A d30Si isotopic view on the climatic role of diatoms: driver or feedback?

大量的单细胞浮游植物（硅藻）的外壳由二氧化硅制成，它们负责将大部分碳从海洋表层输送到海洋深处。因此，硅藻生产力的变化控制着大气中二氧化碳的含量以及海洋深处二氧化碳的输送和储存量。本提案的目的是利用硅藻生产力的特征和新特征，即d30Si，研究硅藻在长时间和短时间尺度上驱动气候变化的作用。我们的目的是找出在过去的50万年里，硅藻生产力的重大变化是否促进了二氧化碳从大气到深海的减少，是否有助于地球从一个没有冰或很少冰的温室世界转变为现在有两极冰盖的现代冰屋世界。此外，我们的目标是建立在一些初步证据的基础上，即硅藻正在随着全球变暖而蓬勃发展，并找出硅藻生产力是否可以作为人为二氧化碳排放的负反馈。随着南极洲周围冰川的退缩和融水流入这一生产力很高的沿海地区的增加，营养物的输入可能会增加，水柱的稳定性也会增强，这两者都可能导致硅藻生产力的提高。我们将建立一个硅藻生产力的记录，再次使用d30Si，在过去的500年里，在南极半岛快速积累的沉积物中。通过以过去500年为目标，我们的分析将捕捉到全新世小冰期（结束于1850年）的最后一次冰川推进和恢复，并允许我们测试硅藻是否随着冰川退缩而持续增加生产力，并评估硅藻对人为强迫冰川退缩的响应是否在这个时间尺度上是前所未有的。

Large blooms of single celled phytoplankton which make their shells out of silica, the diatoms, are responsible for transporting the majority of carbon from the surface ocean to the deep ocean. Changes in the productivity of diatoms therefore control how much carbon dioxide resides in the atmosphere and how much is conveyed and stored in the deep ocean. The aim of this proposal is to investigate the role of diatoms in driving changing climate on long and short timescales using a characteristic and novel signature of diatom productivity, namely the d30Si. Our intention is to find out whether major changes in diatom productivity which would have enhanced the draw-down of carbon dioxide from the atmosphere to the deep ocean, during the last ~ 50 Myrs could have contributed to Earth's transition from a greenhouse world with no or little ice, to the modern ice house world with the current bipolar ice sheets. Further, we aim to build on some preliminary evidence that diatoms are flourishing with global warming and find out whether diatom productivity could act as a negative feedback on anthropogenic emissions of carbon dioxide. As glaciers retreat around Antarctica and the meltwater flux increases into this highly productive coastal zone, there is the potential for increased input of nutrients and also enhanced stability of the water column, each of which can lead to enhanced diatom productivity. We shall construct a record of diatom productivity, again using d30Si, over the last 500 years in rapidly accumulating sediments of the Antarctic Peninsula. By targeting the last 500 years, our analyses will capture the last glacial advance and recovery from the Little Ice Age period (ending 1850) of the Holocene and allow us to test whether diatoms consistently increase productivity as glaciers retreat, and assess whether the diatom response to the anthropogenically forced glacial retreat is unprecedented on this timescale.