This paper presents an under-ice acoustic navigation system developed for Seaglider, a buoyancy-driven autonomous underwater vehicle (AUV), and post-processed navigation results from one of fourteen glider deployments between 2006 and 2014 in Davis Strait. Seagliders typically receive all geolocation information from global positioning system (GPS) signals received while they are at the surface, and perform dead reckoning while underwater. Extended under-ice deployments, where access to GPS is denied due to the inability of the glider to surface, require an alternative source of geolocation information. In the deployments described herein, geolocation information is provided by range measurements from mooring-mounted acoustic navigation sources at fixed, known locations. In this paper we describe the navigation system used in Davis Strait and present navigation results from a six degree-of-freedom Kalman filter using post-processed navigation data.

The northernmost limb of the Atlantic Meridional Overturning Circulation (AMOC), so relevant for understanding decadal climate variability, enters the Nordic Seas as the Norwegian Atlantic Current and continues on to recirculate in the Arctic Ocean. The strength of the Eastern Branch of the Norwegian Atlantic Current has been systematically monitored for over 15 years at the Svinøy section off southern Norway, whereas the strength of the Western Branch has not. We therefore used autonomous gliders to monitor and quantify the strength of this broader branch at the Svinøy section, located 500 km downstream from the Iceland–Scotland Ridge, and at the Station Mike section 300 km further downstream. The gliders' diving depth is 1000 m, spanning the warm Atlantic Water. The current encompasses more than warm Atlantic Water; we find that the transport peaks in two distinct temperature ranges, one around 7.5–8°C (Atlantic Water, carrying 7 Sv (1x10⁶ m³/s)) and another around –0.5°C (Norwegian Sea Deep Water, carrying 12 Sv). Contrary to earlier expectations, our results indicate that the Western Branch carries as much water of Atlantic origin (temperature>7.5°C) as the Eastern Branch. It should therefore be included in future monitoring plans for this region.

Recent community reports on autonomous and Lagrangian platforms and Arctic observing identify the development of under-ice navigation and telemetry technologies as one of the critical factors limiting the scope of autonomous (e.g. floats, AUVs and gliders) high-latitude measurement efforts. These platforms could provide persistent, high-resolution, basin-wide sampling in ice-covered regions and collect measurements near the critical ice–water interface. Motivated by the dramatic advances in temporal and spatial reach promised by autonomous sampling and by the need to coordinate nascent efforts to develop navigation and communication system components, an international group of acousticians, platform developers, high-latitude oceanographers and marine mammal researchers gathered in Seattle, U.S.A. from 27 February – 1 March for an NSF Office of Polar Programs sponsored Acoustic Navigation and Communication for High-latitude Ocean Research workshop.

Workshop participants summarized the current state of knowledge concerning Arctic acoustics, navigation and communications, developed an overarching system specification to guide community-wide engineering efforts and established an active community and steering group to guide long-term efforts and ensure interoperability between elements developed by disparate teams. This presentation will summarize workshop findings and provide an update on recent developments stemming from the EU DAMOCLES and US NSF Arctic Observing Network programs.

This paper describes the numerical features of WHOI Cable, a computer program for analyzing the statics and dynamics of oceanographic cable structures. The governing equations include the effects of geometric and material nonlinearities, bending stiffness for seamless modeling of slack cables, and a model for the interaction of cable segments with the sea floor. The program uses the generalized-α time integration algorithm, adaptive time stepping, and adaptive spatial gridding to produce accurate, stable solutions for dynamic problems. The nonlinear solver uses adaptive relaxation to improve robustness for both static and dynamic problems. The program solves surface and subsurface single-point mooring problems, multi-leg and branched array systems, and towing and drifting problems. User specified forcing can include waves, currents, wind, and ship speed.

As part of the Freshwater Initiative sponsored by the National Science Foundation Office of Polar Programs, a team of scientists from the Applied Physics Laboratory of the University of Washington and the Bedford Institute of Oceanography are investigating freshwater exchange through Davis Strait. This 300-km-wide strait sits between Baffin Island and the west coast of Greenland and acts as the gateway for waters passing between the Canadian Arctic Archipelago and the subpolar North Atlantic. In autumn 2004 the R/V Knorr cruise 179-05 undertook the first of three one-year mooring deployments. Six subsurface moorings, one off-axis sound source, eight bottom landers, and two Seagldiers were deployed successfully slightly north of the Davis Strait sill. Four cross-strait hydrographic lines, complete with sampling for chemical tracers, characterized water mass variability from the southern end of Baffin Bay to the northern tip of the Labrador Sea. The moored array will be recovered, serviced, and redeployed annually for a period of at least three years.