Fluvial carbon fluxes in tropical rivers

The export of fluvial carbon from land to the ocean is an important connection between two of the largest carbon reservoirs in the world. Previous investigations have estimated that river water annually provides 0.80-1.33 Pg of carbon to the world's oceans. This investigation combines a review of published data from 80 tropical (30 degrees N-30 degrees S) rivers, with supplementary, unpublished data concerning 95 additional rivers, mostly from South and Southeast Asia. These rivers deliver approximately 0.53 Pg carbon to the estuaries annually. Of this, 0.21 Pg C is dissolved inorganic carbon (DIC), 0.14 Pg C is dissolved organic carbon (DOC), 0.05 Pg C is particulate inorganic carbon (PIC), and 0.13 Pg C is particulate organic carbon (POC). Rivers in the equatorial region between 3 degrees N and 6 degrees S register high DOC values but low DIC values; the difference is primarily associated with type of soil. Rivers in mainland Asia have the highest specific export rates in terms of DIC, DOC and POC.