published data for the isotopic compositions of H, B, Li, O, Ca, Sr, Nd, Hf, and Pb. The results were mainly obtained by high-precision bulk techniques, such as TIMS and MC-ICPMS. In addition, LA-ICPMS and SIMS isotope data of B, Li, and Pb are presented.

A c c e p t e d M a n u s c r i p t 3 ABSTRACTThe first appearance of skeletal metazoans in the late Ediacaran (~550 million years ago; Ma) has been linked to the widespread development of oxygenated oceanic conditions, but a precise spatial and temporal reconstruction of their evolution has not been resolved. Here we consider the evolution of ocean chemistry from ~550 to ~541 Ma across shelf-to-basin transects in the Zaris and Witputs Sub-Basins of the Nama Group, Namibia. New carbon isotope data capture the final stages of the Shuram/Wonoka deep negative C-isotope excursion, and these are complemented with a reconstruction of water column redox dynamics utilizing Fe-S-C systematics and the distribution of skeletal and soft-bodied metazoans. Combined, these inter-basinal datasets provide insight into the potential role of ocean redox chemistry during this pivotal interval of major biological innovation.The strongly negative  13 C values in the lower parts of the sections reflect both a secular, global change in the C-isotopic composition of Ediacaran seawater, as well as the influence of 'local' basinal effects as shown by the most negative  13 C values occurring in the transition from distal to proximal ramp settings. Critical, though, is that the transition to positive  13 C values postdates the appearance of calcified metazoans, indicating that the onset of biomineralization did not occur under post-excursion conditions. Significantly, we find that anoxic and ferruginous deeper water column conditions were prevalent during and after the transition to positive  13 C that marks the end of the Shuram/Wonoka excursion. Thus, if the C isotope trend reflects the transition to global-scale oxygenation in the aftermath of the oxidation of a large-scale, isotopically light organic carbon pool, it was not sufficient to fully oxygenate the deep ocean. Page 4 of 74A c c e p t e d M a n u s c r i p t 4 Both sub-basins reveal highly dynamic redox structures, where shallow, inner ramp settings experienced transient oxygenation. Anoxic conditions were caused either by episodic upwelling of deeper anoxic waters or higher rates of productivity. These settings supported short-lived and monospecific skeletal metazoan communities. By contrast, microbial (thrombolite) reefs, found in deeper inner-and mid-ramp settings, supported more biodiverse communities with complex ecologies and large skeletal metazoans. These long-lived reef communities, as well as Ediacaran soft-bodied biotas, are found particularly within transgressive systems, where oxygenation was persistent. We suggest that a mid-ramp position enabled physical ventilation mechanisms for shallow water column oxygenation to operate during flooding and transgressive sea-level rise. Our data support a prominent role for oxygen, and for stable oxygenated conditions in particular, in controlling both the distribution and ecology of Ediacaran skeletal metazoan communities.Keywords: Oxygenation; Neoproterozoic; Biomineralisation; Metazoans; Ediacaran; Ecosystems Introductio...

Ocean acidification triggered by Siberian Trap volcanism has been implicated as a kill18 mechanism for the Permo-Triassic mass extinction, but evidence for an acidification event 19 remains inconclusive. To address this, we present a high resolution seawater pH record across 20 this interval, utilizing boron isotope data combined with a quantitative modeling approach. In the 21 latest Permian, the alkalinity of the ocean increased, priming the Earth system with a low level of 22 atmospheric CO 2 and a high ocean buffering capacity. The first phase of extinction was 23 2 coincident with a slow injection of isotopically light carbon into the atmosphere-ocean, but the 24 ocean was well-buffered such that ocean pH remained stable. During the second extinction pulse, 25 however, a rapid and large injection of carbon overwhelmed the buffering capacity of the ocean, 26causing an abrupt and short-lived acidification event that drove the preferential loss of heavily 27 calcified marine biota. kyrs (2) and can be resolved into two distinct marine extinction pulses, with the respective kill 37 mechanisms appearing to be ecologically selective (3). The first occurred in the latest Permian 38 (Extinction Pulse 1; EP1) and was followed by an interval of temporary recovery before the 39 second pulse (EP2) which occurred in the earliest Triassic. The direct cause of the mass 40 extinction is widely debated with a diverse range of overlapping mechanisms proposed, 41 including widespread water column anoxia (4), euxinia (5), global warming (6) and ocean 42 acidification (7). 43Models of PTB ocean acidification suggest that a massive, and rapid, release of CO 2 from 44 Siberian Trap volcanism, acidified the ocean (7). Indirect evidence for acidification comes from 45 the interpretation of faunal turnover records (3, 8), potential dissolution surfaces (9) and Ca 46 3 isotope data (7). A rapid input of carbon is also potentially recorded in the negative carbon 47 isotope excursion (CIE) that characterizes the PTB (10, 11) . The interpretation of these records 48 is, however, debated (12), and of great importance to understanding the current threat of 49 anthropogenically-driven ocean acidification (11). 50Here, we test the ocean acidification hypothesis by presenting a novel proxy record of 51 ocean pH across the PTB, using the boron isotope composition of marine carbonates ( 11 additional counterbalancing alkalinity flux. This is consistent with independent proxy data (6). 129The alkalinity source may have been further increased through soil loss (26) carbon to the atmosphere, yet remarkably, the acidification event occurs after the decline in  13 C, 139when  13 C has rebounded somewhat and is essentially stable (Fig. 2). 140Unlike the first carbon injection, the lack of change in  13 C at this time rules out very 141 13 C-depleted carbon sources, because no counterbalancing strongly 13 C-enriched source exists.

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We present data on the lithium isotope compositions of glass reference materials from the United States Geological Survey (USGS) and the National Institute of Standards and Technology (NIST) determined by multicollector inductively coupled plasma mass spectrometry (MC-ICPMS), thermal ionization mass spectrometry (TIMS), and secondary ionization mass spectrometry (SIMS). Our data on the USGS basaltic glass standards agree within 2 per thousand, independent of the sample matrix or Li concentration. For SIMS analysis, we propose use of the USGS glasses GSD-1G (delta(7)Li 31.14 +/- 0.8 per thousand, 2sigma) and BCR-2G (delta(7)Li 4.08 +/- 1.0 per thousand, 2sigma) as suitable standards that cover a wide range of Li isotope compositions. Lithium isotope measurements on the silica-rich NIST 600 glass series by MC-ICPMS and TIMS agree within 0.8 per thousand, but SIMS analyses show systematic isotopic differences. Our results suggest that SIMS Li isotope analyses have a significant matrix bias in high-silica materials. Our data are intended to serve as a reference for both microanalytical and bulk analytical techniques and to improve comparisons between Li isotope data produced by different methodologies.

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We present data on the concentration, the isotope composition and the homogeneity of boron in NIST silicate glass reference materials SRM 610 and SRM 612, and in powders and glasses of geological reference materials JB‐2 (basalt) and JR‐2 (rhyolite). Our data are intended to serve as references for both microanalytical and wet‐chemical techniques. The δ11 B compositions determined by N‐TIMS and P‐TIMS agree within 0.5% and compare with SIMS data within 2.5%. SIMS profiles demonstrate boron isotope homogeneity to better than δ11 B = 2% for both NIST glasses, however a slight boron depletion was detected towards the outermost 200 μm of the rim of each sample wafer. The boron isotope compositions of SRM 610 and SRM 612 were indistinguishable. Glasses produced in this study by fusing JB‐2 and JR‐2 powder also showed good boron isotope homogeneity, both within and between different glass fragments. Their major element abundance as well as boron isotope compositions and concentrations were identical to those of the starting composition. Hence, reference materials (glasses) for the in situ measurement of boron isotopes can be produced from already well‐studied volcanic samples without significant isotope fractionation. Oxygen isotope ratios, both within and between wafers, of NIST reference glasses SRM 610 and SRM 612 are uniform. In contrast to boron, significant differences in oxygen isotope compositions were found between the two glasses, which may be due to the different amounts of trace element oxides added at ten‐fold different concentration levels to the silicate matrix.

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