D. Wolf et al. 
et al., 2008) and a maximum in semi-desertic and steppic 
plants in different parts of northern Iberia (Gonzälez- 
Samperiz et al., 2006, 2010; Naughton et al., 2016). More- 
over, cold and dry conditions during HS-1 were derived 
from a dominance of steppic vegetation elements in north- 
zentral Iberia (Gil Garcfa et al., 2002), from aeolian activity, 
and a lacustrine record in south-central Iberia (Rendell et al., 
1994; Vegas et al., 2010), as well as from paleoclimate mod- 
eling (Ludwig et al., 2018). 
The Younger Dryas is not expressed in the form of loess 
formation, but instead, in the development of an alluvial 
fan covering a fluvial sequence in the Jarama Valley (12.54 
+0.11 cal ka BP; Wolf et al., 2013), which documents dry 
conditions in central Iberia that are likewise documented in 
a number of other archive studies (Garcfa-Ruiz et al., 2016; 
Gäzquez et al., 2018). 
A hydrological model for central Iberia for MIS 2 
In order to provide a detailed reconstruction of hydrological 
conditions during the late last glacial period in central Iberia, 
we combined results linked to loess dynamics with informa- 
tion about mountain glacier development. Both geomorphic 
systems were strongly determined by moisture availability, 
and a number of well-dated records are available for central 
ıberia (Oliva et al., 2019 and references therein). In central 
ıberian mountain ranges, the maximum ice extent (MIE) 
generally preceded the global LGM (23-19 ka) and was 
already reached 26 to 25 ka ago (Dominguez-Villar et al., 
2013; Oliva et al., 2019; Fig. 14) in the Gredos Mountains 
{Palacios et al., 2011), the Guadarrama Mountains (Palacios 
st al., 2012), and the Sierra de B&jar Mountains (Carrasco 
et al., 2015). In a following period, mountain glaciers retained 
a widespread state until a major glacier retreat preluded the 
onset of deglaciation around 19 ka, in line with a major tem- 
perature increase (Palacios et al., 2012, 2017; Oliva et al., 
2019). Concurrently with HS1, a major readvance took 
place between 17 and 16 ka in the Gredos Mountains 
(Palacios et al., 2011) and at 16.8-16.5 ka in the Iberian 
Range, respectively (Oliva et al., 2019). In the Sierra de 
3€jar Mountains, a readvance was dated between 20.6 + 2.5 
and 17.8 + 1.0 ka, while after a strong retreat until 17.5 + 
0.9 ka, a stabilization of the glacial extent lasted until 
15.5 + 1.0 ka (Carrasco et al., 2015). After 16 ka, central Ibe- 
ran glaciers generally melted away in the course of a strong 
warming linked to the Bgolling-Allergd period. For the Youn- 
ger Dryas cold phase (GS-1: 12.9-11.7 ka b2k, Rasmussen 
et al., 2014), some information from mountain glaciers is 
available that indicates development of small glaciers despite 
generally very arid conditions in Iberia (Garcfa-Ruiz et al., 
2016; Oliva et al., 2019). 
Cold temperatures as well as sufficient moisture availabil- 
ity play a decisive role for ice growth (e.g., Dominguez-Villar 
st al., 2013). While warm season temperatures control the 
melting of glaciers during retreat phases, the buildup of gla- 
ciers strongly depends on cold season snow precipitation. 
It therefore follows that both glacier buildup and loess 
formation during MIS 2 and upper MIS 3 indicate cold con- 
ditions, with glacier advances linked to higher winter precip- 
itation, and, by contrast, loess formation linked to stronger 
arldity periods. The latter is likewise expressed by the isoto- 
pic record of Eagle Cave in the SCS (Fig. 1; Dominguez- 
Villar et al., 2013), which reveals peak phases of aridity con- 
:emporary with HS3 and HS2 that we tentatively correlate 
with loess deposition in the upper Tagus Basın (Fig. 14; 
SU-7 and SU-8). The peak phase of loess formation during 
GS-5/HS3 was characterized by very cold and arid conditions 
in line with lowest North Atlantic SSTs. After the transition to 
1-4, higher SSTs, and thus higher moisture transfer, induced 
less arid conditions in the Iberian interior. During subsequent 
GS-4 and early GS-3, no loess formation was initiated in cen- 
cral Iberia, which we also interpret as an indication of reduced 
aridity. Instead, mountain glaciers reached a state of MIE at 
26 ka (Fig. 14), which indicates increased winter precipita- 
ion. In the middle and late GS-3 (concurrently with HS2 as 
detected in marine records off the Iberian margin), further 
glacial advances were seemingly prevented by increasing 
aridity, which likewise initiated loess formation that contin- 
Jed presumably until the beginning of GI-2. However, 
according to our $'°C,x results, aridity was less pronounced 
during this period (HS2), and together with the still very cold 
:;emperatures, resulted in relatively stable positions of moun- 
:ain glacier margins. After GS-3/HS2 ended, both SSTs and 
:emperatures over the Iberian Peninsula increased during 
he global LGM (lower GS-2.1), leading to higher moisture 
availability and a further glacial advance in the interior 
around 21.3+0.7 ka (Dominguez-Villar et al., 2013; 
Fig. 14). A temperature increase at the end of the global 
LGM initiated major deglaciation in central Iberia that was 
Ärst interrupted by GS-2.1a/HS1, when cold and arid condi- 
ions led to loess formation; however, in this case, it was 
simultaneous with glacier expansion. Similar to the upper 
GS-3/HS2, the reactivation of glacial dynamics provides 
evidence of less pronounced aridity that fits with less cold 
North Atlantic SSTs. After the warming linked to the 
Balling-Allergd period, no loess was formed during 
he Younger Dryas cold phase, probably due to lower dry- 
ness that was further strengthened by resurgent glacier 
Jevelopment. 
Finally, during MIS 2 and upper MIS 3, we see different 
situations of moisture availability related to D-O cycles, 
and in particular to Bond cycles, because loess formation 
was likely linked to the most intense stadial periods in the 
final stages of these Bond cycles that also included Heinrich 
events. While referring again to the remaining uncertainties 
of OSL dating, we tend to differentiate between ‘normal’ 
D-O stadials (e.g., GS-4, lower GS-3, GS-2.2, GS-2.1b-c) 
and D-O stadials comprising Heinrich events (GS-5, upper 
GS-3, GS-2.1), respectively. During a normal stadial, a south- 
ward shift of the polar front was associated with an expansion 
of cold, subaretic water towards the eastern North Atlantic, 
leading to decreased SSTs. Lower SSTs caused a reduction 
in moisture uptake and transfer to continental areas. The 
3southern position of the polar front was linked to enhanced 
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'/Aanann cambridoe oraf/carefterms https’ /Z/idal araf10 1017 /alıa 20720