The Northwestern Greenland Ice Sheet During The Early Pleistocene Was Similar To Today

Abstract

The multi‐million year history of the Greenland Ice Sheet remains poorly known. Ice‐proximal glacial marine diamict provides a direct but discontinuous record of ice sheet behavior; it is underutilized as a climate archive. Here, we present a novel multiproxy analysis of an Early Pleistocene marine diamict from northwestern Greenland. Low cosmogenic nuclide concentrations indicate minimal near‐surface exposure, similar to modern terrestrial sediment. Detrital apatite (U‐Th‐Sm)/He (AHe) ages all predate glaciation by >150 million years, suggesting the northwestern Greenland Ice Sheet had, by 1.9 Ma, not yet incised fjords of sufficient depth to excavate grains with young AHe ages. The diamict contains terrestrial plant leaf wax, likely from land surfaces surrounding the ice sheet. These data indicate that a persistent, dynamic ice sheet existed in northwestern Greenland by 1.9 Ma and that diamict is a useful archive of ice sheet history and process.

Measuring multiple cosmogenic nuclides in glacial cobbles sheds light on Greenland Ice Sheet processes

“…The cobbles were most likely derived from areas of warm-based ice, or areas that had warm-based ice during at least one time, in order for plucking or freeze-on to have occurred. This overrepresentation of erosive areas is similar to biases in records developed from marine sediment cores (Bierman et al, 2016;Christ et al, 2019;Flesche-Kleiven et al, 2002;Helland and Holmes, 1997;Larsen et al, 1994) and studies of sediment emanating from glacial drainages (Nelson et al, 2014). The cobbles therefore resulted from processes operating in sediment source areas beneath the ice sheet, presumably areas of warm-based and erosive ice, rather than the subglacial landscape as a whole.…”

“…However, the depth of scouring, spatial distribution of erosive versus non-erosive areas, and mechanisms of sediment entrainment and transport remain uncertain due to the inaccessibility of the subglacial landscape. Ice retreat during interglacial periods can expose a limited view of surfaces that are usually covered by ice, and studies of sediments deposited in the marine realm (Bierman et al, 2016;Christ et al, 2019;Flesche-Kleiven et al, 2002;Helland and Holmes, 1997;Larsen et al, 1994) provide an offshore view of glacial processes. Analysis of bedrock at the bottom of ice cores (Schaefer et al, 2016) provides a direct sampling of the subglacial landscape, albeit at a single point in space.…”

A multimillion-year-old record of Greenland vegetation and glacial history preserved in sediment beneath 1.4 km of ice at Camp Century

“…Ice cover grew substantially at 3.3 Ma ( 14) and culminated in an expanded GrIS by 2.7 Ma (1). Cosmogenic isotopic analyses of IRD and other glacial-marine sediment suggest that glacial erosion began stripping the preglacial landscape by 7 Ma and had eroded most shallow regolith by 1.8 to 2.0 Ma (2,15). Charcoal and organic debris in outwash near the Hiawatha Crater (16) and pollen in marine sediment in Baffin Bay and the Labrador Sea indicates that boreal forests in humid, cool-temperate to sub-Arctic climates during the Late Pliocene transitioned to tundra vegetation in a cold polar climate during the Early Pleistocene (17,18).…”

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

“…Both in the present and in the geological past, ice streams have been important conduits for ice sheet mass redistribution and sediment delivery to ice sheet margins (Vorren and Laberg, 1997). Mega-scale glacial lineations (MSGLs) are elongated landforms (typically 1-10 km long) that form by the streamlining (Clark et al, 2003) or accretion of subglacial sediments (Spagnolo et al, 2016) beneath fast-flowing ice (Clark, 1993). This association is supported by observations of similar MSGL features beneath the present-day Rutford Ice Stream in West Antarctica (King et al, 2009).…”