Greenland Survey
2001 - 1
Distribution and Variability of Icebergs in
the Eastern Davis Strait 63°N to 68°N
Bureau of Minerals and Petroleum
Prepared by
Håkon Gjessing Karlsen and Jørgen Bille-Hansen
Greenland Survey, ASIAQ
Keld Q. Hansen, Henrik Steen Andersen and Henriette Skourup
Danish Meteorological Institute
Greenland Survey
2001 – 1
Distribution and Variability of Icebergs in the
Eastern Davis Strait 63°N to 68°N
Bureau of Minerals and Petroleum
Prepared by
Håkon Gjessing Karlsen and Jørgen Bille-Hansen
Greenland Survey, ASIAQ
Keld Q. Hansen, Henrik Steen Andersen and Henriette Skourup
Danish Meteorological Institute
Published by: Greenland Survey, ASIAQ
Post Box 1003
DK-3900 Nuuk
Tel: +299 348800
Fax: +299 348801
E-mail: [email protected]
Printed in Denmark, 2001
By Book Partner, Nørhaven Digital
ISSN 1601-3816
ISBN 87-91144-00-0
Preface
In 2000, The Bureau of Minerals and Petroleum (BMP) commissioned The Greenland Survey to
prepare a report compiling and interpreting all available information on the sea ice and especially
the iceberg condition in that part of the eastern Davis Strait, which will be opened for licensing in
year 2001 for hydrocarbon exploration. The Greenland Survey and the Danish Meteorological
Institute has prepared the report as a joint effort. The report endeavour to give an overview of the
seasonal and inter annual distribution of sea ice and icebergs in the licensing area. Main emphasis
has been put on the sea ice and iceberg distribution in the existing licenses, the Fyllas Banke and the
Sisimiut license.
3
Summary and recommendations
probability of an increasing numbers of
icebergs is quite high.
The main objective of the study was to
evaluate, characterize and compare the year
2000 iceberg observations with other data
sources and historical data for the southern
license area, Fyllas Banke, and the northern,
the Sisimiut license area, respectively. Based
on the available data, it was concluded that:
•
The icebergs observed at Fyllas Banke,
from early July until mid-September 2000
probably represent normal seasonal
conditions rather than severe conditions.
•
Evaluating the most representative dataset
for the northern area, i.e. the last decade’s
records of icebergs, it is concluded, that
the year 2000, does not deviate. Then, the
year 2000 can be considered as a normal
year concerning icebergs in the Sisimiut
license area.
In the northern area the West Ice affects the
western margin of the Sisimiut license in the
summer months, July – September. However,
the West Ice rarely has a distribution, which
affects more than the margins of the area to be
opened for licensing in year 2001. The
number of icebergs varied only a little
between spring-summer months and the early
autumn months. Consequently, to minimise
the probability of icebergs it may beneficial to
use February to May as the exploration
period.
For
future
offshore
operations
is
recommended that the iceberg environment
south of the area of interest (Fyllas Banke
licence) or north of the area of interest
(Sisimiut license) is monitored continuously
using satellite images several weeks before
the actual drilling or exploration effort takes
place to be able to ‘forecast’ the iceberg
density (number of icebergs on a certain area)
and enable necessary actions to be taken well
in advance.
It has been shown that the maximum
distribution of multi-year sea ice occurs in
June and the number of icebergs near Fyllas
Banke will reach its maximum one or two
months later. It is therefore reasonable to
expect that the number of icebergs should be
at its lowest from April to July. It has also
been shown that the probability of occurrence
of multi-year sea ice in the Fyllas Banke area
is almost identical regardless if the
exploration period is from April to June or
July to September. David Strait first year sea
ice occurs only occasionally in the Fyllas
Banke area and is only present in April after
severe winters. Consequently, to minimise the
probability of icebergs it may be beneficial to
use April to June as the exploration period.
However, in case the exploration period must
be prolonged into July or even August the
Direct evidence of the iceberg environment is
limited and a baseline is therefore difficult to
establish. RADARSAT satellite images
provide detailed information about iceberg
distribution and density. Consequently, it is
recommended that additional available
RADARSAT scenes should be acquired and
analysed to gather more information about the
iceberg environment variability and to
provide better planning guidance.
4
Contents
Preface .................................................................................................................................................3
Summary and recommendations ......................................................................................................4
1
Introduction ................................................................................................................................7
1.1
Icebergs and Ice Offshore West Greenland..........................................................................8
1.1.1
Main Oceanic Current Conditions................................................................................8
1.1.2
Icebergs and Ice Offshore Southwest Greenland .........................................................9
1.1.3
Icebergs and Ice Offshore Middle West Greenland ...................................................10
2
Data Included in the Study ......................................................................................................12
3
Summary of the Year 2000 Season at Fyllas Banke..............................................................13
4 Summary of Earlier Investigations of the Icebergs at the West Coast of Greenland ........15
4.1
Iceberg Distribution and Characteristics ............................................................................15
4.2
Seasonal Variation in Density Distribution........................................................................15
4.3
Iceberg Mass Distribution ..................................................................................................16
4.4
Draft of Icebergs.................................................................................................................17
4.5
Drift Speed Analysis ..........................................................................................................18
5
Analysis of Ice and Icebergs Drifting into the West Greenland Waters from South.........19
5.1
CFAR filtering of Radarsat SAR data................................................................................19
5.2
Iceberg Data Based on Ice Chart Information 1975 - 2000 ...............................................22
5.3
Iceberg Data based on Ice Chart Information 1958 - 2000 ................................................25
6 Analysis of Icebergs and Ice drifting into the West Greenland Waters from North and
West ...................................................................................................................................................28
6.1
Sea Ice Environment of the Eastern Davis Strait ...............................................................28
6.2
Analysis of Icebergs Observed at the Grand Banks of Newfoundland ..............................29
6.2.1
Statistics on the IIP Area 40° to 52°N and 39°W to 57°W ........................................29
7
Conclusions ...............................................................................................................................31
7.1
Ranking of the Year 2000 Season at Fyllas Banke ............................................................32
7.2
Recommendations and Further Studies..............................................................................32
8 References .................................................................................................................................34
5
70°
80°
Qaanaaq
Baffin
Bay
70°
60°
50°
30°
40°
20°
10°
Upernavik
Greenland
Ittoqqortoorm iit
70°
Um mannaq
Disko
Ilulissat
t
Canada
Aasiaat
Store
Hellefiske
Banke
Sisimiut
Dav
is S
tr a i
Baffin
Island
W est
Navion
Maniitsoq
Fyllas
Banke
60°
Am massalik
Nuuk
Paamiut
Nunarsuit
60°
Cape
Farewell
80°
60°
80°
60° 120°
Labrador
Sea
20°
Norw ay
rad
or
Greenland
Lab
Iceland
UK
100°
0°
50°
C anada
New foun dland
50°
40°
40°
Grand Banks of
Newfoundland
Atlantic Ocean
USA
80°
60°
40°
20°
Figure 1. Sites
mentioned in the
report.
40°
50°
30°
40°
6
1 Introduction
This report gives a short review of the
summer season sea ice and iceberg conditions
in West Greenland waters. Special emphasis
is given to the icebergs1 in the area offshore
West Greenland to be opened for licensing in
2001, Figure 2. Icebergs can cause problems
for drilling operations, especially if they are
big in size and high in frequency. The
environmental consequences of a collision
between a drilling rig and an iceberg could be
serious in an Artic environment.
The distribution of icebergs in the area 63°N
to 68°N and east of 58°W is influenced by the
West Greenland Current going northwards
and the Baffin Island current going
southwards and the interaction between them.
Therefore, investigations reporting on
icebergs and sea ice in the north and south
going currents have been the primary data
sources. Investigations directly related to the
target area have only been performed in
relative short periods of time, but they are
included in this study whenever possible.
A special effort has been made to determine
the amount of icebergs at the Fyllas Banke
(64°N,54°W). Fyllas Banke is particularly
interesting because icebergs there annoyed a
drilling operation performed by Statoil. The
observations took place during an offshore
drilling operation, from early July until midSeptember 2000. It would be desirable to
know if the number, frequency, and
distribution of icebergs observed in the
summer of 2000 were normal or extreme
when compared to available observations.
70°
Aasiaat
68°
The Sisim iut
licence
Greenland
B affin
Island
Sisim iut
66°
Bo rd er w
ith C an ad
a
•
•
50°
Ilulissat
The objectives of the study is to:
•
55°
60°
evaluate and classify the iceberg
observations from the 2000-season,
compare these data with earlier data and
hereby estimate the severity of the season.
M aniitsoq
64°
Nuuk
In 1975 – 78 there has been rather detailed
studies in the block system area, in
connection with exploitation operations
(DHI/GTO, 1979c). These studies were
conducted mainly during the months of June
through October and included investigations
on the distribution and amount of icebergs,
their mass and draft.
W est
N avion
The Fyllas
Banke licence
62°
60°
55°
50°
Figure 2. Map of the investigated area. Block system
and existing licenses offshore West Greenland between
63°N and 68°N.
1
An iceberg is defined as an ice block that reaches a
minimum of 5 meters above sea level, is longer than 15
meters and is broken away from a glacier.
7
1.1.1 Main Oceanic Current Conditions
The general circulation pattern of the ocean
currents, Figure 3, is important since the
iceberg drift patterns mainly respond to the
currents.
In addition to icebergs, sea ice occurs in the
following main types: ”Storis”, mainly multi–
year drift ice and West Ice, mainly first year
drift ice. The sea ice is normally present in the
Davis Strait from November to mid-summer.
The waters off Southwest Greenland, south of
Nuuk, are normally free of sea ice, but can be
covered with sea ice during late winter for
short periods of time. During spring and early
summer months, multi-year sea ice can drift
into the area.
1.1 Icebergs and Ice Offshore West
Greenland
Icebergs occur everywhere in the West
Greenland waters. They are produced from a
large number of glaciers along the coast of
Greenland. Occasionally, many small
icebergs and bergy bits are calved in the
Southwest Greenland fjords, but normally
these ice masses melt quickly, and they rarely
affect ocean areas further offshore. The
glaciers which produce the most and largest
icebergs are located in the Ittoqqortoormiit
area, Figure 1, on the east coast, and in the
Disko Bay on the west coast and north of this
bay (Valeur et al., 1997).
Figure 3. General ocean surface current circulation in
the Greenland water (Nazareth & Steensboe, 1998)
The main currents in the Baffin Bay and
northern Davis Strait are fairly simple. There
is a relative warm north-flowing current along
the Greenland coast and a cold south-flowing
current along the Baffin Island continuing
down to the Labrador coast. However,
transitory eddies influence this basic flow
pattern and cause westward flowing branches
of the Greenland current, which have
significant impact on the numbers of icebergs
and their residence time (Nazareth &
Steensboe, 1998).
In the process of calving from the front of a
glacier, an infinite variety of icebergs, bergy
bits and growlers are produced. Calving can
occur throughout the year. The length of an
iceberg is defined as the longest horizontal
extent of the iceberg above the waterline,
while the width is defined as the shortest
horizontal extent. By height and draft is
meant the maximum vertical extent from the
waterline (Bernitt et al., 1998). Icebergs are
described according to their size and the
following size classification is normally used,
Table 1 (Valeur et al., 1997).
The dominant current in the eastern part of the
Davis Strait is the north going West
Greenland Current. The surface layer (0 - 50
m) of this current is dominated by cold water
from the East Greenland Current, while the
underlying layer consists of warm water from
the Irminger Current - a branch of the North
Atlantic Current (Mosbech et al., 1996).
Table 1. Size classification of iceblocks and icebergs.
Type
Height [m]
Length [m]
Growlers
<1
<5
Bergy bit
1 -5
5 < 15
Small iceberg
5 - 15
15 - 60
Medium iceberg
16 - 45
61 - 120
Large iceberg
46 - 75
121 – 200
Very large iceberg
> 75
> 200
8
1.1.2 Icebergs and Ice Offshore Southwest
Greenland
The icebergs observed near Fyllas Banke
originates from the East Greenland glacial
outlets. Here, thousands of large icebergs are
calved every year. When not grounded or
stationary in fast ice (firmly fixed ice) near the
shore, the icebergs drift southwards with the
East Greenland Current which most of the year
also contain large amounts of multi-year sea ice
from the Arctic Ocean. This sea ice regime is
called “Storis”. Many icebergs drift outside the
sea ice edge and melt relatively quickly,
depending on the water temperature, the
wave/swell action, and the size of the icebergs.
While drifting within the sea ice edge in the
cold East Greenland Current, the deterioration
of the icebergs is significantly slower since sea
ice “protects” the icebergs.
Mixing occurs, especially in the “shallow”
areas off the Continental Shelf. Tidal
generated currents are superimposed on the
general current circulation (DHI/GTO,
1979a).
Under normal conditions, sea ice occurs in the
Cape Farewell area from late December until
early August. Peak season is in spring and early
summer. From Cape Farewell, the West
Greenland Current carries most of these sea
ice/icebergs northwards. Some years the sea
ice drifts into the Fyllas Banke area.
Due to the different melting rates of the multiyear ice and icebergs, the iceberg density in sea
ice-free waters off Southwest Greenland is to a
certain extent controlled by occurrence and
distribution of multi-year ice 1 - 2 months
earlier (Valeur et al., 1997). Therefore, one
may expect the maximum iceberg density off
Southwest Greenland to occur in early and
mid-summer, decreasing to a minimum in the
fall and early winter. Large variations in the
number and size of the distribution of
icebergs rounding Cape Farewell are expected
due to the variability of the currents, the large
distance to major sources, the varying
amounts of ”protecting” sea ice, and of
course, the extreme weather conditions.
Figure 4. Bathymetry of southern Baffin Bay, Davis
Strait and northern Labrador Sea, after (Nazareth &
Steensboe, 1998).
The West Greenland Current, the tide,
meteorological forcing and hydrographic
phenomena generate the general current
conditions along the west coast of Greenland.
The current is strongly affected by local
bathymetric conditions, Figure 4. The drift
tends to be parallel to the isobaths, especially
in relatively shallow areas (Bernitt et al.,
1998; DHI/GTO, 1979c).
An important factor controlling the iceberg
environment offshore Southwest Greenland is
the input of icebergs to the East Greenland
9
growlers, which never affect offshore areas,
Figure 5.
Current at high latitudes during summer.
Frequently, the movements of icebergs are
controlled by the occurrence and drift of sea
ice. If the fast ice in fjords with major iceberg
sources does not melt during summer or if the
East Greenland sea ice does not drift offshore,
a decrease in the amount of icebergs at lower
latitudes near Cape Farewell may be the
result. This event will probably reduce the
input of icebergs to the East Greenland
Current.
The east Greenland icebergs drift southwards
along the coast to Cape Farewell and then
northwestwards, controlled by the West
Greenland Current. Occasionally, under the
effect of wind or in the absence of a welldeveloped Irminger Current, icebergs may
continue south past Cape Farewell reaching as
far as 100 - 200 miles to the south or
southwest. However, the majority goes
northwards under the effects of the relatively
warm West Greenland Current, disintegrating
rapidly, seldom drifting north of latitude
65°N. Some icebergs drift westwards across
the southern Davis Strait to the coasts of
Labrador and Baffin Island where they join
the main stream drifting southwards.
Figure 5. Large-scale iceberg drift pattern in the Davis
Strait. No significant occurrence of iceberg calving
61°N to 68°30´N (Nazareth & Steensboe, 1998).
Some large icebergs may survive several
months if the water temperature remains cold
enough or if the wave action on the icebergs
is low. But even in this low-melt situation,
deterioration is significant. Icebergs from the
major sources in northern Davis Strait and
Baffin Bay will normally not be present near
Fyllas Banke in the sea ice-free season, due to
the flow patterns of the currents in the
southeastern part of Davis Strait.
1.1.3 Icebergs and Ice Offshore Middle
West Greenland
The highest iceberg density and the largest
icebergs occur in the Sisimiut licence area.
The iceberg drift patterns, Figure 5, seem
mainly to respond to the current, Figure 3. In
consistently high wind situations, the effect of
the winds become significant, particularly if
the surrounding area is free of sea ice, and
wind-generated surface water currents may
develop (Nazareth & Steensboe, 1998). The
tidal currents primarily influence the smallscale iceberg movements (Bernitt et al.,
1998).
Generally, the number of offshore icebergs
decreases significantly when drifting north in
the West Greenland Current. In other words, a
large majority of the icebergs present near
Cape Farewell melt here and will never reach
as far north as Fyllas Banke. Local glacial
outlets normally produce bergy bits or
10
Many of the icebergs produced in the Disko
Bay will leave the bay. The icebergs leaving
the bay south of Disko will partly drift
towards north along the coast of Disko Island
and partly drift towards the southwest and
approach the concession areas from the north
(DHI/GTO, 1979c). As a result, most of the
observed icebergs in the northern parts of the
Davis Strait (north of 66°N) are estimated to
originate from glaciers in the Disko Bay and
eastern Baffin Bay.
eastern Davis Strait between 63°N and 67°N
(Valeur et al., 1997).
70°
50 50
5
30 50
13
2
Baffin Island
14 43
52
50
35
17
17
Greenland
2
0
17
50
8
The north going icebergs from the Disko Bay
and the icebergs calving further north will
probably drift along with the general largescale anticlockwise current circulation in the
Baffin Bay. Most of these icebergs leave the
Baffin Bay along the east coast of Canada and
enter the Labrador Current southwest of
Greenland (DHI/GTO, 1979c). Anyway most
icebergs disintegrate near the location they are
produced.
33
40°
18 30 50
11 23
59
16 57
50°
60°
W est Navion
15
2
16
18
11
6
17
60°
11
60°
17
17
5
22
21
12
3
10
28
5
27
7
3
20
22
8
4
6
2
1
10
8
2
8
5
7
0
15
8
8
2
2
3
1
4
6
4
5
4
1
1
1
1
2
0
0
2
1
1
0
Canada
13
Labrador
Most of the icebergs drifting southwards from
Baffin Bay in the western part of Davis Strait
occur within 100 - 150 km of the shore of
Baffin Island. It is well known that the largescale iceberg drift is more or less related to
the presence and drift of sea ice. Northerly
winds and a southwards sea ice drift dominate
the Davis Strait in most of the winter. Ice that
is formed along Baffin Island and carried by
currents into central Baffin Bay and the Davis
Strait and is named West Ice. Sometimes the
West Ice advances to a very easterly position.
It may be expected that a significant amount
of icebergs, which are present 100 - 300
kilometres west of the Disko Bay and the
Uummannaq Fjord, drift southwards to the
central/eastern parts of the southern Davis
Strait. The Fyllas Banke is included in severe
winters. This process seems to occur and is
indirectly proved in the observations from the
pre-season survey conducted by International
Ice Patrol (IIP) in January and February,
Figure 6. Late in the sea ice free period,
icebergs occur infrequently in the central and
50°
3
0
February average of icebergs
1963-1972, 1974-1978
0-1
1-3
3-10
10-59
60°
0
50°
50°
Figure 6. February average 1963 - 1972, 1974 - 1978
of icebergs in the Davis Strait (International Ice
Patrol, 1978).
11
2 Data Included in the Study
1. 19 Radarsat ScanSAR Wide scenes for the
western Cape Farewell area, April September 2000 + data from about 17
reconnaissance flights in June-July 2000.
2. 17 Radarsat ScanSAR Wide scenes for the
western Cape Farewell area, April September 1999 plus data from 13
reconnaissance flights in June-July 1999.
3. 7 Radarsat ScanSAR Wide scenes for the
western Cape Farewell area, April September 1997.
4. 1-3 weekly high resolution ice charts for
the Cape Farewell area based on aerial
data or satellite data for the period 1958 2000.
Data related to the Sisimiut license area:
The data sets analyzed in the present study
could be grouped in: 1). Data sets on the
occurrence of sea ice and icebergs covering
the Fyllas Banke and the Sisimiut license area
and 2). Data sets with parameters of relevance
to the area.
The following data sources were found to
cover the Fyllas Banke and Sisimiut license
area:
1. 20 Radarsat ScanSAR Narrow scenes plus
filter products for Fyllas Banke, early
July-mid-September 2000.
2. Infrequent ScanSAR Wide scenes, spring
and early summer 2000, 1999 and 1997.
3. Iceberg observations recorded onboard
West Navion during the drilling season
2000.
4. Data/ice charts from infrequent ice
reconnaissance flights for the period 1958
- 2000.
5. Charts from reports, showing the iceberg
density, mass and draft distribution
(DHI/GTO, 1979b).
6. Probability charts on the occurrence of sea
ice in July, August and September.
1. Indirect information and data coverage,
latitude and longitude of observed
icebergs, size and class (40 to 52°N and
39°W to 57°W). These data, from “The
International Ice Patrol (IIP) Iceberg
Sightings Database”, were obtained from
the National Snow and Ice Data Center
(NSICC), University of Colorado at
Boulder.
In the present study, it is assumed that the
iceberg input to the East Greenland Current is
constant on an annual basis. Also the sizes
and classes of the icebergs are only known
very roughly. The utilization, analysis and
interpretation are described in Chapter 4 to 6.
Due to limited relevant data covering Fyllas
Banke and the Sisimiut licence area (listed
above), indirect but more frequent data for the
areas were analyzed.
Data related to the Fyllas Banke license area:
12
3 Summary of the Year 2000 Season at Fyllas Banke
are running in the south-north direction,
Figure 4.
More than 200 icebergs, bergy bits and
growlers were registered near West Navion
throughout the drilling season (Bullock et al.,
2001), Figure 7. The precise coordinates of
the drill site were 63°48’47.94” N and
54°27’03.31” W. Based on the Statoil
observations, more than 50% were
characterized as bergy bits or growlers, which
easily may be towed or deflected from the
exploitation site. Due to current eddies or
wind changes, the icebergs entered the area
from various directions, but most icebergs
entered the area from southerly to
northeasterly directions.
Number of targets/icebergs observed
Icebergs were monitored continuously
throughout the drilling operation year 2000 by
the ice watch team onboard the drilling
vessel, West Navion. Especially during the
first month of operation, a relatively large
number (larger than expected) of icebergs
were observed near West Navion and
deflection activities were found necessary and
often carried out by supply vessels.
64.50
64.00
63.50
55.00
54.50
54.00
53.50
53.50
10 UTC
21 UTC
8
6
4
2
0
13 16 19 22 25 28 31 3
Jul
Figure 7. The sites (cross) where the icebergs,
growlers and berg bits were detected around West
Navion (bold cross), in the summer months July,
August and September 2000. The circle around West
Navion has a radius of 12 nautical miles (1 nautical
mile = 1852 m) (Data source: AMEC).
6
9 12 15 18 21 24 27 30 2
5
Aug
8 11 14 17
Sep
Date
Figure 8. Summary of West
observations (Source: AMEC).
Navion
iceberg
It is remarkable that several icebergs,
sometimes 8 - 10 were observed
simultaneously near West Navion (in a radius
of about 15 nautical miles) through the first
weeks of the drilling period in mid-July,
Figure 8. Also periods up to several days with
no or very few iceberg occurred frequently.
Overall there is a significant decline in the
number of icebergs observed from July to
September, probably representing the normal
seasonal
variability
of
the
iceberg
environment of Southwest Greenland.
However, it is theoretically possible that some
icebergs have been in and out of the area
twice (out of the radar observation limit for a
shorter or longer period). The ocean currents
are significantly influenced by the local
bathymetry and more intense near the edge of
the continental shelf. The 1000 m isobaths is
east west oriented in the vicinity of Fyllas
Banke, which explains why some of the
icebergs entered the area from easterly
directions, rather than southerly directions,
although the main drift would be in parallel to
the overall sea bed contour, where isobaths
13
Based on ice chart information, the
distribution of multi-year sea ice (of Arctic
Ocean origin) peaked 29 June 2000 near 63°N
after a couple of weeks with significant
amounts of sea ice (mixed with glacial ice)
near and south of 62°N, Figure 9. Sea ice was
observed between 62°N - 63°N from the first
week of June until the first week of July.
Multi-year ice was present near or west of
48°W from early March until mid-July (close
to normal conditions).
Based on satellite information, it was evident
that in April and May a significant number of
icebergs had passed Nunarsuit (Figure 1) and
were drifting northwards in the West
Greenland Current, see example below from
15 May 2000, Figure 10.
Figure 9. “Typical ice chart” for the Southwest
Greenland waters, summer 2000. The ice chart
indicates that multi-year ice and many icebergs were
present west of Paamiut (Source: DMI). The "Egg
symbols" refer in coded format to the hatched areas.
The uppermost group in an "egg" describes the total
sea ice concentration (in tenths of the surface covered
with ice), partial concentrations (left blank here),
icetype (third group) and floe sizes (fourth group),
combined with additional symbols for bergy water and
few/many growlers/icebergs. In this case the icetype is
multi-year ice arranged in floes less than 100 m in
diameter. For a complete description of the "Egg
code", see http://www.natice.noaa.gov/egg.htm.
Figure 10. Radarsat ScanSAR Wide image over the
Southwest Greenland waters (60°5’N – 62°5’N) from
15 May 2000, 21:00 UTC. Overlay is the
target/iceberg detection filter product, CFAR. The
“Storis” is present to the south. The coastline is
marked in green (Source: Canadian Space Agency, RSI
and DMI).
14
4 Summary of Earlier Investigations of the Icebergs at the West
Coast of Greenland
greater than 10 were never reported in the
1975 - 78 investigation (DHI/GTO, 1979b).
The most detailed information about the
distribution of icebergs was compiled from
1975 to 1978 (DHI/GTO, 1979c). In addition
to the distribution of icebergs, the mass and
draft are the most important iceberg
parameters in connection with drilling
operations. The mass sets the limits for
towing operations, while the maximum draft
determines the “safe level” for installations on
seabed (Bernitt et al., 1998).
The relatively few counts made by The
International Ice Patrol and Canadian Ice
Service in the same area support the 1975 –
78 findings (Valeur et al., 1997).
6 0°
70°
50°
55 °
3
4.1
Iceberg Distribution and
Characteristics
Mean iceberg density along the southwest
coast of Greenland was studied, using a radar
mounted on a survey ship. The radar reached
12 nautical miles from the ship. The survey
ship was crossing along the coast repeatedly.
The observations took place in the months
May through October 1975 - 78. The mean
iceberg density is presented in a grid with
mesh size 1° x 0.33°. The mean value
calculated for each grid cell is representative
for the density of icebergs in that cell, Figure
11.
2
10
4
10
2
7
4
11
31
73
4
2 .5
3
2 .8
20
7
3.4
2.9
3.5
3 .5
27
A as ia a t
3
0
68°
1
B affin
Is la n d
1
0
64 °
4
4
6
0
0 .7
2 .5
1.9
2
1
0
0 .8
2
1 .2
0 .8
0.6 3
3.2
2.2
0 .4
1 .1
0.2
5
0 .5
1
0 .1
0 .2 0
1
1.6
2 .1
0.2
0 .1
0
1
0 .3
0 .9
0
0 .3
0 .2
0 .9
0 .1
0.4
1 .3
0 .3
0.5
0.2
0.4
0 .1
0.5
0.8
0.2
0.8
1.8
0 .4
0.5
1
2.2
1 .5
1.5
3
0 .3
1 .9
2 .6
1 .4
0
1
9
10
M e an d e n sity in n um b e r of
ic e b ergs w ith in 1 2 n a utic al m ile s
60°
S is im iu t
1
0
0
0 .5
2
5
G re e n la n d
0.5
W e s t N a vio n
62°
1
1 .1
0
0.5
2
5
- 130
75
Ilu lis sa t
4
66 °
The minimum iceberg densities were found
between 65°N and 66°N. From this relative
minimum, the iceberg density increased both
towards north and south, reaching mean
densities higher than 6 icebergs in areas south
of latitude 64°N and north of 68°N
(DHI/GTO, 1979b). Although the West
Navion site was not covered in the 1975 –78
investigations, neighbour areas were. The
neighbour grid cells mean counts ranged from
zero to nine, Figure 11.
13 0
2
M a n iits o q
0.5
0 .5
0 .9
N uuk
6
13
8
9
7
6
5
4
55 °
50°
Figure 11. Mean iceberg density, May through October
1975 - 1978 (DHI/GTO, 1979b).
Mean values can mask a big variation, e.g.
one observation with many counts and the rest
with low counts. However, in the area with
minimum densities, 64° – 66°N, counts
4.2
Seasonal Variation in Density
Distribution
In the 1975 – 78 investigation, the seasonal
variation in the number of icebergs was
investigated using the same grid as above and
15
comparing the mean count from May to July
with the counts from August to October. The
densities varied very little between the two
periods north of 65°N. The late summer
counts had a tendency to be lower south of
latitude 65°N.
4.3 Iceberg Mass Distribution
An analysis of the mass distribution versus
latitude and longitude was also included in the
1975 – 78 study. The largest icebergs were
most frequently found south of latitude 64°N
and north of latitude 66°N, Figure 12.
The distribution of icebergs was not uniform
in the grid in the early summer period, May to
July. Going from north to south, the highest
mean densities were found farthest from the
coast between latitude 67°N - 68°N, by
contrast the highest densities were found
nearest to the coast south of latitude 66°N
(DHI/GTO, 1979b).
South of latitude 64°N, the mean mass varied
between 1.4 and 4.1 million ton with
maximum estimated mass of 8 million ton.
Between latitude 64°N and 66°N, mean
masses were between 0.3 and 0.7 million ton,
the maximum mass was 2.8 million ton.
70°
55°
60°
32
2.1
2.5
1.9
12
3.8 7.5
Aasiaat
1.2
1.5
1
Greenland
0.7
Baffin
Island
8.3
4.9
10
3.4
Aasiaat
2.1
Greenland
2
Baffin
Island
Sisimiut
1.8
5.3
68°
2.8
1.3
20
Ilulissat
Ilulissat
4.9
1.6
50°
8
11
68°
55°
60°
70°
50°
Sisim iut
15
1.1
8
66°
66°
0.4
0.7
0.5
0.7
0.3
0.7
0.9
M aniitsoq
0.3
2.5
2.8
1.5
1
1.5
0.9
64°
64°
M aniitsoq
0.1
Nuuk
Nuuk
0.3
0.3
W est Navion
4.1
1.4
W est Navion
8
5.7
2
0.6
Maxim um iceberg m asses
in m illion ton
Mean iceberg m asses
in m illion ton
62°
60°
3.7
0- 1
1- 2
2 - 11
62°
55°
60°
50°
6.2
0.1 - 2.5
2.5 - 7.5
7.5 - 32
55°
50°
Figure 12. Distribution of mean and maximum iceberg masses, May through October 1975 – 1978. In the grid are the
mesh size 1° x 1° (DHI/GTO, 1979c).
16
64°N was 60 - 80 m with a maximum draft of
138 m. Between latitude 64 - 66°N, a
minimum was found with mean drafts of 50 70 m and maximum estimated draft of 125 m.
North of latitude 66°N, the mean iceberg
mass was larger, as a consequence of the
nearby calving in the Disko Bay. The biggest
icebergs were found at the Sisimiut licence
area and in the Disko Bay. At the Sisimiut
licence area the mean masses were estimated
to be near 2 million ton with maximum
estimates of 15 million ton for individual
icebergs. In the Disko Bay, mean masses were
estimated to be in the range of 5 - 11 million
ton and individual maximum estimates on 32
million ton (DHI/GTO, 1979c).
North of 66°N, the mean draft was generally
between 80 and 125 m and the maximum
estimated draft was 187 m. The overall draft
of icebergs in the observation area has been
estimated to be less than 230 m (DHI/GTO,
1979c).
The increasing drafts towards the north
indicate that a significant part of the icebergs
enter the area from the north, probably from
Disko Bay (DHI/GTO, 1979b).
4.4 Draft of Icebergs
The distribution of iceberg draft in the grid
net nearly followed the mass distribution,
Figure 13. The mean draft south of latitude
70°
55°
60°
70°
50°
55°
60°
50°
126
101
Ilulissat
Ilulissat
126 100
68°
90
91
84
81
Aasiaat
137 141
141 141 100
Greenland
72
B affin
Island
Sisim iut
87
125
67
66°
66°
73
59
G reenland
73
Baffin
Island
Sisim iut
53
Aasiaat
155 127
68°
77
M aniitsoq
86
83
71
85
120
125
42
M aniitsoq
73
64°
64°
Nuuk
N uuk
W est Navion
81
W est N avion
65
73
M axim um iceberg drafts
in m eters
Mean iceberg drafts
in m eters
62°
60°
128
53 - 73
73 - 100
100 - 126
62°
55°
50°
60°
138
42 - 85
85 - 128
128 - 155
55°
50°
Figure 13. Iceberg draft distributions in selected sectors on the southwest coast of Greenland, with mean and maximum
draft, May through October 1975 - 1978. In the grid are the mesh size 1° x 1° (DHI/GTO, 1979c).
17
Table 2. One-hour mean iceberg drift velocities (in
cm/s and in km/hr in brackets) at the three drill rig
positions (DHI/GTO, 1979c).
Arco
Chevron
Exceedance Mobil
67°53´N
frequency
65°34´N 66°57´N
54°34´W 54°31´W 56°48´W
50%
20 (0.7)
30 (1.1) 20 (0.7)
10%
36 (1.3)
55 (2.0) 42 (1.5)
1%
58 (2.1)
80 (2.9) 61 (2.2)
0.1%
77 (2.8)
98 (3.5) 77 (2.8)
0.01%
94 (3.4)
116 (4.2) 91 (3.3)
Number of
observations
202
120
969
4.5 Drift Speed Analysis
Iceberg drift velocities were calculated in the
1975 - 78 investigation by using data sampled
by three drill rigs, Mobil, Chevron and Arco
respectively, Table 2. At the Arco and the
Mobil positions, the one-hour mean iceberg
drift speed was about 20 cm/s, while it was
about 30 cm/s at the Chevron site. The drift
direction was depending upon the mass of the
icebergs. Icebergs with masses > 1 106 ton
tended to drift northwards, whereas smaller
icebergs predominantly drifted towards
southeast (DHI/GTO, 1979c).
At positions for the Mobil and the Chevron
rigs, the great majority of one-hour iceberg
drift velocities were towards northern
directions. At the Arco drill rig, located at the
northwestern part of the Store Hellefiske
Banke, the frequency of south going drift
velocities was almost equal to the frequency
of north going drift velocities (DHI/GTO,
1979c).
It appears, that the highest one-hour iceberg
drift speed occurred at the Chevron position,
Table 2. Less than 0.1 % of the icebergs
observed at the Arco and the Mobil rig have
velocities higher than 77 cm/s, but 98 cm/s at
the Chevron rig.
18
5 Analysis of Ice and Icebergs Drifting into the West Greenland
Waters from South
5.1 CFAR filtering of Radarsat SAR data
The problem of detecting icebergs in satellite
SAR data mainly consists of identifying them
against the background sea clutter and,
equally important, reducing ”false alarms”. It
has been found that the normalized second
moment of the probability distribution, the
Power-to-Mean-Ratio (PMR), is very useful
for the detection of possible icebergs against
the background sea clutter. To reduce the
number of spurious targets, iceberg detection
based on the Constant False Alarm Rate
(CFAR) method, has recently been
implemented.
In the DMI (Danish Meteorological Institute)
version the statistics of the background are
described by the gamma distribution (limiting
case of the k distribution). The false alarm
probability is the probability that the backscattered signal, above threshold intensity, is
misjudged as an iceberg, acts as a threshold,
and is used to remove ”false targets”. This
approximation results in significant reduction
in computation time, which is an important
issue in an operational environment (Gill et
al., 2000). The PMR method is not used in
these investigations, because the CFAR
method is found more accurate for iceberg
detection.
63 Radarsat imagery available at the Danish
Meteorological Institute from 1997, 1999 and
2000 covering the Southwest Greenland
waters were reprocessed for the spring and
summer months using the CFAR method. The
accuracy and the limitations of the methods
for detecting icebergs have not been evaluated
thoroughly; however, a relatively large
number of Radarsat scenes were reprocessed
and analyzed to reduce the influence of “real
false icebergs”, i.e. ships, which are
impossible to exclude. In addition, most
images covered the area in the “far range”
part of the images. Here the image quality is
normally very high. Therefore, the results
shown in Table 3 and Table 4 for the
Southwest Greenland waters are believed to
give good estimates of the seasonal and inter
annual variability of the number of icebergs.
A geographical grid (½°Lat. x 1° Long) was
defined and used in the registration and the
statistical analysis of the data sets, Figure 14.
The results are shown in Table 3.
Figure 14. In this grid definition, the number of
icebergs/targets using the CFAR method was counted
in each sector. The grey circle and the tiny frame at the
drilling location outlines areas investigated in details
in the present study, see also Figure 15 and 16.
19
Table 3. Number of targets pr ½°Lat. x 1°Long extracted using the CFAR method. “I” indicates the presence of multi-year sea ice (N show that the number
of targets not registered). The analysis (number of targets) is not corrected for the presence of West Navion, supply vessels, and other ships. The waters
near Fyllas Banke and 'West Navion' is highlighted green (Data source: DMI).
20
targets were detected in the spring months,
April and May.
4) The 2000 season is not significantly
different from year 1999 and 1997.
The results of the analysis of Radarsat
ScanSAR Imagery for the years 1997, 1999
and 2000 using the CFAR method are shown
as averages, in Table 4. Interpretation of
results and conclusions based on only three
years of data always have to be carefully
carried out to avoid misleading results. The
geographical coverage of data for 1997 and
1999 is also limited, however, there are some
important characteristics:
1) The number of targets generally decreases
when the distance to the Greenland shore
increases.
2) The number of targets in the northern part
of the study area (near Fyllas Banke) is
generally smaller than in the southern part.
3) Significant seasonal variability is also
identified. In general, the number of
icebergs peak in July and relatively few
The number of targets was also counted near
the West Navion position, in 1) a 0.25°Lat. x
0.5°Long. grid outlined by 63°40’ – 63°55’N
and 54°10 – 54°40’W, and 2) within 10
nautical miles around West Navion, Figure
14. Table 3 (the two columns to the far right)
compare satellite observations with observations from West Navion. If the satellite data
is corrected for known vessel positions, there
is generally a good agreement between the
data in these two columns, but not a 1:1
correlation. Not all vessel positions are
available and false targets may appear, which
are impossible to exclude in the data set.
Table 4. Average number of targets in ½°Lat. x 1°Long “boxes” using the CFAR method, averaged over the four
sectors 61°N - 62°N, 62°N - 63°N, 63°N - 64°N and 64°N - 65°N. White colour in the tables indicates no data available
(Data source: DMI).
21
The iceberg information from each ice chart
was extracted manually, tabulated and
analyzed by use of simple statistical methods.
The area of interest was divided into five
sectors, Figure 15. For every chart each of the
sectors were characterized by a score (0 to 6),
ranking from excellent to worst ice
environment for a drilling operation, Table 5.
The main areas of interest for sea floor
activity are sectors A and B.
Interpretation of the results was primarily
based on the following simple assumptions:
1) Few/no icebergs in sector 1, 2 and 3 lead
to very few/no icebergs in sector A and B
1 - 3 months later.
2) Many icebergs in sector 1 and 2 lead
probably to many icebergs in sector A and
B 1 - 3 months later.
3) Many icebergs in sector 3 lead not
necessarily to many icebergs in sector A
and B 1 - 3 months later.
Figure 15. Definition of sectors used in the ice chart
study.
Only data recorded in the summer season,
April - September, were found relevant to be
included in the investigations. Sea ice/iceberg
records for 1975 - 2000 or 26 seasons were
studied. Because the number of available data
and the observation dates varied from year to
year, the observations were regarded as
“ensemble measurements”.
5.2 Iceberg Data Based on Ice Chart
Information 1975 - 2000
Data and statistics on the presence of icebergs
near Fyllas Banke are sparse. The icebergs
observed here in summer are only a fraction
of the icebergs that passed the Cape Farewell
area 1 - 3 months earlier.
Table 5. Severity index. The ranking used for each
descriptive wording for iceberg severity.
Index Description
value
No data in this particular area
0
Open water, no icebergs
1
Bergy water (icebergs occur only occasionally)
2
Few icebergs (icebergs occur infrequently)
3
Few/many icebergs (many bergs in some areas)
4
Many icebergs
5
Numerous icebergs
6
Multi-year ice and icebergs
For navigation safety reasons the ice
conditions in the waters near Cape Farewell
are mapped operationally 1 - 3 times a week
using aircraft or in the recent years by using
high resolution SAR satellite images. The ice
charts do not contain specific data on
individual icebergs, but indicate whether there
are many, few or no icebergs. The mapped
areas as well as the contents of information
vary from chart to chart. Direct information
on the amount of icebergs north of 62°N is
infrequent.
The error using this method decreases, when
the number of observations increases.
“Ensemble averages” were calculated daily
22
drilling location in year 2000. Sea ice rarely
occurred in that area and was therefore only
occasionally mapped. Basically, the evaluated
data cannot be regarded as representative for a
long time period. Anyway Table 7 shows that
more severe ice conditions than in the 2000
season, have been observed earlier in sector
A.
over a period of 11 days (5 days before and 5
days after a given reference date). A summary
of the ice chart study and the calculations are
shown in the tables 7 - 9 for sector A, B and
1. The legends in these tables are shown in
Table 5 and Table 6.
Sector A represents the offshore area near the
Table 6. Legend for the tables and parameters in Table 7 - 9.
N_obs
Number of observations available for the reference date in the period 1975 - 2000
Number of observations without sufficient data coverage for the reference date in the period 1975 - 2000
0 (%)
Percentage of the ice observations included Category 0 (Open water, No icebergs)
1 (%)
Percentage of the ice observations included Category 1 (Bergy water)
2 (%)
Percentage of the ice observations included Category 2 (Few icebergs)
3 (%)
Percentage of the ice observations included Category 3 (Few/many icebergs)
4 (%)
Percentage of the ice observations included Category 4 (Many icebergs)
5 (%)
Percentage of the ice observations included Category 5 (Numerous icebergs)
6 (%)
Percentage of the ice observations included Category 6 (Multi-year sea ice and icebergs)
Ave.
Average value of the ice observations in the Categories 1 - 6 for this reference date
frac25
25% fraction of the ice observations in the Categories 1 - 6 for this reference date
median Median of the ice observations in the Categories 1 - 6 for this reference date
frac75
75% fraction of the ice observations in the Categories 1 - 6
me2000 Median of the ice observations in the Categories 1 - 6 for this reference date for 2000 only
me2000 - median (negative values indicate that median for year 2000 observations
∆
were lower than the median for 1975 - 2000)
Table 7. Summary of the results (1975-2000) and statistics in sector A, for legend see Table 5 and Table 6.
23
Table 8. Summary of the results (1975-2000) and statistics in sector B, for legend see Table 5 and Table 6.
Table 9. Summary of the results (1975-2000) and statistics for sector 1, for legend see Table 5 and Table 6.
24
range of the index is between 0 (no ice at all
in the period) and 1 (ice throughout the whole
period), Table 14.
Sector B and sector 1 are located respectively
east and south of Fyllas Banke. Generally
these areas have the “worst” ice conditions in
June and July. In sector 1 almost all iceberg
observations have severity index 1, 2 or 3 in
August and September, but in the year 2000,
the waters were generally characterized by
index 2, which means that some earlier years
had more icebergs than in 2000 and other
years less icebergs. Due to the physics in the
area, it is reasonable to assume that the
pattern would be the same between 63°N 65°N, but the result of deterioration will
normally lead to fewer icebergs. This is to
some extent confirmed, Table 7 and Table 8,
taking into account the low number of
observations in sector A and B.
From time to time the multi-year sea ice drifts
north of 63°N. In order to increase the
resolution of the data in the Fyllas Banke
area, the area between 63°N and 65°N was
split into 18 subsections, Figure 16, and the
occurrence of multi-year sea ice was studied
in each of these subsections. The results of
this high-resolution study are only shown for
“Subsection 10”, which is identical with the
area, where the drilling in year 2000 was
performed, Table 13. Multi-year ice is a rare
phenomenon here and when it enters
“Subsection 10”, it is nearly always in June or
July. The ice observations in year 2000
showed, that the sea ice extended up to 63°N
(near the shore). This is close to normal
conditions and in most of the years studied;
the multi-year ice did not drift north of this
latitude. It is, however, also noted, that there
are several examples of severe ice conditions
in the Fylla Banke area. Then, sea ice and
probably many icebergs can occur near the
Fyllas Banke area until mid-August, although
rarely.
5.3 Iceberg Data based on Ice Chart
Information 1958 - 2000
Multi-year sea ice information for the
Southwest Greenland waters was extracted
from all available navigation ice charts (~100
high resolution icecharts pr. year). Due to the
large amount of data and the nature of multiyear sea ice in the area, the waters were
divided into three sectors:
•
•
•
Multi-year ice observed west of 48°W
Multi-year ice observed 62°N - 63°N
Multi-year ice observed north of 63°N
Every month in the “Storis” season
(December – August) was divided into
weekly intervals and the presence (but not the
amount) of multi-year ice was registered for
each 7 - 8 days period for each of the years
1958 – 2000, Table 10 - 12. This data set does
not include iceberg information and is there
significantly different from the data set for the
period 1975-2000 analyzed in section 5.2.
The “deterioration rate” from “common” to
“occasional” of the meridional multi-year ice
distribution is identified when the tables are
compared. Additionally, a simple multi-year
ice “presence index” was calculated, as
monthly means, for three time periods, July August, April -June and April - August. The
Figure 16. The occurrence of multi-year ice between
63° - 65°N was investigated in a grid net with 18
subsections (½° Lat. x 1° Long).
25
Table 10. The occurrence of multi-year sea ice (M)
west of longitude 48°W. West Ice not included (Data
source: DMI).
Table 12. The occurrence of multi-year sea ice (M)
north of 63°N. West Ice not included. (Data source:
DMI).
Table 11. The occurrence of multi-year sea ice (M)
62°N - 63°N. West Ice not included (Data source:
DMI).
Table 13. The occurrence of multi-year sea ice (M).
West Ice not included The results of the study for
subsection 10 (equivalent to the drilling area in year
2000) for 1958 - 2000 (Data source: DMI).
26
Table 14. Multi-year ice presence index (definition, see
text) categorized into 5 colour groups.
27
6 Analysis of Icebergs and Ice drifting into the West Greenland
Waters from North and West
6.1 Sea Ice Environment of the Eastern
Davis Strait
In the summer season, the currents in the
Davis Straits are the dominant factor
influencing the distribution of sea ice, since
new ice does not form in the summer season.
It is evident that the probability of sea ice
decreases through the summer, Figure 17. The
West Ice is formed along Baffin Island and is
carried by currents into central Baffin Bay
and the Davis Strait. The extent of the West
Ice is at its minimum in October, and it
normally reaches its maximum distribution in
April.
The icebergs observed in the northern parts of
Davis Strait (north of Sisimiut) and at the
Grand Banks of Newfoundland originate from
the glaciers in Disko Bay and eastern Baffin
Bay. The aim of this section is to investigate a
possible connection between the amounts of
icebergs in the two areas. For inter-annual and
seasonal variations in the number of icebergs
passing south of 48°N of eastern North
America, an empirical relationship between
the numbers of icebergs and the distribution
of sea ice has been derived. The distribution
of the Labrador spring ice influences the
number of icebergs present in different years
and was either determined by or closely
correlated to the area covered by midwinter
Davis Strait ice (Marko et al., 1994).
Figure 17. The probability (%) of the occurrence of sea ice, 2. of July, 6. of August and 3. of September. The probability
lines in NW refer to West Ice (Nazareth & Steensboe, 1998).
28
latitude in the IIP data set, it would in turn be
possible to use the IIP data south of 48°N as
an indicator for the number of icebergs in the
Davis Strait.
The West Ice affects the western margin of
the Sisimiut licence area in the summer
months, July - September. However, West ice
rarely drifts into the area covered by the
Sisimiut licence. Charts showing the average
distribution of the sea ice through the years
are available (Nazareth & Steensboe, 1998).
1800
No icebergs
1500
6.2 Analysis of Icebergs Observed at the
Grand Banks of Newfoundland
The
International
Ice
Patrols
(IIP)
observations of icebergs are a main source for
icebergs originating from the Disko Bay and
eastern Baffin Bay. The Ice Patrol’s main
mission is to map the southern limits of the
area of iceberg danger. The iceberg
observations cover the years from 1960 to
2000. The area monitored by IIP covers the
area from 40 to 52°N latitudes and 39 to
57°W longitudes. The data do not provide the
exact number of icebergs south of 48°N, but
the number of observed/estimated icebergs.
The Ice Patrol uses the number of icebergs
drifting south of latitude 48°N as a measure of
the severity of the iceberg season.
1200
900
600
300
0
48
52
56
60
64
68
Latitude
Figure 18. The number of icebergs in relation to
latitude, from Cape Dyer 67°N to Newfoundland 48°N,
through the years 1963 - 1969. The prediction and
confidence limits correspond to the red and green
bounds on the graph.
The equation of the fitted model is:
Number of icebergs = (5800–274000)/latitude
P < 0.00001, r² = 98%
In order to improve the IIP database, new
sampling methods have been employed over
the years. In 1983 and during the first years of
using Side Looking Airborne Radar (SLAR),
there were difficulties in discriminating
between vessels and iceberg targets.
Concurrent with the exploration of the
Hibernia oil field in 1985, an increase in the
estimate of icebergs crossing 48°N was seen
for all four years the exploration lasted. In
1991, reports from ships accounted for over
50% of the icebergs observed. The number of
flights used in iceberg reconnaissance
increased in 1991 resulting in an increase in
the number of iceberg counts. Then, an
improvement in the method of sampling data,
may affect comparisons over time.
Then, there is a statistically significant
relationship between the number of icebergs
and latitude at the 99.9% confidence level.
The model explains 98% of the variability in
number of icebergs, r2 statistics.
The strong regression of the number of
iceberg with latitude, Figure 18, indicates,
that the yearly amount of icebergs south of
48°N can be considered an indicator of the
severity of the iceberg season in the West
Greenland waters north of 66°N.
The close relationships between iceberg
density in the Davis Strait in the winter and
south of 48°N in the spring are physically
explicable. Net southerly drift rates of
approximately 15 km day-1 in areas south of
67°N are typical. Ice and icebergs at 65°N in
Davis Strait should cross 48°N in late May,
6.2.1
Statistics on the IIP Area 40° to 52°N
and 39°W to 57°W
If it were possible to show the dependence
between the number of icebergs in relation to
29
i.e. in the middle of the peak iceberg season
(Marko et al., 1994), Figure 19.
Over the years, the number of icebergs varied:
the minimum number was 0 in 1966 and the
maximum number was 2202, observed in
1984. The iceberg numbers were in minimum
in the 1950s and 1960s in general. A higher
number of icebergs characterized the latest
years, and in the year 2000, 843 icebergs were
observed south of 48°N.
Average numbers of icebergs
1960 - 2000
160
140
120
100
80
In 1975 - 1978 the number of iceberg counts
was low south of 48°N. Indicating that the
severity of the iceberg seasons north of 66°N
in the eastern part of the Davis Strait were
below average in 1975 - 78. Using the past 40
years of iceberg observations one can
conclude that the severity of year 2000 was
above average. However, due the use of
different observation - methods over time, it
may be more reliable only to compare the
numbers for the last ten years, Figure 21.
60
40
20
0
Oct Nov Dec Jan Feb M ar
Apr May Jun
Jul
Aug Sep
Month
Figure 19. Average monthly numbers of icebergs
crossing 48°N extracted from annual IIP counts for the
period 1960 – 2000.
2000
No of icebergs
1600
1200
Average 1961-2000
2000
800
400
o
No. of icebergs, south of 48 latitude
Figure 20 illustrates the annual iceberg counts
south of 48°N. There is a tendency to high
numbers of icebergs to occur in 3 or 4 years
in a row and minimum numbers to occur at
intervals of 4 to 9 years. During the years
1960 - 2000, there was an average of 598
icebergs crossing latitude 48°N.
0
1500
1990
1000
1992
1994
1996
Year
1998
2000
Figure 21. Number of icebergs at the Grand Banks of
Newfoundland south of 48°N in the last 10 years. The
95 % significance limits, red bounds, are indicated.
500
No significant relationship between number
of icebergs and year was found during the last
decade. Therefor, no increase in the number
of icebergs have been found for the years
1990 – 2000.
0
1900
1920
1940
1960
1980
2000
Year
Figure 20. Number of observed/estimated icebergs at
the Grand Banks of Newfoundland south of 48°N, in
the year 1900 - 2000. Based on data from International
Ice Patrol.
30
7 Conclusions
parts of Davis Strait and at the Grand
Banks of Newfoundland.
The main objective of the study was to
evaluate, characterize and compare the year
2000 iceberg observations with other data
sources and historical data. Based on the
available data, it is concluded that:
The following conclusions can be made from
the observations in this report.
The icebergs observed at Fyllas Banke,
from early July until mid-September 2000
probably represent normal seasonal
conditions rather than severe conditions.
The minimum iceberg densities, the icebergs
with the lowest mass, and the icebergs with
the smallest draft, were found between 65°N
and 66°N (DHI/GTO, 1979c). Relative to this
area, the iceberg density, mass and draft
increase both towards north and south. The
increasing iceberg density, mass and draft
towards south and north indicate that a
significant part of the icebergs in the Fyllas
Banke area are of southern origin, while the
largest part of the icebergs in the Sisimiut
licens area are of northern origin. The
icebergs entering the Fyllas Banke area from
the south are mixed with large amounts of
multi-year ice.
Seven individual studies were carried out to
gather new information and to improve
existing iceberg data, for the West Greenland
waters between 63°N - 68°N:
1) Evaluation of the iceberg observations
(recorded by Statoil) during the summer
2000.
2) Evaluation of the results from the
investigation performed by DHI/GTO in
1975 – 1978.
3) Utilization of iceberg detection algorithms
on 67 Radarsat ScanSAR Narrow/Wide
scenes covering the Southwest Greenland
waters for the spring/summer months of
the years 1997, 1999 and 2000.
4) Iceberg information for the waters
between 65°N and Cape Farewell was
extracted from ice charts covering the
period 1975 - 2000, and categorized into 7
“ice severity” classes.
5) Multi-year ice distributions on a weekly
time scale were produced for the years
1958 - 2000 for the waters west of
longitude 48°W, between 62°N - 63°N
and for the waters north of 63°N.
6) High-resolution study of the multi-year
ice distribution in 18 sectors between
63°N and 65°N (including the drilling site
in the summer 2000) for 1958 - 2000.
7) Analysis of a possible connection between
the amounts of icebergs in the northern
The strong regression of the number of
iceberg with latitude, Figure 18, indicates,
that the yearly amount of icebergs south of
48°N can be considered an indicator of the
severity of the iceberg season in the West
Greenland waters north of 66°N, i.e. for the
Sisimiut license area. The 1975 - 1978
seasons were a low iceberg seasons south of
48°N. This implies that the severity of the
iceberg seasons north of 66°N in the eastern
part of the Davis Strait were below average
during the years of investigation in the 1970s.
Evaluating the last decade records of icebergs,
it is concluded, that year 2000, does not
deviate. Then, year 2000 can be considered as
a normal year concerning icebergs in the
Sisimiut license area.
The year to year variation in amount of
icebergs at Fyllas Banke may be related to the
seasonal distribution of ”Storis”. Observations
of ”Storis” in the period 1958 - 2000 make it
probable, that the years 1975 - 1978 can be
31
considered average years in terms of the
number of icebergs south of 65°N. The
number of icebergs and the varying amounts
in the year 1975 – 1978 (pp. 15-18) were
almost similar to the number of iceberg
observed during the summer 2000. Through
the years 1975 - 1978 many icebergs were
observed just east of the West Navion site.
C)
D)
Near Fyllas Banke the waters are normally
free of sea ice. The density of icebergs is low
most of the year. Generally, the multi-year ice
distribution reach it’s maximum in late June
near 63°N, but may be present further north
from spring in severe years until as late as
mid-August.
The number of icebergs between 63 - 65°N is
probably very low in April and May,
increasing quickly during June and reaching
its maximum in July. Then, maximum is
about one month later than the peak of the
multi-year ice distribution. The number of
icebergs declining slowly during August and
September. This pattern is expected to
represent the normal conditions. Deviations
from the pattern are possible, but will
probably follow the distribution of multi-year
ice delayed by 1 - 2 months.
E)
F)
7.1
Ranking of the Year 2000 Season at
Fyllas Banke
It is important to point out that:
A) Multi-year sea ice was not observed at or
near the drilling location, from early July
until mid-September 2000. In the months
July and August multi-year sea ice has
been observed at or near the drilling
locations in 6 of 43 years, Table 13.
Consequently, it may be concluded, that
with respect to presence of multi-year sea
ice year 2000 was not exceptional.
B) Multi-year sea ice was only observed once
north of 63°N in early July 2000. For the
months July and August, multi-year sea
ice has been observed north of 63°N in 13
out of 43 years (1958 -2000) for similar or
longer periods, Table 12. Thus, year 2000
G)
was not exceptional, but probably slightly
above average.
The multi-year sea ice season 2000 was
close to normal compared with the
previous 42 seasons. The season ended in
late July in the Cape Farewell area, which
is marginally earlier than normal.
Observations covering the period 1958 2000 show that the years 1975 - 1978 may
be considered representing a statistical
mean with respect to the presence of
multi-year sea ice at the Fyllas Banke.
Moreover, the amount of multi-year sea
ice is closely related to the amount of
icebergs. Therefore the distribution of
icebergs in the years 1975 - 1978 can be
considered as normal and similar to the
iceberg distribution in the year 2000.
The study indicates that the ice severity
observed in year 2000, for the area
delimited by 60°45’N to 63°N, e.g. south
of Fyllas Banke, was only marginally
different
from
the
statistical
average/median of all observations for
1975 - 2000, Table 9.
The Radarsat data for year 2000 showed
no significant difference between 1997
and 1999, not forgetting that the amount
of relevant data was limited for the years
1997 and 1999, thus the relatively large
number of observed icebergs/targets is
expected to reflect the normal seasonal
variability near Fyllas Banke.
The data sets studied, generally showed
that the “ice severity” at Fyllas Banke
peaks about 1 month after the “ice
severity” peaks further south. The same
pattern was observed in the year 2000
season, also onboard West Navion.
Based on the results of the current study,
summarized, the 2000 season at Fyllas Banke
cannot be characterized as severe, but rather
close to normal.
7.2 Recommendations and Further Studies
One may consider shifting the exploration
season for the Fyllas Banke area from July
32
CFAR algorithms used on Radarsat SAR data,
p.19, have showed great potential and have
been operational through the 2000 field
season for iceberg/target detection. It is
therefore recommend that the CFAR method
should be used on a set of additional historical
Radarsat scenes to increase existing
knowledge of the iceberg environment
offshore West Greenland. A large number of
historical scenes are available for the West
Greenland waters since 1997 and it would be
possible to set up an extended detailed
analysis for the years 1997 - 1999, similar to
the year 2000 study. The CFAR method can
also be used successfully for iceberg detection
in the waters north of Fyllas Banke.
through September to April through June to
lower the probability of icebergs through a
future offshore operation. Davis Strait sea ice
(first year sea ice) occurs only occasionally at
the drilling site in very early spring and is
only present after very severe winters in early
April. Based on the current study the
distribution of multi-year ice peaks in late
June and the number of icebergs near Fyllas
Banke peaks in July. The probability of multiyear sea ice (from the south) north of 63°N is
almost the same in April - June as in July and
August, Table 14. Based on the sea ice record
for 1958 –2000, multi-year sea ice was only
observed twice in April and May (1970 and
1978) near the drilling location. In June,
multi-year sea ice was observed in 7 out of 43
years. Assuming the iceberg season at Fyllas
Banke peaks about one month “after” the
multi-year sea ice season peaks offshore
Southwest Greenland, the spring months may
be a better choice than the summer months.
In the future, more satellite data, field
programs, operational monitoring, and
improvement and/or development of iceberg
detection algorithms are definitely needed.
For strategic planning of a future offshore
operation, it is recommended that the sea ice
and iceberg environment is monitored
continuously using satellite images several
weeks prior to a planned operation to make
possible that necessary actions can be taken
well in advance. It is important to note that
monitoring of sea ice and icebergs may be
applied both in the Sisimiut and the Fyllas
Banke license area.
33
8 References
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Bernitt,L.M., Zorn,R. and Grønbech,J., 1998.
Environmental Conditions at Fylla Bank Licence Area
PL0010 Greenland. Basic Information. 1-63. Danish
Hydraulic Institute.
Marko,J.R., Fissel,D.B., Wadhams,P., Kelly,P.M. and
Brown,R.D., 1994. Iceberg Severity off eastern North
America: Its Relationship to Sea Ice Variability and
Climate Change. Journal of Climate 7, 1335-1351.
Bullock,J.T., Mayo,J., McClintock,J. and Green,S.,
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Nazareth,J. and Steensboe,J., 1998. Physical
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DHI/GTO, 1979b. Environmental Conditions Offshore
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hydraulic institute.
Valeur,H.H., Hansen,C., Hansen,K.Q., Rasmussen,L.
and Thingvad,N., 1997. Physical Environment of
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Part 1 & 2. Technical Report 97-9., 1-188.
Copenhagen, Danish Meteorological Institute.
DHI/GTO, 1979c. Environmental Conditions Offshore
west Greenland. Summary. Data Bank Contents. Vol. I,
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Gill,R.S., Rosengreen,M.K., Andersen,H.S. and
Valeur,H.H., 2000. Detecting Low Concentation of Sea
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34
ISSN 1601-3816
ISBN 87-91144-00-0