Deep-sea ecosystem functioning in a changing climate: consequences of changing sea-ice cover for Arctic benthic ecosystems

深海沉积物构成了全球碳(C)循环的主要储存库，碳埋藏在这些沉积物中构成了在地质时间尺度上固定碳的主要过程。从表层水域下沉的有机物质是深海生物的主要食物来源，它们的摄食和觅食活动控制着这些有机碳是循环进入水柱还是埋藏在沉积物中(碳固存)。深海底栖动物的食物供应依赖于真光层浮游植物的生长，群落组成、输出通量或水华事件时间的变化将直接影响海底POC的供应和周转，进而影响C的固存。但是，由于深海海底的偏远，我们对深海有机质特征、底栖生物多样性和深海POC早期成岩作用之间的相互作用的了解非常有限，因此我们无法可靠地评估或预测气候变化对这一重要生态系统服务的影响。在POC通量特征自然波动强烈和/或远洋环境气候变化明显的地区详细研究海底C循环，似乎是一种有希望获得关于气候变化对深海沉积物中C循环或埋藏的潜在影响的迫切需要的信息，同时提高我们对POM特征与底栖群落之间的相互作用及其在POM早期成岩作用中的作用的了解。海冰是极地海洋生态系统的一个独特特征，而微小的温差可以对这种海冰的范围和厚度产生很大影响，这使得极地海洋生态系统对气候变化特别敏感。事实上，北极和南极都报告了与海冰消退有关的重大生态系统变化。冰藻占北冰洋深海陆架冰盖区域初级生产量(PP)的25%，在北极盆地甚至更多，因此很可能成为深海生物食物的组成部分。此外，冰藻水华在时间和分布上与浮游植物有很大不同，因此在其他食物稀缺的时候为高等生物提供食物。冰藻还含有非常高浓度的所谓“微量营养素”，这是许多海洋生物无法自行合成的基本物质。因此，海冰的消退和随后作为食物来源的冰藻的丧失很可能对深海食物网和生态系统产生重大影响。然而，尽管有很多猜测，但关于冰藻作为底栖生物食物的重要性的信息很少。因此，我们建议通过两种不同的方法来调查气候导致的冰藻丧失(以及可能转向浮游植物)作为北极深海食物网的食物来源的潜在后果：a.冰藻和浮游植物在其整体碳同位素特征以及某些必需脂肪酸的碳同位素特征方面存在差异。因此，我们将利用这种同位素特征的差异来追踪底栖动物对冰藻和浮游植物生物量的吸收。B.一系列现场示踪实验：我们将用示踪剂标记冰藻和浮游藻类，将它们添加到从海底获得的沉积物岩心(所谓的“中间生态系统”)，然后跟踪它们是否以及如何被深海生物代谢。这项工作将与魁北克大学的菲利普·阿查鲍特教授合作，在圣劳伦斯湾和波弗特海的实地活动期间，在加拿大北极地区开展。

Deep-sea sediments form a major reservoir in the global carbon (C) cycle and C burial in these sediments constitutes a major process that sequesters C on geological time scales. Organic matter sinking from surface waters is the main food source for deep-sea organisms, and their feeding and foraging activities control whether this organic C is recycled into the water column or buried in sediments ('carbon sequestration'). Food supply to the deep-sea benthos is reliant on phytoplankton growth in the euphotic zone, and changes in community composition, export flux or timing of bloom events will directly affect the supply to and turnover of POC at the seafloor and, subsequently, C sequestration.However, due to the remoteness of the deep-sea floor, our knowledge of the interplay between organic matter characteristics, benthic biodiversity and the early diagenesis of POC in the deep sea is very limited, and we can therefore neither reliably assess nor predict the consequences of climate change for this important ecosystem service. The detailed study of benthic C cycling in areas of strong natural fluctuations in POC flux characteristics, and/or pronounced climate-induced change in the pelagic environment, seems a promising way to gain urgently needed information on the potential impact of climate change on the cycling or burial of C in deep-sea sediments, while at the same time improving our understanding of the interplay between POM characteristics and benthic communities, and its function in the early diagenesis of POM.Sea ice is a unique feature of polar marine ecosystems and the fact that small temperature differences can have large effects on the extent and thickness of this sea ice makes polar marine ecosystems particularly sensitive to climate change. Indeed, major ecosystem shifts related to retreating sea ice have been reported from both the Arctic and Antarctic. Ice algae account for up to 25 % of the primary production (PP) in ice covered areas on the deep Arctic shelf, and even more in the Arctic Basin, and thus are likely to form an integral part of the diet of deep-sea organisms. Moreover, ice algal blooms differ considerably from phytoplankton in terms of timing and distribution, thus providing higher organisms with food when and where other food is scarce. Ice algae also contain very high concentrations of so-called "micronutrients", essential substances that many marine organisms can not synthesize themselves. The retreat of sea ice and subsequent loss of ice algae as food source is thus likely to significantly impact on deep-sea food webs and ecosystems. However, despite much speculation, very little information is available on the importance of ice algae as food for benthic organisms.We therefore propose to investigate the potential consequences of a climate-induced loss of ice algae (and possible shift to phytoplankton) as a food source for Arctic deep-sea food webs via two different approaches: A. Ice algae and phytoplankton differ in their bulk Carbon isotope signatures, as well as in the Carbon isotope signatures of certain essential fatty acids. We will thus use this difference in isotopic signature to trace the uptake of ice algal and phytoplankton biomass by benthic fauna. B. A series of in situ tracer experiments: we will label both ice algae and planktic algae with a tracer, add them to sediment cores obtained from the seafloor (so-called 'mesocosms'), and subsequently follow whether and how they are metabolized by the deep-sea organisms. This work will be carried out in the Canadian Arctic in collaboration with Professor Philippe Archabault from the University of Quebec, during field campaigns in the Gulf of St. Lawrence and the Beaufort Sea.