POAC 09 - Bedford Institute of Oceanography

POAC 09
Luleå, Sweden
Proceedings of the 20th International Conference on
Port and Ocean Engineering under Arctic Conditions
June 9-12, 2009
Luleå, Sweden
POAC09-130
THE DRIFT OF AN EXCEPTIONALLY-LARGE ICE ISLAND
FROM THE PETERMANN GLACIER IN 2008
I.K. Peterson 1 , S.J. Prinsenberg 1 , M. Pittman 1 and L. Desjardins 2
1
Bedford Institute of Oceanography, Fisheries and Oceans Canada
2 Canadian Ice Service, Environment Canada
ABSTRACT
In the summer of 2008, an ice island with a surface area of over 20 km 2 calved from the
Petermann Glacier, and drifted south through Nares Strait to Baffin Bay. Ice islands (defined as
large pieces of floating ice with a height of about 5 m above sea-level, and an area of from a few
thousand sq.m to 500 km 2 or more, that have broken off an Arctic shelf or floating glacier tongue)
and their fragments are a major hazard for offshore structures on the Grand Banks because of
their relatively low draft and the difficulty of towing them. The ice island was initially tracked
using a combination of Envisat and MODIS imagery, and information on the drift of surrounding
sea ice was obtained using Envisat and AMSR-E imagery. Although the ice island calved in mid-
July, the ice island did not enter Nares Strait for 3 weeks until a major wind event cleared sea ice
from the mouth of the Petermann Fjord.
In mid-September, two satellite-tracked ice beacons were deployed on the ice island in northern
Baffin Bay northeast of Jones Sound. An ARGOS beacon from the Canadian Ice Service
provided a long time series of position data with an accuracy of about 300 m. A prototype
Iridium beacon from the Bedford Institute of Oceanography, designed to transmit hourly GPS
fixes with an accuracy better than 10 m, provided about 2 weeks of position data before it
malfunctioned.
The GPS data initially show inertial oscillations, followed by a grounding event east of Jones
Sound lasting for about one day. Bathymetry data suggest that the water depth at the grounding
site was about 100 m, however soundings in the area are sparse. The ice island then entered Jones
Sound through Glacier Strait, where the bathymetry suggested the ice island had a draft of less
than 60-70 m. After remaining in Jones Sound for about 6 weeks, the ice island resumed its
southward drift through Lady Ann Strait. The effect of wind forcing on the drift is shown using
NCEP/NCAR reanalysis surface winds.
INTRODUCTION
Ice islands and their fragments are a major hazard for offshore structures on the Grand Banks
because of their relatively low draft and the difficulty of towing them. In 2002 and 2003, offshore
operators on the Grand Banks observed a large number of ice islands and tabular icebergs
(Stoermer and Rudkin, 2003), due to a major calving event of the Petermann Glacier in 2000-

2001. The Petermann Glacier is located in northwest Greenland, and seaward of the grounding
line, it consists of a floating glacier tongue about 70 km long and 15.5 km wide (Higgins, 1991).
Another major calving event occurred in the summer of 2008, mostly in the form of a single ice
island over 20 km 2 in area. This paper describes its drift southward, by tracking it using satellite
imagery (Envisat and MODIS), and two satellite-tracked ice beacons deployed on the ice island.
DRIFT FROM THE PETERMANN GLACIER TO JONES SOUND
A MODIS image from 18 July 2008 (Fig. 1) shows the large ice island (A) which calved from the
west side of the glacier by 13 July, and a smaller ice island (B) which calved from the east side
by 16 July. The large ice island calved along a fracture line E similar to the position of the front
in 2000. This fracture line may have formed due to basal melting observed along one of several
channels near the grounding line of the glacier (Rignot and Steffen, 2008).
A
C
Fig. 1. MODIS Image from 18 July 2008 (1920Z) showing two ice islands (A and B) calved from
the Petermann Glacier (C), and sea ice to the north in Nares Strait (D). The bottoms of the arrows
indicate the origin of the ice islands.
The large ice island was tracked using Envisat and MODIS imagery between 13 July and 15
September 2008, when two ice beacons were deployed on the ice island northeast of Jones
Sound. The complete track of the ice island from the Petermann Glacier south to Lancaster Sound
between 13 July and 10 February 2009 is shown in Fig. 2.
Although the ice island calved in mid-July, the ice island did not enter Nares Strait for 3 weeks
until a major wind event cleared sea ice from the mouth of the Petermann Fjord. The mean sea
level pressure pattern between 01 August and 06 August 2008 using NCEP/NCAR reanalysis
data (Kalnay et al., 1996) shows that strong winds blew northward through Nares Strait (Fig. 3).
A passive microwave (AMSR-E) image for July 31 shows high concentrations of sea ice both
B
E
D

across Nares Strait adjacent to the Petermann Glacier, and off the northeast corner of Ellesmere
Island (Fig. 4A). From August 1 to August 4, northward winds caused the sea ice to clear from
the two regions, so that the ice island was able to escape from the Petermann Fjord into Nares
Strait on August 7 (Fig. 4D). As northward winds weakened, ice concentrations off the northeast
corner of Ellesmere Island increased and the ice island drifted southward. It stalled for several
days in northern Smith Sound, then continued south to southern Ellesmere Island, where it drifted
around a bank, closely following the 200 m isobath (Fig. 2; Day of year 251 to 259).
Fig. 2. Drift of ice island from the Petermann Glacier between 14 July 2008 and 10 Feb 2009.
The green line indicates the track derived from satellite imagery, the red line indicates the track
derived from the Argos ice beacon. Locations are marked every 5 days, and labelled every 10
days in Julian days relative to 2008. The 100 m and 200 m isobaths are shown by the light and
dark blue lines respectively.

Figure 3. Mean sea level pressure from 01 Aug to 06 Aug 2008.
A B C
D E F
Fig. 4. AMSR-E images from 31 July to 13 August 2008. Bright tones indicate high ice
concentrations.
DRIFT FROM JONES SOUND TO DAVIS STRAIT
On 15 September 2008, two satellite-tracked ice beacons were deployed from the icebreaker
CCGS Amundsen via helicopter by Dr. Martin Fortier on the ice island in northern Baffin Bay
northeast of Jones Sound. The beacons were deployed about 2.5 km apart along the long axis of

the ice island. A photograph of the ice island taken on 15 September is shown in Fig. 5; freeboard
estimates of the ice island were not obtained.
Fig. 5. Petermann ice island, with CCGS Amundsen in foreground on 15 Sept 2008 at 76.4°N,
77.0°W (Photo courtesy of Dr. M. Fortier (University of Laval)).
A CALIB ARGOS ice beacon manufactured by Metocean Data Systems was deployed for the
Canadian Ice Service and provided position data with an accuracy of about 300 m. A prototype
Iridium beacon built at the Bedford Institute of Oceanography which was designed to transmit
hourly GPS fixes, was also deployed.
The beacon was deployed following replacement of batteries, and provided about 2 weeks of
position data before it malfunctioned. The CEP accuracy is less than 2.5 m, where CEP (Circular
Error Probability) is the radius of a horizontal circle, centered at the antenna’s true position,
containing 50% of the fixes.
Soon after deployment northeast of Jones Sound, the beacons drifted southwestward, making
several clockwise loops (Fig. 6). Rotary motion may be due to tidal currents, or to inertial
currents which are circular motions in a clockwise direction in the northern hemisphere. The
period of the oscillations was consistent with both the inertial period (12.3 hours at 76.35°N) and
the M2 tidal period (12.4 hours). However, the eastward component was not in phase with that
predicted by the WebTide Tidal Prediction Model (DFO, 2009), suggesting the oscillations are
primarily inertial. The amplitude of the inertial oscillations was about 0.2 m/s, which is consistent
with the amplitude of intertial oscillations observed in northwest Baffin Bay with current meters:
0.1-0.2 m/s, with speeds as high as 0.35 m/s (Fissel, 1981). Inertial oscillations are generally a
response to individual wind events, and decay after a few cycles. Wind data from the area (Fig. 7)
shows that the oscillations were preceded by strong northeasterly winds on day 258 (14 Sept).

Fig. 6. Trajectories of ice beacons deployed on ice island between 15 Sept and 18 Nov 2008. The
blue line represents the Argos ice beacon and the red line represents the Iridium GPS beacon.
Fig. 7. Six-hourly wind velocity at 75°N, 82.5°W (top panel), and velocity of ice island (bottom
panel).
Plots of the latitude and longitude show that ice island stopped suddenly on day 266 and
remained stationary for about 1 day (22-23 Sept), suggesting it grounded (Fig. 8). The GPS data

is superimposed on a contour map of bathymetry, derived from a combination of gridded IBCAO
(International Bathymetric Chart of the Arctic Ocean) data and multi-beam data. From Fig. 9, the
water depth at the apparent grounding site was about 100 m, however soundings shown on
hydrographic charts for the area are sparse. When the winds shifted from northwesterly to
northeasterly on day 267, the ice island entered Jones Sound through Glacier Strait, where the
bathymetry suggests the ice island had a draft of less than 60-70 m. Thus the apparent grounding
site probably represents a rise not captured in the bathymetry data. A draft of less than 60-70 m is
consistent with altitude measurements of the front of the Petermann Glacier, which imply a draft
of about 35 m along most of the front (Higgins, 1991).
Fig. 8. Hourly latitude and longitude from the Iridium GPS beacon.
The ice island then drifted westward into Jones Sound where it remained for about 6 weeks,
making several clockwise loops within the eastern end of the sound. A multiple regression model
was used to compare the wind and iceberg velocities, with the iceberg velocity component as the
dependent variable and the wind components as the independent variables. The multiple
correlation component for the u (eastward) component (R=0.40), is higher than for the v
(northward) component (R=0.22), probably because of topographic effects on winds in the sound,
which is oriented in an east-west direction. The regression coefficients for the iceberg u
component imply the iceberg is drifting at 2.8% of the wind speed and 16 degrees to the right of
the wind. However for the iceberg v component, there is negligible correlation with the wind v
component.

Jones Sound
Devon Is.
Ellesmere Is.
Glacier Strait
Lady Ann Strait
Coburg Island
Baffin Bay
Fig. 9. Trajectory of Iridium GPS beacon deployed on ice island (red line), overlain on contoured
bathymetry. The arrow indicates the apparent grounding site.
Table 1. Regression and correlation coefficients for a regression model of the form :
(Ui,,Vi) = a Uw + b Vw + c + ε, where Ui,,Vi are eastward and northward iceberg drift components
respectively, and Uw,Vw are NCEP/NCAR reanalysis surface wind components, a, b, and c are the
regression coefficients, and ε is the error term.
Dependent variable a b R
Ui 0.027 0.008 0.40
Vi -0.010 0.001 0.22
After leaving Jones Sound, the ice island made a small intrusion into Lancaster Sound, reaching
the centre of the sound by about 20 Nov 2008. The total travel time from northern Smith Sound
(on 22 Aug 2008) to Lancaster Sound was 90 days, with about 50 days spent in Jones Sound (24
September – 13 November 2008), leaving a net travel time of 40 days.
From Lancaster Sound in 2008, the Petermann ice island then drifted southward along the coast
of Baffin Island, reaching Davis Strait by the end of January. Thus the travel time from Lancaster
Sound to Davis Strait was less than 2.5 months.

CONCLUSIONS AND DISCUSSION
Understanding of the drift of ice islands and icebergs south from Greenland is important for
predicting the timing of their appearance in areas to the south such as the Grand Banks. The
passive microwave data show the importance of sea ice in determining when the ice islands
escape from the fjords of Greenland into Nares Strait.
The GPS data collected with an Iridium ice beacon indicate an apparent grounding event lasting
about one day east of Jones Sound. Grounding events are common features of iceberg drift in
Baffin Bay, slowing their southward drift (Marko et al., 1982). They are also of interest in
assessing risk to pipelines.
Comparison of the trajectory into Jones Sound with bathymetry data suggests that the draft of the
ice island was less than 60-70 m. Since the iceberg area was about 21 km 2 , assuming a draft of 50
m, a density of 0.9 tonnes/m 3 , and a draft/ freeboard ratio of 7 (Higgins, 1991), the mass of the
ice island is approximately 1100x10 6 tonnes. Since the median mass of an iceberg on the Grand
Banks is 0.11x10 6 tonnes (Newell, 1993), the mass of the ice island is equivalent to 10,000
typical sized icebergs on the Grand Banks, and the mean number of icebergs drifting south of
48°N is about 480 per year.
In northern Smith Sound, the ice island stalled for several days in the same area that ice island
fragments from the Ward Hunt Ice Shelf stalled or drifted eastward in August 1963. This drift
pattern was attributed to a sluggish cyclonic gyre in Kane Basin (Nutt, 1966). Animation of
AMSR-E images from August 2008 also suggests a cyclonic gyre in Kane Basin.
The net travel time from the northern Smith Sound to Lancaster Sound (after subtracting the time
spent in Jones Sound) was 40 days. This is similar to the travel time of the fastest WH-5 ice
island fragments, which drifted from northern Smith Sound to Lancaster Sound in 50 days (Nutt,
1966). Other WH-5 ice island fragments travelled less than half the distance in 50 days.
The travel time from Lancaster Sound to Davis Strait (less than 2.5 months) is similar to the 2
month travel time of the WH-5 ice island from the Ward Hunt Ice Shelf (30 Sept to 01 December
1963). In contrast, the icebergs tracked by Marko et al. (1982) that reached Davis Strait took 8-15
months, and it was estimated that the most likely travel time between Lancaster Sound and Davis
Strait is 3 years. These longer times are probably due to the larger drafts of the icebergs, so that
grounding was more common than for ice islands. They are probably also due to observations
during the open water season, when icebergs are more likely to ground because they are not held
offshore by sea ice.
ACKNOWLEDGEMENTS
We would like to thank Dr. Martin Fortier for deploying the two ice beacons, and Adam
Drozdowski for plotting of bathymetry. This work was funded in part by the Federal Program of
Energy Research and Development (PERD).

REFERENCES
Fisheries and Oceans Canada (2009). DFO WebTide Tidal Prediction Model,
http://www.mar.dfo-mpo.gc.ca/science/ocean/coastalhydrodynamics/ WebTide/webtide.html
Fissel, D.B., 1981. Tidal currents and inertial oscillations in Northwestern Baffin Bay, Arctic
35(1):201-210.
Higgins, A.K., 1991. North Greenland Glacier Velocities and Calf Ice Production,
Polarforschung 60(1):1-23.
Kalnay et al., 1996. The NCEP/NCAR 40-year reanalysis project, Bull. Amer. Meteor. Soc., 77,
437-470.
Marko, J.R., Birch, J.R. and Wilson, M.A., 1982. A study of long-term satellite-tracked iceberg
drifts in Baffin Bay. Arctic, 35, 234-240.
Newell, J.P., 1993. Exceptionally large icebergs and ice islands in Eastern Canadian Waters: A
review of sightings from 1900 to present, Arctic 46(3):205-211.
Nutt, D.C., 1966. The drift of ice island WH-5, Arctic 19(3):244-262.
Rignot, E., and Steffen, K., 2008. Channelized bottom melting and stability of floating ice
shelves, Geophys. Res. Lett., 35, L02503, doi:10.1029/2007GL031765
Stoermer, S.A. and Rudkin, P., 2003. Very Large Tabular Icebergs: Iceberg Season 2002 and the
Past, Report of the International Ice Patrol, pp.51-55.