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 (δ13Catm) 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 δ13Catm has also been observed in dissolved inorganic carbon (δ13CDIC) due to the oceanic pump activity. Corals record environmental conditions by incorporating the ambient water trace elements and isotopes such as the δ13CDIC. Therefore, coral δ13C (δ13CC) can be used as an indicator of the past oceanic pump activity. In this study, we used previous temporal records of δ13CC 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 δ13CC from Clipperton Island, a zone observed as a source zone. We created composite δ13CC 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 δ13Catm record from ice cores. General trends observed in all our selected records seems to follow the δ13Catm 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.