LARGE TABULAR ICEBERGS AND ICE ISLANDS OFF EASTERN
CANADA IN 2001-2003 AND THEIR PROBABLE SOURCE
I. K. Peterson
Fisheries and Oceans Canada, Dartmouth, Canada
ABSTRACT
In 2002 and 2003, offshore operators on the Grand Banks reported an unusually large
number of ice islands and large tabular icebergs up to 20 million tonnes, with drafts
of 65 to 80m. This paper describes sightings of large tabular icebergs and ice islands
in 2001 to 2003 north of the Grand Banks, from Lancaster Sound in the Canadian
Arctic Archipelago to the Labrador and Newfoundland shelves. Based on the
dimensions and surface appearance of the icebergs, the most probable source is the
Petermann glacier. MODIS imagery shows large pieces of ice near the front left the
glacier fjord in August 2000, and large segments broke off the glacier front in the
summer of 2001. Despite above-average calving rates on the eastern side of the
Petermann glacier in 2000 to 2001, the glacier front was within the historical limits.
INTRODUCTION
Icebergs represent a major hazard for offshore structures and marine transportation
off Newfoundland and Labrador. In 2002, offshore operators on the Grand Banks
reported an unusually large number of ice islands and large tabular icebergs
(Stoermer and Rudkin, 2003), which were up to 2km long and over 20 million tonnes,
with a draft of 65 to 80m and a freeboard of 9 to 10m; large numbers were also
observed the following ice season. These icebergs are of particular concern for the
offshore industry because of their large mass and shallow depth, as they are capable
of drifting onto the Grand Banks without grounding. Although the icebergs in open
water can be detected and tracked relatively easily by aircraft and satellite imagery,
their large mass poses a considerable challenge for iceberg management (iceberg
deflection by towing or water cannons). In addition, the icebergs can potentially
produce a large number of small icebergs, bergy bits and growlers which are
particularly hazardous to marine transportation.
The term “ice island” was used in 1952 to refer to large ice masses with lengths as
high as 29km, observed in the Arctic Ocean and Arctic Archipelago between 1946
and 1950 (Koenig et al., 1952) and thought to have originated from the Ellesmere
Island ice shelves. Thus the World Meteorological Organization (WMO) defines an
ice island as “A large piece of floating ice protruding about 5 m above sea level,
which has broken away from an Arctic ice shelf. They have a thickness of 30 to 50 m
and an area of a few thousand square metres to 500 sq. km or more. They are usually
characterized by a regularly undulating surface giving a ribbed appearance from the
air.”
It was noted by Helk and Dunbar (1953) that relatively thin tabular icebergs from
several glaciers in north Greenland often resemble ice islands from the Ellesmere
Island ice shelves. Thus in recent years, “ice island” has been used to refer to them as
well (eg. Higgins, 1989). The glaciers from which they originate have floating
sections, or glacier tongues. The terminal parts break into km-sized “ice islands” that
during long periods are hindered from drifting away by semi-permanent fast-ice in the
fjords or on the inner shelf. Of the North Greenland glaciers capable of producing
large tabular icebergs classifiable as ice islands, only icebergs from the Petermann
glacier and possibly the Ryder glacier are likely to drift south through Nares Strait to
Baffin Bay (Higgins, 1989).
A large tabular iceberg with a length of about 750m and a freeboard of 4 to 5m
observed east off Newfoundland in 1976 was described by Robe et al. (1977). They
suggested three possible sources: the Ward Hunt Ice Shelf, the Petermann Glacier, or
the Humboldt Glacier. However according to Dunbar (1978), the far most probable
source was the Petermann Glacier, because (a) icebergs from the Humboldt Glacier
are higher, of smaller areal extent, and tend to ground in Kane Basin where they
deteriorate, (b) ice islands from the Ward Hunt Ice Shelf have a different surface
pattern, and none were observed in Nares Strait between August 1974 and spring
1975, (c) the low flat shape and surface characteristics of the iceberg are consistent
with the Petermann glacier.
The sightings of ice islands and large icebergs (>300m long) off Eastern Canada from
1900 to 1991 are summarized in Newell (1993). The occurrence is extremely
sporadic, with none documented between 1978 and 1991. However, it is likely that
low icebergs (<10m high) are under-reported because they can be confused with
heavy multi-year floes (Newell, 1993).
Large tabular icebergs observed off Newfoundland in 2002 are described in Stoermer
and Rudkin (2003). Because of the danger such icebergs pose for offshore structures,
a study is underway to compile photographs and other information on large tabular
icebergs and iceberg-producing glaciers, largely as an aid for identifying the source of
the icebergs. This paper describes sightings of large tabular icebergs and ice islands in
2001 to 2003 north of the Grand Banks, from Lancaster Sound to the Labrador and
Newfoundland shelves. It then discusses the most probable source based on the
scientific literature, with additional evidence from satellite imagery.
Ward Hunt Ice Shelf
Ryder Glacier
Petermann Glacier
Lancaster Sound
Humboldt Glacier
Bylot Is.
GREENLAND
Baffin Is.
Voisey’s Bay
LABRADOR
NFLD
GRAND BANKS
Figure 1. Locations of sightings of large tabular icebergs and ice islands in 2001 to
2002 (dots, lower case letters), and 2002 to 2003 (crosses, upper case letters). The
location of a low debris-covered iceberg in Nares Strait (Zentilli et al., 2003) is shown
by an “x “.
LARGE TABULAR ICEBERG AND ICE ISLAND SIGHTINGS
The sightings of ice islands and large tabular icebergs in 2001 to 2003 are
summarized in Figure 1. The sources of the sightings include (a) the Canadian Ice
Service (b) Stoermer and Rudkin (2003), (c) the International Ice Patrol Iceberg
Sightings Database, and (d) D. Christian of C-CORE.
In the Lancaster Sound area, three ice islands were sighted by the CIS in October
2001. The first ice island was originally sighted north of Lancaster Sound off Devon
Island earlier in the fall, but drifted into the northern end of the channel between
Bylot Island and Baffin Island and was sighted on October 27, 2001. It remained
inside the channel until the summer of 2002, when it emerged from the eastern end of
the channel. It then drifted south-eastward along the coast of Baffin Island where it
was encountered by the icebreaker CCG Louis St. Laurent in October 2002 (Fig. 2,
left). The size was estimated to be 2.4km by 2.0km with a minimum freeboard of 9m,
but about twice that in the centre.
Figure 2. Ice island off Baffin Island (69˚30’N 65˚27’W) on 26 Oct 2002, with CCG
Icebreaker Louis St. Laurent, (left). Ice island grounded off Labrador coast near
Voisey’s Bay at 56˚08’N 59˚56’W from 09 April to 21 April 2003 (right). Photos
courtesy of CIS.
The second ice island was sighted on October 27, 2001 east of Bylot Island (at
73˚20’N 76˚07’W). An ice island believed to be the same one was sighted on April
19, 2002 on Nain Bank off the Labrador coast. The third ice island in the Lancaster
Sound area was sighted on October 27, 2001 (at 74˚40’N 77˚00’W).
In 2002, an ice island was sighted off Bylot Island on October 18, and tagged with a
beacon. It drifted towards Bylot Island and remained in fast ice off the east coast of
the island until early Aug 2003, but the beacon signal was lost on 6 Aug 2003.
Many ice island fragments and large tabular icebergs were observed farther south in
the springs of 2002 and 2003 (Fig. 1). Many of these may have originated from the
first three ice islands described above. One of the icebergs, observed in Conception
Bay in May 2002 by D. Christian (C-CORE), was covered with rock and soil debris.
It was estimated to be 250 to 300m long by 50 to 60m wide by 6 to 7m high. The
debris on the iceberg appears similar to that seen on a low medium iceberg in Nares
Strait on 17 August 2001. Based on geological analysis, the latter iceberg is thought
to have originated from the Petermann Glacier, and the debris of the iceberg may
have resulted from landslides or rockfalls along the steep valley walls (Zentilli et al.,
2003).
Another example of an ice island was observed grounded off Voisey’s Bay on April
9, 2003 (Fig. 2, right), and a beacon was placed on it. The ice island remained
stationary until April 21 when the beacon’s signal was lost. Water depths in the
vicinity of the ice island range from 64 to 160m.
PETERMANN GLACIER
General Description
A photograph of the front of the Petermann Glacier (Fig. 3, taken in August 2003 by
D. Forcucci of the U.S. Coast Guard), shows that the surface appearance is very
similar to that of the ice islands and large tabular icebergs observed to the south in
2001 to 2003, and unlike the ribbed appearance of ice islands from the Ward Hunt Ice
Shelf (Jeffries, 1992). It is also similar to the icebergs shown in Robe et al. (1977)
and Dunbar (1978), believed to be from the Petermann glacier.
Figure 3. Petermann Glacier looking toward western side, 10 Aug 2003. Photo
courtesy Dave Forcucci (USCG).
Measurements collected in 1978 indicate that the freeboard of the Petermann glacier
front is 8 to 10m for the eastern margin (1.3km wide), 4 to 6m for the central region
(12km wide) and 2 to 7m for the western margin (2.2km wide), implying glacier front
thicknesses of 72, 40 and 32 m respectively (Higgins, 1991). More recent
measurements are in agreement, with a glacier thickness at the front of about 50m,
but closer to 100m at the eastern end (Eric Rignot, pers. comm.). Thus the freeboard
of the large tabular iceberg observed in 1976 (4 to 5m, Robe et al, 1977) is in
agreement with the freeboard in the main central region. However, the observed
freeboards of the tabular icebergs and ice islands in 2001 to 2003 (9 to 10m) are
somewhat high for the main central region and western margin, but are consistent
with the glacier freeboard for the eastern margin. It is also possible that the glacier
freeboards are larger just inside the glacier front where calving occurs.
The width of the Petermann glacier front is 15.5km wide, the glacier speed is about
0.9km/yr, and the average volume flux at the glacier front is 0.59 km3/yr (Higgins,
1991). This is equivalent to an ice mass flux of 530 million tonnes per year, and an
ice area flux of 14 km2 per year. The position of the glacier front appears to have
remained stable within about 15km since 1876, with segments up to 12km x 10km
breaking away at intervals of 5 to 10 years or more (Higgins, 1991).
MODIS Imagery
MODIS (Moderate Resolution Imaging Spectroradiometer) images from the Terra
satellite are shown in Figure 4 from 31 July 2000 to 07 September 2004. Kennedy
Channel is toward the left, and the eastern margin of the glacier is toward the top of
the images. The first image (31 July 2000) shows many large ice masses, presumably
ice islands, along the eastern margin.
Long fractures or crevasses are also visible on both sides of the glacier, and they
intersect with the glacier sides at an angle of about 45 degrees. Crevasses up to 400m
wide are present within 45m of the glacier front because of shear along the glacier
sides (Higgins, 1991). Intersection angles of 45 degrees between open fractures
(crevasses) and the sides of ice flows in glacier outlets are consistent with the sides
acting as shear boundaries (Erlingsson, 1988).
Between 31 July 2000 and 21 Aug 2000, three of the large ice masses were lost from
the eastern side of the glacier front, leaving a large section protruding in the central
region. On 03 August 2001, it can be seen that this section has broken away and is
drifting into Kennedy Channel. By 13 August 2001, much of the calved ice along the
eastern margin of the glacier has disappeared. On 07 Sept 2004 after three years, the
eastern half of the glacier has advanced, but no calving has occurred (Fig. 4e). Some
ice has been lost from the western half of the glacier, but less than that lost from the
western half in 2000 and 2001.
The change in the position of the glacier front between 31 July 2000 and 21 August
2001 is shown in Figure 5(a). The western half of the glacier advanced about 1km in
agreement the glacier speed given in Higgins (1991). About 70 km2 were lost from
the eastern half of the glacier, compared to an average value of 28 km2 over two
years. Interestingly, the high glacier thicknesses most consistent with the thicknesses
of the 2001 to 2003 icebergs and ice islands are along the eastern margin (Higgins
1991).
(a) 31 Jul 2000
(d) 13 Aug 2001
(b) 21 Aug 2000
(e) Sept 7 2004
North (approx.)
(c) 03 Aug 2001
Figure 4. MODIS images of glacier front of Petermann Glacier, 2000 to 2004.
The position of the glacier front in 2000 and 2001 is also plotted in Figure 5(b), along
with other positions from 1953 to 1992 found in the scientific literature. Most of the
positions from 1953 to 1992 are from Higgins (1991), except for 1975 (Dunbar,
1978) and 1962, 1963 and 1992 (Zhou and Jezek, 2002). It can be seen that the
position of the glacier front in July 2000 approached the historical maximum
(corresponding to 1959) on the eastern side. The position in 2001 did not retreat as far
as the historical minimum (corresponding to 1961) in Higgins (1991). As stated
above, the position of the glacier front appears to have remained stable within 15km
since 1876 (Higgins, 1991) based on data up to 1978, and more recent data are no
exception.
(a)
(b)
Figure 5. Position of glacier front in July 2000 and August 2001 (a), between 1953
and 2001 (b).
The time lag between the early August 2001 calving event and the sightings off
Lancaster Sound (82 days), over a distance of 800 km, implies a drift rate of about
10km/day. In comparison, the WH-5 ice island from the Ward Hunt ice shelf drifted
at 7 to 11km/day from Kennedy Channel to Lancaster Sound between July 24 and
Sept 30, 1963 (Nutt, 1963). It is also possible that some of the ice islands sighted in
2001 to 2003 were from the ice islands which left the glacier area in 2000, but which
may have over-wintered in Kennedy Channel.
CONCLUSIONS
Sightings of ice islands and large tabular icebergs off Eastern Canada from Lancaster
Sound to the Labrador and Newfoundland shelves and Grand Banks in 2001 to 2003
were described. The most probable source of the icebergs is the Petermann glacier
based on (a) the surface appearance, (b) the iceberg freeboards and drafts and (c) the
occurrence of debris on one of the icebergs, which appears similar to that on an
iceberg that was sighted in Nares Strait and is believed to be from the Petermann
glacier. In addition, the drift rate inferred from the date of the 2001 calving and the
Lancaster Sound sightings is consistent with the drift rate of the WH-5 ice island
in1963.
Although there was a rapid retreat of the eastern side of the Petermann glacier in 2000
to 2001, the glacier front was within the historical limits since 1876. The appearance
of unusually high number of ice islands and large tabular icebergs off Newfoundland
is probably also dependent on the size of the calved icebergs: large icebergs are more
likely to reach areas to the south before deteriorating.
Other iceberg sources in Arctic Canada and Greenland have undergone some
dramatic changes in recent years that may be linked to global warming. Among them
are the fracture and calving event of the Ward Hunt Ice Shelf in 2000 and 2002
respectively, and the retreat of the Jacobshavn glacier from 2000 to 2003. The retreat
of the Jacobshavn glacier has been linked to glacier thinning and an increasing glacier
speed (Joughin et al., 2004). The Petermann glacier does not appear to be thinning to
the same degree (Krabill et al., 2004), although the grounding line has retreated
(Rignot et al., 2001).
ACKNOWLEDGEMENTS
I thank Luc Desjardins (CIS), Pip Rudkin (PAL Environmental Services), Denny
Christian and Tony King (C-CORE), Don Murphy (IIP), and John Crealock and
Marcos Zentilli for providing photographs and iceberg information for this project.
This work was funded in part by the Federal Program of Energy Research and
Development (PERD).
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