Reply on RC1

Abstract

<strong class="journal-contentHeaderColor">Abstract.</strong> While subglacial hydrology is known to play a role in glacial dynamics on sub-annual to decadal scales, it remains unclear whether subglacial hydrology plays a critical role in ice sheet evolution on centennial or longer time-scales. Furthermore, several drainage topologies have been inferred but it is unclear which drainage topology is most applicable at the continental/glacial scale. More fundamentally, it is even unclear if the structural choice of subglacial hydrology truly matters for this context. Here we compare three subglacial hydrology topologies as to their contribution to surge behaviour for an idealized Hudson Strait like ice stream. We use the newly updated model BraHms2.0 and provide model verification tests. BraHms2.0 incorporates each of these systems: two process-based forms dominant in the literature (linked-cavity and poro-elastic) and a non-mass conserving zero-dimensional form (herein termed leaky-bucket) coupled to an ice sheet systems model (the Glacial Systems Model, GSM). We also assess the likely bounds on poorly constrained subglacial hydrology parameters and adopt an ensemble approach to study their impact and interactions within those bounds. We find that subglacial hydrology is an important system inductance for realistic ice stream surging but that the three formulations all exhibit similar surge behaviour. Even a detail as fundamental as mass conserving transport of subglacial water is not necessary for simulating a full range of surge frequency and amplitude. However, one difference is apparent: the combined positive and negative feedbacks of the linked-cavity system yields longer duration surges and a broader range of effective pressures than its poro-elastic and leaky-bucket counterparts.