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> Forsiden > Publikationer > Geology of Greenland Survey Bulletin > Vol. 191 Geol. Greenl. Surv. Bull. > Review of Greenland Activities 2001, pp 144-149

GEOLOGY OF GREENLAND SURVEY BULLETIN 191

 
Lake-catchment interactions with climate in the low Arctic of southern West Greenland

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Arctic hydrology plays a central role in the earth's heat
balance and ocean circulation (Vörösmarty et al. 2001).
Future changes associated with human influence on
the climate system are also predicted to cause major
changes in the energy and hydrologic mass balance of
Arctic catchments. Climate change will likely affect per-
mafrost and snowmelt, which dominate Arctic hydro-
logy and control the chemistry of surface runoff (and
hence streams and lakes) as water percolates through
the active layer. However, the controls and dynamic
impact of snowmelt are poorly understood, because
this critical timeframe is often missed by sampling pro-
grammes. In the Søndre Strømfjord area only the broad-
est aspects of hydrologic variability have so far been
documented (Hasholt & Søgaard 1976).
Lakes respond to climatic forcing at a variety of
timescales. For example, at relatively high frequencies
(days), thermal stratification can be weakened or bro-
ken down by increased wind speeds associated with
the passage of frontal systems. Seasonally, lake tem-
peratures reflect annual changes in radiative heating
and ambient air temperatures (Hostetler 1995). Year to
year variability in climate can reduce the ice-free period
(Magnuson et al. 2000; Doran et al. 2002). Over the
longer term, (i.e. Holocene, hundreds to thousands of
years) changes in the hydrological mass balance of
144
Lake-catchment interactions with climate in the low
Arctic of southern West Greenland
N. John Anderson, Sherilyn C. Fritz, Christopher E. Gibson, Bent Hasholt and Melanie J. Leng
K
Greenland
Søndre
Strømfjord
Lake G
Aasivissuit T
asiat
Lake E
0
5 km
Hydrological station
Automatic weather station (AWS)
Thermistor
> 300 m elevation
Lake
Fig. 1. Location map showing study area with hydrological monitoring stations, automatic weather stations and lakes with thermistor
chains. K: Kangerlussuaq.
Geology of Greenland Survey Bulletin 191, 144­149 (2002) © GEUS, 2002
GSB191-Indhold 13/12/02 11:34 Side 144
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lakes reflect hemispheric changes in climate systems and
regional precipitation patterns (Overpeck et al. 1997).
Some of these processes can be recorded in lake sedi-
ments, but it is clear that a better understanding of con-
temporary processes is crucial for interpreting sediment
records unambiguously in terms of climate change.
The area of southern West Greenland between 66°N
and 68°N contains approximately 20 000 lakes. There
is a strong climatic gradient between the Inland Ice
margin and the coast. The zone immediately adjacent
to the ice sheet is continental with low precipitation
(< 170 mm) and a mean annual temperature of ­6°C.
The coastal zone has a reduced annual temperature
range and considerably greater annual precipitation;
the summers are cooler, fog is common, and snow
packs remain late into July. In contrast, closer to the
ice sheet, summers are warmer and drier. Not surpris-
ingly, the limnology of lakes in this area reflects this
strong gradient. Lakes at the coast tend to be dilute
and oligotrophic, whereas closer to the head of Søndre
Strømfjord (Fig. 1), where evaporation exceeds precip-
itation on an annual basis, many of the closed basin
lakes have become `saline' due to long-term evapora-
tion. Catchments close to the head of the fjord are char-
acterised by minimal surface runoff during the summer
­ most runoff is via the active layer and occurs during
the spring thaw. There are often large areas of bare rock,
as well as aeolian deposits (often on the drier, south-
facing slopes), and the more luxuriant vegetation is asso-
ciated with damper hollows and lake outflows (Fig. 2).
Initially, our work in southern West Greenland had
the aim of using the oligosaline lakes as archives of past
changes in effective precipitation. Work to date has pri-
marily been concerned with sediment core studies and
long-term climate change (Anderson & Bennike 1997;
Anderson et al. 2000). More recently, however, field
activity has concentrated on two main aspects of the
interaction of lakes with local and regional climatic vari-
ability: namely, timing of icemelt and patterns of ther-
mal stratification (Anderson & Brodersen 2001).
However, a more complete understanding of the hydro-
logical links between lakes, local climate as well as
their catchments is still lacking, and the rationale for
the present project was therefore to combine these
varying interactions in a more holistic manner.
Aims of the present project
In an attempt to integrate some of the contrasting but
complementary aspects of lake-climate-catchment inter-
actions in West Greenland, it was decided to focus
specifically on a limited number of lakes and their catch-
ment hydrology. Two neighbouring lakes were chosen,
one with an outflow and one without, but both expe-
riencing a similar regional climate and having similar
geology and vegetation. The aim is an integrated study
that combines an energy and hydrological mass balance
of two contrasting lake catchments with measurements
of contemporary and long-term sedimentation in the
145
Fig. 2. The hydrological station at the
outflow from Lake G in August. The
more extensive vegetation growth is
apparent despite there being no flow
from the lake.
GSB191-Indhold 13/12/02 11:34 Side 145
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lakes. As in earlier reports (e.g. Anderson & Brodersen
2001), we here follow the convention of referring to the
fjord as Søndre Strømfjord and the airport at the head
of the fjord as Kangerlussuaq (Fig. 1).
Study sites
Field activity during 2001 was concentrated on two
lakes ­ E and G (Fig. 1) that were identified as possi-
ble study sites during field work in May 2000 (Bindler
et al. 2001). The lakes have contrasting water chemistry
and are reasonably representative of the type of lakes
that occur close to the head of Søndre Strømfjord
(Anderson et al. 2001). Lake E is a closed-basin lake
(mean conductivity is 3000 µS cm
­1
) and is surrounded
by extensive fossil shorelines (Fig. 3). In contrast, Lake
G has an outflow (and consequently lower conductivity,
220 µS cm
­1
) that drains the lake on the north side, flow-
ing via two small ponds and a wetland area (Fig. 4) into
Aasivissuit Tasiat (see Fig. 1).
Field work in 2001
Field work was conducted during three periods: late April
to early May, June and August. The initial field work
undertaken in late April ­ early May used the ice cover
146
Fig. 4. The outflow from lake G, showing
the two ponds and associated wetland
areas. The hydrological station, which is
just visible (arrowed), provides scale.
The lake in the centre of the view is
approximately 100 m across.
Fig. 3. Looking down on Lake E. The
fossil shoreline development on the far
(north-eastern) shore is clear. The upper
limit of the shoreline is approximately 7 m
above present lake level (arrowed).
Width of the lake is c. 500 m.
GSB191-Indhold 13/12/02 11:34 Side 146
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on the lakes as a platform for retrieving sediment cores
(`Russian' and freeze cores) from both lakes (see
Anderson et al. 2000 for a description of field methods).
At the same time, sediment traps and strings of tem-
perature thermistors were also deployed (Anderson &
Brodersen 2001). Both lakes have laminated sediments,
although the quality of laminations at Lake E deterio-
rates with sediment depth. Lake G, however, is char-
acterised by fine, calcite laminated sediments throughout
its length.
The Technicap sediment traps (~1 m high and approx-
imately 25 kg in weight; Fig. 5A) were dropped through
the ice, with the major buoyancy floats at a depth of
3 m to avoid being caught in the ice. The traps, which
are fully automatic with a motorised carousel and 12
collecting bottles (Fig. 5B), were programmed to change
bottles every 18 days.
The hydrological monitoring of the lakes forms an
important component of the present project. In estab-
lishing the hydrological stations prior to the start of the
spring thaw, it was hoped that the changes in flow and
lake level associated with this critical period could be
recorded. The hydrological stations, which are based
on a sturdy V-shaped frame (Fig. 2), include a variety
of sensors (precipitation, pressure transducers for lake
level, snow depth, soil temperature, stream flow) and
a Campbell Scientific CR10X data logger. At Lake G the
station was set up over the outflow. At Lake E, where
there is no outflow, the station was located on the west-
ern shore, straddling the lake margin. In conjunction
with the hydrological station at Lake E, a new automatic
weather station (AWS) was set up at the southern end
of the lake. As well as standard temperature and wind
monitors, this station also included a full suite of radi-
ation sensors, a soil heat-flux sensor and soil temper-
ature recorders. Finally, an initial snow taxation (snow
depth and density) was made for both catchments. Field
activity in June included a detailed mapping of the
catchments using a Trimble 4000SE base station with
two roving systems (a Trimble 4000SE and a Trimble
Pathfinder) differentially corrected against the base sta-
tion. A Topcon GTS-6 was used for more accurate sur-
veying of the terrain immediately surrounding the lake
shorelines. This surveying was to enable the develop-
ment of a digital terrain model for each catchment. Lake
bathymetric surveys were also undertaken.
In an effort to determine sediment transport within
the catchment, a number of simple sediment traps were
set out to determine surface transport and atmospheric
inputs to the lakes. The hydrological stations were
checked in June, and those sensors that could not be
deployed in April were put out in the lakes. An AWS
previously located halfway to the coast was upgraded
and moved to the shore of Lake G. Individual temper-
ature thermistors were put in 15 additional lakes around
the two detailed study sites. These continuous mea-
surements will provide a detailed record of the variability
of icemelt (in spring 2002) and summer temperatures
(for both 2001 and 2002) for a specific area, with good
meteorological control provided by the two AWSs.
In August, the sediment traps were emptied, and the
carousels changed and re-programmed for the next 12
months. Temperature thermistors were relocated to the
central deepest part of each lake on metal wires to
increase their chance of surviving the winter. On all three
visits during the year, samples were taken for chemi-
cal and isotope analyses of surface water, together with
water-column profiling of oxygen, temperature and
conductivity.
147
Fig. 5. A: A Technicap sediment trap on the ice at Lake E prior
to deployment; 26 April 2001. B: A sediment trap lying on the
improvised raft prior to redeployment in August 2001; the col-
lecting bottles are clearly visible.
A
B
GSB191-Indhold 13/12/02 11:34 Side 147
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Discussion
Global climate models predict considerable future
change in the Arctic, although response will not be uni-
form. This variability is clear from a synthesis of long-
term monitoring data, which shows that around Søndre
Strømfjord temperature has declined in the period
1970­2000 (Serreze et al. 2000). Future predicted changes
include altered mass and energy inputs, with resultant
increased precipitation in some areas and decreases in
others. However, our understanding of the hydrologi-
cal cycle in the Arctic is characterised by a relatively
sparse observational network, and the length of mon-
itoring records is often very short and sporadic. Hence
it is difficult to detect trends and identify abnormal
years.
Although our contemporary monitoring programme
is located in a crucial area of the Arctic, where present
hydrological information is limited, by necessity it will
provide only a short-term view of environmental vari-
ation. Our aim, however, is to use this contemporary
hydrological and meteorological data to calibrate long-
term lake response. High-resolution sediment core stud-
ies can then be used to identify decadal trends in lake
water conductivity. These core records can be coupled
with energy-balance models derived from modern hydro-
logical data to estimate the past climate conditions that
were required to produce the past lake level (and lake
water conductivity) changes. The objective of the pre-
sent project, therefore, is to integrate, as far as possi-
ble across a range of temporal scales, longer-term
(102­103 years) to short-term (i.e. seasonal) processes.
In a multidisciplinary approach to palaeoenvironmen-
tal reconstruction, it is also planned to couple geo-
morphic studies of large-scale landscape features, such
as palaeoshorelines and terraces, with the finer scale
record embedded in the sediment cores.
Previously, a number of lake sites with finely lami-
nated sediments have been recorded (Anderson et al.
1999). Although they are not annual (i.e. varves), the
palaeoenvironmental significance of the changing struc-
ture of these laminations is considerable, if the domi-
nant processes and frequency can be determined. Some
of the structure can be readily interpreted, for exam-
ple calcite precipitation and deposition of purple sul-
phur bacteria form unambiguous laminations. It is
unknown, however, whether calcite precipitation in
these lakes occurs under ice (due to salinisation effects
associated with salt expulsion from ice) or during the
summer due to photosynthesis (increasing pH), or how
often this occurs. The processes underlying the inter-
play of other organic/inorganic fractions are even less
clear. The Technicap sediment traps were originally
developed for the marine environment but are ideally
suited to remote Arctic lakes where regular emptying
is problematical. Aspects of our catchment studies are
aimed at determining how much minerogenic matter
is derived from the catchment, as many of the lakes
around the head of Søndre Strømfjord lack discrete
inflows. The amount of material brought in during the
spring thaw is also unknown. Thus the sediment traps
will allow us to couple the lake sediment record with
the climatic/meteorological processes giving rise to the
sediment flux, both from the catchment and within the
lake.
Conclusion
Understanding future changes in the hydrology of Arctic
catchments will be difficult, because of the paucity of
contemporary data. Similarly, our interpretation of past
changes in the hydrological mass balance of lakes and
catchments, as exemplified by fossil shorelines in the
Søndre Strømfjord area, can only be strengthened by
understanding contemporary processes. Combined with
hydrologic mass balances and an assessment of the
geomorphic setting, we aim to quantify seasonal sedi-
ment input through the use of sediment cores and sedi-
ment traps. These historical scenarios and the associated
palaeoclimatic inferences can then be validated by lake
energy balance models (Hostetler 1995).
Acknowledgements
The field work was undertaken with financial support from the
Danish Natural Science Research Council (SNF), National Science
Foundation (NSF, USA) and the European Commission (EMERGE).
Assistance in the field was provided by William Clarke (Department
of Agriculture Northern Ireland, UK), Ulf Thomas, Marianne
Grauert, Mikael Kamp-Sørensen, Kim Edmunds (all University of
Copenhagen) and Neil Rose, Simon Patrick, Sergi Pla, Chris Curtis,
Mike Hughes and Martin Kernan (all University College London,
UK).
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Authors' addresses
N.J.A., Geological Survey of Denmark and Greenland, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark. E-mail: nja@geus.dk
S.C.F., Department of Geosciences, University of Nebraska, 214 Bessey Hall, Lincoln, NE 68588, USA.
C.E.G., Department of Agriculture and Rural Development, Agricultural and Environmental Science Division, Newforge Lane, Belfast
BT9 5PX, UK.
B.H., Institute of Geography, University of Copenhagen, Øster Voldgade 10, DK-1350 Copenhagen K, Denmark.
M.J.L., NERC Isotope Geoscience Laboratory, British Geological Survey, Keyworth, Nottingham, NG12 5GG, UK.
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Review of Greenland Activities 2001, pp 144-149