Biogeosciences www.biogeosciences.net 1726-4170 1726-4189 5 4 2008 10.5194/bg-5-1023-2008 http://www.biogeosciences.net/5/1023/2008/ http://www.biogeosciences.net/5/1023/2008/bg-5-1023-2008.html http://www.biogeosciences.net/5/1023/2008/bg-5-1023-2008.pdf 1023 1031 2008-07-23 Does ocean acidification induce an upward flux of marine aggregates? X. Mari xavier.mari@noumea.ird.nc UR 103 (IRD), Centre IRD de Nouméa, BP A5, 98848 Nouméa cedex, New Caledonia The absorption of anthropogenic atmospheric carbon dioxide (CO₂) by the ocean provokes its acidification. This acidification may alter several oceanic processes, including the export of biogenic carbon from the upper layer of the ocean, hence providing a feedback on rising atmospheric carbon concentrations. The effect of seawater acidification on transparent exopolymeric particles (TEP) driven aggregation and sedimentation processes were investigated by studying the interactions between latex beads and TEP precursors collected in the lagoon of New Caledonia. A suspension of TEP and beads was prepared and the formation of mixed aggregates was monitored as a function of pH under increasing turbulence intensities. The pH was controlled by addition of sulfuric acid. Aggregation and sedimentation processes driven by TEP were drastically reduced when the pH of seawater decreases within the expected limits imposed by increased anthropogenic CO₂ emissions. In addition to the diminution of TEP sticking properties, the diminution of seawater pH led to a significant increase of the TEP pool, most likely due to swollen structures. A diminution of seawater pH by 0.2 units or more led to a stop or a reversal of the downward flux of particles. 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