Latitudinal Distribution of Atmospheric Radiocarbon in the New Zealand Sector of the Southern Ocean Driven by Ocean Upwelling

Abstract The Southern Ocean is a key anthropogenic carbon dioxide (CO 2 ) sink, yet the processes governing the rate of uptake remain only partly understood. We use observations of radiocarbon (Δ 14 C) in atmospheric CO 2 from Southern Ocean shipboard transects to develop latitudinal gradients of Δ 14 C in the surface atmosphere. We present eight years of austral summer observations (2016–2023) from ships of opportunity traveling between New Zealand and Antarctica, along with time series measurements from Baring Head New Zealand, Macquarie Island Australia and Arrival Heights Antarctica. We observe lower Δ 14 C in the 50°S to 70°S latitude band, consistent with upwelling of 14 C‐depleted deep waters in this region. We then combine ocean model simulations of CO 2 and 14 C with atmospheric dispersion model simulations to predict surface atmosphere Δ 14 C and compare with the observations. Our model simulations capture the large scale observed spatial patterns with considerable accuracy. However, the model simulation somewhat underestimates the magnitude of the observed atmospheric Δ 14 C gradient, particularly between 50°S and 60°S. When we artificially increase the strength of the strongest winds over the Southern Ocean in the ocean model, we find an improved match with the Δ 14 C observations, demonstrating that Δ 14 C observations with dense spatial resolution across the Southern Ocean can be useful for testing ocean model and CO 2 exchange parameters.