Controls on the early Holocene collapse of the Bothnian Sea Ice Stream

Abstract

New high‐resolution multibeam data in the Gulf of Bothnia reveal for the first time the subglacial environment of a Bothnian Sea Ice Stream. The geomorphological record suggests that increased meltwater production may have been important in driving rapid retreat of Bothnian Sea Ice during deglaciation. Here we apply a well‐established, one‐dimensional flow line model to simulate ice flow through the Gulf of Bothnia and investigate controls on retreat of the ice stream during the post‐Younger Dryas deglaciation of the Fennoscandian Ice Sheet. The relative influence of atmospheric and marine forcings are investigated, with the modeled ice stream exhibiting much greater sensitivity to surface melting, implemented through surface mass balance and hydrofracture‐induced calving, than to submarine melting or relative sea level change. Such sensitivity is supported by the presence of extensive meltwater features in the geomorphological record. The modeled ice stream does not demonstrate significant sensitivity to changes in prescribed ice stream width or overall bed slope, but local variations in basal topography and ice stream width result in nonlinear retreat of the grounding line, notably demonstrating points of short‐lived retreat slowdown on reverse bed slopes. Retreat of the ice stream was most likely governed by increased ice surface meltwater production, with the modeled retreat rate less sensitive to marine forcings despite the marine setting.

Subglacial water storage and drainage beneath the Fennoscandian and Barents Sea ice sheets

“…Between the predicted subglacial lakes (Fig. 7a), a suite of subglacial meltwater landforms are observed, including eskers and meltwater channels up to 4 km wide (Clason et al, 2016;Greenwood et al, 2017Greenwood et al, , 2016. High energy and high discharge meltwater systems are invoked to explain the observed channel features (Greenwood et al, 2016), and a large, periodically draining subglacial lake proposed upstream of the drainage features (Greenwood et al, 2017) is supported by our results (Fig.…”

“…3a,b) which are prone to drainage with small shifts in ice geometry. Clason et al (2016) suggest that ice flow and grounding line retreat through the Bothnian Sea was influenced by surface meltwater enhanced basal sliding, which is supported by evidence for highdischarge subglacial meltwater conduits (Greenwood et al, 2017(Greenwood et al, , 2016. A propensity for subglacial lake formation in the Gulf of Bothnia and surrounding areas (Fig.…”

Mid-Holocene thinning of David Glacier, Antarctica: chronology and controls

“…Originally designed to track groundingline migration using a moving grid, the flowline model we employ has been described fully elsewhere (e.g. Vieli and Payne, 2005;Nick et al, 2009;Jamieson et al, 2012;Enderlin et al, 2013;Jamieson et al, 2014;Clason et al, 2016;Whitehouse et al, 2017). The underlying theory and governing equations are outlined in Vieli and Payne (2005), and here we describe the components pertinent to our research questions.…”

A 725‐year integrated offshore terrestrial varve chronology for southeastern Sweden suggests rapid ice retreat ~15 ka BP

“…2010; Clason et al . 2016). The style, mechanisms and timing of flow and retreat in the offshore catchment, as well as the nature of coupling to the terrestrial catchment are, however, very poorly constrained (Greenwood et al .…”

“…The southeast corner of Sweden marks a transition between predominantly terrestrial-based ice-sheet retreat over southernmost Sweden and predominantly subaqueous retreat through the BIL. The BIL during deglaciation likely hosted reactivated ice streams (Houmark-Nilsen & Kjaer 2003;Kjaer et al 2003) that made the offshore catchment dynamically distinct from the terrestrial portion and subject to additional retreat forcing: mass loss from not only surface melt, but also subaqueous melt and iceberg calving (Van Den Broeke et al 2009;Rignot et al 2010;Clason et al 2016). The style, mechanisms and timing of flow and retreat in the offshore catchment, as well as the nature of coupling to the terrestrial catchment are, however, very poorly constrained (Greenwood et al 2017).…”