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Baseline Briefing
This section is intended to provide a final overview
of isotopic baselines around the North Atlantic for the
purpose of evaluating the origins of the settlers of
this region. This discussion begins with strontium
isotopes. Knowledge of baseline isotopic values is
essential for the investigation of past human mobility.
Fortunately, considerable data are now available. A
basic principle relates older rocks to higher strontium
isotope ratios in human skeletons. Very old rocks
dominate parts of the North Atlantic region, particularly
in Norway, Sweden, Scotland, Northern Ireland,
and Greenland. Very young rocks with low 87Sr/86Sr
are found in Iceland and the Faroes as part of volcanic
activity at the divergent plate boundary of the
mid-Atlantic ridge. There are intermediate values of
strontium isotope ratios between ~0.709 and ~0.711
that are found in many parts of northwest Europe,
including parts of southern Scandinavia and the North
European Plain, particularly in areas dominated by
glacial and periglacial deposits and coastal regions
where marine diet and sea spray have altered the relations
between human values and geology.
Because Iceland has a distinctive geology of very
young rocks with very low strontium isotope ratios,
detecting the presence of non-local individuals from
older terrains is quite feasible. In a similar fashion,
individuals from Iceland who moved to Greenland
would also have very distinctive strontium isotope
values among the higher 87Sr/86Sr values common
there. The 2 areas of Norse settlement on Greenland
have distinctive 87Sr/86Sr values. For this reason,
movement between the Eastern and Western Settlements
should be visible in the isotope data. On the
other hand, a 87Sr/86Sr distinction among individuals
originating in Norway, northern Britain, and Greenland
is difficult given the generally similar 87Sr/86Sr
values in these areas.
In sum, there is good and bad news for strontium
isotopic studies in the North Atlantic. The
good news is that there are distinct differences
between Iceland and the rest of the North Atlantic.
Local strontium isotope ratios in Iceland fall almost
exclusively between 0.706 and 0.7092. Local
values from Norway, northern Britain, Ireland, and
Greenland are greater than 0.7092. The good news
is also that oxygen may provide some information
on origins and that lead isotopes have the potential
to resolve some of these differences, for example,
between Greenland and Norway.
The bad news is that we cannot at present
distinguish individuals coming from northern
Britain, Ireland, and Norway, so that these potential
homelands for the settlers of Greenland and Iceland
cannot be segregated isotopically. The bad news is
also that there are numerous places with strontium
isotope values between 0.709 and 0.710 that cannot
be separated using 87Sr/86Sr alone. At the same time,
the new information that has been obtained through
isotopic investigations is remarkable, and summarized
in the following pages.
Oxygen isotopes may provide some resolution of
this difficulty, particularly in separating Greenland
individuals, who have more-negative δ18O, from
individuals native to southern Norway and Northern
Britain, who should have less-negative values. On
the other hand, oxygen isotopes exhibit significant
variability and do not always follow expectations.
Oxygen isotopes are considered in more detail in the
next section.
Isotopic Results
Strontium isotope ratios are very useful for
identifying place of origin for the inhabitants
of Iceland and Greenland. Although there are
limitations because of geologies of similar antiquity
across parts of the homeland area, there are still
Conclusions and Reflections
T. Douglas Price*
Abstract - This article summarizes what has been learned from the isotopic investigations of the settlement of the North
Atlantic. In addition, I consider what questions remain and where future research may take us. I begin with a brief synthesis
of the interpretation of human mobility in the North Atlantic region with a specific focus on the issue of local vs. non-local
individuals on Iceland and Greenland. The results of the isotopic analyses provide new insight on the settlement of the North
Atlantic. It is also possible to compare the results from Iceland and Greenland to examine similarities and differences in
the process of colonization. The article concludes with a review of the research questions raised in the introduction to this
volume, some of the answers that have been found, and some of the questions that remain.
Viking Settlers of the North Atlantic: An Isotopic Approach
Journal of the North Atlantic
*Laboratory for Archaeological Chemistry, University of Wisconsin-Madison, Madison, WI 53706, USA; tdprice@wisc.edu.
2018 Special Volume 7:186–192
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meaningful differences. Average 87Sr/86Sr values
from the major areas of interest reveal these
differences (Table 1). These averages include a
high proportion of non-local individuals in the case
of Iceland and Greenland. This variation related
to migration is reflected in part in the standard
deviations, which are highest for Iceland and lowest
for Norway, where most of the inhabitants are native
to the region. The mean values for Norway and
Greenland are very similar but for very different
reasons. The Greenland samples consist of a number
of low values for non-local Icelanders and some high
values for local Greenlanders. The Norwegians are
largely local and reflect values from ~0.709 primarily
in coastal areas to higher values largely inland.
While there are a few lower values, these likely
represent migrants to Norway and are not applicable
for determining a local range for Norway.
The range of 87Sr/86Sr values from Norway has
important implications for the identification of the
first settlers of the North Atlantic. 87Sr/86Sr values
for human enamel from Iceland, for example, fall
between 0.7056 and 0.709. Local Icelandic human
values probably do not reach 0.7092, the highest
isotope source available, because it would require
a fully marine diet, which is not observed in the
13C/12C bone collagen data. Thus, strontium isotope
ratios from Iceland and Norway rarely overlap.
Greenland is another story. Because of the
ancient geology of Greenland, strontium isotope
ratios are generally higher. Bioavailable 87Sr/86Sr
values from archaeological fauna from the Eastern
Settlement fall for the most part between 0.711
and 0.716. Human values at the Eastern Settlement
vary considerably due to diet and the presence of
a high proportion of native Icelanders among the
settlers. However, values at the site of Narsarsuaq,
a later settlement with few or no native Icelanders,
fall largely between 0.710 and 0.720, which likely
best reflects the local human 87Sr/86Sr values in the
Eastern Settlement. This variation in values is very
similar to that recorded for Norway.
Most of the fauna measured in the Western
Settlement had extremely high values between 0.750
and 0.760. A few animals had lower values between
0.710 and 0.720, likely due to home ranges near the
coast. The human samples from the Western Settlement
came from a single site, Sandnes. The average
87Sr/86Sr value for the 11 samples was 0.717 ± 0.066,
with a min–max = 0.7101–0.7314. These values
likely vary widely due to the role of marine resources
in the diet. Although there are 3 individuals from
Sandnes with 87Sr/86Sr values greater than 0.720, it
does not appear possible to distinguish samples below
0.720 at the Western Settlement from either the
Eastern Settlement or Norway on the basis of strontium
isotopes alone. Values above 0.720 are rare or
absent in the Eastern Settlement and Norway.
It is also useful to compare oxygen isotope ratios
of the tooth enamel between areas. We have
substantial data from Norway, pagan Iceland, and
Greenland, and these data are plotted against the
corresponding 87Sr/86Sr values in Figure 1, one of the
more important graphics from our study. Although
there is some overlap between the samples from
Greenland, Iceland, and Norway, there is a very
clear segregation of individuals. It is important
to remember that, especially in the case of the
Greenland and Iceland datasets, there are a number
of non-local individuals included in the plot.
The majority of the Iceland samples fall below
0.709 87Sr/86Sr and above -7.0‰ in δ18O. Most
of the Norwegian samples fall above 0.7095 and
above -8.0‰. The Greenland samples are largely
below -6.0‰ with a very wide range of 87Sr/86Sr.
The difference between the Eastern and Western
Settlements in Greenland can be discerned in the
more negative oxygen ratios and higher 87Sr/86Sr
among the Western Settlement samples.
Table 1. Descriptive statistics for 87Sr/86Sr values from
Norway, Iceland, and Greenland.
Country Count Mean s.d. Min Max
Norway 154 0.7124 0.003 0.7075 0.7317
Iceland 127 0.7087 0.030 0.7056 0.7257
Greenland 51 0.7125 0.005 0.7069 0.7314
Figure 1. Scatterplot of δ18O vs. 87Sr/86Sr of tooth
enamel for Norwegian (yellow), Greenland (green), and
pagan Icelandic (blue) skeletons. The darker green dots
represent the Eastern Settlement, the light green indicate
data from the Western Settlement.
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As noted in Price et al. (2015 [this volume]), the
78 δ18OPDB enamel values from Norway have a mean
of -4.9‰ ± -1.3 with a minimum of -7.7‰ and a
maximum of -1.4‰. Converting these values to precipitation
δ18OSMOW results in a mean of -7.7‰ with
a minimum of -12.1‰ and a maximum of -1.8‰.
While the mean value fits well with the region of
central and southern Norway, the value of -12.1‰ is
found only in Greenland, northern Norway, Sweden,
and Finland, and -1.8‰ is out of range for the European
continent (Bowen and Revenaugh 2003).
In addition to the 3 larger groups that can be identified
in the plot in Figure 1, there are several other
observations that can be made. There are a number
of Greenlanders among the Icelanders, suggesting
that these Greenlanders were born on Iceland. The
3 Greenland samples with strontium isotope ratios
between 0.709 and 0.710 and oxygen isotope ratios
more positive than would fit with the Greenland
local range almost certainly represent individuals
from Norway or the northern British Isles. A large
number of the non-local Icelanders have strontium
and oxygen values that fit closely with the Norwegian
samples and likely confirm their place of origin
somewhere in that country. There are other individuals
from Iceland with extreme strontium and oxygen
isotope ratios that do not appear to fall within the
Norwegian baseline.
There are 2 Norwegians with oxygen isotope
ratios close to -8.0‰ that might well represent individuals
born on Greenland who later moved to Norway
where they were buried. There is also a single
Norwegian with a 87Sr/86Sr value below 0.708 who
falls in the middle of the Iceland group and could
very well have been born on Iceland and died in
Norway. It would seem that the Greenland individuals
with δ18O values below -7.0‰ are locally born
because these values are only very rarely observed
in Iceland or Norway (2 examples). On the other
hand, the Greenlanders with oxygen isotope values
between -5.0‰ and -8.0‰ and strontium isotope
ratios above 0.7092 could also be from Norway. It
is impossible to confirm these suggestions at the
present, but ongoing work with lead isotopes may
provide further resolution.
It is also important to consider the northern
British Isles as a potential homeland for the
Norse settlers of Greenland and Iceland. As noted
elsewhere in this volume, Eckhardt et al. (2009) suggested
a range of δ18O in precipitation (δ18Op ) for the
entire UK between -8.7‰ and -4.7‰. Evans et al.
(2012) summarized the oxygen isotope data for Britain
and identified 2 areas—the eastern side of Britain
where values average approximately -7.5‰ ± 1.8 (2
sd) and the western regions where rainfall levels are
higher and δ18Op averages -5.8‰ ±1.8. The distribution
of δ18Op values (Darling 2004, Toolis 2008)
indicates that values between -5.0‰ and -8.0‰
should be expected for the northern portions of
Britain and Ireland. These areas also have generally
high 87Sr/86Sr values and unfortunately cannot be
distinguished from Norwegian sources. Thus strontium
and oxygen isotope ratios cannot resolve these
2 areas. It is our hope that ongoing work with lead
isotopes from these areas will provide new insights.
A plot of δ13C vs. 87Sr/86Sr for the Norwegians,
Greenlanders, and pagan Icelanders (Fig. 2) is
informative with regard to differences in diet. The
3 sets of values tend to cluster separately, but at the
same time there is a significant overlap. In general
terms, there is some negative correlation between
δ13C and 87Sr/86Sr in which more negative carbon
isotope ratios are found with more positive strontium
isotope values. This relationship reflects the
impact of marine foods, sea spray, and rainfall along
the coasts and a higher proportion of terrestrial foods
inland. The pagan Icelanders generally had a more
terrestrial diet than the Norwegians or Greenlanders,
with the majority of δ13C values between -14.0‰
and -17.0‰. The Greenlanders tended to have the
most-marine diets (highest δ13C values).
A number of the Greenland burials have δ13C
and 87Sr/86Sr values that fall among the Icelanders
and Norwegians (or northern Britain and Ireland),
reflecting their place of origin. There is also
overlap among the Norwegians and Icelanders,
reflecting birth origins as well. The Iceland and
Norwegian burials among the Greenlanders reflect
the homelands of the original settlers. In addition,
Figure 2. Scatterplot of δ13C vs. 87Sr/86Sr for Norwegian
(yellow), Greenland (green), and pagan Icelandic (blue)
graves.
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some of the Greenlanders and Icelanders found
among the Norwegians were very likely inhabitants
of those places who traveled to Norway later in life
and were buried there. The present data shows that
mobility in both directions across the North Atlantic
was quite pervasive and not uncommon.
Questions
Migration is a large and complex issue in the
social sciences. There are many factors involved.
Questions arise concerning conditions at home,
motivations, methods, segments of the population
involved, timing and duration, and reception and
return, among others. Within archaeology, these
questions have been limited by a methodology in
which artifacts were used as a proxy for people
when investigating past human movement. The
development of isotopic and molecular methods
offers a means for directly assessing past human
behavior and activity from human skeletal remains
and rigorously assessing more detailed aspects of
ancient mobility such as the identification of new
arrivals, the rate of movement, the timing and
duration of migration, the population segments involved,
and on occasion, the places of origin.
In the Introduction for this volume, a series of
research questions, repeated below, were raised
regarding the colonization of the North Atlantic.
Following the questions, I provide some responses
that have derived from the isotopic investigations.
1. Where did the colonists come from?
2. Did migration to Iceland and Greenland
continue after the initial period of
colonization?
3. Are there gender, age, and/or status
differences among the migrants?
4. What are major questions, concerns, or
problems about the isotopic data? Strontium?
Oxygen? Lead? Carbon? Nitrogen?
5. Where should isotopic and genetic research
focus in the future?
Origins of the colonists
One of the essential facts regarding the isotopic
proveniencing of human remains is that the technique
is very good for distinguishing local and non-local
individuals, but identifying place of origin is much
more difficult. This limitation arises because different
geographic locations can have similar geological formations
or sediments that cannot be distinguished
isotopically. In the case of the settlement of the North
Atlantic, we are unable to distinguish large parts of
Norway and Sweden from the northern British Isles
and the north of Ireland. Both regions, Scandinavia
and northern Britain/Ireland, have almost identical
geologies composed of ancient Archean gneiss
and metamorphic beds interspersed with granite
intrusions created during the Caledonian mountain
building period. 87Sr/86Sr values in these geological
conditions are usually greater than 0.715. Bioavailable
values are normally lower.
Both of these areas are likely homelands for
the settlers of the North Atlantic. Both the genetic
evidence and some historical documents report a
number of individuals, often female, as coming from
northern Britain and Ireland. At the same time, it is
very clear from the 87Sr/86Sr analyses that the early
inhabitants of Greenland and Iceland came from
several different places. Both the diverse 87Sr/86Sr
values and some differences in oxygen isotope ratios
implicate multiple places of origin.
It is also possible to identify the Icelandic
colonists of Greenland among the skeletal remains
in the Eastern and Western Settlements. Early
Christian graveyards in the Eastern Settlement are
often dominated by Iceland-born inhabitants. In
addition, there are some burials whose combined
strontium and oxygen values point to Norway or
the northern British Isles or Ireland as the place of
origin. The isotopes also provide indications that
some of the settlers of the Western Settlement came
from the Eastern Settlement on Greenland. Finally,
isotope ratios permit us to suggest that several of
the individuals analyzed from Norway were in fact
born on Iceland or Greenland, emphasizing the
mobility among the North Atlantic colonies and the
Norwegian homeland.
Duration of migration
It is clear from the comparison of 87Sr/86Sr values
and radiocarbon dates for some 37 individuals from
Iceland that the arrival of new colonists there continued
through the pagan period. At the same time,
it is also evident that the migration was largely over
by the beginning of the early Christian period, as
there are virtually no non-local strontium isotope
ratios among the burials from this period. We do
not have similar data from Greenland because the
colonization took place largely in the Christian
period. We also do not have a large number of 14C
dates to provide a chronology of the colonization.
However, archaeological and historical evidence
suggests that Greenland was almost continuously
settled until the later years of the colony when
environmental conditions had deteriorated (Masson-
Delmotte et al. 2012). The expansion of population
to the Western Settlement documents the continuing
colonization of the island prior to abandonment.
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Gender, age, status
Age differences in migration in Iceland were not
discernible because our sample was largely adult
individuals and the age at arrival on Iceland was
not related to the age at death and burial. Sex differences
were distinctly notable, however, with a
much higher incidence of migration (2X) among the
females. The exact reasons for this difference are
unknown and suggest that there may have been an
imbalance in numbers between the sexes for some
period of time on Greenland.
Status differences are more difficult to infer
on Iceland, given the absence of artifacts in many
of the graves. In addition, there is the very real
possibility of a bias in the pagan graves that have
been excavated over the years and that provided the
samples for our study. Although the initial aim of
the isotope project was to look at the movement of
people into Iceland, the results of the analysis has
proven to be invaluable when studying the pattern
of settlement and burial practices in Iceland. First of
all, rather than the settlement process having been
relatively quick, spanning only the first 60 years
of the settlement, the data suggests that large-scale
movement of people into the country continued
towards the end of the 10th century. Secondly, when
one compares the results of the strontium analysis
with the demography of the pagan burials, they
seem to indicate that these burials are most likely
a high-status subgroup, comprised to a large extent
of males and immigrants. We may be witnessing
different burial traditions in which not all individuals
in society are interred in a way readily visible
to archaeology. Perhaps as Vésteinsson (2016 [this
volume]) argues, the disparity in burial visibility
marks a distinction between the late-9th-century
founding population and an upper class with foreign
roots and a Norse identity.
Religious status, as distinct from social status,
certainly revealed a major difference in migration on
Iceland. Following the arrival of Christianity ca. AD
1000, migration ceases almost completely, and there
is only 1 likely migrant identifiable from the 44 individuals
in 2 Christian cemeteries that were analyzed.
It is, of course, unlikely that the arrival of Christianity
played a role in the cessation of migration.
Little information on status is available from
the graves on Greenland because of the Christian
tradition of simple burial. Differences between
males and females in isotopic values is clear, with
females having both higher average and greater
variance for 87Sr/86Sr values. These differences suggest
that females may have originally arrived in
smaller numbers than males on Greenland and from
more varied places of origin. Some males and fewer
females came to Greenland from Iceland.
Questions about isotopes
In general terms, isotopic methods for human proveniencing
and determination of paleodiet are well
established, reliable, and useful. There are numerous
examples of the application of these methods in
various parts of the world (e.g., Ambrose et al. 2003;
Copeland et al. 2011; Harrison and Katzenberg 2003;
Montgomery et al. 2000; Price et al. 1994, 2010;
Slovak and Paytan 2011; Tykot 2004). At the same
time, the development of these methods is ongoing,
and new information on sources of variation and
analytical procedures continues to appear. Strontium
isotopes are generally well understood using a deep
background in the geological literatures. Problems
remain because of the widespread occurrence of
87Sr/86Sr values between 0.709 and 0.710 that appear
with many types of marine, fluvial, and glacial
sedimentary deposits. Such widespread similar
values often make the identification of place of
origin a difficult undertaking. In this context, the
use of other isotopic systems is essential in order to
bypass this ambiguity.
Oxygen isotopes remain rather contentious.
There is a significant variation at the individual
and regional level for oxygen isotopes that reduces
the accurate characterization of locally born individuals.
There is also significant variation in δ18O
on a seasonal, annual, and long-term basis. Because
oxygen isotope ratios ultimately reflect atmospheric
temperatures, past climate changes impact these
values and our understanding of changes in these
ratios over time for specific areas is not good. At the
same time, similar oxygen isotope ratios are found
over a large part of the modern temperate regions
of the world. δ18OSMOw values for mean annual
precipitation between -6‰ and -10‰ are common
from North America to West Africa to Europe
(IAEA/WMO 2006). Such homogeneity is not conducive
to distinguishing places of origin.
Lead isotopes offer another avenue for
investigating questions of human provenience.
Limitations are due largely to a lack of information
on variation in lead isotopes and insufficient
understanding of the variation in values found in
humans (Albarède et al. 2012). These isotopes
originate in limited geological sources for lead that
have been isotopically characterized for a number of
places across northern Europe and the North Atlantic.
However, there is currently relatively little information
available on the variation in lead isotopes in
tooth enamel. There are 4 principle isotopes of lead,
which can be used to calculate at least six different
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old geological terrains such as Norway, northern
Britain, and Ireland.
3. The colonization of Iceland continued throughout
the pagan period.
4. Women in the sample from Iceland were twice as
likely to be migrants as men.
5. There was little or no migration to Iceland during
the early Christian period, after AD 1000.
6. Human diet on Iceland varied from largely
terrestrial to largely marine.
7. Human diet on Iceland was determined, at least
in part, by the location of settlement, i.e., coastal
marine vs. inland terrestrial.
8. A number of the settlers of Greenland came from
Iceland, and at least some brought their cows with
them.
9. The Eastern and Western Settlements on
Greenland can be isotopically distinguished
with a combination of strontium and oxygen
isotopes.
10. Diets on Greenland are more marine than
on Iceland and more marine at the Western
Settlement than the Eastern one. Inuit diets are
heavily marine in composition.
11. Some of the first locally born children on Greenland
can be identified at Innoqquasaq (E64).
12. Several of the individuals buried in the Western
Settlement probably came from the Eastern
Settlement.
13. One or 2 individuals from the Western Settlement
were buried in the Eastern Settlement.
14. Migration is a two-way street. Several
Greenlanders were buried on Iceland.
15. In addition, a few Greenlanders and Icelanders
were buried in Norway.
16. Mobility appears to have been commonplace in
the Viking period.
17. Strontium isotope ratios in tooth enamel,
sometimes in combination with oxygen isotopes,
provide a powerful tool for identifying non-local
individuals among human burials.
18. The comparison of collagen and apatite carbon
isotope ratios offers additional insights into past
human diet.
19. Lead isotopes have significant potential for human
proveniencing in the North Atlantic region.
20. Isotopic proveniencing has provided exceptional
new information regarding the peopling of the
North Atlantic.
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