Quantifying PETM Carbonate Burndown and Alkalinity Feedbacks through Cyclostratigraphy

The dissolution of calcium carbonate (CaCO₃) is a key regulator of long-term changes in oceanic CO₂ uptake, through the generation of alkalinity. Geological records from past climatic and carbon-cycle perturbation events contain abundant evidence for ocean acidification and seafloor CaCO₃ dissolution. Such events can thus serve as natural laboratories to assess the role of carbonate compensation in mitigating extreme carbon release and stabilizing the Earth system. In this study, we aim to evaluate the magnitude, rate, and climatic significance of carbonate dissolution for the Paleocene-Eocene Thermal Maximum (PETM, ~56 Ma), the most dramatic of the early Cenozoic hyperthermals. Specifically, we use a new high-resolution record from IODP Site U1514 from the Mentelle Basin in the SE Indian Ocean (paleolatitude: ∼60°S at 50 Ma) to quantify the dissolution of seafloor CaCO₃ deposited prior to the PETM (‘burndown’), in the earliest phases of the event.  Our site is ideally positioned to document this process due to its location in the deep-sea, relatively high sedimentation rates, expanded upper Paleocene record and sensitivity to changes in carbonate saturation. We use precession-scale cyclostratigraphy to create an age model for the late Paleocene and early Eocene at U1514, anchored within 405-kyr astrochronozones and subsequently tied to the established astrochronology of ODP Site 690 in the Weddell Sea, allowing for refined interbasinal stratigraphic alignment across the Southern Ocean. The age model forms the basis for our analysis of ‘burndown’ dissolution and alkalinity generation at our site and across the PETM seafloor. Our work is an important step forward in our ability to quantify alkalinity fluxes from seafloor dissolution and their impact relative to terrestrial weathering, on millenial to orbital timescales.