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

Thielen, K

Thesis

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

Abstract:: 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.

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APA Style

Thielen, K. (2021). Sea ice effects on the upper ocean: internal waves, ice-covered gyres and the seasonal ice zone [PhD thesis]. University of Oxford.

MLA Style

Thielen, K. Sea Ice Effects on the Upper Ocean: Internal Waves, Ice-Covered Gyres and the Seasonal Ice Zone. University of Oxford, 2021.

Chicago Style

Thielen, K. 2021. “Sea Ice Effects on the Upper Ocean: Internal Waves, Ice-Covered Gyres and the Seasonal Ice Zone.” PhD thesis, University of Oxford.
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