Upper Tagus loess formation and the marine atmosphere off the Iberian margin 
J 
evidence of slope processes indicated by higher contents of 
medium and coarse sands. If we solely consider units that 
can be linked to aeolian-dominated sedimentation processes 
{SU-5 to SU-9), maximum mean grain sizes (and by exten- 
sion maximum wind strengths), are seen in SU-7 in the Para- 
{so and Villarubia sections. The same applies to SU-6 in the 
Fuentiduefa section, and to SU-8 in section A3. Furthermore, 
when comparing just average mean values of grain sizes for 
all sections (excluding SU-1 to SU-4), a clear fining gradient 
becomes obvious starting from section A3, followed by Fuen- 
iduena, then Paraiso, and finally Villarubia (Fig. 8). This gra- 
dient is a direct reflection of the vertical distance between the 
loess sections and the river floodplain as the main sediment 
source. It thus exemplifies an increasing effect of particle 
size-sorting due to aeolian transport processes. Because 
loess deposits were accumulated on both sides of the Tagus 
River, this may indicate rather close-to-the-ground winds 
along the Tagus valley instead of winds blowing homoge- 
neously from a specific direction, which makes interpreta- 
tions of horizontal transport distances difficult. Similar 
effects related to wind channeling and acceleration have 
been reported for (e.g.) the Rhöne Valley (Bosgq et al., 2018). 
the formation time of SU-7 could be narrowed to between 
31.7+2.6 and 31.2+2.4 ka, fitting GS-5.2. Even if SU-8 
and SU-7 show an overlap in age uncertainties, both units 
can be clearly distinguished based on field evidence and 
analytical results from sediment samples (Fig. 10). 
When older aeolian deposits are considered, age uncertain- 
äes become larger. This is seen in SU-5, where OSL dating 
suggests formation between 73.0+6.9 and 59.7+4.7 ka, 
although the former date marks a minimum age due to 
signs of sample saturation. However, this period comprises 
MIS 4 including 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), 
which becomes clearer if only the mean ages are used 
‚Fig. 14), and thus is linked to a global cold period (e.g., Cut- 
ler et al., 2003) that has been documented in an Iberian con- 
‚ext (Moreno et al., 2012). The accumulation of SU-4 took 
’lace at the latest around 80.7 + 8.1 or 95.5 + 7.9 ka, accord- 
‚ng to OSL minimum ages. A period during middle MIS 
5 after the formation of the Eemian Interglacial soil seems 
probable, but cannot be determined precisely based on the 
available data. 
A particular case is represented by the loess layer SU-6 that 
was formed within a narrow time frame between 42.5 + 3.6 
ınd 41.3 + 4.0ka (Fig. 14), where the latter date marks a min- 
ımum age estimation because of indications of dose satura- 
Jon. Referring to mean ages, the period that is represented 
ın the middle of MIS 3 took place at the same time as 
GS-11 (42.2-41.5 ka b2k). However, considering the age 
ıncertainties, GS-10 (40.8—40.2 ka b2k), GS-12 (44.3—43.3 
ka b2k), or even GS-9 (39.9-38.2 ka b2k) may also poten- 
Jally overlap with loess deposition in central Spain. 
DISCUSSION 
Timing of aeolian dynamics against the background 
of last glacial climatic changes in the North Atlantic 
region 
Phases of loess deposition 
The information from marine records off the Iberian margin 
/38°N, Sänchez Goßi et al., 2008), a 5'°0 record of the 
NGRIP ice core (Rasmussen et al., 2014), and the timing of 
central Iberian loess dynamics are compiled in Figure 14. 
During MIS 2 and the end of MIS 3, it shows a general tem- 
poral agreement between Greenland stadials (GS), tempera- 
zure reductions in the North Atlantic off the Iberian margin, 
and phases of loess deposition. As shown in the upper part 
of Figure 14, OSL dating results coming from the loess 
sequences in this period (MIS 2-MIS 3) are accompanied 
5y a relative standard deviation in the range of 5-9%. The 
‚esultant age range of a particular OSL date is between 3 ka 
and 5 ka, and potentially covers two to three D-O cycles. 
This demonstrates the challenge of clearly defining the dura- 
(on of loess deposition phases and assigning it to specific GS. 
However, the formation of SU-9 (16.2+ 1.4 ka) perfectly 
agrees with GS-2.1a (17.5-14.7 ka b2k based on GICCO5, 
Andersen et al., 2006; Rasmussen et al., 2014). For SU-8 
(formation between 25.9+2.4 ka and 23.2+1.6 ka), the 
explicitness in the age assessment is reduced, although the 
mean ages again fit well with GS-3 (27.5—23.3 ka b2k). Con- 
sidering SU-7 as the thickest accumulation (formation 
between 31.7+2.6 ka and 28.4+2.4 ka), the mean ages 
span a period of two GS (GS-5.1 between 30.6 ka and 28.9 
ka b2k, and GS-5.2 between 30.8 ka and 32.0 ka b2k). If 
the youngest age from the A3 section (Fig. 4) is ignored, 
Phases of soil development 
Phases of loess deposition are generally linked to harsh envi- 
:onmental conditions. In contrast, phases showing an inter- 
:uption of loess deposition as indicated by surface 
exposure and the initiation of soil forming processes are gen- 
arally assumed to indicate more favorable environmental 
conditions that often accompanied Greenland interstadials 
‘GI, e.g., Fischer et al., 2021) and are therefore interpreted 
as D-O-like events (Rousseau et al., 2017, 2020). Based on 
variations of NGRIP 8!80 and dust concentration, Rousseau 
et al. (2017) calculated onset and duration of the various GIs 
.n the Northern Hemisphere during the last glacial period and 
found a strong conformity between higher GI duration and 
more intense soil development in northwestern Europe as 
.ndicated by loess-paleosol sequences (LPS). Here the ques- 
jon arises as to whether these patterns together with related 
climatic conditions also apply to southern Europe—in partic- 
ılar, the more continental regions of the Iberian Peninsula. 
For example, a compilation of pollen information from 
long continuous marine and terrestrial records by Fletcher 
et al. (2010) revealed that in southernmost Europe, develop- 
ment of temperate forest occurred below 40°N during GI-17 
and 16, GI-14, GI-12, and GI-8. In contrast, between 40°N 
and 44°N latitudes, strong temperate forest development 
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 oraf/careifterms https‘ //idal araf10 1017/mılıa 20720