Isotopic constraints on declining oceanic nutrient inventories weakening the marine soft-tissue biological carbon pump during the last deglaciation

了解在最后一次冰消期（距今19,000至9,000年）大气CO2浓度增加近80 ppm的机制仍然是古海洋学的一个重大挑战。有人提出，冰消期大气中二氧化碳上升的一半可能是由海洋生物碳泵减少造成的，即通过初级生产和有机碳的垂直输出在深海中封存二氧化碳。即使是海洋生物碳泵，也有许多机制和营养循环被提出来驱动这些冰消期的变化。这一问题得到了广泛讨论，但基本上仍未得到解决，因为大多数研究仅侧重于单一机制，因此缺乏连贯的图景。在这个项目中，我们将使用海洋生物地球化学和同位素模型（MOBI）耦合在地球系统气候模型中，以估计氮，铁和溶解有机碳的海洋营养物质库存下降如何影响软组织生物碳泵在最后一次冰消作用的瞬态模拟。我们的项目的新方法将利用碳（13 C和14 C）和氮（15 N）的同位素示踪剂纳入我们的模型。模拟结果与沉积记录中测得的同位素的直接比较，为控制海洋营养物质存量的过程提供了重要的定量约束，从而也为软组织生物泵的强度提供了重要的定量约束。我们将提供一个全面的分析变化的关键限制营养物质清单，以及他们的个人和合并的贡献上升冰消期大气CO2使用一个连贯的多代理模型数据比较。该项目将指出最重要的对气候敏感的海洋养分循环过程，这些过程需要纳入全球气候模型，以改进对未来海洋和气候的预测。

Understanding the mechanisms controlling the nearly 80 ppm increase in atmospheric CO2 concentrations during the last deglaciation (19,000 to 9,000 years before present) remains a major challenge in paleoceanography. It has been suggested that up to half of the deglacial atmospheric CO2 rise may be driven by a reduction the marine biological carbon pump, i.e. the sequestration of CO2 in the deep ocean through primary production and vertical export of organic carbon. Even for the marine biological carbon pump, many mechanisms and nutrient cycles have been proposed to have driven these deglacial changes. This issue is extensively discussed and it remains largely unresolved since most studies focus only on single mechanisms and thus a coherent picture is lacking. In this project, we will use the Model of Ocean Biogeochemistry and Isotopes (MOBI) coupled within an Earth System Climate Model to estimate how declining marine nutrient inventories of nitrogen, iron, and dissolved organic carbon impacted the soft-tissue biological carbon pump in a transient simulation of the last deglaciation. The novel approach of our project will be utilizing the isotope tracers of carbon (13C and 14C) and nitrogen (15N) incorporated in our model. Direct comparisons of simulation results with isotopes measured in sedimentary records provide important quantitative constraints on processes controlling marine nutrient inventories and thus the strength of the soft-tissue biological pump. We will provide a comprehensive analysis on changes to key limiting nutrient inventories, as well as their individual and combined contribution to rising deglacial atmospheric CO2 using a coherent multi-proxy model-data comparison. This project will indicate the most important climate-sensitive marine nutrient cycle processes that need to be incorporated into global climate models to improve predictions of the future ocean and climate.