11 Jan 2022
11 Jan 2022
Status: a revised version of this preprint is currently under review for the journal CP.

The first 250 years of the Heinrich 11 iceberg discharge: Last Interglacial HadGEM3-GC3.1 simulations for CMIP6-PMIP4

Maria Vittoria Guarino1,2, Louise Sime1, David Schroeder3, and Jeff Ridley4 Maria Vittoria Guarino et al.
  • 1British Antarctic Survey, Cambridge, UK
  • 2Department of Engineering and Physical Sciences, University of Leeds, UK
  • 3Department of Meteorology, University of Reading, UK
  • 4Met Office, Exeter, UK

Abstract. The Heinrich 11 event is simulated using the HadGEM3 model during the Last Interglacial period. We apply 0.2 Sv of meltwater forcing across the North Atlantic during a 250 years long simulation. We find that the strength of the Atlantic Meridional Overturning Circulation is reduced by 60 % after 150 years of meltwater forcing, with an associated decrease of 0.2 to 0.4 PW in meridional ocean heat transport at all latitudes. The changes in ocean heat transport affect surface temperatures. The largest increase in the meridional surface temperature gradient occurs between 40–50 N. This increase is associated with a strengthening of 20 % in 850 hPa winds. The stream jet intensification in the Northern Hemisphere in return alters the temperature structure of the ocean heat through an increased gyre circulation, and associated heat transport (+0.1–0.2 PW), at the mid-latitudes, and a decreased gyre ocean heat transport (−0.2 PW) at high-latitudes. The changes in meridional temperature and pressure gradients cause the Intertropical Convergence Zone (ITCZ) to move southward, leading to stronger westerlies and a more positive Southern Annual Mode (SAM) in the Southern Hemisphere. The positive SAM influences sea ice formation leading to an increase in Antarctic sea ice. Our coupled-model simulation framework shows that the classical "thermal bipolar see-saw'' has previously undiscovered consequences in both Hemispheres: these include Northern Hemisphere gyre heat transport and wind changes; alongside an increase in Antarctic sea ice during the first 250 years of meltwater forcing.

Maria Vittoria Guarino 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 cp-2021-187', Anonymous Referee #1, 06 Mar 2022
    • AC1: 'Reply on RC1', Maria Vittoria Guarino, 07 Feb 2023
  • RC2: 'Comment on cp-2021-187', Juan Muglia, 08 Mar 2022
    • AC1: 'Reply on RC1', Maria Vittoria Guarino, 07 Feb 2023

Maria Vittoria Guarino et al.

Maria Vittoria Guarino et al.


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Short summary
We investigate the response of the atmosphere, ocean and ice domains to the large discharge of glacial meltwater occurred during the Last Interglacial period from the melting Laurentide Ice Sheet (Heinrich 11 event). We show that the signal originated in the North Atlantic travels great distances across the globe. It modifies the ocean gyre circulation in the Northern Hemisphere as well as the belt of westerly winds in the Southern Hemisphere, with consequences for Antarctic sea ice.