二氧化碳海气交换通量估计的不确定性

尽管确信海洋是人为CO2 的一个巨大碳汇 ,但其确切的数字及其未来变化趋势至今仍有较大的争议。分析讨论了国内外这方面的研究成果 ,特别是近几年的研究进展 ,指出了在计算海气交换通量时存在的主要问题。计算CO2 气海交换系数的公式尚未取得一致 ,在相同的风速下 ,不同的公式可产生百分之几十的差别。计算的CO2 分压因使用不同的热力学常数表达式而导致不同的结果 ,差值可达 3Pa。进一步讨论了基于观测和模式估计的CO2 气海交换通量的不确定性 ,并指明了模式结果存在的差异。根据CO2 分压的观测资料估计 1 990年和 1 995年全球海洋分别吸收 1 .4 5GtC和 2 .2 5GtC的CO2 ,该估计有 5 0 %的不确定性 ,4个全球海洋环流碳循环模式估计 1 980— 1 989年间海洋每年吸收人为CO2 为 1 .5～ 2 .2GtC。评述了通量的季节变化和年际变化 ,年际变化与发生在太平洋中的厄尔尼诺现象有关。

UNCERTAINTIES IN THE ESTIMATE OF THE AIR-SEA EXCHANGE FLUX OF CARBON DIOXIDE

Although it is believed that the ocean is a huge sink of anthropogenic CO_2, there is still some controversy over the exact figure and its future changes. The achievements on these aspects obtained in the world have been analysed and discussed, particularly on the progress made in the recent years. Main problems for the calculation of air-sea CO_2 exchange fluxes have been pointed out. There has not been a consistent formula for the calculation of exchange coefficient for the CO_2 air-sea exchange. Under the same wind velocity, different formulae can lead to a difference of several tens per cent in the exchange coefficient. Use of different formulae of thermodynamic constants may generate a difference of up to 3 Pa in the calculated partial pressure of CO_2 at surface water. Uncertainties of observation- and model-based estimates of the air-sea flux are further discussed. The difference between the models is indicated. According to the observations of partial pressure of CO_2, it has been estimated that the global ocean took up 1.45 and 2.25 Gt C of CO_2 in 1990 and 1995, respectively, with an uncertainty of 50%. Four global ocean circulation carbon cycle models estimated that the global ocean took up 1.5～2.2 Gt C of anthropogenic CO_2 for the period of 1980—1989. Seasonal and interannual variability of the flux is also discussed. Interannual variations of CO_2 flux are associated with El Nio.