Huang, Lei2024-01-242024-01-24https://udspace.udel.edu/handle/19716/33880The South Indian Ocean (SIO) has been characterized as one of the major heat accumulators among the oceanic basins due to its remarkable warming during the Argo period, which are primarily attributed to the enhanced Indonesian Throughflow (ITF) heat transport. Nevertheless, the temperature increase is not evenly distributed in the whole basin but occurred along with several quasi-decadal cooling events in some specific regions of the SIO. First, we found that compared with the remarkable warming in the upper layer of the Southeast Indian Ocean (SEIO) during the recent global surface warming slowdown, the upper layer of the tropical SWIO undergoes a cooling trend during 2005–2011. This cooling trend is jointly forced by latent heat flux and horizontal heat advection associated with the changes in the surface atmosphere circulation. Second, the observational datasets suggest that the intermediate layer of the subtropical SIO displays significant cooling during the period 2010–2016 mainly because of the upward motion of relatively colder water from the deeper ocean. Compared to the decade-long warming in the upper layer of the SIO, which has been studied extensively, our understanding of temperature change in the intermediate layer is relatively limited. This study further reveals a quasi-decadal temperature cycle in the intermediate layer of the subtropical SIO during the Argo period, which is characterized by a shorter warming period during 2004–2009 and subsequent cooling during 2010–2016. Decomposition of temperature changes suggests that this quasi-decadal temperature variability is primarily driven by the heaving component, which is tightly associated with the local wind variability driven by local and remote climate forcings, whereas the spice change largely contributed by the SAM-related water mass transmission from higher latitudes, is of secondary importance. The impact of water mass spread may be more prominent on longer-term thermal variability in the tropical and subtropical regions. In addition to the quasi-decadal signal, the tropical SWIO displays strong multi-decadal variations. It has been reported that the SWIO experienced a sea level fall from the 1960s to the early 2000s. However, based on up-to-date satellite observations, this study reveals a sea level rise of 4.1±0.6 cm/decade in the tropical SWIO during 2002-2020. The mass component increases at a rate of 1.7±0.1 cm/decade, accounting for 41% of the total sea level rise and indicating an essential impact of mass change on sea level variability in the tropical SWIO. 29% of the total sea level rise is attributed to the steric sea level rise of 1.2±0.5 cm/decade in the upper 2000m. The steric sea level rise in the upper 300m can be attributed to wind-driven Ekman pumping and surface heat flux, whereas it is only of secondary importance to the steric sea level change in the upper 2000m. Conversely, thermal expansion below the thermocline (300-2000m), primarily caused by water mass spread from the Southern Ocean, induces a major contribution to the total change in the upper 2000m. Compared to existing studies that have primarily focused on the wind-driven thermal variations above the thermocline to the sea level variability, this study emphasizes the importance of ocean mass and deeper ocean changes in a warming climate.https://doi.org/10.58088/pwzv-te172024-01-22en