Abrupt Climate Change Experiments: The Role of Freshwater, Ice Sheets and Deglacial Warming for the Atlantic Meridional Overturning Circulation

• Main Authors: Lohmann, G., Zhang, X., Knorr, G.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2016
• Subjects: Greenland; Eisschild*; Polarforschung
• Online Access: https://gfzpublic.gfz-potsdam.de/pubman/item/item_1577937; https://gfzpublic.gfz-potsdam.de/pubman/item/item_1577937_2/component/file_1577938/polfor.2016.013.pdf; https://gfzpublic.gfz-potsdam.de/pubman/item/item_1577937_2/component/file_1577939/polfor.2016.013_a.pdf

In this review paper we summarise a series of numerical abrupt climate change experiments in the context deglaciation. The effects of global warming, deglacial freshwater, and ice sheets for the termination of the last ice age are examined in a model of intermediate complexity and a fully coupled, coarse-resolution climate model. We find that gradual deglacial global warming induces an abrupt strengthening of the Atlantic Meridional Overturning Circulation (AMOC). More generally, if the system is in a bistable window, a linear forcing can yield non-linear AMOC changes. In this sense Northern Hemisphere freshwater hosing only modulates the timing of the AMOC onset. Furthermore, Northern Hemisphere freshwater hosing weakens the AMOC with a potential overshoot, after the freshwater forcing has stopped. Therefore, as a further hypothesis the onset of Bølling/Allerød (B/A) interstadial with warming over Greenland could be related to an increase in AMOC, which is induced by a declining freshwater forcing prior to or in parallel with the transition. In contrast, hosing in the Southern Hemisphere has a relatively minor influence on the AMOC. The associated climate signatures and mechanisms are explored and discussed in this study. In diesem Übersichtsbeitrag stellen wir eine Reihe von numerischen Experimenten zum abrupten Klimawandel am Ende der letzten Eiszeit vor. Die Auswirkungen der globalen Erwärmung, des deglazialen Süßwassers und der Eisschilde auf die Termination und Ozeanzirkulation werden in einem Modell mittlerer Komplexität und einem vollständig gekoppelten Klimamodell untersucht. Unsere Modellergebnisse vermitteln Einsichten in die abrupte Erwärmung in der Nordhemisphäre, das sogenannte Bølling/Allerød (B/A) Nordatlantik Interstadial, und der deglazialen Schmelzwasserpulse. Wir stellen fest, dass die deglaziale globale Erwärmung eine Verstärkung der atlantische Umwälzbewegung (Atlantic Meridional Overturning Circulation, AMOC) induziert. Wenn sich das System in einem bistabilen Fenster bewegt, kann ein ...