A Large Eddy Simulation of Turbid Meltwater Plumes at a Marine-terminating Glacier Front

Yoshimasa Matsumura, Atmosphere and Ocean Research Institute, the University of Tokyo, Kashiwa, Japan, Naoya Kanna, The University of Tokyo, Atmosphere and Ocean Research Institute, Kashiwa, Japan, Shin Sugiyama, Hokkaido University, Institute of Low Temperature Science, Sapporo, Japan and Shigeru Aoki, Institute of Low Temperature Science, Hokkaido University, Sapporo, Japan
Abstract:
To investigate the behavior of subglacier discharge of meltwater and its impact on the oceanic environment in Greenland fjords, a large-eddy simulation (LES) of turbid meltwater plume were performed
using a three-dimensional non-hydrostatic ocean model coupled with a built-in particle tracking system that explicitly represents suspended sediment matter (SSM). The model setup was idealized based on in-situ measurements at the marine-terminated glacier front in the Bowdoin fjold, northwestern Greenland. The model resolution was 2 m (isotropic) and the time step interval was less than 0.1 second, which were sufficiently fine to capture the turbulent nature of plumes and their high frequency disturbance recorded by in-situ observations.

The LES results showed that the buoyancy supply by the underwater discharge of fresh meltwater induced immediate and strong upwelling, and the plume reached the surface with a certain vertical momentum that radially pushed out the surface water. A semicircular structure of ~200 m radius adjoined to the glacier front was clearly formed, which was almost identical to the one visualized by high turbidity in reality.

Since the turbulent plume entrains the saline and nutrient-rich water of Atlantic origin below thermocline, the underwater meltwater discharge acts as a pump for providing nutrients to the photic layer, that may supports primary production and ecosystem in the fjold. The plumes also play an important role for the transport of land-originated SSM to the subsurface of fjord regions, which might restrict the primary production due to shading effect.

We have performed several sensitivity experiments with varying discharge flux and size spectrum of SSM particles for different shapes of glacier-front cavity (e.g. flat, convex, concave). The quantitative effects of those parameters on the mixing ratio of meltwater and embient seawater, nutrient upwell and SSM transport/deposit and associated shading of solar radiation will be discussed.

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