Ice shelf basal melt sensitivity to tide-induced mixing based on the
theory of subglacial plumes
Abstract
Tidal currents are known to influence basal melting of Antarctic ice
shelves through two types of mechanisms: local processes taking place
within the boundary current adjacent to the ice shelf-ocean interface
and far-field processes influencing the properties of water masses
entering the cavity. The separate effects of these processes are poorly
understood, limiting our ability to parameterize tide-driven ice
shelf-ocean interactions. Here we focus on the small-scale processes
within the boundary current and we apply a one-dimensional plume model
to a range of ice base geometries characteristic of Antarctic ice
shelves to study the sensitivity of basal melt rates to different
representations of tide-driven turbulent mixing. Our simulations
demonstrate that the direction of the relative change in melt rate due
to tides depends on the approach chosen to parameterize entrainment of
ambient water into the plume, a process not yet well constrained by
observations. A theoretical assessment based on an analogy with tidal
bottom boundary layers suggests that tide-driven shear at the ice
shelf-ocean interface enhances mixing through the pycnocline. Under this
assumption our simulations predict an increase in melt and freeze rates
along the base of the ice shelf when adding tides into the model. An
approximation is provided to account for this response in basal melt
rate parameterizations that neglect the effect of tide-induced turbulent
mixing