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at site Hu84-21 (Figure 6) off Okak Trough but also at a
farther offshore site Hu91-94 (Figure 7) at Orphan Knoll.
During H1 and H2, the Hudson Strait ice stream reached
at least the middle of the continental shelf and may have
briefly extended farther seaward [Andrews et al., 1993;
Rashid and Piper, 2007]. On the other hand, ice probably
reached only the outlet of Hudson Strait and the innermost
shelf during H0 [Kirby and Andrews, 1999; Rashid and
Piper, 2007]. The presence of ash zone 1 in the Labrador
Sea [Ruddiman and Glover, 1987], transported in sea ice
from a major eruption at the Katla caldera in southern Iceland
during the transition to the YD [Bond et al., 1997], implies
that the surface circulation was probably similar to the pres-
ent. Under these ice margin conditions, the Labrador Current
could have restricted the distribution of freshwater plumes
and icebergs to a narrow corridor on the outer Labrador Shelf
and Labrador Slope. The Labrador Current may have been
stronger during H0 than during earlier H events, focusing
icebergs in a narrow trajectory zone at the shelf edge, as at
present [Chapman, 2000]. Glacial ice probably occupied the
inner Labrador Shelf, based on core chronology and seismic
pro
les in inner Karlsefni Trough [Hall et al., 1999]. Arctic
outflow was blocked by landfast ice until ~10 ka [Zreda et
al., 1999] and the Western Boundary Undercurrent, which
underlies the outer portion of the Labrador Current, followed
modern trajectories during H0 [Fillon and Duplessy, 1980].
5.5. Sedimentological Processes in the H1 and H0 Events
Sediment was dispersed during H events by ice rafting, in
sediment plumes, and by turbidity currents. During H1, ice
rafting carried sediment to the central Labrador Sea [Dow-
deswell et al., 1995; Rashid et al., 2003a] and into the open
North Atlantic Ocean [Grousset et al., 1993; Rashid and
Boyle, 2007]. The main sediment plume is recognized along
the eastern Canadian continental margin [Piper and Skene,
1998]. Carbonate-rich turbidites are present along the NA-
MOC [Rashid and Piper, 2007] and on the SAP [Piper and
Hundert, 2002].
We have estimated the volume of sediment deposited
by estimating the areal extent and thicknesses of H1 and
H0 (Table 2). Each bed is subdivided into deposits of
Table 2.
Estimates of Sediment Types in H0, H1, and a Major Subglacial Outburst on Laurentian Fan
a
Proportion
of Sediment
Volume of Each
Sediment Type (km
3
)
Mean
Thickness
(m)
Total
Volume
(km
3
)
Area
(km
2
10
6
)
References
a
Region
IRD Plume Turbidite
IRD Plume Turbidite
H0 Event
Sohm Abyssal Plain (SAP)
1
0.11
110
0
0
1
0
0
110
1, 2
Northwest Atlantic Mid-Ocean
Channel (NAMOC) spillover
0.1
0.4
40
0
0
1
0
0
40
1, 3
Plume
0.4
0.09
36
0.4
0.6
0
14.4
21.6
0
1, 4
Total by sediment type
b
(%)
8
12
81
H1 Event
Proximal plume
2
0.02
40
0.4
0.6
0
16
24
0
5
Middistance plume
0.1
0.4
40
0.2
0.8
0
8
32
0
5
Distal plume
0.1
0.3
30
0.05
0.95
0
1.5
28.5
0
5, 6
NAMOC proximal turbidites
0.5
0.02
10
0
0
1
0
0
10
3
NAMOC distal mud
0.1
0.4
40
0
0
1
0
0
40
3
SAP
1
0.12
120
0
0
1
0
0
120
2
North Atlantic IRD
0.2
1.6
320
0.8
2
0
256
640
0
7
Total by sediment type
b
(%)
24
62
14
The 19 ka Laurentian Fan Subglacial Outburst
Coarse load
150
0
0
1
0
0
150
8
Laurentian Fan mud
5
0.02
100
0
0
1
0
0
100
8
Distal Sohm AP
0.5
0.3
150
0
0
1
0
0
150
8
Scotian Slope mud
2
0.09
180
0.01
0.99
0
1.8
178.2
0
8
Total by sediment type
b
(%) <1 31 69
a
Sources are as follows: 1, data from this study; 2, Piper and Hundert [2002]; 3, H. Rashid, unpublished data on Labrador Sea cores; 4,
Tripsanas and Piper [2008a] and Tripsanas et al. [2007]; 5, Rashid et al. [2003a]; 6, Piper and Skene [1998]; and 7, Alley and MacAyeal
[1994]; 8, Tripsanas et al. [2008].
b
Estimated uncertainty on volume information is ±20%.
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