Inconsistency between ship- and Argo float-based pCO2 at the intense upwelling region of the Drake Passage, Southern Ocean

• Published in: Frontiers in Marine Science
• Main Authors: Wu, Yingxu, Qi, Di
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Frontiers Media SA 2022
• Subjects: Ocean Engineering; Water Science and Technology; Aquatic Science; Global and Planetary Change; Oceanography; Antarctic; Drake Passage; Southern Ocean; The Antarctic; Antarc*
• Online Access: http://dx.doi.org/10.3389/fmars.2022.1002398; https://www.frontiersin.org/articles/10.3389/fmars.2022.1002398/full

The Southern Ocean absorbs a quarter of anthropogenic carbon dioxide (CO 2 ) from the atmosphere to modulate the climate system. However, less attention has been paid to the CO 2 outgassing phenomenon at the Antarctic Circumpolar Current (ACC) region of the Southern Ocean due to strong upwelling. Recent studies using autonomous biogeochemical-Argo float revealed a greater winter CO 2 outgassing than previously estimated at ACC zone of the Southern Ocean, which, however, remains controversial and urgently needs to be validated. Here we take the Drake Passage as a case study to present new insights into the Southern Ocean carbon cycle and examine the validity of float-based CO 2 outgassing. Upon integrating the ship-based data over the past two decades, we investigate the spatiotemporal variability of sea surface CO 2 partial pressure ( p CO 2 ) in Drake Passage. We show that Drake Passage is acting as a year-round weak CO 2 sink, although some CO 2 uptake is counteracted by winter CO 2 outgassing. The float-based p CO 2 values are overall higher than ship-based values in winter, by 6 to 20 µatm (averaged 14 µatm) at the most intensive upwelling region. We then develop a surface carbon balance calculation (considering mixing between surface, subsurface, and upwelled waters) to estimate the potential of surface p CO 2 increase due to upwelling, and we find that upwelling of CO 2 -rich subsurface waters in Drake Passage cannot support an excess Δ p CO 2 of 14 µatm as suggested by float detections. We further compare our results to previous study and find that, although we used same datasets and obtained comparable results, the way to conclude the bias in float-based p CO 2 would cause significant difference: an uncertainty of ±2.7% (i.e., ± 11 µatm) in float-based p CO 2 estimated by other study seems acceptable, however, it is five times larger than the typical ship-based p CO 2 uncertainty ( ± 2 µatm), and would cause ~180% bias in CO 2 flux estimates. Going forward, there is special need for caution when ...