Joint Seminar: Arctic gateways and Northern Hemisphere glaciation

The climate of the late Pliocene (3.5-2.6 Ma) was considerably warmer than at present as

a result of elevated atmospheric CO2. This warm period was, however, briefly punctuated

by the M2 glacial event (c. 3.3 Ma) in which the Greenland ice sheet is believed to have

formed. The M2 is often described in the literature as a conventional glacial event where

ice grows over the subpolar continent in periods with low CO2 and low boreal summer

insolation. Here we show that additional feedbacks from changes in the ocean circulation

may in fact also have been important for this, and supposedly other glaciations to occur.

Pliocene experiments with the National Center for Atmospheric Research (NCAR) Community

Climate System Model version 4 (CCSM4) show a remarkable sensitivity of the

North Atlantic climate to the configuration of open and closed ocean gateways through

the Bering Strait (BS) and the Canadian Arctic Archipelago (CAA). The AMOC remains

vigorous (warm sea-surface conditions) for all configurations of open and closed gateways,

except for when BS is open and the CAA is closed. This configuration yields a concentrated

freshwater transport to the deep-convection regions around Greenland, which results in a

weakened AMOC and thus a significantly colder North Atlantic.

Using the latest generation of the NCAR coupled climate–ice-sheet model we explore the

importance of these SST feedbacks for Northern Hemisphere glacial inception, with a special

focus on the incipient Greenland ice sheet. Our results show that a conventional glacial

inception only yields small ice caps confined to mountainous and coastal regions of Greenland.

A larger ice sheet is however established when also allowing for the SST feedback.

The status of these ocean straits in the late Pliocene remains unknown, especially the CAA

straits because of the repeated glaciation of this region in the Quaternary. Nevertheless,

offline ice sheet model experiments suggest that it is comparatively easy—low CO2 and

low summer insolation are sufficient—to form a large grounded ice sheet in the Canadian

archipelago that supposedly can obstruct the ocean flow and thereby amplify the glacial

conditions.

Datum

05.10.2016

Uhrzeit

13:30 Uhr

Ort

Bundesstr. 53, room 022/023
Seminar Room 022/023, Ground Floor, Bundesstrasse 53, 20146 Hamburg, Hamburg

ReferentIn

Marcus Löfverström, National Center for Atmospheric Research (NCAR), Climate and Global Dynamics Division (CGD), Boulder, CO, USA

Chair

Marie-Luise Kapsch

Zur Übersicht