Silicon CycLing IN Glaciated environments

极地地区正在经历地球上观测到的最迅速的气候变化：北极和南极一些地区的气温上升速度是全球平均速度的两倍多，极端变暖事件急剧增加，人们担心冰融化对全球系统的影响。海洋生态系统已经对环境变化做出了反应，并放大了环境变化，这对碳埋藏和渔业等重要自然资源产生了重要影响。硅藻是一种重要的微藻，它构成了这些极地生态系统的基础，并为碳从表面流向海底提供了重要的管道。硅藻的微观外壳是由二氧化硅构成的，因此溶解的硅（DSi）是它们生长的关键营养物质。因此，我们需要更好地了解极地环境中的气候敏感过程如何影响近岸、大陆架和开放海洋的硅循环交换，以及它们对区域和全球系统的影响。硅的循环在两极的表现非常不同。越来越多的证据表明，在许多北极地区，DSi到达海洋表面的方式和数量基本上决定了硅藻生长和固定碳的程度。在南极洲周围，营养丰富的近岸大陆架水域与开阔的海洋交换，并通过南极绕极流流入南大洋下游，而南大洋反过来又为全球海洋提供营养。向极地海洋提供DSi这一关键营养物质的来源，特别是冰川风化，以及向地表水提供DSi的物理混合和上涌过程，在未来可能会发生变化，对区域生物生产力和更远的地区产生重大影响。SiCLING将研究北极和南极峡湾冰川沉积物中硅和金属循环之间的联系，从而使我们对峡湾中硅的流动性和生物利用度，高纬度营养平衡以及营养物质流入极地沿海海洋及其他地区的理解发生变化。我们最近的工作表明，冰川是溶解硅（DSi）和活性二氧化硅颗粒（称为ASi）的重要来源。然而，DSi和ASi从冰川峡湾逃逸的过程尚不清楚；这些过程对极地沿海和开放海洋生态系统的DSi供应，以及该系统在未来如何响应和变化具有深远的影响。我们已经证明，在靠近冰川的峡湾内，DSi具有独特的地球化学和同位素指纹——无论我们在北极、南极和像智利巴塔哥尼亚这样的中纬度冰川山区，这种指纹似乎都是一样的。鉴于这一信号的范围和性质，我们认为存在一种重要且普遍存在的机制，控制着DSi进入峡湾，然后进入沿海海洋，作为这种重要营养物质的有效陷阱。我们提出，这种机制并不完全是生物学的，而是与硅和另一种重要的生命元素：铁之间的相互作用有关。冰川风化也会释放出大量的铁，而释放出来的铁能够吸收大量的DSi。这一机制可能是气候敏感的（因为冰川融水的来源和温度/盐度的影响），了解潜在的过程对于预测未来的变化至关重要，特别是在加速极地变暖和陆地冰融化的背景下。SiCLING将是第一个专门关注极地地区动态硅和铁循环之间这些以前被忽视的联系的项目，结合现场和实验室样品的尖端分析以及先进的地球化学模型。

The polar regions are experiencing the most rapid climate change observed on Earth: temperatures are rising in some regions of the Arctic and Antarctic at more than double the global average rate, there has been a dramatic increase in extreme warming events, and there are concerns about the impact of ice melt on global systems. Marine ecosystems are already responding to - and amplifying - environmental change, with important implications for carbon burial and important natural resources such as fisheries. One important type of microalgae, which form the basis of these polar ecosystems and provide an important conduit for carbon flow from the surface to the seafloor, are diatoms. Diatoms build their microscopic shells from silica, and so dissolved silicon (DSi) is a critical nutrient for their growth. As such, we need a better understanding of how climate-sensitive processes within polar environments impact the nearshore, shelf and open ocean exchange of silicon cycling, and their consequences for regional and global systems. The cycling of silicon behaves very differently in the two polar regions. There is increasing evidence that - in many Arctic regions - how and how much DSi reaches the surface ocean essentially sets the degree to which diatoms can grow and fix carbon. Around Antarctica, nutrient-rich nearshore shelf waters exchange with the open ocean and feed downstream via the Antarctic Circumpolar Current into the Southern Ocean, which - in turn - supplies nutrients to the global ocean. The sources of this critical nutrient, DSi, to the polar oceans, especially from glacial weathering, and the physical mixing and upwelling processes that supply DSi to surface waters are likely to change into the future, with significant impacts on regional biological productivity and further afield. SiCLING will investigate links between silicon and metal cycling within glacial sediments in Arctic and Antarctic fjords, resulting in a step-change in our understanding of silicon mobility and bioavailability in fjords, high-latitude nutrient balance, and the flow of nutrients into the polar coastal ocean and beyond. Our recent work has shown that glaciers are a substantial source of both dissolved silicon (DSi) and reactive particles of silica, termed ASi. However, the processes by which DSi and ASi escape glaciated fjords are not understood; these processes have profound implications for the supply of DSi to coastal and open ocean ecosystems in the polar regions, and ultimately how this system will respond and change in the future. We have shown that within fjords, nearer the glaciers, DSi within has a unique geochemical and isotopic fingerprint - and this fingerprint appears to be the same wherever we look: in the Arctic, Antarctic and in mid-latitude glaciated mountain regions like Chilean Patagonia. Given the extent and the nature of this signal, we propose that there is an important and ubiquitous - but yet unknown - mechanism that controls the release of DSi into fjords and then into the coastal ocean, acting as an effective trap of this important nutrient. We propose that this mechanism is not entirely biological, but relates to the interactions between silicon and another important element for life: iron. Iron is also released in large quantities from glacial weathering, and the iron released is capable of mopping up significant quantities of DSi. This mechanism is likely to be climate sensitive (because of the glacial meltwater source and temperature/salinity effects), and understanding the underlying processes will be crucial for predicting future change especially in the context of accelerating polar warming and land-ice melting. SiCLING will be the first project to focus specifically on these previously overlooked links between dynamic silicon and iron cycling in the polar regions, incorporating cutting-edge analysis of field and laboratory samples and advanced geochemical modelling.