The Bølling‐age Blomvåg Beds, western Norway: · PDF fileThe Bølling-age Blomvag Beds, western Norway: implications for the Older Dryas glacial re-advance and the age of the deglaciation

The Bølling-age Blomv�ag Beds, western Norway: implications for theOlder Dryas glacial re-advance and the age of the deglaciation

JAN MANGERUD, JASON P. BRINER, TOMASZ GOSLAR AND JOHN INGE SVENDSEN

Mangerud, J., Briner, J. P., Goslar, T. & Svendsen, J. I. 2017 (April): The Bølling-age Blomv�ag Beds, westernNorway: implications for the Older Dryas glacial re-advance and the age of the deglaciation. Boreas, Vol. 46,pp. 162–184. 10.1111/bor.12208. ISSN 0300-9483.

Blomv�ag, on the western coast of Norway north of Bergen, is a classical site in Norwegian Quaternary science.Foreshore marine sediments, named the Blomv�ag Beds and now dated to the Bølling-Allerød from 14.8 to13.3 cal. ka BP, contain the richest Lateglacial bone fauna in Norway, numerous mollusc shells, driftwood, andflint that some archaeologists consider as the oldest traces of humans in Norway. The main theme of this paper isthat the Blomv�ag Beds are overlain by a compact diamicton, named the Ulvøy Diamicton, which was interpretedpreviously as a basal till deposited during a glacial re-advance into the ocean during the Older Dryas (c. 14 cal.ka BP). Sediment sections of the Blomv�ag Beds and the Ulvøy Diamicton were exposed in ditches in a cemeterythat was constructed in 1941–42 and have subsequently not been accessible. A number of radiocarbon and cosmo-genic 10Be exposure ages demonstrate that the diamicton is not likely to be a till because minimum deglaciationages (14.8–14.5 cal. ka BP) from the vicinity pre-date the Ulvøy Diamicton. We now consider that sea ice and ice-bergs formed the Ulvøy Diamicton during the Younger Dryas. The Scandinavian Ice Sheet margin was located onthe outermost coastal islands between at least c. 18.5 and 14.8 cal. ka BP; however, no ice-marginal deposits havebeen found offshore from this long period. The Older Dryas ice margin in this area was located slightly inside theYounger Dryas margin, whereas farther south it was located slightly beyond the Younger Dryas margin.

Jan Mangerud ([email protected]) and John Inge Svendsen, Department of Earth Science, University of Bergen,PO Box 7803, Bergen 5020, Norway and Bjerknes Centre for Climate Research, All�egt. 70, 5007, Bergen, Norway;Jason P. Briner, Department of Geology, University at Buffalo, Buffalo, NY 14260, USA; Tomasz Goslar, Faculty ofPhysics, Adam Mickiewicz University, Umultowska 85, Pozna�n 61-614, Poland, and Pozna�n Radiocarbon Labora-tory, Foundation of the A. Mickiewicz University, Rubie_z 46, Pozna�n 61-612, Poland; received 21st June 2016,accepted 23rd August 2016.

It was almost a sensation amongst Norwegian scien-tists when in 1941 numerous bones were un-earthedbelow a compact diamicton, interpreted as a basal till,in the village of Blomv�ag, ~30 km northwest of Bergen(Figs 1, 2; Und�as 1942). Some bones were identified asdeer and some wood as spruce, both suggesting a cli-mate similar to the present and it was thereforethought that the fossils originated from a full inter-glacial – in which case the sediments would have beenthe first interglacial beds found in Norway. The boneswere discovered during digging of drainage ditches fora new cemetery and they became known to scientistswhen the workers to their great surprise dug up largewhale bones ~16 m a.s.l. and 2–3 m below the groundsurface (Fig. 3C). They therefore alerted the BergenMuseum (presently the Bergen University Museum)and the geologist Isak Und�as went out to study thesite. He initiated a scientific excavation that alsoinvolved the botanist Knut Fægri and the geologistAstrid Monsen. Several other scientists visited the siteduring the excavations. It soon became clear that the‘deer’ bones had been misidentified and in factstemmed from reindeer. However, wood that was iden-tified as Alnus, Taxus and Picea still suggested an inter-glacial age (Holtedahl 1953).

When the radiocarbon-dating method became avail-able the subtill sediments, later named the Blomv�agBeds (Mangerud 1977), were dated to about 14.5 cal.

ka BP, i.e. during the Bølling (Table 1; Holtedahl 1960;Nydal 1960). Even though it became clear that thestrata were much younger than previously thought, theinterest in the site did not abate for four main reasons:(i) the radiocarbon ages were hitherto the oldest forthe deglaciation of Norway (Holtedahl 1960), (ii) theinferred till capping the Blomv�ag Beds suggested thatthe site had been overrun by a glacial re-advance dur-ing the Older Dryas (Mangerud 1970; Mangerud et al.2011), (iii) the fossil-bearing Blomv�ag Beds contain therichest Lateglacial fauna found in Norway (Lie 1986;Hufthammer 2001), and (iv) it has been argued thatthe flint pieces and bones represent traces of humanoccupation (Lie 1990; Johansen & Und�as 1992), whichwould be 3000 years older than the earliest well-docu-mented human sites in Norway (Breivik 2014).

Surprisingly enough, a full scientific description ofthe site was never published, only a description in apopular science journal (Und�as 1942). Here, wedescribe the site based on available field notes anddrawings of the strata and a number of new radiocar-bon ages as well as 10Be ages of glacially transportederratics. The main theme of this paper is the interpreta-tion of the Ulvøy Diamicton capping the Blomv�agBeds and the implications for the glacial history ofwestern Norway. Mangerud (1970) produced a pollendiagram, supported by several 14C ages, from an adja-cent palaeolake (Dale Bog, Fig. 2) that showed a full

DOI 10.1111/bor.12208 © 2016 Collegium Boreas. Published by John Wiley & Sons Ltd

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and undisturbed Allerød-Younger Dryas sequence oflacustrine sediments. Thus, it became clear that if theUlvøy Diamicton was a till, it had to pre-date the

Allerød, and as the diamicton overlies Bølling-agesediments, the age of the diamicton and the postu-lated re-advance was bracketed to the Older Dryas.Later, Mangerud (1977) considered the interpretationof the diamicton as a till to be so well founded thathe even named it the Ulvøy Till (Fig. 4), againststratigraphical rules that do not accept genetic con-notations to lithostratigraphical units. We thereforenow re-name this unit the Ulvøy Diamicton. Man-gerud (1977) noticed that several radiocarbon agesfrom other sites that post-date final deglaciationyielded similar ages as the youngest ages from belowthe Ulvøy Diamicton, but this was explained by ashort duration of the glacial re-advance and/or dat-ing uncertainties.

The interpretation that the Ulvøy Diamicton is a till,and thus that the ice sheet overran the site during theOlder Dryas, has been generally accepted, but wasquestioned by Krzywinski & Stabell (1984). The ageconsiderations for the Blomv�ag Beds were changedwhen the archaeologist Elisabeth Eriksen (pers. comm.2008) obtained radiocarbon ages on reindeer and otheranimal bones (also cited in Hufthammer 2001) ofwhich the youngest is 13.3 cal. ka BP (Table 1). Thisyoung age was incompatible with the prevailing viewthat the Ulvøy Diamicton is a basal till dating to theOlder Dryas, because the stratigraphy at the adjacentDale Bog demonstrated that this area had been ice free

Fig. 1. A. Map of southern Norway and the northern North Sea, showing the Last Glacial Maximum (LGM) and Younger Dryas (YD) icelimits (white lines) and general ice-flow directions (arrows). Modified from Mangerud et al. (2013). B. The area around Bergen and Blomøy.The line shows the Herdla Moraine of late Younger Dryas age; dashed where assumed. Other sites mentioned in the text are marked:�A = �Agotnes; Lia = Liat�arnet; B = Bjorøy; H = Hamravatn; S = Storum. Near Bergen, 14.1 marks the site where shell fragments are datedto 14.1 cal. ka BP. [Colour figure can be viewed at www.boreas.dk]

Fig. 2. Blomøy Island showing the locations of Blomv�ag Cemetery,Dale Bog and Sele Bog. The areas where 10Be exposure dating sam-ples were collected are marked with the last digits of sample numbers.Contour interval is 20 m. Some summits are marked with altitudes.Modified from www.norgeskart.no. [Colour figure can be viewed atwww.boreas.dk]

BOREAS The Bølling-age Blomv�ag Beds, W Norway 163

http://www.boreas.dk

http://www.norgeskart.no


since 13.9 cal. ka (Table 2). These new ages triggeredthe present investigations aiming to determine whetherthe Ulvøy Diamicton is a till or not; if the UlvøyDiamicton is a till, then all organic remains below thediamicton must pre-date the age of the final deglacia-tion of the site.

Material

The Blomv�ag site is a cemetery that has been impossi-ble to re-excavate. A number of samples from the exca-vations in 1941–1942 are stored, mainly in open boxes,in the Bergen University Museum. The boxes havepieces of paper with a short description of the strati-graphical position of the sample and we were able torelate some of these descriptions to field notes or draw-ings by scientists who participated in the excavations.The samples have been moved several times, and withthe open boxes we cannot exclude the possibility thatsome have been interchanged, but we do not believethat this will influence our conclusions. Some of thefield notes of Isak Und�as, who was the main geologist,are unfortunately lost, but some notes exist. The fieldnotes of Knut Fægri have been crucial for establishing

the stratigraphical position of the samples. One of us(J.M.) also had long talks in the 1960–70s with bothUnd�as and Fægri about the site. A notebook fromAstrid Karlsen who identified wood samples is alsoavailable. We also use 14C ages from sediment sectionsand cores retrieved from adjacent lake basins with theaim of constraining the timing of the final deglaciationfrom the Blomv�ag area and thus to determine if theUlvøy Diamicton is a till. Finally, we collected a seriesof samples from erratic boulders deposited by theretreating ice sheet for 10Be dating.

Dating methods

Radiocarbon dating

The samples previously obtained from the Blomv�agsite were either dated with the conventional method(T-) at the Trondheim Laboratory, or prepared inTrondheim and measured with an accelerator in Upp-sala (Tua-) (Tables 1, 2). These samples were preparedaccording to standard procedures in Trondheim(Nydal et al. 1972), except one of the whale bone sam-ples (T-1899/1). This sample was prepared with the old

Fig. 3. Photographs from Blomv�ag. A. Oblique air photo of Blomv�ag, view towards north. Note the exposed bedrock almost everywhere.The site where the cemetery was later constructed can be seen as a depression rising slightly towards the north, located to the left of thechurch. Dashed white lines mark the positions of the two drainage ditches and solid white lines the two scientific excavations. PhotographWiderøe, 1932. B. Photograph of the excavation site at Blomv�ag Cemetery; view towards SE. Signs of the main drainage ditch, including heapsof boulders, can be seen along the steep bedrock wall. The people in the left part of the photograph mark the scientific excavations. Pho-tograph Knut Fægri, June 1942. C. Whale bones from the Blomv�ag excavations, dated to about 13.8 cal. ka BP. The scale is 20 cm. [Colourfigure can be viewed at www.boreas.dk]

164 Jan Mangerud et al. BOREAS


Table

1.Rad

iocarbon

datesfrom

theBlomv� a

gCem

eterysite,located

at60.5304°N,4

.878°E

.

Lab.ID

Con

v.14C

age1

�1r

DR

Calibratedages

(IntCal13)B19

50Sa

mpleID

givenwhen

dated

Dated

material

Sediment/

Stratigrap

hyd1

3 CReferences

Com

ments

Median3

68%

confidence

interval

From

ToMidpo

int

Half

rang

e

Dates

from

marinemolluscs

Poz-65

953

1270

070

100

1409

013

985

1418

014

083

98Blomv� ag

2014-7

Three

pieces

ofshells,the

largestbeing

8mm

IntheUlvøy

Diamicton

Museum

box

marked‘From

apo

cket

inthetill

atica.

2m

depth

inthemiddle

ditch,

abou

t4m

from

thecorner.

Und� as19

42’.

014

258

1408

214

406

1424

416

2Po

z-65

879

1292

070

100

1451

514

271

1469

914

485

214

Blomv� ag

2014-6

Thick

piece

ofashell,

prob

ably

Mya

orHiatella

Shortlybelow

theUlvøy

Diamicton

Museum

box

marked‘C

layey

tran

sition

albed

(ca.

20cm

)directlybelowthe

till.

I.Und� as

19-10-41’

T-139

13110

350

100

14860

14191

15350

14770

580

H.H

olteda

hl;

Sample2

Mytilu

sedulis

Nyd

al(196

0)The

repo

rted

age

(1270

014C

years)ha

sabu

ilt-

incorrection

for

marinereservoir

ageof

410years

(Man

gerud

1972

).

T-188

212

840

9010

014

377

1412

714

565

1434

621

9Man

gerud;

Blomv� ag

shells

Mytilu

sedulis

Plant-bearing

bed,

3–4m

depthin

large

cross-ditch

�1.1

Gullik

sen

etal.(19

78)

Man

gerud

(197

7)

The

repo

rted

age

(1243

014C

years)ha

sabu

ilt-

incorrection

for

marinereservoir

ageof

410years.

Poz-65

878

1299

070

100

1467

714

450

1493

014

690

240

Blomv� ag

2014-5

Twoshell

fragments,

thelargestis

a1-cm

piece

ofMytilu

s

Low

ermost

sampleat

the

easternendof

theup

per

(northern)

ditch

Museum

box

marked‘Sam

ple

12.2

95–300

cm’.

K.F

ægrifield

notes14

/6/194

2.

014

915

1477

315

103

1493

816

5

(con

tinu

ed)


Table1.

(con

tinu

ed)

Lab.ID

Con

v.14C

age1

�1r

DR

Calibratedages

(IntCal13)B1950

SampleID

givenwhen

dated

Dated

material

Sediment/

Stratigrap

hyd1

3 CReferences

Com

ments

Median3

68%

confidence

interval

From

ToMidpo

int

Half

rang

e

The

follo

wingsixmollusc

samples

from

‘the

southern

cross-ditch’

aredescribedin

Fægri’sfieldno

tes11

/7/194

2an

dmarkedwithdepths

andthus

therelative

stratigrap

hicalo

rder

shou

ldbe

clear

Poz-65

858

1267

070

100

1405

513

960

1414

414

052

92Blomv� ag

2014-4

Shell

fragments2–

8mm.

Con

tainsat

leaston

eMytilu

s

175–18

0cm

.Justbelowthe

diam

icton

Museum

box

marked

‘Blomv� ag7’.

014

197

1404

014

314

1417

713

7Po

z-65

857

1300

070

100

1470

514

488

1496

314

725

238

Blomv� ag

2014-3

Piece

ofMytilu

sedulis

190–19

5cm

Museum

box

marked

‘Blomv� ag6’.

T-169

712

980

150

100

1430

814

961

1463

432

7Man

gerud;

Blomv� ag4

Fragm

entsof

Mod

iolus

mod

iolus

245–25

0cm

�1.4

Gullik

sen

etal.(19

78)

Man

gerud

(197

7)

Museum

box

marked

‘Blomv� ag4’.T

herepo

rted

age

(1257

014C

years)ha

sabu

ilt-

incorrection

for

marinereservoir

ageof

410years.

Poz-65

855

1302

070

100

1475

814

570

1502

414

797

227

Blomv� ag

2014-2

Piece

ofMytilu

sedulis

260–27

0cm

Museum

box

marked

‘Blomv� ag3’.

T-169

612

980

180

100

1464

514

282

1499

314

637

356

Man

gerud;

Blomv� ag2

Fragm

ents

ofMod

iolus

mod

iolus

295–30

5cm

.Low

ermost

shell-bearing

samplein

this

series

�1.7

Gullik

sen

etal.(19

78)

Man

gerud

(197

7)

Museum

box

marked

‘Blomv� ag2’.T

herepo

rted

age

(1257

014C

years)ha

sabu

ilt-

incorrection

for

marinereservoir

ageof

410years.

Poz-65

854

1302

070

014

972

1483

115

137

1498

415

3Blomv� ag

2014-1

Shell

fragments

2–4mm.

Con

tains

Mytilu

s

295–30

5cm

.Low

ermost

shell-bearing

samplein

this

series

Museum

box

marked

‘Blomv� ag2’,i.e.

samebo

xas

sampleT-169

610

014

758

1457

015

024

1479

722

720

014

515

1427

114

699

1448

521

4

(con

tinu

ed)


Table1.

(con

tinu

ed)

Lab.ID

Con

v.14C

age1

�1r

DR

Calibratedages

(IntCal13)B19

50Sa

mpleID

givenwhen

dated

Dated

material

Sediment/

Stratigrap

hyd1

3 CReferences

Com

ments

Median3

68%

confidence

interval

From

ToMidpo

int

Half

rang

e

Dates

from

wha

lebo

nes,prob

ably

thesameindividu

alof

Balaena

mysticetus,Eng

lish:

Bow

head

wha

le,N

orwegian:

Grønlan

dshv

alT-189

9/1

1255

010

010

013

931

1381

414

049

1393

111

8Man

gerud;

Blomv� a

gwha

le

Bow

head

wha

leMud

dysand

�16.6

Gullik

sen

etal.(19

78)

Man

gerud

(197

7)

Dessolved

inHCl;i.e.the

bone

apatiteisda

ted.

Thispreparation

metho

disno

long

erused.A

geom

ittedfrom

the

discussion

.

T-189

9/2

1236

080

100

1371

913

610

1382

913

719

110

Man

gerud;

Blomv� a

gwha

le

Bow

head

wha

leMud

dysand

�17.4

Gullik

sen

etal.(19

78)

Man

gerud

(197

7)

Prepa

redwiththe

EDTA

metho

d,i.e.the

colla

genis

dated.

Tua

-534

812

465

110

100

1383

813

709

1398

713

848

139

Bow

head

wha

leMud

dysand

Ø.W

iig,

pers.com

m.

2015.

Collagenda

te.

The

repo

rted

age

(1202

514C

years)is

correctedfor

440yearsmarine

reservoirage.

Poz-69

682

1251

060

100

1389

013

805

1397

213

888

84Blomv� a

g20

14-15

Bow

head

wha

leMud

dysand

Collagenda

te.A

differentbo

nefrom

theother

wha

lebo

neda

tes.

9.4%

colla

gen(C

/N

at=3.27

).Meanfor

3lastsamples

100

13818

13716

13925

13820

105

Other

bone

samples

Tua

-902

1187

580

100

1325

413

188

1331

813

253

65Eider,

Som

ateria

mollissima.

Norw.:

Ærfug

l

Proba

bly

from

the

mud

dysand

�14.4

Elisab

eth

Eriksen,

pers.com

m.

2008.

Reportedage

(1143

514C

years)is

correctedfor

440yearsmarine

reservoirage

(Steinar

Gullik

sen,

pers.

com.2

008).

(con

tinu

ed)


Table1.

(con

tinu

ed)

Lab.ID

Con

v.14C

age1

�1r

DR

Calibratedages

(IntCal13)B19

50Sa

mpleID

givenwhen

dated

Dated

material

Sediment/

Stratigrap

hyd1

3 CReferences

Com

ments

Median3

68%

confidence

interval

From

ToMidpo

int

Half

rang

e

Tua

-1152

12240

75100

13591

13486

13686

13586

100

Com

mon

guillem

ot,

Uriaaa

lge.

Norw.:

Lom

vi

Proba

bly

from

the

mud

dysand

�16.1

Elisab

eth

Eriksen,

pers.com

m.

2008

.

Reportedage

(1224

014C

years)isno

tcorrectedfor

marinereservoir

age(Steinar

Gullik

sen,

pers.

comm.2

008),b

utaccordingto

A.

K.H

uftham

mer

(pers.comm.

2008)thisbird

feedson

lyon

marinefood

.

Tua

-1153

12645

95100

14033

13905

14142

14023

119

Com

mon

scho

ter,

Melanitta

nigra.

Norw.:

Svartand

Proba

bly

from

the

mud

dysand

�13.7

Elisab

eth

Eriksen,

pers.com

m.

2008

.

Reportedage

(1264

514C

years)isno

tcorrectedfor

marinereservoir

age(Steinar

Gullik

sen,

pers.

comm.2

008).

Thisbird

also

lives

infreshw

ater,

butat

that

timeit

prob

ablyon

lyha

dmarinefood

(A.K

.Huftham

mer,p

ers.

comm.2

008).

Tua

-115

111

605

8513

432

1333

413

539

1343

610

3Bon

eof

reindeer,

Ran

gifer

tarand

us

Proba

bly

from

the

mud

dysand

�17.1

Elisab

eth

Eriksen,

pers.com

m.

2008

.

Poz-69

681

1171

060

1352

813

462

1365

213

557

95Blomv� ag

2014-13

Bon

eof

reindeer,

Ran

gifer

tarand

us.

Norw.

Reinsdy

r

Proba

bly

from

the

mud

dysand

Adifferentbo

nefrom

Tua

-115

1.2.6%

colla

gen

(C/N

at=3.36

).

Meanfor

reindeer

1166

075

1349

013

424

1356

313

493

70

(con

tinu

ed)


Table1.

(con

tinu

ed)

Lab.ID

Con

v.14C

age1

�1r

DR

Calibratedages

(IntCal13)B19

50Sa

mpleID

givenwhen

dated

Dated

material

Sediment/

Stratigrap

hyd1

3 CReferences

Com

ments

Median3

68%

confidence

interval

From

ToMidpo

int

Half

rang

e

Woo

dsamples

T-138

12200

350

14287

13731

14821

14276

545

H.H

olteda

hl;

Sample1

Woo

dNyd

al(196

0)Origina

llyrepo

rted

as12

10014Cyears,

butrecalculated

to12

200(R

.Nyd

alpers.

comm.1

976)

Stored

inspirit.

Poz-67

670

1160

060

1342

913

352

1348

213

417

65Blomv� ag

2014-10

Woo

d.Identified

byA.M

onsen

asPop

ulus

orpo

ssibly

Salix

Mud

dysand

Stored

inun

know

npreservativesin

asm

allg

lass

tube

marked‘33a

’.Pap

erin

theglass

says:‘Woo

dfrom

thebed

immediately

belowthetillin

thelower

cross-

ditch.

Und� as2/7-

42’.

Poz-67

671

1212

060

1398

413

856

1408

513

970

115

Blomv� ag

2014-11

Woo

d.Identified

byA.M

onsen

asSalix

Proba

bly

from

the

mud

dysand

Stored

inun

know

npreservativesin

asm

allg

lass

tube

marked‘34b

’.

Poz-67

672

1137

060

1321

213

148

1327

213

210

62Blomv� ag

2014-12

Woo

dSp

ecies

unkn

own

Proba

bly

from

the

mud

dysand

Stored

inun

know

npreservativesin

alarge,un

marked

glasstube.T

helargestpieceof

woo

din

the

collection.

Mean3last

woo

dda

tes

1170

038

513

608

1312

114

005

1356

344

2

1 Con

ventiona

l14 C

ageisun

correctedformarinereservoirage.

2 DRvalueused

inCalib

7.1forcorrection

formarinereservoirages.

3 Medianforthefullprob

ability

distribu

tion

.


method, namely dissolving the bone in HCl, and it isomitted from the discussion in the present paper,although the age overlaps within a standard deviationwith the parallel sample (T-1899/2) that was preparedwith the Longin (1971) method.

When we started with the new series of radiocarbonages (the Poz- samples) it was clear that we neededhigh accuracy and precision to test the differenthypotheses. An additional problem was that some ofthe samples had been treated with preservatives ofunknown chemical composition. Therefore, specialcare was taken to select and prepare samples in orderto avoid possible contamination. The preparationmethods in the Poznan laboratory generally followedthose described by Brock et al. (2010). From molluscshells, before collecting carbon for 14C, the possiblyrecrystallized outer layer (20–30% of the mass) wasremoved with HCl, and organic coating was removedwith H2O2. From bones, extraction of collagen withthe Longin (1971) protocol was preceded by removalof humic acids, and followed by ultrafiltration of thecollagen (Bronk Ramsey et al. 2004). Quality of thecollagens was indicated by high extraction yields andconfirmed by atomic C/N ratios that appeared(Table 1) well inside the acceptance interval of 2.9–3.5(e.g. Brock et al. 2012). Knowing that the reindeer

bones had been stored in preservatives, before extract-ing collagen, we treated this sample several times withacetone to remove PVA and resistol, alcohol to removeshellac, and water. The issue of preservatives in woodsamples was addressed similarly as with bones, includ-ing additional treatment with gasoline to removepetroleum-descending compounds, and – after thecommon AAA treatment – by extracting alpha-cellu-lose according to the method described by Nemecet al. (2010), thus removing the potentially mobilefraction such as lignins, waxes and resins.

Conventional radiocarbon ages were calibrated vs.the IntCal13 or Marine13 calibration curves (Reimeret al. 2013) for samples of terrestrial or marine origin,respectively, using the CALIB calibration program,version 7.1 (http://calib.qub.ac.uk/calib/). Calibratedradiocarbon ages are referred to 1950 using the desig-nation BP, as for conventional radiocarbon ages. Themarine reservoir correction is significant for the preci-sion sought, especially because there is a plateau in themarine calibration curve at 14.3–14.6 cal. ka BP. Bon-devik et al. (2006) found that that the ΔR value for thiscoast of Norway fluctuated during the Lateglacial, butwas around 100 for much of the period from 14 to13 cal. ka BP. Theoretically, it should be possible todetermine the marine reservoir ages at the site as the

Fig. 4. A time-distance diagram from Mangerud (1977) that shows the glacial-geological interpretation of the succession at Blomv�ag Ceme-tery that has been accepted up to now. The diamicton, on this diagram called the Ulvøy Till, covering the fossil-bearing Blomv�ag Beds, wasconsidered to represent an Older Dryas glacial advance.


http://calib.qub.ac.uk/calib/

Table

2.Rad

iocarbon

datesfrom

Blomøy,� A

gotnes,B

jorøyan

dOs.

Sites

Lat.°N

Lon

g.°E

SampleID

Lab.ID

Con

v.14C

age

�1r

DR

Calibratedages

(IntCal13)B1950

Dated

material

Sediment/

Stratigrap

hyReferences

Median

68%

confidence

interval

From

ToMidpo

int

Half

rang

e

Dalebo

g,Blomøy

60.536

64.87

8T-672

1207

018

013

961

1365

114

192

1392

127

1Gyttjaclay

Low

est

orga

nic

inpa

laeolake

Man

gerud

(197

0)

Dalebo

g,Blomøy

60.536

64.87

826

5–27

2cm

Beta-51

465

1203

011

013

891

1375

814

018

1388

813

0Mosses

Assample

abov

eH.H

.Birks,

pers.com

m.

(201

4)Dalebo

g,Blomøy

60.536

64.87

826

0–26

4cm

Beta-51

464

1211

011

013

973

1380

714

092

1395

014

3Mosses

Slightly

high

erH.H

.Birks,

pers.com

m.

(201

4)Meanfor

3Dale

bogsamples

1392

031

Ham

revatn,

Sotra

60.206

85.08

5513

12–14cm

Poz-48

1712

090

6013

940

1383

314

033

1393

310

0Rhacomitrium

,Polytrichum

,twig

Next

lowermost

sample

Loh

neet

al.

(200

7)

Ham

revatn,

Sotra

60.206

85.08

5513

48–50cm

Poz-48

1812

270

7014

207

1404

914

325

1418

713

8Leaffragm

ents,

mosses

Low

ermost

sample

Loh

neet

al.

(200

7)SeleBog

,Blomøy

60.528

84.89

4289

7–90

0cm

Poz-75

514

1280

070

100

1425

814

082

1440

614

244

162

Shellfragm

ents

Low

ermost

sample

SeleBog

,Blomøy

60.528

84.89

4288

1–88

4cm

Poz-75

515

1269

070

100

1407

813

977

1416

714

072

95Sh

ellfragm

ents

Nextlowest

sample

� Ago

tnes

60.410

5.01

0Sa

mple20

T-102

312

660

150

100

1409

013

819

1428

014

050

230

Shellfragm

ents

Man

gerud

(197

7)� Ago

tnes

60.410

5.01

0Sa

mple20

Poz-67

900

1269

060

100

1407

613

990

1415

614

073

83Sh

ellfragm

ents

Man

gerud

etal.(20

16)

� Ago

tnes

60.410

5.01

0Sa

mple22

Poz-67

901

1281

060

100

1426

414

101

1439

714

249

148

Shellfragm

ents

Man

gerud

etal.(20

16)

Store

Hellervatn,

Bjorøy

60.319

65.16

92Po

z-44

184

1275

070

100

1416

214

025

1426

514

145

120

Shellfragm

ents

Intill

Sk� ar(201

2)

Storum

,Os

60.161

95.41

37Storum

-1Po

z-79

831

1291

060

100

1448

714

271

1466

514

468

197

Hiatella

arctica

Baseof

glaciomarine

clay

Storum

,Os

60.161

95.41

37Storum

-2Po

z-79

870

1295

070

100

1457

814

311

1476

914

540

229

PairedHiatella

arctica

5cm

abov

eStorum

-1Storum

,Os

60.161

95.41

37Storum

-3Po

z-79

871

1290

060

100

1446

614

255

1464

514

450

195

Chlam

ysisland

ica

Greysilt


Table

3.10Besamples

from

Blomv� agan

dLiat� arnet.A

llsamples

witharock

densityof

2.65

gcm

�3 ;zero

rock

surfaceerosion.

Agesaregivenas

conv

ention

al10Beages,i.e.calculatedrelative

totheyear

ofcollection(B2014).For

aprecisecompa

risonwithcalib

rated

14Cages

(i.e.B

1950

)64

yearsshou

ldbe

subtracted.

Sample

Sampletype

Bou

lder

height

(m)

Bou

lder

width

(m)

Lat.(°N

)Lon

g.(°E)

Elevation

(ma.s.l.)

Sample

thick.

(cm)

Topo

.shield.

factor

10Beconcentr.

(atomsg�

1 )

10Beage1

10Beage2

Blomv� ag

14NOR-62

Bou

lder

1.5

1.89

2.3

60.5395

4.88

1635

1.0

1.00

063

600�

2020

1423

1�45

414

707�

469

14NOR-66

Bou

lder

0.6

1.09

1.0

60.5468

4.86

6939

2.0

1.00

065

400�

1400

1468

7�31

615

180�

326

14NOR-69

Bou

lder

11.09

1.5

60.5451

4.86

5641

2.0

1.00

067

000�

1650

1501

6�37

115

519�

384

14NOR-67

Bou

lder

0.8

1.29

1.0

60.5463

4.86

7043

2.5

1.00

048

100�

989

1078

8�22

211

149�

230

14NOR-64

Bedrock

NA

NA

60.5477

4.86

7035

3.0

1.00

072

300�

1390

1644

4�31

716

995�

328

14NOR-61

Bou

lder

1.3

3.09

3.0

60.5380

4.88

1040

1.0

0.99

767

500�

1560

1506

9�35

015

574�

361

14NOR-65

Bou

lder

0.5

1.39

1.0

60.5470

4.86

7056

1.0

1.00

063

100�

1360

1380

2�29

814

264�

309

15NOR-1

Bou

lder

0.5

1.59

1.7

60.54356

4.86

6637

2.0

1.00

063

090�

3053

1420

0�68

914

676�

712

MeanBlomv� ag,

exclud

ingou

tlier(sam

ple-67)

andbedrocksample(-64

)14

501�

505

1498

7�52

2Weigh

tedmeanBlomv� ag,

exclud

ingou

tlier(sam

ple-67)

andbedrocksample(-64)

1451

1�15

114

998�

156

Liat� arnet

14NOR-73

Bou

lder

2.5

4.09

2.0

60.3190

5.11

7031

31.0

0.99

0382

900�

2120

1413

8�36

314

615�

375

14NOR-70

Bou

lder

0.5

1.09

0.7

60.3191

5.11

6232

82.0

197

100�

1880

1630

8�31

716

859�

328

14NOR-71

Bou

lder

10.59

2.0

60.3196

5.11

6031

91.5

194

300�

2460

1591

0�41

716

448�

431

14NOR-72

Bou

lder

1.8

3.09

2.0

60.3193

5.11

7231

01.0

187

000�

1730

1474

3�29

415

241�

304

MeanLiat� arnet

1527

5�10

08Weigh

tedmeanLiat� arnet

1525

0�16

9

1 Western

Norway

prod

uction

rate

(Goehringet

al.2

012a,b

);calculated

usingCRONUSEarth;h

ttp://h

ess.ess.washing

ton.edu/math/al_b

e_v2

2/alt_cal/a

lt_cal.htm

l.2 A

rcticprod

uction

rate

(You

nget

al.2

013);calculatedusingCRONUSEarth;h

ttp://h

ess.ess.washing

ton.edu/math/al_b

e_v2

2/alt_cal/a

lt_cal.htm

l.


http://hess.ess.washington.edu/math/al_be_v22/alt_cal/alt_

http://hess.ess.washington.edu/math/al_be_v22/alt_cal/alt_

Blomv�ag Beds contain both terrestrial and marine fos-sils; this was done by Mangerud (1972). However, thestratigraphical positions of the samples within theBlomv�ag Beds are too poorly known to obtain preciseresults. Because the development of ΔR through theperiod of focus is not precisely known, we calibratedall samples using ΔR = 100. However, Table 1 showssome samples calibrated with other ΔR values. As anexample of the impact of the ΔR value, we consider theage 13 020�70 14C years BP for the basal shell sample.When using ΔR = 0, 100 and 200, the median cali-brated age would be 15.0, 14.8 and 14.5 cal. ka BP,respectively.

In order to cite only one age in the text, and not aninterval, we use the midpoint of the 68% confidenceinterval of the calibrated age and uncertainty as � halfof that interval (Tables 1, 2). We note that the maxi-mum difference between this midpoint and the medianfor the full probability distribution is 39 years and formost samples the difference is <10 years.

Cosmogenic 10Be exposure dating

Eleven erratics and one bedrock sample for 10Be expo-sure dating were collected in 2014 and 2015 from sites1–2 km north of Blomv�ag (n = 8) and from the sum-mit of Liat�arnet (= Lia in Fig. 1B), ~25 km south ofBlomv�ag. Sampled boulders were perched on exposedbedrock, on either mounds or flat surfaces, in positionswhere it is unlikely that they had been moved or over-topped. We sampled the top 2–3 cm of surfaces usinga diamond saw, a method that yields pieces of similarthickness. We sampled mostly flat surfaces and avoidededges, and used a clinometer to measure topographicshielding and a hand-held GPS receiver to record sam-ple location and elevation. The altitude of the varioussample locations north of Blomv�ag ranges from ~35 to~56 m a.s.l. and we are confident that all samples werecollected from above the local marine limit. The sam-ples were prepared for 10Be analysis at the Universityat Buffalo Cosmogenic Nuclide Laboratory. Followingcrushing, sieving and quartz isolation, samples weredigested and beryllium isolated following proceduresdescribed in Young et al. (2013). 10Be/9Be ratios weremeasured at the Center for Mass Spectrometry, Lawr-ence Livermore National Laboratory and normalizedto standard 07KNSTD3110 with a reported ratio of2.85910�12 (Nishiizumi et al. 2007; Rood et al. 2010).Procedural blank ratios range from 1.1910�15 to3.9910�15, equating to background corrections of 1 to4% of the sample total.

The 10Be ages were calculated using the CRONUS-Earth online exposure age calculator (Balco et al.2008; version 2.2 constants 2.2). We adopted a region-ally constrained production rate from southwesternNorway of 4.15�0.15 at g�1a�1 (Goehring et al.2012a, b) with Lm scaling (Balco et al. 2008).

However, for comparison, in Table 3 we have alsoincluded ages calculated with the often-used Arcticproduction rate of 3.96�0.15 at g�1a�1 (Young et al.2013). Snow shielding is not important at these eleva-tions, certainly not at present and we consider neitherduring deglaciation. Some outcrops retain glacial pol-ish; thus, postdepositional bedrock surface erosion isnegligible. The field area has undergone <30 m iso-static-driven emergence since deglaciation (Lohneet al. 2007), and the minor influence this has on the10Be ages may be offset by effects of atmospheric pres-sure changes related to ice-sheet proximity and glacial-world atmospheric compression (Staiger et al. 2007)and the ages that we report are therefore not adjustedfor isostatic uplift.

In the exposure dating community the convention isto report the age in years before the sampling year.Our 10Be samples were collected in 2014 and we usethe designation ‘B2014’ for such calculated ages, but inorder to compare them with radiocarbon ages we con-vert them to refer to 1950, and then use the designation‘B1950’.

The Blomv�ag site

Location and lithostratigraphy

The Blomv�ag site is located about 5 km to the west ofthe Younger Dryas ice-sheet limit (Fig. 1B). The areaaround the cemetery is characterized by exposed gneis-sic bedrock; Quaternary sediments are found only indepressions (Fig. 3A). West of the Blomv�ag church(the building to the right in Fig. 3A) there is a shallowdepression gently rising towards the north, from about13 to 17 m a.s.l. where a cemetery was planned in1941. Most of the descriptions and samples are fromthe upper part where the original surface was at16–17 m a.s.l. The depression to is bounded the eastby an NS–trending bedrock cliff and to the west by agently rising bedrock slope (Fig. 3B). Also to the norththere is a small cliff (Fig. 3A). In order to improve thedrainage for the planned cemetery, a ditch was dugalong the bedrock cliff and a parallel ditch on the otherside of the depression; approximate positions aremarked in Fig. 3A. Two cross ditches, numbered 1 and2, were excavated for scientific purposes, both in theupper part of the area; the deepest was about 5 m deep(Fig. 5A). Scientific ditch no. 2 connected the northernpart of the two drainage ditches whereas no. 1 was anisolated ditch north of no. 2 (Fig. 3A).

Detailed descriptions of the sediments and thestratigraphy are not available and apparently therewere some differences between the ditches. However, aprofile drawing made by Fægri seems to be representa-tive of the stratigraphy (Fig. 6). The excavationsreached bedrock, which in at least some places wascovered by a thin diamicton interpreted as basal till. In


the upper part of this unit there were boulders sur-rounded by irregularly bedded sand (Fig. 7A), proba-bly also of subglacial origin. The main sedimentsuccession can be subdivided into four main units fromthe base: (i) glacial sediments, (ii) fossil-bearing sedi-ments, later named the Blomv�ag Beds (Mangerud1977), (iii) a diamicton, always called ‘till’ by the exca-vating scientists, re-named the Ulvøy Diamicton here,and (iv) sand and gravel layers capping the succession,interpreted as beach sediments deposited during thepostglacial emergence. We will not discuss the upper-most unit further because no datable material wasfound and the given interpretation appears clear.

There is an unconformity between the basal glacialunit and the overlying 1–1.5 m thick Blomv�ag Beds.The lowest part of the Blomv�ag Beds consists of sandwith sparse small shell fragments. Above this sand isthe thickest zone that Fægri described as shelly sand

Fig. 5. Photographs of the excavations at the Blomv�ag Cemetery. A. The east end of scientific excavation 1. On top is postglacial sand andgravel. The Ulvøy Diamicton is between the boulder with a hammer in the distant right-hand corner and the arrow ~1 m lower. Below thearrow are the fossil-bearing Blomv�ag Beds. The heap of boulders to the right in the background probably derives from the diamicton. Pho-tograph Knut Fægri, June 1942. B. The northern part of the eastern drainage ditch showing the Ulvøy Diamicton and overlying sediments.The boundaries were marked on the photo by Und�as who used the term ‘till’ for the diamicton. The fossil-bearing sediments are located belowthe drainage construction seen in the bottom. Photograph Isak Und�as, October 1941. C. The northern part of one of the drainage ditches,probably the eastern ditch. The stratigraphy was not described on the photograph, but the boulder-rich sediment in the foreground is obvi-ously the Ulvøy Diamicton and the postglacial sand and gravel can be seen above the measuring stick in the middle of the photo. PhotographAstrid Monsen, 1941. D. A facies of the Ulvøy Diamicton containing rounded cobbles. Written on the reverse side of the photograph was thatthis is a close-up of the densely packed till. Scale: shaft of a shovel. Photograph Astrid Monsen, 1941.

Fig. 6. Sketch of the northern wall of scientific excavation 2 (thelower cross-ditch) based on a measured profile by Fægri (field notes1942) with some additional information from Und�as (field notes1941–42). This stratigraphy is representative for all ditches takingaccount of variations in facies and bed thicknesses. [Colour figurecan be viewed at www.boreas.dk]



that contains many pebbles in the lower part, but fewerin the upper half (Fig. 6). Und�as described this unit asgravel with shells, but on a sketch he also drew thinbeds of sand, more shell-rich zones and a horizon withmore seaweed. Thus, it seems clear that this unit con-sists of a mixture of sand and gravel, partly as thinbeds or lenses with many shells and especially shellfragments. A few bones were found in this unit, and itcontains organic matter, probably mainly from marineorganisms.

The uppermost zone in the Blomv�ag Beds is brown-ish muddy sand, often termed a mud layer in the fieldnotes. It contains fewer pebbles than the rest of theBlomv�ag Beds. In some field sketches (Fig. 6), thiszone was marked as a separate bed, but it wasdescribed as flames or lenses (Fig. 7B) and was dis-turbed by boulders in the overlying diamicton. Theterm ‘mud’ was ascribed to a high content of organicmatter. The whale bones and most other bones werefound in this upper zone of the Blomv�ag Beds,although several whale bones penetrated into the over-lying Ulvøy Diamicton. Most, and possibly all, piecesof wood also came from this zone, whereas Und�as(1942) mentioned that it contained many fewer shellfragments than the underlying strata.

The Blomv�ag Beds were always interpreted as shal-low-water or beach sediments (Und�as 1942), an inter-pretation that we support. Based on the presentknowledge of sea-level change, it is now possible toestimate the water depth at the site. Figure 8 shows arelative sea-level curve for Blomv�ag, constructed fromdata in Lohne et al. (2007). Following deglaciation,the high tide fell to a level around 18 m a.s.l. duringthe Allerød. The highest area excavated at the Blomv�agCemetery site is located about 17 m a.s.l., suggesting

that the upper part of the Blomv�ag Beds accumulatedin very shallow water and some possibly even in thebeach zone. The presence of driftwood in this unit sup-ports the interpretation that the sediments represent aformer beach. The age of the reindeer bones (13.5 cal.ka BP) corresponds with the start of the sea-level low-stand (Fig. 8), and most other bones and wood mayalso have been deposited during the lowstand period.The youngest 14C ages in the Blomv�ag Beds are 13.4–13.2 cal. ka BP (Table 1). Fossils and sediments datingfrom the last few hundred years of the Allerød aremissing, probably because of non-deposition when the

Fig. 7. Photographs from the excavations at Blomv�ag Cemetery. A. Boulders and bedded sand, interpreted as glacial sediments at the base ofthe excavation. Northern wall of scientific excavation 2. Photograph Knut Fægri, July 1942. B. The southern wall of scientific excavation 2.Boundaries of units are marked by us, following descriptions on the reverse side of the photograph. In the lower right-hand corner, the glacialsediments overlain by the fossil-bearing Blomvag Beds are delimited by dashed white lines. Arrow points to a lens of mud. The upper unit isthe Ulvøy Diamicton. Photograph Knut Fægri, July 1942.

Fig. 8. A relative sea-level curve for Blomv�ag constructed from datain Lohne et al. (2007). The curve represents the high tide level andlow tide should be ~2 m lower. Maximum errors are estimated as 3–5 m in elevation. Note that sea level following deglaciation was at, orclose to, the level of the Blomv�ag Cemetery during the Allerød beforerising 10 m in the Younger Dryas. The age of the upper parts of theBlomv�ag Beds are marked UBB.


water depth became too shallow and/or there waserosion when the overlying Ulvøy Diamicton wasemplaced.

Two observations were especially important for theinterpretation of the Ulvøy Diamicton as a till. Firstly,it was described as a compacted non-sorted sedimentunit that was difficult to dig by spades and picks. Sec-ondly, the Ulvøy Diamicton contains numerous boul-ders. Johansen & Und�as (1992) mentioned a largeerratic at the site, about 20 m long and 4 m high, eventhough it is not evident from the description whether itoverlaid the Blomv�ag Beds or not. The photos showthat the Ulvøy Diamicton contains a range of sedimentfacies. Figure 5A shows a 1-m-thick matrix-supporteddiamicton, apparently somewhat similar to the diamic-ton in Fig. 5B, whereas the diamicton in Fig. 5C con-tains more large boulders. A very different facies isseen in Fig. 5D (and some other photos) where theso-called till consists of rounded gravel, which almostcertainly is re-deposited beach gravel. The diamictoncontained some boulders of rock types originatingfrom the bedrock in Oslofjorden and Danish areas,which were interpreted as iceberg-transported materiallater picked up and deposited on the site by the icesheet. Such rock types are often found below marinelimit along the coast of western Norway and are com-monly considered to have been transported by icebergsor sea ice. Fægri mentioned that shells could be seen inthe diamicton and in places he even refers to thediamicton as a ‘fossil-bearing till’.

Radiocarbon ages

Twenty-four radiocarbon ages are presently availablefrom the Blomv�ag cemetery site (including the whale-bone age we omit); 23 from the Blomv�ag Beds and onefrom the Ulvøy Diamicton (Table 1); 11 are new agesobtained for the present paper. It should be noted thatthe relative stratigraphical position within the Blomv�agBeds is known only for one series of shells (Fig. 9). Forthese samples, the sediment depths were given on thesample boxes. It was mentioned in the field notes thatmost bones were found in the upper parts of theBlomv�ag Beds. Therefore, we have plotted all suchsamples in the upper part (Fig. 9), but emphasize thattheir relative position to each other is unknown.

The mollusc shells yielded the oldest ages; the twooldest yielded identical ages of 14.8�0.2 cal. ka BP(Table 1), and the ages are surprisingly similarthroughout the lowest 1 m of the sediments (Fig. 9).The fact that the dated shells did not yield youngerages upwards in the succession could be explainedeither by rapid deposition or by the re-deposition ofshell fragments. According to the field notes, therewere few shell fragments in the upper part of theBlomv�ag Beds. It is striking that all shell ages are olderthan the whale bones and two of the three marine birdbones. This suggests that molluscs may not have livedat the site during deposition of the upper part of theBlomv�ag Beds when water depths were very shallow.Alternatively, shells could have been dissolved due to

Fig. 9. Radiocarbon and 10Be exposure ages. Samples from the Blomv�ag Beds with known depths (mainly those marked as ‘Molluscs in strat.order’) are plotted correctly relative to each other, assuming that the unit was 1.3 m thick. Most other samples from the Blomv�ag Beds were,however, only described as from ‘the upper part’ and they are here plotted in a random order for efficient use of space. The sample from theUlvøy Diamicton is plotted above the Blomv�ag Beds. Radiocarbon samples from �Agotnes, Sele Bog and Dale Bog, which all should provideminimum ages for deglaciation, are plotted in random vertical positions. All radiocarbon ages as plotted as midpoint and 68% confidenceinterval. Exposure ages from Blomv�ag are shown at the top, including a mean. [Colour figure can be viewed at www.boreas.dk]



more acidic conditions produced by the organic mat-ter, but we find that less probable. The size and compo-sition of the whale bones suggest that they stem fromone individual, and the ages overlap within one stan-dard deviation; the mean age is 13.8�0.1 cal. ka BP(n = 3). The ages of the marine birds range from 13.3to 14.0 cal. ka BP (n = 3).

It is highly probable that the reindeer bones comefrom one individual and the ages also overlap; the aver-age is 13.5�0.07 cal. ka BP (n = 2). Reindeer in Nor-way and Svalbard do not eat seaweed (E. Reimers &N. Tyler, pers. comm. 2015) and even at South Geor-gia, which is sparsely vegetated, the content of seaweedin reindeer rumens was found to be minimal (Leader-Williams et al. 1981). Thus, we consider the reindeerages as secure terrestrial radiocarbon ages. Two of thedated wood pieces yielded ages as young as 13.2�0.1and 13.4�0.1 cal. ka BP (Fig. 9). Finally, we obtainedan age of 14.0�0.2 cal. ka BP on shell fragments froma sample marked ‘from a pocket in the till’, an age sim-ilar to the youngest shell fragments below the diamic-ton.

We conclude that the Blomv�ag Beds accumulatedfrom about 14.8 cal. ka until about 13.3 cal. ka BP(Fig. 9) and that the shell fragments in the UlvøyDiamicton are re-deposited from the Blomv�ag Bedsbelow.

The origin of the Ulvøy Diamicton

In view of the original descriptions and some of thephotographs (Fig. 5B, C), the interpretation of theUlvøy Diamicton as a basal till appears to be plausible.It is also noteworthy that all scientists who worked orvisited the site confidently concluded that it was abasal till. However, the available radiocarbon ages con-tradict this interpretation. If the Ulvøy Diamicton is atill then all fossils below the diamicton have to pre-datethe final deglaciation of the site. Radiocarbon agesfrom three sites located close to the Blomv�ag Cemeteryand described below have provided independent mini-mum ages for the final deglaciation of the area. Due touncertainties surrounding the magnitude of marinereservoir errors, age differences are compared eitherbetween terrestrial samples only, or independentlybetween marine samples.

Dale Bog is a palaeolake, located about 600 m northof the cemetery (Fig. 2). It contains a well-dated fullAllerød-Younger Dryas pollen sequence without anydisturbances, demonstrating that the final deglaciationmust pre-date the Allerød. This led Mangerud (1970)to conclude that the Ulvøy Diamicton, at that timeconsidered to be a till, was deposited by an OlderDryas re-advance of the Scandinavian Ice Sheet(Fig. 4). A sample taken at the base of brownishorganic silt yielded an age of 13.9�0.2 cal. BP on bulkorganic matter (Table 2). There is a 10-cm-thick layer

of bluish-grey silt below the dated level. Later, plantmacrofossils from the same level in a new core weredated to 13.9�0.1 and 13.9�0.1 (H.H. Birks, pers.comm. 2014; Mangerud et al. 2016), yielding a meanage of 13.9�0.1 cal. ka BP for all three samples. Thismean age is 430�80 and 710�70 years older than themean ages of the reindeer bones (13.5�0.07 cal. BP;n = 2) and the youngest wood sample (13.2�0.06 cal.ka BP) from levels below the Ulvøy Diamicton, respec-tively (Fig. 9).

At the �Agotnes site, located on Sotra island(Fig. 1B), an exposure of Allerød-Younger Dryas mar-ine sediments showed no traces of being overridden byglacier ice (Mangerud 1977). The oldest shell samplesfrom this section yielded ages of 14.2 and 14.1 ca kaBP (Table 2). The oldest age is 250�130 and1000�180 cal. years older than the mean value for thewhale bones and the youngest age of marine birdremains below the Ulvøy Diamicton, respectively(Fig. 9).

Sele Bog is located 1.0 km east of the cemetery(Fig. 2) at about 20 m a.s.l. and thus it was locatedbelow sea level during the deglaciation and also duringthe Younger Dryas (Fig. 8). We cored it with a hand-driven ‘Russian’ corer in 2015 in order to obtain ageson marine fossils that would yield minimum ages forlocal deglaciation. During coring we hit bedrockunderneath a 900-cm-thick sediment succession ofmarine and lacustrine sediments. On the bedrock sur-face in the deepest part of the basin, between 900–772 cm, is massive, olive-grey marine silt that containnumerous marine shell fragments, with Mytilus frag-ments at the very base of the core. Radiocarbon datesfrom small shell fragments yielded the ages 14.2 and14.1 cal. ka BP from 900 to 897 and 884 to 881 cmdepth, respectively (Table 2), i.e. up to 420�200 yearsolder than the whale bones and up to 990�180 yearsolder than the marine bird bones below the UlvøyDiamicton at the cemetery (Fig. 9).

At all three sites described above (Dale Bog, �Agot-nes and Sele Bog), we obtained minimum ages for thedeglaciation that are significantly older than severalages from below the Ulvøy Diamicton. Thus, it seemsclear that the earlier conclusion that the Blomv�ag Bedshave been overrun by glacial ice depositing the UlvøyDiamicton (Und�as 1942; Mangerud 1970, 1977; Man-gerud et al. 2011) is incorrect.

The site Storum, in Os, is located south of andslightly farther inland than Blomv�ag, but in a similarposition just outside the Younger Dryas moraine(Fig. 1B). Here, a several-metre-deep excavation downto bedrock was investigated in late autumn 2015. Atthe base was a 10-cm-thick unit of sterile sand proba-bly of glaciomarine origin resting on striated bedrock.The basal sand layer is overlain by a 10-cm-thick bedof bluish-grey silty clay with a few mollusc shells of thespecies Hiatella arctica, above which is a grey silt with


frequent occurrences of the mollusc species Chlamysislandica. These units were in turn covered by severalmetres of marine silt and clay containing, amongstother species, Mytilus edulis and Littorina littorea. Thetwo lowermost Hiatella shells that were collected fromthe silty clay a few cm above the basal sand yieldedsimilar ages of c. 14.5 cal. ka BP and a Chlamys shellfrom a level slightly higher up in the sequence yieldedan age of c. 14.4 cal. ka BP (Table 2). These ages arevery similar to the basal ages from the Blomv�ag Bedsand substantiate our conclusion based on the datafrom the Blomv�ag area that there was no Older Dryasglacial advance that reached beyond the position ofthe Younger Dryas ice margin.

Our alternative interpretation of the sediment suc-cession at the Blomv�ag cemetery is that the UlvøyDiamicton was formed by sea ice and/or icebergs dur-ing the Younger Dryas. It is well known that sea icealong Arctic shores can push and mix shallow-watersediments onto beaches (Kovacs & Sodhi 1980). Ice-berg ploughing is extensively described from high-lati-tude continental shelves, but smaller icebergs havecertainly also drifted into shallow water. During theYounger Dryas, the margin of the Scandinavian IceSheet was calving in the fjord a few km east ofBlomv�ag (Fig. 1B) and it is known that sea ice occu-pied the coastal waters at this time (Kristiansen et al.1988; Svendsen & Mangerud 1990). Relative sea level(Fig. 8) during the Allerød must have been very closeto the highest excavated field on the Blomv�ag cemetery.Subsequently, relative sea level rose ~10 m, culminat-ing during the late Younger Dryas when seasonal seaice would have been common, with icebergs driftingalong the coast in front of the calving ice sheet. As wedo not have access to the diamictic layer that wasdescribed from the cemetery it was impossible for us totest this interpretation against primary observations,but we note that the rounded gravel in Fig. 5D sug-gests that at least some of the diamicton consisted ofre-deposited beach gravel.

Deglaciation history

The oldest radiocarbon ages that we obtained fordeglaciation are from two dated molluscs in theBlomv�ag Beds that both yielded radiocarbon ages of14.8�0.2 cal. ka BP. We generally assume that basalages from lacustrine and marine sequences shouldyield similar ages and that both should be close to thetiming of deglaciation. However, the terrestrial plant-based ages from Dale Bog (13.9 cal. ka) are about900 years younger than the basal shells from theadjacent Blomv�ag Beds (Fig. 9). One explanationmight be that relative sea level was 20–30 m higherthan today during deglaciation (Fig. 8) and thereforeBlomøy was a small island and the vegetation covermay have been very sparse and fragmentary. Another

possible explanation is that marine reservoir agesduring deglaciation were considerably higher thanassumed above. The Sotra Island to the south(Fig. 1B) is much larger than Blomøy but we assumethat they were both deglaciated at approximately thesame time. Radiocarbon ages of plant macrofossilsfrom basal lake sediments in Hamravatn on Sotra(Fig. 1B) yielded 14.2�0.14 cal. ka BP (Table 2)(Lohne et al. 2007). Using the basal macrofossil agesfrom Dale Bog and Hamravatn to calculate ΔR valuesfor shells at Blomv�ag would yield ΔR = 600 years and350 years, respectively. These values are much higherthan those found by Bondevik et al. (2006), but thevalue of the marine reservoir age should be investi-gated further before any firm conclusions can bedrawn.

In contrast to radiocarbon ages that provide mini-mum-limiting age estimates, cosmogenic 10Be exposureages from erratic boulders will in ideal circumstancesprovide the direct timing of deglaciation. Note that inTable 3, we have listed conventional 10Be ages, i.e. cal-culated relative to the year of sample collection(B2014), whereas below, we cite ages relative to 1950(B1950). The 10Be age for seven boulders fromBlomv�ag (Figs 2, 10) range from 15.1�0.4 to10.8�0.2 ka; one 10Be age from ice-sculpted bedrock is16.4�0.3 ka. When one young erratic outlier (10.8 ka)and the old bedrock outlier (16.4 ka) are excluded, themean 10Be age is 14.5�0.5 ka B1950; this mean agewould be 500 years older (14.9�0.5 ka B1950) whenusing the Arctic production rate (Young et al. 2013).

Although we presently cannot achieve a precisionfor the age of deglaciation better than a few hundredyears, mainly limited by the marine reservoir age forradiocarbon and production rate for exposure ages, wenote that both 10Be and 14C ages yield a similar timingof deglaciation. Here, we conclude that the deglacia-tion occurred between 14.8 and 14.5 cal. ka BP(Fig. 12).

The erratic boulders from Liat�arnet, the highestmountain (340 m a.s.l.) 27 km south of Blomv�ag(Fig. 1B), were dated to test if the summit had pro-truded through the ice surface before the lower partsof the islands became ice free. The 10Be ages of the foursamples range from 16.3�0.3 to 14.1�0.4 ka. Themean age of 15.2�1.0 ka B1950 (Table 3) isc. 600 years older than the ages for the Blomv�ag erra-tic boulders and thus may suggest that Liat�arnet was anunatak for a period of a few centuries during the ini-tial deglaciation of the islands, although the ages over-lap within one standard deviation.

Palaeoenvironment and possible humanoccupation

We have not made any new identifications of the fossilsin the Blomv�ag Beds. We assume that there was a


collection of identified molluscs that is now lostbecause no named shells were found in the existingboxes. Molluscs that were identified by Astrid Monsen(Und�as 1942) are given in Table 4. Most important isthat Mytilus and Littorina occur throughout the bedsand shells of Mytilus are present in almost all datedsamples. The specimens identified as Modiolus (Man-gerud 1977) might be misidentified fragments of Myti-lus, but for palaeoclimate interpretations that will notmake any significant difference. The three mentionedspecies are presently found along the entire coast ofNorway, but they do not extend to Svalbard, exceptMytilus, which reappeared during the last decade(Berge et al. 2005). The occurrence of these speciesthus suggests that relatively warm Atlantic waterreached this part of the Norwegian coast during theBølling and Allerød (Mangerud 1977) and that coastalwater temperatures were similar to those of the watermasses along northernmost Norway today. The lowerboundary of the Bølling chronozone as it was definedby Mangerud et al. (1974) represented the first sign of

warming in northwest Europe after the Oldest Dryas.We therefore argue that the presence of Mytilus at thebase of the Blomv�ag Beds suggests they are of Bøllingage; pre-Bølling water would probably be too cold forMytilus and Littorina. The start of Greenland intersta-dial 1e, which is approximately correlated with theBølling (Bj€orck et al. 1998; Lowe & Hoek 2001), isdated to c. 14.6 ice-core ka before 1950 (Rasmussenet al. 2006).

Bones and their identification are described in detailby Lie (1986). The mammals include reindeer, bow-head whale and harp seal. There are bones from anumber of sea birds but also raven and some fishes thattogether support the reconstruction of a climate simi-lar to northernmost Norway today. This means thatthe warmest month (July) probably had a mean tem-perature of 9–10 °C, i.e. 3–4 °C colder than the presentday.

For wood there is a handwritten list of about 100samples apparently identified by Astrid Karlsen. How-ever, quite a few of the pieces appear to be broken parts

A B

C D

Fig. 10. Boulders dated with 10Be. A–C are from Blomv�ag, D is from Liat�arnet. A. 14-NOR-62 (age 14.2�0.5 B2014). B. 14NOR-65 (age13.8�0.3 B2014). C. 14NOR-69 (age 15.0�0.4 B2014). D. 14NOR-71 (age 15.9�0.4 B2014). The fjord towards Bergen can be seen in the back-ground. [Colour figure can be viewed at www.boreas.dk]



from a larger piece. Almost all are identified as Salixor Populus. Four were identified as Betula; two asJuniperus and one as Picea. We cannot judge the qual-ity of the identifications but Salix is an early immi-grant and pieces of Salix as well as Juniperus might befrom local vegetation. Picea is probably driftwoodfrom rivers in Siberia. The frequent occurrence oflong-transported wood, and of bird bones, may pro-vide explanations for transport of seeds and thus theimmigration of plants to coastal Norway after the LastGlacial Maximum.

When he still believed that the Blomv�ag Beds wereof interglacial age, Und�as (1942) mentioned the possi-ble presence of humans, saying: ‘The findings areunique in Scandinavia and it is indeed strange thatsuch a richness of bones and wood have been depositedhere. It is almost only human remains that are missing,but so far nothing is found to indicate that humansplayed a role. The few pieces of flint do not look likehuman tools and I have not seen any small flakes thatfor example are common in the Fosna Culture flintsites’ (translated from Norwegian by us). Rolfsen(1972) and (Mangerud 1973) pointed out that groupsof reindeer hunters lived in Denmark and Germany atthe time the Blomv�ag Beds were deposited and as rein-deer had reached Blomv�ag they said it was reasonable

that some humans had followed the reindeer herdsnorthwards to western Norway. Lie (1986, 1990)argued that the composition of the fauna strongly sug-gests that the bones were remnants of human activityand concluded that ‘the material from Blomv�ag mustbe regarded as the earliest traces so far of human activ-ity in Norway’ (Lie 1990). However, this argument isnow weakened as the new radiocarbon dates indicatethat the Blomv�ag Beds were deposited during severalcenturies and not just during a single human dwellingperiod. Johansen & Und�as (1992) maintained thatsome of the flint pieces from Blomv�ag are human arte-facts. If Lie (1990) and Johansen & Und�as (1992) werecorrect, then humans immigrated to western Norwayabout 3000 years earlier than generally accepted (Brei-vik 2014). This view entered popular books on the his-tory of Norway (Alnæs 1996; Indrelid 1997). However,later the flint material was examined by three archaeol-ogists independently of one another, all concludingthat there is no sign of human work (Bjerck 1994; Eige-land 2012; Fischer 2012), a conclusion repeated inEigeland & Solheim (2012). We follow Bjerck (1994) instating that no findings at Blomv�ag represent reliabletraces of humans. An obstacle for early immigration tosouthern Norway was that the ice-sheet marginblocked the land-connection from Sweden and aroundOslofjorden until about 11 cal. ka BP (Hughes et al.2016).

Position of the Older Dryas ice margin

We concluded above that the interpretation of anOlder Dryas ice advance across Blomv�ag is incorrect,and thus, the Older Dryas ice margin was situated far-ther inland. At the Storum site, described above,located outside but close to the Younger Dryas mor-aine, basal radiocarbon ages are 14.5 cal. ka BP(Table 2, Fig. 11). From Bjorøy (Fig. 1B; Sk�ar 2012)and Bergen (Mangerud et al. 2016), the reported agesof c. 14.1 cal. ka BP from shell fragments included inYounger Dryas tills reveal that these sites were ice freeat 14.1 cal. ka BP prior to being overrun by a re-advance during the Younger Dryas (Fig. 1B).

These ages show that the western coast of Norwayfrom Bjørnefjorden to Fensfjorden and at least as farinland as the Younger Dryas moraine (Fig. 1B)became ice-free during the Bølling. If we accept an ageof about 14 cal. ka BP for the Older Dryas, then theposition of the Older Dryas ice margin must have beeninside, but probably not far inside, the Younger Dryasmargin.

Around the mouth of Hardangerfjorden (Fig. 1A)to the south, the interpretation is the opposite. Here,the Older Dryas margin was slightly beyond theYounger Dryas margin (Fig. 12; Mangerud et al.2016). Furthermore, near Lysefjorden (Fig. 1A), evenfarther south, a dated segment of an Older Dryas end

Table 4. Molluscs in the Blomv�ag Beds. Identified by Astrid Mon-sen, cited from Und�as (1942). Comments translated from Norwe-gian. For some species the presently used names are given below thetable.

Species Comments

Anomia ephippium L. RareAstarte banksii Leach1 Very rareBuccinum undatum L. RareBoreochiton marmoreus Fabr RareBoreochiton ruber Lowe RareCyamium minutum Fabr. RareKellia suborbicularis Mont. RareLittorina littorea L. NumerousLittorina rudis Maton ManyLittorina obtusata L. RareLacuna divaricata Fabr. CommonMacoma calcaria Chemn. ManyMargarita groenlandica Chemn. ManyMargarita helicina Fabr. ManyMya truncata L. Very rareMytilus edulis L. NumerousPecten islandicusM€ull.2 CommonPuncturella noachina L. ManyTectura virginiaM€ull. CommonThracia papyracea Poli Very rareTrophon truncatus Strøm Very rareSaxicava arctica L.3 Very rareBalanus porcatus da Costa4 CommonBalanus crenatus Brug Common

1Astarte montaquiDilwyn.2Chlamys islandicaM€ull.3Hiatella arctica L.4Balanus balanus L.


moraine exists slightly outside the Younger Dryas mor-aines, although in the fjord proper the Younger Dryasoutlet glacier overran this Older Dryas moraine (Bri-ner et al. 2014).

The larger picture of the deglaciation and ice-marginal deposits

During the LGM an ice stream flowed northwardalong the Norwegian Channel off the coastline of west-ern Norway (Sejrup et al. 2016) (Fig. 1A). Glacialstriae and lineations show that ice was flowing almostdue west in the Blomv�ag region (Aarseth & Mangerud1974) and bent northwards as it became confluent withthe Norwegian Channel Ice Stream a short distanceoffshore (Fig. 13; Ottesen et al. 2016). Duringdeglaciation, the Norwegian Channel Ice Streamretreated southward up the channel, leaving openwater along the coast near Blomv�ag so that a new icemargin generally paralleled the coast (Fig. 12).According to marine chronology based on 14C datingof foraminifera, the Norwegian Channel Ice Streamretreated past the Troll field to the west of Sognefjor-den (Fig. 1A) prior to 18.5 cal. ka BP (Sejrup et al.2009), whereas 10Be exposure ages suggest that the ice

Fig. 11. Time-distance diagram showing changes in ice-margin position relative to the position of the Herdla Moraine, negative distance val-ues indicating down-ice (towards west) and positive value up-ice (to east); modified from Mangerud et al. (2016) by adding new ages given inthe present paper. Ages marked distal to the Younger Dryas moraine are: Blomv�ag = Blomv�ag Beds; �A = �Agotnes; S = Sele Bog; H = Ham-ravatn; Storum = the three oldest shells from the site; Lacustrine sediments = Dale Bog; 10Be = the mean for the 10Be ages from Blomv�ag.[Colour figure can be viewed at www.boreas.dk]

Fig 12. Ice margins in western Norway. Ages are given as cal. ka BP.The Younger Dryas margin has been mapped in detail (Andersenet al. 1995), whereas the other margins shown are more schematic.For reference: Bergen and Boknafjorden are shown in Fig. 1A. [Col-our figure can be viewed at www.boreas.dk]




margin may have retreated all the way south to Utsira(Fig. 1A) as early as c. 20.3 ka (Svendsen et al. 2015).

Accepting that the coast (Blomv�ag, etc.) became icefree at 14.8–14.5 cal. ka BP, much later than the Nor-wegian Channel farther west, implies that the ice mar-gin was located just off the coast for 4000 years ormore (Fig. 12). Most surprising with this reconstruc-tion is that there are no ice-marginal deposits reportedin this zone, although scientists have searched for suchdeposits (D. Ottesen, pers. comm. 2016, H. Haflida-son, pers. comm. 2016). This is even more surprisingwhen considering the large sediment volumes depos-ited during a few hundred years along the YoungerDryas ice margin in this same region. We consider thatone part of the explanation could be that the ice flowwas slow and the ice-mass turnover small, which wouldimply limited precipitation in the accumulation area inthe >4000 years prior to 14.8–14.5 ka. This would beconsistent with cold water and increased sea-ice coverin the Nordic Seas during the Heinrich 1 event (Elde-vik et al. 2014). In contrast, ice-mass turnover wasprobably larger during the Younger Dryas, whichshould require more precipitation, a problem we willnot discuss here.

Another interesting feature is the north–south differ-ence in geometry of the ice retreat (Fig. 12). In theBlomv�ag area, the ice margin remained offshore until14.8–14.5 cal. ka BP, whereas towards the south it hadretreated up Boknafjorden by this time (unpublisheddata). Overall, the north–south 15 ka and YoungerDryas ice-margin configurations are similar. The icemargin was located near the ocean in the north, butwell inland in the south (Fig. 12), although the 15 katime slice represented a retreating margin, and the

Younger Dryas pattern resulted from a major re-advance.

Conclusions

• We present 39 radiocarbon ages and 12 10Be expo-sure ages related to the Bølling-Allerød deglaciationof western Norway.

• The final deglaciation of the outermost coast atBlomv�ag, western Norway, took place 14.8–14.5 cal. ka BP, in response to the Bølling warming.

• The Ulvøy Diamicton that earlier has been inter-preted as a basal till and an indication of an OlderDryas glacial re-advance is not a till. We assumethat it was formed by sea ice and/or icebergs duringthe Younger Dryas.

• The Older Dryas ice margin was located close to theYounger Dryas ice-sheet margin in western Nor-way; in some places it was inside and in other placesoutside.

Acknowledgements. – The investigations form part of the researchproject Eurasian Ice Sheet and Climate Interaction (EISCLIM) finan-cially supported by The Research Council of Norway (grant no.229788/E10). Arve Svean, Morten Nordvik Hovland and KristianVasskog participated in coring the Sele Bog. Sandra Cronauer, AvrielSchweinsberg and Alia Lesnek assisted with the processing of 10Beages, and Susan Zimmerman assisted in the measurement of 10Be/9Beratios. Elisabeth Eriksen and Øystein Wiig allowed us to use unpub-lished radiocarbon dates and Svein-Olaf Dahl allowed us to use radio-carbon ages from the Master’s thesis of Matilde Sk�ar. Eva Bjørsethfinalized the illustrations. The reviewers John Lowe and Ola Fredin,and the Editor Jan A. Piotrowski, suggested a number of changes thatimproved the manuscript. To all we proffer our sincere thanks.

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The Bølling‐age Blomvåg Beds, western Norway: · PDF fileThe Bølling-age Blomvag Beds, western Norway: implications for the Older Dryas glacial re-advance and the age of the deglaciation