Ventilation age and remineralisation rates in polar and sub-polar regions as an indicator for climate change (VENTILATE)

The oceans uptake of atmospheric CO2 is connected both to physical and biological processes. This uptake has been very important for the Earths climate, modulating the effect of man-made CO2 since the industrial revolution.

However, with the continuing increase of CO2 in the atmosphere and the observed climate change, it is uncertain how the ocean’s uptake will be affected in the future.

A key knowledge here is the link between the physical processes and the oceanic carbon cycle. To increase our understanding of this link is the overall aim of VENTILATE.

VENTILATE will evaluate decadal changes (from early 1980s until today) in ventilation of the Nordic Seas (Greenland, Iceland, and Norwegian Seas) and the Arctic Ocean.

With ventilation we mean the renewal of water at larger depths, with water from the ocean surface. For this we will utilise the trace gases chlorofluorocarbons (CFCs) and sulphur hexafluoride (SF6), which are mixed down into the ocean surface from the atmosphere, and then transported to the ocean interior through mixing processes.

These tracers give a mean to estimate how old water from different depths are, where water mass age is defined as the time since that water was in contact with the atmosphere.

VENTILATE aims to improve our understanding of how fluxes of carbon are affected by the ventilation state. This goes both for the physically driven process of uptake and surface-to-deep water transport of man-made CO2, and of biologically driven uptake and vertical transport of carbon.

By combining data of dissolved oxygen and water mass ages we can infer the amount of vertically exported carbon from biological production.

In VENTILATE we will use a state-of-the-art Earth system model (NorESM) to simulate ventilation rates and carbon fluxes in the Nordic Seas.

This will make it possible to test different assumptions and relationships that will help us understand the complex links that exist between ocean, climate and carbon cycle in northern high latitudes, but also serve as an innovative validation for the model performance and benchmark for future improvements.

An example can be seen in Fig. 1 above, where a comparison is made between observational based inventory of anthropogenic CO2 (Cant) in the Nordic Seas, and one based on model simulation.