Recent Shift in the Warming of the Southern Oceans Modulated by Decadal Climate Variability

• Published in: Geophysical research letters Vol. 48; no. 3
• Main Authors: Wang, Lina, Lyu, Kewei, Zhuang, Wei, Zhang, Weiwei, Makarim, Salvienty, Yan, Xiao‐Hai
• Format: Journal Article
• Language: English
• Published: 16.02.2021
• Subjects: decadal variability; isopycnal heave; ocean heat content; Southern Ocean; spice; water mass
• ISSN: 0094-8276; 1944-8007
• DOI: 10.1029/2020GL090889

It has been reported that the Southern Hemisphere oceans experienced rapid warming during the decade‐long global surface warming slowdown (2003–2012) and the earlier period of the Argo record (2006–2013). In this study, we analyze updated observations to show that this rapid warming has slowed down, leading to less contribution of the Southern Hemisphere oceans to the global ocean heat storage (∼65% over the available Argo period 2006–2019). Two warming hotspot regions, the southeast Indian Ocean and South Pacific Ocean, have experienced cooling over 2013–2019. This decadal shift is related to variations in the Southern Annular Mode and Interdecadal Pacific Oscillation. The isopycnal deepening (shoaling) forced by changing winds dominated the regional ocean temperature changes over the earlier warming (later cooling) period. Our finding demonstrates how decadal variability modulates long‐term climate change and provides important observational information for the ongoing calibration of decadal prediction systems. Plain Language Summary The global ocean has been warming up, as it absorbs most of the extra heat in the Earth system due to anthropogenic climate change. Regional patterns and magnitudes of ocean warming vary with time due to the natural fluctuations of the coupled air‐sea system. Since 2006, the international Argo program has been providing continuous real‐time ocean observations in the upper 2,000 m from a near‐global array of autonomous profiling floats. Previous studies based on the earlier Argo record (2006–2013) have shown rapid warming in the Southern Hemisphere Oceans and most of the global ocean heat storage occurred in the Southern Hemisphere. However, updated observations show that this rapid warming has slowed down and was even changed to cooling in certain regions since 2013. This shift is mainly driven by changing winds through the downwelling of the upper‐layer warmer waters over the earlier period and the upward pumping of subsurface cooler waters over the later period. Overall, the findings of this study highlight the importance of maintaining the current ocean observing system in order to obtain extended and reliable ocean records, which are necessary for revealing the long‐term climate change signals of anthropogenic warming. Key Points The rapid warming in the Southern Hemisphere extratropical ocean has slowed down since around 2013 The observed shift is related to decadal variations in the Southern Annular Mode and Interdecadal Pacific Oscillation The regional ocean temperature changes are primarily induced by the vertical heave of isopycnals in response to changing winds