As part of a coordinated international effort to quantify (and eventually monitor) the variability of fluxes connecting the Arctic and Atlantic Oceans and to understand the role played by the Arctic and sub-Arctic in steering decadal scale climate variability, an integrated observing system will provide year-round measurements of volume, liquid freshwater and ice fluxes across 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 (presently undertaking their first extended science missions) to address all aspects of flow through Davis Strait, including some measurements that have not previously been technologically feasible. System components include:
- A sparse array of five subsurface moorings, each instrumented with an upward looking sonar, an Acoustic Doppler Current Profiler (ADCP) and a single conductivity-temperature (CT) sensor, will provide time series of upper ocean currents, ice velocity and ice thickness. These measurements will be 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.
- Seven trawl and iceberg resistant bottom landers, instrumented with ADCPs and CT sensors, will be deployed across the Baffin and Greenland shelves to quantify variability associated with strong, narrow coastal flows.
- Acoustically navigated Seagliders will provide year-round, repeated, high-resolution hydrographic sections across the Strait. The resulting sections will be combined with the moored array data to produce sections of absolute geostrophic velocity and to estimate volume and freshwater fluxes. The glider navigation system includes eight acoustic sources operating at 780 Hz, 180 db. Each source will transmit 3-6 times per day, with each transmission lasting approximately 90 seconds. Sources will be anchored at widely spaced positions (roughly 50-100 km separation) north and south of the mooring line.
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, this observing system will make 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 will provide 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 may 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 will provide a significant new observational tool, opening important regions of high latitude oceans to intensive measurement programs.
This project involves one cruise per year (September/October 2004, 2005, 2006 and 2007, 2008, 2009, 2010) to service the moored array. During these cruises, we would like to conduct limited hydrographic surveys of the Davis Strait region (please see attached chart), during which we will measure temperature, salinity, dissolved oxygen, chlorophyll concentration and selected chemical properties. To facilitate proper deployment of the moored array, we would also like to conduct a bathymetric survey. This would be performed using the R/V Knorr’s multi-beam system at the start of the 2004 field effort. In addition to these cruises, smaller filed operation will be conducted from chartered fishing boats (likely from Nuuk) to service Seagliders. The glider effort will entail at least one small boat operation per year (2005, 2006, 2007, 2008, 2009, 2010), with additional excursions undertaken as necessary to rescue and service vehicles experiencing unexpected problems. |
