An empirical assessment of dissolved organic carbon fluxes to oceans under climate change

Abstract

Climate change is a primary concern in the coming decades, affecting temporal and spatial patterns in temperature and hydrology worldwide. These variations will undoubtedly affect the global carbon balance. The export of riverine dissolved organic carbon (DOC) to the oceans is crucial for maintaining the carbon balance and sustaining the oceanic food web. Recent modelling quantified historical DOC exports and future daily discharges delivered to the oceans. We intend to compare historical (1971–2000) and future (2071–2100) DOC deliveries from large rivers using an easy-to-use equation that integrates future air temperatures, soil organic carbon contents, and hydrological dynamics under a changing climate. On a set of 338 large rivers, we found future global DOC exports to the oceans of 136.9 ± 35.8 and 148.1 ± 38.9 TgC y−1 in the RCPs 2.6 and 8.5. Compared to the historical flux of 126.1 ± 32.6 TgC y−1, global variations are not significant. However, regional trends were found. Among all watersheds, cold catchments returned the most significant rises of +0.07 ± 0.02 and + 0.13 ± 0.03 TgC y−1, resulting in increases of +28 % and + 55 % for RCPs 2.6 and 8.5, respectively. Moreover, the usual spring freshet in these catchments, which delivers most of the DOC, occurs earlier (10 and 18 days, respectively). This paper highlights the high variability in future dissolved organic carbon (DOC) deliveries to the oceans, particularly in high latitudes. These increases might affect the local and global sustainability of aquatic ecosystems.