Temperature microstructure during the IPY: quantifying the impact of warm subsurface water on melting of Arctic sea ice

Arctic sea ice is at present on track to achieve a record minimum in extent during September 2007. While solar energy input to the ocean through openings in the sea ice is accelerating the melting process, there is another potentially important source of heat in the near-surface layer of the ocean. Historically, this layer of warm water of Atlantic Ocean origin has been isolated from the surface sea ice by an intermediate layer of low salinity water. During the 1990's the salinity of that layer increased significantly and the barrier to upward heat penetration became weaker at a time of increased temperature of the Atlantic water layer. We hypothesize that variability in the temperature and salinity of these upper layers of the Arctic Ocean, notably warming of the Atlantic layer and salinification (or weakening) of the overlying cold halocline, will result in enhanced upward heat fluxes which can significantly impact the rates of melting or freezing of sea ice in the Arctic Ocean. We propose to quantify the effects of variations in the upper ocean temperature and salinity on vertical heat flux by measuring the turbulent heat flux beneath autonomous buoys that will be deployed on drifting Arctic sea ice during the International Polar Year. As part of the UK International Polar Year (IPY) contribution to a growing integrated Arctic Ocean Observing System (iAOOS), the Scottish Association for Marine Science (SAMS) will build and deploy in 2008 two ice-tethered profilers (ITPs) of their own design under NERC funding of the Arctic Synoptic Basin-wide Oceanography (ASBO) project. Over the course of their 1-2 year lifetimes, these ITPs will drift across the central Arctic Ocean basins with the sea ice on which they were deployed, relaying back in near-real time temperature and salinity data from the upper layers of the ocean waters over which the sea ice has drifted. As presently designed, and with the existing NERC ASBO support, the SAMS ITPs will resolve the vertical structure and horizontal extent of the important upper-ocean water masses. We propose to augment the SAMS ITPs with fast-response temperature sensors to measure turbulent temperature fluctuations and to determine the vertical heat flux through the upper ocean layers along the ITP Arctic drift paths. Fast-response thermistors are the standard sensors for measuring oceanic temperature signatures of mixing, and have been employed for many years on ship-based profiling turbulence packages. In recent years, fast-response thermistors have been mounted on profiling floats and moorings. The proposed work will be a new application of this well-established measurement technique, and as such represents an advance in measurement capability for the iAOOS during the IPY. The ITPs will be deployed on the Canadian side of the Lomonosov Ridge in the mean path of the trans-polar ice drift, and will thus yield measurements along trajectories that cross the major ridge systems and upper ocean currents of the Eurasian Basin. These will be first basin-scale measurements of turbulent fluctuations through the upper ocean structure (mixed layer, cold halocline, and Atlantic water) in the Arctic Ocean, and as such will vastly increase the areal coverage of data on mixing in the Arctic, as well as yield new insight into the impacts of variability of the upper ocean on overall heat budget of the Arctic, including the impact on sea-ice melting and growth.