Towards an intensified summer CO2 sink behaviour in the Southern Ocean coastal regions. (April 2020)

• Record Type: Journal Article
• Authors: Monteiro, Thiago; Kerr, Rodrigo; Orselli, Iole B.M.; Lencina-Avila, Jannine M.
• Is Part Of: Progress in oceanography. Volume 183(2020)
• Publication Date: 2020-04
• Subjects: Carbon cycle -- Carbonate system -- Antarctica -- Biogeochemistry -- Austral summer; Oceanography -- Periodicals; 551.4605
• DOI: 10.1016/j.pocean.2020.102267
• Languages: English
• ISSNs: 0079-6611

Abstract

Highlights: We analysed the CO2 system in an important region of the Southern Ocean. The Gerlache Strait acts as a stronger CO2 sink than nearby open ocean areas during the austral summer. We identified both strong and near-equilibrium sink scenarios for FCO2 from 1999 to 2017. The pattern of variability of FCO2 has changed since 2012 to a higher frequency of years with a strong CO2 sink . Abstract: The Southern Ocean is a globally important carbon sink region. However, the austral coastal zones are usually not considered in global estimations due to their general undersampling and large regional dynamics. Thus, estimations of carbon uptake in the Southern Ocean may differ considerably from current values, i.e., without accounting for coastal regions. Here, we conducted a case study in the Gerlache Strait, an ecologically important Antarctic coastal zone. We show that the net sea–air CO2 flux (FCO2 ) in the strait may reach the same or greater magnitudes than those in large open sea regions around Antarctica during summer, despite having a much smaller area. A large mean FCO2 of –31 ± 19 mmol m −2 d –1 was observed in the strong CO2 sink years (i.e., FCO2 < –12 mmol m −2 d –1 ), in contrast to –1 ± 7 mmol m −2 d –1 in CO2 near-equilibrium conditions (i.e., CO2 sea–air difference ≈ 0). This variability is mainly modulated by phytoplankton activity and likely upwelling processes. We also identified two cycles of variability with 2-year and 4-year periodicities from 1999 to 2017. The 2-year periodicity becomes stronger after 2012, intensifying the strong CO2 sink scenario in the Gerlache Strait. Our findings reinforce the importance of polar coastal zones as CO2 sinks during the austral summer and the need to broaden our understanding of the role of these regions at other time scales.