<p>Silicate weathering alters the biogeochemical compositions of the lithosphere, hydrosphere, and atmosphere, and thereby regulates both nutrient cycling and habitable temperatures on Earth, but tracing silicate weathering effectively remains a challenge. Potassium (K) isotopes have been proposed as a tracer of silicate weathering intensity spatially, but there is a significant gap in how and why K isotopes trace silicate weathering temporally. Here we investigate seasonal variations in dissolved K isotopes in the middle Yellow River, which drains a large area of homogeneous loess that represents the average geochemical composition of the upper continental crust, and experiences significant climatic seasonality driven by the East Asian monsoon. We find that K isotopes show strong seasonality as a function of aluminosilicate neoformation following silicate dissolution, and thus could serve as a tracer of silicate weathering intensity. We derive an empirical relationship of δ⁴¹K_rw = −0.07 × ln(W/D) − 0.38, where W(silicate chemical weathering)/D(denudation) refers to silicate weathering intensity.</p>