Marine Ice Sheet Instability in the Former British-Irish Ice Sheet Linked to Rising Boreal Summer Insolation From 23 ka.

Abstract:

Recent work has shown that marine sectors of the remaining ice sheets could exhibit rapid deglaciation linked to potential changes in oceanic forcing factors. Our ability to identify potential causes of marine ice sheet instability is limited by the scarcity of suitable analogues from the palaeo-record where evidence of rapid deglaciation can be linked to changes in the various potential forcing factors.

Of the former Pleistocene ice sheets, the British-Irish Ice Sheet (BIIS) provides a useful analogue with large amounts of previous work providing detailed contextual information. Its western margin was marine terminating and drained by numerous fast flowing ice streams while its position next to a major surficial artery of the Atlantic Meridionial Overturning Circulation (AMOC) rendered it potentially sensitive to small climatic perturbations.

Here we present new cosmogenic exposure ages that constrain the collapse of a marine sector of the former British and Irish Ice Sheet to ca. 20 ka. By comparing our new terrestrial dating constraints to proximal marine sediment records, including a new δ¹⁸O_Nps record, we are able to untangle the possible forcing mechanisms of this instability. The collapse occurs during an interval of generally cold surface conditions without significant large-scale oceanic reorganization. Increased calving driven by an increase in surface melt provides an alternative potential mechanism to link marine ice sheet instability to an increase in summer air temperature driven by rising boreal insolation after 23 ka suggesting potential hypersensitivity to small forcings with implications for understanding the vulnerability of marine sectors of remaining ice sheets.