McClelland H L O, Barbarin N, Beaufort L, Hermoso M, Ferretti P, Greaves M, Rickaby R E M
Department of Earth Sciences, University of Oxford, South Parks Road, Oxford, OX1 3AN, UK.
CEREGE CNRS-IRD-Aix Marseille Univ, Avenue Louis Philibert, BP80 13545 Aix en Provence cedex 04, France.
Sci Rep. 2016 Sep 28;6:34263. doi: 10.1038/srep34263.
Coccolithophores are single-celled photosynthesizing marine algae, responsible for half of the calcification in the surface ocean, and exert a strong influence on the distribution of carbon among global reservoirs, and thus Earth's climate. Calcification in the surface ocean decreases the buffering capacity of seawater for CO, whilst photosynthetic carbon fixation has the opposite effect. Experiments in culture have suggested that coccolithophore calcification decreases under high CO concentrations ([CO(aq)]) constituting a negative feedback. However, the extent to which these results are representative of natural populations, and of the response over more than a few hundred generations is unclear. Here we describe and apply a novel rationale for size-normalizing the mass of the calcite plates produced by the most abundant family of coccolithophores, the Noëlaerhabdaceae. On average, ancient populations subjected to coupled gradual increases in [CO(aq)] and temperature over a few million generations in a natural environment become relatively more highly calcified, implying a positive climatic feedback. We hypothesize that this is the result of selection manifest in natural populations over millennial timescales, so has necessarily eluded laboratory experiments.
颗石藻是单细胞光合海洋藻类，其钙化作用占海洋表层钙化作用的一半，对全球储库间的碳分布进而对地球气候有着重大影响。海洋表层的钙化作用会降低海水对二氧化碳的缓冲能力，而光合固碳作用则有相反效果。培养实验表明，在高二氧化碳浓度（[CO(aq)]）下，颗石藻的钙化作用会减弱，构成一种负反馈。然而，这些结果在多大程度上代表自然种群以及几百代以上的反应尚不清楚。在此，我们描述并应用一种新颖的原理，对最丰富的颗石藻科——诺氏石藻科所产生的方解石板的质量进行尺寸归一化处理。平均而言，在自然环境中历经数百万代[CO(aq)]和温度逐渐同步升高的古代种群，钙化程度相对变得更高，这意味着存在一种正气候反馈。我们推测，这是自然种群在千年时间尺度上表现出的选择结果，因此必然在实验室实验中未被发现。
