As part of coordinated domestic and international efforts to (1) quantify the variability of fluxes connecting the Arctic and subpolar oceans, (2) understand the role played by the Arctic and sub-Arctic in steering decadal scale climate variability and (3) establish a pan-Arctic integrated observing network, we are developing an integrated observing system to monitor exchanges at the critical Arctic -- sub-Arctic gateway at Davis Strait. Fluxes through the Strait represent the net integrated Canadian Archipelago throughflow, modified by terrestrial inputs and oceanic processes during its southward transit through Baffin Bay. By the time they reach Davis Strait, Arctic waters already embody most of the transformations they undergo prior to exerting their influence on the deepwater formation sites in the Labrador Sea. This makes the Strait an ideal site for monitoring temporal and spatial variability in the critical upstream boundary condition for Labrador Sea convection. Measurements at Davis Strait will be used to study how fluctuations in the Arctic freshwater system modulate deep water formation to the south, thus influencing the associated meridional overturning circulation (MOC). The system employs complementary techniques, combining mature technologies with recent developments in autonomous gliders to address all aspects of flow through Davis Strait, including some measurements that have not previously been technologically feasible. The components of the system include:
A sparse array of subsurface moorings, each instrumented with an upward
looking sonar, an Acoustic Doppler Current Profiler (ADCP) and a single
conductivity-temperature (CT) sensor, provides time series of upper ocean
currents, ice velocity and ice thickness. These measurements are
used to estimate the ice component of freshwater flux, provide
an absolute velocity reference for geostrophic shears calculated from
Seaglider hydrographic sections, and derive error estimates for our
lower-frequency flux calculations.
Trawl and iceberg resistant near bottom moorings, instrumented with ADCPs and CT sensors, are deployed across the Baffin and Greenland shelves to quantify variability associated with strong, narrow coastal flows.
Acoustically navigated Seagliders provide year-round, repeated, high-resolution hydrographic sections across the Strait. The resulting sections are combined with the moored array data to produce sections of absolute geostrophic velocity and to estimate volume and freshwater fluxes.
By quantifying, with robust error estimates, the spatial and temporal variability of the Canadian Archipelago throughflow system at a location critical for assessing its impact on deep water formation in the North Atlantic, the observing system makes a major contribution to SEARCH and ARCSS objectives. In addition to the immediate impacts of improved estimates of freshwater inputs to the Labrador Sea, the array provides an initial data set with which to study the relationships between Arctic freshwater system variability and large scale atmospheric fluctuations (e.g. the North Atlantic Oscillation (NAO)). The combination of emerging and existing technologies implemented in the observing system can serve as a prototype for accurate long-term monitoring of freshwater and ice fluxes in high latitude environments subject to seasonal or permanent ice cover. Finally, acoustically navigated autonomous gliders capable of extended missions in ice covered environments provide a significant new observational tool, opening important regions of high latitude oceans to intensive measurement programs.