New marine ΔR values for Arctic Canada

Abstract

For more than four decades, the reporting of 14C dates on marine molluscs from Arctic Canada has been notable for the lack of consistently applied marine reservoir corrections. We propose that the common approach of reporting Canadian Arctic marine 14C dates using presumed time-invariant reservoir corrections be abandoned in favour of calibration of 14C dates, using the current standard protocol. This approach best facilitates inter- and intra-regional correlation, and correlation with other geochronometers. In order to enable the consistent calibration of marine 14C dates from Arctic Canada, we analysed a 14C database of 108 marine mollusc samples collected live between 1894 and 1956, and determined regional reservoir offset values (ΔR) for eight oceanographically distinct regions. The following new ΔR values should be used for 14C calibration: NW Canadian Arctic Archipelago, 335 ± 85 yrs; Foxe Basin, 310 ± 90 yrs; NE Baffin Island, 220 ± 20 yrs; SE Baffin Island, 150 ± 60 yrs; Hudson Strait, 65 ± 60 yrs; Ungava Bay, 145 ± 95 yrs; Hudson Bay, 110 ± 65 yrs; and James Bay, 365 ± 115 yrs.

Full text

Research Paper
New marine
D
R values for Arctic Canada
q
Roy D. Coulthard
a
,
*
,
1
, Mark F.A. Furze
b
,
1
, Anna J. Pie
nkowski
a
,
1
, F. Chantel Nixon
a
, John H. England
a
a
Department of Earth & Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada
b
Earth & Planetary Sciences, Department of Physical Science, Grant MacEwan University, P.O. Box 1796, Edmonton, Alberta T5J 2P2, Canada
article info
Article history:
Received 19 August 2009
Received in revised form
2 February 2010
Accepted 10 March 2010
Available online 17 March 2010
Keywords:
Radiocarbon
Reservoir correction
Calibration
Arctic
D
R
Molluscs
abstract
For more than four decades, the reporting of
14
C dates on marine molluscs from Arctic Canada has been
notable for the lack of consistently applied marine reservoir corrections. We propose that the common
approach of reporting Canadian Arctic marine
14
C dates using presumed time-invariant reservoir
corrections be abandoned in favour of calibration of
14
C dates, using the current standard protocol. This
approach best facilitates inter- and intra-regional correlation, and correlation with other geo-
chronometers. In order to enable the consistent calibration of marine
14
C dates from Arctic Canada, we
analysed a
14
C database of 108 marine mollusc samples collected live between 1894 and 1956, and
determined regional reservoir offset values (
D
R) for eight oceanographically distinct regions. The
following new
D
R values should be used for
14
C calibration: NW Canadian Arctic Archipelago,
335 85 yrs; Foxe Basin, 310 90 yrs; NE Baffin Island, 220 20 yrs; SE Baffin Island, 150 60 yrs;
Hudson Strait, 65 60 yrs; Ungava Bay, 145 95 yrs; Hudson Bay, 110 65 yrs; and James Bay,
365 115 yrs.
Ó2010 Elsevier B.V. All rights reserved.
1. Introduction
Thousands of
14
C dates on molluscs collected from raised
marine deposits provide the overwhelming foundation for past ice
sheet reconstructions and relative sea level changes throughout
Arctic Canada. Despite the pervasive use of these dates, marine-
based Quaternary
14
C chronologies are still hampered by the
poorly constrained application of marine reservoir corrections.
This becomes especially problematic when comparing and corre-
lating marine
14
C dates between regions and with differently
derived chronologies (e.g. terrestrial
14
C dates, terrestrial cosmo-
genic nuclide dates, ice core chronologies, tephrachronology,
lichenometry). Although
14
C calibration curves and computer
programs have been widely available for several decades (Stuiver
et al., 1986, 1998a,b; Stuiver and Braziunas, 1993; Stuiver and
Reimer, 1993; Reimer et al., 2004a, 2009; Hughen et al., 2004),
the Quaternary community has been slow to adopt calibration for
Canadian Arctic chronologies. Instead, marine dates are still
routinely reported in “corrected”
14
C years by subtracting an
assumed time-invariant marine reservoir correction, or its equiv-
alent, as was common in the 1970s (e.g. Dyke and Prest, 1987;
Lemmen, 1989; England, 1990, 1996, 1999; Evans, 1990; Stravers
and Syvitski, 1991; Stravers et al., 1992; Hodgson et al., 1994;
Bell, 1996; Dyke et al., 1996a,b, 2002, 2005; Dyke, 1998, 1999,
2004; Ó Cofaigh, 1999; Ó Cofaigh et al., 2000; Atkinson, 2003;
England et al., 2004, 2006, 2009; England and Furze, 2008). Here
we review the inherent problems with this previous approach, and
recommend the adoption of the standard protocol (e.g. Stuiver and
Polach, 1977; Stuiver et al., 1986; van der Plicht and Hogg, 2006;
Stuiver et al., 2010) in the reporting and calibrating of Canadian
Arctic
14
C chronologies, using the new
D
R values presented. This
will enable meaningful correlations between alternatively derived
chronologies within the constituent regions of northern Canada,
and will further allow for correlations to regions elsewhere. Our
objective is to provide clear, statistically sound justification for the
derivation and adoption of reservoir corrections and a robust basis
for marine
14
C calibration for Arctic Canada.
1.1. Previous reporting of marine radiocarbon dates from
Arctic Canada
Modern, standardized protocols for reporting marine
14
C dates
have been used for several decades and are widely accepted by the
Quaternary community (e.g. Stuiver and Polach, 1977; Stuiver et al.,
1986). However, the failure to fully adopt the standard protocols in
the Canadian Arctic necessitates a review of previous approaches
used in the region. It was known prior to the early 1970s that
q
Polar Continental Shelf Project (PCSP) Contribution 02609.
*Corresponding author. Tel.: þ1 780 937 8540; fax: þ1 780 492 2030.
E-mail address: roy.coulthard@ualberta.ca (R.D. Coulthard).
1
These authors have contributed equally to this publication.
Contents lists available at ScienceDirect
Quaternary Geochronology
journal homepage: www.elsevier.com/locate/quageo
1871-1014/$ esee front matter Ó2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.quageo.2010.03.002
Quaternary Geochronology 5 (2010) 419e434

carbon isotope fractionation affected
14
C dating results, but marine
carbonate dates were not routinelycorrected for
d
13
C fractionation.
This results in many marine carbonate samples appearing to be
older than contemporaneous terrestrial samples. Although Stuiver
and Polach (1977) argued for the standardization of all
14
C dates
to the terrestrial standard of
d
13
C¼25&,defining a “conventional
radiocarbon age”, the Geological Survey of Canada (GSC) Radio-
carbon Laboratory, which dated many Canadian Arctic samples, did
not adopt the Stuiver and Polach (1977) standard until 1992. Prior
to that, the GSC normalized all marine dates to
d
13
C¼0&, reducing
raw marine
14
C dates by 406.76 yrs (often cited as 400 or
410 yrs) relative to conventional
14
C dates of the same absolute
age. This was done in order to maintain approximate consistency
with their earlier non-normalized (
d
13
Cw0&) dates (Lowdon and
Blake, 1970; McNeely and Brennan, 2005).
Complicating the issue of fractionation, the apparent offset
between terrestrial and marine
14
C dates in the North Atlantic
Ocean (marine reservoir age, R) caused by differential uptake of
14
C
in these reservoirs, was calculated to be approximately 400 yrs,
thus broadly equivalent to non-normalized marine
14
C dates, or
those normalized to
d
13
C¼0&(e.g. Mangerud, 1972). Conse-
quently, many marine
14
C dates continued to be reported in this
manner. Although higher Rvalues were subsequently determined
for the Canadian Arctic Archipelago (CAA; Fig. 1) where an average
Rof 750 50 yrs was calculated (Mangerud and Gulliksen, 1975),
most researchers continued to use the older convention instead (e.
g. Blake, 1975). As
14
C dates on marine shells began to be more
frequently reported as conventional
14
C ages, these were often
corrected by subtracting 410 yrs to account for North Atlantic R, and
for consistency with older GSC dates (e.g. England, 1990). As late as
Fig. 1. Map of study area, showing sample locations and places mentioned in the text. Sample numbers correspond to sites in Table 1. Abbreviations: BI, Bylot Island; BS, Barrow
Strait;FC, Foxe Channel;FHS, Fury and Hecla Strait;FS, Frozen Strait;JS, Jones Sound;LS, Lancaster Sound; MP, Melville Peninsula; NS, Nares Strait;RWS, Roes Welcome Sound; SI,
Southampton Island; UP, Ungava Peninsula; VMS, Viscount Melville Sound.
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434420

the early 2000s, a presumed time-invariant Rof 400 or 410 yrs
continued to be the de facto standard for Arctic Canada (e.g. Dyke,
2004; Dyke et al., 2002, 2005; Ó Cofaigh et al., 2000; Atkinson,
2003; England et al., 2004, 2006). Troublingly, little consistency is
evident in the corrections applied to marine
14
C dates from the CAA
between individual papers (e.g. R¼410 yrs: Lemmen, 1989;
England, 1990, 1996, 1999; Evans, 1990; Hodgson et al., 1994; Bell,
1996; Dyke, 1999; Atkinson, 2003; England et al., 2004, 2006;
R¼400 yrs: Dyke, 1998, 1999; Dyke and Savelle, 2000;
R¼450 yrs: Stravers and Syvitski, 1991; Stravers et al., 1992;
Kaufman et al., 1993). In fact, multiple corrections have been used
in the same study without explanation (e.g. 400 and 410 yrs:
Dyke, 1999;450 and 550 yrs: Briner et al., 2009).
In an effort to refine the retreat chronology of the Laurentide Ice
Sheet, Dyke et al. (2003, conference abstract) proposed six regional
reservoir corrections (here termed R
R
) for Canadian waters based
on
14
C dates on molluscs collected live between 1884 and 1959.
These R
R
values range from 450 to 800 yrs, with a value of
740 yrs applied to the northwestern CAA. This R
R
of 740 yrs has
been adopted by some researchers (England and Furze, 2008;
England et al., 2009), but without clear documentation of its deri-
vation. Indeed, although 740 yrs was initially recommended as
the appropriate R
R
for the northwestern CAA (Dyke et al., 2003),
Dyke (2004) used a correction of 760 yrs for sites in the same
region. McNeely and Brennan (2005) subsequently made available
a revised database of all GSC marine
14
C dates and included the
original Dyke et al. (2003) abstract as their recommendation for R
R
values (including the 740 yr correction for the northwestern CAA).
Unlike Mangerud and Gulliksen (1975), Dyke et al. (2003), Dyke
(2004) and McNeely and Brennan (2005) provided no standard
deviations for their proposed R
R
values. Following the McNeely and
Brennan (2005) compilation, the database of
14
C dates on pre-bomb
live-collected molluscs used by Dyke et al. (2003), was made
available on-line (McNeely et al., 2006). This new compilation
included 127 dates from Arctic Canada, and tabulated the labora-
tory reported age, species, feeding mode, and calculations of
site-specific reservoir age (here termed R
L
) for each sample.
However, no guidingdocumentation or recommendation for use of
this database was provided, and although samples were ascribed to
several proposed oceanographic regions, no R
R
values were
presented. It is apparent that reservoir corrections need to be
addressed in a consistent and systematic fashion by researchers
working in Arctic Canada.
1.2. The history of marine reservoir correction
Given the inconsistent application of marine reservoir correc-
tions outlined above, we review the methodological and statistical
foundations of marine reservoir corrections focusing on Arctic
Canada. We emphasize that regionally applicable reservoir
corrections that are properly documented and consistentlyapplied
are overdue. The absence of such corrections obfuscates rigorously
based chronologies of late Quaternary environmental change.
To clarify the concept of “reservoir correction”,Stuiver et al.
(1986) defined it as “the difference between conventional
14
C
ages of samples grown contemporaneously in the atmosphere and
the other carbon reservoir”(p. 980). Thus with marine samples, the
age of the “other reservoir”is the apparent
14
C age of carbon in the
ocean itself. Although often considered to be constant (see Section
1.1), it is intuitively apparent that the age of the ocean reservoir is
highly variable in both time and space due to variations in
14
C
production in the atmosphere (Stuiver et al., 1986) as well as ocean
circulation, upwelling and ventilation (e.g. Stuiver and Braziunas,
1985). Within oceanographically distinct regions, however, the
spatial variability of regional reservoir age (R
R
) at a specific time can
be described statistically, and several regional studies of reservoir
corrections have used this approach (e.g. Reimer et al., 2002;
Reimer and McCormac, 2002; Southon et al., 2002; Ascough
et al., 2005; Culleton et al., 2006; Taylor et al., 2007; Petchey
et al., 2008; Olsen et al., 2009).
Despite the apparent usefulness of regional marine reservoir
corrections, it has long been recognized that the assumption of
time-invariance of any proposed marine reservoircorrection (R
R
)is
simplistic, and limits the usefulness of time-specificR
R
values
(Stuiver et al., 1986; Stuiver and Braziunas, 1993; Hughen et al.,
2004; Mangerud et al., 2006). Variability of the apparent age of
the marine reservoir is ultimately a function of the variability of
14
C
production in the atmosphere, modulated substantially by fluctu-
ations in ocean circulation and ventilation (Stuiver and Braziunas,
1993). Due to the large volume of the global ocean, and its
relatively slow circulation and ventilation processes, temporal
variations in atmospheric
14
C production are markedly attenuated
within the ocean reservoir. Consequently, although a regional
reservoir correction may be established for a specific location and
time, the application of such a correction to samples of greatly
differing actual age introduces an unquantified, potentially signif-
icant additional error to dates and chronologies.
1.3. Radiocarbon calibration
While long-term global tree ring chronologies spanning the
entire Holocene record past
14
C variability in the atmosphere (e.g.
Reimer et al., 2009), no equivalent marine record of annual
14
C
variability exists. Instead, Holocene
14
C variability within the global
ocean is usually described with an ocean model that can be used for
14
C calibration purposes (e.g. Stuiver et al., 1986, 1998b; Stuiver and
Braziunas, 1993; Marine09, Reimer et al., 2009). Compared to
long-term annual records of atmospheric
14
C variations (e.g.
IntCal09, Reimer et al., 2009), the modelled variations in the marine
record are smoothed and attenuated (Reimer and Reimer, 2001;
Hughen et al., 2004; Reimer et al., 2009). The difference between
these parameters defines the variable global mean ocean reservoir
correction applicable at any time, R(t).
Unlike terrestrial samples, which can be calibrated directly to
the IntCal09 curve, the calibration of marine
14
C dates requires an
additional correction, termed
D
R, which is the difference between
R
R
and R(t) (Stuiver et al., 1986). By using an appropriate regional
D
R (here termed
D
R
R
), marine
14
C dates can be easily calibrated
using the Marine09 calibration curve (Reimer et al., 2009) and
a calibration programme such as CALIB 6.0 (Stuiver et al., 2010). To
afirst approximation, R
R
will parallel R(t) in a time-invariant
fashion because both reservoirs respond proportionally to atmo-
spheric forcing. Therefore,
D
R
R
will remain approximately constant,
assuming that the regional oceanographic characteristics remain
similar through time (Stuiver et al., 1986; Mangerud et al., 2006).
In addition to the problems with time variance of R
R
, if marine
14
C
dates are calibrated using an R
R
value and the IntCal09 atmospheric
curve, a large number of intercepts often result, which provide
a false sense of precision to calibrated dates. Consequently,
calibration of marine
14
C dates using an appropriate
D
R
R
value and
the Marine09 dataset best accounts for the variability of the ocean
reservoir through time, avoids the pitfalls of using assumed
time-invariant R
R
values, and ensures greater accuracy of calibrated
marine
14
C dates.
1.4. Reporting of
14
C dates
As described above, consistency in the reporting of
14
C dates
from Arctic Canada has until now been lacking. In order to redress
this issue, we reiterate that all dates should be reported following
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434 421

the conventions outlined by Stuiver and Polach (1977), and elabo-
rated on by Stuiver (1980, 1983), Mook (1986), Long (1995) and
van der Plicht and Hogg (2006). The following information should
be included when reporting
14
C dates: the laboratory number; the
laboratory reported date and standard deviation; the sample
isotopic fractionation (
d
13
C, assumed or measured); the conven-
tional
14
C date (1
s
); and the original citation if previously pub-
lished. Calibrated dates should be reported following the protocol
outlined in the Radiocarbon instructions for authors (http://www.
radiocarbon.org/Authors/author-info.pdf). It is important to report
the utilized calibration dataset; the utilized
D
R
R
value with stan-
dard deviation; the reported confidence interval for the calibrated
date (1 or 2
s
; 68.2% or 95.4%); and the calibration program, all with
appropriate citations.
1.5. Calculating
D
R for Arctic Canada
In this paper we present new regionally applicable marine
reservoir offset (
D
R) values for the Canadian Arctic (Fig. 1), derived
from the data tabulated by McNeely et al. (2006). On the basis of
oceanographic criteria, we define eight regions across the CAA
(Fig. 2). For each region, we present new values of
D
Rand provide
recommendations for their use in
14
C calibration. Elsewhere in
Canada fossil sites containing contemporaneous marine and
terrestrial materials have permitted similar determinations of
marine reservoir corrections (e.g. Hutchinson et al., 2004; Richard
and Occhietti, 2005; Rayburn et al., 2006). However, in much of
Arctic Canada, the rarity of terrestrial organic material accompa-
nying marine shells at the same site all but precludes this approach.
WGC
0 500 1000 km
BC
1
2
3
4
5
6
7
8
Fig. 2. Regional subdivisions and generalized oceanography of Arctic Canada used in the text. Abbreviations: WGC, West Greenland Current;BC, Baffin Current.
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434422

2. Regional setting
In general, the waters of the CAA consist of varying quantities of
Arctic Ocean surface waters and northwest Atlantic Ocean surface
waters, modified by local- and regional-scale mixing processes, sea
ice and fluvial input. Arctic Ocean surface waters experience little
ventilation compared to more temperate oceans due to the
perennial sea ice cover of the Arctic Ocean basin (Bradley and
England, 2008). By comparison, North Atlantic surface waters are
relatively well mixed and exchange carbon with the atmosphere
throughout the year (England, M.H., 1995). As a result, Arctic Ocean
waters have a greater apparent
14
C age than North Atlantic waters
(Bradley and England, 2008). As differences in regional carbon
reservoirs are primarily determined by oceanographic processes,
we have divided Arctic Canada into eight regions based on their
distinctive oceanographies, outlined below (Fig. 2).
Region 1, the NW CAA, consists of the islands between the
Arctic Ocean, the North American mainland, Greenland and Baffin
Bay, but excluding the islands of Hudson Bay, Baffin Island, and the
Baffin Bay coast of southeast Ellesmere and Devon islands (Figs. 1
and 2). The islands of the NW CAA are separated by relatively
narrow and shallow channels (predominantly <300 m deep)
through which Arctic Ocean water flows southeastward. The
magnitude of water transport through the CAA from the Arctic
Ocean to the Labrador Sea is considerable, similar to the flux
passing through Fram Strait (between Greenland and Europe;
Fig. 1;Aagaard and Carmack, 1989; Kliem and Greenberg, 2003).
Unlike Fram Strait, however, only Arctic Ocean surface water
transits the archipelago today en route to Baffin Bay due to the
many shallow sills (85e140 m depth) in th e NW CAA (Barry, 1993;
Prinsenberg and Hamilton, 2005). Substantial local and seasonal
variability exists within the generalized southeastward flow
through the archipelago. Throughout much of the year, Region 1 is
covered by sea ice, although seasonal variations in ice duration
and thickness occur (Barry, 1993). The eastern and southern
channels (e.g. Lancaster Sound, Amundsen Gulf; Fig. 1)usually
open during summer and freeze again in autumn, and are domi-
nated by first-year, landfast sea ice. In contrast, the western and
northern channels of the CAA (e.g. Viscount Melville Sound;
M’Clure Strait; Fig. 1) are characterized by multi-year landfast ice,
and hence are rarely ice-free during summer. The overwhelming
dominance of Arctic Ocean surface water in the NW CAA, modified
by variable local sea ice conditions supports the unity of Region 1.
Foxe Basin (Region 2; Figs. 1 and 2), is a shallow (<100 m water
depth) inland sea that deepens towards the south (<400 m depth)
and is connected to Region 1 (NW CAA) only via the narrow and
shallow Fury and Hecla Strait. Foxe Basin is connected to Hudson
Strait (Region 5) by Foxe Channel (Fig. 1) and to Hudson Bay
(Region 7) in the southwest through the narrow Frozen Strait/Roes
Welcome Sound passage (Fig. 1). Dense, cold waters are produced
in the northern part of Foxe Basin through sea ice formation and
consequent brine rejection during winter. These waters sink and
flow southward to deeper parts of the basin, but are forced into
a geostrophic balance, resulting in a cyclonic circulation of bottom
waters (Prinsenberg, 1986a; Ingram and Prinsenberg,1998). These
dense, saline waters are replaced by lighter, fresher surface waters
originating from Region 1 via Fury and Hecla Strait, whereas
outflow from Foxe Basin is mainly into western Hudson Strait
(Region 5; Figs. 1 and 2;Prinsenberg, 1986a; Jones and Anderson,
1994; Ingram and Prinsenberg, 1998). Region 2 is perennially
ice-covered with landfast sea ice in the north and pack ice in the
south, but is often ice-free during September. Autumn storms and
strong tides in the shallow basin lead to water column mixing on
an annual basis (Prinsenberg, 1986a; Ingram and Prinsenberg,
1998).
NE Baffin Island (Region 3) comprises the east coast of Baffin and
Bylot islands between the eastern terminus of Lancaster Sound and
the relatively shallow sill (670 m depth) in Davis Strait east of Baffin
Island (Figs. 1 and 2). Region 3 is dominated by waters exiting
Region 1 through Lancaster, Jones and Smith sounds and Nares
Strait (Figs. 1 and 2). These low-salinity waters flow southward
along the northeast shore of Baffin Island as a surface layer (the
Baffin Current) up to 500 m deep (Fig. 2;Ingram and Prinsenberg,
1998). A lesser component of the Baffin Current is derived from
the weak, southward return flow of the warm West Greenland
Current that recurves across Smith Sound between Ellesmere
Island and NW Greenland (Figs. 1 and 2). An extensive, biologically
important polynya with large seasonal variability, the North Water,
develops in Smith Sound during the ice season due to ice diver-
gence, warm-water upwelling, and density driven overturning
(Ingram and Prinsenberg, 1998). As a result of the variability of
water masses in the area, we exclude samples from Smith Sound
from both regions 1 and 3 (Fig. 2). First-year pack ice is found
throughout the northern part of Baffin Bay from fall to spring. The
Baffin Current transports much of this ice southward, as well as
icebergs derived from numerous calving centres along the west
coast of Greenland (Fig. 2;Barry, 1993).
In the northern Labrador Sea, the Baffin Current is joined by the
warmer return-flow waters of the West Greenland Current
(southern branch; Figs. 1 and 2). Together, these waters flow
southward along southeast Baffin Island, which constitutes Region
4 on the basis of this water mixing (Fig. 2;Barry, 1993). A portion of
the southern Baffin Current flows westward into Hudson Strait
(Region 5; Figs. 1 and 2), the deep channel connecting Hudson Bay
to the Labrador Sea. Baffin Current waters in Hudson Strait flow at
the surface along the north side, while fresher water originating in
Hudson Bay and Foxe Basin flows along the south side of Hudson
Strait back to the Labrador Sea (Figs. 1 and 2;Cherniawsky and
LeBlond, 1987; Straneo and Saucier, 2008). Strong tidal currents
cause a high tidal range in Hudson Strait, generating extensive
vertical mixing that produces a relatively uniform water mass in
Region 5 (Fig. 2).
Ungava Bay (Region 6; Fig. 2) is a relatively shallow embayment
(generally <150 m) along southeastern Hudson Strait (Fig. 1).
A portion of the low-salinity waters flowing eastward along
southern Hudson Strait enter Ungava Bay en route to the Labrador
Sea (Figs. 1 and 2). This current flows cyclonically around the bay
and then exits to the northeast. The waters of Ungava Bay are
similar to those of southern Hudson Strait, but are fresher due to
a substantial fluvial input entering the bay (Drinkwater,1986). Only
the northeastern part of Ungava Bay has warmer, saltier waters due
to the influence of the Labrador Sea. As a result of the shallower
bathymetry and substantial fluvial input, Ungava Bay water (Region
6) is less well mixed than Hudson Strait water (Region 5; Fig. 2).
Hudson Bay (Region 7) is a large (>10
6
km
2
), relatively shallow
(<235 m deep) inland sea characterised by 8e9 months of first-
year sea ice cover (Figs. 1 and 2;Barry, 1993). To the northeast,
Hudson Bay is connected to the Labrador Sea via Hudson Strait
(Region 5), although exchange and renewal of deepwater is limited
by the relatively shallow connection between Hudson Bay and
Hudson Strait (Fig. 1;Prinsenberg, 1986b,c; Ingram and
Prinsenberg, 1998). To the northwest, Hudson Bay is linked to
Foxe Basin (Region 2) through Frozen Strait/Roes Welcome Sound
(Figs. 1 and 2). Colder, relatively dense, saline waters enter Hudson
Bay from these two regions, sinking below the surface layer due to
their higher density. Conversely, Hudson Bay surface water is
relatively fresh due to widespread fluvial input and in situ sea ice
melting, and flows cyclonically back to Hudson Strait with limited
vertical mixing due to density stratification (Prinsenberg, 1986b,c
Ingram and Prinsenberg, 1998; Wang et al., 1994). We consider
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434 423

Hudson Bay, excluding James Bay, to constitute a single region for
this study.
James Bay (Region 8; Fig. 2) is a small, shallow (<28 m)
embayment at the base of Hudson Bay (Fig. 1). James Bay water can
be distinguished from that of Hudson Bay due to its low salinity, the
result of abundant fluvial input and seasonal sea ice melt. Water of
higher salinity derived from Hudson Bay enters from the northwest
and is diluted and heated as it flows cyclonically around James Bay,
exiting to the northeast (Fig. 2). Although Region 8 is also
ice-covered for most of the year, ice break-up is earlier than in
Hudson Bay (Prinsenberg, 1986c). A brackish water layer (w1e2m
thick) caps James Bay in late spring, limiting vertical mixing
(Prinsenberg, 1986b; Ingram and Prinsenberg, 1998).
3. Samples and calculation methods
3.1. Samples
All of the
14
C dated marine organisms used in this study were
previously reported by McNeely et al. (2006), and come from the
pre-bomb mollusc collections of the Canadian Museum of Nature;
the Museum of Comparative Zoology, Harvard University; and the
Geological Survey of Canada. Previously, only a small number of
these samples from the CAA and North Atlantic Ocean were
reported in the literature (Mangerud and Gulliksen, 1975).
Our study only uses the 127 Canadian Arctic dates from the
McNeely et al. (2006) database of 315
14
C dates on live-collected
marine organisms. Specifically, we excluded all samples from
outside the CAA, as well as collections made after 1956 due to the
potential influence of bomb
14
C, which began to significantly affect
the ocean reservoir after this time (e.g. Druffel, 1997; Hua et al.,
2005). Additionally, the majority of
14
C dates for deposit feeders
such as the protobranch bivalve Portlandia arctica were omitted due
to the spuriously old apparent ages obtained on these samples in
many parts of Arctic Canada underlain or influenced by carbonate
bedrock (Dyke et al., 2002; England et al., 2003, 2004). Deposit-
feeding genera such as Nucula,Nuculana,Leda,Yoldia,Yoldiella,
Portlandia, and Macoma (Ockelmann, 1958; Lubinski, 1980) are all
potentially subject to this so-called “Portlandia Effect”(Forman and
Polyak, 1997; Dyke et al., 2002; England et al., 2003, 2004). The
degree of offset between detrital and filter feeders can be highly
variable (<500e2200
14
C yrs) and the site-specific or regional
variations in this effect remain poorly understood (England et al.,
2003). Only one sample of P. arctica was retained in our database
where it was one of only two samples for Region 3 (NE Baffin Is.,
Site 16, Table 1,Figs. 1 and 2). This sample was collected from
a region of crystalline rock substrate, and P. arctica has been shown
to return reliable results in such geological settings where old,
14
C
depleted carbon-rich substrates are absent (e.g. England et al.,
2003, 2004). None of the species included in the present study
are known to have specific estuarine or brackish environmental
affinities. Nonetheless, all appear to tolerate the wide range of
salinities that characterize Arctic and glaciomarine environments,
with considerable salinity gradients within and between fjords and
open shelf environments (Table 2). In brackish and estuarine
environments uptake of terrestrially sourced dissolved inorganic
carbon by filter-feeders, as well as hard water effects, can result in
marked offsets between apparent and actual ages (Keith et al.,
1964; Petchey et al., 2008). However, all of the samples used in
the present study (Table 1) exhibit
d
13
C ratios within the range
typical for marine carbonate (1e2&; extended range 4e4&),
and show no influence of either soil (52&) or freshwater
(92&) carbonate (Stuiver and Polach, 1977).
Where replicate analyses of the same sample were reported by
McNeely et al. (2006), we determined an error-weighted pooled
mean value for that sample using the methods of Ward and Wilson
(1978; Case I). Lastly, two samples from Smith Sound, SE Ellesmere
Island, were excluded as they were collected from a site of known
water mass mixing in northernmost Baffin Bay and probably do not
represent NW CAA waters (Figs. 1 and 2;Barry, 1993; Ingram and
Prinsenberg, 1998). Dates on non-molluscan marine carbonate
(from the cirripeds Balanus balanoides and Balanus crenatus)were
retained from the McNeely et al. (2006) database. We consider
these sessile filter-feeding barnacles to secrete calcium carbonate
in a similar fashion to the Mollusca and with the same degree of
d
13
C fractionation (e.g. Chappell and Polach, 1972). Collectively,
after removing samples, the Arctic dates from the McNeely et al.
(2006) database were reduced from 127 to 108 samples (Table 1).
Taxonomic, ecological, and life-habit information for each of the 24
taxa used in our study is presented in Table 2.
Following Mangerud et al. (2006), we assume that molluscan
shell carbon was fixed, on average, five years before the specimens
were collected. For example, we assume that a mollusc collected in
1920 fixed its carbon(on average) in 1915. This assumption is based
upon the known lifespans of many of the dated molluscs (Table 2),
which commonly do not exceed 10e20 years, but fix carbon
throughout their lifetime (Shumway and Parsons, 2006). In
exceptional circumstances, however, molluscan lifespans can be
considerably longer (e.g. Sejr et al., 2002). Although the actual
median life-age of an individual mollusc at the time of collection
can be established by annual growthband counting (e.g. Culleton
et al., 2006; Scourse et al., 2006), no such analyses were made
prior to
14
C dating reported for our samples (Table 1). Thus we
consider our universal five-year median mollusc life-age to be
a conservative correction, accounting for the average time of
carbon-fixing for each dated mollusc, where the entire sample
(as opposed to an individual growthband or 5-year growthband
interval) was dated.
3.2. Corrections applied to the data
One previous obstacle to calibration of
14
C dates from the Cana-
dian Arctic was how to treat
14
C measurements that were uncor-
rected for
d
13
C fractionation. For uncorrected marine
14
C dates with
known
d
13
C values, this correction can be easily calculated (see
Stuiver and Polach,1977; Donahue et al., 1990; Reimer et al., 2004b).
However, for non-normalized marine samples (e.g. GSC-474, Site 4,
Fig.1,Table 1), it is necessary touse a statistical approach. Using 1550
d
13
C measurements made on
14
C dated marine shells (McNeely and
Brennan, 2005), we computed a pooled average
d
13
C value of
1.02 1.32&for molluscs. This is approximately equivalent to
a correction of 423 21 yrs. Non-normalized dates can be recalcu-
lated using this
d
13
C value according tothe methods of Donahue et al.
(1990) and Reimer et al. (2004b). A spreadsheet for this purpose is
also available at http://intcal.qub.ac.uk/calib/fractionation.html
(Stuiver et al., 2010). Dates normalized using either approach can
subsequently be calibrated like other conventional
14
C dates. An
additional modification to the original McNeely et al. (2006) dataset
in our study was the reduction of the standard deviation of all GSC
dates by half in order to facilitate comparison with conventional
14
C
dates. GSC dates were always reported with 2
s
error terms (Lowdon
and Blake, 1970) rather than 1
s
, as per conventional
14
C dates
(Stuiver and Polach, 1977).
3.3. Calculating site-specific
D
R(
D
R
L
)
To differentiate between individual, site-specific values and
regionally applicable average values of
D
R, we introduce the terms
D
R
L
to describe sample-specific
D
R, and
D
R
R
to describe regional
average
D
R.
D
R
L
was determined using Equation (1) and the
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434424

Table. 1
Sample characteristics. Sample locations are shown in Fig. 1, Regions are shown in Fig. 2.
Region
a
Site Laboratory No. Taxona Locality Latitude Longitude
14
C Age
d
13
C Collection Marine09
b
D
R

N

W yrs BP &Year yrs BP 
14
C yrs ±
11 CAMS-34653 Bathyarca glacialis Dophin & Union Str., NU 69.13 116 880 50 2.49 1915 448 23 432 50
NW CAA n[24 1 TO-8054
c
Bathyarca glacialis Dophin & Union Str., NU 68.88 115.08 990 70 0.73 1915 448 23 542 70
1 UCIAMS-6010
c
Bathyarca glacialis Dophin & Union Str., NU 68.88 115.08 855 25 0.73 1915 448 23 407 25
1 CAMS-57295 Mytilus edulis Dophin & Union Str., NU 68.77 114.7 830 40 0.6 1914 448 23 382 40
1 CAMS-57296 Musculus discors Dophin & Union Str., NU 68.77 114.7 730 40 1.1 1913 448 23 282 40
2 GSC-117
d
Mytilus edulis Coronation Gulf, NU 67.92 114.67 630 50 0.09 1916 448 23 182 50
3 CAMS-57297 Hiatella arctica Bathurst Inlet, NU 68.02 110.13 680 30 2.2 1915 448 23 232 30
4 TO-8062 Mya truncata Prince Patrick Is., NT 76.2 119.42 700 50 1.89 1952 466 23 234 50
4 GSC-474
d
,
e
Buccinum sp. Prince Patrick Is., NT 76.25 119.33 743 78 n/a 1952 466 23 277 78
5 CAMS-57304 Serripes groenlandicus Ellef Rignes Is., NU 78.78 103.5 860 40 2.6 1954 468 23 392 40
6 UCIAMS-6011 Astarte crenata Slidre Fd, NU 80 86.25 905 20 1.55 1955 469 24 436 20
6 TO-8064
c
Astarte montagui Slidre Fd, NU 80 86.25 1000 60 0.39 1955 469 24 531 60
6 UCIAMS-6013
c
Astarte montagui Slidre Fd, NU 80 86.25 910 20 0.39 1955 469 24 441 20
6 CAMS-33138 Serripes groenlandicus Slidre Fd, NU 80 86.25 810 50 1.48 1955 469 24 341 50
6 CAMS-33139 Musculus discors Slidre Fd, NU 80 86.25 730 50 1.37 1955 469 24 261 50
6 CAMS-34646 Astarte borealis Slidre Fd, NU 80 86.25 770 50 0.75 1955 469 24 301 50
7 GSC-1916
d
Astarte borealis Rice Strait, NU 78.76 74.73 780 25 0.9 1898 462 23 318 25
7 GSC-2672
d
Balanus crenatus Rice Strait, NU 78.76 74.73 640 50 1.7 1898 462 23 178 50
7 T-1544 Astarte borealis Rice Strait, NU 78.75 74.92 690 70 1.1 1898 462 23 228 70
8 T-1543 Astarte borealis Jones Sound, NU 76.75 88.53 840 70 1.1 1900 460 23 380 70
8 T-1542 Astarte borealis Jones Sound, NU 76.5 84.5 720 70 0.8 1899 461 23 259 70
8 GSC-1920d Astarte borealis Ellesmere Is., NU 76.5 83.92 800 30 1 1899 461 23 339 30
8 TO-8043 Astarte borealis Craig Hbr, NU 76.21 81 660 80 1.4 1953 467 23 193 80
9 CAMS-57301 Hiatella arctica Arctic Bay, NU 73.02 85.12 770 40 1.8 1954 468 23 302 40
210 CAMS-35484 Clinocardium ciliatum Murray Maxwell Bay, NU 70.01 80.2 620 40 0.35 1956 470 24 150 40
Foxe Basin n[26 10 CAMS-47240 Serripes groenlandicus Murray Maxwell Bay, NU 70.01 80.2 700 40 1.21 1956 470 24 230 40
10 CAMS-47242 Hiatella arctica Murray Maxwell Bay, NU 69.95 80.32 670 40 0.8 1956 470 24 200 40
10 CAMS-35487 Hiatella arctica Cape Jensen, NU 69.73 77.63 640 50 2.38 1956 470 24 170 50
10 TO-8033 Musculus discors South Passage, NU 69.69 80.88 740 50 1.43 1956 470 24 270 50
10 CAMS-33145 Clinocardium ciliatum Fury & Hecla Str., NU 69.62 81.11 780 50 0.66 1956 470 24 310 50
10 CAMS-33147 Hiatella arctica Fury & Hecla Str., NU 69.62 81.11 790 50 1.99 1956 470 24 320 50
10 CAMS-34657 Balanus sp. Fury & Hecla Str., NU 69.62 81.11 700 50 0.98 1956 470 24 230 50
10 TO-8040 Hiatella arctica Fury & Hecla Str., NU 69.62 81.11 820 60 2.18 1956 470 24 350 60
10 CAMS-35486 Musculus discors Tern Is., NU 69.4 80.88 710 50 2 1956 470 24 240 50
10 TO-8039
c
Astarte montagui Turton Bay, NU 69.38 81.74 960 60 1.17 1956 470 24 490 60
10 UCIAMS-6016
c
Astarte montagui Turton Bay, NU 69.38 81.74 930 20 1.17 1956 470 24 460 20
10 CAMS-34651 Serripes groenlandicus Hooper Inlet, NU 69.34 81.73 690 50 0.57 1956 470 24 220 50
10 CAMS-35483 Astarte montagui Hooper Inlet, NU 69.34 81.73 800 40 0.3 1956 470 24 330 40
10 CAMS-35485 Musculus niger Hooper Inlet, NU 69.34 81.73 730 50 0.78 1956 470 24 260 50
10 GSC-6098
d
Astarte borealis Hooper Inlet, NU 69.34 81.73 740 40 0.96 1956 470 24 270 40
10 TO-8037
c
Astarte borealis Hooper Inlet, NU 69.34 81.73 910 50 1.69 1955 469 24 441 50
10 UCIAMS-6015
c
Astarte borealis Hooper Inlet, NU 69.34 81.73 880 20 1.69 1955 469 24 411 20
10 TO-8038 Astarte borealis Hooper Inlet, NU 69.34 81.73 730 50 1.71 1956 470 24 260 50
10 UCIAMS-6564 Hiatella arctica Hooper Inlet, NU 69.34 81.73 735 20 1.71 1956 470 24 265 20
10 CAMS-47243 Hiatella arctica Hooper Inlet, NU 69.31 81.59 720 50 1.37 1955 470 24 250 50
11 CAMS-47239 Musculus discors Rowley Is., NU 69.27 77.8 700 40 0.34 1956 470 24 230 40
12 CAMS-47241 Musculus discors Cape Wilson, NU 66.92 81.33 810 40 1.61 1955 470 24 340 40
13 UCIAMS-6014 Astarte borealis Repulse Bay, NU 66.52 86.25 765 20 1.9 1955 470 24 295 20
13 CAMS-33146 Musculus discors Repulse Bay, NU 66.47 86.2 690 50 2.31 1955 470 24 220 50
14 CAMS-33144 Astarte borealis Schooner Hbr, NU 64.4 77.93 760 50 1.49 1953 467 23 293 50
(continued on next page)
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434 425

Table. 1 (continued)
Region
a
Site Laboratory No. Taxona Locality Latitude Longitude
14
C Age
d
13
C Collection Marine09
b
D
R

N

W yrs BP &Year yrs BP 
14
C yrs ±
315 UCIAMS-6562 Musculus discors Bylot Is., NU 72.8 77 690 20 1.3 1955 469 24 221 20
NE Baffin Is., n[216 GSC-3671
d
Portlandia arctica Cape Macculloch, NU 72.45 74.87 680 40 0.4 1894 466 23 214 40
417 TO-5979
c
Mya truncata Pangnirtung, NU 66.15 65.73 550 40 1.3 1952 466 23 84 40
SE BaffinIs 17 TO-8042
c
Mya truncata Pangnirtung, NU 66.15 65.73 520 70 0.01 1952 466 23 54 70
n[817 CAMS-57300 Musculus discors Pangnirtung, NU 66.13 65.67 680 40 0.9 1953 467 23 213 40
17 CAMS-57303 Musculus discors Cumberland Sd., NU 63 65 530 30 0.3 1953 467 23 63 30
18 CAMS-57299 Hiatella arctica Frobisher Bay, NU 62.83 66.58 600 40 0.9 1953 467 23 133 40
18 CAMS-57302 Hiatella arctica Frobisher Bay, NU 62.83 66.58 660 40 1.9 1953 467 23 193 40
19 UCIAMS-6563 Musculus discors Ct. Warwick Sd., NU 62.73 65.48 650 20 1.97 1951 465 23 185 20
19 GSC-1889
d
Chlamys islandica Watts Bay, NU 62.66 66.8 650 40 3.35 1952 466 23 184 40
520 CAMS-46551 Crenella faba Cape Dorset, NU 64.23 76.55 450 40 2.36 1954 468 24 18 40
Hudson Strait 20 CAMS-46556 Hiatella arctica Cape Dorset, NU 64.23 76.55 580 40 2.01 1954 468 24 112 40
n[520 CAMS-46559 Mya truncata Cape Dorset, NU 64.23 76.55 540 50 2.68 1954 468 24 72 50
20 CAMS-34648 Mya truncata Hudson Strait, NU 64.33 75.58 600 50 2.85 1954 468 24 132 50
21 CAMS-46546 Mytilus edulis Wakeham Bay, NU 61.63 71.97 500 50 0.25 1920 448 23 52 50
622 CAMS-46555 Cyclocardia borealis Ungava Bay, NU 60.07 69.43 450 40 2.42 1949 463 23 13 40
Ungava Bay 23 UCIAMS-6570 Hiatella arctica Leaf Bay, NU 58.92 69.02 565 20 1.09 1947 462 23 103 20
n[23 23 TO-8036 Hiatella arctica Leaf Bay, NU 58.91 68.98 680 70 2.27 1949 463 23 217 70
23 UCIAMS-6571 Astarte borealis Ungava Bay, NU 58.83 68.3 590 20 2.57 1950 464 23 126 20
23 TO-8019 Crenella faba False River, NU 58.62 67.85 660 50 1.66 1947 462 23 198 50
24 UCIAMS-6565 Mya arenaria Ungava Bay, NU 59.5 67.5 535 25 1.32 1950 464 23 71 25
25 CAMS-34644 Hiatella arctica Keglo Bay, NU 59.17 65.75 540 50 0.83 1947 462 23 78 50
25 GSC-6107
d
Clinocardium ciliatum Keglo Bay, NU 59.17 65.75 480 80 1.48 1947 462 23 18 40
25 TO-5980 Cyclocardia borealis Keglo Bay, NU 59.17 65.75 650 40 3.19 1947 462 23 188 40
25 TO-8061 Musculus discors Keglo Bay, NU 59.17 65.75 670 50 1.48 1947 462 23 208 50
26 UCIAMS-6574 Clinocardium ciliatum “Adlorilik”, NU 59.49 65.34 520 20 1.21 1950 464 23 56 20
26 CAMS-34654
c
Astarte borealis “Adlorilik”, NU 59.48 65.25 650 50 1.71 1950 464 23 186 50
26 UCIAMS-6022
c
Astarte borealis “Adlorilik”, NU 59.48 65.25 585 20 2.49 1950 464 23 121 20
27 TO-8023
c
Cyclocardia borealis Cap William-Smith, NU 60.35 64.97 600 50 2.97 1949 463 23 137 50
27 UCIAMS-6018
c
Cyclocardia borealis Cap William-Smith, NU 60.35 64.97 595 20 2.97 1949 463 23 132 20
27 TO-8034 Hiatella arctica Jackson Is., NU 60.4 64.97 520 50 2.39 1949 463 23 57 50
27 TO-8022 Musculus niger Forbes Sound, NU 60.4 64.87 570 60 2.01 1949 463 23 107 60
27 UCIAMS-6021
c
Astarte borealis Port Burwell, NU 60.42 64.83 750 20 1.54 1904 455 23 295 20
27 UCIAMS-6579
c
Astarte borealis Port Burwell, NU 60.42 64.83 765 20 1.54 1904 455 23 310 20
27 CAMS-33148 Mya truncata Port Burwell, NU 60.41 64.83 630 50 2.63 1948 462 23 168 50
27 TO-8021 Mytilus edulis Forbes Sound, NU 60.37 64.78 740 60 0.81 1949 463 23 277 60
27 CAMS-46554 Musculus discors Button Is., NU 60.63 64.65 520 40 2.59 1950 464 23 56 40
27 UCIAMS-6573 Hiatella arctica Button Is., NU 60.63 64.65 560 20 1.91 1950 464 23 96 20
728 CAMS-46553 Hiatella arctica Churchill, MB 58.83 94.07 500 40 2.18 1953 467 23 33 40
Hudson Bay 29 CAMS-46545 Mytilus edulis Richmond Gulf, NU 56.5 76.6 630 40 0.06 1920 448 23 182 40
n[12 29 CAMS-46561 Mytilus sp. Richmond Gulf, NU 56.25 76.33 580 50 0.23 1920 448 23 132 50
30 CAMS-47247 Mytilus edulis Great Whale River, NU 55.28 77.75 570 50 0.29 1949 463 23 107 50
31 CAMS-46552 Musculus discors Foxe Channel, NU 63.68 80.2 560 40 2.18 1953 467 23 93 40
31 CAMS-34647 Clinocardium ciliatum Evans Strait, NU 63.6 82 480 50 1.79 1953 467 23 13 50
31 CAMS-46560 Hiatella arctica Evans Strait, NU 63.6 82 670 50 1.21 1953 467 23 203 50
32 CAMS-33149 Clinocardium ciliatum Bencas Is., NU 63 82.65 690 50 2.27 1954 468 23 222 50
32 CAMS-46549 Mya truncata Bencas Is., NU 63 82.65 590 40 2.18 1954 468 23 122 40
32 CAMS-46557 Clinocardium ciliatum Bencas Is., NU 63 82.65 530 50 0.75 1954 468 23 62 50
32 CAMS-47244 Clinocardium ciliatum Coats Is., NU 62.98 82.68 600 40 -1.26 1954 468 23 132 40
32 CAMS-46547 Cyclopecten groenlandicus Cape Pembroke, NU 62.95 81.84 510 40 1.87 1954 468 23 42 40
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434426

Marine09 calibration curve for the year of carbon fixing (Reimer
et al., 2009).
D
R
L
¼
14
CMarine09
age
ðafter Stuiver et al:; 1986Þ(1)
Where the inferred carbon-fixing date was intermediate between
the 5-year resolution of the Marine09 dataset, the annual value of
Marine09 was interpolated. As the last data point in Marine09 is
1950, an additional 1951 data point was extrapolated according to
the 1945e1950 trend. The standard deviation (
s
L
) in the calculation
of
D
R
L
was calculated by propagating only the standard deviation of
the
14
C age. The standard deviation in the Marine09 dataset was
excluded here because it is incorporated in the calibration process
(e.g. Calib 6.0, Stuiver et al., 2010).
3.4. Calculating
D
R
R
The error-weighted pooled mean (
D
R
R
) of the individual
D
R
L
values from each oceanographic region was calculated using
Equation (2), following the method of Reimer and Reimer (2001)
and Stuiver et al., (2010). Following this protocol, the standard
deviation of the resulting
D
R
R
values is determined using Equation
(3), the standard deviation in the mean value itself (s
pooled
); or
Equation (4), the square root of the weighted average variance (
s
R
).
D
R
R
¼P
n
i¼1
D
R
L
s
L
P
n
i¼11
s
L
ðafter Bevington;1969Þ(2)
s
pooled
¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
1
P
n
i¼11
s
L
sðafter Bevington;1969Þ(3)
s
R
¼ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
n
n1P
n
i¼1

D
R
L

D
R
R
s
L

2
P
n
i¼11
s
L
v
u
u
u
tðafter Bevington;1969Þ(4)
In order to describe the internal variability of
D
R
L
within our
dataset we calculated
c
2
values for each region according to the
method of Ward and Wilson (1978; Equation (5);Table 3).
c
2
¼X
n
i¼1

D
R
L
i

D
R
R

s
L
i
2
ðafter Ward and Wilson;1978Þ(5)
We report
c
2
with respect to the critical acceptance values, and
normalized by dividing by the number of degrees of freedom
(n1) in the dataset for that region (e.g. Bondevik and Gulliksen,
in Mangerud et al., 2006). In the case that
c
2
/(n1) is 1, it
indicates that the measurement uncertainties explain the vari-
ability, whereas when
c
2
/(n1) 1, there is additional variability
not explained by the measurement uncertainty. We have used the
methodology of Bondevik and Gulliksen (in Mangerud et al., 2006)
to additionally estimate the external variability of the data (
s
ext
)in
regions where
c
2
/(n1) 1. The estimate of total variability (s
total
)
using this method is lower than that calculated using Equation (4)
except for Regions 7 and 8 (Hudson Bay and James Bay; Figs. 1 and
2;Table 3). As the datasets used to calculate our new
D
R
R
values are
relatively small, we report the highest estimate of the standard
deviation as s
max
, in order to maximize accuracy in dates calibrated
using these new values (Table 3).
4. Results
We report marine reservoir corrections for the CAA and
adjoining subarctic marine waters as
D
R
R
, which we consider to be
833 CAMS-48978 Mya sp. South Twin Is., NU 53.12 79.87 750 40 2.04 1920 448 23 302 40
James Bay 34 CAMS-46757 Hiatella arctica Paint Hills Island, NU 52.95 79 720 40 1.18 1920 448 23 272 40
n[834 CAMS-46760 Mytilus edulis Paint Hills Island, NU 52.95 79 740 40 -0.76 1920 448 23 292 40
34 CAMS-46761 Mytilus edulis Old Factory Bay, NU 52.6 78.75 810 40 -1.01 1920 448 23 362 40
35 CAMS-46755 Mytilus edulis Charlton Is., NU 52 79.5 970 40 -0.02 1941 458 23 512 40
35 CAMS-48979
c
Mytilus edulis Charlton Is., NU 52 79.5 950 40 2.01 1920 448 23 502 40
35 CAMS-46759
c
Mytilus edulis Charlton Is., NU 52 79.5 1050 40 -2.43 1920 448 23 602 40
35 UCIAMS-6017
c
Mytilus edulis Charlton Is., NU 52 79.5 845 20 2.01 1920 448 23 397 20
a
Taxonomic names corrected from McNeely et al. (2006) according to the Integrated Taxonomic Information System on-line database (http://www.itis.gov) retrieved July 7 2009, and Rosenberg (2005). See Table 2.
b
Marine09 values for year of carbon fixing, assumed to be 5 years prior to collection, from, and interpolated from Reimer et al., (2009).
c
Multiple analyses of the same individual speciman from the same location were combined as error-weighted pooled means according to Case 1 of Ward and Wilson (1978).
d
Updated GSC dates are reported from McNeely and Brennan (2005). We report GSC dates as conventional radiocarbon dates with 1
s
standard deviation, rather than 2
s
as originally reported by the laboratory.
e
GSC-474 was originally a non-normalized radiocarbon date. It is here reported as a conventional radiocarbon date normalized according to Reimer et al., 2010 and Section 3.2, this paper.
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434 427

Table 2
Selected taxonomic and ecological information regarding species described in this study.
Taxon
a
Taxonomic synonyms e
commonly used
a
Common name Habit
b
Substrate
b
Salinity Temp
range (

C)
Depth range
(m)
Max.
lifespan
(yrs)
Feeding
mode
b
References
Gastropods
Buccinidae
Buccinum spp.
(Linnaeus, 1758)
whelk epi. 1to>45e100 >10 carn. Peacock, 1993; Ten Haller-Tjabbes
and Boon, 1995
Bivalves
Sareptidae
Portlandia arctica
(J.E. Gray, 1824)
P. typica, Yoldia arctica,
Nucula arctica, Nucula glacialis
arctic nutclam,
arctic yoldia
in. m, ms, mg 26 63e340 det. Peacock, 1993
Arcidae
Bathyarca glacialis
(J.E. Gray, 1824)
glacial bathyark epi. 32 1.5 to 7 5e4000 susp. Peacock, 1993
Mytilidae
Mytilus spp.
(Linnaeus, 1758)
mussel epi. susp.
Mytilus edulis
(Linnaeus, 1758)
many, inc. M. minganensis,
M. notatus, M. pellucidus,
M. petasunculinus, M. retusus,
M. spathulinus, M. subsaxatilis,
M. trigonus, M. variabilis,
M. vulgaris
blue or edible
mussel
epi. r 7 10 to 30 0e25 13 susp. Peacock, 1993;Zotin and
Ozernyuk, 2004;Tebble, 1976
Musculus discors
(Linnaeus, 1767)
M. laevigatus, M. substriata,
Modiolaria discors
discordant mussel epi. r 9e19 1to>80e25 susp. Peacock, 1993;Tebble, 1976
Musculus niger
(J.E. Gray, 1824)
Modiolaria niger black mussel epi. s,m,c 9e19 1to14 3e380 susp. Peacock, 1993;Tebble, 1976
Crenella faba
(Müller, 1776)
Mytilus faba, Modiola arcica bean crenella epi. susp.
Pectinidae
Chlamys islandica
(Müller, 1776)
Pecten islandicus, P. tenuis Iceland scallop epi. 2to14 7e80 18e23 susp. Peacock, 1993;Shumway
and Parsons, 2006
Cyclopecten
greenlandicus
(G.B. Sowerby II, 1842)
Pecten greenlandicus, P.vitreus,
Arctinula greenlandicus
Greenland
glass-scallop
epi. susp.
Astartidae
Astarte crenata
(J.E. Gray, 1824)
A. acuticostata, A. quadrans,
A. subaequilatera, Nicania crenata,
crenualte astarte in. s, mg, sg 33 2to7 30e700 susp. Peacock, 1993
Astarte borealis
(Schumacher, 1817)
A. richardsoni, A. saintjohnensis,
A. semisulcata, Tridonta borealis
boreal astarte in. s, mg, sg 8e15 2to15 0e40 8e10 susp. Peacock, 1993;Selin 2007;
Tebble, 1976
Astarte montagui
(Dillwyn, 1817)
A. banksii, A. compressa, A. fabula,
A. globosa, A. pulchella, A. striata,
A. warhami, Tridonta montagui
narrow-hinge
astarte
in. s, mg, sg 9e19 2to14 0e100 susp. Peacock, 1993;Tebble, 1976
Cardiidae
Clinocardium ciliatum
(Fabricus, 1780)
C. arcticum, C. boreale,
C. dawsoni, C. hayesi,
C. pubescens
hairy cockle in. 2to9 5e40 susp. Peacock, 1993
Serripes
groenlandicus
(Mohr, 1786)
Cardium groenlandicus,
C. hyperboreum, Venus islandica
Greenland smooth
cockle
in. 2to9 3e120 susp. Peacock, 1993
Cyclocardia borealis
(Conrad, 1831)
Cardiata borealis, C. vestita,
Venericardia borealis, V. morsei
northern
cyclocardia
in. susp.
Myidae
Mya spp.
(Linnaeus, 1758)
softshell clam in. 0e70 susp. Peacock, 1993
Mya arenaria
(Linnaeus, 1758)
M. acuta, M. communis,
M. corpulenta, M. mercenaria,
M. subtruncata,
softshell clam,
sand gaper
in. s, m, sm, sg 6 0e70 susp. Peacock, 1993;Bousfield, 1960;
Tebble, 1976
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434428

Mya truncata
(Linnaeus, 1758)
M. ovals, M. maxima, M. ovalis,
M. pelagica, Sphenia swainsonii
short clam,
blunt gaper
in. s, sg, c 8e17 2to17 0e70 >50 susp. Peacock, 1993; Camus et al., 2005;
Bousfield, 1960; Tebble, 1976
Hiatellidae
Hiatella arctica
(Linnaues, 1767)
H. biapetra, H. oblonga,
Mya arctica, Mya byssifera,
Saxicava arctica
arctic hiatella,
wrinkled rockborer
epi./
in.
m, s, r20e11 0e120 126 susp. Ockelmann, 1958;Peacock, 1993;
Tebble, 1976;Bousfield, 1960
Crustacea
Balanidae
Balanus spp.
(Da Costa, 1778)
barnacle epi. r susp.
Balanus balanus
(Linnaeus, 1778)
Balanus porcatus rough or northern
ridged barnacle
epi. r 0e>180 3e10 susp. Bousfield, 1960
Balanus crenatus
(Bruguière, 1789)
crenalated or
notched acorn
barnacle
epi. r 0e>100 3e10 susp. Bousfield, 1960
a
Valid taxonomic names and synonyms according to the Integrated Taxonomic Information System on-line database (http://www.itis.gov) retrieved July 7 2009, and Rosenberg (2005).
b
Abbreviations: epi. ¼epifaunal, in. ¼infaunal, c ¼clay, m ¼mud, s ¼sand, g ¼gravel, r ¼rock, ms ¼muddy sand, mg ¼muddy gravel, sm ¼sandy mud, sg ¼sandy gravel, carn. ¼carnivore, det. ¼detrital feeder,
susp. ¼suspension feeder.
Table 3
Recommended regional reservoir offset values
D
R
R
for regions in Arctic Canada Regions are shown in Fig. 2.
Region Locality Number of
D
R
R
s
pooled
s
R
c
2(n-1):0.05
c
2/n-1
s
measb
Population
s
pop
s
extc
s
totald
s
maxe
D
R
R
Samples
a
Weighted Mean Mean Recommended Values
n
14
C yrs
14
C yrs
14
C yrs
14
C yrs
14
C yrs
14
C yrs
14
C yrs
14
C yrs
14
C yrs
14
C yrs
1 NW CAA 24 (22) 335 9 85 92.17<32.67 4.39 40 310 86 76 76 85 335 85
2 Foxe Basin 26 (24) 309 7 89 148.57<35.17 6.46 35 274 72 62 63 89 310 90
3 NE Baffin Is. 2 220 18 4 0.02<3.84 0.02 N/A 218 5 N/A N/A 18 220 20
4 SE Baffin Is. 8 (7) 151 12 59 20.40<12.59 3.4 32 150 60 51 52 59 150 60
5 Hudson Strait 5 66 20 62 7.57<9.49 1.89 45 70 58 37 42 62 65 60
6 Ungava Bay 23 (20) 144 6 93 212.94<30.14 11.21 28 129 83 79 79 93 145 95
7 Hudson Bay 12 109 12.75 65 23.77<19.68 2.16 4 112 67 67 67 67 110 65
8 James Bay 8 (6) 364 17 110 24.64<11.07 4.93 42 382 120 113 114 114 365 115
a
n is the number of original
D
RL measurements, and the value in brackets is the number of unique sites after replicate analyses indicated in Table 1 were combined.
b
estimated standard error is the pooled mean error multiplied by the square root of n, where nis the number of samples;
s
meas
¼S
pooled
*On.
c
external variance is found by subtracting measurement variance from total population variance;
s
ext
¼O(
s
pop
2
e
s
meas
2
).
d
uncertainty includes external variance; S
total
¼O(S
pooled
2
+
s
ext
2
).
e
S
max
¼highest of S
pooled
,S
total
or
s
R
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434 429

time invariant to a first approximation, instead of regional reservoir
ages, R
R
, which vary considerably through time (Stuiver et al., 1986).
Consequently, we provide no time-invariant R
R
values for Arctic
Canada and expressly discourage their use (see discussion by
Bondevik and Gulliksen in Mangerud et al., 2006). Although we do
not report R
R
values here, we wish to note that our data also indi-
cate greater variability of R
R
, determined from the
c
2
test, than of
D
R
R
, as would be expected where
D
R
R
has minimal time-dependant
variability (e.g. Stuiver et al., 1986).
Our regional valuesof
D
R
R
are presentedin Table3, rounded to the
nearest 5 years. The values vary between 65 60 yrs for Hudson
Strait (Region 5; Fig. 2) and 365 115 yrs for James Bay (Region 8;
Fig. 2). Regions influenced primarily by Arctic Ocean surface waters
and perennial sea ice such as the NW CAA (Region 1), Foxe Basin
(Region 2) and NE Baffin Island (Region 3) exhibit generally higher
D
R
R
values than do regions influenced by North Atlantic surface
waters (Fig. 2;Table 3). Regions with North Atlantic (Labrador Sea)
water input, less extensive sea ice and more atmospheric exchange
(SEBaffineRegion 4; HudsonStraiteRegion 5; UngavaBay eRegion
6; Hudson Bay eRegion 7) exhibitrelatively lower
D
R
R
values (Fig. 2;
Table 3). Shallow basins with limited connectivity to the open ocean,
such as James Bay (Region 8) and Foxe Basin (Region 2), also show
elevated
D
R
R
values (Fig. 2;Table 3). Ungava Bay (Region 6) and Foxe
Basin (Region 2) in particular show the highest internalvariability, as
indicated by their high
c
2
scores (Table 3). In contrast, Hudson Strait
(Region 5) and NE Baffin Island (Region 3) show the lowest internal
variability, although this may be the result of the limited data
available from these regions (Table 3).
5. Discussion
Our study makes use of the most extensive database of live-
collected, pre-bomb marine molluscs from Arctic Canada (McNeely
et al., 2006). It represents the first attempt to provide quantitatively
derived, regionally applicable
D
R
R
values for the CAA and Hudson
Bay. We intend these new
D
R
R
values to be used for meaningful
14
C
calibration in place of more simplistic and arbitrary marine reser-
voir corrections that have until recently dominated the literature.
Critically, our new
D
R
R
values should facilitate the standardized
conversion of marine-based
14
C compilations (e.g. Dyke et al.,
1996a, 2005; Dyke, 2004) into calibrated years.
5.1. The importance of using the correct regional reservoir
offset,
D
R
R
We have divided Arctic Canada into eight oceanographically
defined regions, each based upon distinct water mass characteris-
tics and circulation patterns (Section 2). Our regional divisions
differ from those of McNeely et al. (2006) in that we account for the
return flow of the West Greenland Current east of southern Baffin
Island, the combined Baffin/Labrador Sea Current that enters
Hudson Strait from the northwest Labrador Sea, and the south-
westward deflection of the West Greenland Current in Smith Sound
between southeast Ellesmere Island and Greenland (Figs. 1 and 2;
e.g. Drinkwater, 1986; Barry, 1993; Ingram and Prinsenberg, 1998).
The primary difference in boundaries between McNeely et al.
(2006) and our study is that our Region 7 (Hudson Bay) includes
D
R
L
sites in northern Hudson Bay (Sites 31 and 32; Table 1;Fig. 1).
In contrast, McNeely et al. (2006) assigned the same locations to
their Foxe Basin region. We consider Foxe Basin to be oceano-
graphically distinct from northern Hudson Bay (e.g. Fig. 2).
Although the oceanography of each of our defined regions is
broadly distinct from one another,
D
R
L
is nonetheless non-uniform
within each region with significant external variability in the data
(Table 1 and 3). In the two regions with the highest variability as
indicated by
c
2
scores, Ungava Bay (Region 6) and Foxe Basin
(Region 2), the standard deviation of the data at individual sites
with multiple samples from the same coordinates shows nearlythe
same variability as the entire regional dataset (e.g. Keglo Bay, site
25; Hooper Inlet, site 10, Table 1). As the samples used were
museum specimens, it is uncertain if samples from the same
coordinates were collected from the same specific site, or if they
were collected from nearby within the precision of the coordinates
provided. Given the lack of any clear trend in the data, and the
occurrence of the full range of regional variability at individual
sites, we attribute the variability among
D
R
L
sites within each
region to very localized, and perhaps site-specific factors such as
ventilation (e.g. seasonal sea ice extent and duration), upwelling,
and density-driven mixing at a local scale (e.g. Barry, 1993; Melling,
2000). A more expansive record of the specific collection site (e.g.
depth, temperature, substrate, open ocean or within an embay-
ment etc.) would facilitate more conclusive statements about site-
specific factors influencing
D
R
L
. As none of the dated samples have
particularly unusual
d
13
C values (Table 1) that would be indicative
of freshwater or terrestrial carbon uptake, we consider the influ-
ence of terrestrially derived “old”carbon to be minimal.
Given the extremely high localized variation in physical
parameters of Arctic waters, particularly on inter- and intra-annual
scales, the substantial variability in
D
R
L
values is not surprising.
Specifically, in regions defined by their large scale oceanography,
the variability of
D
R
L
should be essentially stochastic.
D
R
R
, being the
regionally derived mean of all
D
R
L
sites, accounts for and accom-
modates the observed variability of
D
R
L
within an appropriately
defined region. Our
D
R
R
values approximate this stochastic
behaviour within the limitations of the available data. When cali-
brating marine
14
C dates, it is thus important to adopt the most
appropriate
D
R
R
value and to avoid using the
D
R
L
value from the
nearest site, or a subset of nearby sites (e.g. Utting and Little, 2007;
Lajeunesse, 2008). Such an approach may exaggerate the impor-
tance of outlying
D
R
L
values and lead to less accurate chronologies.
Evidently, our
D
R
R
values would be improved by the addition of
more
D
R
L
data. However, the paucity of molluscs from Arctic
Canada collected live prior to nuclear bomb testing poses a chal-
lenge to further refinement of this work. Independent assessments
of
D
R
R
may still be possible using subfossil shells if those molluscs
occur with independent chronological markers such as a tephra
bed or within marine sediments containing estuarine vegetation of
the same absolute age.
5.2. Comparison with other studies
Earlier studies of regional reservoir offset (
D
R
R
) in Arctic Canada
have also been constrained by a scarcity of data. Prior to the
McNeely et al. (2006) database becoming available, only three
reservoir correction sites were available on southeast Ellesmere
Island (Fig. 1;Mangerud and Gulliksen, 1975) to calculate
D
R
R
¼325 45 yrs for the CAA (roughly equivalent to Region 1;
Stuiver et al., 1986; Stuiver and Braziunas, 1993). This value was
used subsequently by Blake (1992) to calibrate his
14
C dates from
eastern Ellesmere Island. More recently as part of a North Atlantic
compilation study, Mangerud et al. (2006) recalculated this
D
R
R
value to be 337 66 yrs (Bondevik and Gulliksen in Mangerud et al.,
2006)or33866 yrs using a slightly different approach (Man-
gerud in Mangerud et al., 2006). Our Region 1 dataset used for
calculating
D
R
R
includes the three Mangerud and Gulliksen (1975)
data points along with an additional 21 from McNeely et al. (2006).
Our new
D
R
R
value for the NW CAA (Region 1) of 335 85 yrs is in
good agreement with Mangerud and Gulliksen (1975) and
Mangerud et al. (2006), being well within 1
s
of the previous
D
R
R
estimates.
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434430

For NE Baffin Island (Region 3; Fig. 2), Briner et al. (2007)
determined a reservoir correction value from interbedded fossil
plant detritus and mollusc shells in a section mid-way along Clyde
Inlet, a fjord on eastern Baffin Island, Arctic Canada. We used the
reported dates to recalculate a site-specific
D
R
L
of 210 97 yrs.
Notably this value is defined for the time during which the plant
detritus grew (9270 130 cal BP). The excellent agreement with
our calculated
D
R
R
¼220 30 yrs (valid for the early 20th century)
provides some confidence in our
D
R
R
value, and in the approximate
time-invariance of
D
R
R
within the region.
Sherwood et al. (2008) calculated the surface water
D
R
R
value for
the northwest Labrador Sea (Fig.1) in a recent study of live-collected,
annually banded, gorgonian coral (Keratoisis ornata) adjacent to SE
Baffin Island. Their
D
R
R
value (from three coral specimens) of
132 23 yrs is in good agreement with our mollusc-derived
determination of 150 60 yrs for the same area (Region 4; Fig.1). As
the samples that constitute the foundation of our calculations are
predominantly molluscs collected from nearshore shallow marine
sites (McNeely et al., 2006), the three deepwater coral samples of
Sherwood et al. (2008) were omitted from our study. However, their
inclusion does not significantly alter our
D
R
R
value for Region 4
(150 60 yrs without coral, 140 50 yrs with coral). In each of the
these cases (Mangerud and Gulliksen, 1975; Mangerud et al., 2006;
Briner et al., 2007; Sherwood et al., 2008) the close agreement of
previously published
D
R
R
values with our new calculations is
encouraging and suggests that our
D
R
R
values calculated for the
remaining regions should be similarly meaningful.
5.3. Constraints and future work
We recognize several limitations of our dataset. Firstly, although
we are confident that we have appropriately addressed the broad
oceanographic variability across the CAA in defining our regions,
the
D
R
L
data are not uniformly distributed across the regions. For
example, Region 3 (NE Baffin Island; Fig. 2) is represented by only
two data points, occurring in close proximity to each other (Fig. 1).
Similarly, some parts of Region 1 (NW CAA) and Region 7 (Hudson
Bay) are under-represented (Figs. 1 and 2). The dating of more
live-collected, pre-bomb marine molluscs from Arctic Canada,
especially from under-represented regions, would better constrain
the stochastic variability of
D
R
L
within a region, and increase the
accuracy of
D
R
R
. As molluscs collected live after 1956 cannot be
used to constrain
D
R
R
due to variable uptake of bomb
14
C by the
ocean (e.g. Weidman and Jones, 1993; Hua et al., 2005), future
studies must rely upon additional historical collections in museums
and archives. In particular, collections from the Franklin search era
of Royal Navy expeditions or later expeditions, whose collections
remain unrecognized, may prove fruitful.
Secondly, we recognize that a carbon-fixing correction of 5 yrs
is an arbitrary approximation of the potential lifespan of individual
molluscs. Currently, the lifespan of several mollusc species is poorly
constrained, if known at all (Table 2). Many taxa also have the
potential for extended longevity in high latitude environments (e.g.
Sejr et al., 2002; Camus et al., 2005). This renders a simple
size-based estimate of their age-at-death inaccurate. However, the
dating of individual growthbands as a means of establishing
D
R
R
more accurately introduces extra dating uncertainties due to
seasonal to annual variations in molluscan metabolism, habitat,
and local
14
C reservoir fluctuations (Ingram, 1998; Kennett et al.,
1997; Dye, 1994; Wefer and Berger, 1991; Kranz et al., 1989, 1987;
Killingley and Berger, 1979; Keith et al., 1964). These variations
are typically averaged in larger multi-year (multi-growthband)
samples and may potentially be magnified by the random selection
of narrow growthband material (Culleton et al., 2006). To overcome
this problem, Culleton et al. (2006) recommend the dating of larger
(w1e2 cm) shell fragments sampling the growth axis of the
mollusc, thereby averaging potential short-term fluctuations in
local
14
C reservoir ages. Where there is no requirement to preserve
archived material, whole shell dating would also achieve the same
end. However, where whole shell dates are derived from individ-
uals with extended longevity (e.g. Sejr et al., 2002; Camus et al.,
2005), sectioning and growthband counting to establish the life
age of the mollusc (e.g. Butler et al., 2009) would better constrain
the median year (or median five-year interval) of carbon fixing. This
would permit correlation to a more representative point on the
Marine09 calibration curve (Reimer et al., 2009), itself resolved at
five-year intervals.
Thirdly, this compilation of
D
R
R
values is explicitly applicable to
ocean circulation and ventilation conditions similar to those at the
time of sample collection, i.e. during the late 19themid 20th
century. Following Mangerud et al. (2006) we consider variation in
D
R
R
to be within the quoted standard deviation since the mid-
Holocene, when oceanographic conditions have remained broadly
similar, and possibly beyond. Support for extending the range of
usefulness back to the early Holocene is provided by the similarity
between our NE Baffin
D
R
R
value and
D
R
L
calculated for
9270 130 cal BP based on the data of Briner et al. (2007), however,
this is only a single site, and this conclusion warrants caution.
During periods of non-analogous oceanographic conditions, such as
those during Marine Isotope Stage 2, deglaciation, and the Younger
Dryas, the magnitude and variability of
D
R
R
is expected to differ
significantly from the values presented in this paper (e.g. Bondevik
et al., 2006; Bradley and England, 2008; Muscheler et al., 2008). The
dating of contemporaneous terrestrial and marine sub-fossil
material from definitively correlative settings could in the future
provide individual estimates of
D
R
L
for both analogous and non-
analogous conditions. However, such sites are rare in Arctic Canada
due to the scarcity of vegetation and low marine productivity, with
the discovery of new sites further complicated by inaccessibility,
and limited reconnaissance work.
Our study provides new
D
R
R
values for Arctic Canada, defined
on the basis of regional oceanography. The adoption of the cali-
bration of marine
14
C dates by the Canadian Arctic Quaternary
community, using the
D
R
R
values presented here, will provide the
chronological rigour hitherto lacking from many published
14
C
chronologies from the region. More importantly, it will permit
more reliable and meaningful comparisons between
14
C and other
chronologies (e.g. terrestrial and marine
14
C, cosmogenic radio-
nuclide dating, ice cores, varves and tephra). The adoption of
standard protocols, utilized extensively elsewhere (e.g. Reimer and
Reimer, 2001; Ascough et al., 2005; Culleton et al., 2006; Petchey
et al., 2008), will further help to refine existing chronologies and
may provide new insights into the timing and forcing of prom-
inent palaeoenvironmental events recorded in Arctic Canada.
Critically, calibrated chronologies can be easily updated as new
marine calibration curves and new
D
R
L
sample data become
available.
6. Conclusions and recommendations
The calibration of marine
14
C dates requires the incorporation
of a regionally valid reservoir offset,
D
R
R
.As
D
R
R
is a function of
ocean circulation and ventilation, regions should be defined
primarily on the basis of oceanographic criteria. To account for
local variability within a specific region,
D
R
R
should be the
error-weighted pooled mean of all appropriate
D
R
L
measure-
ments from that region.

D
R
R
values calculated for molluscs from Arctic Canada vary
according to region (Table 3,Fig. 2), and the following values
should be utilized: Region 1, NW CAA, 335 85 yrs; Region 2,
R.D. Coulthard et al. / Quaternary Geochronology 5 (2010) 419e434 431

Foxe Basin, 310 90 yrs; Region 3, NE Baffin Island,
220 20 yrs; Region 4, SE Baffin Island, 150 60 yrs; Region 5,
Hudson Strait, 65 60 yrs; Region 6, Ungava Bay, 145 95 yrs;
Region 7, Hudson Bay, 110 65 yrs; Region 8, James Bay,
365 115 yrs.
Although our recommendations for
D
R
R
reflect the available
data, the values can be readily revised, if more pre-bomb
mollusc samples are dated or a new marine calibration curve is
published. Following Mangerud et al. (2006), our recommen-
dations are given for ocean circulation and ventilation similar
to today. The variability of
D
R
R
during much of the Holocene is
probably within the quoted error due to the similarity of
oceanographic conditions. However, pre-early Holocene values
of
D
R
R
are probably significantly different (Bondevik et al.,
2006; Bradley and England, 2008).
Acknowledgements
We wish to acknowledge the contributions of R. McNeely and
A.S. Dyke (GSC) and J. Southon (University of California, Irvine) who
compiled the original data used in our study. Numerous
14
C dates
have been obtained throughout Arctic Canada primarily by
researchers from the GSC, and the University of Alberta, funded for
over three decades by NSERC grants to J. England and graduate
students with logistical support provided throughout by Polar
Continental Shelf Project (NRCan, Ottawa). We thank J. Turnbull
(NOAA/ESRI) for helpful advice on
14
C dating and an informal
review. P.J. Reimer (Queen’s University Belfast), E. Druffel (Univer-
sity of California, San Diego) and K. Buro (Grant MacEwan Univer-
sity) kindly provided advice and information on statistical
calculations related to reservoir correction. We thank T. Lakeman,
J. Vaughan and C. Dow (University of Alberta) for helpful conver-
sations that improved this manuscript. Funding was provided by an
Alberta Ingenuity Fund Studentship and NSERC PGS B Award to
Coulthard, Canadian Circumpolar Institute awards to Coulthard,
Furze, Nixon, and Pie
nkowski, Northern Scientific Training Program
(INAC) awards to Coulthard and Nixon, as well as an NSERC
Northern Chair awarded to England. We are grateful to F. Petchey
and A. Hogg (Waikato University), and two anonymous reviewers
whose comments greatly improved our manuscript.
Author contributions
Coulthard, Furze and Pie
nkowski each contributed equally to
this work. Coulthard was responsible for the statistical calculations
on which the new ΔRvalues are based. Furze was responsible for
molluscan autecology, and the selection of appropriate pre-bomb
molluscs from the McNeely et al. (2006) database from which our
new ΔRvalues are calculated. Pie
nkowski was responsible for the
oceanographic determination of our ΔRregions. Nixon drafted the
figures, provided feedback and suggested editorial improvements.
England co-proposed the research and provided extensive back-
ground information on past radiocarbon reporting practise, and
suggested many useful editorial improvements to the manuscript.
Editorial handling by: A. Hogg
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