Late Wisconsinan glacial landsystems on Atlantic Canadian shelves: New evidence from multibeam and single‐beam sonar data

Abstract

Multibeam sonar surveys in the past decade, augmented by single-beam data from the OLEX charting system, reveal landsystems on Atlantic Canadian shelves that are diagnostic of Late Wisconsinan ice-sheet dynamics. Four landsystems are described. (1) The Bay of Fundy landsystem comprises two contrasting sets of bedforms, and is interpreted as evidence of topographically controlled fast-flowing ice adjacent to slower-moving ice.(2) The German Bank landsystem off southwest Nova Scotia is comprised of glacially fluted terrain overprinted by De Geer moraines and arcuate recessional moraines. We infer that a flow of grounded glacial ice out of the Bay of Fundy was followed by steady retreat, punctuated by at least one major re-advance. (3) The Placentia Bay landsystem consists of a convergent field of streamlined landforms with superimposed De Geer moraines, overprinted in one area by flutings. We infer that this landsystem was formed in the onset zone of fast-flowing ice, and that overprinting was due to a re-advance of ice from offshore. (4) The south coast of Newfoundland landsystem, which includes arcuate, fjord-mouth moraines and a coast-parallel, fluted moraine, indicates strong topographic control on a retreating marine ice margin as it reached a fjord coastline. These submarine glacial landsystems are not inconsistent with a conceptual model showing Late Wisconsinan ice advance to shelf edges, rapid calving retreat along deepwater channels and slower retreat of ice margins grounded in shallow water. The re-advances documented two of the study areas have parallels in the Last British Ice Sheet, confirming that the reorganization of marine-based ice sheets, caused by calving in embayments, led to internally forced re-advances.

Ice streams in the Laurentide Ice Sheet: Identification, characteristics and comparison to modern ice sheets

“…25 in Fig. 12; Grant, 1989;Keigwin and Jones, 1995;Shaw et al, 2006Shaw et al, , 2009Eyles and Putkinen, 2014). This ice stream occupied a well-defined trough that runs for more than 700 km from the Gulf of St Lawrence to the shelf edge, and with an overdeepening of about 400 m and a width of 70 to 100 km.…”

“…3). More extensive datasets are available from Atlantic Canada, which records a number of ice streams operating in glacial troughs carved into the continental shelf (Shaw, 2003;Shaw et al, 2006;Todd et al, 2007;Shaw et al, 2009;Todd and Shaw, 2012;Shaw et al, 2014). In their updated inventory, Margold et al (2015) also used the International Bathymetric Chart of the Arctic Ocean (IBCAO: Jakobsson et al, 2000) and more detailed swath bathymetry data from the Canadian Arctic (ArcticNet, 2013) to identify several new ice streams and confirm others that were previously hypothesised based only on terrestrial evidence.…”

“…45 and 130 in Fig. 12; Shaw, 2003;Shaw et al, 2006Shaw et al, , 2009Rashid et al, 2012), and which fed into the Laurentian Channel Ice Stream to the south. Ice from Newfoundland was also drained through the Placentia Bay-Halibut Channel Ice Stream (no.…”

“…This ice stream occupied a well-defined trough that runs for more than 700 km from the Gulf of St Lawrence to the shelf edge, and with an overdeepening of about 400 m and a width of 70 to 100 km. As such, a deep calving bay has been inferred to have developed in the Gulf of St Lawrence during deglaciation, forcing a significant retreat of the Laurentian Channel Ice Stream at the time when ice complexes still survived on Newfoundland and Nova Scotia, and drained to the ocean through several smaller ice streams (Stea et al, 1998;Shaw, 2003;Shaw et al, 2006;Todd et al, 2007;Shaw et al, 2009;Todd and Shaw, 2012). Indeed, Newfoundland hosted an independent ice complex that was drained to the north and north-east by ice streams in the Notre Dame Channel and the Trinity Trough (nos.…”

Deglaciation of the Laurentide Ice Sheet from the Last Glacial Maximum

“…Much of the evidence was based on the terrestrial glacial geological record, but the recognition of discrete layers of ice rafted debris (IRD) in North Atlantic sediment cores (Heinrich, 1988) had also begun to implicate episodic ice streaming, particularly in Hudson Strait, as being primarily responsible for their deposition (Bond et al, 1992;Andrews and Tedesco, 1992;MacAyeal, 1993;Marshall and Clark, 1997a, b;Andrews, 1998). In addition, the burgeoning growth of marine geophysical techniques saw a large number of ice stream footprints identified in offshore settings, particularly in Atlantic Canada (Shaw, 2003;Shaw et al, 2006;Todd et al, 2007;Shaw et al, 2009), but also in the Canadian Arctic Archipelago (MacLean et al, 2010) and in Hudson Bay (Ross et al, 2011). These techniques, allied with the growth of remote sensing studies across large regions of the ice sheet bed enabled a large number of ice streams to be identified (e.g.…”