Sensitivity of Heinrich-type ice-sheet surge characteristics to boundary forcing perturbations

Abstract. Heinrich-type ice-sheet surges are one of the prominent signals of glacial

climate variability. They are characterised as abrupt, quasi-periodic episodes

of ice-sheet instabilities during which large numbers of icebergs are released from

the Laurentide ice sheet. The mechanisms controlling the timing and occurrence

of Heinrich-type ice-sheet surges remain poorly constrained to this day. Here,

we use a coupled ice sheet–solid Earth model to identify and quantify the

importance of boundary forcing for the surge cycle length of Heinrich-type

ice-sheet surges for two prominent ice streams of the Laurentide ice sheet – the

land-terminating Mackenzie ice stream and the marine-terminating Hudson ice

stream. Both ice streams show responses of similar magnitude to surface mass

balance and geothermal heat flux perturbations, but Mackenzie ice stream is more sensitive to

ice surface temperature perturbations, a fact likely caused by the warmer

climate in this region. Ocean and sea-level forcing as well as different frequencies of the same

forcing have a negligible effect on the surge cycle length. The simulations also

highlight the fact that only a certain parameter space exists under which ice-sheet

oscillations can be maintained. Transitioning from an oscillatory state to a

persistent ice streaming state can result in an ice volume loss of up to 30 %

for the respective ice stream drainage basin under otherwise constant climate

conditions. We show that Mackenzie ice stream is susceptible to undergoing such

a transition in response to all tested positive climate perturbations. This

underlines the potential of the Mackenzie region to have contributed to

prominent abrupt climate change events of the last deglaciation.