Anthropogenic Carbon in the Arctic Ocean: Perspectives From Different Transient Tracers

Abstract

In this study we investigated the physical characteristics of the Atlantic layer in the Arctic Ocean (AO) and its role in the distribution and storage of anthropogenic carbon (Cant). The novelty of this work is to use the Transit Time Distribution method (TTD) with the radionuclides 129I and 236U and its comparison to the commonly applied gas tracers, CFC‐12 and SF6. Overall, our examination of two distinct tracer pairs, along with the novel TTD method in comparison to a classical approach, revealed a notable agreement, highlighting the robustness of these Cant estimates. The TTD analysis based on radionuclides showed that whereas the Eurasian Basin has shorter transit times and is dominated by strong mixing conditions, the Amerasian Basin is characterized by longer transit times and a strong advective flow. Overall, the Cant concentrations obtained from radionuclides confirm that the distribution in the AO follows its circulation patterns, with higher concentrations in the Eurasian Basin (∼50 μmol kg−1) compared to the Amerasian one (∼36–42 μmol kg−1). An estimated partial inventory of 0.85 ± 0.17 and 1.0 ± 0.03 Pg C was assessed for 2015 from the novel application of TTD with radionuclides and gas tracers, respectively. Finally, we identified the saturation of gas tracers as a larger source of uncertainty for Cant estimation compared to the uncertainty associated to different radionuclides' input functions, thus remarking the importance of including non‐saturation dependent tracers, such as radionuclides, as an additional tool to support Cant estimates in the AO.

Temporal Variability of Ventilation in the Eurasian Arctic Ocean

“…Notably, the area close to the Lomonosov Ridge does not follow this trend, likely due to the influence of the AOBC. This current has a circulation time of 9-12 years from the Fram Strait to the North Pole (Karcher et al, 2011;Raimondi et al, 2023;Smith et al, 2011) and therefore rejuvenates water masses in this area quicker than the observed multidecadal change. This suggests that the multidecadal variability in ventilation surpasses the time it takes for the AW to reach the North Pole.…”

“…Additionally, for the measurements in the AO, we used a saturation determined in the Greenland Sea rather than directly from the sampling area. Uncertainties in the saturation pose a potentially significant error in tracer applications (Raimondi et al, 2023;Shao et al, 2013). Nevertheless, the saturation typically varies over time at higher latitudes due to fluctuations in the winter mixed layer depth and the atmospheric growth rate of the tracers (Jeansson et al, 2010;Tanhua et al, 2008).…”