Dynamic boreal summer atmospheric circulation response as negative feedback to Greenland melt during the MIS-11 interglacial

Abstract

Abstract. The unique alignment of orbital precession and obliquity during the Marine Isotope Stage 11 (MIS-11) interglacial produced perhaps the longest period of planetary warmth above preindustrial conditions in the past 800 kyr. Reconstructions point to a significantly reduced Greenland ice sheet volume during this period as a result, although the remaining extent and volume of the ice sheet are poorly constrained. A series of time slice simulations across MIS-11 using a coupled climate model indicates that boreal summer was particularly warm around Greenland and the high latitudes of the Atlantic sector for a period of at least 20 kyr. This state of reduced atmospheric baroclinicity, coupled with an enhanced and poleward-shifted intertropical convergence zone and North African monsoon, favored weakened high-latitude winds and the emergence of a single, unified midlatitude jet stream across the North Atlantic sector during boreal summer. Consequent reductions in the lower-tropospheric meridional eddy heat flux over the North Atlantic therefore emerge as negative feedback to additional warming over Greenland. The relationship between Greenland precipitation and the state of the North Atlantic jet is less apparent, but slight changes in summer precipitation appear to be dominated by increases during the remainder of the year. Such a dynamic state is surprising, as it bears stronger resemblance to the unified-jet state postulated as typical for glacial states than to the modern-day interglacial state.