Insight to the coupling of terrestrial and ocean systems under rapid climate change and high CO2 conditions

Changes in the flux of sediment and organic carbon from the continents to the coastal ocean may play an important role in organic carbon (org C) burial and preservation in coastal sediment, but the role of these processes in regulating org C burial over longer time scale is poorly known. Studying geologic climate change events gives an opportunity to investigate the responses of ocean and terrestrial systems under extreme conditions like elevated greenhouse gases that are relevant to Earth’s future. One such example is the Paleocene Eocene Thermal Maximum (PETM), which is characterized by global temperature increases of 5-8○C in less than 10,000 yr and release of >2000 Gt of 13C-depleted C to the atmosphere. We studied sediment and organic carbon burial through the PETM in nearshore marine sediments from the Wilson Lake core (New Jersey, U.S). The sediments were separated to Particulate Organic Carbon (POC) and the Mineral Bound Carbon (MBC) in order to assess whether these fractions reflected different org C sources, transport and burial processes. We measured carbon isotopes and wt% of C and N on both fractions, nitrogen isotopes of total and inorganic N on the MBC fraction and wt% of organic N and inorganic N in the sediment. Our results show that the MBC fraction is composed of old org C sources and fresh terrestrial and marine carbon, while the POC fraction is dominated by fresh org C of terrestrial origin. Organic C/N and concentrations of inorganic nitrogen suggest dominant input of terrestrial organic matter during the PETM and a mix of marine and terrestrial during pre- and post-PETM periods. Based on our records, the PETM can be divided into 3 periods during which MBC burial is dominated by different process. Environmental perturbation during the first period resulted in re-depositon of pre-PETM sediment and MBC. During the second period wet seasonal conditions drove high inputs of terrestrial material, diluting marine org matter despite relatively high sea level. During the third period sea level dropped and the carbon isotopes values of POC and MBC were strongly decoupled, suggesting winnowing and re-deposition of PETM sediments on the shelf. Our multi proxy approach allows us to study the response of the terrestrial and oceanic system to rapid, deep-time climate change and demonstrate that re-suspension of sediments and changes in the terrestrial sedimentary and organic flux are the main processes influencing org C preservation at this site.