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- Database used
- Download the Atlas (.mat) of salinity (~700Mo) , temperature (~700Mo) , sigma-0 (~600Mo)
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The vertical structure of the Southern Ocean is determined from the combination of two distinct datasets: the Argo database and the WOCE Southern Ocean Data Base (SODB from Orsi and Withworth 2005 database). The Argo international program has seeded all of the world's oceans since 1999 and is particularly important in the Southern Ocean which is historically poorly sampled. As of 2008, this database includes about 100,000 Southern Ocean profiles and continually increases (see here).

These data were collected and made freely available by the International Argo Project and the national programs that contribute to it. We only use profiles which have passed the Argo real-time quality control, containing information on their position, date, temperature (T) and salinity (S) profiles. Most Argo profiles sample T and S from the surface to 2000m depth every 10 days.

The SODB consists of about 93,000 hydrographic (bottle and CTD) stations south of 25 S. The primary source is the World Ocean Atlas 98 (WOA98) and its successor, World Ocean Database 2001 (WOD01), which have been augmented with the World Ocean Circulation Experiment (WOCE) observations and also with stations coming directly from investigators. Each station was individually quality controlled by comparison to nearby WOCE stations. This work of collection and quality control have been performed and made freely available ( Orsi and Whitworth, 2005).

The Argo project contributes about half of the total number of Southern Ocean profiles, and it provides very important sampling. In fact, the two datasets are complementary in space and time. The first years of ARGO sampling provides more profiles in the center of ocean basins, and during austral winter and spring, than decades of historical data (see here).

Our first goal was to establish the long term monthly 3-dimentional mean of temperature, salinity and potential density (sigma-0) fields. We selected the T-S profiles defined between 10 and 1500 m. This 1500 m level was chosen as the best compromise between the deepest possible level and including a maximum number of data profiles. For deeper levels, Argo don't bring additional information and we refeer to classical Atlas product such as the Southern Ocean Atlas provided by Orsi and Whitworth, 2005.

For the first time, the ship and Argo monthly coverage allows to monthly map T/S database with confidence.

Potential density, in-situ temperature and salinity have been projected on the basis of EOFs calculated as eigenvectors of the covariance matrix of the vertical profiles (e.g. Mercier et al, 1993; Paillet and Mercier, 1997; Jamous, 1991; Sultan et al., 2007). This method allow to conserve most of the vertical variance, while filtering out small-scale features and providing vertically consistent fields. As we want to resolve the surface seasonal cycle and keep as much month to month consistency as possible for the interior structure, we first compute the inerior structure with every profiles. Then for each month, before projection, every profiles is fitted to the deep climatological stucture.

The horizontal EOF coefficients have been interpolated onto a half degree regular grid spanning the Southern Ocean from 70 S to 25 S following a 2-D loess fitting method (Ridgway et al., 2002). For each month, we used the 4 first modes to reconstruct the potential density, salinity, temperature fields, each fields being then reconstruct with more than 99.7 % of the total variance.



Examples:

1) Density field at 500m in Winter

2) Vertical structure of the Density field between 110 and 140 E (South of Australia) in Summer

3) Vertical structure of the Density field between 110 and 140 E (South of Australia) in Winter