*2.2. 13C Atomic Enrichment (AE) of Particulate Organic Carbon and Dissolved Inorganic Carbon*

Dissolved inorganic carbon (DIC) progressively enriched in the two balloons with 13CO2 (Figure 4A). The enrichment trends were similar for the two balloons after t4, with an important increase in the DIC atomic enrichment until t20 (up to 58.1 and 61.1% for Tl1 and Tl2, respectively). The increase in AE tended to stabilize after t20. Final levels of enrichment were 61.5 and 64.6% for Tl1 and Tl2, respectively (Figure 4A). Atomic enrichment (AEPOC) increased sharply after t4 for the two balloons until the end of the experiment. Enrichment levels at t24 were 25.2 and 34.7% for Tl1 and Tl2, respectively (Figure 4B).
