Changjiang floods enhance the CO2 uptake of the East China Sea

Abstract:

The understanding of how anomalously large river floods affect the CO₂ uptake in the coastal oceans, especially for the river-dominated marginal seas, is unclear. Here we report the effect of the Changjiang flood in July 2010 on the CO₂ uptake of the East China Sea (ECS). We had performed the underway measurements of the air and sea surface fCO₂ with hydrographic variables from July 7^th to 17^th 2010 during the flood event in the field survey. The results showed that fCO_2w ranged from 97.3 to 467.4 matm, with an average of 291.7 ± 63.3 (n=1599), which was under-saturated relative to atmospheric CO₂ (380.2 ± 1.2 matm, n=686). The fCO₂ distribution exhibited a typical pattern spatially, varying from the normal summer. The serious flood brought huge amounts of runoff waters with terrigenous materials, including nutrients for phytoplankton, to the ECS. The flood-induced biological production largely took place in the plume area (i.e., Changjiang diluted water, CDW, Salinity <31‰) along with low fCO₂ (249.7 ± 26.0 matm), which occupied the 1/2 of total survey area. Overall, the flood in July 2010 induced a net strong CO₂ sink (-4.0 molC m^-2 yr^-1). Moreover, similar consequences of the floods in the ECS were observed from a 14-year observation (1998-2011) that the Changjiang floods significantly enhance the CO₂ uptake in the ECS. The results further show the CO₂ uptake in the ECS in July 1998 and 2010 about 10 times the amount during non-flooding periods in the past decades. As the frequencies of floods increase world wide as a result of climate change, the contribution of the flood-enhanced CO₂ uptake in the coastal ocean shall be further examined via a long-term observation.