Topsoil organic matter build‐up in glacier forelands around the world

Since the last glacial maximum, soil formation related to ice-cover shrinkage has been one major sink of carbon accumulating as organic matter (SOM), a phenomenon accelerated by ongoing global warming. In recently deglacierized forelands, processes SOM accumulation, including those that control and nitrogen sequestration rates biogeochemical stability newly sequestered carbon, remain poorly understood. Here, we investigate build-up during initial stages (up 410 years) topsoil development in 10 glacier forelands distributed on four continents. We test whether net accumulation (i) depends time since deglacierization local climatic conditions (temperature precipitation); (ii) is accompanied decrease its (iii) mostly due an increasing contribution from plant origin. measured total concentration (carbon, nitrogen), relative hydrogen/oxygen enrichment, stable isotopic (13C, 15N) functional groups (C-H, C=O, C=C) compositions, distribution pools different thermal stability. show content increases with faster experiencing warmer climates. The shows consistent trends across studied chronosequences. During first decades development, low amount dominated thermally pool small highly thermolabile pool. decreases age at all sites, indicating storage labile centuries suggesting inputs (SOM depleted nitrogen, enriched hydrogen aromatic carbon). Our findings highlight potential vulnerability stocks proglacial areas decomposition suggest their durability largely plants.