Astronomical (paleo)climate forcing amplified by oxygen minimum zone dynamics

The 100 and 400 kyr eccentricity cycles are present in many Mesozoic and Cenozoic records but appear especially prominent during the warmer intervals. Their occurrence in deep marine records of these intervals demonstrates that astronomical forcing not only impacts the regional environment but also alters climate conditions and carbon cycle dynamics on a global scale. Yet, the pathways by which regional insolation changes amplify to global scale climate perturbations remain poorly understood, particularly in greenhouse climates where climate-sensitive ice sheets are absent. Here, we present the first-ever Earth system model simulations that closely replicate the 100 kyr climate-carbon cycles in an ice-free world, using only insolation forcing as a driver. Subtle changes in nutrient fluxes and marine organic carbon burial have the potential to drastically alter the ocean buffering capacity – a key mechanism that amplifies astronomical climate variability via the preferential partitioning of carbon to atmospheric CO₂. The presence of extensive oxygen minimum zones, where the interplay between sedimentary nutrient (phosphate) regeneration and terrestrial nutrient runoff regulates organic carbon burial, lies at the foundation of the mechanism presented here.