Relative roles of plume and coastal forcing on exchange flow variability
of a glacial fjord
Abstract
Glacial fjord circulation determines the import of oceanic heat to the
Greenland Ice Sheet and the export of ice sheet meltwater to the ocean.
However, limited observations and the presence of both glacial and
coastal forcing - such as coastal-trapped waves - make uncovering the
physical mechanisms controlling fjord-shelf exchange difficult. Here we
use multi-year, high-resolution, realistically forced numerical
simulations of Sermilik Fjord in southeast Greenland to evaluate the
exchange flow. We compare models, with and without a plume, to
differentiate between the exchange flow driven by shelf variability and
that driven by subglacial discharge. We use the Total Exchange Flow
framework to quantify the exchange volume fluxes. We find that a decline
in offshore wind stress from January through July drives a seasonal
reversal in the exchange flow increasing the presence of warm Atlantic
Water at depth, that the exchange flux in the summer doubles with the
inclusion of glacial plumes, and that the plume-driven circulation is
more effective at renewal with a flushing time 1/3 that of the
shelf-driven circulation near the fjord head.