Geomorphic and sedimentary signatures of early Holocene deglaciation in High Arctic fiords, Ellesmere Island, Canada: implications for deglacial ice dynamics and thermal regime

摘要

Integrated studies of glacial geomorphology, sedimentology, marine-limit elevations, and radiocarbon dating in two adjacent fiords on southwestern Ellesmere Island indicate that early Holocene regional deglaciation was characterized by a two-step retreat pattern, where initial rapid breakup of marine-based ice preceded slower, terrestrial retreat. These data also indicate interfiord variations in early Holocene deglacial thermal regime, and illustrate the role of fiord topography as a control on glacier retreat. In Starfish Bay, deglacial landform-sediment associations are preferentially located at fiord-side topographic irregularities, and record ice-proximal glaciomarine sedimentation during stillstands at pinning points. Abundant fine-grained subaquatic outwash indicates that the retreating trunk glacier was characterized by a warm-based thermal regime. The discrete location of these deposits and associated radiocarbon dates suggest rapid early Holocene deglaciation of the outer and middle fiord, interrupted by brief stillstands at pinning points, and subsequent stabilization and slower retreat in the inner fiord. Similar rapid early Holocene deglaciation occurred in Blind Fiord. However, the dominance of lateral meltwater channels and lack of fine-grained subaquatic outwash in this fiord suggest that trunk ice was predominantly cold-based during retreat. Initial rapid deglaciation was succeeded by stabilization and slower, terrestrial retreat when the trunk glacier reached the inner fiord. A prominent belt of glaciogenic landforms at the heads of both fiords is inferred to mark this stabilization. [References: 61]