Where AUV's Dare: Sub-glacial discharge plumes

Lead Research Organisation: Scottish Association For Marine Science
Department Name: Scottish Association For Marine Science

Abstract

There are few oceanic regimes not yet sampled by direct observation; indeed, arguably, there is only one: the vertical boundary zone, just ~10s m wide, where glaciers meet seawater. This project will focus on the dynamical processes by which freshwater in this thin boundary zone is assimilated into the adjacent sea. From the tidewater glaciers of Antarctica to Greenland and Svalbard, the precise nature of submarine melting, submarine discharge and surface runoff are known to have feedbacks on the circulatory mechanisms which draw warm oceanic waters towards the ice walls. In the polar regions of both hemi-spheres the combination of coastal geometry and high latitude predicate circulation schemes with lateral boundary intensification due to Earth rotation. Unraveling hypothesized1 feedbacks between discharge and circulation presents a double challenge to observation: one ideally suited to unconventionally-deployed AUVs (icewalls) and Gliders (narrow boundary currents). Scale interactions over such a range (cms to kms) will always defy exhaustive explanation based on observation alone, but are well suited to variable geometry hydrodynamic numerical modelling. Kronebreen, the fastest retreating glacier on Svalbard, exhibits all of the canonical features of tidewater glaciers noted above, and will be the primary geo focus for this studentship. The objective will be to elucidate the dynamical processes involved in submarine melting and circulation near tidewater glaciers, using novel autonomous observations and numerical modelling.

Location:
Kronebreen is the major outlet glacier of the Kongsfjorden system, west Svalbard2. Due to the proximity of the research settlement of Ny Alesund (including airstrip) a considerable knowledge base exists on the oceanographic and glaciological setting of the system, an archetype of ocean/tidewater glacier interaction.
Instrumentation:
Previous studies demonstrate the need to measure to within 1km of lateral boundaries to correctly characterize fjord circulation impinging on a glacier3. A glider will be deployed for 7 days, measuring hydrography and depth averaged currents.
Sampling to within 10m of a vertical and unstable ice wall presents the biggest challenge. Methods are being developed to deploy AUVs from UAVs into this zone. Systems will be trialed in a more benign environment (a UK sealoch) before deployment in Svalbard. A secondary method involves a monofilament tethered AUV, proven by our Norwegian colleagues.
Standard CTD+VMADCP methods will characterize the fjord interior and adjacent shelf (West Spitsbergen Current).
Models:
Bergen Ocean Model (BOM) and MITcgm have been configured for the KF system and will be available as a functional interpretive tool for this studentship.
Analytic techniques:
Starting with standard techniques (DAC-referenced geostrophy from gliders, TS and shear variance mixing analyses from CTD/ADCP, dominant momentum term scaling of model o/p), the student will then be encouraged to explore new analysis techniques relevant to constant pressure AUV data for quantifying horizontal mixing.

The NEXUSS CDT provides state-of-the-art, highly experiential training in the application and development of cutting-edge Smart and Autonomous Observing Systems for the environmental sciences, alongside comprehensive personal and professional development. There will be extensive opportunities for students to expand their multi-disciplinary outlook through interactions with a wide network of academic, research and industrial / government / policy partners. The student will be registered at SAMS UHI, and hosted at SAMS. Specific training will include:
Physical oceanography data analysis techniques using matlab
AUV and Glider operations at the Scottish Marine Robotics Facility
Hydrodynamic modelling techniques in UNIX environment, at SAMS and in NPI Tromso

Publications

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