Ocean Controls onhigh-latitude Climate sensitivity - a Pliocene case study

The Pliocene Epoch (5.3-2.6 million years ago) is a warm period of particular interest, when boundary conditions of the climate system were similar to the present, but sea level was higher and today’s polar and subpolar regions were as warm as or warmer than predicted in future scenarios. High northern latitudes are thought to have been especially warm; however, how these warm, high-latitude conditions were maintained is an open question, in part given the apparently contradictory observational evidence in the Nordic Seas.

The Nordic Seas link the North Atlantic and Arctic Oceans, and is a small but dynamically important part of the global ocean. In today’s climate, they form a region of strong atmosphere-ocean exchange, vigorous mixing of water masses and deep convection. The Nordic Seas offer a unique opportunity to study the exchange of salt, heat and mass between the North Atlantic and Arctic oceans in situations with a warmer climate than at present. OCCP aims to resolve conflicting views on the role of the Nordic Seas in determining high northern latitude climate and the degree of Arctic amplification during a key warm period in Earth’s history, the Pliocene. We will adopt a multidisciplinary approach. New, multi-proxy data characterizing the Nordic Seas water column during the Pliocene will be generated and combined with published data from the North Atlantic/Arctic region. The reconstructions will be combined with results from model experiments designed to investigate the large-scale dynamics of the region. The model results will be used to identify key processes responsible for the observed high latitude climate of the Pliocene and the role of the Nordic Seas “gateway” between the North Atlantic and Arctic. This approach will enable us to make substantial progress towards understanding the mechanisms behind the apparent high sensitivity of the Arctic in warm climates, the role of the Nordic Seas in the arctic amplification of Pliocene warming, and will ultimately help constrain the long-term sensitivity of the climate system in a warming world.

The guiding hypotheses to be tested in this project are whether:

  • the ocean circulation and northern limb of the AMOC may operate differently from today under climatic boundary conditions close to modern.
  • prior estimates of Pliocene oceanic warmth and oceanic heat advection towards the Arctic are overestimated, and earlier estimates of Pliocene Arctic amplification may have been too high.