Stacking coral δ13C records: spatial and temporal variability of the Pacific ocean’s carbon pump along the Anthropocene

            Oceans absorb atmospheric CO₂ depending on physicochemical exchanges and can act as sink or source for the atmospheric CO₂. On a global scale, these source and sink zones vary both spatially and temporally. In the Pacific Ocean, the tropical zone is a strong source of CO₂, whereas north and south subtropical zones are strong sinks. Atmospheric δ¹³C values (δ¹³C_atm) have decreased over the last decades in response to the increase of the anthropogenic CO₂ influx, also known as the Suess effect. The temporal reduction in δ¹³C_atm has also been observed in dissolved inorganic carbon (δ¹³C_DIC) due to the oceanic pump activity. Corals record environmental conditions by incorporating the ambient water trace elements and isotopes such as the δ¹³C_DIC. Therefore, coral δ¹³C (δ¹³C_C) can be used as an indicator of the past oceanic pump activity. In this study, we used previous temporal records of δ¹³C_C Porites spp. corals, distributed across eighteen locations spread over subtropical and tropical areas of the Pacific Ocean. We added to this dataset a new record of δ¹³C_C from Clipperton Island, a zone observed as a source zone. We created composite δ¹³C_C record at Clipperton Island. We focused on long-term variability and investigated trends. Long-term trends are compared with the long-term trends of the sea-air CO₂ fluxes from instrumental data period and with the long-term trend of reconstructed δ¹³C_atm record from ice cores. General trends observed in all our selected records seems to follow the δ¹³C_atm decreasing trend observed from ice core record. Meanwhile, we distinguished time breakpoint on each of our composites with different slopes at different timing. Time breakpoints seem to occur earlier, in records located within actual sink zones, whereas the change in slope occurred more recently in records originating from source zones. This study provides new insights into the spatial and temporal variability of the past oceanic pump activity.