Journal of the North Atlantic
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2014 Special Volume 6
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Introduction
The Norse colonization of Greenland (AD 986–
ca. AD 1450) presents an excellent framework to
study the relationship between a community and
its environment. Norse settlers took advantage of
favorable climatic conditions during the Medieval
Climate Anomaly around the end of the 10th century
(Mann et al. 2009, Moberg et al. 2005) to extend their
pastoral activities into the subarctic of southwestern
Greenland. The Eastern Settlement, which today corresponds
roughly to the Municipality of South Greenland
(Kommune Kujalleq), has been particularly well
documented by archaeological research in terms of
agro-pastoral practices (e.g., Buckland et al. 2009,
Commisso and Nelson 2008, Dugmore et al. 2005),
demographic pressure (Lynnerup 1996), and lifestyle
and dietary habits (Arneborg et al. 1999, Perdikaris
and McGovern 2007) as well as the localization of archaeological
sites (e.g., Algreen-Møller and Madsen
2006, Guldager et al. 2002). After centuries of abandonment,
the same areas were re-occupied by farmers
using conventional agricultural methods beginning in
the early 20th century.
In this context, the Eastern Settlement provides
palaeoenvironmental scientists with an ideal model
to examine the transition from a pristine to an anthropogenic
landscape. As well, studies of natural
archives can provide insight into the environmental
conditions surrounding known historical events and
the evolution of the Norse colonies in Greenland.
Over the last forty years, many palaeoenvironmental
studies have been conducted in the
Eastern Settlement and its surroundings. Different
types of palaeoenvironmental archives have been
investigated, each one advancing knowledge of
environmental change and the history of the Norse
in Greenland. These archive types are manifold
(soils, mires or lake deposits, fjord sedimentary
sequences), and their sensitivity to climate or human
forcing is likewise varied. Since the work of
Bent Fredskild (1973), peat deposits have been
most frequently studied to evaluate the response to
medieval Norse farming. Using biological proxies
(pollen, coprophilous fungi spores, and diatoms)
as well as abiotic proxies (e.g., LOI, geochemis-
Lake Sediments as an Archive of Land Use and Environmental Change in
the Eastern Settlement, Southwestern Greenland.
Vincent Bichet1,*, Emilie Gauthier1, Charly Massa1, and Bianca B. Perren1
Abstract - Palaeoenvironmental studies from continental and marine sedimentary archives have been conducted over
the last four decades in the archaeologically rich Norse Eastern Settlement in Greenland. Those investigations, briefly
reviewed in this paper, have improved our knowledge of the history of the Norse colonization and its associated environmental
changes. Although deep lakes are numerous, their deposits have been little used in the Norse context. Lakes that
meet specific lake-catchment criteria, as outlined in this paper, can sequester optimal palaeoenvironmental records, which
can be highly sensitive to both climate and/or human forcing. Here we present a first synthesis of results from a well-dated
2000-year lake-sediment record from Lake Igaliku, located in the center of the Eastern Settlement and close to the Norse
site Garðar. A continuous, high-resolution sedimentary record from the deepest part of the lake provides an assessment
of farming-related anthropogenic change in the landscape, as well as a quantitative comparison of the environmental impact
of medieval colonization (AD 985–ca. AD 1450) with that of recent sheep farming (AD 1920–present). Pollen and
non-pollen palynomorphs (NPPs) indicate similar magnitudes of land clearance marked mainly by a loss of tree-birch pollen,
a rise in weed taxa, as well as an increase in coprophilous fungi linked to the introduction of grazing livestock. During
the two phases of agriculture, soil erosion estimated by geochemical proxies and sediment-accumulation rate exceeds the
natural or background erosion rate. Between AD 1010 to AD 1180, grazing activities accelerated soil erosion up to ≈8 mm
century-1, twice the natural background rate. A decrease in the rate of erosion is recorded from ca. AD 1230, indicating a
progressive decline of agro-pastoral activities well before the end of the Norse occupation of the Eastern Settlement. This
decline could be related to possible climate instabilities and may also be indirect evidence for the shift towards a more
marine-based diet shown by archaeological studies. Mechanization of agriculture in the 1980s caused unprecedented soil
erosion up to ≈21 mm century-1, five times the pre-anthropogenic levels. Over the same period, diatom assemblages show
that the lake has become steadily more mesotrophic, contrary to the near-stable trophic conditions of the preceding millennia.
These results reinforce the potential of lake-sediment studies paired with archaeological investigations to understand
the relationship between climate, environment, and human societies.
In The Footsteeps of Vebæk—Vatnahverfi Studies 2005-2011
Journal of the North Atlantic
1 University of Franche-Comté, UMR CNRS 6249 Chrono-Environnement, 16 route de Gray, F-25030 Besançon cedex,
France. *Corresponding author - vincent.bichet@univ-fcomte.fr.
2014 Special Volume 6:47–63
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2014 Special Volume 6
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try), researchers from the University of Aberdeen
(Edwards et al. 2008, 2011; Golding et al. 2011;
Schofield and Edwards 2011; Schofield et al. 2008,
2010) have concentrated on palaeoenvironmental
change during the Norse period. Studies using mire
and pond deposits, soil sections, and archaeological
trenches greatly advance knowledge of land use by
the Norse, despite the inherent difficulties with discontinuous
records and attendant dating problems
(Edwards et al. 2008, 2011).
Although lakes are common landscape features
in South Greenland, palaeoenvironmental investigations
of lacustrine sediments are scarce. Assuming
that localized human impacts could overprint climatic
features, regional palaeoclimatic studies and
reconstructions have been preferentially conducted
on marine sediments from fjords (e.g., Jensen et
al. 2004, Kuijpers and Mikkelsen 1999, Lassen et
al. 2004, Roncaglia and Kuijpers 2004) or on lakes
beyond Medieval settlement areas (Andresen et al.
2004, Fréchette and de Vernal 2009, Kaplan et al.
2002). There are a few relatively old studies based
on lacustrine sediments from within Norse settlements
aimed at characterizing human impact (Sandgren
and Fredskild 1991).
The expansion of the Norse and the development
of the Eastern Settlement, as well as its demise, were
probably partially driven by climate change (Dugmore
et al. 2007, 2012; Massa et al. 2012a; Patterson
et al. 2010; Stuiver et al. 1995). Consequently, the
establishment of high-resolution climatic reconstructions
for this region is critical to understanding
the Norse adaptability to climate change. Ice-core
δ18O data highlight climatic fluctuations and can be
compared to Norse historical records. But available
glacial records are far from the settlement geographically,
altitudinally, and climatically (the Dye-3 core
site is located 475 km from the settlement, whereas
GISP2 and GRIP are more than 1300 km away), and
δ18O and snow accumulation rates record temperature
and precipitation at the inland ice summit ≈3000
m above the Norse sites (Vinther et al. 2010).
In order to obtain 1) a continuous high-resolution
environmental archive and 2) a quantitative reconstruction
of past temperatures at a decadal scale in
the Eastern Settlement, we cored the deepest part of
Lake Igaliku in the center of the archaeological area,
at the threshold of the Vatnahverfi district. Here, we
review previous palaeoenvironmental studies in the
Eastern Settlement, present lake archives as a potent
paleoenvironmental tool, and discuss the main results
obtained from Lake Igaliku.
Natural Archives and Previous Studies in the
Eastern Settlement
Fredskild’s pioneering studies
Bent Fredskild (1973, 1978, 1992) was one of the
pioneering investigators in this area. He established
a biochronology for the Holocene in Greenland and,
more particularly, in the Qassiarssuk area of the
Eastern Settlement (Fig. 1), from ponds (Comarum
Sø) and peat deposits (Comarum Mose, Galium
Kaer, Qassiarsuk).
Fredskild’s investigations documented Holocene
vegetation history and landscape evolution, showing
the immigration of taxa and the appearance of
Salix, Juniperus, and then Betula. Using pollen
and plant macrofossils, Fredskild also documented
the arrival of Norse farmers in the 10th century and
their perceptible impact on the environment through
scrub clearance, the creation of hay meadows, and
the introduction of non-indigenous taxa. However,
due to the age of the studies, the radiocarbon dates in
Fredskild’s work are few in number and imprecise,
and erosion identified in the sediments (Fredskild
1973, 1978; Sandgren and Fredskild 1991) could not
be quantified.
Peat deposits and archaeological soils
Complementing the early work of Fredskild and
creating high-resolution palaeoecological records,
Schofield et al. (2008, 2010), Schofield and Edwards
(2011), Edwards et al. (2008, 2011), and Golding
et al. (2011) have studied numerous peat deposits,
ponds, and archeological trenches in the Eastern
Settlement, in the Qorlortoq Valley, Tasiusaq, and
Qinngua (Qassiarsuk area), in Sissarluttoq (10 km
south from Igaliku, on the west side of the Igaliku
fjord), and in Sandhavn (Nanortalik area) (Fig. 1).
Age–depth models are not straightforward from
these deposits, as peat and soil accumulation can be
discontinuous (e.g., with hiatuses) and peat-columns
are often truncated by local use for fuel, roofing, or
bedding material. In addition, peat is often contaminated
by old carbon, which complicates dating (Edwards
et al. 2008). Despite these difficulties, peat,
soil, and pond deposits provide sensitive records of
vegetation changes during the Norse period. One
such example is from a drainage-ditch soil profile
in the center of the Norse Garðar settlement ruins
(about 2 km from our site at Lake Igaliku), where
pollen and insect remains provide compelling
evidence for both manuring and irrigation practices
during the Norse period (Buckland et al. 2009).
Lake sediments as archives of climate changes
Near the Eastern Settlement, two lacustrine
sequences (Lakes Qipisarqo and N14) have been
Journal of the North Atlantic
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2014 Special Volume 6
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studied for palaeoclimatic reconstruction (Fig. 1).
Lake Qipisarqo is located near a glacial tongue flowing
from the Qassimiut lobe, about 80 km northwest
of our investigation area. A first study based on
biogenic silica and organic matter measurements
documented palaeo-productivity in relation to past
temperatures (Kaplan et al. 2002). A later study
reconstructed climatic parameters (temperature,
precipitation), from pollen assemblages using the
modern analogue technique (Fréchette and de Vernal
2009).
Lake N14 is located on an island near Kap Farvel.
The palaeoclimatic interpretation of this sequence
is based mainly on high-resolution biogenic silica
measurements (interpreted as temperature/precipitation)
and on sulphur flux estimates (a storminess parameter;
Andresen et al. 2004). Although these two
records document the Holocene period at a multicentennial
to decadal scale, they are both heavily
influenced by maritime climate, and do not necessarily
capture the climatic changes experienced by the
Norse in the more continental inner fjord area.
Marine sediments
Two marine sediment cores from the outer and
inner part of Igaliku Fjord (cores PO 243-443 and
PO 2342-451; Fig. 1) were investigated to document
local palaeohydrographic conditions for the last
Figure 1. Map of southwestern Greenland and the Norse Eastern Settlement showing the location of the current localities
of the area (white squares), main Norse ruin groups (black dots), modern farms (black triangles), and the main sites of
mentioned palaeoenvironmental studies (white circles).
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3200 years (Jensen et al. 2004, Lassen et al. 2004,
Roncaglia and Kuijpers 2004). The authors detailed
the climatic variations that occurred during the transition
from the “Medieval Warm Period” to the Little
Ice Age and their implications for Norse settlement.
To date, these studies stand alone in providing a
record of past climate change during the historical
period for the Eastern Settlement. More recently, the
study of ice-rafted debris deposited in the Narsaq
Sound (core Ga3-2; Fig. 1) documented the dynamics
of the local glacial termination in response to
Holocene climate changes (Nørgaard-Pedersen and
Mikkelsen 2009). As in the aforementioned lakesediment
studies, these marine sequences have a
temporal resolution that is too low to accurately assess
the environmental changes that occurred during
the historical period. Although the fjord deposits
provide information about terrestrial flux (Roncaglia
and Kuijpers 2004), these marine sedimentary archives
cannot be used to evaluate land-use–induced
changes clearly.
The Opportunity Presented by Lake Sediments
Complementing earlier studies, high-resolution
lake-sediment archives provide insights into the
long-term development of terrestrial and aquatic
ecosystems in the archaeological area. Palaeoclimatic
and palaeoenvironmental records established
from lake sediment cores offer the opportunity
to highlig-t changes that occurred during a specific
time period. In particular, they may provide
evidence for processes associated with the transition
from pristine to human-dominated environmental
conditions and may also provide perspectives on the
functioning of modern ecosystems and landscapes
(Battarbee and Bennion 2011, Dearing et al. 2008,
Giguet-Covex et al. 2011, Ramrath et al. 2000).
In order to maximize the palaeoenvironmental
interpretation of the historical period, study sites
must meet specific criteria, mainly related to the
catchment–lake relationship. Among these conditions,
the most important are:
(i) Sedimentation rate. The sedimentary record
must be sufficiently thick with a high age–depth ratio
to allow for high-resolution, multiproxy analyses.
Except for X-ray fluorescence, most non-destructive
core-scanning sensors (e.g., γ-density, magnetic susceptibility)
do not analyze sub-millimeter measurements,
and classical destructive analyses (e.g., biotic
contents, geochemistry, grain-size distribution) need
at least 3–5-mm samples. If annual resolution is
not feasible, decadal resolution is often realistic.
For decadal resolution, sediment accumulation rate
(SAR) has to be at least 0.4 mm yr-1. At low altitude
(e.g., under 500 m asl) in soil- and till-covered
catchments of southwestern Greenland, sequences
cored in the deepest parts of lakes show varying
SARs. Recent literature (Andresen et al. 2004;
Fréchette and de Vernal 2009; Massa et al. 2012a,
2012b; unpublished data from the Ultimagri Project
[University of Franche-Comté, Chrono-environment
Laboratory]) indicates that mean values range from
0.1 mm yr-1 to 0.6 mm yr-1 for the last two millennia.
Regionally, at higher altitudes, lake-sediment
accumulation rates are often lower, mainly due to
poor soil development and low internal biological
processes, and are less amenable to high-resolution
investigations.
(ii) Age control. The age control of lake cores is
usually based on measuring the decay of radiogenic
isotopes. For dating the most recent 150 years, the
short-lived radio-isotopes 137Cs and 210Pb are easily
used in most cases (Appleby and Olfield 1978).
However, the best way to date older deposits is
using 14C in terrestrial plant remains. Accelerator
mass spectrometry (AMS) dating requires a few
milligrams of organic matter. In vegetated areas
of southern Greenland, fragments of wood, twigs,
or leaves are often present in sediments. At Lake
Igaliku (see below), a 60-mm-diameter core taken
in 21 m of water produced fourteen terrestrial plant
macrofossils within the upper 95 cm. If terrestrial
plant remains are too scarce to produce a robust
age-depth model, other substances like humic acids
or aquatic macrofossils can be used, taking into account
a reservoir effect due to the in-lake or in-soil
recycling of carbon (Abbott and Stafford 1996, Olsen
et al. 2012, Wolfe et al. 2004). Where possible,
the use of bulk sediment should be avoided because
of the mixing of the organic fractions.
(iii) Simple catchment-basin properties. Detrital
inputs to the lake basin must reflect the dual control
of climate and anthropogenic processes. For this
consideration, there are no absolute conditions, but
closed-basin lakes and those fed by runoff are preferred
to lakes in which major fluvial detrital inputs
may overprint the response of subtle soils erosion
due to land use (Edwards and Whittington 2001).
Sites with catchments containing glacial outwash
plains subject to wind erosion and strong aeolian
fluxes should be avoided. Otherwise, sedimentary
anthropogenic imprints depend on the archaeological
site density (or intensity of land-use processes)
in the catchment and catchment area:lake area (or
lake volume) ratio. In very large lakes, the signal
from an adjacent archaeological site is likely to be
diluted, and small lakes can offer a better record of
anthropogenic processes.
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(iv) Continuous sedimentation. Ideal sedimentary
sequences should be continuous, with no hiatuses,
disturbances, or mass-wasting deposits. Catchments
and lakes with gentle slopes enhance the probability
of undisturbed sequences. Deep basin sequences
are better than littoral deposits where the stratigraphy
could be affected by ice scouring of the bed
or by wind-generated turbulence and mixing of the
sediment–water interface. In any case, an acoustic
survey with a sub-bottom profile should be used to
document the lake sediment stratigraphy and possible
discontinuities and optimize the location of the
coring site.
Lakes which meet the above criteria are ideal
and can provide knowledge of anthropogenic and
palaeoenvironmental changes through time, complementing
data provided by terrestrial and archaeological
archives.
The Example of Lake Igaliku, at the Heart of the
Eastern Settlement
Local and historical setting
Lake Igaliku (unofficial name; 61º00'N–45º26'W,
15 m asl) is located in the low valley between the
head of Igalikup Kangerlua (Igaliku fjord) and
Figure 2. Map showing (a) the region around Lake Igaliku including the catchment area (grey dashed line), roads (black
dashed lines), modern buildings (black rectangles), and current hay fields (grey shaded areas), as well as the archaeological
site of Garðar, and (b) the bathymetry of the lake and the coring location.
Journal of the North Atlantic
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2014 Special Volume 6
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were central to the re-development of contemporary
agriculture in southwestern Greenland. Since 1980,
after the climate crisis of the 1960s/1970s (Egede
and Thorsteinsson1982, Greenland Agriculture Advisory
Board 2009), two sheep farms (more than
1000 sheep) were established in the catchment, and
around 30 ha of hayfield were created on the shore of
the lake to produce winter fodder for stabling (Figs.
2a, 3).
Because of these two phases of farming in the
catchment during the last millennium (Norse and
modern), Lake Igaliku is an excellent site to compare
and explore environmental changes and the
complex relationship between climate, landscape,
and human societies.
Core and sediment chronology
In order to obtain a continuous high-resolution
environmental archive, the deepest part of Lake
Igaliku was cored from a floating platform, using
piston and gravity corers. A 4-m-long sandy silt
Holocene composite sequence was collected, with
the upper 100 cm spanning the last 2000 years.
The upper 100 cm of the core is composed of very
finely stratified brownish sandy silt with black
horizons rich in ferrous iron oxide (Fig. 4). From
≈5 cm, the sandy silts give way to black clayey
silts up to the sediment–water interface. The Xradiographs
reveal continuous sedimentation with
distinct lamina (≈6 mm), indicating that sediments
are not bioturbated. The sequence does not contain
Tunulliarfik fjord (Erik’s fjord) (Figs. 1, 2a). It is
a north–south oriented lake with a surface area of
34.6 ha and a maximal depth of 26 m (Fig. 2b). The
3.55-km2catchment area is without an inlet, but has
a small outlet on the northern shore that drains into
the Tunulliarfik fjord. The topography of the catchment
is characterized by a large, gently sloped plain
(3.1 km2) surrounded in the western part by a low,
rounded hill (130 m asl). The highest relief is to the
northeast reaching 300 m asl. The rocks underlying
most of the catchment are Proterozoic granites partly
covered by arkosic sandstones and lavas that outcrop
on the hills.
The lake is located within 2 km of the modern
village of Igaliku, which was the Norse Garðar, settled
ca. AD 1000, soon after the landnám (Gad 1970,
Jones 1986). Garðar rapidly became a place of
prime importance for Norse society (Episcopal seat
and assembly site; Krogh 1967, Nørlund and Roussell
1929, Sanmark 2009). Archaeological structures
suggest that Igaliku-Garðar was a high-status farmstead
with probably the largest holding of livestock
in Norse Greenland (Christensen-Bojsen 1991, Mc-
Govern 1991). The chronology of the abandonment
of Garðar is unclear, but it is generally accepted
that it must have occurred sometime in the mid- to
late 15th century (Dugmore et al. 2009). The site of
Garðar was settled and farmed again in the 18th century
(Arneborg 2007). Modern pastoral agriculture
began in 1915 (Austrheim et al. 2008). During the
20th century, the village of Igaliku and surroundings
Figure 3. View of Lake Igaliku and surrounding fields (looking towards the north).
Journal of the North Atlantic
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2014 Special Volume 6
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that date. A sharp increase in the SAR, up to 1.9 mm
yr-1, is noted during the 20th century.
Sampling and sediment analyses
The core was contiguously sampled. The top 10
cm were sampled in 0.5-cm slices, and below
10 cm, sampling intervals (≈1 cm) were chosen by
using X-ray image to ensure homogenous samples
according to the varying lithology. Sampling
resolution is between 2 to 32 years per sample for
geochemical proxies and diatoms, and 25 to 80
years for pollen and organic non-pollen palynomorphs
(NPP).
Core analysis was based on a multidisciplinary
approach using indicators that track catchment dynamics
(i.e., vegetation [Gauthier et al. 2010], sediment
yield [Massa et al. 2012b]) and lake trophic
changes (organic geochemistry and diatoms [Perren
et al. 2012b]). A suite of geophysical (γ-density
any mass wasting, rapid deposits due to slumps, or
high-energy inflows which could disrupt the age–
depth model.
For the upper 100 cm, the chronology (Fig. 4) is
based on 16 AMS radiocarbon dates (28 for the whole
core) on terrestrial plant macrofossils (14 twigs and
leaves) and aquatic bryophytes (2 samples) corrected
for reservoir effect (Massa et al. 2012a). In addition,
the last two centuries (the upper 15 cm) are dated by
210Pb and 137Cs using α spectroscopy. The age-depth
model is based on the Monte-Carlo Method (Blaauw
2010), which allows for the robust estimation of the
relative uncertainty and takes into account the entire
probability distribution of calibrated 14C dates (for
table of radiocarbon dates and details, see Massa et
al. 2012b). The age-depth model is almost linear until
ca. AD 1010, with a mean (SAR) of ≈0.4 mm yr-1.
After that, the SAR rises to a maximum of 0.8 mm
yr-1 around AD 1150, and decreases gradually after
Figure 4. Stratigraphy and age-depth model of the Lake Igaliku core for the last two millennia. The probability distributions
of calibrated radiocarbon dates are displayed with laboratory reference number. The chronology of the upper 15 cm is based
on 210Pb and 137Cs measurements. See Massa et al. (2012) for detailed comment.
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and magnetic susceptibility with a Geotek Multi-
Sensor Core Logger), geochemical (Avaatech XRF
Core Logger, ICP-AES, Corg, Ntot, δ15N, δ13C),
and biological proxies (pollen, non-pollen palynomorphs
[NPP], and diatoms) were analyzed.
Here, we synthesize the proxies that assess catchment
dynamics, highlighting the impacts of farming
activities during the medieval and modern periods.
The parameters used are not a priori linked to human
or climate-forcing individually, but their combined
analysis, variations at different time scales, and
comparison with the archaeological and historical
data allows for human impacts to be resolved.
Vegetation changes and historical grazing
indicators
The current vegetation around Igaliku is a classic
subarctic tundra, dominated by scrub juniper (Juniperus
communis), Crowberry (Empetrum nigrum)
heaths, and highly deciduous and productive grey
willow (Salix glauca), dwarf birch (Betula glandulosa),
and downy birch (Betula pubescens). Pollen
concentration in the lake sediments is related to
the pollen rain directly falling on the lake surface;
however, pollen which has been brought into the
lake with inflowing waters or with surface runoff
may also accumulate (Hicks and Hyvärinen 1999).
Therefore, variation in pollen content is a response
to changing environmental conditions in plant and
pollen productivity and plant density, as well as a
response to increased allochthonous material from
the catchment. Allochthonous material may also
include NPPs and coprophilous fungi, which grow
indiscriminately on herbivore dung (Bell 2005)
and indicate the presence of herbivores around the
lake (Davis and Shafer 2006, van Geel and Aptroot
2006). Nevertheless, the arboreal pollen content of
Lake Igaliku for the last two millennia indicates
relatively stable vegetation (IGA1). Since 3 ka BP,
southern Greenland underwent Neoglacial cooling
shown by a progressive decrease in the influx of
arboreal/shrub pollen (Massa et al. 2012a).
At this sampling resolution, climate changes are
poorly recorded by vegetation (except for recent climate
warming, which is recorded by a huge increase
of Betula). However, anthropogenic forcing is easily
detectable. The first sign of Norse settlement (IGA
2a; Fig. 5), is a decrease in downy birch and juniper
from 1000 to 1150 cal. BC, which resulted in an
overall decrease in arboreal/shrub pollen from 60
to 45%. Nevertheless, these values remain higher
than the birch percentages recorded in most of the
peat records adjacent to the Norse ruins. Meanwhile,
coprophilous fungi spores synchronously increase
indicating the occurrence of herbivores in the catchment.
Small amounts of coprophilous fungi appear
before the medieval period, suggesting that wild
herbivores, probably caribou, may have been grazing
in the area (Davis and Shafer 2006, Gauthier et
al. 2010, Schofield and Edwards 2011, van Geel and
Aptroot 2006). Another impact associated with the
landnám is the rise in moss and fern spores, probably
associated with erosion, as suggested by the denudation
rate. The loss of arboreal taxa, and the concomitant
rise in coprophilous fungi, moss, and fern spores
are a likely response to grazing pressure, erosion of
soil, and the development of agro-pastoralism in the
catchment during the landnám.
From the mid-12th century (IGA2b), percentages
of coprophilous fungi as well as Rumex acetosatype
pollen (a combination of pollen from Rumex
acetosa, R. acetosella, and Oxyria dygina) increase.
The Norse agricultural “weeds” R. acetosa and R.
acetosella are common in grazed environments
and are traditionally regarded as evidence of Norse
settlement in south Greenland (Edwards et al. 2008,
Fredskild 1973). The first occurrences of this pollen
type, before the Norse period, probably correspond
to local production of Oxyria pollen or long-distance
transport. The Igaliku sequence shows a certain lag
between the first clearance, introduction of cattle
and the development of R. acetosa-type (Bichet et
al. 2013, Gauthier et al. 2010). However, palynological
data from peat deposits rarely record such a
lag except in Tasiusaq, where there is a very precise
chronology for vegetation changes between ≈AD
1000–AD 1100 (Edwards et al. 2008).
At the beginning of the 14th century (IGA 2c),
pollen and NPP document the steady decrease of
all grazing pressure and erosion indicators. These
changes are likely a response to a reduction in
grazing herbivores and could be chronologically related
to the end of the development of plaggen (i.e.,
man-made soil) at Igaliku (Buckland et al. 2009).
Coprophilous fungi disappear almost completely
around AD 1400, and the tundra vegetation returns
to almost pristine conditions. However, agricultural
weeds and some native ruderal herbs (e.g., Rumex
acetosa-type and Plantago maritime; Edwards et al.
2008) remain present.
For almost five centuries, the vegetation remained
stable (IGA2d). After ca. 1950, trees and
shrubs decrease, weeds, apophytes, and coprophilous
fungi increase, all in response to the new phase
of grazing pressure and the re-establishment of
farming activities (IGA2e).
Estimating soil erosion in the Igaliku Lake
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Figure 5. Percentage pollen diagram for trees, shrubs and heaths, herbs, aquatics, coprophilous fungi, and pteridophytes. Exaggeration curves x2 for Thalictrum and Juniperus,
and x10 for all other taxa except Betula pubescens, B. glandulosa, Salix, Poaceae, and Cyperaceae.
Journal of the North Atlantic
V.Bichet, E.Gauthier, C. Massa, and B.B. Perren
2014 Special Volume 6
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(BMC) of 420 mg cm-3 was measured using 25
samples of soil surface horizon collected in the lake
catchment. For details, see Massa et al. (2012b).
Calculated values of DR are a first approximation of
real land erosion. Use of this method assumes that
SAR is representative of the entire lake bottom, and
the values of DR are given as an average erosion
yield on the global surface of the catchment.
The first millennium and the pre-landnám period
show relatively stable soil erosion that ranges between
2.5 and 5 mm century-1 in response to natural
climate variability. The high detritic inputs (Ti) and
low productivity (C:N) around AD 250 suggests a
cooling which corresponds to relatively low temperatures
in the Arctic between AD 165–AD 345
(Kaufman et al. 2009). The low C:N and Ti values
at ca. AD 400 indicate low erosion and/or high algal
productivity which could be linked to a warmer time
interval (AD 375–AD 415) recorded in the Arctic
(Kaufman et al. 2009). The most detritic period at
AD 470–AD 550 roughly corresponds to a cooling
in the nearby Igaliku Fjord (Jensen et al. 2004, Lassen
et al. 2004), and to cold atmospheric conditions
and enhanced advection of EGC water masses in the
Narsaq Sound (Nørgaard-Pedersen and Mikkelsen
2009), as well as a decrease in biological productivity
in Lake N14 (Andresen et al. 2004).
Extensive sand horizons in lakes and soil profiles
in the area of Sondre Igaliku have been linked
to Norse erosion (Fredskild 1978, Jakobsen 1991,
Sandgren and Fredskild 1991). Some authors suggested
however that these deposits could be partly
the result of enhanced wind activity between the 9th
and 14th centuries (Kuijpers and Mikkelsen 2009,
Lassen et al. 2004), which would have produced a
large amount of clastic material transported from
the nearby well-developed sandur. However, Lake
Igaliku is not located in a glacial valley, and an
increase in wind strength during Norse period may
have played only a minor role in the high sediment
supply into Lake Igaliku compared with farming
activities. Soon after the Norse arrival, land
clearance (indicated in pollen data by a decrease
in woody taxa) and the introduction of sheep led
to a rapid increase in soil erosion to a maximum
of 8 mm century-1, twice the background level,
around AD 1180 (Fig. 6). The maximum values in
C:N ratio and Ti between ca. AD 1030 and ca. AD
1230 suggest a strong impact of Norse farming
during this period. Compared with historical data,
maximum erosion appears a few decades after the
appointment of the first bishop, when Garðar was
probably close to its maximum development and
activity. First evidence of erosion caused by land
catchment
The hypothesis of overexploitation of the environment
has been frequently proposed as a major
cause of the collapse of the medieval Norse society
in Greenland (e.g., Diamond 2005; Edwards et al.
2008; Fredskild 1973, 1988; Gad 1970; Jacobsen
1987; Jakobsen 1991; McGovern et al. 1988). Estimating
the chronology of the terrigenous flux into
the Lake Igaliku may help to further evaluate the
validity of this explanation.
Among the geochemical proxies studied, titanium
(Ti) is a conservative lithogenic element that
participates in very few biogeochemical processes
(Kauppila and Salonen 1997, Koinig et al. 2003).
Higher Ti concentrations in the sediment point to enhanced
physical weathering of alumino-silicates in
the watershed, which can be due to climatic changes
or to erosion from land use (Kylander et al. 2011).
The Ti profile (Fig. 6) remains relatively stable before
AD 1010, with an average value of 3200 ppm.
The concentration then increases, with peak values
of 4400 ppm between AD 1010 and AD 1335. After
that time, Ti concentrations fall to an average of
3650 ppm, which is 14% more than the pre-landnám
baseline. Beginning ca. AD 1960, the titanium content
increases sharply to reach the maximum values
of the profile at around 4600 ppm during the 1980s.
Bulk sediment C:N ratios are widely used in
palaeolimnology for assessing the abundance of
terrestrial and aquatic components of organic matter
(e.g., Kaushal and Binford 1999). For Igaliku,
C:N ratios between 11.5 and 16 indicate a mixture
of lacustrine and terrestrial contribution to the organic
matter (OM) pool (algae: ≈4–10, lacustrine
plants: ≈6–9, land plants: ≥20; Meyers and Ishiwatari
1993). Values above 14 during the period AD
1010–AD 1335 and after ca. 1960 indicate increases
in terrestrial OM input resulting from soil erosion.
The covariance of Ti and C:N ratio demonstrates
that they constitute two robust, but related, proxies
of soil erosion.
Soil erosion can be quantified by calculating the
mean denudation rate (DR; Fig. 6). DR, expressed in
mm century-1, is calculated as follows:
([MARmin*Lake area] / catchment area)
DR =
[BMC*1000]
Mass accumulation rates of minerogenic matter
(MARmin) were calculated according to Enters et
al. (2008) using wet bulk density, water content,
minerogenic matter content (deduced from organic
carbon measurement), and SAR derived from the
age–depth model. A mean bulk mineral content
Journal of the North Atlantic
V. Bichet, E. Gauthier, C. Massa, and B.B. Perren
2014 Special Volume 6
57
windiness during the Little Ice Age (Willemse et al.
2003) but may also reflect four centuries of Norse
farming, which could have decreased the resilience
of the soils for a long time.
From the beginning of the 20th century to ≈1960
(± 5 yr), corresponding to the re-establishment of
farming at Igaliku, none of the sedimentary parameters
reveals any significant increase of erosion
around the lake of Igaliku (Fig. 6). Since ≈1960, the
grazing pressure (shown by a decline in woody taxa
and a rise in coprophilous fungi [Fig. 5]) caused a
progressive increase in detrital parameters. Soil erosion
accelerated beginning in 1969 (± 4 yr), with a
sharp increase in Ti and C:N ratio, reaching ≈11 mm
century-1 in 1988 (± 2.5 yr), slightly more than during
the medieval period. Around 1988, major earthworks
and digging of drainage ditches were carried
out in both hayfields (Fig. 3), which caused soil
erosion to increase dramatically up to 21 mm century-
1. After 1997 (± 2 yr), the erosion rate decreased
continuously, whch may mark the stabilization of the
material remobilized by the drainage work.
Farming activities and their consequences on
water quality: The diatom signal
In a lake catchment, detrital organic matter and
nutrient inflows due to animal dung and fertilizers
may produce an excessive load of nitrogen (N) and
phosphorus (P) and induce an increase in lake primause
around Lake Igaliku also pre-dates the formation
of an anthropogenic soil horizon at Garðar between
by 100 years (ca. AD 1110–AD 1370; Buckland
et al. 2009) and constitutes one of the oldest
evidence of human impact in the area.
Soil erosion is perfectly synchronized with
the grazing pressure recorded by the amount of
coprophilous fungal spores (grazing indicators;
Gauthier et al. 2010). The grazing pressure and associated
soil erosion remained high until ≈AD 1335,
with high values and large amplitude fluctuations of
the C:N ratio indicating a destabilization of soils in
the watershed. Interestingly, our data also indicate a
substantial decline of agro-pastoral practices around
Lake Igaliku and reduced soil erosion beginning
≈AD 1230, well before the end of the Norse Eastern
Settlement. After ≈AD 1335, grazing pressure
decreased as indicated by the return of coprophilous
fungal spores to pre-landnám background values.
At the same time, the dwarf-shrub community
recovered and soil erosion decreased to reach presettlement
values.
After the demise of the Norse colony and during
the following four centuries of cool and dry Little
Ice Age conditions (Jackson et al. 2005, Kaufman
et al. 2009, Willemse et al. 2003), the C:N ratio returned
to natural values, and soil erosion decreased
to 3 mm century-1. Higher Ti concentrations are likely
due to eolian dust inputs linked to the enhanced
Figure 6. Sediment accumulation rate (SAR), minerogenic mass accumulation rate (MARmin—translated to soil-denudation
rate), organic mass accumulation rate (MARorg), titanium concentration measured by ICP-AES (points) and calibrated
from XRF scan results (curve),and C:N atomic ratio from the last 2000 years of the sediment archive of lake Igaliku. The
grey shaded areas highlight the periods of Norse and modern farming.
Journal of the North Atlantic
V.Bichet, E.Gauthier, C. Massa, and B.B. Perren
2014 Special Volume 6
58
ry productivity. Lake-water trophic status reflects the
nutrient balance between the lake and its catchment,
and palaeoecological records of this balance help to
illustrate the agricultural pressure on these systems
(Anderson et al. 1995, Bradshaw et al. 2005).
Among the studied parameters, diatoms provide
insight into lake trophic changes over time and
document nutrient enrichment in response to local
agriculture. Over 140 species of diatoms from 25
genera were identified from the sediments of Lake
Igaliku (see Perren et al. 2012a for details), and
the flora is typical of dimictic oligotrophic West
Greenlandic lakes (Perren et al. 2012b). During
the last two millennia, diatom assemblages in the
lake have been remarkably stable and poorly linked
with climate changes. The Norse period has slightly
higher relative frequencies of Cyclotella stelligera
constrained to the period ca AD 1280–1350. However,
the abundance of Fragilaria tenera, the main
mesotrophic planktonic taxon stays under 5% of the
total population (Fig. 7). During that time, despite
grazing activities that used manure fertilization to
increase soil nutrient levels (Buckland et al. 2009;
Commisso and Nelson 2007, 2008; Ross and Zutter
2007), the diatom assemblages were almost undisturbed
and the lake remained at a low trophic level.
For the same period, the pastoral land use inferred
by diatom changes appears to be better recorded at a
pond site at Sissarluttoq (Edwards et al. 2011) than
at the Lake Igaliku, where the nutrient input is probably
diluted due to the lake size.
In contrast, modern farming practices have produced
a large ecological response from the diatom
community, which reflect increased nutrient inputs
and a change in the lake’s trophic status. Although
diatoms appear to be stimulated by recent global
warming (Box et al. 2009), the sharp increase of
Fragilaria tenera since 1980, which recently
reached more than 35% of the diatoms assemblage,
strongly indicates nutrient enrichment of lake water
within the last 30 years (Perren et al. 2012). This
trophic shift is likely a response to the ≈200–250
kg.ha-1.yr-1 of N fertilizers that are deployed for hayfield
production around Lake Igaliku (Miki Egede,
farmer, Igaliku, Greenland, pers. comm.) as well
as the effluent from the sheep stables that currently
drains into the lake.
A history of Norse and modern agriculture
As shown above, selected proxies from the sediments
of Lake Igaliku provide a detailed account of
farming history and its impact on the local environment.
During medieval times, events in the lake
record are consistent with the archaeological documentation
of the Norse at Igaliku. The first evidence
of human impact appears ≈AD 1000, a few years
Figure 7. Comparison of environmental changes recorded by the Igaliku Lake system during the last 2000 years. (A) Vegetation
change (grazing indicators correspond to the sum of coprophilous, microrrhizal fungi, and Norse apophytes (e.g.,
Rumex acetosa-type and Ranunculus acris-type)); (B) Catchment soil-denudation rate and main historical cultural events;
(C) Lake trophic status evaluated by mesotrophic diatoms (e.g., Fragilaria tenera); and (D) Climate change illustrated by
Arctic temperature anomaly (from Kaufman et al. 2009) and Dye 3 winter δ18O (from Vinther et al. 2010). The grey shaded
areas highlight the periods of Norse and modern farming.
Journal of the North Atlantic
V. Bichet, E. Gauthier, C. Massa, and B.B. Perren
2014 Special Volume 6
59
after the landnám (Fig. 7). Then, the increase of
anthropogenic signals (pollen, NPP, and soil erosion
parameters) indicates a progressive development of
agro-pastoral activities until ≈AD 1230. Maximum
erosion appears a few decades after the appointment
of the first bishop (AD 1126) when Garðar was
probably close to its maximum development and
activity. However, compared with modern farming
standards (Montgomery 2007), the highest level
of Norse soil erosion recorded at Igaliku (8 mm.
century-1) falls within the framework of sustainable
agricultural practice.
After ≈AD 1230, soil-erosion indicators began
to decrease but remained at a high level, with largeamplitude
fluctuations until ≈AD 1335. Climate records
are too poorly resolved or too far removed on
the inland ice to describe the weather conditions of
this period in detail and their effects on the growing
season. Since the mid-12th century, a regime of more
extreme climatic fluctuations was inferred from
outer Igaliku Fjord, with more influence of the cold
East Greenland Current resulting in more sea ice and
lower summer temperatures after ≈AD 1245 (Jensen
et al. 2004). A succession of harsh winters is also
noted in the Dye-3 winter δ18O record toward the end
of the 12th century (Vinther et al. 2010). This drop in
temperatures may have led to a significant reduction
in numbers of sheep and grazing pressure because
cold years in such marginal agricultural areas as
southern Greenland can have dramatic consequences
for livestock.
After ≈AD 1335, our data indicate a substantial
decline of agro-pastoral practices around Lake Igaliku.
This last decline occurred a few decades before
the death of the last bishop known to have lived at
Garðar. This finding suggests that farming activity
was already in decline before this historical event and
well before the end of the Norse Eastern Settlement.
The palaeoenvironmental evidence for a decrease
in anthropogenic impacts is consistent with
archaeological evidence of Norse adaptation to
worsening climate conditions. During this period,
the reduction of agricultural dependence is demonstrated
by archaeofauna from several Norse farms
and human isotopic data showing an increasing
proportion of subsistence from hunting, fishing, and
sealing sources (Arneborg et al. 1999, Dugmore et
al. 2012, Enghoff 2003, Mc Govern et al. 1996, Mc-
Govern and Pálsdóttir 2006).
During the first step of the modern re-establishment
of agriculture, from the beginning of the 20th
century to ≈1960, the lake record suggests that the
effect of sheep grazing around the lake was minimal.
Erosion yield increased sharply after 1960 and became
marked after 1988. These two periods of soil
erosion, 1960–1988 and 1988–2007, are consistent
with the two modern agricultural phases of south
Greenland (Egede and Thorsteinsson 1982). The
former corresponds to the first phase of free-ranging
sheep, whereas the latter is the expression of intensified
practices and hay-field management that followed
the agrarian reform of 1982. That reform was
related to the successive harsh winters of 1966/1967,
1971/1972, and 1976/1977 which starved and killed
nearly 60% of the sheep in Greenland (Greenland
Agriculture Advisory Board, 2009). As a result of
current agricultural practices, the Igaliku Lake system
is currently undergoing the most important environmental
change of the last 2000 years, with soil
erosion three times greater than during the Norse
tenure. At the same time, nutrient impacts from
industrial fertilizers have outpaced the geochemical
and biological resilience of the lake, which is
becoming mesotrophic like its more southerly European
counterparts. Faced with a climate crisis and
the resulting decrease in agricultural productivity,
the Norse adapted their dietary habits and lifestyle,
whereas modern society has used intensive practices
and industrial processes to guard against failure.
Towards a local climate reconstruction
In the Eastern Settlement area, climate variability
and its effects on the growing season drove adaptation
or failure as much for Norse settlers as for modern
Greenlandic farmers. A detailed reconstruction
of short-lived climatic events during the medieval
period and a reliable reconstruction of temperature
variations at the local scale would greatly help assess
the role of climate change on Norse population
habits and migrations.
While lake sediments have the temporal resolution
necessary to capture the full range of climate
variability, their suitability for palaeotemperature
reconstructions is usually limited due to the lack of
direct quantitative proxies. In suitable hard-water
lakes (when the evaporative effect on lake-water
δ18O is low), authigenic calcite may reliably record
the lake-water δ18O, which is controlled by the δ18O
of precipitation, itself strongly correlated to the
mean annual temperature at high latitudes (Masson
Delmotte et al. 2012). However, lakes in southern
Greenland are poorly buffered, and calcite is largely
absent there. So, our ongoing studies at Lake Igaliku
are now focused on two ways of extracting palaeotemperatures
records. The first involves chironomid
larvae for both the analysis of chitin δ18O and species
assemblage-based temperature inference. The latter
uses alkenone biomarkers, which are highly resistant
organic compounds produced by phytoplankton,
where molecular long-chain saturation depends
Journal of the North Atlantic
V.Bichet, E.Gauthier, C. Massa, and B.B. Perren
2014 Special Volume 6
60
Acknowledgments
The authors are grateful to M. Campy, H. Grisey, C.
Petit, and B. Vannière, for technical help during the coring
campaign in Greenland. This research is supported by the
University of Franche-Comté, the University of Burgundy,
the Burgundy Regional Council, the French Polar Institute
(IPEV), and the ANR CEPS “Green Greenland” project. We
acknowledge the two anonymous reviewers for their helpful
and constructive remarks to improve the manuscript.
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