New cetacean r values for arctic north

Based on an exhaustive compilation of previously published marine mammalradiocarbon dates both live-harvested materials and subfossils from the Canadian Arctic ArchipelagoCAA, new, stati

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New cetacean D R values for Arctic North America and their

implications for marine-mammal-based palaeoenvironmental

reconstructions

a Earth & Planetary Sciences Division, Department of Physical Sciences, MacEwan University, Edmonton, Alberta T5J 4S2, Canada

b School of Ocean Sciences, College of Natural Sciences, Bangor University, Menai Bridge, Anglesey, Wales LL59 5AB, UK

c Department of Earth & Atmospheric Sciences, University of Alberta, Edmonton, Alberta T6G 2E3, Canada

to reconstruct Holocene sea-ice histories The use of such reconstructions has hitherto been complicated

by uncertain marine reservoir corrections precluding meaningful intercomparisons with data reported incalibrated or sidereal years Based on an exhaustive compilation of previously published marine mammalradiocarbon dates (both live-harvested materials and subfossils) from the Canadian Arctic Archipelago(CAA), new, statistically-derivedd13C andDR values are provided Averaged13C values are:16.1 1.1&(bone collagen; n¼ 193) for bowhead (Balaena mysticetus); 14.4 0.5& (n ¼ 44; dentine) for beluga(Delphinapterus leucas);14.8 1.9& (teeth and tusks; n ¼ 18) and 18.0 4.7& (n ¼ 9; bone collagen)for walrus (Odobenus rosmarus).DR values are 170 9514C years for bowhead (n¼ 23) and 240 6014Cyears for beluga (n¼ 12) Scarce data preclude calculation of meaningful, statistically robust walrusDR.Using the newDR values, an expanded and revised database of calibrated bowhead dates (651 dates;many used in previous CAA sea-ice reconstructions) shows pronounced late Quaternary spatio-temporalﬂuctuations in bone abundance Though broadly resembling earlier bowhead subfossil frequency data,analysis of the new expanded database suggests early- and mid-Holocene increases in whale abundance

to be of longer duration and lower amplitude than previously considered A more even and persistentspread of infrequent low-abundance remains during“whale free” intervals is also seen The dominance

of three eastern regions (Prince Regent Inlet & Gulf of Boothia; Admiralty Inlet; Berlinguet Inlet/BernierBay) in the CAA data, collectively contributing up to 88% of all subfossil remains in the mid-Holocene, isnotable An analysis of calibrated regional sea-level index points suggests that severance of the AdmiraltyInlet-Gulf of Boothia marine channel due to isostatically-driven regression may have played a signiﬁcantrole in enhanced whale mortality during this interval Comparisons between the newly calibratedbowhead data and other regional sea-ice proxy data further highlight spatial and temporal discrepancies,potentially due to regional asynchronicities and variable sensitivities in proxy response to climate andoceanographic forcing However, the limited number of deglacialepostglacial marine records continues

to hamper extensive intercomparisons between marine mammal and other proxy datasets Nevertheless,

an examination of assumptions inherent in linking bowhead subfossil frequencies, population densities,and sea-ice thickness and distribution, shows that such relationships are highly complex Factors such asbroad sea-ice preferences, variable mortality rates and causes, long distance carcass transport, variablecoastline and basin/channel geometries, and changing emergence rates all complicate the correlation ofwhale bone abundance to sea-ice histories

1 IntroductionRadiocarbon-dated marine mammal remains have been widelyused to reconstruct late Quaternary relative sea-levels, palae-oenvironments, and human occupation in Arctic North America(e.g.,Dyke and Morris, 1990; Dyke et al., 1991, 1996a, 2011; Dyke

* Corresponding author Tel.: þ1 780 633 3918.

1 All authors contributed equally to this publication.

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and Savelle, 2001; Savelle et al., 2012) Such dates have historically

been reported in uncorrected radiocarbon years, or have had

assumed reservoir corrections (R) applied to them (Dyke et al., 1991,

1996a; Dyke and Savelle, 2001; Dyke and England, 2003),

compli-cating meaningful intercomparisons with other proxy records

re-ported in calibrated or sidereal years Coulthard et al (2010)

discussed this problem regarding molluscan chronologies,

providing statistically-based regional reservoir offset values (DRR)

for calibration of Canadian Arctic Holocene radiocarbon dates Here,

we provide the ﬁrst, statistically-derived d13C and regional DR

values for marine mammal-based radiocarbon chronologies from

Arctic Canada, present an expanded, revised regional database of

calibrated marine mammal dates, and conduct a spatio-temporal

analysis of bowhead whale (Balaena mysticetus) remains as a

palaeo-sea-ice proxy

Historically, marine mammal dates have been considered of

dubious quality due to the challenges associated with correcting for

d13C fractionation for different species and different types of

re-mains, besides the complexity of marine reservoir corrections for

migrating species In the archaeological community,McGhee and

Tuck (1976)andTuck and McGhee (1984)argued that 14C dates

on marine organisms should simply be ignored due to the difﬁculty

of comparing them with terrestrial materials, despiteArundale’s

(1981) call for a more moderate approach Dyke et al (1996b)

recommended a reservoir correction ofw200 years for bowhead

dates whereasDyke et al (1999)reported walrus dates without

reservoir correction, as little data existed by which to derive a

meaningful value Mangerud et al (2006) calculated reservoir

corrections andDR from live-harvested 19th century whales in the

European Atlantic, suggesting DR values of w7 years for both

baleen and toothed whales, reﬂecting their food source in the ocean

surface layer In the Canadian Arctic Archipelago (CAA),Dyke and

Savelle (2009) proposed an increase in the bowhead reservoir

correction (R) from 200 to 400 years, similar to changes proposed

for molluscan R (Dyke et al., 2003) Notably, no statistically-based R

orDR for CAA marine mammals has previously been attempted

Nevertheless, radiocarbon-dated marine mammal remains from

emergent Arctic coastlines have long been used to reconstruct

deglacial to postglacial sea-level histories (Blake, 1961, 1970;

Salvigsen, 1978; Dyke, 1979, 1980) Aside from marine molluscs

and driftwood, bowhead remains form the basis of Holocene

sea-level curves from the central and eastern CAA and Svalbard

(Blake, 1975; Salvigsen, 1978; England, 1983; Dyke et al., 1991, 2011;

Dyke, 1998) Given their comparative scarcity, walrus (Odobenus

rosmarus), beluga (Delphinapterus leucas), and narwhal (Monodon

monoceros) are seldom employed as Holocene sea-level index

points While offshore sinking, landward crawling (walrus), and

sea-ice push can complicate altitudinal relationships, careful

con-struction of emergence curves derived from a range of different

index points may identify and negate the distorting effects of

“sinkers” and “crawlers” on sea-level reconstructions (Dyke, 1980,

1993; Dyke et al., 1991, 1999)

The potential of marine mammals as Holocene sea-ice proxies

was noted early in their use as sea-level indicators (Salvigsen, 1978;

Dyke, 1979, 1980; Evans, 1989; Bednarski, 1990) Fundamental to

this approach is the close relationship between sea-ice and the

distribution of these animals, given their dependence on sea-ice for

breeding, feeding, and resting (Moore and Reeves, 1993; Stirling,

1997; Laidre et al., 2008) Consequently, long- and short-term

changes in sea-ice extent and thickness should affect species

dis-tributions (Vibe, 1967; Reeves et al., 1983) Therefore, the subfossil

record should reﬂect local abundance and occupation changes

(Dyke and Morris, 1990; Dyke et al., 1996a) This approach has been

used extensively in the CAA, where decades of intenseﬁeldwork,

primarily by the Geological Survey of Canada (GSC), have generated

hundreds of elevationally-constrained radiocarbon dates on vidual marine mammal specimens An even greater number ofobservations, the age of which can be determined by plotting theirelevation on well-constrained sea-level curves, has been recorded(Dyke et al., 1996a; Savelle et al., 2000)

indi-Based on an exhaustive compilation of previously publishedmarine mammal radiocarbon dates from Arctic North America, wehere provide newd13C andDR values for bowhead (B mysticetus)and beluga (D leucas), andd13C values for walrus (O rosmarus).These values are based on both live-harvested (known age) mate-rials (walrus, beluga), and co-occurring driftwood and bowheadwhale subfossils The assembled database (Table S1) includes 809marine mammal dates from the CAA, expanding previous compi-lations and enabling direct comparison with other marine andterrestrial data reported in terrestrial14C, calibrated, and siderealyears We use this new dataset to perform a spatio-temporalanalysis of subfossil B mysticetus occurrence as a presumed func-tion of Holocene sea-ice variability, with valuable implications formarine mammal palaeoecology This approach permits compari-sons with previous cetacean-based reconstructions and emergingalternative marine proxies, and allows the critical re-evaluation ofmarine mammals as sea-ice indicators

2 Biology, ecology, and taphonomy of whales and walrus

Most arctic marine mammals are poorly represented in the lateQuaternary CAA, though bowhead and walrus are notable excep-tions Proportionally, bowheads represent the largest subfossilcomponent (>600), with lesser walrus (<100) and rare beluga andnarwhal (collectively<25;Table S1) Essential to the calculation ofsea mammald13C andDR, and central to any discussion regardingtheir palaeoecology and use as palaeoenvironmental proxies, is anunderstanding of their biology, ecology, mortality, and taphonomy.Below, we review these factors for the main indicator species

2.1 Balaena mysticetus Linnaeus 1758 (bowhead, Greenland right,

or Arctic right whale)

The only endemic Arctic baleen whale, B mysticetus (20 mlength, 60e100 tons;Reeves et al., 1983; Nerini et al., 1984), feeds

on crustacean zooplankton (copepods, euphausiids), though dietand dietary behaviour vary seasonally and spatially (Carroll et al.,1987; Lowry, 1993; Laidre et al., 2008), with feeding likely mini-mized during winter (Carroll et al., 1987; Würsig and Clark, 1993)

Of thefive extant stocks, all reduced by historic whaling (Woodbyand Botkin, 1993; Reilly et al., 2012), the Bering-Chukchi-Beaufortstock is the largest (w10,500; George et al., 2004), with lesserpopulations (each350) found in the Sea of Okhotsk, Davis Strait(Davis Strait/Baffin Bay/CAA), Hudson Bay (Hudson Strait/HudsonBay/Foxe Basin) and Svalbard-Barents Sea (Boertmann et al., 2009;Reilly et al., 2012) Some Atlantic-Pacific gene flow is suggestedduring the Holocene (Borge et al., 2007; McLeod et al., 2012) andrecently via the Northwest Passage (Heide-Jørgensen et al., 2011), aregion previously thought to isolate Beaufort Sea and Baffin Baywhales (Harington, 1966; Dyke et al., 1996a)

Their apparent association with the seasonal sea-ice margin(Vibe, 1967; Fredén, 1975; Salvigsen, 1978; Reeves et al., 1983) un-derpins the use of dated bowheads for CAA summer pack-ice re-constructions (Dyke and Morris, 1990; Dyke et al., 1996a; Dyke andSavelle, 2001; Dyke and England, 2003) Such association broadlyholds true with whales on Paciﬁc and Atlantic CAA marginsmigrating seasonally with pack-ice ﬂuctuations (Carroll andSmithhisler, 1980; Reeves et al., 1983) Nevertheless, the relation-ship between bowheads and sea-ice is complex, ice thickness andcover preferences changing seasonally (Reeves et al., 1983; Mate

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et al., 2000; Bogoslovskaya, 2003; Laidre et al., 2008) Whales

overwintering in Hudson Strait/northern Hudson Bay closely

associate with the ice marginal zone, occurring within 300 km of

maximum sea-ice extent and preferring 35e65% ice cover, whereas

ice edge and polynya environments are chosen in late spring

(Reeves and Heide-Jørgensen, 1996; Bogoslovskaya, 2003; Koski

et al., 2006; Ferguson et al., 2010) During summer and autumn,

when NW Atlantic stock ranges extend into the CAA (Foxe Basin,

Cumberland Sound, Lancaster Sound, Gulf of Boothia, Prince Regent

Inlet, Fig 1;Moore and Reeves, 1993), bowheads dwell in open

water to heavy ice cover (max.>95%, annual and multi-year ice;

Moore et al., 2000; Ferguson et al., 2010)

Bowheads are exceptionally long-lived (w200 years), have slow

growth and sexual maturation (females: 15 years, 12.5e14.0 m

length), and low reproduction rates (Koski et al., 1993; Philo et al.,

1993; George et al., 1999), with senescence considered the primary

mortality factor (Philo et al., 1993) Their close afﬁliation with

sea-ice is likely due to predator avoidance (primarily Orcinus orca;Ford

and Reeves, 2008) coupled with food availability (George et al.,

1994; Finley, 2001) Mortality due to ice entrapment has been

documented, and carcasses have been observed frozen in sea-ice

(Tomilin, 1957; Marquette and Bockstoce, 1980; Bogoslovskaya

et al., 1982; Mitchell and Reeves, 1982) During entrapment,

whales typically drown due to exhaustion (Laidre pers com., 2012),

though they can break>20 cm thick ice (Carroll and Smithhisler,

1980; George et al., 1989; Philo et al., 1993; Würsig and Clark,

1993) The degree to which ice entrapment represents a signicant mortality cause in modern or Holocene populations is un-known (Philo et al., 1993) However, subfossil length distributionsfrom Admiralty Inlet, Bafﬁn Island, resemble modern populations,suggesting random, not size-selective mortality (Savelle et al.,

fi-2000) consistent with frequent and climate-dependent sea-iceentrapment throughout this 8000 year record It is unclear whetherdocumented Arctic strandings occurred live or post-mortem, ascarcasses canfloat for days to weeks (cf.Schäfer, 1972; Marquette,1978; Marquette and Bockstoce, 1980; Bogoslovskaya et al., 1982;Finley, 2001), potentially drifting significant distances with sur-face currents or freezing into, and being carried by, sea-ice Thoughcarcasses frequently ground intertidally, as many as 50% of datedCAA fossils occur well below their contemporaneous isostaticallyraised shorelines (“sinkers”;Dyke and Morris, 1990) Arctic climateand permafrost, coupled with the large bowhead size (cf.Schäfer,

1972; cf.Espinoza et al., 1998) favours post mortem skeletal ervation, despite scavenging (Chesemore, 1968; Bentzen et al.,

pres-2007)

2.2 Delphinapterus leucas (Pallas 1776) (beluga, belukha, or whitewhale) and Monodon monoceros Linnaeus 1758 (narwhal)Beluga and narwhal are medium-sized (3e5 m length, 1500e

1900 kg) toothed whales, which inhabit sea-ice covered Arctic tosub-Arctic waters (Laidre et al., 2008), occur in pods of tens to

(1996), Bogoslovskaya (2003), Koski et al (2006) , and Ferguson et al (2010) Abbreviations used in the map are: Adm In ¼ Admiralty Inlet; A.R Is ¼ Amund Ringnes Island; Cam Is ¼ Cameron Is.; Cor Is ¼ Cornwallis Island; Eg Is ¼ Eglinton Island; E.R Is ¼ Ellef Ringnes Island; Grin Pen ¼ Grinnell Peninsula; Norw B ¼ Norwegian Bay; Stef.

Is ¼ Stefansson Island; Well Ch ¼ Wellington Channel.

M.F.A Furze et al / Quaternary Science Reviews 91 (2014) 218e241 220

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hundreds (COSEWIC, 2004a, 2004b), and may interbreed (sexual

maturity atw6 and w5e8 years, respectively;Heide-Jørgensen and

Reeves, 1993; COSEWIC, 2004a, 2004b; Heide-Jørgensen and

Laidre, 2006) Whereas adult beluga have 34e38 teeth (Tomilin,

1957), narwhal possess merely two upper canines, one of which

develops into a prominent (2e3 m) tusk in most males (Best, 1981)

Beluga teeth grow in dentine growth layer groups (GLGs) deposited

as one layer per year (Stewart et al., 2006; earlier studies suggested

two annual GLGs,Goren et al., 1987; Heide-Jørgensen et al., 1994)

The beluga diet, though largely based on Arctic (Boreogadus saida)

and polar cod (Arctogadus glacialis), varies with region, ice

condi-tions, and season (Bluhm and Gradinger, 2008) Narwhal feeding,

which relies onﬁsh (A glacialis; B saida; Greenland halibut

Rein-hardtius hippoglossoides) and squid (Gonatus fabricii), may be

maximized during winter (Laidre et al., 2003; Laidre and

Heide-Jørgensen, 2005; Bluhm and Gradinger, 2008)

Both cetaceans undertake extensive seasonal migrations and

exhibit high site ﬁdelity (Heide-Jørgensen et al., 2003a, 2003c;

Luque and Ferguson, 2010) Beluga pods migrate seasonally

be-tween summering (coastal estuaries, rivers, bays) and wintering

grounds (offshore, pack-ice-covered areas;Loseto et al., 2006) The

total beluga population (w150,000) is distributed in several stocks

which may overlap seasonally and interbreed (cf.Suydam et al.,

2001) Canadian stocks comprise the St Lawrence River (w1000

animals); Beaufort Sea (Alaska-Canada, w39,000); Ungava Bay

(size unknown); eastern Hudson Bay (w2000e3000), western

Hudson Bay (23,000); Cumberland Sound (1500); and eastern High

Arctic-Bafﬁn Bay (w21,000;Laidre et al., 2000; Innes et al., 2002;

COSEWIC, 2004a; Jefferson et al., 2012a) The latter population

migrates between wintering grounds in West Greenland (Disko

Island-Maniitsoq) and CAA summering grounds (Prince Regent

Inlet/Peel Sound estuaries; Innes et al., 2002; Heide-Jørgensen

et al., 2003c), though w7900 animals overwinter in the North

Water Polynya (cf.Innes et al., 2002; Heide-Jørgensen et al., 2003c)

and some individuals likely overwinter in CAA shore leads

(Lan-caster Sound, Jones Sound; Heide-Jørgensen et al., 2002) rather

than travelling to Greenland Narwhal (total populationw80,000)

inhabit eastern Arctic Canada, Greenland, Russia, Svalbard and Jan

Mayen (Gjertz, 1991; COSEWIC, 2004b; Jefferson et al., 2012b) They

prefer heavily ice-covered offshore waters during winter (Bafﬁn

Bay;Heide-Jørgensen et al., 2003a; Laidre et al., 2004), while the

primary Canadian summering ground is the CAA (w50,000e

70,000 animals; Peel Sound, Prince Regent Inlet/Gulf of Boothia,

Admiralty Inlet, Eclipse Sound;Innes et al., 2002)

Both species are relatively long-lived (30e50 years), and

indi-vidual beluga as old 77 years have been reported (Harwood et al.,

2002; Luque and Ferguson, 2010) Aside from senescence and

hunting, mortality factors include predation (orca, polar bear),

pathogens (Kenyon and Kenyon, 1977; Fay, 1978; Nielsen et al.,

2001), and ice entrapment (Siegstad and Heide-Jørgensen, 1994;

Suydam et al., 2001; Heide-Jørgensen et al., 2002), although both

species are capable of breaking thin ice (Porsild, 1922; Siegstad and

Heide-Jørgensen, 1994) Ice entrapment and stranding may

pro-mote predation by polar bears (Smith and Sjare, 1990;

Heide-Jørgensen et al., 2002) Like bowheads, beluga and narwhal

car-cassesﬂoat and drift with currents (Martineau et al., 2002) and can

be frozen into sea-ice (Porsild, 1922)

2.3 Odobenus rosmarus (Linnaeus 1758) (walrus)

Walrus are tusked, gregarious pinnipeds (Atlantic regions: max

w3.2 m length, 1100 kg) that inhabit Arctic continental shelves

year-round (COSEWIC, 2006) They are restricted by their shallow

diving abilities (80 m depth), using mobile sea-ice for resting and

breeding, and swimming between land and sea-ice haul outs (Fay,

1982; Gjertz et al., 2001; Schreer et al., 2001) During winter toearly spring, they occupy pack-ice interspersed with leads andpolynyas In summer, females and juveniles stay within pack-icewhile males occupy coastal sites (Fay, 1985; Ray et al., 2006).Walrus primarily feed on bivalves (Mya truncata, Hiatella arctica,Serripes groenlandicus; Shefﬁeld et al., 2001; Born et al., 2003)though occasionally they feed on seabirds (Mallory et al., 2004),seals (Lowry and Fay, 1984),ﬁsh, and whales (Fay, 1985) Whetherthis represents aberrant behaviour or opportunism remainsdebated

The two recognized subspecies, O rosmarus rosmarus (easternCanadian Arctic, Greenland, Svalbard, western Russian Arctic) and

O rosmarus divergens (Bering-Chukchi seas, coastal Alaska, WrangelIsland, Beaufort Sea;Fay, 1985; Knutsen and Born, 1994; Wiig andGjertz, 1996) are presumed separated by central CAA multi-yearsea-ice (Harington, 1966), despite some evidence of Holocene ge-netic exchange (Andersen et al., 1998) The modern population,much decimated by harvesting (pre-1931; Born et al., 1995), ishighest in the Paciﬁc (w200,000 animals;Ray et al., 2006) ExtantCanadian Atlantic stocks are found in south and east Hudson Bay(500? walrus), northern Hudson Bay-Davis Strait (6000), Foxe Basin(5500), and Bafﬁn Bay (1500;Born et al., 1995; COSEWIC, 2006).The walrus life span isw30 years (COSEWIC, 2006); mortalityfactors include senescence, predation (polar bear, orca;Calvert andStirling, 1990), pathogens (Fay, 1978; Nielsen et al., 2001; Serhir

et al., 2001), and violent death by other walrus at haul-out sites(Loughrey, 1959; Fay and Kelly, 1980) Mass mortality has beenattributed to exhaustion from sustained open sea exposure due tosea-ice loss (Fischbach et al., 2009) Walrus can break ice (20 cmthickness) with their tusks or skull (underwater), and can alsotravel (6 km) over ice or land to ﬁnd open water though this putsthem at risk of predation, starvation, freezing, and disorientation(Richard and Campbell, 1988; Calvert and Stirling, 1990) Deadwalrus landward of their contemporaneous shorelines, resultingfrom either anomalous behaviour or disorientation, are docu-mented from the CAA (Thorsteinsson, 1958; Dyke, 1979; Dyke et al.,

1999), Svalbard (Lauritsen et al., 1980), Russia (Perﬁl’ev, 1970), andthe Champlain Sea (Grant, 1989; Harington et al., 1993), similar topinnipeds from modern Antarctic settings (Stirling and Kooyman,1971; Banks et al., 2010)

If dying offshore, walrus typically undergo “bloat and float”(floating, sinking, floating with decomposition gas build-up;

Schäfer, 1972; Espinoza et al., 1998); carcassesﬂoat for weeks tomonths with surface currents before beaching (on ice-free coasts),potentially travelling 100’s of kilometres (Fay, 1978) Upon beaching

of cadavers, or where death occurs at shoreline haul-outs, physicaland chemical processes (sea-ice, waves) disarticulate and scatterbones (Espinoza et al., 1998; Dyke et al., 1999) Most common Ho-locene walrus remains are isolated tusks, crania, and mandibles.Individuals that die inland experience lesser post mortem disartic-ulation and bone scattering compared to littoral carcasses and areoverrepresented in the Holocene record (Dyke et al., 1999) Asidefrom shoreline mortality and carcass stranding (at sea-level), andlandward crawling (above sea-level), signiﬁcant numbers of CAAHolocene walrus are offshore sinkers, complicating their use as sea-level indicators (Dyke et al., 1999)

3 DR derivation and calibration of radiocarbon dates3.1 Marine mammal samples and database construction

We conducted a comprehensive literature search of marinemammal radiocarbon dates from Arctic Canada and northwestGreenland (Table S1) The primary sources of bowhead data are GSCpublications (e.g., Dyke and Morris, 1990; Dyke et al., 1996b)

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Walrus dates were primarily compiled fromDyke et al (1999)and

archaeological references therein Data from live-collected beluga

are fromStewart et al (2006)and Campana (pers comm 2012)

Narwhal dates are predominantly from GSC surﬁcial geology maps

(e.g.,Dyke and Hooper, 2000) Remaining dates (seal) are chieﬂy

from the archaeological literature (e.g.,Morrison, 1989, and

refer-ences therein) All data were cross-referenced with Harington

(2003) and the Canadian Archaeological Radiocarbon Database

(Morlan, 2005), which provided additional information (e.g.,

co-ordinates, material) not reported in the original publications

Original sources are given for each date inTable S1 Our compiled

database encompasses 651 bowhead whale (on 609 individuals),

103 walrus (98 individuals), 21 narwhal (21 individuals), 33 seal (31

individuals), and one beluga dates

3.2 Marine mammald13C

For calculation of averaged13C values, considered representative

of a species, only dated specimens with measured d13C were

selected and samples considered non-ﬁnite were excluded Our

selection encompasses bone collagen measurements from 193

bowhead and 9 walrus samples (Tables 1andS1) Additionally, 18

d13C measurements on walrus tusks and teeth (primarily collagen)

are available For beluga, 44 measuredd13C values on dentine are

available (Stewart et al., 2006) Arithmetic averages ofd13C were

calculated based on available data for each group (Table 1) For

bowhead bone collagen, the standard deviation of the average was

calculated assuming data were representative for the entire

pop-ulation using Equation (1) The small sample size of all other

groups, requires the assumption that only a subset of the

popula-tion is represented, as per Equapopula-tion(2)

afterWard and Wilson (1978)

For both equations,sis the pooled standard deviation, x is the

measuredd13C, x is the averaged13C value, and n is the number of

d13C measurements

The resulting averaged13C values are reported inTable 1 Of the

total 628 bowhead collagen dates, 193 dates have measured and

recordedd13C values and 378 dates were formerly non-normalized

due to lack of measuredd13C and could not previously be directly

compared with conventional radiocarbon dates Using our newd13C

values, we report all our dates (Table S1) as conventional

radio-carbon dates (normalized tod13C¼ 25&;Donahue et al., 1990;

Reimer et al., 2004; spreadsheet available athttp://intcal.qub.ac

uk/calib/fractionation.html,Stuiver et al., 2013)

3.3 DR calculation

3.3.1 Bowheads

Dyke et al (1996b)compared driftwood and whale bone datesfrom the same raised shorelines to estimate bowhead R for the CAA,assuming contemporaneity of both materials In addition to thesedata, we use driftwood dates byBlake (1975), Dyke (1998, 2000),Dyke and Savelle (2009), andDyke et al (2011) We calculate andreport onlyDR; more appropriate for calibration than R and subject

to lesser temporal variability (Stuiver et al., 1986; Coulthard et al.,

2010) ApparentDR of accordant bone and driftwood samples iscalculated using the following procedure:

1 Calibration of driftwood date into calibrated years (Calib 6.0,

Stuiver et al., 2013)

2 Identiﬁcation of the global ocean modelled radiocarbon agecontemporaneous with the calibrated driftwood date (equiva-lent Marine09 age in14C years;Table 2) from the Marine09(Reimer et al., 2009) spreadsheet (www.radiocarbon.org/IntCal09%20ﬁles/marine09.14c)

3 Subtraction of conventional whale bone age (in14C years) fromthe equivalent Marine09 age (in 14C years) to determineapparentDR

Aside from accordant boneedriftwood pairs, many sites havethese materials elevationally separated by a small amount (typi-cally3 m) In such cases, apparentDR may still be determined bycorrecting the bone date for the elevation-equivalent age differenceusing published relative sea-level curves (e.g.,Blake, 1975; Dyke

et al., 1991, 2011; Dyke, 1998) prior to calculating DR (Step 3.)sensuDyke et al (1996b)

In calculating apparent DR, the following assumptions aremade:

i To aﬁrst approximation, whales and trees (e.g., Picea, Pinus,Larix) have similar life spans (Viereck and Johnston, 1990;George et al., 1999) Therefore, whale boneedriftwood pairsare assumed to haveﬁxed their carbon at approximately thesame time

ii Whale bone and driftwood record the age of the shorelinefrom which they are collected

iii All whale bone in our comparisons is assumed to belong to asingle population that can be described by a singleDR value.Whereas signiﬁcant differences may exist between individual

DR values for whales from the western (Beaufort Sea/Paciﬁc)and eastern (Bafﬁn Bay/Atlantic) populations, all driftwoodewhale pairs are most likely from eastern whale stocks giventheir geographic distribution (Harington, 1966; Dyke et al.,1996a)

iv Once apparent DR values are calculated, sample pairs thatcontradict Assumption ii are identiﬁed As the Eastern CAAbowhead population lives in Arctic Canada and Bafﬁn Baywaters throughout the year (Heide-Jørgensen et al., 2003b;Boertmann et al., 2009), bounding whaleDR values can beassumed by adopting the regional maximum and minimum

DR values for marine organisms in equilibrium with seawaterbicarbonate (molluscs;Coulthard et al., 2010) These valuesare 335 8514C years for the NW CAA (Coulthard et al., 2010)and 10 80 14C years for eastern Bafﬁn Bay (WestGreenland,Table S2; McNeely et al., 2006) Therefore onlycomparisons yielding an apparentDR between10 and 335

14C years are considered valid As whales migrate withinthese regions, we apply this assumption only for easternCanadian Arctic subfossils, but not for western Arctic/Beau-fort Sea bowheads.DR values outside the accepted range have

Table 1

Archipelago Originald13 C values are included in Table S1

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Bowheadedriftwood pairs used to derive individual values of apparentDR.

Locality a Wood

lab code b

14 C age wood

14 C yrs BP

Calibrated wood age cal yrs BP

Equivalent marine09 c age

14 C yrs BP

Whale lab code b,d

14 C age whale

14 C yrs BP

Wood elevation m

Whale elevation m

Elevation diff.

m

Emergence rate m/ka

Whale age correction

Corrected whale age

14 C yrs BP

ApparentDR

14 C yrs

Reference (dates and emergence rates)

Valid?

Russell Island GSC-4002 3820 35 4214 4140 26 S-2662 3822 111 14.7 14.6 0.1 4 Add 25 yrs for

0.1m of emergence

3847 111 293 114 Dyke et al.

1991 ; 1996 Russell Island GSC-2240 3630 30 3942 3950 27 S-2662 3822 111 14.3 14.6 0.3 4 Subtract 75

yrs for 0.3m

of emergence

3747 111 203 114 Dyke et al.

1991 ; 1996 Cape Richard

Collinson

GSC-4387 4070 30 4558 4410 26 S-2919 4697 92 17.25 16.5 0.75 5 Add 150 yrs

for 0.75m of emergence

4847 92 437 95 Dyke et al.

1991 ; 1996 Cape Richard

Collinson

GSC-4343 8680 45 9627 8979 28 S-2964 8702 166 59 57 2 29 Add 69 yrs for

2 m of emergence

8771 166 208 168 Dyke et al.

1991 ; 1996 Hollist Point GSC-3962 3660 30 3984 3995 26 S-2589 4302 101 12 12 0 N/A 4302 101 307 105 Dyke et al.

1991 ; 1996

Hollist Point GSC-3936 8230 55 9200 8544 30 S-2588 9022 136 58.5 58 0.5 29.41 Add 17 yrs for

0.5 m of emergence

9039 136 495 139 Dyke et al.

1991 ; 1996

Prescott Island GSC-4503 3470 35 3751 3803 26 S-2921 3462 77 11 9 2 4 Add 500 yrs

for 2 m of emergence

3975 77 172 81 Dyke et al.

1996

Guillemard Bay GSC-3989 4400 70 4965 4737 26 S-2861 4652 87 16 18 2 6 Subtract 328

yrs for 2 m of emergence

4324 87 413 90 Dyke et al.

1991 ; 1996

Guillemard Bay GSC-3989 4400 70 4965 4737 26 S-2600 5017 97 16 17 1 6 Subtract 164

4853 96 116 100 Dyke et al.

1991 ; 1996

Foss Fiord GSC-5077 4680 40 5404 5031 25 S-3345 5257 92 36.5 37.5 1 10 Subtract 100

5160 92 129 95 Dyke et al.

1996

Easter Cape GSC-239 940 65 849 1294 25 S-3099 1257 62 3 4 1 3.51 Subtract 285

972 62 322 67 Dyke et al.

1996 Lavoie Point GSC-5428 4170 30 4715 4504 26 S-3427 4057 141 9 8.5 0.5 3.07 Subtract 165

yrs for 0.5 m

of emergence

3892 141 612 143 Dyke et al.

1996 Lavoie Point GSC-5428 4170 30 4715 4504 26 S-3414 4077 131 9 9.25 0.25 3.07 Subtract 81

yrs for 0.25m

of emergence

3996 131 508 134 Dyke et al.

1996; Dyke 2000

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Table 2 (continued )

Locality a Wood

lab code b

14 C age wood

14 C yrs BP

Whale lab code b,d

14 C age whale

14 C yrs BP

Wood elevation m

Whale elevation m

Elevation diff.

m

Emergence rate m/ka

Corrected whale age

14 C yrs BP

ApparentDR

14 C yrs

3567 160 170 162 Dyke et al.

1996

Owen Point GSC-5771 3750 40 4111 4074 25 S-3528 3510 150 16 15 1 4.51 Add 222 yrs

3747 150 327 152 Dyke et al.

1996; Dyke 1998

Owen Point GSC-5810 3350 80 3590 3681 26 S-3528 3510 150 15 15 0 N/A 3510 150 171 152 Dyke et al.

1996; Dyke 1998

Owen Point GSC-5815 1400 25 1309 1778 26 S-3529 2175 140 9.25 9.5 0.25 3.52 Subtract

71yrs for 0.25m of emergence

2104 140 326 142 Dyke 1998

Porden Point GSC-5782 3800 80 4192 4130 26 S-3532 3955 150 20 18 2 4.73 Add 423 yrs

4378 150 248 152 Dyke et al.

1996; Dyke 1998

Porden Point GSC-5786 3740 30 4097 4071 26 S-3532 3955 150 17.5 18 0.5 4.73 Subtract 106

yrs for 0.5 m

of emergence

3854 150 217 152 Dyke et al.

1996; Dyke 1998

Porden Point GSC-5847 2280 30 2313 2621 26 S-3533 2820 150 13.5 13 0.5 4.73 Add 106 yrs

for 0.5 m of emergence

2926 150 305 152 Dyke et al.

1996; Dyke 1998

yrs for 1.25 m

of emergence

2556 150 16 152 Dyke et al.

1996; Dyke 1998

Porden Point GSC-5812 2060 30 2029 2398 26 S-3534 2110 170 9 8 1 3.95 Add 253 yrs

2363 170 35 172 Dyke et al.

1996; Dyke 1998

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Porden Point GSC-5846 1850 30 1785 2178 27 S-3534 2110 170 8 8 0 N/A 2110 170 68 172 Dyke et al.

1996; Dyke 1998

Porden Point GSC-5816 690 25 661 1109 26 S-3536 1080 150 2.5 2.8 0.3 3.95 Subtract 76

yrs for 0.3m

of emergence

1004 150 105 152 Dyke et al.

1996; Dyke 1998

yrs for 0.5 m

of emergence

1298 140 189 142 Dyke et al.

1996; Dyke 1998

yrs for 0.75m

of emergence

3076 150 454 152 Dyke et al.

1996, Dyke 1998

Bere Bay GSC-5805 2090 30 2062 2424 26 S-3537 2725 200 8 10.5 2.5 3.83 Subtract 653

yrs for 2.5 m

of emergence

2072 200 352 202 Dyke et al.

1996 Point Refuge GSC-1952 3070 35 3295 3401 27 S-3564 3320 150 16.5 16.5 0 N/A 3320 150 81 152 Dyke et al.

1996; Dyke 1998

Triton Bay GSC-5952 1760 35 1666 2076 27 S-3568 2260 200 7.25 7 0.25 2.14 Add 117 yrs

for 0.25m of emergence

2377 200 301 202 Dyke et al.

1996; Dyke 1998

Lovell Point GSC-5861 7780 40 8559 8099 27 S-3598 7850 180 41 40 1 12.82 Add 78 yrs for

1 m of emergence

7928 180 171 182 Dyke et al.

1996; Dyke 1998

Cape Storm GSC-839 4390 30 4945 4715 26 GSC-1021-2 4580 30 17.5 16.5 1 6.59 Add 154 yrs

Cape Storm GSC-1545 6540 130 7442 6946 27 GSC-1498-1 7260 40 38 38 0 N/A 7260 80 314 84 Blake 1975

Murray Bay UCIAMS-42168 6195 20 7081 6550 27

UCIAMS-43982

7115 20 33.5 34.5 1 11.96 Subtract 84

yrs for 1m of emergence

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Locality a Wood

lab code b

14 C age wood

14 C yrs BP

Whale lab code b,d

14 C age whale

14 C yrs BP

Wood elevation m

Whale elevation m

Elevation diff.

m

Emergence rate m/ka

Corrected whale age

14 C yrs BP

ApparentDR

14 C yrs

Trang 10

likely been affected by complicating factors including: depositional up/down slope remobilization (wood, whalebone); shallow water stranding (bone); deep-water sinking(bone;Dyke et al., 1996b).

post-Once apparent individual whaleDR values (DRI) are calculatedand screened, an error-weighted mean (DRR) can be calculatedusing equations (3) to (5), followingCoulthard et al (2010)

Pn

i ¼ 1DRs2IiIi

Pn

i¼ 1s12 Ii

(3)

afterBevington (1969)

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi1

Pn

i¼ 1s12 Ii

vu

afterBevington (1969)

For Equations(3)e(5),sIis the standard deviation forDRI, spooled

is the standard deviation of the mean, andsRis the square root ofthe weighted average variance The larger of spooled or sR isconsidered the standard deviation of for DRR The internal vari-ability of the data is described byc2values

3.3.2 BelugaBelugaDR values are based on 12 radiocarbon dates on dentinefrom four live-harvested whales (Stewart et al., 2006; Campana,pers com 2012; Table 3) Sclerochronology permits radiocarbondating of individual, annual GLGs of known age, back-calculatedfrom the date of harvesting All used GLG radiocarbon dates pre-date 1955 and are thus unaffected by bomb radiocarbon

Following Coulthard et al (2010), Equation (6) is used tocalculate individual dentine DRI, where individual 14C ages areassigned to the midpoint of the dated GLGs and the global averagemarine reservoir age (Marine09age) for that year is determined from

Reimer et al (2009) Equations(3)e(5)are then used to calculatebelugaDR

afterStuiver et al (1986)

3.3.3 WalrusThe possibility of walrus and driftwood stranding on the sameraised shoreline is less likely than for bowheads Walrus have beenknown to die well inland above contemporaneous sea-level(“crawlers”; Richard and Campbell, 1988; Calvert and Stirling,1990; Dyke et al., 1999) The only two available direct walrus-driftwood comparisons (Dyke et al., 1996b) indicate an apparentnegativeDR, i.e their ocean reservoir age is less than that of theglobal ocean - highly unlikely in the CAA given the restrictedventilation and the regional molluscan DR (335 85 years;

Coulthard et al., 2010) A single live-collected (AD 1915) carbon dated walrus bone (K-347; 590 5014C years;Tauber, 1979;

radio-Table S1) from Thule, Greenland, produced an apparent DR of

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125 5514C years (assuming 30 year life span and bone collagen

carbonﬁxing on sexual maturity at age w5) The original date was

re-calculated byOlsson (1980)as 645 5014C years, yielding an

apparentDR of 180 5514C years Both values seem excessive given

theDRRof west Greenland molluscs (10 8014C years;Table S2;

McNeely et al., 2006) As Thule is located at the transition between

West Greenland waters and Arctic Ocean waters, this single sample

may not be diagnostic of either region or may be otherwise

incor-rect As no other data are available (locally or regionally), we

strongly discourage the use of this or any other single measurement

as the basis for regionalDR (DRR) as this may lead to inaccurate

chronologies (cf.Coulthard et al., 2010)

3.4 d13C andDR results

Results ofd13C andDR calculations are tabulated inTables 1 and

4, respectively Bowhead bone collagen produces an averaged13C

value of16.1 1.1& (n ¼ 193) Walrus teeth and tusks yield an

averaged13C value of14.8 1.9& (n ¼ 18), whereas walrus bone

collagen shows an averaged13C value of18.0 4.7& (n ¼ 9) For

live-harvested beluga from SE Bafﬁn Island, 44d13C dentine

mea-surements yield an average of14.4 0.5& Insufﬁcient data and

uncertain data quality preclude the calculation of reliabled13C and

DR values for other groups (seal, narwhal;Table S1)

DR values (Table 4) are 170 9514C years for bowheads (n¼ 23)

and 240 6014C years for beluga (n¼ 12) Notably, bowheadDRR

would be 175 36014C years (n¼ 57) if the data had not been

screened As this average is nearly identical, our screening

proce-dure appears justiﬁed Importantly, whereas beluga were sampled

from a single restricted area (SE Bafﬁn Island), bowheadedriftwood

pairs were collected over a much larger geographic region,

encompassing much of the central and eastern CAA

For western CAA bowheads (Amundsen Gulf, west/southwest

Victoria Island, Prince Patrick and Eglinton islands), ourDR value

should be considered a minimum because Beaufort Sea whalesoverwinter in the Bering and Chukchi Seas where molluscanDRmay exceed 45014C years (McNeely et al., 2006) We additionallyanalysed six whale boneedriftwood pairs from southwestern Vic-toria Island (Table 5;Dyke and Savelle, 2000b, 2000c, 2003, 2004)which indicate aDR ofw30014C years may be more appropriate forthis region We consider this value to be unacceptably uncertaindue to an insufﬁcient number of sample sites and slow emergencerates If this value is correct, whale dates from the Beaufort Seapopulation calibrated using our (eastern) CAA value woulddecrease byw140 years

4 Spatio-temporal patterns in calibrated bowhead dates4.1 Previous work

The derivation of a CAA bowheadDR value (170 9514C years)permits the calibration of B mysticetus dates in the expandeddatabase (Table S1) and thus permits a new spatio-temporal anal-ysis of bowhead whale subfossil distribution as a presumed func-tion of Holocene sea-ice variability Similar previous analyses (in

14C years;Dyke and Morris, 1990; Dyke et al., 1996a) indicate abimodal distribution in bowhead remains, interpreted as a four-fold palaeoclimatic division characterized by fluctuating boneabundance, and thus sea-ice conditions centred on M’ClintockChannel and Viscount Melville Sound (Fig 1) Highly abundantremains from the immediate deglacial (8.514C ka BP) are attrib-uted to limited sea-ice due to high-volume meltwater export.Critically, the M’Clintock Channel/Viscount Melville Sound plug ofmulti-year sea-ice, thought to isolate Pacific and Atlantic stocks(Harington, 1966), is considered absent Central CAA bowheads atthis time are assumed to be of Pacific stock, Atlantic whales beingexcluded by a still-glaciated eastern Parry Channel (Dyke et al.,1996a) The rapid decline in remains at w8.5e5 14C ka BP is

a Estimated standard error is the pooled mean error multiplied by the square root of n, where n is the number of samples;smeas ¼ s pooled *On.

b External variance is found by subtracting measurement variance from total population variance;sext ¼ O(s 2

pop s2 meas ).

c Uncertainty includes external variance; s total ¼ O(s 2

pooled þs2 ext ).

d s max ¼ highest of s pooled , s total orsR

b Marine09 values are from, and interpolated from Reimer et al (2009)

Trang 12

interpreted as an exclusion of whales due to the establishment ofHolocene oceanography, resulting in multi-year sea-ice accumula-tion in southern M’Clintock Channel and Gulf of Boothia.

A mid-Holocene resurgence in bowhead subfossils is inferred tosignal climatic amelioration and a diminished M’Clintock ice plug.Admiralty Inlet shows an unprecedented subfossil peak at 4e3.514C ka BP, interpreted as high-density summer bowhead occu-pation Notably, this fjord system remains connected to southernPrince Regent Inlet via Bernier Bay and Berlinguet Inlet untilw214C ka BP (Hooper, 1996) due to isostatic depression Subsequent(<3.014C ka BP) low bone frequencies are attributed to a Neoglacialre-expansion of the M’Clintock ice plug (Dyke et al., 1996a), thoughBelcher and Wellington channel records are less clear Navy BoardInlet and Eclipse Sound exhibit pronounced abundance peaks (2.7e2.514C ka BP) during this“reduced whale” interval

Late-Holocene bowheads (n ¼ 9; <2.5 14C ka BP) on northDevon, western Ellesmere, and Axel Heiberg islands (Fig 1) areascribed to polynya development due to isostatically-drivenshoaling of inter-island sills (Dyke and England, 2003), implyingprevious exclusion of whales by pervasive sea-ice Dyke andEngland (2003)attribute the contradiction with declining mid- tolate-Holocene bowhead subfossils in the central CAA (Dyke et al.,1996a) to regional climate variations In Amundsen Gulf, sub-fossils are absent during deglaciation (w11.114C ka BP;Dyke andSavelle, 2000a, 2000b, 2001), but abundant later at 10.2e8.5

14C ka BP.Dyke and Savelle (2001)assign this pattern to tion prior to the opening of Bering Strait and re-entry of Paciﬁcbowheads thereafter Remains are scarce throughout the later Ho-locene, increasing only after 1.514C ka BP.Crockford and Frederick(2007)suggest Neoglacial conditions in the Bering Sea block BeringStrait with sea-ice between 4.7 and 2.514C ka BP, excluding Paciﬁcbowheads from the Arctic Ocean

deglacia-Individual occurrences north of assumed modern ranges are ofnote.Evans (1989)reports a narwhal tusk (w6.814C ka BP) fromnorthwest Ellesmere Island, interpreted as a 400e700 km north-ward range extension during a period of limited sea-ice A bowhead(w7.514C ka BP) from northern Axel Heiberg Island is attributed tosimilar ameliorated conditions (Bednarski, 1990) Bothﬁnds date to

a period considered by Dyke et al (1996a) as general climatedeterioration and increased sea-ice excluding whales from much ofthe CAA An earlier (w10.414C ka BP) bowhead skull from EllefRingnes Island (Atkinson, 2009) is explained by early deglacialmeltwater-driven sea-ice export permitting the entry of whales, in-keeping with earlier hypotheses (Dyke and Morris, 1990; Dyke

250 cal yr age bins for histogram plotting Where multiple datesexist on the same individual (e.g., GSC-1496;Table S1), we includedonly the oldest available date on bone collagen using a standardshort NaOH treatment (e.g.,Minami et al., 2004), contamination ofyounger dates with recent organic material being considered morelikely (e.g., Dyke, 1980; Dyke and Morris, 1990) Dates deemederroneous based on glaciological and sea-level constraints wereomitted (e.g., TO-316;Table S1)

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