FLOAT CONTRIBUTION IN THE SOUTHERN OCEAN OBSERVING SYSTEM

Position of drifters deployed during last campaign. Actual position available at http://nettuno.ogs.trieste.it/jungo/argoitaly/floats.html

Position of floats deployed during last campaign. Actual position available at http://nettuno.ogs.trieste.it/jungo/argoitaly/drifters.html

Research programs over the past 15 years have demonstrated that sustained observations of the SO (Southern Ocean) are feasible. For example, repeated hydrographic sections have been used to quantify the evolving ocean inventory of heat and carbon, to demonstrate that changes are occurring throughout the full depth of the SO, and to provide a platform for a wide suite of interdisciplinary observations. Satellites are providing circumpolar, year-round coverage of physical and biological variables and sea ice properties. Moorings are providing time-series information on velocities and water properties in critical regions. Bottom pressure recorders (often enhanced with inverted echo sounders) are routinely monitoring flows of the major current systems at key choke points like Drake Passage, whilst conventional tide gauges at coastal locations are useful in this context and also for a range of other applications, including long-term sea level variability and change studies.

Classical oceanographic data collected by ships (CTD casts, along track measurements, XBT/XCTD casts, etc…) in the SO are deeply affected by temporal and spatial limitations. Ice cover and sea-weather conditions, limit the sampling at the summer season and in some geographic areas. The development of autonomous profiling floats now allows broad-scale, year-round measurements of the interior of the SO (to 2 km depth) to be made for the first time. The ocean beneath the sea ice, inaccessible with traditional platforms, is being measured with special polar profiling floats and miniaturized oceanographic sensors attached to marine mammals. Moreover, ocean gliders now offer the possibility of making real-time multi-disciplinary measurements of the upper 1000 m of the water column, and have recently been deployed for the first time around Antarctica. Measurements of biological distributions and processes using net tows, continuous plankton recorders, and acoustics are providing new insights into the coupling of physical, biogeochemical and ecological processes. Autonomous underwater vehicles are exploring the ocean deep beneath ice shelves.

All of the key science challenges require sustained, broad-scale measurements of the ocean state, measurements that can only be obtained using autonomous platforms such as profiling floats. Basic principles of float functioning is described here (Functioning)

A sustained commitment to maintenance of a profiling float array in the SO is critical. One of the most important research projects dedicated to float implementation and data collection also in the SO is the ARGO (Array for Real-time Geostrophic Oceanography) programme. A short summary of the ARGO programme is offered at this link (ARGO)

ARGO has made a particularly significant contribution to observations of remote areas like the SO. The number of profiles collected from ARGO floats is already higher than the number of profiles collected during the entire history of ship-based oceanography in this region. Floats with oxygen sensors are beginning to be deployed in the SO and we can anticipate that with time the capacity to measure additional variables from floats will increase. The float array needs to extend to seasonally ice-covered seas, through the use of ice-capable floats and acoustic tracking of floats. The first priority is to maintain the ARGO network at the nominal ARGO density (1 float per 3 degree longitude x 3 degree latitude square, or roughly 970 floats south of 40°S). The extension of the system to sample under sea ice is also important, as some of the most important changes are occurring near the ice shelves and within the sea ice zone. Floats capable of deeper profiling would be of particular value in the SO, where significant changes have been observed below 2000 m. Oxygen sensors will provide useful information on ventilation processes and the carbon cycle. Sensors to measure a wider range of biological and chemical parameters (e.g. bio-optics, CO2 system, nutrients) are needed to relate variations in the physical environment to biogeochemistry and ecosystem processes.

The Italian contribution to float population in the Mediterranean Sea, Black Sea and in the SO is represented by activities developed in the framework of ARGO-ITALY.

ARGO-ITALY is the Italian component of a worldwide in situ global observing system, based on autonomous profiling floats, surface drifters, gliders and ship-of-opportunity measurements. It is primarily focused on the Italian seas, and the Mediterranean and Black seas, and includes observations of temperature, salinity, currents and biogeochemical/optical properties of seawater. The ARGO-ITALY objective is to provide a significant and sustained Italian contribution to the global ocean monitoring.

The ARGO-ITALY objective is to provide a significant and sustained Italian contribution to the global ocean monitoring. ARGO-ITALY contributes to international programs such as ARGO and Euro-ARGO (global monitoring of water properties with profiling floats), GDP (Global Drifter Program to measure near-surface temperature and currents), EGO (gliding vehicles to measure water properties) and SOOP (Ship-Of-Opportunity Program to temperature profiles) which have been developed to monitor the entire World Ocean on a long term basis. ARGO-ITALY is a cost-effective long-term monitoring system that is a unique source of information to study the role of the oceans on the climate system. It also provides the data required by operational ocean monitoring systems in order to improve significantly extended forecasts of the atmosphere and oceans.

ARGO-ITALY contributes to programs of operational oceanography, such as MOON (Mediterranean Operational Oceanography Network) and MyOcean (FP7 European project) and is essential for the production of marine core and downstream services products of GMES (Global Monitoring for Environment and Security). It is also an important component of GEOSS (Global Earth Observation System of Systems). ARGO-ITALY is funded by the Italian Ministry of Instruction, University and Research (MIUR) since 2011.

ARGO-ITALY activities in the S.O. started in 2013 and are still ongoing.

The number of total floats released in the S.O. and the amount of floats per year are both increasing. Table 1 shows the number and details of floats per year and a rapid link to cruise details.

Year

Number of floats

Number of drifters

Cruise Details

Ship

PNRA expedition

2013

3

0

report

R/V Araon

XXVIII

2014

7

0

report

R/V Italica

XXIX

2015

10

10

report

R/V Araon

XXX