Early organic carbon and nitrogen accumulation in a Pyrenean site: From rock to peat across the Late Glacial–Early Holocene transition

Understanding carbon-climate feedbacks during past climate transitions is critical to projecting long-term Earth system responses. Peatlands, though covering only 3–4 % of the terrestrial surface, play a disproportionate role in the global carbon cycle. Yet, Late Glacial peatlands in southern Europe remain understudied due to their rarity and fragmented records. This study provides a sub-centennial, multi-proxy reconstruction (15–10 cal kyr BP) from the Bassa Nera peat bog in the Central Pyrenees, combining total organic carbon (TOC), total nitrogen (TN), carbon accumulation rates (CAR), stable isotopes (δ¹³C, δ¹⁵N), diatom assemblages, and charcoal influx. During the Oldest Dryas (GS-2 stadial), low TOC and TN suggest limited microbial activity under dry conditions. Despite climatic variability during the Bølling/Allerød (GI-1 interstadial), organic and isotopic signals remained damped. The Younger Dryas (GS-1 stadial) marks a shift, with abrupt peaks in TOC and TN (∼12.8 cal kyr BP), signaling the onset of organic accumulation. Sustained peat development begins around 12.3 cal kyr BP, accelerating in the Early Holocene with increased C/N ratios, charcoal influx, and isotopic changes, indicating higher terrestrial productivity and wetter conditions. Principal Component Analysis reveals evolving organic matter sources linked to regional vegetation dynamics. Bassa Nera is among the earliest peat-forming systems in the mountains of southern Europe, offering novel insights into long-term carbon accumulation patterns in montane settings. These findings highlight the role of early postglacial peatlands in shaping regional carbon dynamics and emphasize the need to incorporate underrepresented southern systems into global carbon and climate assessments.