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The McMurdo Dry Valleys of Antarctica formed by extensive glacial erosion, yet currently exhibit hyperarid polar conditions canonically associated with limited chemical and physical weathering. Efficient chemical weathering occurs when moisture is available, and polythermal subglacial conditions may accommodate ongoing mechanical weathering and valley incision. Taylor Valley, one of the MDV, hosts several Pleistocene glacial drift deposits that record prior expansions of Taylor Glacier and sediment redistribution, if not sediment production. We present U-series isotopics of fine-grained sediments from these drifts to assess the timescales of physical weathering and subsequent chemical alteration. The isotopes ²³⁸U, ²³⁴U, and ²³⁰Th are sensitive to both chemical and physical fractionation processes in sedimentary systems, including the physical fractionation of daughter isotopes by energetic recoil following radioactive decay. By comparing U-series isotopic measurements with models of U-series response to chemical weathering and physical fractionation processes, we show that Pleistocene drift sediments record histories of significant chemical alteration. However, fine-grained sediments entrained in the basal ice of Taylor Glacier record only minor chemical alteration and U-series fractionation, indicating comparatively recent sediment comminution and active incision of upper Taylor Valley by Taylor Glacier over the Pleistocene. In addition, the results of this study emphasize the utility of U-series isotopes as tracers of chemical and physical weathering in sedimentary and pedogenic systems, with particular sensitivity to radionuclide implantation by α-recoil from high-U authigenic phases into lower-U detrital phases. This process has occurred extensively in >200 ka drifts but to a lesser degree in younger deposits. U-series α-recoil implantation is an important physicochemical process with chronometric implications in other hyperarid and saline sedimentary systems, including analogous Martian environments. 

Early in the history of the Solar System, the giant planets — including Jupiter and Saturn — migrated under gravity into different orbits around the Sun, causing an epoch of chaos and collisions. Radioactive isotopes in asteroids record the thermal imprint of these collisions, and a broad survey of meteorites now constrains the timing of the migration to approximately 11 million years after the Solar System formed. 

Abstract The element abundances of stars, particularly the refractory elements (e.g., Fe, Si, and Mg), play an important role in connecting stars to their planets. Most Sun-like stars do not have refractory abundance measurements since obtaining a large sample of high-resolution spectra is difficult with oversubscribed observing resources. In this work we infer abundances for C, N, O, Na, Mn, Cr, Si, Fe, Ni, Mg, V, Ca, Ti, Al, and Y for solar analogs with Gaia Radial Velocity Spectrometer (RVS) spectra (R= 11,200) usingTheCannon, a data-driven method. We train a linear model on a reference set of 34 stars observed by Gaia RVS with precise abundances measured from previous high-resolution spectroscopic efforts (R> 30,000–110,000). We then apply this model to several thousand Gaia RVS solar analogs. This yields abundances with average upper limit precisions of 0.04–0.1 dex for 17,412 stars, 50 of which are identified planet (candidate) hosts. We subsequently test the relative refractory depletion of these stars with increasing element condensation temperature compared to the Sun. The Sun remains refractory depleted compared to other Sun-like stars regardless of our current knowledge of the planets they host. This is inconsistent with theories of various types of planets locking up or sequestering refractories. Furthermore, we find no significant abundance differences between identified close-in giant planet hosts, giant planet hosts, and terrestrial/small planet hosts with the rest of the sample within our precision limits. This work demonstrates the utility of data-driven learning for future exoplanet composition and demographics studies. 

This dataset contains uranium and thorium isotopic compositions (U-234, U-235, U-238, Th-230, Th-232) and major element compositions (Al, K, Na, Ca, Fe, Mn, reported as oxides) for silicate sediments from glaciogenic drifts associated with advances of Taylor Glacier in Taylor Valley, Antarctica. Isotopic measurements were obtained by ID-TIMS in the Keck Isotope Facility at UC Santa Cruz and elemental measurements were obtained by ICP-OES in the Plasma Analytical Laboratory. All measurements include fully propagated analytical and systematic (e.g. isotopic tracer) uncertainties. Chemical index of alteration was calculated from major element data. Prior to measurements, sediments were sieved to ≤125 μm grain sizes, separated into quartz-feldspar-rich and clay-rich aliquots by hydraulic settling, and subjected to sequential chemical extractions ("leaching") prior to silicate digestion. 

Subglacial mineral precipitates record ocean forcing of Heinrich events and widespread subglacial groundwater connectivity.