ORGANIC AND INORGANIC CARBON BURIAL OF THE NEOGENE OCEAN (Invited Presentation)

The carbon isotopic composition of marine carbonates is among the most widely used indicators of past global carbon cycle variations. Traditionally, marine carbonate δ¹³C variability has been interpreted as representing the fraction of organic relative to inorganic carbon buried in sediments over time, assuming a fixed isotopic composition of carbon supply to the surface system. However, this interpretation is currently facing fundamental challenges, as emerging evidence suggests much greater variability in carbon sources and sinks, encompassing both fluxes and isotopes.

By utilizing over five decades of data collected by the International Ocean Discovery Program, we have constructed mass accumulation rates of organic and inorganic (carbonate) carbon since the early Miocene, encompassing hundreds of marine sites worldwide. Subsequently, these data underwent statistical analysis to compute regional and global carbon burial rates for both organic and inorganic carbon. The carbonate burial data also allowed us to assess changes in carbonate compensation depths for each major basin over time. Collectively, the results from these "bottom-up" approaches challenge the classic isotope mass balance paradigm, emphasizing the need to rethink fundamental aspects of the global carbon cycle.