Preprints
https://doi.org/10.5194/egusphere-2022-959
https://doi.org/10.5194/egusphere-2022-959
 
04 Oct 2022
04 Oct 2022

The role of buoyancy forcing for northern North Atlantic SST variability across multiple time scales

Bjørg Risebrobakken1, Mari F. Jensen2, Helene R. Langehaug3, Tor Eldevik4, Anne Britt Sandø5, Camille Li4, Andreas Born2, Erin L. McClymont6, Ulrich Salzmann7, and Stijn De Schepper1 Bjørg Risebrobakken et al.
  • 1NORCE Norwegian Research Center, Bjerknes Centre for Climate Research, Bergen, Norway
  • 2Department of Earth Sciences, University of Bergen and Bjerknes Centre for Climate Research, Bergen, Norway
  • 3Nansen Environmental and Remote Sensing Center, Bjerknes Centre for Climate Research, Bergen, Norway
  • 4Geophysical Institute, University of Bergen and Bjerknes Centre for Climate Research, Bergen, Norway
  • 5Institute of Marine Research, Bjerknes Centre for Climate Research, Bergen, Norway
  • 6Department of Geography, Durham University, Durham, UK
  • 7Department of Geography and Environmental Sciences, Northumbria University, UK

Abstract. Analyses of observational data (from year 1870 AD) show that Sea Surface Temperature (SST) anomalies along the pathway of Atlantic Water transport in the North Atlantic, the Norwegian Sea and the Iceland Sea are in-phase at multidecadal time scales. In-phase SST anomaly relationships are also observed over hundreds of thousands of years during parts of the Pliocene (5.23–5.03, 4.63–4.43 and 4.33–4.03 Ma). However, when investigating CMIP6 SSP126 future scenario runs (next century) and Pliocene reconstructions (5.23–3.13 Ma), three additional phase relations emerge: 1) The Norwegian Sea is out of phase with the North Atlantic and the Iceland Sea (Pliocene; 4.93-4.73 and 3.93–3.63 Ma); 2) The Iceland Sea is out of phase with the North Atlantic and the Norwegian Sea (Pliocene; 3.43–3.23 Ma); 3) The North Atlantic is out of phase with the Norwegian and Iceland Seas (future trend). Hence, out of phase relationships seem to be possible in equilibrium climates (Pliocene) as well as in response to transient forcing (CMIP6 SSP 126 low-emission future scenario). Since buoyancy is a key forcing for inflow of Atlantic Water to the Norwegian Sea, we investigate the impacts of buoyancy forcing on the phase relation between SST anomalies in the North Atlantic, Norwegian and Iceland Seas. This is done by performing a range of idealized experiments using the Massachusetts Institute of Technology general circulation model (MITgcm). Through these idealized experiments we can reproduce three out of four of the documented phase relations: in-phase relationships under weak to intermediate fresh water forcing over the Nordic Seas; the Iceland Sea out of phase with the North Atlantic and the Norwegian Sea under weak atmospheric warming over the Nordic Seas; and the North Atlantic out of phase with the Norwegian and Iceland Seas under strong atmospheric warming over the Nordic Seas. We suggest that the unexplained phase relation, when the Norwegian Sea SSTs are out of phase with the North Atlantic and the Iceland Sea, may reflect a response to a weakened Norwegian Atlantic Current compensated by a strong Irminger current, or an expanded East Greenland Current.

Bjørg Risebrobakken et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on egusphere-2022-959', Pepijn Bakker, 31 Oct 2022
  • RC2: 'Comment on egusphere-2022-959', Anonymous Referee #2, 04 Dec 2022

Bjørg Risebrobakken et al.

Bjørg Risebrobakken et al.

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Short summary
Four different phase relations are documented in past reconstructions, observation-based records and future projections of North Atlantic, Norwegian and Iceland Seas sea surface temperature relations. While in-phase is the expectation and the norm, out of phase relations occur in low and intermediate emission scenarios and in past warm climate states in equilibrium with a CO2 level comparable to the future scenarios. The out of phase relations may result from changes in buoyancy forcing.