The evolution of the global carbon and silicon cycles are thought to have contributed to the long-term stability of the Earth's climate [1][2][3] . Many questions remain, however,

Tracing silicate weathering processes in the permafrost-dominated Lena River watershed using lithium isotopes. Geochimica et Cosmochimica Acta 245 , pp. 154-171.

Seawater lithium stable isotope ratios, represented by δ7Lisw (‰), hold key information about the evolution of global climate and the carbon cycle over geologic time. Reconstructions based on foraminifera suggest an ~9‰ increase in δ7Lisw over the past 60 m.y., interpreted as reflecting changes in the silicate weathering regime that may have contributed to global cooling over this time. However, culture experiments suggest that vital effects in foraminifers might cause varied δ7Li fractionation that could have affected past records. Thus, other archives are needed to determine whether the observed rise in foraminifer δ7Li values over the Cenozoic indeed reflects secular changes in δ7Lisw. Such archives would also open possibilities for robust determination of δ7Lisw deeper in geologic time. We analyzed δ7Li compositions in modern brachiopods (n = 34) and found a relatively narrow range of +24.2‰ to +28.8‰ (mean = +26.8‰; 1σ = 0.5‰), similar to the range reported for inorganic calcite precipitated from seawater. These results confirm that brachiopods are good candidates for providing a representative record of δ7Lisw. We present data from fossil specimens dating from 65 Ma to ca. 700 ka, finding that fossilized brachiopods record a similar magnitude of change in δ7Lisw as foraminifers. These results are the first to corroborate the ~9‰ increase in Cenozoic δ7Lisw and open possibilities for generating robust records ofδ7Lisw in deep time, prior to foraminifer evolution.

Phosphorus is an essential element for life, and the phosphorous cycle is widely believed to be a key factor limiting the extent of Earth's biosphere and its impact on remotely detectable features of Earth's atmospheric chemistry. Continental weathering is conventionally considered to be the only source of bioavailable phosphorus to the marine biosphere, with submarine hydrothermal processes acting as a phosphorus sink. Here, we use a novel 29Si tracer technique to demonstrate that alteration of submarine basalt under anoxic conditions leads to significant soluble phosphorus release, with an estimated ratio between phosphorus release and CO2 consumption (∑PO43−/∑CO2) of 3.99 ± 1.03 µmol mmol−1. This ratio is comparable to that of modern rivers, suggesting that submarine weathering under anoxic conditions is potentially a significant source of bioavailable phosphorus to planetary oceans and that volatile‐rich Earth‐like planets lacking exposed continents could develop robust biospheres capable of sustaining remotely detectable atmospheric biosignatures.