DOI: 10.6096/11
title: Vertical sections of in-situ temperature over 25 years in the Southern Ocean

description: Gridded XBT temperature sections from the SURVOSTRAL project  provide a unique multi-decadal observational dataset of temperature across the Southern Ocean from Hobart (Tasmania, 42.9°S, 147.3°E) to Dumont d’Urville (Adelie Land, 66.6°S, 140.0°E), starting in 1992.  Gridded temperature sections are based on XBT temperature profiles collected each year during the summer heating cycle from early spring (Oct/Nov) to autumn (Mar), over the depth range from the surface down to 900 m. 
XBT data were collected aboard the French supply vessel L’Astrolabe, with the support of the French Institut Polaire Emile Victor (IPEV), the LEGOS research laboratory, the CSIRO Marine and Atmospheric Research division. and the National Oceanic and Atmospheric Administration (NOAA). 
This XBT section is part of the SOP (Ships of Opportunity) network and CLIVAR, and is referred to as section IX28 (<a href="https://doi.org/10.18142/172">https://doi.org/10.18142/172</a> ). 
The dataset consists of 25 years (November 1992 to February 2017) of 10238 expendable bathythermograph (XBT) profiles on this section between Hobart, Australia and Dumont d’Urville, Antarctica. Measurements are collected from an average of six transects per year between late October and early March. 
Depending on ice and weather conditions, XBT measurements are sampled every 35km, with a finer 18km sampling across the energetic polar frontal region from 49°S to 54°S. Temperature profiles extend down to 900 meters depth with a vertical resolution of about 0.7 meters. The XBT temperature profile accuracy is +/-0.1°C. XBT profiles have been corrected for temperature and depth biases depending on the probe type. All corrected XBT measurements can be retrieved from the IMOS website (<a href="http://thredds.aodn.org.au/thredds/catalog/IMOS/SOOP/SOOP-XBT/DELAYED/Line_IX28_Dumont-d-Urville-Hobart/catalog.html">http://thredds.aodn.org.au/thredds/catalog/IMOS/SOOP/SOOP-XBT/DELAYED/Line_IX28_Dumont-d-Urville-Hobart/catalog.html</a>).
Individual XBT profiles are then mapped onto a regular meridional-vertical section from North to South, following the mean path of the Astrolabe’s transect, with 0.5° resolution in latitude (increasing to 0.25° in the polar frontal zone from 49-54°S), with 2m depth resolution down to 800 m depth. XBT profiles sampled further than 3° in longitude from the mean path of the Astrolabe are removed from the analysis. 
Different types of gridded products are available : 
1)    Climatological monthly mean temperature sections are calculated for each month during the austral summer ONDJFM period and averaged over 25 years (6 monthly mean temperature sections). 
2)    Austral summer (NDJF) mean temperature sections are constructed for each year from 1993 to 2017, allowing us to track the interannual temperature evolution (25 annual summer mean temperature sections).
3) Temperature values and anomalies measured for each profile of SURVOSTRAL program, gridded on mean path. Temperature anomaly profiles are constructed by subtracting the climatological monthly mean temperature value at each latitude and depth from each XBT profile. For detalis, see Auger et al. 2021.