A Pervasive Millennial-Scale
Cycle in North Atlantic
Holocene and Glacial Climates
Gerard Bond,* William Showers, Maziet Cheseby, Rusty Lotti,
Peter Almasi, Peter deMenocal, Paul Priore, Heidi Cullen,
Irka Hajdas, Georges Bonani
Evidence from North Atlantic deep sea cores reveals that abrupt shifts punctuated what
is conventionally thought to have been a relatively stable Holocene climate. During each
of these episodes, cool, ice-bearing waters from north of Iceland were advected as far
south as the latitude of Britain. At about the same times, the atmospheric circulation
above Greenland changed abruptly. Pacings of the Holocene events and of abrupt
climate shifts during the last glaciation are statistically the same; together, they make up
a series of climate shifts with a cyclicity close to 1470 6 500 years. The Holocene events,
therefore, appear to be the most recent manifestation of a pervasive millennial-scale
climate cycle operating independently of the glacial-interglacial climate state. Amplifi-
cation of the cycle during the last glaciation may have been linked to the North Atlantic’s
thermohaline circulation.
More than 20 years ago, Denton and
Karle´n (1) made two provocative sugges-
tions about the climate of our present in-
terglacial or Holocene period. Having
found what appeared to be synchronous
advances of mountain glaciers in North
America and Europe, they concluded that
Holocene climate was much more variable
than implied by broad trends in pollen and
marine records. On the basis of radiocarbon
chronologies of the glacial advances, they
further suggested that the climate variations
were part of a regular millennial-scale pat-
tern, which when projected backward coin-
cided with climate shifts of the preceding
glaciation and when projected forward pre-
dicted a progressive warming over the next
few centuries.
Despite its important implications, Den-
ton and Karle´n’s concept of a predictable,
millennial-scale climate rhythm has not
been widely accepted, partly because it has
been difficult to find corroborating evi-
dence in other climate records. For exam-
ple, measurements of oxygen isotopes,
methane concentrations, and snow accu-
mulation in Greenland ice cores reveal no
evidence of millennial-scale fluctuations
during the Holocene, except perhaps for a
brief cooling about 8200 years ago (2).
Many researchers now view the Holocene
climate as anomalously stable (3). Recent
evidence from deep sea sediments in the
Nordic Seas (4) suggests that Holocene cli-
mate there was even more stable than
climate during the last interglaciation
(Eemian).
In 1995, however, O’Brien et al. (5)
demonstrated from measurements of soluble
impurities in Greenland ice that Holocene
atmospheric circulation above the ice cap
was punctuated by a series of millennial-
scale shifts. The most prominent of those
shifts appeared to correlate with Denton
and Karle´n’s glacial advances. Encouraged
by the findings of O’Brien and her col-
leagues, we launched an investigation of
deep sea Holocene sediments in the North
Atlantic, anticipating that the shifts in at-
mospheric circulation above the ice cap
were part of a much larger climate pattern
that left its imprint in the deep sea record.
Here, we report the results of that investi-
gation, showing that the North Atlantic’s
Holocene climate indeed exhibits variabil-
ity on millennial scales, and we then com-
pare the Holocene variations with climate
shifts of the last glaciation.
We analyzed Holocene sediment in two
cores from opposite sides of the North At-
lantic (Fig. 1), VM 28-14 (64°479N,
29°349W; 1855 m of depth) and VM 29-
191 (54°169N, 16°479W; 2370 m of depth).
High-resolution accelerator mass spectrom-
eter radiocarbon datings of planktonic fora-
minifera demonstrate that both cores have
thick and nearly complete Holocene sec-
tions (Table 1 and Fig. 2). Core top ages are
less than 1000 years (all ages are in calendar
years B.P. unless otherwise indicated). Sed-
imentation rates in both cores exceeded 10
cm per 1000 years, more than sufficient to
resolve millennial-scale variability, and the
rates were nearly constant (Fig. 2). We
sampled both cores at intervals of 0.5 to 1
cm (equivalent to a resolution of 50 to 100
years), and in each sample we measured
nine proxies (6).
The Holocene signal: Episodes of ice-
rafting. The most conspicuous evidence of
variations in the North Atlantic’s Holo-
cene climate comes from the same three
proxies that we used to document ice-raft-
ing in the North Atlantic during the last
glaciation (7). One proxy is the concentra-
tion of lithic grains, defined as the number
of grains with diameters greater than 150
mmin1gofcore. At both sites we found a
series of increases in grain concentrations,
which, although of much smaller magnitude
than those of the last glaciation, are distinct
and reach peak values several times that of
the ambient grain concentrations (Fig. 2).
The other two proxies are petrologic
tracers, defined as the percentages of cer-
tain types of lithic grains. One of the tracers
is fresh volcanic glass, which comes from
Iceland or Jan Mayen, and the other is
hematite-stained grains, mostly quartz and
feldspar, that come from sedimentary depos-
its containing red beds (Fig. 3) (7). During
each of the lithic events, both tracers dis-
play prominent increases well above the 2s
counting error (Fig. 2) (8).
These lithic/petrologic events demon-
strate that ice-rafting episodes also occurred
during the Holocene. Age differences of
lithic/petrologic maxima between the two
sites are within the 2s calendar age error
(Fig. 2 and Table 1); hence, the events
cannot be local in origin. Regional changes
in carbonate dissolution or in winnowing of
fine sediment could not have produced the
petrologic changes we measured, and in
neither core could we find evidence of cur-
rent laminations or cross-bedding, making
it unlikely that the events were produced by
strong bottom currents [see also caveats in
(9)].
Hence, contrary to the conventional
view, the North Atlantic’s Holocene cli-
mate must have undergone a series of
abrupt reorganizations, each with sufficient
impact to force concurrent increases in de-
bris-bearing drift ice at sites more than 1000
km apart and overlain today by warm, large-
ly ice-free surface waters of the North At-
lantic and Irminger currents. The ice-rafted
debris (IRD) events exhibit a distinct pac-
ing on millennial scales, with peaks at about
1400, 2800, 4200, 5900, 8100, 9400,
G. Bond, M. Cheseby, R. Lotti, P. Almasi, P. deMenocal,
P. Priore, and H. Cullen are at the Lamont-Doherty Earth
Observatory of Columbia University, Route 9W, Pali-
sades, NY 10964, USA. W. Showers is in the Department
of Marine, Earth and Atmospheric Sciences, North Caro-
lina State University, 1125 Jordan Hall, Raleigh, NC
27695, USA. I. Hajdas and G. Bonani are in the AMS
14
C
Lab, ITP Eidgeno¨ssische Technische Hochschule (ETH)
Honeggerberg, CH-8093 Zurich, Switzerland.
*To whom correspondence should be addressed. E-mail:
gcb@lamont.ldgo.columbia.edu
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10,300, and 11,100 years ago.
Ocean forcing of the Holocene signal.
We argue that the immediate cause of the
Holocene ice-rafting events was a series of
ocean surface coolings, each of which ap-
pears to have been brought about by a
rather substantial change in the North At-
lantic’s surface circulation. The most con-
sistent evidence of ocean surface coolings is
the succession of prominent increases in
Globigerina quinqueloba (Fig. 2), a species
that today dominates the planktonic fora-
miniferal populations in cool Arctic waters
north of Iceland (10). Corroborating that
evidence are increases in abundances of
Neogloboquadrina pachyderma (s.), the polar
planktonic foraminifera, during the first
four events (events 5 to 8), and marked
decreases in abundances of the warm-water
planktonic species N. pachyderma (d.) dur-
ing middle and late Holocene events (Fig.
2). Although some of the faunal shifts are
not large, all are defined by more than one
species, and they are correlative at two
widely separated sites. Moreover, because
the foraminiferal concentrations increased
markedly during most events (Fig. 2), it is
unlikely that the assemblages were modified
by carbonate dissolution.
Analysis of stable isotopes in G. bulloides
and N. pachyderma (d.) in the two cores
produced isotopic evidence of cooling at
the level of the Younger Dryas event—as
60ϒW
80ϒN
70ϒN
60ϒN
50ϒN
40ϒN
40ϒW20ϒW20ϒE40ϒE0ϒ
Fig. 1. Location of cores we analyzed and principal surface currents in the
North Atlantic and Nordic Seas. The green dots and green line are loca-
tions of COADS temperature estimates and the profile in Fig. 4A. The line
from A to B is the line of the cross section of petrologic data shown in Fig.
4B. Small dots and plus signs are locations of core tops analyzed for the
two petrologic tracers; numbers (from left to right) are percentage of
hematite-stained grains, percentage of Icelandic glass, and core locator
number [core locations and site numbers can be obtained from the first
author; see also (17 )]. Shaded red area encloses core tops with $10%
hematite-stained grains. Dashed black line encloses core tops with $15%
Icelandic glass. Histogram insert summarizes core top data for hematite-
stained grains showing contrast in percentages north and south of the
Denmark Strait and Iceland-Faeroes frontal systems, indicated by blue
shading. Locations of red beds in East Greenland and Svalbard are from
(7). Surface currents: EGC, East Greenland Current; JMC, Jan Mayen
Current; WSC, West Spitsbergen Current; EIC, East Iceland Current;
WGC, West Greenland Current; LC, Labrador Current; NAC, North Atlantic
Current; IC, Irminger Current.
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