The effects of eddies on the decline of primary production in the ocean
The decline of primary production in the oceans is one of the most alarming consequences of anthropogenic climate change. This decline could indeed lead to a decrease in marine biomass and fishing activities, as highlighted in the recent IPCC and IPBES reports for stakeholders.
Projections of the evolutions of ocean primary production for the 21st century are made with climate models. Due to computational time constraints, their horizontal resolution in the ocean is about 100 kilometres. Ocean eddies occurring at finer spatial scales are therefore not resolved but are included by parameterisations.
In order to increase the resolution and get rid of parameterisations, the study uses a very simplified version of climate models partly representing the North Atlantic Ocean. This simplified model allows climate projections to be made at different horizontal resolutions: from 100 km (parameterised eddies) to 4 km (resolved eddies). In line with climate model projections, all projections made with the simplified model predict a sharp decline in primary production. However, this decline is sensitive to resolution: in the 4 km resolution projections it is half as strong as in the 100 km resolution projection. This difference is due to the subsurface transport of nutrients necessary for primary production. This transport is itself very sensitive to the horizontal resolution of the model.
These results obtained in a simplified framework are obviously only one element of a much more complex response of the ocean to climate change. Nevertheless, they encourage us to work on taking better account of the effects of eddies on the transport of nutrients in order to better predict the future evolution of marine biomass and fishing potential.
Laboratoire d’Océanographie et du Climat : Expérimentations et Approches Numériques (LOCEAN-IPSL, Sorbonne Université,/CNRS/IRD/MNHN)
Laboratoire de Météorologie Dynamique (LMD-IPSL, École Normale Supérieure/PSL University, CNRS, École Polytechnique, Sorbonne Université)
Oceanic primary production decline halved in eddy-resolving simulations of global warming. Author(s): Damien Couespel et al. https://bg.copernicus.org/articles/18/4321/2021/