Heuzé et al. (2020) Global decline of deep water formation with increasing atmospheric CO2

C. Heuzé, M. Mohrmann, E. Andersson and E. Crafoord (2020). Global decline of deep water formation with increasing atmospheric CO2. EarthArXiv. doi:coming.

We analysed the 1% CO2 idealised run of 30 CMIP6 models and found:

  • Globally, open ocean deep convection ceases around 600 ppm. We instead enter a new regime, with large areas of mixed layers not exceeding 500 m;
From Fig 1: Hotspots of deep water formation in the North Atlantic and their decline with rising CO2 concentration (inserts). Black line is the multimodel mean (30 models); dark shading = 75% of the models; light shading = 90%.
  • Unlike what was found in studies based on individual models, deep convection does not start in the Arctic Ocean;
  • Consequently, the flows of North Atlantic Deep Water and Antarctic Bottom Water (AMOC and Southern MOC) fall at half their pre-industrial values;
From supp. Fig. 1: The Atlantic Meridional Overturning Circulation (AMOC) and Southern MOC at 30S are halved by the end of the run. Black line is the multimodel mean (30 models); dark shading = 75% of the models; light shading = 90%.
  • The main reason is a global large increase in stratification, which is caused by rising upper ocean temperatures and/or surface freshening. Trends in wind are insignificant; the wind cannot break the stratification.

We submitted this to Nature Climate Change. Twice. The first time in October 2019, the manuscript featured “only” 13 models. We were asked to resubmit once we had more models. The second version, with 30 models and more robust methods, was rejected in October 2020 for not being dramatic enough (my interpretation).
None of us is paid to work on this project. We all need to concentrate on more exciting things (e.g. the MOSAiC data), and, simply, it stopped being fun a long time ago. So sure, we could have played the peer-review game with another journal and forced ourselves through another year of selling this paper. Instead, following advice received from the community, we put the manuscript on EarthArXiv, in hope that it can be useful in its present state.

Click here for the full-text

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out /  Change )

Google photo

You are commenting using your Google account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s