Lacustrine organic carbon burial dynamics regulate Aptian-Albian greenhouse-cooling climate oscillations

Investigating terrestrial response to typical greenhouse periods is essential to understand past and present climate-carbon-cycle interactions. The Cretaceous climate transition is thought to be related to carbon cycles, yet the role of lacustrine systems in modulating global carbon-climate feedback remains poorly constrained. Here, we present a high-resolution biogeochemical record from an Aptian-Albian paleolake in northwestern China, integrating biomarkers, nitrogen isotopes, and elemental proxies. We reveal that warm-humid climates during the early Aptian amplified lacustrine organic carbon burial via intensified denitrification, methane cycling, and nutrient fluxes, potentially reinforcing oceanic anoxic event 1a (OAE1a) hyperthermal conditions through N₂O/CH₄ emissions. Subsequent nitrogen limitation triggered cyanobacterial dominance, sustaining carbon sequestration under moderate weathering and contributing to cooling the late Aptian climate. A transient early Albian warming phase shifted the nitrogen pool towards NH₄⁺ and favored the bloom of eukaryotic algae, aligning with global OAE1b carbon burial and serving as one of the contributors to the late early Albian cooling climate. These dynamics demonstrate that paleolakes acted as both carbon sinks and greenhouse gas sources, exerting a critical but previously overlooked feedback on Cretaceous climate oscillations. Our findings highlight the dual role of lacustrine systems in past carbon cycle perturbations, offering insights for refining the relationships between the carbon cycle and climate changes in the Cretaceous.