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

随着巴拿马海道在大约4 Ma BP关闭，大陆冰盖开始增加，特别是在北方。这一持续的过程最终导致了明显的晚更新世冰期-间冰期循环，这是我们最近气候的特征。上新世-更新世世界气候变冷与大陆冰盖的逐步增加有关，这在许多基于IODP岩心沉积物材料的古海洋学重建中得到了很好的证明。然而，对于上新世-更新世气候变化与低纬度和高纬度海洋营养条件之间的联系以及不同海洋之间富含营养的水团的交换，仍然非常缺乏知识。特别是，与记录低纬度高产地区过去营养条件变化的记录相比，我们错过了海洋气候变化的详细记录。基于纳米比亚和秘鲁沿岸上升流区有机物的615 N信号，我们的目标是调查过去4 Ma的东部边界流系统中的营养条件的海洋环流和全球变冷的变化可能产生的影响。这可能允许重建的变化，在平流的营养丰富的水体和营养利用，以及它们的平衡与反硝化和固氮的过程。这些对过去营养条件的重建，加上过去环流和生产力的其他代用记录，应该能够揭示在百万年时间尺度上全球气候变化背景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.