(Table 1) Comparison of diatom-bound and bulk sedimentary d15N values of ODP Holes 175-1082A and 175-1084A

The Matuyama Diatom Maximum (MDM) is a time of peak opal accumulation from 2.6 to ~2.0 Ma within the Benguela Current upwelling system that was initiated by increased influence of Southern Ocean water on the eastern South Atlantic. We measured opal, total organic carbon (TOC), and CaCO3 fluxes and C and N stable isotopes in sediments deposited from 2.4 to 1.95 Ma at Sites 1082 and 1084 to explore the biogeochemical dynamics within the Benguela region. The infusion of Southern Ocean water delivered dissolved nutrients and Southern Ocean flora and fauna, resulting in local opal accumulation increasing up to 8 g/cm**2/ky and the production of diatom mats. Some d15N measurements of diatom-bound organic matter indicate that the mats grew within the Benguela region. The bulk sediment d15N records are taken to reflect changes in the d15N of nitrate in the incoming water, where lower values at 2.4 Ma reflect less nitrate utilization in the Antarctic. A long-term increase in relative nitrate uptake in the Southern Ocean is evidenced by the gradual increase in d15N toward 1.9 Ma.

马塔伊马硅藻繁盛期（Matuyama Diatom Maximum, MDM）指2.6 Ma至约2.0 Ma期间，本格拉上升流系统（Benguela Current upwelling system）内蛋白石沉积通量达到峰值的时段，其形成源于南大洋水对南大西洋东部区域影响的增强。本研究对1082和1084站位2.4 Ma至1.95 Ma期间沉积的沉积物中的蛋白石、总有机碳（total organic carbon, TOC）与碳酸钙（CaCO₃）沉积通量，以及碳、氮稳定同位素进行了测定，以探究本格拉区域内的生物地球化学动力学过程。南大洋水的注入携带来溶解态营养盐与南大洋动植物区系，进而促使当地蛋白石沉积通量最高可达8 g/cm²/ky，并形成了硅藻垫。部分针对结合于硅藻的有机质的δ¹⁵N测定结果显示，此类硅藻垫生长于本格拉区域内部。沉积物全样的δ¹⁵N记录被用以反映输入水体中硝酸盐的δ¹⁵N变化：2.4 Ma时较低的δ¹⁵N值反映出南极区域的硝酸盐利用程度偏低。δ¹⁵N值随时间逐步升高至1.9 Ma，这一现象证明南大洋的相对硝酸盐摄取率存在长期提升的趋势。