Dai¹, Minhan, Weidong Zhai¹, Wei-Jun Cai², Yongchen Wang² and Zhaohui Wang²

¹Marine Environmental Laboratory, Xiamen University, Xiamen 361005, China, Tel: 86-592-218-2132, Fax: 86-592-218-0655, E-mail: mdai@xmu.edu.cn and ²Departments of Marine Sciences, the University of Georgia, Athens, Georgia, USA

High partial pressure of CO₂ and its maintaining mechanism in a large subtropical estuary - the Pearl River estuary, China

Increasing attention has been given to the significance of CO₂ outgassed from world river and estuarine systems in the global carbon budget. We report in this presentation the distribution of surface water pCO₂ and dissolved oxygen (DO) and associated carbonate parameters in the Pearl River estuary, a large subtropical estuary in China based upon data from three cruises (summer of 2000, late spring of 2001, and fall of 2002).

A high pCO₂ level range as £ 4000 µatm at salinity < 1 in all three seasons were measured using a continuous measurement system. pCO₂ distribution overall mirrors DO cross the salinity gradient. Based upon the linear relationship between excess CO₂ and apparent oxygen utilization (AOU) in the surface water, we are able to conclude that biologically aerobic respiration process likely plays the most significant role in maintaining such high pCO₂ in the upstream of the estuary elucidated. Upper limit of pCO₂ can be estimated as 5500 ~ 7000 µatm accordingly. Impacts of temperature and salinity and chemical enhancement by CaCO₃ precipitation are secondary processes responsible for high pCO₂.