What Is Polar Argo?
Polar Argo refers to the subset of Argo floats operating south of 60°S and north of 60°N. Although these regions were not included in the original Argo design (learn about the Polar Argo Design here), floats have been deployed there since the early stages of the program, with the first floats deployed as early as 1999 and 2001, poleward of 60°S and 60°N, respectively.
The main advantage of using Argo floats in the high-latitude oceans is that they are able to sample autonomously throughout the winter, a season that has been drastically undersampled by research vessels due to the widespread sea ice coverage and the harsh weather conditions. From the more than 45000 profiles collected by Argo floats in its first 16 years of operation, approximately 40% were winter profiles. By comparing these numbers with the about 14,000 ship-born profiles that were collected in the more than one-hundred-year period of traditional shipborne oceanographic sampling (1900-2013), from which only 20% are winter profiles, it becomes clear that Argo has considerably improved our ability to observe the full seasonal cycles of the physical processes in the Polar oceans.
To date (early June 2020), 52142 profiles have been collected north of 60°N and 61420 south of 60°S, by 693 and 1026 different floats, respectively, from which 86 and 216 are currently active. The self-updating map below from the Argo Information Center, shows the last location of the operational Polar Argo floats.
The presence of sea ice, however, represents a hazard for the integrity of the floats and prevents their communication with satellites, necessary for data transmission and the determination of the profiles positions. Klatt et al. (2007) reported that from the standard floats deployed in the seasonal ice region of the Weddell Sea, originally designed to operate in open water environments, only a few were able to survive the winter season, once they encountered ice. They estimated a probability of survival of about 40% under these conditions and attributed such high mortality to physical damage to the antennas inflicted by the sea ice. This could occur during float transmission, a process that required long periods at the surface since the floats were using Systeme Argo (see the Technical Innovations page), giving enough time for the float to be crushed between ice floats, or while hitting the ice from below when attempting to surface. Since then, the survival rates of floats operating in the high latitudes has increased and is now comparable with those of the floats operating in lower latitudes, thanks to many adaptations tailored to improve their performance in these icy environments. Such adaptations include:
- More resistant hardware, to withstand occasional encounters with sea ice.
- Ice avoidance strategies, to abort the float ascending trajectory before hitting the sea ice from below (see also the Technological innovations page).
- Ability to store under-ice profiles, which are not transmitted immediately after sampling.
- Methods to determine the floats under ice positions.
To learn more about the continuous work of the Argo community to overcome all the technical challenges associated with float operation under the ice, click here.
The animations below shows the positions of the Polar Argo profiles between 2011 and 2019. The under-ice and near-ice profiles (closer than 50 km from the ice edge) were identified by selecting the profiles which position was interpolated, instead of obtained via satellite, and comparing their positions with the daily sea ice concentration maps from the Satellite Application Facility on Ocean and Sea Ice (OSI-SAF). However, the actual number of profiles under the ice is larger, since the positions of some profiles are still missing, but they could be estimated in the future when a reliable method becomes available.
Please click on maps nearby to start the animations showing the growth in Argo profiles in the polar regions.
The recent progress in the Northern Hemisphere has been possible thanks to pilot projects aiming to study specific processes in the Arctic region. For example, the Stratified Ocean Dynamics in the Arctic and the Arctic Heat Open Science Project made possible aerial deployments of ALAMO floats in the Beaufort Gyre and the Chukchi Sea, and the GREEN EDGE research project, designed to study the phytoplankton spring bloom in the Baffin Bay, kick-started the use of BGC-PROICE floats in the Baffin Bay. In the Southern hemisphere, the largest initiative is the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM), which aims to increase our understanding of the role of the Southern Ocean in climate change and biogeochemistry. For more about these projects visit the Polar Argo Pilot Arrays page.
Keep in mind that the Argo network floats are just a part of the mosaic of instruments and platforms necessary to observe the Polar Regions appropriately. In the multi-year ice environments of the Arctic proper, for example, ice tethered profilers are a more suitable alternative. For a list of pages related to Polar oceanography click here.
Our community is happy to assist countries and institutions interested in deploy floats in the polar oceans. Please visit the Polar Argo Contacts page to find the right people for your scientific purposes and region of interest.