The extent of ice on the continental shelf off Hudson Strait during Heinrich events 1-3

2007 ◽  
Vol 44 (11) ◽  
pp. 1537-1549 ◽  
Author(s):  
Harunur Rashid ◽  
David JW Piper
Keyword(s):  
Debris Flow ◽  
Continental Shelf ◽  
Outer Shelf ◽  
Laurentide Ice Sheet ◽  
Ice Streams ◽  
Sea Floor ◽  
Heinrich Events ◽  
Heinrich Event ◽  
Seismic Reflection Profiles ◽  
Inner Continental Shelf

North Atlantic Heinrich events, which dispersed widespread sediment plumes and icebergs, originated principally from Hudson Strait ice streams of the Laurentide Ice Sheet. The dynamics and extent of these ice streams across the wide continental shelf seaward of Hudson Strait are not well understood. High-resolution airgun seismic reflection profiles from the outer shelf and slope show an acoustically incoherent, prograded unit at least 30 m thick. This unit has been sampled by piston cores and corresponds to a carbonate-rich diamicton unit interpreted as a glacigenic debris flow, locally overlain by carbonate-rich mud turbidites, dated as corresponding to Heinrich event 3 (H3). Younger glacigenic debris flow deposits are lacking. These data are compared with the seismic-stratigraphic record on the continental shelf, where a regional erosion surface at 10–200 m depth below the sea floor truncates Tertiary strata and is overlain by a 50 m thick diamicton (?subglacial till) sheet and is correlated with the H3 glacigenic debris flows. Above this unit, at least two distinct diamicton sheets terminate on the inner continental shelf. These data imply that grounded Laurentide ice crossed the continental shelf during H3, delivering large amounts of diamicton to the continental slope, but during the younger Heinrich events H1 and H2, no detectable record of diamicton was left on the outer shelf or slope. These findings account for observed differences between H3 and younger Heinrich events in the Labrador Sea.

scholarly journals Calving Bay dynamics and ice sheet retreat up the St. Lawrence Valley system

2011 ◽  
Vol 31 (3-4) ◽  
pp. 347-356 ◽  
Author(s):  
R. H. Thomas
Keyword(s):  
Continental Shelf ◽  
Ice Sheet ◽  
Lake Ontario ◽  
Complete Removal ◽  
Laurentide Ice Sheet ◽  
Ice Shelf ◽  
Ice Streams ◽  
Geological Evidence ◽  
Grounding Line ◽  
Flow Through

Ice streams that drain marine ice sheets are particularly susceptible to catastrophic retreat because they flow through bedrock troughs, and grounding line migration would produce a calving bay filled either with an ice shelf or with icebergs. Geological evidence suggests that a calving bay formed in the Laurentian Channel and the St. Lawrence valley after the late-Wisconsin maximum. Retreat rates in this calving bay are calculated for a variety of possible models assuming that locally the late-Wisconsin Laurentide ice sheet extended to the edge of the continental shelf. If an ice shelf forms in front of the retreating grounding line, and the shear stress between the ice shelf and its margins is one bar, retreat continues for only 150 km. Further retreat requires lubrication by ice with a strain-dependent preferred crystal fabric that develops between the ice shelf and its sides, or by complete removal of the ice shelf. Under these conditions the first 300 km of retreat takes at least 3000 to 6000 years. Thereafter, further retreat is rapid until, if a lubricated ice shelf is present, a new equilibrium grounding line is established about 1100 km from the edge of the continental shelf. If massive calving of icebergs occurred at, or near the grounding line, then retreat would continue up the St. Lawrence valley through to Lake Ontario. Of the various models considered, the minimum time taken for retreat from a point 300 km inland from the edge of the continental shelf through to Lake Ontario is about 2000 years.

USGS Advances in Integrated, High-Resolution Sea-Floor Mapping: Inner Continental Shelf to Estuaries

2007 ◽  
Author(s):  
Jane F. Denny ◽  
William C. Schwab ◽  
David C. Twichell ◽  
Thomas F. O'Brien ◽  
William W. Danforth ◽  
...  
Keyword(s):  
High Resolution ◽  
Continental Shelf ◽  
Sea Floor ◽  
Sea Floor Mapping ◽  
Inner Continental Shelf

scholarly journals Sea-floor texture and physiographic zones of the inner continental shelf from Salisbury to Nahant, Massachusetts, including the Merrimack Embayment and Western Massachusetts Bay

2015 ◽  
Author(s):  
Elizabeth E. Pendleton ◽  
Walter A. Barnhardt ◽  
Wayne E. Baldwin ◽  
David S. Foster ◽  
William C. Schwab ◽  
...  
Keyword(s):  
Continental Shelf ◽  
Massachusetts Bay ◽  
Sea Floor ◽  
Inner Continental Shelf

IODP Exp. 374 provides clues into the Antarctic Ice Sheet contribution to sea level changes

2021 ◽  
Author(s):  
Laura De Santis ◽  
Denise Kulhanek ◽  
Robert McKay
Keyword(s):  
Continental Shelf ◽  
Sea Level ◽  
Ocean Circulation ◽  
Ross Sea ◽  
Ice Sheet ◽  
Outer Shelf ◽  
Ice Streams ◽  
Antarctic Ice Sheet ◽  
Global Sea Level ◽  
The Antarctic

<p>The five sites drilled during International Ocean Discovery Program (IODP) Expedition 374 recovered the distal geological component of a Neogene latitudinal and depth transect across the Ross Sea continental shelf, slope and rise, that can be combined with previous records of ANDRILL and the Deep Sea Drilling Project Leg 28. This transect provides clues into the ocean and atmospheric forcings on marine ice sheet instabilities and provides new direct constraints for reconstructing the Antarctic Ice Sheet contribution to global sea level change. Site U1521 recovered a middle Miocene record that allows identification of the different processes that lead to the expansion and retreat of ice streams emanating from the East and West Antarctic Ice Sheets across the Ross Sea continental shelf. This site also recovered a semi-continuous, expanded, high-resolution record of the Miocene Climatic Optimum in an ice-proximal location. Site U1522 recovered a Pleistocene to upper Miocene sequence from the outer shelf, dating the step-wise continental shelf–wide expansion and coalescing of marine-based ice streams from West Antarctica. Thin diatom-rich mudstone and diatomite beds were recovered in some intervals that provide snapshot records of a deglaciated outer shelf environment in the late Miocene. Site U1523 targeted a Miocene to Pleistocene sediment drift on the outermost continental shelf and informs about the changing vigor of the eastward flowing Antarctic Slope Current (ASC) through time. Changes in ASC vigor is a key control on regulating heat flux onto the continental shelf, making the ASC a key control on ice sheet mass balance. Sites U1524 and U1525 cored a continental rise levee system near the flank of the Hillary Canyon. The upper ~50 m at Site U1525 belong to a large trough-mouth fan deposited to the west of the site. The lower 100 m at Site U1525 and the entire 400 m succession of sediment at Site U1524 recovered near-continuous records of the downslope flow of Ross Sea Bottom Water and turbidity currents, but also of ASC vigor and iceberg discharge. Analyses of Exp. 374 sediments is ongoing, but following initial shipboard characterization, the intial results of sample analysis, the correlation between downhole synthetic logs and the associated seismic sections provide insight into the ages and the processes of erosion and deposition of glacial and marine strata. Exp. 374 sediments are providing key chronological constraints on the major Ross Sea seismic unconformities, enabling reconstruction of paleo-bathymetry and assessment of the geomorphological changes associated with Neogene ice sheet and ocean circulation changes. Exp. 374 results are fundamental for improving the boundary conditions of numerical ice sheet, ocean, and coupled climate models, which are critically required for understanding past ice sheet and global sea level response during warm climate intervals. Such data will enable more accurate predictions of ice sheet behavior and sea level rise anticipated with future warming. </p>

Sidescan-sonar imagery of the shoreface and inner continental shelf, Wrightsville Beach, North Carolina

1998 ◽  
Author(s):  
E. Robert Thieler ◽  
William C. Schwab ◽  
Mead A. Allison ◽  
Jane F. Denny ◽  
William W. Danforth
Keyword(s):  
North Carolina ◽  
Continental Shelf ◽  
Sidescan Sonar ◽  
Inner Continental Shelf
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