Laurentide Ice Sheet Dynamics from 35 to 7
ka: Sr-Nd-Pb Isotopic Provenance of NW
North Atlantic Margin Sediments

Donald C. Barber,

PhD dissertation, Geological Sciences,
University of Colorado-Boulder, 2001

This dissertation presents Sr-Nd-Pb isotopic
sediment provenance data and radiocarbon
dates that elucidate the dynamics of the
northeastern Laurentide Ice Sheet during the
last glacial/deglacial cycle. These data
constrain the sources, quantities and timing of
Laurentide ice and meltwater inputs during
the 500 – 1,000 year-long intervals, termed
Heinrich (H) events, when icebergs inundated
the North Atlantic.
Key findings include: 1) Sediment from as far
west as Keewatin was transported to the
Labrador Sea during H-events, implicating an
ice stream flowing southeast down the axis of
Hudson Strait during these events. 2) An ice
stream in Cumberland Sound (north of
Hudson Strait) advanced onto the shelf
repeatedly during the Late Wisconsin. 3) On
the Labrador Sea slope, sediment
accumulation rates typically increased 8-fold
during H-events and the IRD-poor, laminated
silts and clays comprising the detrital
carbonate-rich H-layers imply that turbid
subglacial meltwater plumes coincided with
the increased iceberg flux. 4) Ice and
meltwater inputs from Hudson Strait (i.e.,
H-events) occurred less frequently and at
different times than those from the
Cumberland Sound ice margin; this
asynchrony implies non-climatic or complex
climatically forced behavior of the Hudson
Strait ice stream. 5) In the Labrador Sea, the
isotopic composition of the glacial
hemipelagic deposits is interpreted as a
binary mixture dominated by Canadian
Shield-derived sediment (>80%) with the
relative fraction of an East Greenland basaltic
end-member varying inversely with overall
Laurentide ice sheet extent. 6) The
east-central margin of the Greenland Ice
Sheet delivered icebergs and detritus to the
NW North Atlantic around the time of, and
possibly before, the Hudson Strait H-events.
7) Statistical age errors for down-core
time-series are minimized by using an
ordinary least-squares-fit regression for
depth-age models; however, the placement of
dates with respect to lithofacies boundaries is
a key consideration. 8) The deglaciation of
Hudson Bay and concomitant drainage of
proglacial Lakes Agassiz and Ojibway
occurred near the onset of the 8.2 kyr cold
event, implying that increased freshwater flux
to the North Atlantic triggered the cold event by
altering the ocean thermohaline circulation.

For more info email: dbarber@brynmawr.edu