Dickson J A D
Department of Earth Sciences, University of Cambridge, Downing Street, Cambridge, CB2 3EQ, UK.
Science. 2002 Nov 8;298(5596):1222-4. doi: 10.1126/science.1075882.
Opinion has long been divided as to whether the Mg/Ca ratio of seawater remained constant during the Phanerozoic or underwent substantial secular change. Existing empirical evidence for the Mg/Ca of ancient seawater provides a poorly resolved and often controversial signal. Echinoderm fossils that have retained their bulk original chemistry, despite micrometer-scale changes, preserve a record of seawater Mg/Ca and confirm that major changes in Mg/Ca occurred during the Phanerozoic. Echinoderms from the Cambrian and from the Carboniferous to the Triassic indicate a seawater Mg/Ca of approximately 3.3, whereas echinoderms from the Jurassic to the Cretaceous indicate a Mg/Ca of approximately 1.4. The present seawater Mg/Ca is approximately 5.
关于显生宙期间海水的镁钙比是保持恒定还是经历了显著的长期变化，长期以来一直存在分歧。现有的关于古代海水镁钙比的经验证据提供了一个分辨率低且常常有争议的信号。尽管有微米级别的变化，但保留了其整体原始化学组成的棘皮动物化石保存了海水镁钙比的记录，并证实了显生宙期间镁钙比发生了重大变化。寒武纪以及石炭纪至三叠纪的棘皮动物表明海水镁钙比约为3.3，而侏罗纪至白垩纪的棘皮动物表明镁钙比约为1.4。目前海水的镁钙比约为5。
