Sea ice effects on the upper ocean: internal waves, ice-covered gyres and the seasonal ice zone

• Main Author: Thielen, K
• Other Authors: Wells, A
• Format: Thesis
• Language: English
• Published: 2021
• Subjects: Antarctic; Arctic; Southern Ocean; The Antarctic; Antarc*; Sea ice
• Online Access: https://ora.ox.ac.uk/objects/uuid:6764666b-92ef-41fa-890f-0d810cc2bade

The polar oceans are currently experiencing significant changes. Arctic and Antarctic sea ice extent and volume are changing, with a poorly constrained implication for future climate. Understanding the interactions between sea ice and the underlying ocean is fundamental for understanding current changes, and predicting future ice-states. In this thesis I study several aspects of the under-ice boundary layer and the coupling to the deeper polar ocean. First, I conduct numerical simulations of fluid flow using the Lattice Boltzmann Method to investigate the effects of stratification and roughness on ice-ocean drag and heat flux below a ridged ice floe overlaying a stably stratified ocean. It is found that sea ice generated internal waves can cause order of magnitude variations in the simulated drag coefficient and modest variations in area-integrated heatflux and its spatial distribution. A parameterization is developed for wave drag as a scaling law in terms of upper ocean velocity, stratification, and ridge geometry. To understand the potential impact, this parameterization is applied to an idealized conceptual model of an ice-covered ocean gyre. The model extends previous descriptions of ocean density variation subject to applied wind stress to account for ice-ocean wave drag and a simple treatment of ocean surface stress redistribution within the ice via a viscous ice rheology. I find that in certain stratification regimes, inclusion of internal wave effects significantly alters ice-velocity and ice-ocean stress with implications for the freshwater content of the gyre. I also explore how seasonal variations in ice cover impact the water mass properties of the Southern Ocean. A 1D ice-ocean model is adapted and compared to oceanographic float observations in the Antarctic seasonal ice zone. I find that Ekman upwelling has a leading order impact on the seasonal evolution of the upper ocean water masses and stratification.