Turbulent ocean-to-ice heat transfer: Laboratory and numerical studies
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Date
2018-05-09
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Johns Hopkins University
Abstract
This thesis explores turbulent ocean-to-ice heat transfer and consists of two main studies. The first is a laboratory experiment on the time evolution of an ice layer cooled from below and subjected to a turbulent shear flow of warm water from above. This experiment is motivated by observations of warm water intrusion into the ocean cavity under Antarctic ice shelves, accelerating the melting of their basal surfaces. Either partial transient melting or complete melting of the ice occurs in our experiments depending on the strength of the applied turbulent shear flow, which is represented in terms of its Reynolds number $\Rey$. The ice consequently reforms at a rate independent of $\Rey$. A one-dimensional model for the evolution of the ice thickness is derived from the experimental results. Applying our model to field measurements at a site under the Antarctic Pine Island Glacier ice shelf yields a predicted melt rate that exceeds present-day observations. Arctic sea ice is also rapidly declining. In the second study, we use large eddy simulation (LES) to investigate numerically the turbulent entrainment of heat from the mixed layer, a mechanism that is possibly partly responsible for the observed sea ice loss. We model the Arctic Ocean's Canada Basin, which features a perennial anomalously warm Pacific Summer Water (PSW) layer at the base of the mixed layer and a summertime Near-Surface Temperature Maximum (NSTM) within the mixed layer, trapping heat from solar radiation. The ice drift velocity and initial temperature profiles are varied in our simulations. The results show that the presence of the NSTM enhances heat entrainment from the mixed layer. Additionally there is no PSW heat entrained under the parameter space considered. We propose a scaling law for the ocean-to-ice heat flux, which depends on the initial NSTM temperature anomaly and the ice-drift velocity. In an extension of this LES study, we investigate, the effect of varying the ice basal surface roughness $z_0$ over three orders of magnitude, all other parameters being kept constant. As $z_0$ is increased, the heat flux to the ice basal surface increases to a peak value, then decreases.
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turbulent heat transfer, ice-ocean interaction