College of Earth, Ocean and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97331, USA.
Department of Earth and Planetary Sciences, University of California, Davis, California 95616, USA.
Nat Commun. 2017 May 15;8:15441. doi: 10.1038/ncomms15441.
The relationship between seawater temperature and the average Mg/Ca ratios in planktic foraminifera is well established, providing an essential tool for reconstructing past ocean temperatures. However, many species display alternating high and low Mg-bands within their shell walls that cannot be explained by temperature alone. Recent experiments demonstrate that intrashell Mg variability in Orbulina universa, which forms a spherical terminal shell, is paced by the diurnal light/dark cycle. Whether Mg-heterogeneity is also diurnally paced in species with more complex shell morphologies is unknown. Here we show that high Mg/Ca-calcite forms at night in cultured specimens of the multi-chambered species Neogloboquadrina dutertrei. Our results demonstrate that N. dutertrei adds a significant amount of calcite, and nearly all Mg-bands, after the final chamber forms. These results have implications for interpreting patterns of calcification in N. dutertrei and suggest that diurnal Mg-banding is an intrinsic component of biomineralization in planktic foraminifera.
海水温度与浮游有孔虫平均 Mg/Ca 比值之间的关系已得到充分证实，为重建过去的海洋温度提供了重要工具。然而，许多种浮游有孔虫的壳壁内显示出交替的高镁带和低镁带，仅凭温度无法解释。最近的实验表明，形成球形终壳的 Orbulina universa 种内壳内 Mg 变异性由昼夜光/暗循环控制。在具有更复杂壳形态的物种中，Mg 不均匀性是否也具有昼夜节奏尚不清楚。在这里，我们显示在培养的多室种 Neogloboquadrina dutertrei 的标本中，高 Mg/Ca 方解石在夜间形成。我们的结果表明，N. dutertrei 在最后一个室形成后会添加大量方解石和几乎所有的 Mg 带。这些结果对解释 N. dutertrei 中钙化模式具有重要意义，并表明昼夜 Mg 带是浮游有孔虫生物矿化的内在组成部分。
