R. Steinfeldt et al.: Anthropogenic carbon in the Atlantic 3847 Figure 4. (a–d) Zonal mean sections showing the fraction f of young Cant-bearing water. (c–d) Difference in zonal mean Cant concentrations between the value calculated from a variable 1/0 ratio and no dilution and a variable 1/0 ratio with dilution. The Cant fields are based on tracer data from the whole period (1982–2021), and the reference year is 2020. (e–f) Zonal mean sections of 1tCanomant for a variable 1/0 ratio (Cant calculated for 2020 with data in 2020 minus Cant calculated for 2020 based on tracer data in 1990, i.e., Cant2020 ? Cant1990?2020). Contour lines are shown as in Fig. 2. For details, see the text. Note the uneven breaks in the color scale. Boundary Current (DWBC) of the tropical Atlantic and in- vestigating the NADW therein as a mixture of young and old water contributions. We apply the same principle here, but in contrast to the previous study, we extend this approach to the entire Atlantic Ocean. G = f ·Gyoung + (1? f ) ·Gold (3) Gold is assumed to not contain CFCs and also no Cant; thus we do not need to consider it here. The additional parameter f describes the fraction of younger water and 1?f the dilution with old water. Eq. (1) then becomes C (x, tref) = ?? 0 C0 (tref? ?) · f ·Gyoung (x, tref,? ) d?. (4) The dilution of younger water with an old component can be interpreted as follows: in the North Atlantic, the younger water can be interpreted as NADW and the old water as ad- https://doi.org/10.5194/bg-21-3839-2024 Biogeosciences, 21, 3839–3867, 2024