SEA LEVEL, THE CARBON CYCLE, AND CLIMATE FEEDBACKS OVER THE PAST 66 MILLION YEARS

We evaluate feedbacks of carbon burial with sea level over the past 66 million years using carbon isotopes from mean deep water (δ¹³C_MDW), the large mobile carbon reservoir. Previous studies reconstructed barystatic sea level (BSL), the ice-volume component of Global Mean Sea Level (GMSL),using δ¹⁸O_MDW and Mg/Ca paleotemperatures with ±10 m error (Miller et al., 2020), but estimates older than 48 Ma were uncertain due to highly variable Mg/Ca data (Cramer et al., 2011). Here we constrain paleotemperatures older than 48 Ma with a new Mg/Ca Oridorsalis record from deep Pacific Site 577 providing a more reliable BSL record. Periodic δ¹³C_MDW variations were dominated by long eccentricity (405 kyr) and short obliquity (41 kyr) astronomical beats, with recurring long obliquity (1.2 Myr), eccentricity (2.4 Myr and quasi 100 kyr), and precessional (19/23 kyr) cycles. High δ¹³C_MDW and C-org burial occurred in warmer climates on long time scales primarily due to high sea levels, but in colder climates on Milankovitch time scales due to increased ocean circulation. Our analysis of recent CO₂ compilations shows that: 1) high atmospheric CO₂ was associated with high sea level and high burial of organic carbon on continental margins; and 2) decreasing CO₂ largely attributed to temperature-weathering feedback was associated with increased ice volume, falling sea level, and decreased organic carbon burial.