Orbital control on marine biological productivity at the Oligocene-Miocene transition? Influence on global cooling and pCO2atm.

在第一个建议期间，我们调查了渐新世-中新世过渡，一个快速冷却和南极冰延伸的时期，在本研究计划的5个ODP站点中的3个。这一地质时期的标志是全球碳储量的变化，反映在1‰的正碳同位素偏移和δ 13 C信号明显的400 kyrs旋回性。在该项目中，我们分析了在渐新世-中新世边界的时间间隔内，开阔海洋生物生产力是否增加，并导致海洋沉积物中额外和同位素耗尽的碳的封存，以及海洋生产力变化是否与δ 13 C循环相匹配。来自3个大西洋ODP地点的第一个结果证实了我们的假设，即海洋生产力的变化是轨道强迫的，我们可以表明，海洋生产力，气候变化和pCO 2atm之间的联系，通过在大西洋沉积物中的CO2封存。我们在此申请资金以结束调查。在接下来的工作中，我们将通过分析印度-太平洋的两个ODP地点来扩大我们记录的区域覆盖范围，这将使我们能够了解在渐新世-中新世过渡期观察到的生产力增加是大西洋还是全球现象。这一问题将为L. Francois的模拟实验奠定基础。我们进一步的目标是重建大气中的二氧化碳浓度在冷却期通过陆地植物群和气孔密度的分析。

During the first proposal period, we investigated the Oligocene-Miocene transition, a period of rapid cooling and Antarctic ice extension, at three of 5 ODP Sites planned in this study. The geological period is marked by a change in global carbon reservoirs, as reflected in a 1‰ positive carbon isotope excursion and distinct 400 kyrs cyclicity in the δ13C signal. In the project, we analyse whether open ocean biological productivity increased during the time interval at the Oligocene-Miocene boundary and led to the sequestration of additional and isotopically depleted carbon in marine sediments, and whether marine productivity variations match the δ13C cycles. First results from 3 Atlantic ODP locations confirm our hypotheses that marine productivity variations are orbitally forced and we could show that there is a link between marine productivty, climate change and pCO2atm via CO2 sequestration in sediments in the Atlantic Ocean. Here we apply for funds to conclude our investigation. In the work to come, we will extend the regional coverage of our records by analyzing two ODP sites in the Indo-Pacific ocean, that will allow to see whether the observed productivity increase at the Oligocene-Miocene transition is an Atlantic or a global phenomenon. This question will be the basis for modeling experiments of L.Francois. We further aim to reconstruct atmospheric carbon dioxide concentrations during the cooling period by means of an analysis of terrestrial flora and stomatal density.