Upper Tagus loess formation and the marine atmosphere off the Iberian margin 
25 
gradients of SSTs and atmospheric pressure, which resulted 
in an increase in storm frequency with a deflection of wind 
tracks over the interior Iberian Peninsula. Although condi- 
(ons in central Iberia were significantly drier during stadials 
as compared to interstadials, air masses still carried enough 
moisture for glaciers to have a balanced mass equilibrium 
or even a surplus leading to glacier growth, at least in winter- 
time. During Heinrich stadials, exceptionally high aridity 
affected central Iberia due to polar-front displacement farther 
zouth to the Iberian margin. This intensified downturn in 
SSTs largely prevented moisture transfer to central Iberia 
and hindered glacier growth without leading to large melting 
oecause of cold temperatures. Additionally, reinforced tem- 
perature and pressure gradients led to marked storminess in 
inland areas that activated processes of deflation, aeolian 
iransport, and loess formation. 
that led to intensified processes of frost weathering in the fram- 
ing mountain ranges. Periods that were linked to an interrup- 
tion of loess deposition with simultaneous soil development 
are assumed to indicate higher environmental moisture avail- 
ability during interstadial periods. Accordingly, we found 
aigher moisture availability during the middle to upper MIS 
5, in line with the most prolonged Greenland interstadials 
GI-23 and GI-21, as well as during the lower MIS 3. The mid- 
dle to upper MIS 3 (GI-9 to GI-5) corresponds to very weak 
ndications of soil development. Finally, no pedogenic pro- 
cesses were detected during MIS 2, which may indicate an 
\ncreasing aridification in the course of MIS 3 and MIS 2. 
In summary, and based on an extensive multi-proxy 
ıpproach, we found that during GS-5 (including HS3), a max- 
.mum in loess formation coincided with maximum aridity 
‘highest values of 8'°C..) and cold-related sediment supply 
as well as extremely cold SSTs off the Iberian margin (Sal- 
Jueiro et al., 2014). After a phase of reduced aridity that 
led to regional MIE in central Iberian mountains under still 
very cold temperatures, GS-3 (including HS2), which was 
already linked to less arid conditions as seen in the lower 
8'°Cyax values, had reduced loess formation. Apparently, 
he global LGM (23-19 ka) was mild enough in central Ibe- 
a that the aeolian system remained inactive, while a second 
peak in glacier dynamics took place that was in line with mod- 
erate SSTs (Eynaud et al., 2009). As indicated by our results, 
conditions during HS1 were again arıd enough to enable loess 
formation. 
Our results also allow some important statements with 
‚egard to the frequently discussed habitability of central Ibe- 
1a in the context of hominine occupation. We found that con- 
ditions during the upper MIS 3 and MIS 2 were generally 
colder than in the periods before. However, the sudden disap- 
pearance of Neanderthals in the region shortly before 42 ka 
‘see review in Wolf et al., 2018) exactly matched a phase 
of loess formation reflecting a period of maximum aridity 
ander presumably warmer conditions. After an occupation 
zap, evidence for modern humans was found 25 ka, when 
he Tagus loess record suggests arid (but not extremely 
arid) and still cold conditions. Thus, we assume that moisture 
availability instead of cold temperatures was the limiting fac- 
:°or controlling bioproductivity, and thus habitability, in the 
central Iberian region. Additionally, we assume that aridity 
combined with warmer temperatures led to enhanced evapo- 
ration and thus, higher hostility to human occupation as com- 
pared to a coamhination of ariıdity and cold conditions 
CONCLUSIONS 
Our results suggest a strong coupling between marine dynam- 
ics in the North Atlantic and the behavior of geomorphic sys- 
tems in central Iberia during most of the last glacial period. The 
marine-terrestrial coupling is mainly based on a coincidence in 
ime between marine cold spells and phases of loess deposition 
in the upper Tagus Basin. More specifically, we found such a 
coincidence during the most intense Greenland stadials in the 
final stages of the Bond Cycles that are GS-2.1a (17.5—-14.7 ka 
b2k), GS-3 (27.5-23.3 ka b2k), GS-5.1 (30.6-28.9 ka b2k), 
and GS-5.2 (30.8—-32.0 ka b2k) for MIS 2 and the upper 
MIS 3, noting that a definite correlation with loess deposition 
phases is affected by dating uncertainties inherent to the OSL 
dating procedure. Likewise, during MIS 4, loess deposition 
coincided with marine cooling in the course of GS-18 (63.8— 
59.4 ka b2k), GS-19.1 (69.4-64.1 ka b2k), and GS-19.2 
{70.4-69.6 ka b2k), although the age uncertainties of the dep- 
ositional ages in the loess sections are very high. All of these 
phases show a good correlation with Heinrich events that 
were detected in marine records off the Iberian margin, 
which may indicate functional relationships. However, during 
ihe middle MIS 3, loess formation correlates to GS-11 (42.2- 
41.5 ka b2k) or, considering the age uncertainties, to GS-10 
(40.8—40.2 ka b2k) or GS-12 (44.3-43.3 ka b2k), instead of 
the bracketing stadials GS-9 and GS-13 that were linked to 
Heinrich events 4 and 5. 
We see that the link between the most intense marine cold 
phases and loess formation in the interior of Iberia (at least dur- 
ing MIS 4, MIS 2, and upper MIS 3) was established through 
pronounced environmental aridity because of strongly reduced 
North Atlantic SSTs off the Iberian margin, and thus lack of 
moisture transfer to inland areas. Strong aridity that led to 
che diminishing of vegetation cover together with stronger 
winds caused by reinforced temperature and pressure gradients 
formed the basic prerequisites for intense aeolian dynamics, 
including deflation processes and loess formation. We also 
found that after 35 ka, loess formation was most likely sup- 
ported by a higher sediment supply to the river floodplains 
as main deflation areas. This may indicate colder temperatures 
ACKNOWLEDGMENTS 
This work was supported by the German Research Foundation 
‘DFG) (FA 239/17-1, and FA 239/18-1). We would like to thank 
B. Winkler and S. Gerstenhauer (Technische Universität Dresden) 
‚or lab work. Moreover, we are grateful to Philipp Baumgart and Flo- 
an Schneider for their support in fieldwork and rock magnetic mea- 
surements. Finally, we would also like to thank Philipp Schulte 
(RWTH Aachen), Denis-Didier Rousseau (CNRS, Paris), and an 
anonymous reviewer for their constructive remarks. 
Downloaded from https://www.cambridge.org/core. IP address: 77.191.167.9, on 05 Feb 2021 at 17:09:02. subject to the Cambridge Core terms of use. available at 
attns‘/Aanany cambridae ora/careifterms https‘ //idal ara410 1017/maıbıa 20720