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in the early to mid-Holocene. Rosenberg et al. (
2011
) mapped four successive lake
deposits in southern Arabia with ages of around 125 ka, around 100 ka, around 80 ka
and early Holocene, comparable with the speleothem ages from Yemen and Oman.
During any of these wetter intervals, prehistoric humans could have crossed the desert.
There was a long dry interval in southern Arabia between around 75 ka and 10.5 ka,
when human movement across the desert would have been very difficult.
The Quaternary speleothem records from the Negev Desert are more complex
than those of Oman and Yemen and require more subtle interpretation. The
18
O
13
C variations in speleothems from caves scattered in the southern and central
Negev Desert have thrown light on past changes in surface vegetation and the probable
source of the rainfall associated with speleothem formation. The speleothems indicate
significant wet phases at 350-310, around 310-290, 220-190 and 140-110 ka, with
all except the 310-290 ka humid phase coinciding with interglacial events (Vaks et al.,
2007
;Vaksetal.,
2010
). The wet phases were also coeval with episodes of sapro-
pel accumulation in the eastern Mediterranean, discussed in
Section 18.8
(see also
Chapter 10
), which occurred during times of greater discharge into the Mediterranean
from the Nile and now defunct Saharan rivers. The 140-110 ka humid phase in the
southern Negev was synchronous with the last interglacial wet phases evident in the
speleothems in southern Yemen and northern Oman analysed by Fleitmann et al.
(
2003a
;
2009
;
2011
). Nevertheless, only certain wet phases in the Negev Desert coin-
cide with interglacial phases (e.g., 200-190, 137-123 and 84-77 ka), while others
(e.g., 190-150, 76-25 and 23-13 ka) coincide with glacial phases (Vaks et al.,
2006
).
The
and
18
O values in speleothems from the northern Negev showed that the primary
rainfall source was from the eastern Mediterranean, with some possible contribution
from tropical southern sources during interglacial episodes. Vaks et al. (
2003
) found
that during glacials, there was a southward migration of the desert boundary on the
eastern flank of the central mountain ridge of Israel, but there was no change relative
to the present during interglacials (Vaks et al.,
2003
). The D/H ratios in speleothem
fluid inclusions showed that glacial climates were cooler with less evaporation over
the eastern Mediterranean (Matthews et al.,
2000
; McGarry et al.,
2004
). Quantitative
reconstructions of LGM temperature and rainfall are rare, but Affek et al. (
2008
)
used 'clumped isotope' thermometry (see
Chapter 7
), and were able to show that
temperatures in Soreq Cave south-west of Jerusalem were 6-7
°
C cooler than today
during the LGM and 3
C cooler at 56 ka. One valuable by-product of such data is that
they allow more rigorous testing of the climate models that are used in reconstructing
global circulation during the LGM. The linear dunes in the southern Negev were more
active during the LGM, when it was wetter than it is today, than they were during the
more arid early Holocene (Roskin et al.,
2011a
; Roskin et al.,
2011b
). Although this
may seem counter-intuitive, the explanation is simple: stronger winds and an abund-
ant supply of sand at that time. This is in strong contrast to the Sahara and Arabia,
where the dunes were mobile during the hyper-arid LGM and during the cold, dry
°
