The variety and distribution of submarine glacial landforms and implications for ice-sheet reconstruction

Abstract

Glacimarine processes affect about 20% of the global ocean today, and this area expanded considerably under cyclical full-glacial conditions during the Quaternary (Fig. 1) . Many of the submarine landforms produced at the base and margin of past ice sheets remain well preserved on the seafloor in fjords and on high-latitude continental shelves after the retreat of the ice that produced them. These glacial landforms, protected from subaerial erosion and beneath wave-base and tidal currents in water that is often hundreds of metres deep, are gradually buried by both hemipelagic and glacimarine sedimentation; they may be preserved over long periods in the geological record if palaeocontinental shelves are not reworked by subsequent glacier advances or bottom currents ). This means that, first, submarine glacial landforms can be observed at or close to the modern seafloor after retreat of the last great ice sheets from their most recent Quaternary maximum about 18-20 000 years ago using swath-bathymetric mapping systems and, secondly, buried glacial landforms may also be identified and examined within glacial-sedimentary sequences from Quaternary and earlier ice ages using seismic-reflection methods.The development of multibeam echo sounding over the past two decades, coupled with high-accuracy GPS positioning, has allowed morphological mapping of the seafloor at an unprecedented level of detail. In this paper, the variety of submarine glacial landforms observed in modern, Quaternary and more ancient sediments is described. Landforms produced subglacially, those formed at and beyond marine ice-sheet margins, together with the slope processes and bottom currents likely to result in their reworking, are considered along with the sediment volumes of these landforms and the time they take to develop. This is followed by discussion of the significance of submarine glacial landforms and landform-assemblages for reconstruction of the form and flow of past ice sheets, including the former extent and flow direction of ice sheets, whether they are flowing fast as ice streams or slowly in inter-ice stream areas, the nature and rate of ice-sheet deglaciation, conditions at past ice-sheet beds, and inferences on the characteristics of the basal hydrological system and past climatic conditions.

Sedimentary processes at ice sheet grounding‐zone wedges revealed by outcrops, Washington State (USA)

“…Lidar data from Whidbey Island reveal that these features possess foreset slopes of 4-10°, exhibit sinuous topset-foreset crestlines, and are overprinted by lineations noted above (Figure 4). These features are tentatively interpreted as GZWs, given the strong geomorphological resemblance to known GZWs (Ottesen et al, 2005;Dowdeswell et al, 2016;Halberstadt et al, 2016;Simkins et al, 2016Simkins et al, , 2017b and internal stratigraphic architecture which reflects grounding zone processes, to be discussed in detail in later sections. These features are tentatively interpreted as GZWs, given the strong geomorphological resemblance to known GZWs (Ottesen et al, 2005;Dowdeswell et al, 2016;Halberstadt et al, 2016;Simkins et al, 2016Simkins et al, , 2017b and internal stratigraphic architecture which reflects grounding zone processes, to be discussed in detail in later sections.…”

The De Long Trough: a newly discovered glacial trough on the East Siberian continental margin

“…The acoustic stratigraphy and morphology of the continental slope seaward of the grounding line deposits is typical of TMF sediments described on other high-latitude continental margins (Ó Cofaigh et al, 2003;Dowdeswell et al, 2016;Batchelor and Dowdeswell, 2014). The laterally discontinuous lenses of acoustically transparent material are glacio-genic debris flows and are interspersed with segments of acoustically laminated sediments, deposited when the ice stream retreated from the shelf edge.…”

“…3). TMFs commonly approach areas of 10 3 -10 5 km 2 and are most pronounced on shallow continental slopes (< 4 • ) (Ó Cofaigh et al, 2003;Dowdeswell et al, 2016). The TMF in front of the De Long Trough has an average slope angle of 1.2 • and is steeper above 1300 m b.s.l.…”

“…MSGL are often found beneath and/or on top of GZWs (Jakobsson et al, 2012a), which supports the interpretation that GZW formation occurs during stillstands of fast-streaming ice. GZWs typically have much larger length-to-height ratios than terminal moraines, which are more commonly found in inter-ice stream regions on glaciated margins and are associated with slower ice flow velocities (Ottesen and Dowdeswell, 2009;Batchelor and Dowdeswell, 2015;Dowdeswell et al, 2016).…”

Evidence for Multiple Superposed Fluvial Deposits Within Reuyl Crater, Mars

“…Morphologically, these SRs (Figures a and ) appear similar to eskers, whose origin is related to glacial landforms (Burr et al, ; Lefort et al, ). Further, some terrestrial eskers have been reported with fan‐shaped deposits or outwash fans (Chandler et al, ; Dowdeswell et al, ; Gorrell & Shaw, ). In this regard, we examined their glacial association and found that (1) Reuyl is located in the near‐equatorial region, where the probability of glacial features is low.…”