The Arctic Ocean - Ventilation Timescales, Anthropogenic Carbon and Variability in a Changing Environment

在北极，气候变化最为明显。例如，北冰洋的海冰覆盖面积急剧减少，这反过来又影响到该区域的热平衡以及海洋和大气的环流。深水的形成包括溶解气体进入海洋内部的运输，称为通风。相应的人为碳吸收量在北冰洋非常大，是温室气体排放的重要缓冲区。它的知识对于可靠的气候情景至关重要。通风时间尺度可以通过测量某些示踪剂来确定，这些示踪剂通过其与时间相关的输入函数或放射性衰变来携带时间信息。然而，传统的示踪剂，如CFC-12和六氟化硫（SF6），以及一系列现代的，所谓的"美杜莎示踪剂"在北冰洋的最深处是检测不到的。新的原子阱痕量分析（ATTA）方法现在可以测量海水中的放射性同位素39Ar，从而准确地覆盖过去无法精确分辨的年龄范围。结合上述示踪剂以及放射性碳（14 C），年龄分布函数和通风时间尺度，因此可以确定整个水柱。这一方法得到了稀有气体测量的补充，以确定地表的饱和度异常以及长寿命的人为放射性同位素236 U和129 I，作为大西洋水的标志，并使北大西洋和北冰洋之间的交换研究成为可能。在这个项目中，我们将在中部的ODEN破冰船上进行考察期间采集和测量所有提到的示踪剂样品。2021年的北冰洋这些数据用于确定过境时间分布的模型参数，这些参数反过来又为计算人为碳的水柱清单提供了基础。研究结果将与海洋地球化学方法进行比较，并用于估算海洋酸化率。补充示踪剂数据提供了关于北大西洋区域环流和海洋表面过程的见解。为了分析气候效应可能导致的年代际变化，我们还将分析来自北极的历史示踪剂数据。此外，通过结合不同的创新方法，我们期望获得重要的方法学见解以及海洋模型的基于数据的边界条件。因此，该项目的成果将为更好地了解北冰洋的环流和通风、海洋的碳吸收能力以及北极和全球气候变化的后果作出广泛贡献。

In the Arctic, climate change is most apparent. This shows for example in the strong decrease of the Arctic Ocean’s sea ice cover, which in turn influences the region’s heat balance and the circulation in the ocean and the atmosphere. The formation of deep water encompasses the transport of dissolved gases into the ocean’s interior, known as ventilation. The corresponding uptake of anthropogenic carbon, which is disproportionally large in the Arctic Ocean, acts as an important buffer for greenhouse gas emissions. Its knowledge is crucial for reliable climate scenarios.The ventilation timescales can be determined by measurements of certain tracers, which carry time information by their time dependent input function or radioactive decay. However, classical tracers such as CFC-12 and sulfurhexafluoride (SF6) as well as a series of modern, so called “Medusa Tracers” are not detectable in the deepest parts of the Arctic Ocean. The new Atom Trap Trace Analysis (ATTA) method now allows for measurements of the radioisotope 39Ar in seawater and thus for coverage of exactly the age range that could not be precisely resolved in the past. In combination with the mentioned tracers as well as radiocarbon (14C), age distribution functions and ventilation timescales can thus be determined for the entire water column. This approach is complemented by measurements of noble gases to determine saturation anomalies at the surface as well as the long-lived anthropogenic radioisotopes 236U und 129I, which act as markers of Atlantic water and enable the study of the exchange between the North Atlantic and the Arctic Ocean.In this project we will take and measure samples for all mentioned tracers during an expedition on the icebreaker ODEN in the Central Arctic Ocean in 2021. The data serve to determine model parameters of transit time distributions, which in turn provide the basis for the calculation of the water column inventory of anthropogenic carbon. The results will be compared to biogeochemical approaches and used to estimate ocean acidification rates. The complementing tracer data provide insights about the circulation in the North Atlantic realm and about processes at the ocean surface. To analyze the decadal changes expected to result from climatic effects, we will additionally analyse historic tracer data from the Arctic.Furthermore, from the combination of different innovative methods we expect important methodical insights as well as data-based boundary conditions for ocean models. The results of this project will thus make extensive contributions to an improved understanding of the circulation and ventilation of the Arctic Ocean, the carbon uptake capacity of the oceans and the consequences of the changing Arctic and global climate.