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

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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.