Polar Profiling Floats: An Autonomous Observational Array for IPY and Beyond
Arctic Research Initiative
2007 Funded Project
The International Polar Year of 2007-2008 will be an exciting opportunity to develop a better understanding the polar seas and their implications for the global oceans and climate. High latitudes lack systematic observations that are now being carried out in temperate latitudes as part of the global ocean observing system. Descriptions of the circulation and the temporal changes in heat and salt content can now be made at lower latitudes using satellite altimetry and the Argo float program (see, for example Lyman, et. al., 2006), Extending these observations to high latitudes to document variability and change will require new technologies and strategies organized into a long-term observational program. For that part of the Arctic Ocean that is ice-covered all year, Ice-Thethered Profiliers (ITPs) will provide the necessary coverage (Toole and Proshutinsky, WHOI). For the increasing fraction of the Arctic that has open water for part of the year, another approach must be found.
A proposed deployment of six Polar Profiling Floats (PPFs) within the Arctic Ocean will demonstrate how they can contribute to an observational array delivering hydrographic and ocean velocity data during IPY and beyond for the partially ice covered portion of the Arctic Ocean. In an earlier NSF funded effort, we demonstrated that these floats can find open leads in the ice and send their data back to shore. However, software errors prevented these floats from working for more than a few months so that their scientific utility could not be demonstrated to support a large array of floats. The proposed PPF array will be a first step toward an Arctic version of the Argo float program. Support for the larger array will be requested from NSF. The modest array of six PPFs will provide the necessary demonstration of their scientific utility.
The PPFs will provide vertical profiles of pressure, temperature, salinity, and oxygen once every five days over the estimated four-year life span. To get the position of the float, it will either record its position using signals from sound sources between each surfacing or by GPS fixes when the float penetrates through the ice, providing a sub-surface Lagrangian velocity record or displacement for each float. PPFs are relatively small and cheap and can be deployed easily be one person from a ship, plane or other platform of opportunity. They can operate on shelves, in the marginal ice zones and in deep water and are not dependent on the availability of e.g. multi-year ice floes.The PPFs will make it possible to study some of the key features of the Arctic climate system, e.g. the Arctic Ocean boundary current, vertical heat flux to the sea ice, lateral spreading of Atlantic Water and enable year-round monitoring of the state of the Arctic Ocean. Combined with the ITP measurements, this array of profiling floats will provide a data set that can be used to characterize the present state of the circulation, heat, and salt content within the upper two kilometers of the Arctic Ocean, particularly along the boundary current regions of the Eurasian basin and along the mid-ocean ridge. An analysis of this data will examine the strength of the current and the heat and salt fluxes along these boundaries to determine whether there is significant recirculation of Atlantic water or if the entire ocean is involved in the modification of this water mass and loss of heat to the upper layers. An analysis of the dissolved oxygen data in conjunction with the hydrographic data and velocity data will determine how important lateral fluxes are to the local ecosystem.