Environmental Engineering Reference
In-Depth Information
high percentages of mesothermic elements correlate with low values of
18
O, which
indicate warm-temperate phases
...
In contrast, steppe elements together with high
18
O values indicate colder phases'. In the Montalbino Jonico section 13 warm-
temperate phases have been recognized and are dominated by
Quercus
spp.; the in-
tervening steppe phases are dominated by
Artemisia.
Eight of these warm-temperate
phases are correlated with interglacials, that is MIS (marine isotope stages) 23, 25,
27, 29, 31, 33, 35 and 37. Although any single study is limited in relation to the
area it represents such studies provide insight into a period for which there is little
land-based evidence. Overall, it is generally considered that these and other cycli-
cal environmental changes recorded in Mediterranean (and other ocean sediment)
cores are due to the orbital forcing parameters of obliquity and precession, and that
the latter is a key component in precipitation receipts, which is also a major factor
in sapropel formation (see above).
Further information on this middle stage of the Quaternary derives from the Hula
Basin, Israel. Pollen analysis (Horowitz, 1989) of sediments from this infilled lake
basin shows that climatic cycles were characterized by forest during wetter and
cooler glacial stages, and as conditions became drier and warmer maquis commu-
nities developed and eventually steppe during interglacials (see comments above re
moisture availability being reduced in the eastern Mediterranean region when com-
pared with the western Mediterranean region due to monsoon effects). As this mid-
dle stage of the Quaternary drew to a close the last remaining elements of Tertiary
tropical communities disappeared, at least in the central part of the Mediterranean as
is indicated by the Montalbano Jonico (southern Italy) pollen data discussed above.
In a recent review of literature from the Iberian peninsula Mijarra
et al.
(2009) sug-
gest that the last tropical taxa in the eastern basin also disappeared probably due to
the intensification of glacial cyclicity, which involved lower temperatures during the
cold stages. The implication for Mediterranean mountains, especially in the north
and west, is that temperature-sensitive species disappeared from high elevations as
treelines receded during cold stages. Mountain vegetation communities in the south
were less acutely affected but were unlikely to have remained unaltered. As for the
east, relatively few records and the vexed issue of monsoonal influence (see above)
make any general conclusions difficult.
1
×
10
6
to 20
×
10
3
years ago
Evidence for environmental change during the later part of the Quaternary period
is more widespread than that for earlier times. In particular there are several deep
sedimentary sequences from lake basins in the Mediterranean region that have been
investigated and that provide an additional and complementary perspective on this
interval, besides marine sediments. The locations of these lake basins are given in
Figure 2.3 and further detail is given in Table 2.1. There are no long records from
the south of the Mediterranean Basin. Moreover, none of those from the north or
east of the basin are at high altitude and so they do not directly record changes in
