Repeated ice streaming on the northwest Greenland continental shelf since the onset of the Middle Pleistocene Transition

Andrew M W Newton,Mads Huuse,Paul C Knutz,David R Cox

doi:10.5194/tc-14-2303-2020

Abstract

Abstract. Ice streams provide a fundamental control on ice sheet discharge and depositional patterns along glaciated margins. This paper investigates ancient ice streams by presenting the first 3D seismic geomorphological analysis of a major glacigenic succession offshore Greenland. In Melville Bugt, northwest Greenland, six sets of landforms (five buried and one on the seafloor) have been interpreted as mega-scale glacial lineations (MSGLs) that provide evidence for extensive ice streams on outer palaeo-shelves. A gradual change in mean MSGL orientation and associated depocentres through time suggests that the palaeo-ice flow and sediment transport pathways migrated in response to the evolving submarine topography through each glacial–interglacial cycle. The stratigraphy and available chronology show that the MSGLs are confined to separate stratigraphic units and were most likely formed after the onset of the Middle Pleistocene Transition at ∼1.3 Ma. The MSGL record in Melville Bugt suggests that since ∼1.3 Ma, ice streams have regularly advanced across the continental shelf during glacial stages. High-resolution buried 3D landform records such as these have not been previously observed anywhere on the Greenland continental shelf margin and provide a crucial benchmark for testing how accurately numerical models are able to recreate past configurations of the Greenland Ice Sheet.

Highlights

The northwest sector of the Greenland Ice Sheet (GrIS) is currently experiencing some of the largest mass losses across the ice sheet (Mouginot et al, 2019)
The interpretation of the corrugated features as Mega-scale glacial lineations (MSGLs) set 5 is less robust due to the lack of 3D data, and whilst it is not possible to unequivocally rule out that these features are something else, such as iceberg scours, an interpretation of MSGLs is supported by the location of these features in topset strata above the glacial unconformity that marks the top of unit A9, suggesting the presence of grounded and erosive ice on the outer continental shelf, conditions generally associated with MSGL formation
This study provides a seismic geomorphological analysis offshore northwest Greenland and documents, for the first time, several sets of buried MSGLs on the Greenland margin

Summary

Introduction

The northwest sector of the Greenland Ice Sheet (GrIS) is currently experiencing some of the largest mass losses across the ice sheet (Mouginot et al, 2019). Seismic reflection data have been used to explore evidence of older glaciations and show that the GrIS repeatedly advanced and retreated across the continental shelves of west and east Greenland through much of the late Pliocene and Pleistocene (Hofmann et al, 2016; Knutz et al, 2019; Laberg et al, 2007; Pérez et al, 2018). These seismic data show that the GrIS extent has varied by hundreds of kilometres throughout the Pleistocene and offer additional constraining observations to borehole and outcrop data that provide conflicting evidence that Greenland could have been nearly ice-free or persistently icecovered for parts of the Pleistocene (Bierman et al, 2016; Schaefer et al, 2016). Whilst ice streams are thought to have been present in Melville Bugt since ∼ 2.7 Ma (Knutz et al, 2019), these landforms provide new, direct, and detailed evidence of ice flow pathways for six episodes of ice stream advance onto the outer continental shelf of Melville Bugt from ∼ 1.3 Ma

Background

Methods

Subglacial landforms

Palaeo-ice streams

Conclusions