, 118 (2005);
et al. V. Masson-Delmotte
Greenland Moisture Origin
GRIP Deuterium Excess Reveals Rapid and Orbital-Scale Changes in
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SSTs in individual ocean basins may have less
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21. B. Dong, R. Sutton, Geophys. Res. Lett. 29, 1728 (2002).
22. R. Zhang, T. Delworth, J. Clim., in press.
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Geophys. Res. Lett. 31, L12205 (2004); 10.1029/
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30. R.T.S. is supported by a Royal Society University
Research Fellowship. D.L.R.H. is supported by the
NERC Centres for Atmospheric Science. We are
grateful to colleagues at the Met Office Hadley
Centre for providing the HadISST and HadSLP data
sets and results from the C20 global SST experi-
ments. We thank J. Hurrell for valuable comments on
Supporting Online Material
Materials and Methods
Figs. S1 to S3
6 January 2005; accepted 20 May 2005
GRIP Deuterium Excess Reveals
Rapid and Orbital-Scale Changes
in Greenland Moisture Origin
V. Masson-Delmotte,1* J. Jouzel,1A. Landais,1M. Stievenard,1
S. J. Johnsen,2,3J. W. C. White,4M. Werner,5
A. Sveinbjornsdottir,3K. Fuhrer6
The Northern Hemisphere hydrological cycle is a key factor coupling ice
sheets, ocean circulation, and polar amplification of climate change. Here we
present a Northern Hemisphere deuterium excess profile covering one
climatic cycle, constructed with the use of d18O and dD Greenland Ice Core
Project (GRIP) records. Past changes in Greenland source and site temper-
atures are quantified with precipitation seasonality taken into account. The
imprint of obliquity is evidenced in the site-to-source temperature gradient at
orbital scale. At the millennial time scale, GRIP source temperature changes
reflect southward shifts of the geographical locations of moisture sources
during cold events, and these rapid shifts are associated with large-scale
changes in atmospheric circulation.
The atmospheric water cycle plays a key role in
climate change.At various time scales, changes
involved in key processes within the climate
system, such as the growth of ice sheets or the
freshwater budget of the ocean. Here we use an
integrated tracer of the water cycle, the isotopic
composition of the ice preserved in Greenland,
to decipher changes in Greenland moisture
origin over the last glacial cycle.
Water stable isotopes ratios (d18O or dD)
from polar ice cores are commonly used as past
temperature proxies (1, 2), a function made
possible by the progressive distillation of heavy
water isotopes when air masses cool toward
polar regions (3–5). Comparison of Greenland
temperature (Tsite) values derived from ice
d18O using the observed modern spatial
gradient with alternative paleothermometry
methods yields a systematic underestimation
of past surface annual mean temperature
changes, both at glacial-interglacial (6–8) and
rapid-events time scales (9–13). Such discrep-
ancies are thought to arise from variability in
the Northern Hemisphere hydrological cycle,
either from changes in moisture source areas
(14) or from changes in the seasonality of
precipitation (15, 16).
We used high-precision continuous water
stable isotope measurements made on the
Hemisphere deuterium excess d 0 EdD j (8 ?
d18O)^ profile covering one climatic cycle
(17). This deuterium excess record, together
with a method to account for changes in pre-
cipitation seasonality, was then used to quan-
tify past changes in Greenland moisture source
Figure 1 shows both d18O and deuterium
excess profiles for the last È100,000 years
(i.e., excluding the lowest part of the profiles
characterized by ice flow disturbances) (18).
The excess profile reveals well-defined features
at glacial-interglacial time scales, with a 5 per
mil (°) increase during the last climatic
transition (5), as well as for Dansgaard-
Oeschger (D/O) events characterized by large
(up to 5°) excess changes, in antiphase with
d18O changes. Similar rapid excess changes
are also recorded in the North Greenland Ice
Core Project (NorthGRIP) ice core for D/O
events 18 to 20 (13). Such deuterium-excess
variations essentially result from the fact that,
with respect to equilibrium processes, kinetic
isotopic effects play a much larger relative role
ford18O than for dD. In turn, deuterium excess
in polar snow, dsnow, is largely driven by
nonequilibrium processes (i.e., evaporation at
the ocean surface and condensation of water
vapor when snow forms). Deuterium excess in
water vapor over the ocean is mainly influ-
enced by sea surface isotopic composition, sea
surface temperature (SST), source temperature
(Tsource), and relative humidity. This imprint of
oceanic conditions (here considered only in
terms of Tsource) in the moisture source areas is
largely preserved in the deuterium excess
signal recorded in polar snow (19). In turn,
whereas dsnow(d18O or dD) depends primarily
on local temperature Tsiteand to a lesser degree
on Tsource, one can show that the opposite is
true for dsnow(20, 21).
Combining d18O and deuterium excess
profiles allows us to estimate both Tsiteand
Tsource. This dual approach, based on the
inversion (22) of a dynamically simple isotopic
model (23), is now used for interpreting
isotopic measurements performed on Antarctic
cores (24–26). Although useful for the last
millennium and for the Holocene in Greenland
(20, 27), this methodology leads to unrealistic
results when applied directly to the long-term
GRIP data (21). We show here that this
difficulty can be overcome if this inversion ac-
countsforthe seasonality ofsnowprecipitation,
as suggested by general circulation model
simulations. This allows us to interpret the
d18O or dD GRIP data in terms of Tsiteand
Tsourcechanges in a consistent way, both for
glacial-interglacial changes and for D/O events,
thus providing high-resolution information on
the source conditions and the reorganizations
of the water cycle during slow and rapid cli-
Seasonal characteristics are relatively well
known for central Greenland_s present-day
climate. Field observations suggest a year-
1IPSL/Laboratoire des Sciences du Climat et de
l’Environnement (LSCE), UMR CEA-CNRS, CEA Saclay,
91191 Gif-sur-Yvette, France.2Department of Geo-
physics, Juliane Maries Vej 30, University of Copen-
hagen, DK-2100 Copenhagen, Denmark.
Institute, University of Iceland, Dunhaga 3, Reykjavik
107, Iceland.4Institute of Arctic and Alpine Research
Institute and Department of Geological Sciences,
Campus Box 450, University of Colorado, Boulder, CO
80309, USA.5Max Planck Institute for Biogeochemistry,
Postbox 10 01 64, D-07701 Jena, Germany.6Physics
Institute, University of Bern, Sidlerstrasse 5, CH-3012
*To whom correspondence should be addressed.
R E P O R T S
1 JULY 2005VOL 309 SCIENCEwww.sciencemag.org
on June 4, 2013
round snowfall at Summit with a slightly larger
winter half-year accumulation due to intense
episodic storms (28). The seasonal variations
are strongly imprinted in d18Osnow, which
closely follows the temperature changes. As
shown by detailed shallow ice core and pit
studies, there is also a well-documented dsnow
seasonal cycle that lags variations in temper-
ature, dD, and d18O by È2 to 3 months (5, 29).
of the ocean, which results in a 2- to 3-month
lag between mid-latitude ocean surface temper-
ature and continental surface air temperature.
In contrast, glacial conditions inhibit winter
snowfall because of the modification of the
the winter storm tracks by (i) the Laurentide ice
sheet, and (ii) the modified latitudinal ocean
surface temperature gradients and increased
extent of sea ice (30). Modeling results sug-
gest a large change in precipitation season-
ality toward a dominant summer contribution
(15, 16). We also expect an enhanced dsnow
seasonal amplitude due to increased glacial
Greenland continentality. The È2- to 3-month
lag of the deuterium excess cycle, thermally
driven, should be essentially unchanged.
A detailed sensitivity analysis shows that a
simple half-year (summer-winter) approach is
well adapted to account for these seasonality
changes for reconstructing site and source
temperature records (21). Whereas the winter-
summer difference is large for dsnow, it is small
(less than 1°) for the deuterium excess
because of its seasonal lag. Hence, seasonality
has a strong impact on estimates of Tsitebut a
much weaker influence on Tsource, as these two
variables are driven by dsnowand dsnow, re-
spectively. The glacial decrease in winter
precipitation results in amplified seasonally
corrected isotopic signals by a factor that is
also influenced by the changes in the summer-
winter isotopic amplitude E(21), equation 5^.
We account for seasonality when two con-
ditions linked with sea-ice extent and Lauren-
is assumed to inhibit local moisture supply
when the site temperature is below a certain
threshold T1directly derived from the ice d18O
record, and (ii) to reflect the fact that the
winter moisture advection is related to the size
Fig. 1 (left). From top to bottom: ice volume indicated by seawater
d18Osw(31); 200-year resampled GRIP d18O and deuterium excess d (bold
lines represent isotopic profiles smoothed using the first two components of
a singular spectral analysis, which represents a low-pass filter below
10,000 years); and obliquity (43). Analytical precisions are T0.05° for d18O
and T0.50° for dD, resulting in a precision of T0.64° for deuterium excess.
Horizontal dashed lines identify thresholds T1and T2used for the seasonality
correction. Vertical lines point to selected rapid events (from left to right:
Younger Dryas, cold phases of D/O events 11, 12, and 22).
From top to bottom: log(Ca) (39); 200-year reconstructed site-to-source
temperature gradient (black solid line) and obliquity fluctuations (black
dashed line); site temperature (DTsite) reconstructed using various methods
Fig. 2 (right).
[spatial slope without seasonality correction, blue; our inversion with
seasonality correction but without source correction, red; our full isotopic
inversion with seasonality correction, black; the use of a constant slope
fitting with the LGM borehole estimate (32), green]; source temperature
(DTsource) reconstruction from full inversion. Results are displayed as
anomalies from modern conditions (present-day GRIP site temperature is
È –32-C and GRIP source temperature is È20-C). Bold lines represent
smoothed reconstructions as for Fig. 1.
R E P O R T S
www.sciencemag.org SCIENCEVOL 309 1 JULY 2005
on June 4, 2013
of the Laurentide ice sheet, we account for
seasonality changes only when the Laurentide
is large enough. We use here a second thresh-
old, T2, derived from the marine benthic d18O
sea level record, itself closely related to the
size of the Laurentide (31). Ensemble simu-
lations of seasonality correction and full iso-
topic inversion are then performed within a
a consistency with robust estimates of site tem-
perature amplitudes obtained with independent
methods (Table 1) for the Last Glacial Max-
imum (LGM), Younger Dryas, BLlling-
AllerLd, and D/O events 12 and 19 constrains
the thresholds T1(d18O of ice G –36.4°) and
T2(ocean d18O G 0.4°), and also the am-
plification coefficient, to a value of 2.0.
shown in Fig. 2, showing a warming of
È21.5-C from the LGM to the Holocene
Eestimate based on the 2000-year period
centered at 21,000 years ago (21 ka)^. Our
reconstruction for D/O events 18 and 20 is also
consistent with independent estimates of site
temperature changes obtained using gas frac-
tionation (performed in this latter case on
the NorthGRIP core located 300 km north-
northwest of the GRIP site) (Table 1). Figure2,
which compares various approaches to recon-
structing Tsitechanges from water isotopes,
clearly shows the importance of accounting for
seasonality. However, there is also a signifi-
cant influence of the source temperature (full
inversion, black curve), which results in a
systematic shift of the warm part of each D/O
event toward colder temperatures. This is due
to the antiphase between the d18O (or dD) and
excess rapid variations: When Greenland is
warm, the moisture source is colder, and if this
is not corrected for, temperature estimates will
be too cold (and vice versa). Neglecting changes
in moisture source and using a constant tem-
poral isotope-temperature slope of half the
spatial slope (32) is therefore inadequate to
reconstruct past Greenland temperatures from
d18O and could induce an overestimation of
some rapid-events temperature change by up to
40% (Fig. 2 and Table 1). In other words, the
apparent isotope-temperature slope varies at all
time scales (13).
Source temperature changes, DTsource(Fig.
2), mimic the initial excess record (Fig. 1)
with a glacial-interglacial amplitude of È6-C.
Rapid Tsourcechanges of 2- to 4-C occur
simultaneously but in antiphase with rapid
Tsiteevents, which is remarkable given that
these two climate variables appear in phase at
longer orbital scales; the large amplitude of
rapid events in deuterium excess is partly due
to large changes in Greenland temperature
itself (21) and is less marked after isotopic
inversion in Tsource. As is the case for Antarc-
tica, an imprint of obliquity fluctuations in
deuterium excess and source temperature can
be seen, although this is limited to the period
from 20 to 80 ka. The mechanisms at work
are probably the same as in Antarctica. In low
latitudes, a low obliquity is associated with a
high local mean annual insolation, which
should result in higher SST Eas recently sug-
gested by a modeling experiment (33)^ and
thus in a more intense evaporation. A low
obliquity also implies a decrease in high-
latitude insolation and temperature (34). The
resulting increased insolation gradient is asso-
ciated with a more intense meridional tem-
perature gradient (Fig. 2) and a more intense
atmospheric transport (35). These two effects
together yield a dominant role for warm low-
latitude sources when obliquity is low, thus
explaining the observed link between deute-
rium excess and obliquity. However, such a
link is not observed between 20 and 10 ka
and before 80 ka, possibly because these two
periods—which correspond to large ice sheet
changes (deglaciation and glacial inception,
respectively)—are characterized by changes
in Northern Hemisphere stationary waves
forced by ice sheet growth or decay. Finally,
high obliquities (e.g., at 30 and 70 ka)
correspond to a high polar amplification (ratio
of long-term changes in Tsiteto Tsourceup to
6), whereas periods with low obliquity (e.g.,
at 10, 50, and 90 ka) coincide with a reduced
polar amplification (ratio of change around 2).
North Atlantic SST records (36) show large
glacial-interglacial fluctuations, with thermal
amplitudes reaching typically È10-C at 45-N
and È5-C at 35-N (37), significantly higher
than the glacial-interglacial source temperature
change reconstructed here. A detailed inspec-
tion of DTsource(Fig. 2), which resembles the
initial deuterium excess record (Fig. 1), also
points to important differences at millennial
with Greenland D/O events recorded in Tsite,
whereas DTsourcereconstruction suggests an
out-of-phase relation between Tsourceand Tsite
during rapid changes.
Our proposed interpretation is that these
noticeable differences (amplitude of LGM-to-
modern changes and millennial-scale events)
result from drastic changes in the polar front,
the geographical location of Greenland_s main
moisture sources, and the atmospheric water
cycle during glacial times (5). When Greenland
is cold and surrounded by an extensive sea ice
cover, mid-latitude oceans are much colder than
today and cannot provide much moisture to
Greenland.Evaporation is, however, maintained
at lower subtropical and tropical locations,
providing precipitation in central Greenland
ture source shift of 5- in latitude is compatible
both with the LGM DTsitevalues and with local
summer SST reconstructions. This is also con-
sistent with temperature and salinity latitudinal
profiles estimated from marine sediments, re-
flecting the shift of the dominant evaporative
areas during rapid events (38).
Such a large-scale reorganization of the
time scales is indirectly confirmed by the cal-
cium composition of GRIP ice, a parameter re-
flecting (i) the strength of GRIP dust sources
the efficiency of dust transport to Greenland
(39). The strong correlation between log(Ca)
and d18O of ice was previously noted (39), but
the similarity is even better with this recon-
structed site-to-source temperature gradient
(R20 0.86 at 100-year time step and R20 0.88
at 5000-year time step between 8 and 100 ka). In
particular, a warmer site and a colder source at
È50 to 55 ka result in a decreased meridional
temperature gradient, exactly at the time of mini-
mum calcium concentration. The meridional
temperature gradient also shows a 40,000-year
modulation paralleling obliquity fluctuations
(Fig. 1). Wehavealreadypointedoutthatmean
annual insolation, and thus obliquity, strongly
We suggest that they also indirectly control the
strength of the dust source: A larger obliquity
should correspond to a decreased annual mean
tropical ocean temperature and an increased
the summer monsoons, thereby decreasing the
continental dust sources.
Our interpretation of the d18O and d GRIP
data provides a consistent picture of changes
occurring over the last 100,000 years in
Greenland and in the North Atlantic. Our
findings confirm model results by showing that
Table 1. Estimates of site temperature changes and comparison with two methods to estimate
temperature changes using the water stable isotopes from GRIP ice cores. DTsitefull inversion, results of
the full isotopic inversion after seasonality correction; DTsiteconstant slope, estimate from ice d18O only,
with a constant slope before 8 ka (32).
Last Glacial Maximum –23- T 3-C (8)
–21.5- T 3-C
10.9- T 3-C
9.7- T 3-C
13.9- T 3-C
9.8- T 3-C
17.1- T 3-C
11.7- T 3-C
11- T 3-C (44)
10- T 4-C (9)
12- T 3-C (12)
11- T 3-C (13)
16- T 3-C (11, 13)
11- T 3-C (13)
R E P O R T S
1 JULY 2005 VOL 309SCIENCEwww.sciencemag.org
on June 4, 2013
when seasonality is accounted for, reasonable Download full-text
local temperature estimates can be drawn from
the GRIP isotopic record; the correction due to
source temperature changes is of lesser impor-
tance at glacial-interglacial scales than during
rapid events. Moreover, the comparison be-
tween our estimate of DTsourceand available
North Atlantic sediment-based SST reconstruc-
tions suggests that large changes in geograph-
ical moisture source location occur both at the
orbital and millennial scales. We show that
DTsourcereflects obliquity changes and that
DTsourceand DTsiteare of opposite sign, both
at orbital and millennial time scales. The
influence of obliquity on deuterium excess
and moisture origin, already identified for
Antarctica, is confirmed for Greenland. When
cold conditions prevail in the mid- and high
latitudes, the moisture origin shifts to milder
southward locations (5). Finally, we point to
striking similarities between the calcium-dust
records and the site-to-source temperature gra-
dient; both are strongly modulated by obliquity,
and the coupled climate model results suggest
that obliquity could be linked with dust source
areas through the land-sea temperature contrast.
At the millennial time scale, the site-to-source
temperature fluctuations highlight large-scale
changes in atmospheric circulation, which is
consistent with the observation of simultaneous
rapid climate changes at polar, temperate, and
tropical latitudes (40) also recorded in Green-
land ice chemistry and methane fluctuations
(41). Modeling studies have indeed shown that
Northern Hemisphere storm tracks are influ-
enced not only by the topography of the ice
sheets but also by the sea-ice extent and the
meridional temperature gradients (30).
Such large changes in the atmospheric hy-
are not fully represented in the intermediate-
complexity climate models commonly used to
understand the mechanisms of abrupt events.
Nonetheless, they could play a key role in the
generation of instabilities of the ice sheets and
the ocean circulation, amplified by changes in
sea-iceextent,ashas beensuggested forthelast
glacial inception (42).
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Supporting Online Material
Materials and Methods
10 December 2004; accepted 20 May 2005
A Magnetic Nanoprobe
Technology for Detecting
Molecular Interactions in Live Cells
Jaejoon Won,1Mina Kim,1Yong-Weon Yi,1Young Ho Kim,2
Neoncheol Jung,2Tae Kook Kim1*
Technologies to assess the molecular targets of biomolecules in living cells are
lacking. We have developed a technology called magnetism-based interaction
capture (MAGIC) that identifies molecular targets on the basis of induced
movement of superparamagnetic nanoparticles inside living cells. Efficient
intracellular uptake of superparamagnetic nanoparticles (coated with a small
molecule of interest) was mediated by a transducible fusogenic peptide. These
nanoprobes captured the small molecule’s labeled target protein and were
translocated in a direction specified by the magnetic field. Use of MAGIC in
genome-wide expression screening identified multiple protein targets of a drug.
MAGIC was also used to monitor signal-dependent modification and multiple
interactions of proteins.
Modern medicine faces the challenge of
developing safer and more effective therapies.
However, many drugs currently in use were
identified without knowledge of their molecu-
lar targets (1, 2). Bioactive natural products
are an important source of drug leads, but
their modes of action are usually unknown
(2). Elucidation of their physiological targets
is essential for understanding their therapeutic
and adverse effects, thereby enabling the de-
velopment of second-generation therapeutics.
Moreover, the discovery of novel targets of
clinically proven compounds may suggest new
therapeutic applications (3). Target identifica-
tion (ID) is also important in chemical biology,
where high-throughput screening is used to iden-
tify small molecules with a desired pheno-
type (4, 5). Despite the great benefits of such
1Department of Biological Sciences, Korea Advanced
Institute of Science and Technology, Daejeon 305-
701, Korea.2CGK Co. Ltd., Daejeon 305-701, Korea.
*To whom correspondence should be addressed.
R E P O R T S
www.sciencemag.org SCIENCE VOL 309 1 JULY 2005
on June 4, 2013