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stratigraphy for MIS 4 and late 5 was established by corre-
lating the G. bulloides
δ
Arctic waters in the Nordic Seas [Eynaud et al., 2009], but
the reconstructed SST values are more in the range of the
modern subpolar gyre. Nevertheless, the data clearly show
that the Arctic or even Subarctic Front was located in the
range of 39°N during Heinrich and Greenland stadials, while
the hydrographic Polar Front seems to have been located
somewhere close to 41°N [Eynaud et al., 2009]. Such a close
spacing of hydrographic fronts, but on a more longitudinal
scale, is today observed off New Foundland and in the
Norwegian Sea [Dickson et al., 1988], i.e., in regions where
Atlantic surface waters come in close vicinity to (sub)polar
waters. On the latitudinal scale, such steep temperature gra-
dients are known from the Last Glacial Maximum (LGM)
[Pflaumann et al., 2003]. The front near 39°N would gener-
ally mark the southern edge of the Heinrich IRD belt, in
accordance with evidence from the western basin [Hemming,
2004], but this does not mean that icebergs did not cross this
boundary and deposited their IRD farther to the south [Bard
et al., 2000; Toucanne et al., 2007; Voelker et al., 2006; Zahn
et al., 1997]. From the percent N. pachyderma (s) records,
however, it becomes quickly obvious that Heinrich stadials
1, 4, and 6 had a stronger impact on the hydrography in the
Sines region than in the Gulf of Cadiz (site MD99-2339)
(Figure 3) where percent N. pachyderma (s) values were
signi
18
O records of cores MD95-2040 and
MD95-2042. Stratigraphic control within MIS 6 follows the
work of Margari et al. [2010], whereas for the section older
than MIS 6, the new benthic
δ
18
O record was tuned to the
LR04 stack [Lisiecki and Raymo, 2005]. The core now has a
bottom age of 360 ka (MIS 10/11 boundary) that is signifi-
-
cantly younger than the age obtained by Thouveny et al.
[2004] through extrapolation.
5. SURFACE WATER GRADIENTS AND
IMPLICATIONS FOR THE POLAR FRONT POSITION
5.1. Conditions During the Last 80 kyr
The compilation of the existing high-resolution planktic
foraminifer derived-SST and percent N. pachyderma (s) re-
cords (Figure 3) visibly reveals the strong impact the Hein-
rich stadials had in this region and the temperature gradients
that existed within a latitudinal band of only 7°. The Heinrich
stadials are clearly distinguished by maxima in percent N.
pachyderma (s) and the coldest SST in all records. The
coldest SST during Heinrich and Greenland stadials were
recorded at the two northernmost sites SU92-03 and MD99-
2331 with SST
su
in the range of 4°C to 6°C during the
Heinrich stadials. Cooling at these sites occurred during the
whole period of a Heinrich stadial, and percent N. pachyderma
(s) generally exceeded 90%, values today associated with
polar water masses [Eynaud et al., 2009]. While these values
are the coldest/highest in our compilation, conditions were
more extreme just 2° farther to the north in the Bay of Biscay
[Sánchez-Goñi et al., 2008; Toucanne et al., 2009] where
percent N. pachyderma (s) was close to 100% during the
Heinrich stadials and most Greenland stadials. If one com-
pares the records of cores MD99-2331 and MD95-2040
(Figure 3), also separated by about 2° latitude, another grad-
ual change appears. At the latter site at 40.6°N, maximal
percent N. pachyderma (s) was more in the range of 80% to
90% resulting in 2° warmer surface waters. Despite the
warmer conditions at site MD95-2040, the overall shape in
the percent N. pachyderma (s) and SST curves is similar in
the three sites north of 40°N setting them apart from the ones
farther to the south and con
cantly lower (<16%).
Even smaller-scale regional differences can be investigated
using the three records off Sines (MD95-2041, MD95-2042,
and MD01-2444, Figure 3). The two core sites at 10°W,
i.e., farther offshore, tend to record slightly warmer SST
not only during the cold climate events but also during some
Greenland interstadials (for an explanation see section 5.2).
Site MD01-2444 especially reveals warmer SST during the
Greenland interstadials indicating that this site was more
strongly in
uenced by subtropical AzC waters than the other
two sites, either from being located underneath a northward-
extending meander of the Azores Front or from being in
u-
enced by a paleo-IPC (Figure 1a). Sporadically, the SST was
even warmer than those recorded farther to the south at site
MD99-2339. On the other hand, sites MD01-2444 and
MD99-2339 experienced the colder conditions during the
first half of Greenland interstadial 8 more strongly than sites
MD95-2042 and MD95-2041. This cooling was more pro-
nounced at the three northern sites (MD95-2040, MD9-2331,
and SU92-03, Figure 3) and must therefore have been ad-
vected from the north to the south, most likely with the more
offshore-located PC. Thus, high regional variability linked to
the position and shape of fronts and/or upwelling system
dynamics also occurred under glacial climate conditions and
needs to be taken into account when impacts of abrupt
climate change are discussed and compared to climate model
results.
rming the hydrographic bound-
ary between 40°N and 38°N described by Salgueiro et al.
[2010] as a robust feature.
South of 38°N, the percent N. pachyderma (s) values, with
the exception of one data point during Heinrich stadial 4 in
core MD01-2444, did not exceed 60% (Figure 3), and cold-
est SST during Heinrich stadials were in the range of 8°C to
10°C, i.e., 2° or more warmer than at site MD95-2040. The
percent N. pachyderma (s) values are those associated with
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