Side 28
Humlum,
Christiansen, Hansen, Hasholt, Jakobsen & Nielsen:
Institute of Geography, University of Copenhagen,
Øster
Voldgade 10, DK-1350 Copenhagen K, Denmark.
M.Rasch: Arctic Station, 3953 Qeqertarsuaq/Godhavn,
Greenland.
Danish Journal of
Geography 95: 28-41, 1995.
A study area at the
northeastern shore of Mellemfjord, in the western part
of Disko Island, near the western maximum limit of the
Greenland Ice Sheet during the Quaternary, was chosen
for an analytic landscape study. Interactions between
climate and landscape processes are designated for
future detailed process research and monitoring. The
project will focus on climatology, hydrology, energy
exchanges at the terrain surface, mass fluxes and
terrain element dynamics. Glacial, periglacial, fluvial
and coastal landforms, soils and ecosystem record (in
e.g. lakes and estuaries) will be used as geoindicators
in this interdisciplinary analytic landscape
investigation. Investigations in the about 100
km2 test area were initiated during the
summer of 1993 and preliminary results are presented
below.
Key words: West
Greenland, Disko, Holocene landscape
evolution,
palaeoclimatology
High-latitude, cold-climate
regions are recognised to be vital components in shaping
global climate and are likely to respond significantly
to future climate changes. The boreal and arctic regions
are thought to be particularly sensitive to regional or
global climatic changes (see, e.g. Eddy et al. 1988,
Etkin 1990, Maxwell 1992, Koster 1993). The seasonal
snow cover is important in this respect, causing wide
fluctuations to occur annually in surface energy balance
because of ice and snow phase changes. During snowmelt
the overall terrain albedo often changes from a high of
0.8 to a low of 0.2 at a time when the incoming solar
radiation is near an annual maximum. Therefore, the
seasons that characterise the climate of temperate
regions are exaggerated in polar regions in both
duration and amplitude. Also on timescales of decades or
longer, climate variability is greater than in other
climatic regions (Koster 1993). Any assessment of the
effects of global climatic change clearly requires a
thorough understanding of contemporary geomorphic
processes operating in the arctic and antarctic realms.
In the past half-decade or so,
Washburn (1985) and French (1987) have attempted to
identify research problems in arctic geomorphology and
to highlight research themes and trends in the field.
Several general as well as specific topics were
recognised such as palaeoenvironmental studies,
frost-related processes, pingos, palsas, mass wasting
processes, nivation, and ground ice.
Generally speaking,
palaeoclimatic inferences drawn from geomorphologic data
should be based on an understanding of the relationship
between climate and terrain element dynamic, such as
e.g. glacier fluctuations. Complex interactions exist
between prevailing regional and local climatic
conditions, regional and local topography, energy
exchange at the terrain surface, mass-fluxes and terrain
element dynamics. The individual terrain element
dynamics represents integrated responses to these
factors. Due to differences in the above factors, even
similar terrain elements within a geographically
restricted area may display different responses to
identical climatic changes. This obviously represents a
potential pitfall for palaeoclimatic and modern-climatic
studies using observational data on isolated terrain
elements such as i.e. glaciers, moraines, rockglaciers,
pingos, ice wedges, dunes, rivers, soils and coastal
features. However, by adopting a broader approach,
including many different terrain elements, local and
regional climatic influences may be identified and
evaluated. Preliminary results from the initiation of
such a study are outlined below.
General
and Climate within Disko Island
Topography
Disko Island (8600 km2) is situated in central West
Greenland, outside the coast of the mainland (Fig.l).
The island is mainly made up by Tertiary lavas, and the
landscape is a typical, arctic, plateau basalt landscape
with cirque carved lava plateaus and U-shaped valleys
and fjords. The upper land surface rises gradually from
about 800 m asl. in the southwestern part of the island
to more than 1900 m asl. in the northeastern part
(Fig.2A).
Climatic conditions within
Disko Island can be inferred only in general outline,
because only one meteorological station is presently
being operated on Disko at the town Godhavn (Fig.l).
This climate station has been operated since 1923. In
Godhavn the present (1960-1990) mean annual
Side 29
Figure 1:
Location map showing Disko Island place names and the
study area (black square)
air temperature
is -3.9°C; the coolest month is March
(-15.1 °C),
while July is the warmest month (7.1 °C). The
mean
annual precipitation at Godhavn is about 400 mm
w.e. Most of the precipitation
(75 %) usually falls during the period June to December
with advection of moist, maritime air masses from the
south and southwest along the Davis Strait. The
remaining period is comparatively dry, as it is
dominated by cold and dry continental polar air masses
from the Inland Ice. Approximately 60-70 % of the mean
annual precipitation is snow and in Godhavn persistent
snow cover is registered from late September to late
May.
The prevailing wind at Godhavn
is from the east (44.6 %), but in the period May to
August westerly winds (21.6 %) dominate. Mean wind speed
is at a maximum during the autumn and early winter,
while minimum values occur in February to April, and in
this period calms are frequent (20-30 %). In general the
wind directions are greatly influenced by orographic
conditions, and valley winds are widespread . In the
day-time up-valley winds dominate in the summer period
and down-valley winds dominate during the night-time and
the winter period.
At Qutdligssat,
at the northeastern coast of the island, a
meteorological station was operated 1961-72. The
mean
annual air temperature was -4.3°C (sea level),
coolest
Figure 2: A:
Topographic map of Disko Island. Areas below 500 m are
shown as while, while areas above j'OOO m are shown in
black. Doited areas 500-1000 m asl. B: Present ice cover
of Disko Island. Glaciers and isolated firn areas
(black) are mapped from aerial photographs taken in the
late summers of 1953 and 1964. The Mellemfjord study
area is outlined
Side 30
month was March (-17.0°C),
warmest month was July (6.6 °C). The mean yearly
precipitation was low, about 200 mm w.e. Generally
speaking, from what little is known, it appears that
climate along the southwestern coast of the island is a
polar, maritime climate, while along the northern and
eastern coasts the climate is more continental. Also the
central part of the island is probably rather dry; at
least this is what the flora and glaciation level
(Humlum 1985, 1986) indicate. Precipitation shadow due
to local topography and the neighbourhood of the
Greenland Ice Sheet further to the east is assumed to be
responsible for these overall climatic contrasts within
Disko Island.
The sea around Disko Island is
usually ice-covered from late December to late May.
Break-up of the ice cover primary depends on the
occurrence of large swelles caused by strong southerly
and southwesterly winds, associated with increased
cyclonic activity in the Davis Strait during the spring
and early summer. At sea level, the resultant wind is
from NE and E during October-February, while winds with
westerly component dominate during the summer. The zonal
flow from E is probably the result of cold air flowing
off the Greenland Ice Sheet due to the almost permanent
surface inversion, caused by strong radiational cooling.
During summer, this outflow is interrupted in the
coastal regions by the advection of warm air from S and
SW along the Davis Strait. At higher levels meridional
air flow from S and SSE dominate, according to upper-air
observations from Egedesminde 65 km S of Godhavn (Humlum
1987).
Present
Glaciation of Disko Island
At present Disko Island
supports an extensive local glaciation, covering about
20% of the island (Fig.2B). A total of 954 ice caps,
valley glaciers, cirque glaciers and isolated firn areas
were mapped from aerial photographs taken late in the
summer of 1953 and 1964. Although the largest glaciers
are found around the 900 km2 ice cap
Sermerssuaq in the eastern part of the island, glaciers
occur in almost every part of Disko Island.
The surface form of the
glaciation level shows the effect of the above mentioned
climatic differences within the island (Humlum 1985,
1986). Generally, the glaciation level (GL) rises inland
from about 600-800 m asl. at the southwestern coasts,
reaching above 1500 m asl. in the northeastern part of
the island. The isoglacihypses curve around the west and
south side of the island. Gradients of the GL-surface
are variable, ranging from sm/km to more than 60 m/km.
Small values are usually met over the central part of
the island, while large values occur near the coasts.
Interpretations of the geometry of GL-surfaces are
affected by the time-transgressive nature of the
glaciation level. Probably climatic and topographic
controls are integrated over a period of decades or even
centuries in the case of high-arctic glaciers. However,
the local GL must in some way be related to an
elevation, where, over several years, the net balance is
zero on glaciers. As such, information on the integrated
control of net radiation, air temperature, precipitation
and snow drift must be contained within the elevation
and surface form of the glaciation level.
On aerial photographs
large-scale niveoeolian accumulation and deflation forms
are clearly visible above the equilibrium line for many
glaciers on Disko Island. These features display a local
relief of 5-30 m, and are probably quite permanent
forms, caused by snow drift by dominant winds from SSE
during several years (Humlum 1987). Observations on
upper-air conditions at Egedesminde, 65 km SE of
Godhavn, lend support to this conjection. At sea level,
the resultant wind is from NE and E during October while
winds with westerly component dominate during the
summer, just as is the case at Godhavn. However, at the
850 Mb level (usually at 1150-1450 m asl.) the air flow
is primarily meridional from S and SSE in all seasons,
with maximum southerly component from January to June
(Humlum 1987). This is according to the recurrent
suggestion that the atmospheric circulation in the
Greenland area includes a substantial meridional
component (Putnis 1970). The mean monthly wind speed
recorded at the 850 Mb level is often more than 20
knots. The mountain plateaus on Disko Island are thus
exposed to significant snow drift from S and SSE during
the winter, a feature that appears to represent a major
control on the present glaciation (Humlum 1987).
The
Mellemfjord Study Area
The Mellemfjord study area
(Fig.l and 2B) was chosen for several reasons. The
region is situated in the western part of Disko Island
and is thus near the western maximum limit of the area
reached by the Greenland Ice Sheet during the
Quaternary. Deglaciation was probably early, and the
potential ice-free period covered by different terrain
archives therefore long. The terrain is varied, with
both alpine
Side 31
Figure 3:
Geomorphic map of the Kugssuaq area, showing main
terrain elements. Glaciers and permanent snow cover are
white, areas deglaciated since the Little Ice Age are
shown in medium grey. L=lakes. A-avalance tracks.
R=rockglaciers. T-talus slopes. B-fiuvial plain.
P-pingos. M-raised marine terrases. Dl sampling
stations. Position of camp and meteorological station at
Sarqardlit Ilordlit is shown in the lower part of the
figure. Numbers in brackets are altitudes in meters asl.
Curve equidistance 50m.
and plateau
topography represented. Terrain elements
are
asymmetrically distributed, with clear NS contrasts,
creating a landscape with great geomorphic
diversity.
The 25 km long Mellemfjord is
3-5 km wide. Preliminary echo soundings indicate water
depths of 80-170 m. During the Wisconsin, Mellemfjord
was partly filled with a large valley glacier,
terminating on the shelf shortly outside the present
fjord mouth. This glacier drained local ice from valleys
north and south of Mellemfjord. The fjord is exposed
towards the southern Baffin Bay, and the potential for
preservation of geomorphic results of past variations of
both sea ice cover and wave activity is good, especially
around river mouths, where sediments are fed into the
fjord. Earlier investigations (see, e.g. Ingolfsson et
al. 1990) show the upper marine limit to be situated
about 60 m (9000 BP) above the present sea level in the
Mellemfjord area.
A 105 km2 study area
situated on the northeastern shore of Mellemfjord was
designated for future detailed research (Fig.2B and 3).
From a topographic point of view this test area consists
of three main terrain units. 1. The 60 km2
Kügssuaq valley to the northwest. 2. A 35 km2
mountain (994 m asl., no official name) south of the
Kügssuaq valley. 3. A 1.5 km wide glaciofluvial plain in
the Iterdlagssüp kügssua valley with associated delta,
ending into the inner part of Mellemfjord. Below, these
three areas will be addressed collectively as the
Kügssuaq area.
Climate
An automatic weather station
was established in the Kügssuaq area in August 1993. The
station is placed 35 m a.s.l. on a representative
surface at the northeastern shore of Mellemfjord, west
of Sarqardlit Ilordltt (Fig.3).
Global solar radiation,
reflected solar radiation and the incoming and outgoing
net radiation are measured at a 2 meter level as well as
air temperature, relative humidity, wind speed and wind
direction. Soil temperatures are measured at the 3- and
75-cm levels. All sensors are measured and integrated
over a 2 hour period for storage with a solid state data
logger. In figure 4, a temperature record is shown from
the period August 1993 to October 1994. The daily mean
air temperature in Mellemfjord is approximately 5 °C
below the daily mean air temperature in Godhavn.
The somewhat
colder climate in Mellemfjord, when
compared to
Godhavn, is primarily due to a stronger effect
Figure 4: Air
temperatures at Godhavn and Mellemfjord in the period
from 20 August 1993, to 25 October 1994. Mean
temperature 1 September 1993 - 31 August 1994:
Mellemfjord -7.8 °C, Godhavn -4.9 °C.
Side 32
of shadows from the
surrounding mountains and a more prevalent cloud cover,
by which a smaller amount of solar energy reaches the
ground. The sun is below the horizon from late November
to mid January, and in this period the daily mean air
temperature is -15 to -20 °C. In the autumn, calms
prevail for days, whereas in the winter and spring cold
catabatic winds (-20 to -30 °C) are blowing from the
easterly directions, only interrupted by "warm" winds
(-5 to -15 °C) blowing from westerly directions, when
moist, maritime air masses reach the area. During the
summer season, up-valley winds (NW) dominate during the
daytime, while down-valley winds (SE) dominate during
the night-time.
Present
Glaciation
Three cirque glaciers are found
along the steep southeastern side of Kügssuaq valley.
The opposite valley side, exposed towards SE, is without
glaciers and the general terrain gradient is smaller. On
mountain plateaus (900-1100 100 m asl.) NW of the
valley, however, three ice caps are situated (Fig.3).
All glaciers are small, between 0.1 and 2
km2. No mass balance measurements have yet
been carried out on the glaciers within the study area.
Later in this paper, the result of a computer simulation
experiment on the glaciers within the study area will be
outlined.
The cirque glaciers are
situated within deep cirques, and substantial amounts of
talus are supplied to the glacier surface from the free
rock faces above. Below the equilibrium line these
glaciers are therefore partly covered by supraglacial
debris and the fronting Little Ice Age moraines are very
conspicuous. Some of these even have a rockglacier as
regards appearance. In contrast, no prominent moraines
are found around the plateau ice caps, probably due to
the lack of supraglacial debris sources. Their former
Little Ice Age extension is shown by zones of less
vegetation cover and less weathering of boulders. In
general, the glaciers have melted 100-300 m back from
their maximum Little Ice Age position.
Probably the glaciers within
the study area reached their Little Ice Age maximum
extension around 1900 AD, as is known to be the case for
glaciers in the southern part of the island, around
Godhavn. There exist, however, no earlier observations
on glaciers in the Mellemfjord area.
Periglacial Landforms
Periglacial
landforms are widespread, underlining that the
area is situated within the
zone of permafrost, probably in the southern part of the
continuous permafrost zone. The daily mean air
temperature in Mellemfjord appears to be considerably
below the daily mean air temperature in Godhavn (see
above). Judging from the initial meteorological
observations 1993-94, the mean yearly air temperature at
sea level may be as low as about -8 C°. Deglaciation was
probably early, about 9,100-8,000 BP (Donner 1978,
Ingolfsson et al. 1990) and periglacial processes have
been dominant within the study area since then.
Several rockglaciers, both
fossile and active, line the valley sides exposed toward
NW and N. Some rockglaciers are extending all the way
from a free face to the main valley bottom while others
only cover the lower part of the valley sides. The
largest rockglaciers are glacier-derived while the
smaller ones seem to be talus-derived (Humlum 1983,
1988a). Active talus cones are found particularly on the
steepest NW exposed mountain sides. It seems as if they
have been even more active in an earlier period, as the
lower part of the talus cones in several places is
partly covered by a solifluction sheet.
Large active avalanche tracks
(Fig.3) covered by large angular boulders are leading
from many funnel-shaped ravines on the NW-side of the
main Kügssuaq valley, showing that huge amounts of snow
accumulate in these valleys during wintertime.
Accumulation of drifting snow by winds from S may be
important in this respect (see above). On the plateaus
north of the Kügssuaq valley nivation processes and
solifluction are especially important.
Prominent solifluction lobes
are widespread on most parts of the Kügssuaq valley
sides, revealing that solifluction is a dominant
process. This indicates precipitation in the study area
to be relatively large, reflecting the position close to
the western coast of Disko Island.
Concerning minor periglacial
landforms, particularly the pingo remnants streaching
across the glaciofluvial plain at the mouth of the
Iterdlagssüp Kügssuaq valley are of interest. The
position of these pingos on the highest parts of the
salt marsh flats at the junction between the
glaciofluvial plain and the delta, compared with the
knowledge of Holocene sea-level changes in the western
part of Disko Island (Donner 1978, Frich &
Ingolfsson 1990, Ingolfsson et al. 1990), has led to the
conclusion that these pingos probably evolved as open
system pingos during the Little Ice Age period 1400 to
1900 A.D. (Christiansen, manuscript).
The raised
marine terraces at Sarqardlit Ilordlit (Fig. 10,
discussed below) are important for an indirect
dating of
Side 33
Figure 5:
Raised marine terraces at Sarqardlit Ilordlit. In the
front of the lower terrace (a fossil coastal cliff)
active ravines with small alluvial cones can be seen.
Person for scale.
several periglacial terrain
features developed on the terraces. The front of the
lowermost terrace is furrowed by ravines 3-4 m deep and
10 to 20 m long, some still active. In front of the
ravines small sediment cones are found, probably
accumulated during snowmelt in the early spring (Fig.s).
At the fronts of the two higher raised marine terraces
only remnants of ravines are found and today sliding and
solifluction are the active periglacial processes. In
contrast to the uppermost terraces the lowermost terrace
front has no vegetation and is steeper. Being positioned
close to sea level, particularly the front of this
terrace is exposed to snowdrift during wintertime. The
result is large accumulation of drifting snow in the
ravines, which keep the ravines growing, especially
during the snow melt season. On the higher terraces
deposition of drifting snow is smaller and solifluction
seems to represent the dominant process. Earlier in the
Holocene, when the uppermost terraces were situated
close to sea level, with substantial snow drift during
winter, they probably had the same appearance as the
lower terrace today.
Monitoring of some of the
smaller periglacial terrain features within the study
area has been initiated by way of recurrent photography
in order to detect changes in form and size.
Hydrology and Fluvial Geomorphology
The Kügssuaq valley drainage
basin (55 km2) opens towards SW. The
topographic divide follows basalt plateaus partly
covered by glaciers (Fig.3). The valley slopes of the
basin are of marked asymmetry, the S-facing slope is
rather gentle with
many watercourses. The N-facing slope
is dissected
by cirque glaciers feeding the few streams.
The main stream originates in
the eastern part of the basin. From the topographic map
it is seen that this stream has five rather long and
branching tributaries coming from the S-facing slope and
only three rather short tributaries from the N-facing
slope. According to the Strahler classification the
basin is of fourth order. Considering the topographic
map, there are 2 3rd order, 5 2nd order and 18 Ist order
streams in the catchment. The main stream passes basalt
benches in minor canyons; between these canyons braided
reaches are found. Near the outlet to the sea the main
stream runs through a 30 m deep steep-sided valley
eroded into a major till ridge running across the valley
mouth. The lower part of the profile is carved in solid
rock. The bottom width varies from 5-10 meters.
Near the outlet of the main
stream a stable cross-section (D6) suitable for
discharge measurements was found (Fig.3) and a gauging
of the water table was carried out simultaneously with
discharge measurements. At the same cross-section
samples of water were collected below minor falls where
total mixing could be assumed. The water samples were
used for calibration of a Partech IR transmissometer
that was installed together with a datalogger for
continuos recording of sediment concentration. A
reconnaissance trip was carried out along the main
stream and the lower part of its tributaries. Water
samples were collected and filtered through Whatman GF/F
filters with a nominal retention diameter of 0.7 micron.
Also the conductivity and the temperature of water in
the tributaries and the main-stream were measured.
During a four-day period in
mid-August the maximum water depth at the gauging
station dropped from 0.56 m to 0.52 m. This lowering was
interrupted by a rise of app. 5 cm on 22 August caused
by a rainfall of 11 mm. A daily variation of app. 2 cm
was observed with a maximum around 09h PM. The measured
discharge varied from 0.914 to 0.627 mV, a preliminary
stage discharge relationship: Q (mV) = 8.35*( max.depth
(m))386 was found, yielding r=0.984. Due to
the low range of depths this relationship should be
tested at higher stages before general use. The water
temperature at the gauging station varied from 2-4 CC.
The conductivity varied from 36.4 to 37.1 //S/cm.
Measured concentration of suspended sediment varied from
3.7 to 4.2 mg/1, however, the transmissometer
registrations showed a multipeaked maximum on 22 August
indicating concentrations up to 80 mg/1 (Fig.6).
Side 34
Figure 6:
Approximate concentration of suspended sediment measured
in the Kugssuaq river.
The transmissometer
registration also indicates a slight daily variation in
concentration, probably due to a contribution of
sediment rich meltwater from the glaciers. The
multipeaked appearance indicates a contribution from
different sources reacting differently on the rainfall
event. Sediment transport during periods without
rainfall was normally 200 - 400 kg/d during the
observation period. The concentration during the
rainfall event on 22 August, however, indicates that
transport could be as much as 20 times higher, which
shows the importance of a continues registration for a
reliable computation of the fluvial sediment transport.
The reconnaissance trip showed
that it was possible to distinguish among three main
types of water courses in the basin: Firstly,
watercourses mainly fed by rainfall and nonperennial
snowpatches. These watercourses are characterised by
being dry or with very low discharge values during the
investigation period in August. Conductivity was around
35 yuS/cm and sediment concentration 1 - 2 mg/1. They
are situated on the lower part of the south facing
slope. Secondly, watercourses fed by rain and snow
through sources from the basalt benches, major
accumulations of loose sediment and swamps. The
discharge is
large and rather stable.
Conductivity showed a variation from 24 - 55 //S/cm
indicating a possibility for further classification.
Sediment concentration was low, about 2 - 4 mg/1.
Thirdly, watercourses fed by perennial snowpatches or
glaciers. The discharge is high showing a daily
variation. The temperature was 0.8 - 2 °C. The
conductivity was around 35 /^S/cm. The water from the
glaciers was clearly sedimentladen, the colour varied
from white to brown depending on the lithology. Measured
sediment concentration was quite low: 35 - 38 mg/1 but
significantly higher than in the other watercourses
within the test area.
The chemical composition of
water samples from the study area was analysed. Sampling
localities are shown in figure 3. The precipitation
sample was collected at the camp site (D7). The results
of the chemical analysis are shown in table 1. In
general the content of ions is very low ranging from
app. 4 to app. 9 ppm., which is in good accordance with
the low conductivity values. However, three types of
water could be distinguished: 1. Low alkalinity and low
content of ions. 2. Higher alkalinity and higher content
of ions. 3. Intermediate with higher iron content.
Water type 1 is represented by
samples Dl and D4 (Fig.3). The samples are characterised
by runoff from glaciers. Type 2 is represented by D2,
D3, D6 and D7 , the three first samples are from
watercourses with bare soil during the summer period. It
is interesting that the precipitation sample is very
similar, partly because of a higher concentration of
NaCl, compared with type 1 that receives runoff from
winter precipitation. Mainly it can be concluded that
the summer precipitation has a higher content of salt
from the sea than the winter precipitation, because
Table 1:
Chemical analyses of water samples from the test area
Side 35
the sea is covered by ice
during the winter. Type 3 is represented by D5 only.
This is also glacial runoff, but the higher content of
ions could be explained by a larger part of subglacial
runoff. The iron content could be explained by
weathering of the substratum.
The results from the field
study proved that the selected basin was well suited for
further studies of fluvial sediment transport processes
in this environment that is considered typical for major
parts of the western Disko Island.
Soil
types
Soils in the Mellemfjord area
and at other sites visited along the southern coast of
Disko Island normally reveal polysequent soil profiles.
Soil horizon features in fossil and buried soil profiles
and the character of disturbance and cover can yield
important information on past ecosystem conditions.
A specific period of soil
development, probably during the early Hoiocene climatic
warm period, has resulted in quite distinct
differentiation of soil horizons. This soil type is
obviously developed in a period with little horizon
mixing processes by cryoturbation and with quite stable
geomorphic conditions in general. The parent material of
this old soil is often two-layered, which is a general
characteristic of most soils in Greenland (Jakobsen,
1991 & 1992). Mostly coarse textured tills and
glaciofluvial ma
Figure 7:
Polysequent soil profile. Explanation in text.
terials are covered by a mantle
of late-glacial fine sand/ loess. During the Late
Wisconsin deglaciation, before the coverage of the
landscape by vegetation, these fine grained sediments
were probably eroded by winds from the extensive barren
areas close to the retreating glacier margins.
At all studied sites a strong
disturbance is observed of this early Holocene soil,
caused by increasing geomorphic activity. Probably the
intensity of especially cryoturbation, solifluction,
fluvial or aeolian processes has increased markedly in
the later part of the Holocene.
As an example, a typical
polysequent soil profile from the study area is shown in
figure 7. The oldest soil, horizons 3A, 3Bv and 3BC, is
an arctic brown soil developed in the early Holocene
two-layered parent material, sandloess covering till.
Two major Holocene events have occurred at this specific
site. A covering by a younger aeolic sediment, horizons
2A and 2BC, and a final deposition of solifluction
material, horizon AC. The disturbance and disruption of
soil horizons are assumed to be due to horizon mixing
caused by the latest soiifiuction/cryoturbation
activity.
A series of variations of
this typical polysequent soil is observed in the
landscape. In poorly drained and/or sloping landscape
segments cryoturbation and solifluction processes have
been intense and caused strong mixing and disruption of
the early Holocene soil horizon development. At
well-drained, flat sites only little cryoturbation is
seen
Side 36
Figure 8: A
buried podzol. Profile about 65 cm high
in the soils,
and the only observed coverage of the early
Holocene
soil is an aeolic soil layer. An example of this is
shown in figure 8 and table 2.
A buried, but undisturbed arctic Podzol is developed in
a well-drained two-layered sandloess covered
coarse-sandy parent material, only covered by a
coarse-sandy aeolic layer. A more detailed study of the
distribution of polysequent soil profiles on Disko
Island and datings of larger plant fragments belonging
to fossil Holocene landscape surfaces are planned, and
may give an important contribution towards the
understanding of Holocene landscape evolution and
climate history in central West Greenland.
Ecosystem Records in Lake Sediments
In the northern part of the
Kügssuaq valley a small lake is located close to the
watershed. The terrain around the lake was probably
deglaciated early in the Late Wisconsin. An evaluation
of the lake surroundings shows a small catchment area
comprising several landscape thresholds. At present, the
sediment influx to the lake is assumed to be small, but
changing climatic conditions during the Holocene and
probably even earlier must have left an interesting
sedimentological, palynological and geochemical archive
in sediments accumulated in the lake. Generally, a low
rate of sedimentation is expected during the Holocene
period and the lake sediments are assumed to be
dominated by various types of fine grained low carbon
containing gyttja. Lake sediment corings as those
carried out in several
Table 2:
Profile characteristics of the buried podzol in Fig. 8.
Colour: Munsell Soil Colour (dry). %C analysed by LECO
and pH measured in a 1:2.5 w/w soil: 0.01 M
CaCl2 suspension.
Side 37
Figure 9: A
series of recurved beach ridges, which indicate littoral
drift f rom the west (right), characterises the cuspate
foreland at Sarqardlit llordlit.
lakes in East
Greenland, on Ammassalik Island, are planned
for the
project period.
Coastal
Studies
Several coastal stretches in
Mellemfjord offer excellent subjects studying Holocene
relative sea-level changes and recent marine impact on
the arctic environment. In 1993 the coastal
investigations were carried out at a coast section
called Sarqardlit llordlit at the NE shore of
Mellemfjord (Fig.3).
The Holocene marine limit in
Mellemfjord is about 60 m and the relative sea level
history of Disko was one of steady uplift before 3 ka BP
(Donner 1978, Frich & Ingölfsson 1990, Ingölfsson et
al. 1990). Extensive transgressive barriers at several
localities on Disko, sometimes situated in front of a
fossil coastal cliff (Rasch and Nielsen 1994), suggest
that the relative sea level has been below the present
one during late Holocene and that the relative sea level
variation of the nearest past was one of submergence.
Sarqardlit llordlit is situated
at the mouth of a large valley, Iterdlagssüp kügssua,
joining the Mellemfjord from the north (Fig. 3). At the
mouth of this valley an extensive, tidal influenced
delta is deposited, The delta flat is dominated by low
wave energy and low littoral drift. No detailed
fieldwork was carried out in 1993 on the delta, except
for reconnaissance surveying including an echo sounding
profile. These preliminary observations indicate
potentials for studying undisturbed sequences of
Holocene submarine sedimentation.
West of the delta three cuspate
forelands have developed, the easternmost is shown in
fig. 9. The forelands terminate in a series of marine
terraces at 41, 38, 33, 25, 18 and 8 m asl.. The
terraces indicate marine deposition throughout the
Holocene (Donner 1978). A fossil coastal cliff separates
the lowermost terrace from the cuspate forelands.( (
Fig. 5).
The geometric pattern of the
recent and sub-recent beach ridges constituting the
forelands indicates that the forelands originate from
easterly directed littoral drift. The beach ridges are
exclusively built-up by pebbles derived from local
alluvial fans. Each foreland encloses lagoon deposits.
On the easternmost foreland the lagoon is still in
connection with the fjord. During the 1993
investigation, the geomorphology of the forelands was
mapped (Fig. 10), profile surveyings were carried out
and three cores were obtained from the lagoon deposits.
The distribution of the
individual ridge heights and the degree of weathering
and lichen coverage of the surface particles (indicative
of age) are of special interest. These parameters
together with information from the lagoon cores will
contribute to the superficial knowledge of late Holocene
relative sea-level variations in central West Greenland.
The morphostratigraphy of the cuspate forelands suggests
that the late Holocene coastal history was one of
regression followed by transgression again followed
Side 38
Figure 10: Map
indicating the main structures of the geomorphology at
Sarqardllt Ilordlit, including the outline of an assumed
submerged cuspate foreland.
by regression
and transgression. As the lagoon cores contain
organic material absolute dating of these sea level
events may be possible.
Preliminary surveyings and echo
soundings revealed a special submarine configuration and
sediment distribution about 2 m below the present mean
sea level offshore the easternmost cuspate foreland
(Fig. 10). The configuration might be the submerged
remnants of a cuspate foreland. If further
investigations verify this interpretation, Sarqardllt
Ilordlit may become an important research area for the
study of Neoglacial relative sea-level fluctuations in
West Greenland.
Analytic
Computer Studies
A 3D digital terrain model has
been established for the Kügssuaq area (Fig.l 1).
Topographic data were digitised from official 1:250,000
maps. These and associated data on geomorphic terrain
types have been used as input in an analytical terrain
model, to calculate e.g. radiation for the individual
terrain segments, given certain meteorological
parameters.
As an example, illustrating
the potential of this approach, the calculated net
energy input (net short-wave radiation + net long-wave
radiation + sensible heat flux) for July is shown in
figure 11. From this it is seen that the net energy
input is at maximum (about 250 Wm"2) for the
sea surface, due to the low albedo for water. On the
other hand, certain terrain units (Fig.s) such as narrow
valleys, free rock faces exposed towards NW and
glaciated areas are characterised by very low values
(<75 Wm"2), partly due to topographic
induced shadow, partly due to high albedo. Gently
sloping valley sides and valley bottoms receive
intermediate values about 100-170 Wirf2.
Concerning the present
glaciation, energy considerations are important. In
figure 12 the mean July net energy input is shown as a
function of terrain segment altitude, with glaciated
terrain segments emphasised. Considering only the
glaciated terrain segments, these are seen to fall in
two groups, representing glacier surface segments above
and below the equilibrium line (ELA), respectively. At
ELA 20-50 Wm"2 are received at the glacier
surface during July, lowest values at ELA's situated
around 500 m asl. (glaciers situated within deep
cirques) and maximum values at ELA's found on ice caps
on the 900-1100 m asl. mountain plateaus. Taking the
whole ablation season June-August as a 100 day period,
and calculating the appropriate mean values for each
month, about 350 mm w.e. are lost each sum
Side 39
Figure 11: The
Mellemfjord test area as seen in 3D perspective from SW.
The lower diagram shows the spatial distribution of the
mean energy balance for July, as seen from the same
viewpoint as the upper diagram. Values were calculated
using a monthly mean air temperature at sea level of 7
°C, a mean cloud cover of 40%, a mean wind speed of
2ms1 and mean lapse rate of 0.0065 °C m
mer at ELA for the cirque
glaciers, while about 650 mm w.e. are lost at ELA on the
ice caps. Typical meteorological summer values as
regards air temperature, cloud cover and wind speed
measured at Godhavn were adopted for this experiment, as
the Mellemfjord meteorological station is still in its
first year of operation.
If glaciers within the
Kügssuaq area are assumed to be in equilibrium at
present, the above estimated ablation values must
represent the winter accumulation at ELA's. The low
accumulation values calculated for the cirque glaciers
indicate the low snow accumulation requirement for
glaciers within topographical incised valleys like the
cirque valleys. On the other hand, the high accumulation
requirement estimated for the ice caps points towards
the very exposed nature of these glaciers, situated on
mountain plateaus. Probably they only exist due to
accumulation from winter snow drift across the plateaus
by the southerly meridional upper-air flow discussed
above.
Side 40
Figure 12: Mean
July energy balance for the individual terrain elements
within the Mellemfjord test area. Values were calculated
using a monthly mean air temperature at sea level of 7
°C, a mean cloud cover of 40%, a mean wind speed of
2ms1 and a mean lapse rate of 0.0065 °C
m'1. Terrain segments covered by snow or
glacier ice are shown in dark grey. Compare with lower
diagram in figure 11.
Access to improved data on
meteorological parameters and geomorphological data
obtained from the now-operating automatic weather
station in Mellemfjord, as well as improved
geomorphological mapping will clearly contribute towards
a higher-quality output from computer models such as
that outlined above. This is important, as the purpose
of the present model is to provide data to obtain
knowledge of various climatic controls on the
distribution of geomorphic- and vegetational units
within the study area.
References
Christiansen,
H. H. (1995): Observations on open system pingos
in
a marsh environment, Mellemfjord, Disko Island, central
West Greenland. Geografisk Tidsskrift 95: 42-48.
Donner, J.
(1978): Holocene History of the West Coast of
Disko,
central West Greenland. Geografiska Annaler, 60(A),
No. 1-2:63-72.
Eddy, J. A., Meier, M. F.
and Roots, E. F. (eds.) (1988): Arctic
Interactions. Recommendations for an Arctic Component in
the International Geosphere-Biosphere Programme. Office
for Interdisciplinary Earth Studies, Boulder, Colorado.
Etkin, D. A.
(1990): Greenhouse warming: Consequences for
arctic
climate. J.Cold Reg. Eng., 4: 54-66.
French, H. M.
(1987): Periglacial geomorphology in North
America:
current research and future trends. Ecological
Bulletins,
38: 5-16.
Frich, P. &
Ingolfsson, O. (1990): Det holocæne sedimentationsmiljø
ved Igpik samt en model for den relative landhævning i
Disko Bugt området, Vestgrønland. Dansk Geologisk
Forening, Årsskrift for 1987-89: 1-10.
Humlum, O.
(1983): Rock glacier types on Disko, central West
Greenland. Geografisk Tidsskrift, 82: 59-66.
Humlum, O. (1984):
Altitudinal trends of talus-derived lobate rock glaciers
on Disko, central West Greenland. XXV. Internat. Geogr.
Congress, Royal Danish Geographical Society, Occasional
Papers, V01.7: 35-39.
Humlum, O.
(1985): The glaciation level in West Greenland.
Arctic and Alpine Research, 17(3): 311-319.
Humlum, O.
(1986): Mapping of glaciation levels: comments on
the effect of sampling area size. Arctic and Alpine
Research,
18(4): 407-414.
Humlum, O.
(1987): Glacier behaviour and the influence of
upper-air conditions during the Little Ice Age in
Disko,
central West Greenland. Geografisk
Tidsskrift, 87: 1-12.
Humlum, O. (1988a): Rock
glacier appearance level and rock glacier initiation
line altitude: a methodological approach to the study of
rock glaciers. Arctic and Alpine Research, 20(2):
160-178.
Humlum, O.
(1988b): Natural cairns on rock glaciers as an
indication
of a solid ice core. Geografisk
Tidsskrift, 88: 78-82.
Ingolfsson, 0., Frich, P.,
Funder, S. and Humlum, O. (1990): Palaeoclimatic
implications of an early Holocene glacier advance on
Disko Island, West Greenland. Boreas, 1990(4): 297-311.
Jakobsen, B.
H. (1991): Multiple processes in the formation of
subarctic Podzols in Greenland. Soil Science, vol.
152, no. 6:
414-426.
Jakobsen, B. H. (1992):
Aspects of the genesis, geography and evolution of the
of soils in Greenland. Proceedings of the 1
.International Conference on Cryopedolgy. Pushchino.
SNG. p. 71-84.
Koster, E. A.
(1993): Global Warming and Periglacial Landscapes.
In: The Changing Global Environment, ed. N.Roberts,
Blackwell, Cambridge, USA, pp. 127-149.
Maxwell, B. (1992): Arctic
Climate: Potential for Change under Global Warming. In:
Physiological Ecology, ed. H.A. Mooney, Stanford
University, Stanford, California, pp.ll-34.
Putnis, P.
(1970): The Climate of Greenland. In: World Survey
of Climatology, ed. S.Orvig, Elsevier, Amsterdam,
pp.3-128.
Rasch, M. and Nielsen, N.
(1994): Holocene relative sea-level changes indicated by
morpho-stratigraphic sequences; Signifik, Disko Island,
West Greenland. Geografisk Tidsskrift, 94: 37-45.
Washburn,A.L (1985):
Periglacial Problems. In: Field and Theory: Lectures in
Geocryology, eds. M.Church and O. Slaymaker, University
of British Columbia Press, Vancouver, 8.C., pp. 166-202.