Ocean processes influencing free floating ice melting rates

The melting of marine-terminating ice shelves, glaciers, and icebergs into the polar oceans is an issue of significant importance for Earth's climate system. Accelerated mass loss from the Antarctic and Greenland ice sheets, driven by anthropogenic climate change, has spurred the development of ice-ocean models to predict future impacts of their decline. However, accurately modelling ice melting in large-scale ice-ocean frameworks is challenging due to the scarcity of precise data-based parameterisations. A major obstacle is the intricate interaction between submarine ice and seawater caused by complex fluid dynamics. Particularly, there is a lack of research on how ocean stratification, submarine wave-induced oscillations, and internal waves, which are prevalent phenomena in polar areas, impact melting rates. This thesis explores these interactions through simplified laboratory experiments. In the second chapter, we investigate the melting response of a vertical wall of ice to salt stratified environments at relatively warm ambient temperatures and near-fresh salinities. Under these conditions, the melting of the ice is characterised by heterogeneity and is mainly influenced by double-diffusive convection along with buoyancy-driven flows in both the surrounding environment and the meltwater plumes. This heterogeneity leads to regular patterns called scallops, shaped by competing flows, and their vertical wavelengths determined by the theoretically suggested stratification lengthscale. Even in warm, fresh conditions, average ice melting rates are governed by temperature-dependent power laws, consistent with previous research, and are slower than those in an unstratified environment. Our findings have implications for the inclusion of stratification in iceberg and vertical glacier sidewall melting parameterisations. In the third chapter, we investigate the melting response of ice in harmonic vertical motion in unstratified environments under geophysically relevant conditions. It is demonstrated that when oscillatory motion surpasses a certain speed, it creates a dynamically rich environment around the ice, characterised by vortices and turbulence overtaking naturally convecting meltwater plumes. The melting rate is linked to this motion through a critical velocity, determined by the meltwater plume velocity under quiescent conditions; beyond this threshold, the melting follows a power law in relation to the oscillation velocity, consistent with steady-flow models. Additionally, above a certain oscillation frequency, surface scallops appear that differ from those in stratified environments. These insights are vital for improving iceberg models, especially in capturing the effects of underwater ocean swell and waves on sidewall melting. In the fourth chapter, we expand on both our previous investigations with melting ice in stratified environments along with the introduction of internal wavefield forcing. Integrating an internal wavefield creates a complex, spatially varying dynamic environment near the ice face, distinguished by oscillating double-diffusive layers that vary throughout the fluid column according to the internal wave dispersion relation. Under the conditions studied, melting rates are affected by the relative speed of the wave near the ice. Higher frequency waves with increased velocities result in greater average melting rates. Our findings offer significant insight into the melting dynamics that occurs when internal waves interact with ice shelves, glaciers, and large tabular icebergs. These laboratory experiments reveal key insights into the complicated dynamics of the ice-fluid interface and introduce refined parameterisations for future ice-ocean models. Although some important aspects of real ocean settings are not included, these experiments deliver new and significant data sets that are beneficial for testing numerical models and comparing with oceanographic data.