Sensitivity of coccolithophores to carbonate chemistry and ocean acidification

摘要

About one-third of the carbon dioxide (CO_2) released into the atmosphere as a result of human activity has been absorbed by the oceans~1, where it partitions into the constituent ions of carbonic acid. This leads to ocean acidification, one of the major threats to marine ecosystems~2 and particularly to calcifying organisms such as corals~(3-4), foraminifera~(5-7) and coccolithophores~8. Coccolithophores are abundant phytoplankton that are responsible for a large part of modern oceanic carbonate production. Culture experiments investigating the physiological response of coccolithophore calcification to increased CO_2 have yielded contradictory results between and even within species~(8-11). Here we quantified the calcite mass of dominant coccolithophores in the present ocean and over the past forty thousand years, and found a marked pattern of decreasing calcification with increasing partial pressure of CO_2 and concomitant decreasing concentrations of CO_3~(2～). Our analyses revealed that differentially calcified species and morphotypes are distributed in the ocean according to carbonate chemistry. A substantial impact on the marine carbon cycle might be expected upon extrapolation of this correlation to predicted ocean acidification in the future. However, our discovery of a heavily calcified Emiliania huxleyi morphotype in modern waters with low pH highlights the complexity of assemblage-level responses to environmental forcing factors.%如“颗石藻”等钙化生物对因大气中二氧化碳rn浓度增加而发生的海洋酸化的反应的性质，是rn预测未来碳循环及其对由人类活动造成的变化rn的反馈的关键。在实验室中所做实验对了解这rn个司题几乎没有帮助，因为它们通常所跟踪的rn只是所选择的某一种生物对少数几种变化了的rn参数做出的反应。通过分析当代表层海水样本rn和化石沉积芯，Beaufort等人发现，溶解的rnCO_2的增加引起钙化速度的加快，而重度钙化rn的“颗石藻”形态的丰富程度则依赖于碳酸盐rn化学。然而，在具有低pH值的现代水域中重rn度钙化的“赫氏颗石藻”(Emiliania huxleyi)的rn意外发现，却表明海洋对CO_2增加的反应是复rn杂的。