Beyond the bipolar seesaw: Toward a process understanding of interhemispheric coupling

• Published in: Quaternary science reviews Vol. 192; pp. 27 - 46
• Main Authors: Pedro, Joel B., Jochum, Markus, Buizert, Christo, He, Feng, Barker, Stephen, Rasmussen, Sune O.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 15-07-2018
• Subjects: Antarctic Circumpolar Current; Antarctic Isotope Maximum; Atlantic Meridional Overturning Circulation; Bipolar ocean seesaw; Dansgaard–oeschger event; Millennial-scale climate variability; Sea ice; Southern Ocean; Dansgaard–oeschger event; Antarctic Circumpolar Current; Atlantic Meridional Overturning Circulation; Southern Ocean; Bipolar ocean seesaw; Millennial-scale climate variability; Antarctic Isotope Maximum; Sea ice
• ISSN: 0277-3791; 1873-457X
• DOI: 10.1016/j.quascirev.2018.05.005

The thermal bipolar ocean seesaw hypothesis was advanced by Stocker and Johnsen (2003) as the ‘simplest possible thermodynamic model’ to explain the time relationship between Dansgaard–Oeschger (DO) and Antarctic Isotope Maxima (AIM) events. In this review we combine palaeoclimate observations, theory and general circulation model experiments to advance from the conceptual model toward a process understanding of interhemispheric coupling and the forcing of AIM events. We present four main results: (1) Changes in Atlantic heat transport invoked by the thermal seesaw are partially compensated by opposing changes in heat transport by the global atmosphere and Pacific Ocean. This compensation is an integral part of interhemispheric coupling, with a major influence on the global pattern of climate anomalies. (2) We support the role of a heat reservoir in interhemispheric coupling but argue that its location is the global interior ocean to the north of the Antarctic Circumpolar Current (ACC), not the commonly assumed Southern Ocean. (3) Energy budget analysis indicates that the process driving Antarctic warming during AIM events is an increase in poleward atmospheric heat and moisture transport following sea ice retreat and surface warming over the Southern Ocean. (4) The Antarctic sea ice retreat is itself driven by eddy-heat fluxes across the ACC, amplified by sea-ice–albedo feedbacks. The lag of Antarctic warming after AMOC collapse reflects the time required for heat to accumulate in the ocean interior north of the ACC (predominantly the upper 1500 m), before it can be mixed across this dynamic barrier by eddies.
•We evaluate the thermal ocean seesaw hypothesis using simulations, data and theory.•The global ocean, not the Southern Ocean, accumulates heat when the AMOC collapses.•Eddies gradually mix the heat anomalies across the Antarctic Circumpolar Current, melting sea ice.•Ice-albedo feedback amplifies surface warming, increasing heat flux to Antarctica.