(SGER): Experiments on the Effects of the Magnesium-Calcium Ratio of Seawater on Carbonate Skeletal Secretion

(SGER)：海水镁钙比例对碳酸盐骨骼分泌影响的实验

• 批准号: 0202849
• 负责人: Steven Stanley
• 金额: $ 2.1万
• 依托单位: Johns Hopkins University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2002
• 资助国家: 美国
• 起止时间: 2002-02-01 至 2003-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0202849&HistoricalAwards=false
• 关键词: SGER; Experiments; Effects; Magnesium; Calcium

There is now powerful evidence that changes in the Mg/Ca ratio of seawater have produced the oscillations during Phanerozoic time between intervals when nonskeletal carbonates precipitating from seawater have consisted of low-Mg calcite and intervals when these chemical precipitates have consisted of high-Mg calcite and aragonite. In previous work that focused on patterns in the geologic record, we showed that throughout Phanerozoic time biologically simple carbonate-secreting organisms, especially those that hypercalcify (produce massive skeletons or generate sediment rampantly) have adhered to the 'calcite sea'/'aragonite sea' pattern. This correspondence implies that simple organisms hypercalcify only when the Mg/Ca ratio of ambient seawater favors their mineralogy. Thus far, PI's research has been based on patterns in the geologic record. They are now embarking on an entirely new approach: they plan to conduct laboratory experiments to test the effects of the Mg/Ca ratio on the calcification of living organisms. Specifically, they plan three kinds of controlled aquarium experiments that they anticipate will be particularly tractable. They will determine whether, when grown in water having low and very low ('Permian' and 'Cretaceous') Mg/Ca ratios, (1) specimens of coralline algae, which secrete high-Mg calcite in modern seawater, incorporate less Mg into their skeletons than when they are grown in modern seawater; (2) specimens of aragonitic algae grow at lower rates than when grown in modern seawater; and (3) calcareous nannoplankton, which secrete calcite, experience more rapid population growth than comparable populations cultured under identical conditions but with an ambient Mg/Ca ratio equal to that of modern seawater. (in other words, when extant species of nannoplankton are grown in 'Cretaceous' seawater, in which the Mg/Ca ratio is close to unity and there is a large total concentration of dissolved Ca, will they bloom as their ancestors did in the 'chalk seas' of the Cretaceous?).

现在有强有力的证据表明，海水中Mg/Ca比值的变化在中生代期间产生了振荡，在从海水中沉淀的非骨架碳酸盐由低镁方解石组成的时间间隔和这些化学沉淀物由高镁方解石和文石组成的时间间隔之间。 在以前的工作中，集中在地质记录的模式，我们表明，在整个中生代生物简单的碳酸盐分泌生物，特别是那些hypercalcification（产生大量的骨骼或产生沉积物猖獗）坚持“方解石海”/“文石海”模式。 这种对应关系意味着，简单的生物hypercalcification只有当周围海水的Mg/Ca比有利于他们的矿物。 到目前为止，PI的研究一直基于地质记录中的模式。他们现在正在着手一种全新的方法：他们计划进行实验室实验，以测试Mg/Ca比例对生物体钙化的影响。 具体来说，他们计划了三种受控的水族馆实验，他们预计这些实验将特别容易处理。 他们将决定，当生长在水有低和非常低的（二叠纪和三叠纪）Mg/Ca比值，（1）在现代海水中分泌高镁方解石的珊瑚藻标本，其骨骼中的Mg含量比在现代海水中生长时少;（2）文石藻标本的生长速度比在现代海水中生长时慢;（3）分泌方解石的钙质微型浮游生物比在相同条件下但环境Mg/Ca比等于现代海水中的环境Mg/Ca比下培养的可比种群经历更快的种群增长。(in换句话说，当现存的微型浮游生物在“白垩纪”海水中生长时，其中Mg/Ca比接近1，并且溶解的Ca的总浓度很大，它们会像它们的祖先在白垩纪的“白垩海”中那样开花吗？