Mass estimates and morphometric meassurements of Discoaster species and Sphenolithus from Ceara Rise ODP Site 927

Mass estimates for Late Miocene and Pliocene (8.6-3.25 Ma) Discoaster species and Sphenolithus are determined using samples of the equatorial Atlantic (Ceara Rise: ODP Site 927). Based on morphometric measurements, 3D computer models were created for 11 Discoaster species and their volumes calculated. From these, shape factors (ks) were derived to allow calculation of mass for different-sized discoasters and Sphenolithus abies. The mass estimates were then used to calculate the contribution of nannofossils to the total nannofossil carbonate. The discoaster contribution ranges from 10% to 40%, with a decreasing trend through the investigated interval. However, our estimates of total nannofossil carbonate from size-corrected abundance data are consistently 30-50% lower than estimates from grain-size measurement; this suggests that data based on mass estimates need to be interpreted with caution.

利用来自赤道大西洋（塞阿拉隆起：ODP 站点 927）的样本，对上新世晚期至更新世（8.6-3.25 Ma）的 Discoaster 物种及 Sphenolithus 的质量进行了测定。基于形态计量学的测量结果，为 11 个 Discoaster 物种构建了三维计算机模型，并计算了其体积。据此，推导出形状因子（ks），以便对不同尺寸的 Discoaster 和 Sphenolithus abies 进行质量计算。随后，利用这些质量估计值计算了纳米化石对总纳米化石碳酸盐的贡献。Discoaster 的贡献率介于 10% 至 40%，在研究区间内呈下降趋势。然而，基于尺寸校正丰度数据的总纳米化石碳酸盐估计值，与基于粒度测量的估计值相比，始终低 30-50%；这表明基于质量估计的数据需要谨慎解读。