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It has long been recognized that the advent of vascular plants in the Paleozoic must have changed silicate weathering and fundamentally altered the long-term carbon cycle. Carbon cycle models are frequently employed to quantify the effect of this state change in the Earth system. These models have suggested that plants likely played a key role in modulating atmospheric CO2 in the past, with the largest plant-induced changes to the system in the late Paleozoic. These studies have, for the most part, focused on the effects of plants on weathering via their impacts on the soil environment. Yet, plants also modify the hydrological cycle, which may also have had implications for global weathering. Here, we evaluate the consequences of plant evolutionary innovation that have not been previously incorporated into carbon cycle models by coupling a one-dimensional vapor transport model to a reactive transport model of silicate weathering.
The mantle sources of mid-ocean ridge basalts beneath the Indian and Pacific oceans have distinct isotopic compositions with a long-accepted boundary at the Australian–Antarctic Discordance along the Southeast Indian Ridge. This boundary has been widely used to place constraints on large-scale patterns of mantle flow and composition in the Earth’s upper mantle. Sampling between the Indian and Pacific ridges, however, has been lacking, especially along the remote 2,000 km expanse of the Australian–Antarctic Ridge. Here we present Sr, Nd, Hf and Pb isotope data from this region that show the Australian–Antarctic Ridge has isotopic compositions distinct from both the Pacific and Indian mantle domains.
Application of retardation filters has revolutionized the use of multi-collector inductively coupled plasma mass spectrometry (MC-ICPMS) for the measurement of U-series disequilibria. Here, we present an evaluation of the application of retardation energy filters coupled with ion counting detectors for the measurement of U-series disequilibria by MC-ICPMS. We show that: 1) The RPQ minimizes backgrounds caused by ions experiencing irregular flight paths at high masses of uranium series nuclides. This reduced background is important for low count rate measurements and has enabled us to develop an improved method for the determination of 226Ra/228Ra ratios using a dual SEM/RPQ collector block.