Observations and Numerical Modelling of the Influence of Glacial Meltwater Influx on Water Circulation and Properties in Admiralty Bay, Antarctica

The impact of glacial meltwater influx on the Antarctic waters’ circulation is undeniably important yet still insufficiently understood. Previous studies revealed some mechanisms of tidewater glacial discharge and its impact on water physical, chemical and biological properties in specific coves, but there is scarce information on general principle of its transport, mixing and feedback on water hydrodynamics. In time of unparalleled glacial melting, injection of growing volume of meltwater must influence general circulation of the adjacent ocean. Moreover, since it influences marine ecosystems, it is vital to be able to forecast its spreading and mixing. Understanding character of this impact and defining mechanisms of glacial meltwater transport and mixing in ocean waters depending on the coastal and bottom topography, season and external forcing is the long-term goal of this project.

The first aim of this study was to precisely trace glacial meltwater presence in different locations and distances from the glacial front to assess its instantaneous distribution and define its characteristics. In Admiralty Bay, King George Island, Antarctica, repeated measurements of water properties in small tidewater glacial subcoves have been carried out in a proximity to five glacial fronts (measurements conducted as close as 50 m from the icefront), both at the water surface and along vertical profiles (for detailed localization see lime-coloured boxes in attached Figure). The selected bodies of water differ between each other in terms of depth, surface area, sill depth, length of ice–water boundary, glacial front grounding depth and height, and complexity of the coastline. Hence, they represent a wide variety of glacial fronts adjacent to Admiralty Bay and similar bays in the surrounding area. Since the measurement campaign have been repeated on average 10 times in each of the studied coves attained dataset is unprecedented among Antarctic coastal waters’ investigations.

Our measurements demonstrate that the glacial meltwater influx is influencing all measured water properties (salinity, temperature, pH, oxygenation, turbidity, dissolved organic matter content, chlorophyll A, phycoerythrin), with notable unexpected increase of pH values. Presence of glacial meltwater in water has a significant yet nonlinear relation with phytoplankton quantities and distribution. Moreover, the collected data have shown that the cove’s bottom and coastline topography alter the spreading of glacial meltwater.

The following step was to understand the general water circulation in Admiralty Bay to be able to formulate reliable boundary conditions in proximity of the studied glacial fronts for subsequent glacial outflow modelling. To that end, we used Delft3D (version 4) model of general circulation, on curvilinear grid with temperature and salinity distribution, currents, tides, and wind considered as drivers of oceanic impact in Admiralty Bay (the outline of the grid is shown in the attached Figure). Our results have been compared with in situ CTD measurements carried out in all seasons in the central part of the bay (area outlined in purple box in the Figure).