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18 Osw/ice volume calibration [Schrag et al., 2002] as de-
scribed earlier [Flower et al., 2004]. Accordingly, deglacial
δ
δ
was north of these latitudes, a switch was triggered whereby
meltwater entered the North Atlantic and caused AMOC
reduction [Clark et al., 2001]. Regardless of where meltwa-
ter was routed during stadials, this hypothesis predicts melt-
water flow to the Gulf of Mexico during D-O interstadials.
Hill et al. [2006] presented paired Mg/Ca and
18 Osw values can be compared directly with modern
18 Osw values
originally published. The new ice volume-corrected δ
18 Osw of about 1
δ
, in contrast to the
δ
18 Osw
18 Osw-ivc) con
18 O data
from Orca Basin core MD02-2551 from approximately 45 to
28 ka that argued against the original version of this hypoth-
esis. Calculated
data (
rm major episodic negative spikes
from approximately 16.5 to 12.9 ka followed by a rapid
increase of 2.3 at approximately 12.9 ka inferred to repre-
sent the cessation event (Figure 6). Clearly, both the major
meltwater spike and the cessation event are preserved in
δ
δ
δ
18 Osw values indicated
five minima that
did not appear to match the nine D-O interstadials in this
interval. Indeed, the δ
δ
18 Osw.
Although diversion of meltwater from the Gulf of Mex-
ico to the North Atlantic may have triggered the Younger
Dryas, such a diversion does not appear to have triggered
the Oldest Dryas event, known in Greenland as stadial 2a
[Walker et al., 1999] and in the North Atlantic as the
Heinrich 1 stadial [Barker et al., 2009]. Simple rerouting
of meltwater to the North Atlantic might be expected to
yieldnosouthernroutedmeltwater during the Oldest
Dryas. Yet we record at least two major negative δ
18 Osw record exhibited greater simi-
larity to global sea level change [Siddall et al., 2003] and
Antarctic air temperature based on Byrd ice core
18 O on the
Greenland Ice Sheet Project 2 timescale [Johnsen et al.,
1972; Blunier and Brook, 2001]. In particular, the largest
and longest negative
δ
18 Osw excursion seemed to corre-
spond to the A1 Antarctic warming centered at 38.5 ka [Hill
et al., 2006]. The minimum values (about
δ
)are
considerably higher than during the last deglaciation, which
may relate to different ages of the ice melted and their
associated
0.5
18 Osw
18 O compositions [Marshall, 2009]. Here we
extend the MD02-2551 data set, update the chronology using
the MARINE09 14 C calibration [Reimer et al., 2009], and
compare to the new EDML ice core
excursions of >1.5
between 17 and 14.5 ka, interrupted
by a brief return to modern
δ
18 Osw values of about 1
at
approximately 15.4 ka (Figure 6). The earlier excursion
appears to be accompanied by distinctive illite clay miner-
alogy derived from the eastern LIS ablation zone (Ohio
River drainage), while other excursions marked by smectite
clay mineralogy were derived from the Missouri River
drainage [Sionneau et al., 2010]. Sea level is known to
have risen by about 20 m during this interval [Fairbanks,
1989], but Antarctica is considered to have contributed
<14 m throughout the last deglaciation [Denton and
Hughes, 2002]. Furthermore, the southern Laurentide ice
margin was far south of potential eastern outlets [Lowell et
al., 1999, 2009]. Accordingly, we suggest that the Gulf of
Mexico served as a major outlet for LIS meltwater and an
integrator of the Mississippi River drainage basin, through-
out the last deglaciation until the onset of the Younger
Dryas.
δ
18 O record [EPICA
Community Members et al., 2006] to reassess these
δ
findings.
18 Osw record on the MARINE09 timescale
The new δ
18 Osw minima during the 48
con
rms
ve
δ
-
28 ka interval
that do not match D-O interstadials 4
-
12 (Figure 7). Instead,
18 Osw minima better match the five AIM events
from the EDML ice core
the ve δ
18 O record [EPICA Community
Members et al., 2006]. Furthermore, these AIM events are
associated with distinct CO 2 maxima from the Byrd ice core
[Ahn and Brook, 2008]. The match between Antarctic warm
events, CO 2 maxima, and inferred LIS meltwater input to the
Gulf of Mexico suggests episodic bipolar warming enhanced
by greenhouse feedbacks, at least during Northern Hemi-
sphere summers that controlled LIS ablation. Southern
Hemisphere warming is reflected in Antarctic air tempera-
ture, but synchronous Northern Hemisphere warming is in-
ferred here from coeval LIS meltwater input to the Gulf of
Mexico. These findings are consistent with far-field manifes-
tations of the
δ
6. TESTING THE MELTWATER ROUTING
HYPOTHESIS DURING MIS 3
Antarctic climate signature
in the equatorial
Could meltwater from the LIS and European ice sheets
have caused D-O coolings during MIS 3? Clark et al. [2001]
summarized the evidence from the last deglaciation that
meltwater routing was controlled by the southern extent of
the LIS and suggested that the D-O events have a similar
cause. Speci
Paci
c Ocean [Stott et al., 2002; Lea et al., 2006] and in the
Greenland dust record [Barker and Knorr, 2007]. Overall,
our observation of LIS ablation during AIM events raises the
possibility that summer LIS melting may be in
uenced by
the Antarctic climate signal including greenhouse gas
changes. Taken together, the deglacial and MIS 3 records
support our inference that the Gulf of Mexico served as a
major outlet for LIS meltwater throughout the last glacial
cycle until the onset of the Younger Dryas.
cally, when the southern LIS margin was south
of about 43°
owed south and
allowed normal AMOC and hence warm climates in the
North Atlantic region. But when the southern LIS margin
-
49°N, meltwater would have
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