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Natural Variability of Greenland Climate, Vegetation, and Ice Volume During the Past Million Years


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The response of the Greenland ice sheet to global warming is a source of concern notably because of its potential contribution to changes in the sea level. We demonstrated the natural vulnerability of the ice sheet by using pollen records from marine sediment off southwest Greenland that indicate important changes of the vegetation in Greenland over the past million years. The vegetation that developed over southern Greenland during the last interglacial period is consistent with model experiments, suggesting a reduced volume of the Greenland ice sheet. Abundant spruce pollen indicates that boreal coniferous forest developed some 400,000 years ago during the "warm" interval of marine isotope stage 11, providing a time frame for the development and decline of boreal ecosystems over a nearly ice-free Greenland.
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DOI: 10.1126/science.1153929
, 1622 (2008); 320Science
et al.Anne de Vernal,
and Ice Volume During the Past Million Years
Natural Variability of Greenland Climate, Vegetation, (this information is current as of June 20, 2008 ):
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olivines in the light isotopes of Fe (and the heavy
isotopes of Mg) (16, 20).
The extent of equilibrium isotope fractionation
is mainly controlled by the relative mass dif-
ference between the isotopes, and more fraction-
ation happens in isotopes with a larger relative
mass difference (14, 24).IftheFeisotopicvaria-
tion in the lava lake was produced by equilibrium
isot o pe fract io na ti on , Mg isotopes should show
more significant fractionation than Fe isotopes
because of their larger relative mass difference.
Furthermore, kinetic isotope fractionation driven
by th ermal and chemical diffusion should also
result in larger fractionation in Mg isotopes as
compared with that in Fe isotopes (16, 17, 20).
The absence of Mg isotope fractionation in Kilauea
Iki lavas may result from the low-precision iso-
topic analysis of Mg relative to Fe (e.g., 0.1
versus 0.04), which prevents the detection of
Mg isotopic variation. More likely, the presence
of Fe isotope fractionation and the absence of Mg
isotope fractionation may reflect the influence of
Fe oxidation states on kinetic or equilibrium iso-
tope fractionation (as compared with those of Mg,
two oxidation states of Fe exist in terrestrial mag-
matic systems) (5, 25).
Our study suggests that, unlike Li and Mg
isotopes (2, 3), Fe isotopes fractionate during ba-
saltic differentiation at both whole-rock and crys-
tal scales. Mineral compositions should therefore
be used to help interpret whole-rock basalt Fe
isotopic data. The elevated d
Fe of crustal igne-
ous rocks, which is more evolved than that in
basalts, could be explained by fractional crystal-
lization (10).
References and Notes
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F. von Blanckenburg, Geochim. Cosmochim. Acta 71,
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Lett. 268, 330 (2008).
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Lett. 252, 342 (2006).
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Principles, B. O. Mysen, Ed. (Geochemical Society,
University Park, PA, 1987), vol. 1, pp. 241258.
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available as supporting material on Science Online.
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Geochim. Cosmochim. Acta 71, 3833 (2007).
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Isotopes, C. M. Johnson, B. L. Beard, F. Albarede, Eds.
(Mineralogical Society of America, Washington, DC,
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24. H. C. Urey, J. Chem. Soc. (London) 1947, 562 (1947).
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H. L. Krivoy, U.S. Geol. Surv. Prof. Pap. 537-E, 1 (1970).
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U.S. Geol. Surv. Open-File Rep. 94-684, 1 (1994).
28. Discussions with S. Huang, A. T. Anderson Jr., F. M. Richter,
are appreciated. We thank three anonymous reviewers for
constructive comments. This work was supported by a
Packard fellowship, the France Chicago Center, and NASA
through grant NNG06GG75G to N.D.
Supporting Online Material
SOM Text S1 to S5
Fig. S1
Tables S1 to S4
29 February 2008; accepted 12 May 2008
Natural Variability of Greenland Climate,
Vegetation, and Ice Volume During
the Past Million Years
Anne de Vernal* and Claude Hillaire-Marcel
The response of the Greenland ice sheet to global warming is a source of concern notably because of its
potential contribution to changes in the sea level. We demonstrated the natural vulnerability of the ice
sheet by using pollen records from marine sediment off southwest Greenland that indicate important
changes of the vegetation in Greenland over the past million years. The vegetation that developed over
southern Greenland during the last interglacial period is consistent with model experiments, suggesting a
reduced volume of the Greenland ice sheet. Abundant spruce pollen indicates that boreal coniferous forest
developed some 400,000 years ago during the warm interval of marine isotope stage 11, providing a
time frame for the development and decline of boreal ecosystems over a nearly ice-free Greenland.
he potential for sea-level rise, caused by
melting of the Greenland ice-sheet as sur-
face air temperature increases, is consid-
erable (1). Although there is evidence that the
velocity of ice streams flowing into the ocean and
cently (2, 3), large uncertainties remain about the
long-term stability of the ice sheet. The climate
Fig. 4. Modeling of Fe
isotopic variations dur-
ing magmatic differen-
tiation in Kilauea Iki
lava lake (12). Solid
lines represent calcu-
lated Fe isotopic com-
positions of residual
melts during fractional
crystallization by assum-
ing a Rayleigh distilla-
tion process with average
crystal-melt fractionation
factors (Dd
0.1, 0.2, and 0.3.
Dashed horizontal lines
represent calculated mix-
ing lines between the
most magnesian melt
from the 1959 eruption
Fe = 0, 0.1, and 0.2 (black squares)]. The blue star
represents the most magnesian melt (MgO = 10.7 wt %; assumed d
Fe = 0.11). The green bars
represent the ranges of measured d
Fe and estimated MgO in olivine grains from two drill core samples
(MgO = 33.6 to 39.8 wt % and 41.9 to 42.7 wt %; table S3). Sample crystallization sequences are the same
as those in Fig. 2. Error bars indicate 95% CI of the mean.
Melt + olivines
MgO (wt%)
Fe = –0.41 to + 0.01
Fe = –1.10 to + 0.09
Fe (‰)
20 JUNE 2008 VOL 320 SCIENCE www.sciencemag.org1622
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and ice volume of Greenland seem to have varied
considerably in the recent geological past, as shown
by paleoecological data indicating a warmer re-
gional climate and reduced ice volume during the
last interglacial period (4) and by biogenic remains
of coniferous trees from forests that grew on Green-
land during Pliocene and early-to-mid-Pleistocene
times some hundred thousands to million years ago
(5, 6). However, although the climate and ice sheet
history of Greenland during the last climatic cycle
are well documented by isotope and geochemical
records from ice cores, which reveal high sensitiv-
ity to sea-surface conditions over the northern
North Atlantic Ocean (7), very little is known
about conditions preceding the onset of the last
glaciation because of the lack of continuous direct
records. On one hand, glacial activity on Green-
land over millions of years is evidenced by ice-
rafted debris in marine cores from continental
margins (8), but the precise size of the Greenland
ice sheet and its relative stability over time remain
unknown. On the other hand, sedimentary out-
crops from the Greenland coasts and near-shore
marine sediment cores suggest the recurrence of
relatively warm climatic conditions during the past
(5, 6, 9), but the duration and timing of these
phases remain uncertain. We used the pollen con-
tent of sediment cores from the Ocean Drilling
Program (ODP) site 646 on the continental rise,
off southern Greenland (Figs. 1 and 2), as an in-
dependent proxy for assessing the dominant type
of vegetation and the timing of the last forested
episodes. The stratigraphy of the cores was estab-
lished from d
O in foraminifer shells (10), which
permits correlation with the stack marine isotope
stratigraphy of Lisiecki and Raymo (11)andthe
setting of a time scale (12) (fig. S1).
One difficulty in interpreting pollen assem-
blages from marine sediments is the identification
necessarily exotic and derives from more or less
long-distance transport. T wo main transport mech-
anisms have to be taken into account: atmospheric
transport by winds, and hydrodynamic transport
through runof f, rivers, and marine currents. The
long-distan ce atmospher ic tran sport of pollen re-
sults in low concentrations with distorted assem-
blages characterized by an overrepresentation of
Pinus pollen grains that show exceptional aerial
dispersion properties (13). Along continental mar -
gins, detailed studies have shown that most of the
pollen in marine sediments is due to fluvial inputs
from adjacent lands, therefore allowing direct com-
parison with terrestrial palynostratigraphy (14). In
the Labrador Sea, pollen analyses along a near-
shore to offshore transect showed that atmospheric
transport is accompanied with an asymptotic de-
crease in the concentration of pollen from the coast-
line and an increase in the relative proportion of
GEOTOP Geochemistry and Geodynamics Research Center
Université du Québec à Montal, Case Postale 8888,
succursale Centre-Ville, Montréal, Québec H3C 3P8, Canada.
*To whom correspondence should be addressed. E-mail:
Fig. 1. Location of ODP
site 646 (58°12.56 N,
48°22.15 W; water
depth 3460 m) in the
northern North Atlantic
and of other coring sites
referred to in the text:
HU-90-013-013 (58°12.59
N, 48°22.40 W; water
depth 3379 m); ODP
site 647 (53.19.9 N,
45°14.7 W, water depth
3862 m); and HU-84-
030-003 (53.19.8 N,
45°14.7 W, water depth
3771 m). The Dye 3 cor-
ing site, where spruce
DNA was found, is indi-
cated by a blue square
(6). The white arrows
correspond to the mean
surface vector wind from
June to September based
on the 1968-to-1996 clima-
tology [see the National
Centers for Environmen-
tal Prediction/National
Center for Atmospheric
Research reanalysis (www.], available from the Earth System Research Laboratory, Physical
Science Division, of the National Oceanic and Atmospheric Administration ( The thin
, respectively. The blue
arrows schematically illustrate the surface ocean circulation pattern along the Greenland coast, in the
Labrador Sea, and in Baffin Bay. The dashed green line corresponds to the present-day northern limit of the
potential natural tree line or cold evergreen needle-leaf forest in Biome models (27).
Fig. 2. Stratigraphy and chronology of the upper 76 m at ODP site 646 (58°12.56N, 48°22.15 W; water
depth 3460 m) based on
OmeasurementsinNeogloboquadrina pachyderma (10) and correlation with the
stack curve LR04 of Lisiecki and Raymo (11). The abundance of pollen grains and spores of pteridophytes is
expressed in concentration per cm
of sediments. Sedimentation rates are uniform and average 7.8 cm per ka,
which permits the assumption that pollen concentrations are approximately proportional to fluxes (fig. S1)
(12). The vertical gray bands correspond to modern values of concentrations, and the horizontal green bands
correspond to phases with concentrations at least twice that of those recorded during the late Holocene. SCIENCE VOL 320 20 JUNE 2008
on June 20, 2008 www.sciencemag.orgDownloaded from
Pinus (15). Pliocene to recent pollen contents at
offshore sites from the northwest North Atlantic
(ODP site 647, core sample HU84-030-003) (Fig.
1), where mostly wind inputs can be recorded, are
characterized by pollen fluxes lower than 0.5 grain
and largely dominated by Pinus (16).
The analyses of Arctic snow, Greenland ice, and
pollen traps along the southern Greenland edge
show an exotic component from boreal forests of
North America, but illustrate that long-distance
atmospheric transport is responsible for low inputs
(17, 18). Therefore, the large-amplitude variations
in pollen content from the southern Greenland
margin records at ODP site 646, with fluxes
well above modern or Holocene (that is, the past
1 1, 500 years) values, can be interpreted as reflecting
changes in hydrodynamic inputs from a relatively
proximal source-vegeta tion located on southern
Greenland (12). Furthe r evidence for the promi-
nence of proximal sources during interglacials is
provided by the comparison of total pollen content
to long-distance transported grains of Pinus (12).
The pollen record of the last million years at
ODP site 646 shows important variations both in
concentrations [thus fluxes, because sedimentation
rates remained fairly constant in the study se-
quence (12)] and dominance of the main taxa
(Figs.2and3andfigs.S2andS3)(12). Pollen
concentrations vary by orders of magnitude, from
less than 10 grains cm
to more tha n 10
. In general, low concentrations are recorded
during glacial stages. Minimum values (close to
zero) characterize the marine isotope stage (MIS)
6, indicating very low fluxes from both long-
distance and proximal sources, which is consistent
with extensive development of the Laur entide and
Greenland ice sheets (9). Higher concentrations
are seen in interglacial sediments. The Holocene
is characterized by concentrations of about 100
grains cm
. The assemblages include inputs from
the boreal forest of southeastern Canada linked to
predominant southwest-northeast summer winds,
but show components (12) that are from more-
proximal shrub-tundra vegetation.
Earlier interglacial stages record much higher
pollen concentrations than the Holocene. Those of
MIS 5e are five times higher, and the concen-
trations of pteridophytes spores are also higher .
The assemblages are characterized by dominant
Alnus and abundant spores of Osmunda (Fig. 3B
and fig. S2). In core sample HU-90-013-013 col-
lected near ODP site 646 (19), more detailed anal-
yses of MIS 5e document the pollen succession
(Fig. 4). A rapid increase of Alnus occurred during
an early phase of MIS 5e characterized by high
summer sea-surface temperatures, which suggests
rapid development of shrub tundra after the ice
retreat (9). The subsequent increase of Osmunda
represents a unique event in the last million years.
It coincides with maximum sea-surface temper-
atures in winter and suggests the development of
dense fern vegetation over southern Greenland un-
der climatic conditions not unlike those of the
modern boreal forest, given the present distri-
bution of the genus. Osmunda expanded possibly
in a la r g e geog r ap h i c a l do m a in, because spores
were identified at the base of ice cores drilled in
the Agassiz ice cap (20). Toward t h e end of MIS
5e, pollen and spore influxes decreased concomi-
tantly with the augmentation of herb percentages.
This event corresponds to the fi r st ste p to w a r d
higher d
OvaluesinGlobigerina bulloides and
Neogloboquadrina pachyderma. It suggests a
change to the herb tundra resulting from regional
cooling at the onset of ice growth.
MIS 7, the penultimate interglacial period, dif-
fered from MIS 5e in many respects (Fig. 3C).
Sea-surface temperatures never reached those of
MIS 5e, and the pollen and spore content of sed-
iment remained lower . Its pollen assemblages are
characterized by dominant herb taxa (notably
Poaceae and Cyperaceae), suggesting the devel-
opment of tundra along southern Greenland coasts.
The MIS 1 1 interglacial is different than others
because of its near 50,000-year duration [374 to
424 thousand years ago (ka) (11)]. At site 646,
MIS 11 is also unique because of pollen concen-
trations one order of magnitude higher than those
of the Holocene, the dominance of Picea spp., and
the occurrence of Abies pollen grains (Figs. 2 and
3D and fig. S2). The dominance of Picea from the
beginning to the end of the interglacial period sug-
gests the presence of forest vegetation throughout
the entire interval, at least over southern Greenland.
The base of MIS 1 1 is marked by higher pro-
Fig. 3. (A to E)Stratig-
raphy, sea-surface temper-
atures, and concentration
of dominant pollen and
spore taxa during the
present interglacial pe-
riod [MIS 1 (A)], the last
interglacial period [MIS
5e (B)], MIS 7 (C), MIS
11 (D), and MIS 13 (E).
Sea-surface temperatures
are estimated from dino-
cysts [the thin lines are
best estimates from five
modern analogs and the
thick lines correspond to
three-point running av-
erag e s (28)]. Dinocyst as-
semblages were reported
by de Vernal and Mudie
(29). The modern sea-
surface temperatures at
0.7°C and 7.3 ± 1.1°C
in winter and summer, re-
spectively [data from the
World Ocean Atlas, 2001
(30)]. Among pollen assem-
blages, herb taxa include
mostly Pocacea, Cyperace-
ae, and Asteraceae. Shrub
pollen is dominated by
Alnus and Betula with the
occasional occurrence of
Salix and Ericaceae (fig. S2).
Pinus has been excluded
because of its overrepresen-
tation due to long-distance
atmospheric transport.
20 JUNE 2008 VOL 320 SCIENCE www.sciencemag.org1624
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portions of shrub and herb pollen, indicating more
open vegetation and a cooler climate, but Picea
was probably already present regionally , taking
into account the fact that its concentrations reached
hundreds of grains per cm
. The covariance of d
in planktic foraminifers and of Picea concentra-
tio ns suggests a synchronous ice retreat and early
forest development, a maximum of Picea concen-
tration when maximum sea-surface temperatures
occurred, and a concomitant glacial onset and
forest decline at the end of MIS 11. The devel-
opment of spruce forest over Greenland probably
indicates relatively mild conditions (6)anda
substantial reduction of the Greenland ice sheet
during the long MIS 11 interglacial period. How-
ever , precise paleoclimatic and paleoecological in-
ferences from pollen or DNA are uncertain without
knowing the species of conifer trees. The identifi-
cation of Picea pollen grains down to the species
level is difficult because of uniform morphologica l
characteristics of the genus. Nevertheless, detailed
microscopic examination suggests the occurrence
of several species, among which Picea abies
dominated (fig. S4). In northern Europe and
Fennoscandia, Picea abies is a common conifer
tree of montane and boreal environments that
often occurs at the tree limit and acted as a pi-
oneer along emerging postglacial coasts (21).
Growth of Picea abies is fostered by high July
temperatures and cool and snowy winters, but
has a low temperature threshold (2.6°C) for the
initiation of bud and stem growth. Picea abies
has adapted to survive severe climate; it can
persist for hundreds of years by vegetative prop-
agation. Therefore, its development, at least over
southern Greenland during MIS 11, does not nec-
essarily imply a zonal climate that was warmer
than at present, because the northern tree limit
and the Picea abies timberline occur now near
the polar circle in Europe. However, it certainly
indicates ice-free conditions over a large area of
Greenland, and thus a much-reduced ice-sheet
volume, otherwise katabatic winds (22)would
have restricted any forest development.
Before MIS 11, the pollen content was rarely
less abundant than it was during the Holocene,
thus suggesting vegetation that was generally as
extensive as it is at present. Pollen was particu-
larly abundant during MIS 13 (Figs. 2 and 3E),
but Picea concentrations did not reach values as
high as those during MIS 11, thus suggesting
shrub-tundratype vegetation.
In conclusion, although the pollen record
from site 646 does not provide a direct picture of
climate changes over Greenland, it yields impor-
tant information that helps link fragmentary
terrestrial records into a continuous sequence.
Furthermore, the pollen record is as a proxy for
the ice volume of Greenland in two ways. First, it
provides information on pollen production, and
thus on the vegetation density on adjacent land,
which implies ice-free conditions. Second, it
depends on the distance to site 646 from the
source vegetation, which has been shorter during
ice-free episodes in southern Greenland because
of low relative sea levels that are a result of iso-
static adjustment. A substantially reduced Green-
land ice volume seems to have characterized MIS
5e, 1 1, and 13, as well as the Pliocene (23), indi-
cating a long-term sensitivity of the Greenland
ice sheet to warm temperatures. Among warm
climate intervals of the last million years, MIS 11
stands out in terms of forest vegetation spreading
over southern Greenland. Thus, if the melting of
Greenland and other Arctic ice caps are assumed
to have contributed to the equivalent of a 2.2- to
3.4-m-higher sea level during MIS 5e (24), we
may assume that they contributed some more
during MIS 11. The actual volume of the ice-
sheet decline during these episodes is difficult to
estimate, but it did occur under natural forcing
with an atmospheric partial pressure of CO
parts per million by volume (25). During MIS 5e,
particularly high summer insolation probably con-
tributed to the Greenland ice melt (4), whereas
the long duration of MIS 1 1 might explain the
retreat of the ice sheet under an insolation pattern
that is similar to that of the Holocene (26). The
data presented here provide evidence of the
vulnerability of the Greenland ice sheet to natural
forcing and should increase concerns about its
fate during the anticipated global warming.
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financial support from the Natural Sciences and
Engineering Resear ch Council of Canada and the Fonds
Quécois de Recherche sur les Sciences de la Nature et
les Technologies.
Supporting Online Material
Materials and Methods
Figs. S1 to S4
10 December 2007; accepted 9 May 2008
Fig. 4. Close-up on the stratigraphy of the last
interglacial period (MIS 5e) from core sample HU-90-
013-013, collected near ODP site 646. Shown are the
isotope stratigraphy based on Globigerina bulloides
and Neogloboquadrina pachyderma (19), the sea-
surface temperatures estimated from dinocysts (28),
and the concentration and percentages of the
dominant pollen and spore taxa. The percentages
of Osmunda were calculated from the pollen sum,
excluding spores. SCIENCE VOL 320 20 JUNE 2008 1625
on June 20, 2008 www.sciencemag.orgDownloaded from
... It has been shown, for instance, that the accuracy of GIA corrections for global mean sea-level rise during the Last Interglacial (the Eemian) are highly dependent on uncertainties in our understanding of ice-sheet configuration and the duration of deglaciation for the largest ice-mass in the northern hemisphere, the North American Laurentide Ice Sheet (LIS) during the preceding glacial terminations (e.g.; Dendy et al., 2017;Dyer et al., 2021). While strong evidence exists to show that nearcomplete deglaciation of southern Greenland occurred during MIS 11 by ∼418 ka (e.g., De Vernal and Hilliare-Marcel, 2008;Reyes et al., 2014;Hatfield et al., 2016), nothing is known about the history of LIS retreat during T5. ...
... Hatfield et al., 2016). The average PG mixing of 48% is shown by a dashed line; (J) Labrador Sea ODP Site 646 pollen data (De Vernal and Hilliare-Marcel, 2008; core site shown in Fig. 2), showing Picea (dark green) and total (minus Pinus; light green) pollen concentrations. Site 646 data plotted on the MD99-2227 age model following Reyes et al. (2014); (K) EPICA Dome C CO 2 concentration (ppm) with typical early Holocene peak concentrations of 265ppm (red dashed line; Lüthi et al., 2008 on AICC2012 chronology of Bazin et al., 2013). ...
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Termination (T) 5, ∼424 ka, involved the biggest deglaciation of land-ice mass during the Quaternary. Warming and ice-sheet retreat during T5 led to an exceptionally long period of interglacial warmth known as Marine Isotope Stage (MIS) 11, ∼424-395 ka. A detailed understanding of the history of continental ice-sheet decay during T5 is required to disentangle regional contributions of ice-sheet retreat to sea-level rise (that range between ∼1 and 13 m above present day) and to correct it for glacio-isostatic adjustments (GIA). Yet little is known about the timing and magnitude of retreat during this time of the volumetrically most important continental ice sheet in the Northern Hemisphere, the Laurentide Ice Sheet (LIS). Here we present new authigenic Fe-Mn oxyhydroxide-derived high-resolution records of Pb isotope data and associated rare earth element profiles for samples spanning T5 from Labrador Sea IODP Site U1302/3. These records feature astronomically-paced radiogenic Pb isotope excursions that track increases in chemical weathering of North American bedrock and freshwater routing to the Labrador Sea via Hudson Straits associated with LIS retreat. Our records show that LIS retreat during T5 began 429. 2 ± 7.9 ka (2σ) and likely occurred over a longer timescale (by ∼10 to 5 kyr) than that observed for T2 and T1. They also show that Hudson Bay Ice Saddle collapse (and therefore LIS break-up) occurred ∼419 ± 4.7 ka (2σ), around the same time as best estimates of southern Greenland deglaciation, but ∼12 kyr before LIS deglaciation and the sea-level high-stand associated with the latter half of MIS 11 likely occurred. Our findings therefore highlight that ice-mass loss on North America likely played an important role in the seemingly protracted nature of T5 sea-level rise. A comparison of the deglaciation histories of the LIS and the southern Greenland Ice Sheet during T5, T2 and T1 also demonstrates that the well-constrained history of regional ice-sheet retreat during T1 is not always applicable as a template for older late Pleistocene terminations in GIA modelling.
... However, this explanation for more intense Asian summer monsoon does not apply for the Indian monsoon, which is weaker if the NH ice sheets are larger (Zhisheng et al., 2011). Furthermore, many high-latitude NH localities indicate a rather warm and humid climate during those interglacial periods, incompatible with larger NH ice sheets (Prokopenko et al., 2002;Wright and Flower, 2002;De Vernal and Hillaire-Marcel, 2008;Alonso-Garcia et al., 2011a;Melles et al., 2012;Hao et al., 2015;Lozhkin et al., 475 2017;Barker et al., 2019;Wang et al., 2023). In addition, MIS 14 stands out in the benthic δ 18 O records as a moderate glacial period with short duration (e.g. ...
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Changes in sea-level are linked to glacial-interglacial variability and have been claimed as the main factor controlling the production of carbonate platform factories. The Maldives archipelago (Indian Ocean), composed of two rows of atolls that enclose an inner sea, is a very sensitive region to sea-level changes. The sediments of the Inner Sea, offer an excellent study site to explore the impact of sea-level changes on carbonate platforms. Elemental geochemical composition records, obtained by X-ray fluorescence (XRF) core-scanning, from the Maldives Inner Sea (IODP Site U1467), have been used in this work to evaluate the influence of orbitally-driven sea-level fluctuations on the carbonate production and export from the neritic environment into the Maldives Inner Sea over the last 1.3 million years. High Sr aragonite-rich carbonates (HSAC) from neritic settings are deposited in the Maldives Inner Sea during sea-level highstand intervals, increasing the values of the Sr/Ca ratio. In contrast, during sea-level lowstand periods large areas of the atolls were exposed or unable to grow and the demise in the carbonate production and sediment export is reflected as low Sr/Ca values in the Inner Sea. However, we propose that sea level is not the only factor controlling the production of HSAC during sea-level highstands since several interglacial periods before and after the Mid-Brunhes event (MBE, ~430 ka) indicate high carbonate production (high Sr/Ca). The intensity of the summer monsoon and the Indian Ocean Dipole probably modulated the production at the atolls. Marine Isotope Stage 11 stands out as a period with high sea-level and rather high carbonate production in the Maldives platform. This extraordinary carbonate production in the Maldives atolls (and in other low latitude carbonate platforms) probably contributed to the Mid-Brunhes dissolution event through a strong shelf-to-basin fractionation of carbonate deposition.
... The MIS 5e warmth is evident in the decreased abundance of N. pachyderma to <10% in cores 37JPC and Hu90-08 (Fig. 4), implying an insignificant influence by the polar water masses at this time within the western SPG (Irvalı et al., 2016) on the SE Grand Banks and the Newfoundland Basin. Numerous previous studies (e.g., Jouzel et al., 1993;McManus et al., 1994;de Vernal and Hillaire-Marcel, 2008;Govin et al., 2012;NEEM, 2013) have shown that the MIS 5e was a stable warm period of the last glacial cycle. However, a decrease in the % G. inflata in the SW SPG cores 37JPC and Hu90-08 suggests the subpolar water mass invaded during 126-120 ka. ...
Past studies of marine sediments of the North Atlantic documented millennial-scale sea-surface cooling related to the Dansgaard-Oeschger events that influenced the oceanic fronts and surface hydrology during the last glacial cycle. Most studies have focused on using ice-rafting, single or multiple species of planktonic foraminifers' abundances, and geochemistry to assess environmental changes. However, detailed planktonic foraminiferal assemblage data in the North Atlantic Transition Zone (NATZ) and subpolar gyre (SPG) for the full last glacial cycle are scarce. Here we report planktonic foraminiferal abundances, oxygen isotopes, and ice-rafted detritus (IRD) counts from two sediment cores, Hu9007-08 and Hu71022-377, collected from the Milne seamount of southwestern SPG (SW SPG) and NATZ, respectively. Further, we have used the published planktonic foraminiferal assemblage, IRD, and isotopic data from the eastern and western SPG to provide an integrated reconstruction of changes in the surface water masses and dynamics of the Polar, Arctic, and subarctic fronts (PF, AF, and SAF, respectively). Despite the overall warmth of the SW SPG (near the Newfoundland Basin) compared to the eastern SPG during marine isotope stage (MIS) 5, the North Atlantic-wide cooling events C24 and C21 were still identified in the SW SPG. Further, the planktonic foraminiferal abundances in cores EW9303-37JPC (i.e., scarce Neogloboquadrina pachyderma and abundant Globigerinoides inflata) and Hu9007-08 reveal a relatively warm MIS 5e compared to the Holocene. However, the decrease in the abundance of G. inflata suggests that the SW SPG was influenced by the seasonal presence of subpolar waters and possibly a southward shift in the oceanic frontal systems between ∼126 and ∼120 ka. During the Heinrich ice-rafting events, when meltwater flooded the surface North Atlantic, the PF, AF, and SAF shifted southward, and the polar/subpolar water masses briefly invaded the western and eastern SPG and NATZ. In the early part of MIS 3 (60–40 ka), the oceanic frontal system shifted northward from its position during MIS 4. The SPG and NATZ gradually warmed, and the subpolar species Globigerina bulloides in cores Hu9007-08, Hu71022-377, and CH69-K09 increased in the middle of MIS 3 (i.e., 38–30 ka), suggesting continuous sea surface warming while the oceanic frontal systems continued to move northward. This hydrological environment rapidly cooled in the late MIS 3-MIS 2 (30–19 ka), with the PF shifted southward to the mid-latitude (∼45°N) during the Last Glacial Maximum. During the last deglaciation-Holocene, the regions of cores Hu9007-08 and Hu71022-377 were mainly influenced by the warm North Atlantic Current, and the SAF was located north of both cores. This study presents the first large-scale water mass movements and frontal changes in the SPG and NATZ to better understand the dynamics of the surface circulation in the North Atlantic during the last glacial cycle.
... In past interglacial periods, the GIS was likely smaller than present (de Vernal & Hillaire-Marcel, 2008;Schaefer et al., 2016), with potential impacts on moisture delivery to the Arctic. The handful of paleoclimate archives that span multiple interglacial periods in this region (Knutz et al., 2019;Miller et al., 2022;NEEM Community Members, 2013) offer an opportunity to use this multi-proxy approach to explore the nature and extent of these impacts. ...
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Plain Language Summary Continental ice sheets alter atmospheric circulation, influencing global heat and moisture distribution. Records of atmospheric circulation during previous periods of ice‐sheet retreat can provide insights into the changes that are possible in the future. This study examines summer atmospheric circulation in Baffin Bay from 12,000 to 7,000 years ago, a period of dramatic ice‐sheet retreat. Precipitation isotopes reflect moisture source, which responds to changes in air temperature and atmospheric circulation. This study uses records of temperature and precipitation isotopes from the same sediment archive to tease apart the influence of temperature from that of atmospheric circulation. The precipitation isotopes in this record distinct changes in moisture sources, which a climate model simulation suggests was caused by retreating ice sheets. Before about 10 ka, when the Laurentide Ice Sheet (LIS) covered eastern Canada, summer winds in Baffin Bay shifted regularly between south and north, carrying air with unique temperature and precipitation isotope signatures. As the LIS retreated, the Greenland Ice Sheet (GIS) remained relatively large and dominated atmospheric circulation, causing a rapid shift to southeasterly winds. As the GIS retreats in the future, atmospheric circulation may undergo similar rapid changes.
... It is critical to better understand the sensitivity of the GrIS, and its ecosystems relative to different climate states as human-induced climate change increases in magnitude and duration. Our understanding of GrIS past history mostly relies on indirect archives, such as marine sediments (Larsen and others, 1994;de Vernal and Hillaire-Marcel, 2008;Bierman and others, 2016;Tripati and Darby, 2018;Christ and others, 2020) or seismic surveys (e.g. Knutz and others, 2019) that allow insights about GrIS behavior over millions of years (Tripati and Darby, 2018). ...
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We present new data from the debris-rich basal ice layers of the NEEM ice core (NW Greenland). Using mineralogical observations, SEM imagery, geochemical data from silicates (meteoric ¹⁰ Be, εNd, ⁸⁷ Sr/ ⁸⁶ Sr) and organic material (C/N, δ ¹³ C), we characterize the source material, succession of previous glaciations and deglaciations and the paleoecological conditions during ice-free episodes. Meteoric ¹⁰ Be data and grain features indicate that the ice sheet interacted with paleosols and eroded fresh bedrock, leading to mixing in these debris-rich ice layers. Our analysis also identifies four successive stages in NW Greenland: (1) initial preglacial conditions, (2) glacial advance 1, (3) glacial retreat and interglacial conditions and (4) glacial advance 2 (current ice-sheet development). C/N and δ ¹³ C data suggest that deglacial environments favored the development of tundra and taiga ecosystems. These two successive glacial fluctuations observed at NEEM are consistent with those identified from the Camp Century core basal sediments over the last 3 Ma. Further inland, GRIP and GISP2 summit sites have remained glaciated more continuously than the western margin, with less intense ice-substratum interactions than those observed at NEEM.
Black spruce (Picea mariana [Mill.] B.S.P.) is a dominant conifer species in the North American boreal forest that plays important ecological and economic roles. Here, we present the first genome assembly of P. mariana with a reconstructed genome size of 18.3 Gbp and NG50 scaffold length of 36.0 kbp. A total of 66,332 protein-coding sequences were predicted in silico and annotated based on sequence homology. We analyzed the evolutionary relationships between P. mariana and 5 other spruces for which complete nuclear and organelle genome sequences were available. The phylogenetic tree estimated from mitochondrial genome sequences agrees with biogeography; specifically, P. mariana was strongly supported as a sister lineage to P. glauca and 3 other taxa found in western North America, followed by the European Picea abies. We obtained mixed topologies with weaker statistical support in phylogenetic trees estimated from nuclear and chloroplast genome sequences, indicative of ancient reticulate evolution affecting these 2 genomes. Clustering of protein-coding sequences from the 6 Picea taxa and 2 Pinus species resulted in 34,776 orthogroups, 560 of which appeared to be specific to P. mariana. Analysis of these specific orthogroups and dN/dS analysis of positive selection signatures for 497 single-copy orthogroups identified gene functions mostly related to plant development and stress response. The P. mariana genome assembly and annotation provides a valuable resource for forest genetics research and applications in this broadly distributed species, especially in relation to climate adaptation.
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Past interglacial climates with smaller ice sheets offer analogs for ice sheet response to future warming and contributions to sea level rise; however, well-dated geologic records from formerly ice-free areas are rare. Here we report that subglacial sediment from the Camp Century ice core preserves direct evidence that northwestern Greenland was ice free during the Marine Isotope Stage (MIS) 11 interglacial. Luminescence dating shows that sediment just beneath the ice sheet was deposited by flowing water in an ice-free environment 416 ± 38 thousand years ago. Provenance analyses and cosmogenic nuclide data and calculations suggest the sediment was reworked from local materials and exposed at the surface <16 thousand years before deposition. Ice sheet modeling indicates that ice-free conditions at Camp Century require at least 1.4 meters of sea level equivalent contribution from the Greenland Ice Sheet.
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The Marine Isotope Stage 11c (MIS-11c) interglacial is an enigmatic period characterized by a long duration of relatively weak insolation forcing, but is thought to have been coincident with a large global sea level rise of 6–13 m. The configuration of the Greenland Ice Sheet during the MIS-11c interglacial highstand is therefore of great interest. Given the limited data constraints, model-based analysis may be of use, but only if model uncertainties are adequately accounted for. A particularly under-addressed issue in coupled climate and ice sheet modeling is the coupling of surface air temperatures to the ice model. Many studies apply a uniform “lapse rate” accounting for the temperature differences at different altitudes over the ice surface, but this uniformity neglects both regional and seasonal differences in near-surface temperature changes. Herein we provide the first such analysis for MIS-11c Greenland that addresses these uncertainties by comparing 1-way coupled CESM and ice sheet model results from several different downscaling methodologies. In our study, a spatially- and temporally-varying temperature downscaling method produced the greatest success rate in matching limited paleodata constraints, and suggests a peak ice volume loss from Greenland during MIS-11c of near 50 % compared to present day (~3.9 m contribution to sea level rise). This result is on the lower bound of existing data- and model-based studies, partly as a consequence of the applied one-way coupling methodology which neglects some feedbacks. Additional uncertainties are examined by comparing two different present-day regional climate analyses for bias correction of temperatures and precipitation, a spread of initialization states and times, and different spatial configurations of precipitation bias corrections. No other factor exhibited greater influence over the simulated Greenland ice sheet than the choice of temperature downscaling scheme.
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Previous pollen analyses of ice cores from Devon and Ellesmere islands have contributed considerably to our knowledge of past climate in the Canadian High Arctic. In this case, in 1979, bulk (35–83 litres) water samples were melted down a hole 139 m deep, drilled to bedrock, 1.2 km from the top of the flow line in Agassiz Ice Cap in northern Ellesmere Island. Analysis of ten of these samples, plus some taken in very dirty ice from the melt tank during drilling 7 years ago, has yielded pollen concentrations that, together with the oygen-isotope (6) signatures, suggest the Agassiz Ice Cap began its growth during the last interglacial period. A discrepancy between melt-tank and bulk-sample pollen concentrations is believed to be due to a loss of pollen from the melt-tank samples during the drilling process.
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Correlations of isotopic and palynological records from deep sea cores in Baffin Bay and Labrador Sea with terrestrial palynological sequences, supported by a few Th/U chronological controls, allow the establishment of a regional climatostratigraphic scheme for the Late Pleistocene climatic fluctuations in eastern Canada. During the climatic optimum of isotopic substage 5e, warmer conditions than present prevailed both on land and in oceanic surface water masses. The 5e/5d transition is marked by an abrupt shift in 818O values in Baffin Bay and Labrador Sea as a consequence of ice growth over circumpolar areas of northeastern Canada. From substage 5d to substage 5a, the Baffin Bay border lands experienced glacial conditions while subarctic to cool-temperate and humid climates persisted over Labrador Sea and Atlantic Canada. A short (<104yrs) stage 4 is recorded in deep sea cores with high 8'8O values. It corresponds to the Early Wisconsinan southward extension of the Laurentide Ice Sheet dated at ca. 80,000 yrs in the central St. Lawrence Lowland. There is no clear evidence of full glacial conditions in the Atlantic Provinces during this episode. Stage 3 (Middle Wisconsinan) corresponds in the isotopic records to large oscillations in 818O values suggesting meltwater transits in both Baffin Bay and Labrador Sea. The ice cover remained relatively extensive over eastern Canada, although some areas experienced ice-marginal conditions : in the Atlantic Provinces, notably on Cape Breton Island, hemiarctic to subarctic climate is inferred from palynological records; in the Appalachian foothills of Quebec glacial Lake Gayhurst developed some 46,000 yrs ago. During isotopic stage 2 (Late Wisconsinan), the Laurentide Ice Sheet reached its maximum extent while satellitic ice-caps developed over the Atlantic Provinces. In deep sea cores, high 818O values mark the full glacial conditions of isotopic stage 2, although slightly lower values in western Labrador Sea indicate discrete but continuous meltwater influxes. An early melting phase of the northeastern margin of the Laurentide Ice Sheet is recorded shortly after 16,700BP. The full ice-retreat is observed after ca. 11,000BP. At that time, southeastern Canada was already largely ice-free. Finally, the optimum climatic conditions of isotopic stage 1 settled diachronously in the adjacent basins of eastern Canada.
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Glacial till, glaciomarine diamictites, and ice-rafted detritus found in marine cores collected off the shore of southeast Greenland record multiple Late Cenozoic glaciations beginning in the Late Miocene. Distinct rock assemblages and seismic stratigraphic control correlate the diamictites with glaciation of the southeast Greenland margin. Glaciers advanced to the sea during several intervals in the Pliocene and Pleistocene. North Atlantic glaciation may have nucleated in southern Greenland rather than further north because of the high mountains and the high levels of precipitation in this region.
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We present a 5.3-Myr stack (the "LR04" stack) of benthic δ 18 O records from 57 globally distributed sites aligned by an automated graphic correlation algorithm. This is the first benthic δ 18 O stack comprised of more than three records to extend beyond 850 ka, and we use its improved signal quality to identify 24 new marine isotope stages in the early Pliocene. We also present a new LR04 age model for the Plio-Pleistocene derived from tuning the δ 18 O stack to a simple ice model based on June 21 insolation at 65 • N. Stacked sedimentation rates provide additional age model constraints to prevent overtuning. Despite a conservative tuning strategy, the LR04 benthic stack exhibits significant coherency with insolation in the obliquity band throughout the entire 5.3 Myr and in the precession band for more than half of the record. The LR04 stack contains significantly more variance in benthic δ 18 O than previously published stacks of the late Pleistocene as the result of higher resolution records, a better alignment technique, and a greater percentage of records from the Atlantic. Finally, the relative phases of the stack's 41-and 23-kyr components suggest that the precession component of δ 18 O from 2.7–1.6 Ma is primarily a deep-water temperature signal and that the phase of δ 18 O precession response changed suddenly at 1.6 Ma.
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Previous pollen analyses of ice cores from Devon and Ellesmere islands have contributed considerably to our knowledge of past climate in the Canadian High Arctic. In this case, in 1979, bulk (35–83 litres) water samples were melted down a hole 139 m deep, drilled to bedrock, 1.2 km from the top of the flow line in Agassiz Ice Cap in northern Ellesmere Island. Analysis of ten of these samples, plus some taken in very dirty ice from the melt tank during drilling 7 years ago, has yielded pollen concentrations that, together with the oygen-isotope (6) signatures, suggest the Agassiz Ice Cap began its growth during the last interglacial period. A discrepancy between melt-tank and bulk-sample pollen concentrations is believed to be due to a loss of pollen from the melt-tank samples during the drilling process.
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New observations of long-distance pollen transport to southern Greenland are recorded during the last 2 weeks of May, 2003. The results indicate northeastern North America as the source area of the transported pollen grains as shown in earlier investigations. Backward trajectories indicate that transport occurred twice during the first week corresponding to a time of maximum pollen flux emitted to the atmosphere in the source area. A large percentage of exotic pollen grains were identified, about 11% of the total counted. However, transport during the second week appears to have occurred during a single day at a time of reduced pollen emission into the atmosphere, which was subjected later to severe washout. As a result, only 1% of the total pollen spectra was identified as exotic grains. The back trajectories modeled by the HYSPLIT application differ somewhat from those previously identified in 2002. Although in both years air passing over southern Greenland at 3000 m carried out the main transport, additional transport could have occurred at a much lower altitude in 2003.
A multi-technique approach has been used to study a Pliocene shallow water marine deposit, designated the I OE le de France Formation, in North-East Greenland. The sequence is correlated on the basis of 87 Sr^ 86 Sr ratios in shells and palaeomagnetic studies with the Gauss normal polarity chron, which is dated to between 2.60 and 3.58 Ma years BP. This dating is in accordance with amino acid epimerisation and evidence from dinoflagellates, foraminifers and molluscs. Sediments, marine molluscs and foraminifers show that the sequence was deposited on the inner shelf, below storm wave base. Seawater temperatures were much higher than today, as demonstrated by the occurrence of a number of southern extra-limital species. The same applies to air temperature, and the few remains of land plants may indicate a forested upland with Picea and Thuja. A number of extinct taxa are present, including Nucula jensenii that is erected as a new species.
The pollen content of 77 snow samples, collected at 41 sites in the Canadian Arctic, the adjacent Arctic Ocean and Greenland can be used to identify source regions that produced the assemblages. The major vegetation zones of northern Canada produce distinctive pollen assemblages, and principal components analysis (PCA) indicate that these assemblages are retained even in snow on the sea ice surface. It is shown that pollen percentages and concentrations are related to the density of the regional vegetation and to the distance to the source of more productive regions. Because the pollen grains may be transported for great distances (even to the central regions of the Arctic Ocean), they may be used to indicate the source of that pollen and the trajectory of the air masses that carried and deposited them. Pine is particularly valuable in this sense because it has longer trajectories than other tree pollen. For example, there are indications of "over-the-pole" transport of pollen from higher pine pollen concentrations at the North Pole than on northern Ellesmere Island. Pollen concentrations of certain taxa change significantly at ˜75°N, north of which the concentrations become lower, thereby suggesting that there is a climatic boundary at that latitude. Therefore it would appear that studies of the concentration of pollen in snow have the potential for determining past and present characteristics of atmospheric circulation and also for helping in the development and interpretation of paleoenvironmental records in regions without vegetation, such as ice caps.
Aim The Holocene spread of Picea abies in Fennoscandia is well established from many sites and thus provides an opportunity for detailed study of the dynamics of tree spread and population expansion. Early‐ and mid‐Holocene macrofossil evidence for presence of P. abies in Fennoscandia has questioned traditional interpretations of the timing and direction of its spread. This paper aims to determine when, from where and by which pathways P. abies spread into Fennoscandia. Understanding the character and dynamics of this spread may give insight into the general understanding of Holocene tree spread. Location The north‐western distribution of P. abies in Europe, including Norway, Sweden, Finland, Estonia, Latvia, Lithuania, north‐western Russia, parts of Byelorussia and Poland. Methods Holocene pollen diagrams with independent dating control were collected from this region. The timing of the onset of the continuous curve, the timing of the rise of the curve, the first appearance of frequencies of 1%, 3%, 5%, and 10%, as well as timing and the maximum amount of P. abies pollen, was obtained from these pollen diagrams. A GIS analysis was used to display the data and interpolate ages over the area under investigation. Results Maps are presented showing a clear ESE to WNW trend in the spread of P. abies for all characters interpolated. The timing of the rise of the curve was difficult to use as sites east of the Baltic have slowly rising P. abies frequencies while the western sites often show a rapid rise. Main conclusions The spread of P. abies in Fennoscandia and adjacent areas can be separated into two phases: (i) A rapid early Holocene spread out of Byelorussia and northern Russia at low population density giving rise to small outpost populations, possibly as far west as the Scandes Mountains. (ii) A mid‐ to late Holocene front‐like spread at high population densities moving from east to west into the Baltic Republics and Finland, into northern Scandinavia and then moving south and west towards its present‐day distributional limits.
A new calibration database of census counts of organic-walled dinoflagellate cyst (dinocyst) assemblages has been developed from the analyses of surface sediment samples collected at middle to high latitudes of the Northern Hemisphere after standardisation of taxonomy and laboratory procedures. The database comprises 940 reference data points from the North Atlantic, Arctic and North Pacific oceans and their adjacent seas, including the Mediterranean Sea, as well as epicontinental environments such as the Estuary and Gulf of St. Lawrence, the Bering Sea and the Hudson Bay. The relative abundance of taxa was analysed to describe the distribution of assemblages. The best analogue technique was used for the reconstruction of Last Glacial Maximum (LGM) sea-surface temperature and salinity during summer and winter, in addition to sea-ice cover extent, at sites from the North Atlantic (n=63), Mediterranean Sea (n=1) and eastern North Pacific (n=1). Three of the North Atlantic cores, from the continental margin of eastern Canada, revealed a barren LGM interval, probably because of quasi-permanent sea ice. Six other cores from the Greenland and Norwegian seas were excluded from the compilation because of too sparse assemblages and poor analogue situation. At the remaining sites (n= 54), relatively close modern analogues were found for most LGM samples, which allowed reconstructions. The new LGM results are consistent with previous reconstructions based on dinocyst data, which show much cooler conditions than at present along the continental margins of Canada and Europe, but sharp gradients of increasing temperature offshore. The results also suggest low salinity and larger than present contrasts in seasonal temperatures with colder winters and more extensive sea-ice cover, whereas relatively warm conditions may have prevailed offshore in summer. From these data, we hypothesise low thermal inertia in a shallow and low-density surface water layer.