The Pliocene had a climate in equilibrium with a CO2 forcing comparable to the present (ca. 400 ppm), and it was 2-3°C warmer globally. Synthesised Pliocene (5.3-3.15 Ma) sea surface temperature (SST) records document variable equilibrium SST patterns in the Northern Seas, where the Norwegian Sea is out of phase with the SST changes taking place in the northeastern North Atlantic and Iceland Sea.
The latter record represents Arctic surface water, whereas the other two represent Atlantic water on its way north. Furthermore, the Pliocene SST gradient between the northeastern North Atlantic and the Norwegian Sea was enhanced relative to the Holocene and present, counterintuitive to what might be expected in a warmer world.
In the suggested synthesis paper, we will
- document the SST changes taking place over the course of the Pliocene, test if the anti-phase relationship of the shifting SST gradients is time-scale dependent,
- document and compare with SST patterns as seen in other sources of equilibrium scenarios (e.g. NorESM control and future runs and/or other databases) and existing long data sets (e.g. HadlSST),
- review existing relevant knowledge,
- set up a hypothesis related to, and an overview of, potential factors controlling the different equilibrium SST patterns and temperature gradients in the Northern
- Seas over long time scales (e.g. depth of the Greenland-Scotland Ridge and its influence on meridional heat transport, wind patterns, changes in the Arctic fresh water balance due to a closed Canadian Arctic Archipelago and on/off Bering Strait, Subpolar Gyre dynamics, and whether an enhanced gradient was related to surface or deep circulation change), for example using an in-house dynamical model (MITgcm) and existing Pliocene ESM runs,
- evaluate, relate and discuss the suggested factors’ relevance to the variable warmer world SST patterns and gradients.
The suggested paper idea will integrate a broad aspect of the BCCR competence on the Northern Seas to explore equilibrium states of the ocean under a globally warmer climate. We will utilize information from synthesised paleo-SST records and existing long models runs, including simplified and fully coupled climate models.
Paper aimed at Review of Geophysics or similar type of journal.
Leader: Bjørg Risebrobakken