Response of the Southern Ocean biological carbon pump to climate-related changes in iron supply

南大洋（SO）在调节海洋碳吸收从而调节地球气候方面发挥着重要作用。假设冰期较高的粉尘沉积减轻了SO中铁的限制，并有助于大气CO2的减少。在SO和现代人工海洋铁肥实验（OIFs）中观察到的自然铁肥事件证实了浮游植物生长对铁添加的积极响应。然而，这种初级生产的增加是否会导致碳出口和储存的增加，以及海洋碳泵对铁供应变化的反应如何受到气候变化的影响，这些都是有争议的。EIFEX（欧洲铁施肥实验，2004年在SO中进行）是唯一一个在施肥水体中检测到碳输出显著增加的OIF。这种增加的出口流量归因于藻华结束时硅藻种形成聚集体和质量下沉。然而，先前的模拟研究未能重现观测到的碳输出变化，这表明需要修改铁供应和利用、颗粒动力学和控制浮游植物华流进化过程的模型参数化。此外，在自然受精地区，硅藻休眠孢子对碳输出做出了重大贡献，迄今为止，全球海洋碳循环模型完全忽略了这一点。拟议的项目将基于EIFEX期间的EIFEX观测和自然铁肥事件，确定SO生物碳泵的关键驱动因素（如浮游植物群落组成、颗粒和营养动态），改进这些关键驱动因素的模型表示，重新评估SO中铁肥对碳封存的影响，并预测海洋碳循环对未来铁供应变化的响应。

The Southern Ocean (SO) plays a fundamental role in regulating the oceanic carbon uptake and thus the Earth's climate. Higher dust deposition during glacial periods was hypothesised to have alleviated iron limitation in the SO and contributed to the drawdown of atmospheric CO2. Observations of natural iron fertilisation events in the SO and modern artificial ocean iron fertilisation experiments (OIFs) confirmed the positive response of phytoplankton growth to iron addition. It is however debatable if such an increase of primary production leads to an increase of carbon export and storage, and how the response of the marine carbon pump to changes in iron supply is affected by climate change. EIFEX (the European Iron Fertilisation Experiment, carried out in 2004 in the SO) is the only OIF during which a significant increase in carbon export in the fertilised waters was detected. This increased export flux was attributed to the formation of aggregates by diatom species and mass sinking during the bloom termination. The previous modelling study however, failed to reproduce the observed changes in carbon export, indicating that the model parameterisations of iron supply and utilisation, particle dynamics and of processes controlling phytoplankton bloom evolution need to be revised. Further, a significant contribution to carbon export in naturally fertilised regions is made by diatom resting spores, which is so far completely ignored in global modelling of the marine carbon cycle. The proposed project will determine the key drivers of the SO biological carbon pump (e.g. phytoplankton community composition, particle and nutrient dynamics) based on EIFEX observations during EIFEX and of natural iron fertilisation events, improve the model representation of these key drivers, reassess the impact of iron fertilisation in the SO on carbon sequestration and predict responses of marine carbon cycle to future changes in iron supply.