Nitrogen cycling in low-latitude upwelling systems related to Plio-Pleistocene climate change

大约在距今4 Ma BP，巴拿马海道开始关闭，大陆冰盖开始增加，尤其是在北半球。这个持续的过程在明显的晚更新世冰期-间冰期旋回中达到顶峰，这是我们最近的气候特征。上新世-更新世世界气候变冷与大陆冰盖的逐步增加有关，这在基于IODP岩心沉积物物质的许多古海洋学重建中得到了很好的记录。然而，关于上新世-更新世气候变化与低纬度和高纬度海洋营养条件以及不同海洋之间富营养水团交换的联系，存在着严重的知识缺乏。特别是，与记录低纬度高产地区过去营养状况变化的记录相比，我们缺少海洋气候变化的详细记录。基于纳米比亚和秘鲁沿海上升流区有机质的615N信号，研究了近4 Ma海洋环流和全球变冷对东部边界流系统过去营养条件的可能影响。这可以重建富营养水团平流和养分利用的变化，以及它们与反硝化和固氮过程的平衡。这些对过去养分条件的重建，以及其他关于过去环流和生产力的代理记录，将揭示在全球气候变化的百万年时间尺度下，高产地区生物地球化学循环的作用。

With the onset of the closure of the Panama seaway at about 4 Ma BP, continental ice-sheets started to increase, particulary in the northern hemisphere. This ongoing process culminated in pronounced late Pleistocene glacial-interglacial cycles which characterized our climate in the recent past. The Pliocene-Pleistocene cooling of the world climate associated with step-wise increases in continental ice sheets is well documented in many paleoceanographic reconstructions based on sediment material from IODP cores. However, a strong lack of knowledge exists with respect to the linkages of Plio-Pleistocene climate changes and the marine nutrient conditions in low and high latitudes as well as to the exchange of nutrient-rich water masses between the different oceans. Particularly we miss detailed records of ocean climate change in comparison with records documenting past changes of nutrient conditions in high productive regions at low latitudes. Based on the 615N signal of organic matter from coastal upwelling areas off Namibia and Peru, we aim to investigate possible effects of changes in ocean circulation and global cooling on past nutrient conditions in eastern boundary current systems for the last 4 Ma. This may allow to reconstruct variations in the advection of nutrient-rich water masses and in nutrient utilisation as well as their balance with the processes of denitrification and nitrogen fixation. These reconstructions of past nutrient conditions, together with other proxy records for past circulation and productivity, should unravel the role of biogeochemical cycling in high productive regions in the context of global climate change on million-year time scales.