We conduct laboratory experiments on the time evolution of an ice layer cooled from below and subjected to a turbulent shear flow of warm water from above. Our study is motivated by observations of warm water intrusion into the ocean cavity under Antarctic ice shelves, accelerating the melting of their basal surfaces. The strength of the applied turbulent shear flow in our experiments is represented in terms of its Reynolds number Re, which is varied over the range 2.0 × 10 3 Re 1.0 × 10 4 . Depending on the water temperature, partial transient melting of the ice occurs at the lower end of this range of Re and complete transient melting of the ice occurs at the higher end. Following these episodes of transient melting, the ice reforms at a rate that is independent of Re. We fit our experimental measurements of ice thickness and temperature to a onedimensional model for the evolution of the ice thickness in which the turbulent heat transfer is parameterized in terms of the friction velocity of the shear flow. The melting mechanism we investigate in our experiments can easily account for the basal melting rate of Pine Island Glacier ice shelf inferred from observations.
Arctic sea ice has declined rapidly in recent decades. The faster than projected retreat suggests that free‐running large‐scale climate models may not be accurately representing some key processes. The small‐scale turbulent entrainment of heat from the mixed layer could be one such process. To better understand this mechanism, we model the Arctic Ocean's Canada Basin, which is characterized by a perennial anomalously warm Pacific Summer Water (PSW) layer residing at the base of the mixed layer and a summertime Near‐Surface Temperature Maximum (NSTM) within the mixed layer trapping heat from solar radiation. We use large eddy simulation (LES) to investigate heat entrainment for different ice‐drift velocities and different initial temperature profiles. The value of LES is that the resolved turbulent fluxes are greater than the subgrid‐scale fluxes for most of our parameter space. 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 temperature anomaly in the NSTM layer and the ice‐drift velocity. A case study of “The Great Arctic Cyclone of 2012” gives a turbulent heat flux from the mixed layer that is approximately 70% of the total ocean‐to‐ice heat flux estimated from the PIOMAS model often used for short‐term predictions. Present results highlight the need for large‐scale climate models to account for the NSTM layer.
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