Polar Argo Design
The number of floats required to extend the core Argo array beyond 60°S and 60°N was estimated by developing a 3 x 3° grid over the global oceans and finding grid cells (with a depth of 2000m or greater) in the Southern Ocean, or 1000m or greater, in the Arctic Ocean. The grid cells that are ice free in summer were identified by mapping the median ice extent limit (1979-2000) from the NOAA National Ice Centre data. The density coefficient of floats per grid cell is x1.
This results in a target number of floats of 326 in the Southern Ocean (orange cells in map below) and 141 in the Arctic Ocean (grey cells in the map below).
Taking into account partial grid cells with depths greater than 2000 m for the Southern Ocean yields a slightly higher target of 360 active floats (including 85 RAFOS-equipped floats in the Weddell Sea and 110 floats in the Ross Gyre).
This analysis does not take into account the shrinking summer ice extent in the Arctic. It should be noted that in the Arctic proper, a mix of platforms will be required (i.e. both Argo floats and ice tethered profilers) to better deal with expected multi-year ice conditions in the Central Arctic. In the Central Arctic an observing system has been installed within the French framework “Observatoire Français de l’Arctique” which is based on ice tethered floats which collect real time simultaneous observations of the ocean, the sea ice, the snow and the atmosphere. The network consisting of 15 stations covers mainly the Beaufort Gyre and the Arctic transpolar drift. The deployment has started back in 2012 in the IAOOS project and is financed for a 7 year period so far. It should also be noted that large areas in the Arctic are within territorial waters and will require increased international cooperation in order to reseed floats.
The map below shows how well we are meeting the design goals for Argo. Blue areas indicate regions that are undersampled and where gaps in the array are likely to develop. Conversely, red areas indicate regions that are well sampled. The polar oceans in both hemispheres are currently under-sampled with substantial gaps opening up in the southernmost sectors of the Southern Ocean and in parts of the Arctic.