ELSEVIER
Earth and Planetary Science Letters 164 (1998) 317–333
Provenance of Heinrich layers in core V28-82, northeastern Atlantic:
Ar=39 Ar ages of ice-rafted hornblende, Pb isotopes in feldspar grains,
and Nd–Sr–Pb isotopes in the fine sediment fraction
40
S.R. Hemming a,Ł , W.S. Broecker a , W.D. Sharp b , G.C. Bond a , R.H. Gwiazda a,1 ,
J.F. McManus a,2 , M. Klas a , I. Hajdas c
a Lamont-Doherty Earth Observatory, Rt. 9W, Palisades, NY 10964, USA
Berkeley Geochronology Center, 2455 Ridge Rd., Berkeley, CA 94709, USA
c Institute für Teilchenphysik, ETH Honggerberg, 8093, Zurich, Switzerland
b
Received 3 April 1998; revised version received 15 September 1998; accepted 25 September 1998
Abstract
Several correlatable layers of sediment, rich in ice rafted grains, have been documented in the North Atlantic. The most
notable within the last glacial cycle are the Heinrich layers, layers extremely rich in ice rafted detritus and generally barren
of foraminifera within the North Atlantic ice rafted detritus (IRD) belt. The view of these layers is that they represent
events where great armadas of icebergs were launched into the North Atlantic. The importance of the Heinrich layers lies
in their connection with abrupt climate change in the North Atlantic, and perhaps globally. There is a growing number of
published provenance studies of the Heinrich layers in the North Atlantic, based on a variety of methods. However, there is
little overlap of methods applied to the same samples. In this contribution, we present a multi-component provenance study
of Heinrich layers H1, H2, H4 and H5 from core V28-82 in the eastern North Atlantic. Our results indicate that virtually
the entire inventory of terrigenous clastic detritus in Heinrich layers H2, H4 and H5 came from ancient continental sources
surrounding the Labrador Sea. Although Heinrich layer H1 is similar in many respects, it appears to have some significant
differences relative to the other three.  1998 Elsevier Science B.V. All rights reserved.
Keywords: Ar-40=Ar-39; paleoclimatology; North Atlantic; Pb=Pb; provenance
1. Introduction
Heinrich layers occur in an approximately east–
west belt across the North Atlantic (Fig. 1). Close
Ł Corresponding
author. Tel.: C1 914 365 8417; Fax: C1 914
365 8155; E-mail: [email protected]
1 Current address: University of California, Environmental
Toxicology=Institute of Marine Sciences, 1156 High Street,
Santa Cruz, CA 95064.
2 Current address: Woods Hole Oceanographic Institute, Woods
Hole, MA 02543.
scrutiny of North Atlantic Quaternary sediments is
revealing numerous other layers rich in ice rafted detritus. Yet Heinrich layers, especially H1, H2, H4 and
H5, remain the most prominent sedimentary features
in late glacial North Atlantic sediments. Heinrich
layers are recognized as intervals of anomalously
high relative abundance of terrigenous detritus in the
coarse sediment fraction [1]. The six originally identified layers within Marine Isotope Stages 2 through
4 [1] can be split into two groups. Heinrich layers
H1, H2, H4 and H5 are characterized not only by
0012-821X/98/$ – see front matter  1998 Elsevier Science B.V. All rights reserved.
PII: S 0 0 1 2 - 8 2 1 X ( 9 8 ) 0 0 2 2 4 - 6
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S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
319
trast, Heinrich layers H3 and H6 have high %IRD,
but unremarkable numbers of lithic grains per gram
(Fig. 2) and sediment flux [2], little or no apparent
increase in detrital carbonate in eastern cores [5,12],
and little difference in isotopic provenance indicators
relative to ambient sediments [7–11]. The subjects
of this contribution are Heinrich layers H1, H2, H4
and H5, called here the carbonate-bearing Heinrich
layers.
The high proportion of coarse detritus within carbonate-bearing Heinrich layers is, in part, a product
of very low foraminifera abundance, possibly due
to lowered productivity or sediment dilution [5,6].
Abundant evidence suggests Heinrich layers were
deposited very rapidly, and may have lasted only
a few hundred years [2–4,13]. Previous work has
consistently demonstrated that Heinrich events occurred at late in the buildup to especially cold times
and were rapidly followed by brief warm periods,
approaching interglacial conditions [5,6,12,14–17].
Heinrich layer H1 is an exception to this generality,
in that there appears to be a 1000 year lag between
the ice rafting event and abrupt warming [12].
1.1. Anatomy of a Heinrich layer
Fig. 2. Stratigraphy of V28-82 (data from [2] and [10]). X axis is
either %IRD in the >150 µm fraction (solid line with circles) or
number of lithic grains >150 µm per gram of sediment (dashed
line with squares). The number of lithic grains counted per gram
is divided by 75 to make the data scale with the %IRD. Also
shown are the locations of the four samples used in this study
(arrows on inside left point to depths with labels H1, H2, H4,
and H5, also depths given in Appedix A, see EPSL Online
Background Dataset and Table 2) and the detrital carbonate
percentages (Table 3). The numbers outside the right side of the
chart are 14 C ages corrected for an assumed 400 year reservoir
age (Table 1).
high %IRD but also by greatly increased numbers of
lithic grains per gram (Fig. 2), high sediment flux
[2–4], dramatic increases in detrital carbonate [5,6],
and extreme isotopic compositions [7–11]. In con-
However they are caused, carbonate-bearing
Heinrich layers appear to require a series of repeated, anomalous, glacialogical processes within
the northern portion of the Laurentide ice sheet.
They have razor sharp bases, and thus must have had
extremely sharp onsets. Broecker et al. [18] made a
detailed assessment of H1 and H2 from DSDP core
609. Their results emphasize the decline in numbers
of foraminifera during the Heinrich events within
the IRD belt and the change in slope of the 14 C
age versus depth across these intervals. Because the
abundance of foraminifera is so low in the Heinrich
layers, it is difficult to interpret the relative timing
of decrease in percent of N. pachyderma (s.). Additionally, the fraction of N. Pachyderma (s.) in H2 is
so close to one, that it is not a sensitive tempera-
Fig. 1. Maps of the North Atlantic. (a) Isopach (10 cm contour interval) of Heinrich layer H2. Contouring is based on thickness data
from published measurements of thickness from a large number of cores [5,9,13]. See also treatments by Refs. [53,54]. The distribution
of sedimentary basins containing abundant carbonate deposits is shown in the black areas [5]. (b) Map of major basement terranes with
characteristic 40 Ar=39 Ar ages in the North Atlantic [23] and surface current pattern taken from Ruddiman [55] and Bond et al. [5].
320
S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
ture measure. To the best of the marine sediments’
ability to record them, Heinrich layers occur within
the coldest parts of the record where North Atlantic
Deep Water was probably already dramatically reduced (e.g., [13,19]). Additionally, they are rapidly
followed by dramatic warm intervals [5,6,14], with
the possible exception of H1.
One of the keys to understanding the Heinrich layers is the identity of their sediment source(s). Bond
et al. [5] used simple geological reasoning, including the high abundance of detrital carbonate and the
pattern of Heinrich layer thinning, to propose a major source in eastern Canada (Fig. 1a). Their study
left open the acknowledged possibility of substantial
iceberg contributions from the Gulf of St. Lawrence.
Subsequently the issue of synchronicity of ice rafting from multiple sources was identified as an important question for resolving the mechanism driving
Heinrich layers, i.e., climate vs. glacialogical control.
Although several provenance analyses have been applied to the study of Heinrich layers, there has been
little geographic overlap and little overlap in procedures, both omissions that may account for some
of the discord in interpretation [20]. Geochemical
and isotopic provenance studies have been reported
for the Heinrich layers, mostly based on analysis of
the fine grain fractions or on bulk sediment samples
[3,4,7–9,11,21]. A different approach, isotopic analysis of coarse grains of feldspar and hornblende, was
employed by Gwiazda et al. [10,22,23]. By picking
coarse feldspar and hornblende grains, only portions
of the sediment of ice rafted origin were analyzed.
The conclusions reached by the various studies are
not entirely consistent, ranging from multiple sources
[11] to dominantly one source [10,22,23] to carbonate-bearing Heinrich layers. The goal of the current
study is to use an integrated approach to the carbon-
ate-bearing Heinrich layers, the four most prominent
in the last glacial cycle, in a single sediment core
from the North Atlantic in order to evaluate their similarities and to resolve some of the open questions
remaining from previous provenance studies.
We report new results from 40 Ar=39 Ar analyses
of individual hornblende grains, Pb isotopes from
individual feldspar grains, Sm–Nd isotopes from
bulk <63 µm sediment, and Sr and Pb isotopes
on bulk, de-carbonated, <63 µm sediment samples
from carbonate-bearing Heinrich layers H1, H2, H4,
and H5 in core V28-82 (49º270 N, 22º160 W, 3935m).
We chose to study only these Heinrich layers for
the current report because it is apparent that they
have the simplest provenance, and thus provide a
good test series from which to work out the most
viable approaches to IRD provenance studies. Work
on the other Heinrich layers is in progress. V28-82
is located in the eastern North Atlantic within the
heart of the IRD belt (Fig. 1). The stratigraphy is
shown in Fig. 2, and newly acquired 14 C ages are
given in Table 1 and indicated in Fig. 2. The data
reported here add to the suite of hornblende and
feldspar data and grain counts previously collected
by Gwiazda et al. [10,22,23] and to sediment flux
studies of McManus et al. [2].
2. Analytical procedures
Samples from core V28-82 were collected by
scraping sediment from a small interval, generally
a centimeter. Subsequently the sample was washed
through a 63 µm sieve. Grain counts of numbers
of lithic grains per gram and %IRD were made on
the >150 µm fraction. Grain counts to determine
the percent of the lithic fraction composed of detrital
Table 1
14 C dates on N. pachyderma from V28-82
Depth (cm)
Weight (mg)
80–81
115–116
120
138.5–139.5 b
224–226
8.9
19.7
19.2
24.7
24.4
a Corrected
b
δ13 C (š)
0.5 (1.2)
0.4 (1.2)
1.0 (1.2)
3.2 (1.2)
0.2 (1.2)
14 C
age
18580
22680
24500
22160
35880
for a 400 year reservoir age.
This measurement is from within H3, and ‘too young’ ages seem to be a characteristic.
š1¦
14 C
age (corrected) a
130
200
230
180
550
18180
22280
24100
21760
35480
S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
carbonate were made on the 63 to 150 µm fraction.
Black to dark green minerals with cleaved surfaces
(mostly hornblende) were picked from the >150 µm
fraction for 40 Ar=39 Ar dating. Feldspar grains were
picked from the >250 µm fraction for Pb isotope
measurement.
Single step laser fusion 40 Ar=39 Ar data for individual hornblende grains were collected at the
Berkeley Geochronology Center. Hornblende grains
were cleaned by ultrasonic treatment in distilled water. Samples were irradiated in the Cd-lined, in core
facility (CLICIT) at the Oregon State reactor. J (D
1:010ð10 2 š5ð10 5 ), the value used for determining the age based on co-irradiated monitor standards
of ‘known’ age, was calculated from analyses of
co-irradiated Fish Canyon sanidine monitor standard,
assuming an age of 27.84 Ma. This standardization
corresponds to a 40 Ar=39 Ar age of 520 Ma for the
Mnhb hornblende monitor standard, and is consistent
with that used by Gwiazda et al. [23] and thus the
results are directly comparable. Single grains were
heated using an Ar ion laser with a defocused, two
millimeter-wide beam. Ages for each step were calculated from Ar isotope ratios corrected for mass discrimination, interfering nuclear reactions, procedural
blanks and atmospheric Ar contamination. Details of
the procedures for irradiation and analysis, and values used to correct for interfering nuclear reactions
are similar to those given by Renne [24].
Individual feldspar grains were weighed into Savillex teflon vials, and sonicated in a mixture of 6
N HCl and 7 N HNO3 for 30 minutes. Following
this preliminary leach and after rinsing the residue
3 times with distilled water, the grains were leached
for 5 minutes in 4 N HF in a sonicator, and subsequently rinsed again. The residue was dissolved in
concentrated HF. A 10% aliquot was taken of the
solution and spiked with a 208 Pb spike. Pb was separated from the samples using standard HBr chemistry
on 100 µl columns.
Sr and Pb isotope analyses were made on <63
µm, bulk de-carbonated samples. Samples were decarbonated by leaching with 1 N HCl and rinsing
with distilled water. Samples were dissolved in HF
with a trace of HNO3 in Parr bombs at 220ºC for
36 hours. Samples were then dried and taken up
in 12 N HCl and bombed at 200ºC for 12 hours.
Pb was separated first by standard HBr chemistry
321
on 100 µl columns. The wash from this procedure was dried and passed through Sr-spec resin
(Eichrom Industries) in 3 N HNO3 , and eluted with
water. For Sm–Nd isotopes, 100 mg samples were
fused with 400 mg of lithium metaborate and dissolved in 30 ml of 1 N HCl. After dissolution,
10% aliquots were taken and spiked with the Stony
Brook mixed rare earth element (REE) spike containing 145 Nd and 149 Sm. REE were co-precipitated
with iron and aluminum using NH4 OH and then
purified using standard cation exchange chemistry
with 2 N HCl and 4 N HNO3 for removing most
elements, and 4 N HNO3 for elution. For isotope
analysis, Nd was separated from the other REEs
using methylactic acid on cation resin. Isotope analyses were made on a VG sector 54–30 mass spectrometer at Lamont-Doherty, except for some Pb
analyses of feldspar samples and the Sm and Nd
isotope dilution analyses, which were made at Stony
Brook. Pb was analyzed using the standard silica
gel-phosphoric technique, in static mode at LamontDoherty and on a single collector 12” radius Nier
type NBS mass spectrometer at Stony Brook. Filament temperatures were maintained between 1250º
and 1350º. Values for Pb standard SRM982, measured at Stony Brook (n D 10) are 207 Pb=206 Pb
D 0.46663(18), 208 Pb=206 Pb D 0.99817(75), and
206
Pb=204 Pb D 36.651(35). Values for Pb standard SRM981, measured at Lamont-Doherty (n D
10) are 206 Pb=204 Pb D 16.880(15), 207 Pb=204 Pb D
15.418(17), 208 Pb=204 Pb D 36.469(54), 207 Pb=206 Pb
D 0.91335(28). Data reported in Tables 2 and 3 are
corrected for mass fractionation based on the appropriate standard measurements. Sr was loaded with
3 N HNO3 on W filaments with a TaCl5 solution
and run in multidynamic mode, using a power law
correction with 86 Sr=88 Sr of 0.1194 as a normalizing
factor. A signal intensity of 2 ð 10 11 amps (š10%)
was maintained on mass 88. The value measured for
Sr standard SRM987 is 87 Sr=86 Sr D 0.710276(27)
(n D 6). Nd was loaded with 3 N HNO3 on Re side
filaments with Re center filaments for ionization. A
1 ð 10 12 amp signal was obtained on 187 Re and
then the side filament was turned up to maintain a
144
Nd signal of at least 5 ð 10 12 amps. Nd isotopic
composition was measured in multidynamic mode,
using a power law correction with 146 Nd=144 Nd of
0.7219. The value measured for Nd standard La Jolla
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S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
was 143 Nd=144 Nd D 0.511835(25) (n D 8). Reported
numbers are corrected by adding 0.000030 to the
measured ratios.
3. Results
3.1. Individual grains
Analysis of individual grains within the >150
µm fraction allows evaluation of sediment sources
that are clearly of ice rafted origin. Due to its relatively common occurrence and good retention of Ar,
the 40 Ar=39 Ar ages of individual hornblende grains
provide important insights into the age spectrum of
ice rafted sediment sources. The temperature below which hornblende retains Ar is approximately
400º to 550ºC [25], and thus hornblende 40 Ar=39 Ar
ages are reset by high-grade metamorphic events.
40
Ar=39 Ar ages of individual hornblende grains from
Heinrich layers H1, H2, H4, and H5 in V28-82 are
almost all Early Proterozoic, between 1.7 and 1.9
billion years (Appendix A which is presented as a
EPSL Online Background Dataset 3 and Fig. 3).
3
http==www.elsevier.nl=locate=epsl, mirror site:
http:==www.elsevier.com=locate=epsl
These results are identical to those reported for H2
from V28-82 by Gwiazda et al. [23], and these results double the number of individual grains dated
from H2.
Although Gwiazda et al. [23] could not discriminate the hornblende age spectra from Heinrich layer
H2 and ambient ice rafted detritus, they did find
somewhat different Ca=K ratios as measured by the
37
Ar=39 Ar. Ca=K is estimated by multiplying the
37
Ar=39 Ar (Appendix A, see EPSL Online Background Dataset 3 ) by 2 [24]. The range of Ca=K for
hornblende grains from all the Heinrich layers within
core V28-82 (Fig. 3b) are similar to those measured
by Gwiazda et al. [23]. Additionally, the fraction of
grains with Ca=K of 8:33 š 3:63 is similar: H1 0.63,
H2 0.67, H4 0.71, and H5 0.64, compared to 0.64 for
H2 from Gwiazda et al. [23].
Due to the tendency for feldspar (especially
K-feldspar) to exclude U and Th in the mineral
structure and to sequester Pb, the Pb isotope composition of feldspar is a good measure of the initial
Pb isotope composition at the time the feldspar crystallized. Accordingly, Pb isotopes in feldspar grains
are excellent tracers of their sources. The Pb isotopic
compositions of feldspar grains (Table 2) from H4
and H5 from core V28-82 are comparable to those
reported from H2 [22] from this core (Fig. 4). In
Table 2
Pb isotope data from residues of feldspar grains from core V28-82
206 Pb=204 Pb
Err a (in-run%)
207 Pb=204 Pb
Err a (in-run%)
208 Pb=204 Pb
Err a (in-run%)
17.7
12.9
34.1
15.7
24.2
59.1
21.429
14.464
13.793
13.820
21.238
12.216
0.011
0.004
0.004
0.040
0.008
0.004
15.998
15.001
14.759
14.797
16.960
13.714
0.008
0.004
0.005
0.044
0.007
0.005
34.941
34.638
36.742
34.324
36.692
32.159
0.019
0.010
0.012
0.101
0.014
0.011
1.60
0.50
1.00
0.30
1.20
41.9
46.5
252.9
57.8
101.1
14.980
15.685
15.124
14.909
14.737
0.004
0.006
0.017
0.015
0.011
15.165
15.336
15.109
15.162
14.989
0.004
0.006
0.018
0.016
0.012
35.666
35.702
35.069
35.675
34.915
0.010
0.014
0.040
0.036
0.027
1.10
1.10
1.00
0.20
1.00
20.3
4.4
24.1
41.2
13.5
16.447
16.502
15.455
14.243
15.511
0.004
0.004
0.006
0.013
0.009
15.343
15.498
15.279
14.785
15.116
0.004
0.004
0.006
0.013
0.009
37.828
35.952
35.443
34.225
35.342
0.009
0.009
0.014
0.031
0.021
Sample
Weight (mg)
60–61 cm
0.80
0.20
0.20
0.50
0.30
0.20
194–195 cm
244–245 cm
a Error
Pb (ng)
reported as 2¦m of in-run results. External reproducibility of standard is 0.04%=a.m.u.
S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
323
Fig. 3. Frequency plots from Heinrich layers in V28-82 (including data from H2 from [23]). (A) Frequency plots of 40 Ar=39 Ar ages of
individual hornblende grains from H1, H2, H4 and H5 from V28-82. (B) Frequency plots of Ca=K of individual hornblende grains (with
age range from 1.6 to 1.9 Ga) from H1, H2, H4 and H5 from V28-82. The ratio of this limited age range was used by Gwiazda et al.
[23] to demonstrate that even within populations of this age range there are differences in the chemistry of hornblende grains within H2
compared to hornblende from ambient glacial sediment. Each of the Heinrich layer samples studied here gives similar indications of the
geochemistry of the source region.
contrast, grains from ambient sediment (near H2) in
V28-82 contain a large fraction of feldspar with distinctly different Pb isotope compositions [22]. The
consistency of the Pb isotope results from the Heinrich layer and the contrast from the background is
further consistent with the episodic contribution of a
distinct iceberg source to the North Atlantic during
Heinrich events.
The composite sample from H1 [10] is within
the range of measured values from the other three
Heinrich layers, but the six individual grains reported here stand out from the individual grains of
the others. Although the number of analyses is small,
grains from H1 appear to indicate more variability
of sources. However, all grains from H1 as well as
the others appear to be from ancient terranes. Fur-
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S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
ther work is underway to examine the provenance
of H1 and H11 on Terminations I and II, respectively.
3.2. Bulk sediment samples
The most abundant published isotope measurements for North Atlantic sediment samples are Sr
isotopes, and there are also many Nd isotope analyses reported [9,11]. In order to make direct comparisons with these published studies, we made Sr
and Sm–Nd isotope analyses on the four Heinrich
samples from V28-82 as well. Due to the solubility
of Sr in water and the large geochemical contrast
between Rb and Sr, the Sr isotope composition of
terrigenous clastic sediment is sensitive to the Rb=Sr
ratio, the initial Sr isotope composition, and the
age of the source. In contrast, because of the very
similar geochemical behavior of the two rare earth
elements Sm and Nd, the most important control
on the Sm–Nd isotope system is generally the time
of extraction from the mantle [26]. Accordingly, Sr
and Nd measure complementary yet contrasting aspects of sediment provenance. Sr and Nd isotopic
compositions from the >63 µm fraction of Heinrich
layers H1, H2, H4, and H5 from V28-82 are similar
to those measured on bulk de-carbonated sediments
by Revel et al. [11] for Heinrich layers in the IRD
belt (Fig. 5). Specifically, "Nd of V28-82 samples
ranges from 20 to 26 and 87 Sr=86 Sr from 0.7259
to 0.7285 (Table 3).
As noted above, the most important control on
the Sm–Nd isotope system is the time of extraction from the mantle. Although there are exceptions,
under most conditions geochemical processes that
take place during metamorphism, weathering, and
sediment transport do not greatly alter the rare earth
element patterns of the resulting materials. Thus, the
Sm–Nd depleted-mantle model age, TDM , of sediment is taken to be a good estimate the average mantle extraction age of the mixture of sediment sources
(e.g., [27,28]). Sm–Nd isotope data from Heinrich
Fig. 4. Conventional plots of Pb isotope data from individual
feldspar grains, composite feldspar samples and bulk, de-carbonated fine fraction from Heinrich layers H1, H2, H4 and H5 from
V28-82. All X -axes are 206 Pb=204 Pb. Error bars are smaller than
symbols in (A) and (C), and 207 Pb=204 Pb error bars in (B) are
slightly larger than the symbols (Table 2). Data for individual
feldspar grains from H2 are from Gwiazda et al. [22], and those
of composite feldspar samples from Gwiazda et al. [10]. For
reference, the Stacey and Kramers [30] model for continental Pb
evolution is shown as the solid curves, and the Labrador Sea
Reference Line (LSRL, 2.7–1.8 Ga slope), based on data from
H2 in core HU-033-009 from the Labrador Sea [22], is shown as
the dashed line. In (C) the four H2 samples with small arrows
pointing to them are the same four samples that appear as a horizontal array with 207 Pb=204 Pb of about 14.9 in (B) (also shown
with arrows). (B) is an expanded view of the tightly clustered
data from (A).
S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
325
Fig. 5. "Nd vs. 87 Sr=86 Sr of samples H1, H2, H4, H5 and H11 from V28-82. Data from H11 are unpublished. Also included are published
analyses from Revel et al. [11] from samples designated by them as Heinrich layers. Different symbols are used to indicate samples from
within the IRD belt and from north of the IRD belt. In general, mixing between continental sources would follow a straight line on such
a plot due to the relatively similar Sr=Nd concentration ratios. Shown for reference is a mixing curve such as used by Grousset et al.
[9] between Iceland and Baffin Bay sources, as well as a vertical line indicating mixing of continental sources of various ages (but with
similar 87 Sr=86 Sr and a horizontal line indicating mixing of Archean sources with a range of Rb=Sr. The curvature of the Iceland Baffin
Bay mixture is a function of the high Sr=Nd concentration ratio in basalt sources compared to continental crust. Note that the data do not
conform to a simple mixing relationship between Iceland detritus and that represented by Heinrich layers within the IRD belt, though
there may be Icelandic detritus in the samples. Instead they require a much broader spectrum of continental end members.
layers H2, H4 and H5 indicate a source with model
ages of 2.4 to 2.7 billion years. Such mantle extraction ages characterize much of the Superior
and Churchill Provinces of the Canadian Shield (e.g.,
[11,29]), the locations of which are shown in Fig. 1.
Heinrich layer H1 also has an ancient provenance,
although the 2.2 billion-year model age indicates that
there must additionally be a significant contribution
of post-Archean material (Fig. 6).
Pb isotope compositions of the <63 µm fractions
of Heinrich layers in V28-82 are distinctive, with
very low ratios compared to normal rock compositions which would lie near the right end of the
Stacey and Kramers [30] Pb evolution model shown
Table 3
Grain counts and geochemical data from V28–82
Sample Lithics a Forams a dc b IRD c Nd
depth (#=g)
(#=g)
(%) (%) (ppm)
(cm)
147 Sm=144 Nd 143 Nd=144 Nd
60
96
194
244
0.1065
0.0972
0.1094
0.0986
5418
5684
5190
5956
447
117
63
34
9
13
15
16
86.5
89.9
98.3
97.6
9.9
16.1
15.9
13.6
0.511518
0.511278
0.511233
0.511258
"Nd
21.8
26.5
27.4
26.9
87 Sr=86 Sr 206 Pb=204 Pb 207 Pb=204 Pb 208 Pb=204 Pb
0.726380
0.725893
0.728593
0.727823
16.981
16.457
16.861
16.451
15.324
15.287
15.339
15.339
37.568
37.558
38.477
37.416
a Data from McManus et al. [2]. The depths of these counts are not precisely the same as the depths in the table. They are 60, 98, 192,
and 245 cm.
b The percentage of detrital fraction that is carbonate (dc).
c Data from Gwiazda et al. [10,22].
326
S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
Fig. 6. Plot of f Sm=Nd vs. "Nd (plot devised by Shirey and Hanson, [54]; f Sm=Nd is 147 Sm=144 Nd=0.1963
1, "Nd is 104 ð
1)) to show Sm–Nd isotope data from H1, H2, H4 and H5 from V28-82. Mixing on such a plot is linear.
(143 Nd=144 Nd=0.512636
Shown for reference are lines representing TDM of 2.7 Ga (Superior Province, e.g., [54–56] and 1.9 Ga (approximately youngest of
model ages in provinces that were formed during the Early Proterozoic; e.g., [57]) depleted mantle model ages, intersecting at the present
estimation of average depleted mantle (DM, mantle model from Taylor and McLennan, [27]). The steep line labeled Iceland is the array
of values for volcanic rocks from Iceland [58]. The horizontal dashed lines represent most of the range of continental crust values of
f Sm=Nd , and mixing among continental sources would lie along approximately horizontal lines. The relatively young TDM for H1 of
about 2.2 Ga, suggests a significant contribution from continental sources younger than Archean. Data from H11 in V28-82 (TDM 1.5
Ga) are unpublished.
in Fig. 4. In fact the values are close to those of the
feldspars. This unradiogenic character of the Pb isotopes requires that they were derived from a source
with a very low U=Pb and Th=Pb for a long time. In
the context of hornblende ages and Pb isotope data
from feldspars, it is most likely that the time of U
and Th depletion relative to Pb happened at about 1.8
billion years ago. In this case the µm (238 U=204 Pb)
of the sediment source since 1.8 Ga has been about 2
to 4, in contrast to normal continental crustal values
of 8 to 12 necessary to produce the rock compositions mentioned above. The implied Th=U is about
7 to 8 (except H1 which is 5), in contrast to normal
continental crustal values of about 4. Both the low
U=Pb and high Th=U are consistent with depletion
of these elements during a high grade metamorphic
event, which is further consistent with the apparent
paleoisochron derived from the individual feldspar
grains, and with the dominance of Early Proterozoic
relative to Archean hornblende ages.
3.3. Detrital carbonate grain counts
Detrital carbonate contents of Heinrich layers H2,
H4, and H5 samples are 13 to 16% (Table 3), similar to those found in Heinrich layers from DSDP
609 [5] but significantly lower than the 25 to 30%
recorded from Orphan Knoll [12]. The detrital carbonate content of H1 is 9%, lower than the other
samples from Heinrich layers in V28-82, and lower
than reported values in other cores [5,12]. Assuming
perfect stratigraphic correlation between the Heinrich layers from Orphan Knoll and those from cores
V28-82 and DSDP 609, there must be a dilutant
to the sediment that reduces that detrital carbonate
content of the IRD fraction by a factor of almost 2.
This result is surprising in light of the isotopic data
from these V28-82 samples which appear to point to
a simple source, and one that is entirely compatible
with the inferred Hudson Strait source of the detrital
carbonate [5].
S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
4. Discussion
4.1. Advantage of multiple component provenance
studies
Isotope data from bulk sediments provide valuable insights into possible source areas, but they
are unable to allow distinctions between derivation
from single sources or mixtures except in rare cases
of unusual compositions. Thus they are best used
in conjunction with as many other tracers as possible and preferably with data from individual detrital
components (e.g., [28]). In this study we attempt to
evaluate the degree of mixing to Heinrich layers in
the eastern portion of the IRD belt by taking a multiple component approach to four prominent Heinrich
layers in V28-82. We report analyses from (1) individual grains of hornblende (40 Ar=39 Ar, Appendix
A, see EPSL Online Background Dataset 4 ), (2)
individual grains of feldspar (Pb isotopes, Table 2),
(3) Nd isotope analyses from bulk <63 µm fraction
and Sr and Pb isotope analyses from bulk, de-carbonated samples of the <63 µm fraction of H1, H2,
H4, and H5 from V28-82 (Table 3), and (4) lithic
grain counts from the same samples (Table 3). Hornblende and feldspar analyses are directly comparable
to those of Gwiazda et al. [10,22,23], Sr and Nd
analyses are directly comparable to those of Grousset et al. [9] and Revel et al. [11], and lithic grain
counts are comparable to those of Bond et al. [5] and
Bond and Lotti [12]. Although core V28-82 has a
relatively low overall sedimentation rate, it provides
an excellent record of the Heinrich layers, and thus
is an ideal location at which to compare the various provenance approaches that have been applied.
The provenance interpretation from the feldspar and
hornblende data is clear in the Heinrich layers of
V28-82. They came from a terrane formed during
the Late Archean (ca. 2.7 billion years) and metamorphosed during the Early Proterozoic (ca. 1.75
billion years) as described by Gwiazda et al. [22,23].
The Nd, Sr and Pb isotope data from the <63 µm
fraction are completely explained by the geological
history outlined above. In fact, the isotope data from
such a source terrane encompass the values of Sr and
4
http==www.elsevier.nl=locate=epsl, mirror site:
http:==www.elsevier.com=locate=epsl
327
Nd isotopic compositions from samples of Heinrich
layers in the IRD belt (Fig. 6).
4.2. Comparison to other provenance studies of the
Heinrich layers
The K–Ar ages of fine grained sediments from
H1, H2, H4, and H5 in the Dreizack region of the
eastern North Atlantic are all about 1 billion years
in contrast to the ambient sediments that have 0.4
billion years K–Ar ages [7,8]. K=Ar ages of the fine
fractions of H2 from V28-82 and from Orphan Knoll
[31,32], measured by the 40 Ar=39 Ar method, are
also about 1 billion. The close agreement between
fine grained samples in the Labrador Sea (Orphan
Knoll, Fig. 1) and eastern North Atlantic (V28-82
and Dreizack, Fig. 1) indicates that even the finest
grain sizes in the Heinrich layers, even far to the
east, are dominated by ice rafted sources from the
Labrador Sea.
The 1 billion year age of the Heinrich layers is
reasonably explained by mixing of minerals from
basement rocks of the Canadian Shield with Paleozoic clay minerals and mica from terrigenous clastic
sediments overlying portions of the continental terranes surrounding the Labrador Sea. Indeed the large
percentage of detrital carbonate is a clear indication
of substantial ancient sedimentary rock contributions
to the Heinrich layers. Additional evidence of ancient sedimentary rock sources to the Heinrich layers
comes as a byproduct of examining alkenones for
sea surface temperature estimates. Rosell-Melé et al.
[17] have found organic pigments that require recycling of ancient organic rich material of sedimentary
origin within the youngest Heinrich layers.
All of the data discussed in the previous paragraphs appear to be explainable in a simple way
with a provenance from the Hudson Strait region
as originally proposed by Bond et al. [5]. However, the contrast between detrital carbonate grain
percentages from Orphan Knoll [12], compared to
those from DSDP 609 [5] and V28-82 (Table 3)
seem to suggest a significant dilution (about 2ð) of
the coarse grained fraction (i.e., detrital carbonate)
of the Labrador Sea source in Heinrich layer samples from cores in the eastern North Atlantic. More
data will be required to resolve the apparent conflict
between detrital carbonate indications of great sedi-
328
S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
ment dilution on the one hand, and other provenance
indicators of a single dominant source. A possible
explanation is that there may be a turbidite contribution in some parts of the Orphan Knoll section due
to vigorous turbidity currents in the NAMOC (North
Atlantic Mid Ocean Channel) of the Labrador Sea
[33].
4.3. Problems with extending this approach outside
the IRD belt and into ambient glacial sediments
Isotopic analyses of individual grains have provided an unmatchable view of sedimentary provenance within the Heinrich layers [10,22,23]. However, there are complications with extending single
grain provenance studies outside of the Heinrich layers. Outside of the IRD belt, the portion of coarse
detritus is diminished, even within the Heinrich layers. It is also likely that the reduction in abundance
of coarse grains is accompanied by an increase in
the number of contributing sources. Consequently,
more grains would be necessary to characterize the
provenance, but fewer grains are available for analysis. Within the IRD belt, Heinrich layers are easy
to spot due to the bright white appearance that
results from the high abundance of detrital carbonate against the generally dark color of the ambient
glacial age sediment. In fact, they are so distinctive that they are actually good marker horizons for
stratigraphic correlation. There is no doubt that a
very high resolution record of IRD sources from
intervals outside the Heinrich layers would provide
important insights into ocean — ice sheet interactions in the North Atlantic at other times. However,
detailed stratigraphic correlation becomes more difficult with less distinctive layers. We suggest that
this work is nevertheless important, ant that high
resolution petrological counts, species counts, and
stable isotope stratigraphy, combined with magnetic
intensity records and abundant 14 C chronology can
provide the information necessary to sample wisely
outside of the Heinrich layers.
In addition to the difficulty of tracing Heinrich
layers outside of the IRD belt, it is also difficult to
make a practical sample plan for studying ambient
sediment within the IRD belt. Because there are so
many ice rafting ‘events’ in the North Atlantic, the
question of where to sample in order to monitor am-
bient glacial detritus is difficult to answer. Gwiazda
et al. [22,23] reported analyses of individual feldspar
and hornblende grains from above and below H2
from three cores, one from the Labrador Sea (HU87033-009), one from the western Atlantic that was selected to have maximum contribution from the Gulf
of St. Lawrence (V23-14) and one from the eastern
Atlantic (V28-82). Gwiazda et al. [22] also reported
analyses of composite feldspar samples from a larger
number of core samples from within and from above
and below H2. It is clear from comparing the values
from individual grains with composite samples from
the same layer that the composite analyses reflect
average mixes from a number of sources. Pb isotope
analysis of feldspar, both on individual grains and on
populations, clearly distinguish Heinrich layers H1,
H2, H4 and H5 from those of ambient samples and
H3 and H6. However, ambient sediments and H3=H6
contain a wide variety of compositions, clearly from
multiple sources [10,22], and it is not possible to
quantify the number of contributors without a large
number of single grain analyses from a single layer.
4.4. Contrast between H1 and the other
carbonate-bearing Heinrich layers in core V28-82
Heinrich layer H1 occurred during the interval
of Termination I at about 14.4 radiocarbon years
before present. Accordingly, we are particularly interested to know if it has characteristics that set it
apart from the other events. Although there are many
similarities relative to the other three Heinrich layers
studied here, H1 has some significant differences.
The Sr and Pb isotope compositions of the de-carbonated >63 µm fraction of all four samples are
very similar. Additionally, the 40 Ar=39 Ar hornblende
ages (and Ca=K of the Early Proterozoic portions),
the Pb isotope compositions of composite feldspar
samples [10], and the K=Ar ages of the fine fractions
[7,8,31] are indistinguishable. However, the detrital
carbonate content of H1 is only 9%, in contrast to
13 to 16% for the other three layers, and the "Nd
is 22 (TDM D 2:2 Ga), in contrast to 26 to 27
(TDM D 2:5 Ga) for the other three (Table 3). Heinrich layer H11 is also located at a glacial termination
(Termination II). It can be seen from Fig. 6 that H11
is even more different than ‘normal’ Heinrich layers
H2, H4, H5. More work is underway to examine the
S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
provenance of these two terminal Heinrich layers,
but it stands to reason that there may have been more
sources contributing to the icebergs during the final
collapse of the ice sheets.
4.5. Ocean–ice sheet interactions and climate
change
The recognition and interpretation of Heinrich
layers as armadas of icebergs launched from the
Hudson Strait [1,5,6] renewed interest in the glaciology of the Laurentide ice sheet. The profound climate fluctuations that appear to be tied to the Heinrich events in North Atlantic records raised the question of whether large ice sheets surrounding the
North Atlantic could actually drive climate change in
the region (e.g., [34–36]). The link of this glacialogical process to climate is the influence of topography
of the Laurentide ice sheet on the position of the
jet stream and the high pressure cell over the North
Atlantic, and accordingly the sea surface temperature
in the North Atlantic.
Several observations from the marine record have
called on a purely glacialogical mechanism for the
Heinrich layers into question. Bond and Lotti [12]
demonstrated the existence of numerous ice rafting
events in high resolution North Atlantic sediment
records. These events, including the Heinrich events,
can be reasonably correlated with cold air temperatures in Greenland ice cores and cold sea surface
temperature [12,14]. Bond and Lotti [12] concluded
that the Heinrich events are merely an unusually
large ice sheet response to periodic climatic forcing.
Additionally, there is a growing body of evidence for
correlative abrupt climate changes in many parts of
the globe (e.g., [37–41]). It could be that all these
recorded, high-frequency oscillations are driven by
millennial scale climate variability, and that the presence of large ice sheets merely has a magnifying
effect on records in the North Atlantic as suggested
by Bond and Lotti [12]. Given that Heinrich layers may be simply an extreme response to climate
change, there are still serious questions about the role
of the events in the rapid climate changes that followed. Changes in the jet stream related to changes
in ice sheet topography and temporary loss of fresh
meltwater to the North Atlantic, that may have immediately followed the Heinrich layers, could have
329
had a substantial impact on North Atlantic circulation and thus climate. Whatever the ultimate driver
of the system, a glacialogical mechanism is probably
the best way to explain the unusually large response
recorded in the Heinrich layers, and thus their study
must include land, sea and air-based observations.
4.6. Significance of V28-82 results to glacial
geology of the Canadian Shield
Despite extensive Quaternary mapping in Canada,
the locations of ice centers and paths of disintegration of the Laurentide ice sheet remain contentious,
and are subjects of ongoing investigation (e.g., [42–
45]). Of particular interest to studies of Heinrich
layers is the question of whether there was a single ice dome centered over Hudson Bay during the
Last Glacial Maximum (e.g., [46]), or whether there
were multiple ice domes (e.g., [47]). The Hudson
Bay dome configuration is an important part of the
geophysical binge=purge models of Heinrich events
(e.g., [34–36,48,49]).
The sequence of events proposed by Mayewski
et al. [50] and assumed in glacialogical models
of MacAyeal and Alley [34–36] and Verbitski and
Saltzman [48], or the ice shelf model of Hulbe [51]
makes good sense with regard to observations of
Heinrich layers. In particular, a dual mode of buildup
into the Hudson Bay dome and then catastrophic
collapse through the Hudson Strait is well suited
to explain the abrupt and anomalous occurrences of
Heinrich layers in the marine sediment record. It is
also compatible with their pattern of distribution and
other indications of sediment provenance. However,
the glacialogical field evidence on southern Baffin
Island [52] and eastern Hudson Bay [44] raises questions about this hypothesis. Miller et al. [52] reported
that there is little field evidence to support the existence of a major ice stream along the Hudson Strait.
In contrast, they have found abundant evidence for
repeated events where ice flowed across, rather than
along the Strait. Parent et al. [44] report evidence of
ice flow westward into the eastern shore of Hudson
Bay through Marine Isotope Stage 2 and possibly
Stage 3, and this evidence appears to be in direct
conflict with the existence of an ice dome centered
over Hudson Bay. Additionally, oxygen isotope evidence from remaining Baffin Island ice caps [45]
330
S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
appears to further contradict the Hudson Bay ice
dome hypothesis.
With further isotope work on the moraines of the
region, combined with comparisons from the marine
record, it may be possible to uniquely identify the
path of Heinrich layer detritus, and possibly other
ice-rafting events. The geology of the region is a
complicated mixture of Archean and Early Proterozoic terranes [29], and this may be an advantage for
sorting out the details of ice flow to marine outlets in
the vicinity of the Labrador Sea. South of the Hudson Strait, on the Ungava Peninsula, Archean rocks
of the Minto sub-province of the Superior Province
occur within Ungava Bay, and Early Proterozoic of
the Torngat Mountains to the east along the Labrador
coast. Other ancient terranes (e.g., Nain Province) lie
east of the Torngat Mountains along the Labrador
coast. North of the Hudson Strait lies the Churchill
Province, a region of pervasive Early Proterozoic
metamorphism, mostly overprinting Archean terranes (Rae Province) (Fig. 1b). Paleozoic carbonate
deposits (Fig. 1a) cover the floor of Hudson Strait.
The Pb isotope compositions of individual feldspar
grains as well as the 40 Ar=39 Ar ages of individual
hornblende grains in the Heinrich layers of core
V28-82 require ancient continental sources such as
the Early Proterozoic metamorphic terranes of the
Churchill Province interpreted by Gwiazda et al.
[10,22,23] to be the dominant sediment source. The
isotope studies are further consistent with previous
interpretations based on detrital carbonate abundance
[5]. Based on mapped geological province boundaries [29], combined with the information obtained
from feldspar and hornblende grains, it appears to
be a reasonable conclusion that the IRD was derived
from sources to the North of the Ungava Peninsula,
within the Churchill (Rae) Province. However, in
order to make a conclusive statement, it would be
necessary to verify the isotopic composition of Pb
in feldspars and 40 Ar=39 Ar hornblende ages from
moraines on the Ungava Peninsula and other parts of
the Labrador coast.
The data we report here are inconsistent with a
large contribution to the Heinrich layers from the St.
Lawrence drainage or indeed from other continental areas which would contribute other than detritus
with the Archean–Early Proterozoic history defined
by the isotope systems. The data are most consistent
with a relatively limited area of origin within the
region surrounding the Labrador Sea. They do not
require an ice stream surging through the Hudson
Strait, but they are entirely compatible with that hypothesis. In summary, extensive contributions from
much older (Archean) rocks, or much younger rocks
of middle and late Proterozoic and Paleozoic ages,
or from Iceland, are inconsistent with the results, and
in this way the results strongly limit the area of ice
berg launching, most likely to the Churchill region,
from the continental masses around the Labrador
Sea. However, the Churchill Province is a large and
varied province, and there is reason to be optimistic
that the source region can eventually be pinpointed
even better. The reason that even narrower location
of the ice rafted detritus sources is important is to
better constrain the mechanisms operating to drive
these dramatic glacialogical events and the climatic
causes and=or responses that appear to be globally
correlated with them.
5. Conclusions
Radiogenic isotope evidence from carbonatebearing Heinrich layers H1, H2, H4 and H5 in the
eastern North Atlantic are consistent with the bulk of
terrigenous sediments derived from the ancient continental sources surrounding the Labrador Sea, and
are inconsistent with a large contribution from the St.
Lawrence region, Iceland, or Europe. Heinrich layer
H1 has an additional contribution from a younger
source. The difference in provenance between H1
and the other three Heinrich layers studied here is
seen in about 5 epsilon units higher 143 Nd=144 Nd ratios from samples in core V28-82 and lower detrital
carbonate contents relative to the other Heinrich layers in core V28-82. In contrast, the additional source
is not seen in hornblende or feldspar analyses from
V28-82 or in the 87 Sr=86 Sr ratio. Although the provenance of these Heinrich layers appears to be well
constrained, there are some remaining observations
to be explained. Among them are the contrast in
detrital carbonate abundance between Orphan Knoll
and cores from the eastern North Atlantic. Further
integrated studies are necessary to finally resolve
issues related to provenance, pathways, and causes
of ice rafting in the North Atlantic. In addition to
S.R. Hemming et al. / Earth and Planetary Science Letters 164 (1998) 317–333
more detailed provenance studies, more effort needs
to be devoted to constraining stratigraphic relations
within North Atlantic sediment cores, sediment flux
both spatially and temporally, and to characterizing potential sediment sources, especially along the
western margin of the North Atlantic and the land
surrounding the Labrador Sea.
Acknowledgements
W.F. Ruddiman and an anonymous reviewer are
thanked for their thorough and constructive comments on the manuscript. Thanks go to Troy Rasbury
for discussion and for help with Pb isotope analyses
at Stony Brook, and to Gil Hanson for generously
allowing SRH to make analyses at Stony Brook.
Discussions with Johan Kleman, Ingmar Borgström,
Dave Marchant, George Denton, and Michel Parent
about the glacial geology, and with Scott McLennan, Gil Hanson, Sean Higgins and Claude HillaireMarcel on provenance matters are also appreciated.
Thanks are also due to Paul Renne and others at the
Berkeley Geochronology Center for making SRH
welcome, to Steve Goldstein for access to the isotope lab at Lamont and for providing a reference for
Icelandic compositions, and to Gary Hemming for
analytical and editorial help. This paper is funded in
part by a grant=cooperative agreement from the National Oceanic and Atmospheric Administration and
in part by the National Science Foundation OCE9633554. The views expressed herein are those of
the authors and do not necessarily reflect the views
of NOAA or any of its subagencies. Support for
the curating facilities of the Lamont-Doherty Earth
Observatory Deep-Sea Sample Repository is provided by the National Science Foundation through
Grant OCE94-02150 and the Office of Naval Research through Grant N00014-I-0186. This is Lamont-Doherty Earth Observatory contribution 5864.
(CL)
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