Environmental Engineering Reference
In-Depth Information
Quaternary in the Atlas Mountains and there is no dating control. Nevertheless it is
important to note that Suc (1984), Suc
et al.
(1995), Suc and Popescu (2005) and
Popescu
et al.
(2010) date the onset of cold/glacial stages to 2.6
10
6
years ago,
which is in agreement with dating of ice-derived material in Atlantic sediment cores
(e.g. Shackleton
et al.
, 1984; Haug
et al.
, 2005) and is in accord with the dating of
the newly agreed base of the Quaternary at Monte San Nicola, Sicily (see above). In
contrast the Hula Basin pollen record indicates substantial cooling, which, coupled
with increased precipitation, favoured forest formation during cold/glacial stages
and steppe communities during subsequent interglacials. This difference between
the western and eastern Mediterranean, namely dry-cool glacials and humid-warm
interglacials in the western Mediterranean as opposed to moist-cool glacial and dry-
warm interglacials in the eastern Mediterranean (Horowitz, 1969; Subally
et al
.,
1999; Subally and Quezel, 2002), has been recently resolved. It relates to the mon-
soon influence, which in controlling humid air mass transport over the central-
eastern Mediterranean induces moister phases during glacials and conversely drier
phases during interglacials, a process forced by precession (Joannin
et al
., 2007a,b;
Suc
et al
., 2010).
Further evidence for environmental conditions during this early stage of the Qua-
ternary derives from exposed sections of marine sediments and a range of marine
cores which contain sapropels, that is, laminated sediments rich in organic material.
These central-eastern Mediterranean sapropels have earlier Miocene counterparts
known as black shales and all have been the focus of extensive investigation (for
commentaries see Bethoux and Pierre, 1999; Meyers, 2006; Emeis and Weissert,
2009). During the last 3
×
10
6
years at least 80 sapropels have been deposited,
which are considered to mirror changes in the density of the ocean water and its
ability to mix. What is particularly significant is that these characteristics are linked
with the climatic warming and cooling associated with climatic cycles. Major in-
creases in freshwater inputs to a saltwater basin cause stratification, which precludes
mixing. Consequently surface layers remain oxygenated but deep layers become
anoxic (i.e. depleted of oxygen). This kills benthic organisms and inhibits their de-
composition; their remains become incarcerated in the accumulating sediment and
thus enhance the organic content to produce a sapropel. Periods of increased rainfall
would have generated an increased influx of freshwater (Hilgen, 1991; Suc
et al.,
2010) as would a greater volume of glacial meltwater deriving from the Alps or
the Mediterranean mountains, or from sources bordering the Atlantic Ocean whose
impacts would have fed into the Mediterranean via the Straits of Gibraltar. These
processes would have operated during warm stages and would thus have promoted
substantial sapropel formation, which was limited during cold stages. As Hilgen
(1991) and Suc
et al
. (2010) suggest, based on evidence from sedimentary se-
quences from southern Italy (notably the Crotone sequence), the palaeoenvironmen-
tal record may reflect the response of vegetation to the strong interaction between
precession and obliquity during climatic cycles. Such relationships are difficult to
unravel but emphasize the complex links between global climate and the carbon
cycle (Mannion, 2006).
×
