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.
Monitoring the Antarctic sea-ice is essential for improving our knowledge of the Southern Ocean. We used satellite sea-ice concentration data for the 2002-2020 period to retrieve the sea-ice extent (SIE) and analyze its variability in the Pacific sector of the Southern Ocean. Results provide observational evidence of the recurring formation of a sea-ice protrusion that extends to 60° S at 150° W during the winter season. These activities are carried on in the framework of the ACCESS and SWIMMING projects of the PNRA.Our findings show that the northward deflection of the southern Antarctic Circumpolar Current front is driven by the Pacific Antarctic Ridge (PAR) and is associated with the enhanced sea-ice advance. The PAR also constrains anticyclonic and cyclonic eddy trajectories, limiting their interaction with the sea-ice edge. These factors, within the 160° W - 135° W sector, determine an average SIE increase of 61,000 km2 and 46,293 km2 per year more than the upstream and downstream areas, respectively.
Abstract Monitoring the Antarctic sea‐ice is essential for improving our knowledge of the Southern Ocean. We used satellite sea‐ice concentration data for the 2002–2020 period to retrieve the sea‐ice extent (SIE) and analyze its variability in the Pacific sector of the Southern Ocean. Results provide observational evidence of the recurring formation of a sea‐ice protrusion that extends to 60°S at 150°W during the winter season. Furthermore, we discuss how the Pacific‐Antarctic Ridge (PAR) influences this phenomenon. Our findings show that the northward deflection of the southern Antarctic Circumpolar Current front is driven by the PAR and is associated with the enhanced sea‐ice advance. The PAR also constrains eddy trajectories, limiting their interaction with the sea‐ice edge. These factors, within the 160°W–135°W sector, cause an average SIE increase of 61,000 km 2 and 46,293 km 2 per year more than the upstream and downstream areas, respectively.
Abstract. This study presents the water column temperature data collected during several cruises on board the Italica, Araon and Laura Bassi research vessels, in the framework of the Climatic Long-term Interaction for the Mass balance in Antarctica (CLIMA), Southern Ocean Chokepoints Italian Contribution (SOChIC), and Marine Observatory of the Ross Sea (MORSea) projects, funded by the Italian National Antarctic Research Program (PNRA). Data were collected between New Zealand and the Ross Sea during the austral summers from 1994/1995 to 2023/2024. Across this chokepoint of the Antarctic Circumpolar Current, XBT Sippican T7 probes were launched with a regular 20 km sampling, providing temperature profiles with a vertical resolution of 65 cm and a maximum nominal depth of 760 m. All temperature profiles underwent a rigorous quality control, including a general malfunctioning verification, the removal of spikes, the consistency check of adjacent profiles, the comparison to regional oceanographic features and satellite altimetry observations, and a final visual check by operator. Data quality checks led us to discard about 12 % of acquired XBT measurements. This dataset contributes to the improvement of our understanding of Southern Ocean features, being highly valuable for studies focusing on climate variability, especially across the Antarctic Circumpolar Current and its fronts. Furthermore, we expect that the collected XBT data will serve as a useful tool for the calibration and validation of recent satellite observations and for the improvement of Southern Ocean oceanographic simulations.
The Subantarctic region of New Zealand is marked by a unique and complex bathymetry that includes an ocean ridge and a substantial submarine plateau known as the Campbell Plateau. This plateau is located near the Pacific sector of the Southern Ocean, and plays a vital role in the export of heat, salt, and nutrients into the lower thermocline, primarily through the formation of mode waters. In the present study, Argo floats data from 2003 to 2023 are used to identify the main water masses along the eastern margin of the Campbell Plateau. This region, located at the boundary between subtropical and subantarctic fronts, is characterized by the formation of Sub-Antarctic Mode Water (SAMW) and Antarctic Intermediate Water (AAIW), which make an important contribution to the broader oceanic circulation patterns. First results reveal the presence of eight distinct water masses in the study region and emphasize their peculiar seasonal variability. A decadal analysis describes colder waters in the period 2003-2013 compared to 2014-2023, while significant changes in salinity are observed in 2017-2018. Water mass identification, depicted through Temperature-Salinity plots, is consistent with existing literature, but can also provide new insights on the interaction between subantarctic and subtropical waters. This research contributes to describe the ocean dynamic of Subantarctic New Zealand. The use of Argo float data provides an unprecedented level of detail in examining the spatial and temporal resolution of an area located between two different current systems, whose changes potentially influence the global and Southern Ocean circulation patterns, with consequent implication on the climate.
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