Atmospheric and Ocean CO₂ Measurements in the South Indian Ocean Made by Two Uncrewed Surface Vehicles in 2022 and 2023

Abstract. During the second half of 2022 and the first several months on 2023, a pair of Uncrewed Surface Vehicles (USVs) collected high-resolution (~5-km sampling) measurements of ocean and atmosphere pCO₂, air temperature and humidity, wind, ocean skin temperature, sea surface temperature, salinity, ocean color (Chlorophyll α), dissolved oxygen, and ocean current velocity between roughly 13.5° E and 82° E and between the Subtropical Front (STF) and the Subantarctic Front (SAF). The mission track spanned from the Agulhas Return Current south of South Africa to the northern boundary of the Antarctic Circumpolar Current downstream of the Kerguelen Plateau. The primary goal of the mission was to collect data within cyclonic and anticyclonic eddies to quantify CO₂ fluxes to better understand physical processes (upwelling and downwelling) that that can contribute to carbon cycling in addition to the biological pump. In this paper, we present an overview of the mission, details on the data collected, and a preliminary look at calculated surface pCO₂, separated into cyclonic/anti-cyclonic/no-eddy conditions.