Timeline for generation of polynyas can improve climate models
For the first time, the key processes leading to large openings in the Antarctic sea ice at Maud Rise in 2016 and 2017 have been synthesized into a complete timeline. The timeline can improve climate models and provide a more realistic representation of the impact of these openings – also called polynyas – on climate change in the Southern Ocean.
Polynyas are large openings in the sea ice that occur in Antarctica in wintertime. Coastal polynyas are generated by winds, but out at sea, polynyas are formed by so-called convection – the redistribution of water mass that occurs when ocean currents bring warm, salty water to the surface and melt the ice from below, causing the surface water to become heavy and sink towards the ocean floor.
In her thesis, Birte Gülk, doctoral student at the Department of Marine Sciences, has combined the theories of many previous studies and synthesized a timeline over the large polynya Maud Rise, which occurred due to unusually strong ocean currents during the winters of 2016 and 2017 and became as large as Switzerland from barely being visible at all.
First time timeline for key processes
“For the first time, I can provide a timeline of all the processes that were important in generating the Maud Rise polynyas in 2016 and 2017. I have also managed to create a model that describes the generation of polynyas and how the convection occurs," says Birte Gülk, doctoral student at the Department of Marine Sciences, University of Gothenburg.
Polynyas have a major impact on the climate. The upwelling warm salty water releases stored heat and carbon dioxide into the atmosphere. But this process also mitigates climate change, as it drives the formation of denser water masses that plunge to the ocean floor, carrying carbon dioxide from the atmosphere down to the ocean depths. The effects of a polynya can persist in the ocean for years after they have formed.
More reliable climate models
So far, it has been very difficult to reproduce how polynyas form and how large they can become. Researchers have only been able to determine their formation afterwards, using models in combination with observational data. Therefore, it has also been difficult to assess the potential impact of polynyas on climate. In previous global ocean and climate models, researchers have used a simplified approach to represent convection. In these cases, the polynyas became either too large or non-existent.
“When I created the timeline, I used a slightly more complicated, more realistic method of representing convection. If we can use more realistic methods in terms of convection and polynya generation, we will get a more reliable result in terms of deep water formation and carbon dioxide uptake. This in turn gives a more realistic picture of the impact of polynyas on climate change in the Southern Ocean,” says Birte Gülk.
Contact
Birte Gülk
Doctoral student, Department for Marine Sciences
Email: birte.gulk@gu.se
Dissertation takes place on 22 May 2024.
Link to thesis:: On the generation of Maud Rise polynyas in the Weddell Sea.
Writer: Annika Wall
Polynyas have a major impact on the climate. When a polynya opens, it allows an exchange of heat, nutrients and gases between the ocean and the atmosphere. The rising warm, salty water releases stored heat and carbon dioxide into the atmosphere. This process not only affects local weather patterns, but also mitigates climate change, as it also drives the formation of denser water masses that plunge to the ocean floor, taking carbon dioxide from the atmosphere along the way.
The effects of a polynya can persist in the ocean for years after they have formed. They can change the way water moves and how currents carry heat towards the continent. The dense waters that form here can spread across the global ocean.
Some of the same processes that were involved in the forming polynyas, such as the upwelling of deep and salty water, are also driving a general reduction in sea ice in the Southern Ocean.
