Kvartære geosystemer

Dynamics of abrupt climate change through ocean-sea ice interactions

PhD Candidate: Jonathan Winfield Rheinlænder

Supervision: Kerim H. Nisancioglu (UiB), Lars Henrik Smedsrud (GFI, UiB) and David Ferreira (University of Reading)

Project funding: European Research Council (ice2ice) - http://ice2ice.b.uib.no

Project period: December 2015 – December 2018


My phD thesis focuses on the role of ocean circulation and sea ice in driving abrupt changes in climate that occured throughout the last glacial period, known as Dansgaard-Oeschger events. By learning more about the dynamics and processes that lead to these events we can get a better understanding and perspective on present-day climate change.

The first part of my PhD project explores the dynamics behind rapid disappearance of sea ice associated with a phenomenon known as open-ocean polynyas. Polynyas are «large openings in the sea ice cover» and forms when relatively warm deep water, which normally sits well below the sea ice, is injected into the surface layer where it causes ice to melt.

By using a numerical climate model, I aim to understand the intriquite details of how this warm water is suddenly lifted, and show how even small changes in ocean stratification (the layering of the ocean), can lead to instabilities in the water column and cause warm water to reach the sea ice thus presenting a mechanism to rapidly remove sea ice with potential consequences for global climate.

The second part of my thesis is about understanding the conditions nessecary to support the existence of a large sea ice cover in the Northern Hemisphere and identify important processes and mechanisms that causes the climate system to transition between warm and cold states.

To this end, I use a coupled atmosphere-ocean-sea ice model with idealized geometry to test how changes in ocean circulation preconditions the propencity for sea ice to form in the northern high latitudes. In addition, I look at the influence of ocean mixing on driving transitions between warm and cold climate states.