Chemical enhancement of the CO2 gas exchange at a smooth seawater surface

✍ Scribed by Joachim Kuss; Bernd Schneider

• Publisher: Elsevier Science
• Year: 2004
• Tongue: English
• Weight: 343 KB
• Volume: 91
• Category: Article
• ISSN: 0304-4203
• DOI: 10.1016/j.marchem.2004.06.007

✦ Synopsis

Tank experiments were conducted to quantify the chemical enhancement of the CO 2 gas exchange and its dependency on turbulence and pH. Positive and negative CO 2 partial pressure differences were generated between the headspace and the seawater sample. The gas exchange transfer velocities (k) were determined by recording the CO 2 concentrations in the headspace using an IR CO 2 analyser. Acidified seawater samples were used to determine non-enhanced transfer velocities and provided the reference to calculate enhancement factors, the ratio of the enhanced k and the non-enhanced k. Different surface turbulence was generated by circulating the headspace at different flow rates. Chemical enhancement was only observed at low turbulence, which corresponded to k values of 2.5-4 cm h À1 . Different enhancement factors a were observed during CO 2 invasion (a=1.34) and CO 2 evasion (a=1.08). These differences were attributed to different pH (8.6 and 7.9, respectively) originating from different CO 2 partial pressures in water during uptake and release experiments. An exponential fit was used to describe a as a function of pH: a=1.6Â10 À8 e 1.98pH +1 (kb4 cm h À1 ). The resulting enhancement factors, which are only partly consistent with previous experimental and model studies, indicate that chemical enhancement may be important for regional and temporal CO 2 budgets whereas the effect on the global CO 2 balance is negligible.