Pacific modulation of accelerated south Indian Ocean sea level rise during the early 21st Century

Abstract

The south Indian Ocean has shown an unprecedented sea-level rise during the early 21st Century. Sea-level rise in the south Indian Ocean is found to be 37% quicker than the global mean sea-level during 2000–2015. Observational datasets and long-term proxy records identify Pacific origin of the south Indian Ocean sea-level rise. Our results indicate that co-evolution of the cold phase of Pacific decadal oscillation (PDO) and prolonged La Niña-like condition enhances the equatorial Pacific easterlies. Stronger in-phase association of these major Pacific climate modes and equatorial Pacific easterlies enhances the Indonesian throughflow (ITF), transporting fresh and warm water anomalies from western tropical Pacific into the south Indian Ocean. As a result, south Indian Ocean sea-level rise has accelerated more than the global, with 40% contribution from the halosteric sea level primarily through the ITF transport and a secondary from the local processes during 2000–2015. The co-evolution of PDO and the south Indian Ocean sea level is also evident from the long-term proxy records indicating that the association is part of an internal mode of variability modulated on decadal time-scales. The finding from the study cautions that accelerated heat and freshwater intrusion from the western Pacific with the co-evolution of PDO and La Niña-like condition may lead to the accelerated sea-level rise and marine heat waves in the south Indian Ocean imposing threats to the life of coral reefs and marine ecosystems.