Robot Measures Air-Sea Carbon Dioxide Exchange in Southern Ocean

By Janet Sprintall

Unique air and ocean surface observations of the Southern Ocean from a 22,000 km, 196-day circumnavigation around Antarctica by an Uncrewed Surface Vehicle


Flux of carbon dioxide determined from the USV measurements during the 196-day circumnavigation in the Southern Ocean (some dates are indicated by an *). Blue colors (negative) indicate carbon flux into the ocean; red colors (positive) indicate outgassing. Black lines indicate the mean position of the major oceanic zones within the Southern Ocean that are separated by sharp frontal gradients in temperature and salinity. Credit: Sutton et al. [2021], Figure 2

The Southern Ocean is a notoriously difficult environment in which to make oceanic measurements. The wind is fierce, the waves are high, and the winter is long. This makes it especially challenging for obtaining measurements at the air-sea interface such as needed for estimating the carbon dioxide (CO2) exchange between the atmosphere and the ocean. Yet, the Southern Ocean is known to play an enormous role in the uptake of both carbon and heat from the atmosphere and so is of importance to the global climate system.

Sutton et al. [2021] report on new measurements needed to estimate the air-sea CO2 flux obtained from an Uncrewed Surface Vehicle (USV) that circumnavigated the Antarctic continent. The hourly measurements showed regional variations in the CO2 flux related to the different oceanic frontal zones that characterize the Southern Ocean (see figure above).

The fine-scale temporal and spatial variability resolved by the USV data were used to assess potential biases in float and ship-based CO2 flux estimates in the Southern Ocean that had somewhat conflicting views of Southern Ocean CO2 flux. The authors suggest that the discrepancy was likely due to regional and interannual variations in the measurement periods.

They call for an integrated multi-platform approach to obtaining better coverage of the CO2 flux consisting of air-sea measurements from USVs, water column measurements from floats along with ship-based measurements to fill observational gaps so as to better understand measurement uncertainties and variability in the Southern Ocean.

This article appeared on the Eos website at https://eos.org/editor-highlights/robot-measures-air-sea-carbon-dioxide-exchange-in-southern-ocean