Long-term temperature trends in Antarctic water masses across the New Zealand–Antarctica chokepoint

A 29-year time series of summer Expendable Bathythermographs (XBT) data collected along the New Zealand-Antarctica 'chokepoint' of the Antarctic Circumpolar Current (ACC) was used to analyse the temperature variability of the surface and intermediate layers of the Southern Ocean (SO) from 1994 to 2023. Our findings confirm previous studies, showing an overall warming of the SO over the past 30 years and that the northernmost portion of the ACC exhibits significant warming, while areas south of the Polar Front experience no significant temperature trends.
Additionally, as different masses across the Antarctic Circumpolar Current can be representative of different regions of the SO on a variety of spatial and temporal scales, we focused on the estimation of the temperature trend associated. Our analysis reveals strong warming trends of approximately 0.27°C/decade and 0.13°C/decade respectively for Sub Antarctic Mode Water - SAMW and Antarctic Intermediate Water - AAIW over the study period, while Antarctic Surface Water - AASW and Circumpolar Deep Water - CDW show negligible and/or not significant trends.