Abstract
Abstract. The inflow of Atlantic Water to the Arctic Ocean is a crucial determinant for the future trajectory of this ocean basin with regard to warming, loss of sea ice, and ocean acidification. Yet many details of the fate and circulation of these waters within the Arctic remain unclear. Here, we use the two long-lived anthropogenic radionuclides 129I and 236U together with two age models to constrain the pathways and circulation times of Atlantic Water in the surface (10–35 m depth) and in the mid-depth Atlantic layer (250–800 m depth). We thereby benefit from the unique time-dependent tagging of Atlantic Water by these two isotopes. In the surface layer, a binary mixing model yields tracer ages of Atlantic Water between 9–16 years in the Amundsen Basin, 12–17 years in the Fram Strait (East Greenland Current), and up to 20 years in the Canada Basin, reflecting the pathways of Atlantic Water through the Arctic and their exiting through the Fram Strait. In the mid-depth Atlantic layer (250–800 m), the transit time distribution (TTD) model yields mean ages in the central Arctic ranging between 15 and 55 years, while the mode ages representing the most probable ages of the TTD range between 3 and 30 years. The estimated mean ages are overall in good agreement with previous studies using artificial radionuclides or ventilation tracers. Although we find the overall flow to be dominated by advection, the shift in the mode age towards a younger age compared to the mean age also reflects the presence of a substantial amount of lateral mixing. For applications interested in how fast signals are transported into the Arctic's interior, the mode age appears to be a suitable measure. The short mode ages obtained in this study suggest that changes in the properties of Atlantic Water will quickly spread through the Arctic Ocean and can lead to relatively rapid changes throughout the upper water column in future years.
Highlights
1.1 The role of Atlantic Water in the Arctic OceanThe Arctic sea-ice extent in 2019 was one of the lowest in the satellite record but in line with the long-term trend of declining ice cover (e.g., Meredith et al, 2021)
In addition to the main contribution coming from the solar heating of the surface mixed layer in summer (Carmack et al, 2015), recent work has highlighted the contribution of the inflow of warm Atlantic Water (AW) through the Fram Strait to the observed sea-ice decrease (Polyakov et al, 2005, 2017; Årthun et al, 2019)
The compilation of 129I and 236U concentrations presented in this study allows for a synoptic view of these two tracers across the Arctic Ocean and Fram Strait
Summary
1.1 The role of Atlantic Water in the Arctic OceanThe Arctic sea-ice extent in 2019 was one of the lowest in the satellite record but in line with the long-term trend of declining ice cover (e.g., Meredith et al, 2021). In addition to the main contribution coming from the solar heating of the surface mixed layer in summer (Carmack et al, 2015), recent work has highlighted the contribution of the inflow of warm Atlantic Water (AW) through the Fram Strait to the observed sea-ice decrease (Polyakov et al, 2005, 2017; Årthun et al, 2019). This is especially relevant for the Eurasian Basin of the Arctic Ocean, and the process is commonly known as “Atlantification”.
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