The Bjerknes Centre is a collaboration on climate research, between the University of Bergen, Norce, the Institute of Marine Research, Nansen Environmental and Remote Sensing Centre.

Model simulations show that currents and water masses in the Atlantic changed regionally in warm and cold stages of the last interglacial. Photo: Emil Jeansson

Large variations in the South Atlantic during the last interglacial

During the last interglacial, there were large variations in the circulation in the South Atlantic, both at the surface and at depth. The overturning circulation in the Atlantic was still maintained.

The last interglacial may serve as an analog to future climate conditions. A study recently published in Scientific Reports finds that the thermohaline circulation in the Atlantic was relatively stable, despite basin-wide regional changes in the interior South Atlantic. 

The authors – from the Bjerknes Centre for Climate Research, the Geophysical Institute at the University of Bergen, Uni Research, and Heidelberg University – also emphasize that inferring past climate variability from proxy records should be done with caution.  

Substantial regional variations between warm and cold periods

The ocean absorbs excess heat and carbon dioxide released to the atmosphere. Understanding how the circulation in the world oceans responded to changes in past climates, is crucial for anticipating unexpected changes in the future. 

In the study, the Norwegian Earth System Model (NorESM) was used to simulate the last interglacial period. Comparing warm and cold stages of the interglacial, showed that the Atlantic thermohaline circulation – the overturning circulation – was relatively stable. However, there were substantial regional differences in the interior of the South Atlantic. 

The changes were associated with the Southern Ocean ventilation. The pathways of Antarctic bottom water showed a clear east-west contrast between the different climate states. 

Complex response demands careful use of data

The study demonstrates that contrasting climate conditions, such as warm and cold periods of the last interglacial, could have large spatial variations both at the surface and in the interior of the ocean. At the same time, the strength and structure of the overturning circulation in the Atlantic was maintained. 

Based on their simulations with the Norwegian Earth System Model, the authors note that changes in the large-scale circulation in the oceans in a changing climate are complex. This makes it challenging to infer past climate variability from sparse geological proxy records. The authors stress that this should be done with caution, preferably in combination with model data.

Reference

Luo, Yiming; Tjiputra, Jerry; Guo, Chuncheng; Zhang, Zhongshi & Lippold, Jörg (2018): Atlantic deep water circulation during the last interglacial. Scientific Reports, 8, 4401. DOI:10.1038/s41598-018-22534-z. https://www.nature.com/articles/s41598-018-22534-z