The kaolinite shuttle links the Great Oxidation and Lomagundi events

The ~2.22–2.06 Ga Lomagundi Event was the longest positive carbon isotope excursion in Earth’s history and is commonly interpreted to reflect perturbations in continental weathering and the phosphorous cycle. Previous models have focused on mechanisms of increasing phosphorous solubilization during weathering without focusing on transport to the oceans and its dispersion in seawater. Building from new experimental results, here we report kaolinite readily absorbs phosphorous under acidic freshwater conditions, but quantitatively releases phosphorous under seawater conditions where it becomes bioavailable to phytoplankton. The strong likelihood of high weathering intensities and associated high kaolinite content in post-Great-Oxidation-Event paleosols suggests there would have been enhanced phosphorus shuttling from the continents into marine environments. A kaolinite phosphorous shuttle introduces the potential for nonlinearity in the fluxes of phosphorous to the oceans with increases in chemical weathering intensity.

The late-Holocene records of sediment provenance/weathering in the Wular Lake catchment, Northwest Himalaya

<p>The Wular Lake (area ~189 km<sup>2</sup>) in the Kashmir Valley (area ~16,000 km<sup>2</sup>) is fed by the Jhelum River, which is a large Himalayan tributary of the Indus River. The lake catchment seasonally receives precipitation from tropical (Indian Summer Monsoon, ISM) and subtropical (Western Disturbances, WD) moisture sources. Thus, the lake sediments provide a unique opportunity to explore the high-resolution archive of the synoptic-scale weathering intensity and pattern in the Northwest Himalaya under past hydroclimatic conditions. In this study, radiogenic Sr and Nd isotope compositions and lithic fractions (sand, silt, and clay) have been determined on detrital phases of a 2.2 m long sediment core retrieved from the Wular Lake. The <sup>14</sup>C-AMS chronology of this core presents the sedimentary records of the last 4.2 ka. The Sr and Nd isotope data indicate that the lake sediments deposited during the late-Holocene are mostly sourced from the Tethyan Himalaya rather than other major lithologies. The marginal downcore variations of ±1.5 ε<sub>Nd</sub> unit (except two anomalous datapoints with large uncertainties at 0.8 ka and 2.0 ka) reveal no major shifts in the sediment provenance during the late-Holocene. On the other hand, the significant downcore variations are observed in <sup>87</sup>Sr/<sup>86</sup>Sr (>0.001–0.004) showing well-resolved periods of higher and lower values than the late-Holocene average. The <sup>87</sup>Sr/<sup>86</sup>Sr data unbiased by the grain-size sorting and carbonate contents seem to indicate a temporal dominance of chemical and physical modes of silicate weathering in the Northwest Himalaya before and after ~2 ka, respectively. Interestingly, an abrupt shift in the <sup>87</sup>Sr/<sup>86</sup>Sr data during the Little Ice Age (~0.4–0.1 ka) reveals a multi-decadal response of the silicate weathering intensity in synchrony with the northern hemisphere temperature anomaly.</p><p> </p>