variability in time and space of benthic recolonization at the
end of a sapropel. The end of enhance monsoon seems to
mark a sharp and widespread (basinwide) onset of deep
water oxygenation due to resumption of strong convective
deep-water formation.
Sapropels are more common in the eastern Mediterranean
(east of the Strait of Sicily) than in the western Mediterranean, where they are also known as Organic Rich Layers
(ORLs) (Rogerson et al. 2008).
As suggested by Rohling et al. (2015), the eastern
Mediterranean is more sensitive to development of deep-sea
anoxia than the western Mediterranean, because of differences in the efficiency of deep-water renewal.
For a long time, the relationship between insolation
changes associated with precession cycles and impacts on
hydrological changes through fresh water inputs has been
invoked as causal link to explain sapropel occurrences
(Rossignol-Strick et al. 1982). Nevertheless, there are many
different contexts in, which sapropels have occurred since
the Miocene (Rohling et al. 2015). For instance, the role of
the cryosphere was certainly different during Pliocene and
Pleistocene. For Quaternary, it has been shown that, superimposed to the major effect of African monsoon and
enhancement of freshwater from the Nile river, other forcing
factors have to be accounted for. The imprint of
glacial-interglacial cycle and associated sea level changes
has been shown to contribute strongly for sapropel occurring
during deglaciation as S1 (Rohling et al. 2015; Grimm et al.
2015).
Most recent advance on S1 sapropel modeling
Modeling represents also a unique tool to investigate the
responses of the Mediterranean basin to different external
forcing factors from insolation changes to associated hydrological perturbations that may produce sapropel events.
Two important developments have been down recently
concerning sapropel modeling: much longer simulation and
much higher spatial resolution.
Superimposed to precession cycles, since one million
years the 100 ky glacial-interglacial cycle has also affected
sapropel occurrence (Köng et al. 2017). Recent modeling
studies (Grimm et al. 2015) aimed to simulate the S1 from its
onset. A more specific scenario, involving a preconditioning
of cold and poorly salted water coming from the last Heinrich event, was suggested as a possible cause for the S1
formation.
Another important issue is to reach high resolution to
capture convection patterns in the Mediterranean basin.
Using a coupled AOGCM (Atmospheric-Ocean Global
Circulation Model) including a regional Mediterranean Sea
model (1/8° much higher than previously used), Vadsaria
et al. (2019) have revisited the impact of Nile hosing fresh
water increase on triggering sapropel S1. This improvement
allows for better simulating the intermediate and deep convection occurring in winter (Adloff et al. 2015).
Moreover, the simulation of oceanic tracer as Nd allows
one to validate changes in ocean dynamics (Ayache et al.
2016).
Sulphur
The sulfur cycle is of interest to climatologists because it
leads to the formation of sulfuric acid (H 2 SO 4 ), a submicronic aerosol that reflects solar radiation efficiently (direct
effect) and which, due to its highly hygroscopic nature, has a
physical influence on clouds (indirect effect). It is formed in
the atmosphere by the oxidation of SO 2 whose emission
level through the combustion of fossil reserves is 35–45 Tg
per year. The IPCC estimates that due to the increase in
sulfate aerosols in the atmosphere, anthropogenic emissions
of SO 2 could be responsible for a radiative forcing of
−0.4 W/m
2 , an opposite forcing but equivalent to about one
third of the radiative forcing linked to the increase of CO 2 in
the atmosphere (+1.2 W/m
2 ). However, as noted above, the
comparison between these two values is of limited
Fig. 23.15 Left, sapropels within a sediment core recovered in 2001 during RV Meteor cruise M51-3 (Hemleben et al. 2003) (photograph by
Eelco. J. Rohling and Kristian.C. Emeis). Right, late Pliocene sapropel layers outcropping at Punta Piccola (Plancq et al. 2015)
23 Biogeochemical Cycles and Aerosols Over the Last Million Years
289
end of a sapropel. The end of enhance monsoon seems to
mark a sharp and widespread (basinwide) onset of deep
water oxygenation due to resumption of strong convective
deep-water formation.
Sapropels are more common in the eastern Mediterranean
(east of the Strait of Sicily) than in the western Mediterranean, where they are also known as Organic Rich Layers
(ORLs) (Rogerson et al. 2008).
As suggested by Rohling et al. (2015), the eastern
Mediterranean is more sensitive to development of deep-sea
anoxia than the western Mediterranean, because of differences in the efficiency of deep-water renewal.
For a long time, the relationship between insolation
changes associated with precession cycles and impacts on
hydrological changes through fresh water inputs has been
invoked as causal link to explain sapropel occurrences
(Rossignol-Strick et al. 1982). Nevertheless, there are many
different contexts in, which sapropels have occurred since
the Miocene (Rohling et al. 2015). For instance, the role of
the cryosphere was certainly different during Pliocene and
Pleistocene. For Quaternary, it has been shown that, superimposed to the major effect of African monsoon and
enhancement of freshwater from the Nile river, other forcing
factors have to be accounted for. The imprint of
glacial-interglacial cycle and associated sea level changes
has been shown to contribute strongly for sapropel occurring
during deglaciation as S1 (Rohling et al. 2015; Grimm et al.
2015).
Most recent advance on S1 sapropel modeling
Modeling represents also a unique tool to investigate the
responses of the Mediterranean basin to different external
forcing factors from insolation changes to associated hydrological perturbations that may produce sapropel events.
Two important developments have been down recently
concerning sapropel modeling: much longer simulation and
much higher spatial resolution.
Superimposed to precession cycles, since one million
years the 100 ky glacial-interglacial cycle has also affected
sapropel occurrence (Köng et al. 2017). Recent modeling
studies (Grimm et al. 2015) aimed to simulate the S1 from its
onset. A more specific scenario, involving a preconditioning
of cold and poorly salted water coming from the last Heinrich event, was suggested as a possible cause for the S1
formation.
Another important issue is to reach high resolution to
capture convection patterns in the Mediterranean basin.
Using a coupled AOGCM (Atmospheric-Ocean Global
Circulation Model) including a regional Mediterranean Sea
model (1/8° much higher than previously used), Vadsaria
et al. (2019) have revisited the impact of Nile hosing fresh
water increase on triggering sapropel S1. This improvement
allows for better simulating the intermediate and deep convection occurring in winter (Adloff et al. 2015).
Moreover, the simulation of oceanic tracer as Nd allows
one to validate changes in ocean dynamics (Ayache et al.
2016).
Sulphur
The sulfur cycle is of interest to climatologists because it
leads to the formation of sulfuric acid (H 2 SO 4 ), a submicronic aerosol that reflects solar radiation efficiently (direct
effect) and which, due to its highly hygroscopic nature, has a
physical influence on clouds (indirect effect). It is formed in
the atmosphere by the oxidation of SO 2 whose emission
level through the combustion of fossil reserves is 35–45 Tg
per year. The IPCC estimates that due to the increase in
sulfate aerosols in the atmosphere, anthropogenic emissions
of SO 2 could be responsible for a radiative forcing of
−0.4 W/m
2 , an opposite forcing but equivalent to about one
third of the radiative forcing linked to the increase of CO 2 in
the atmosphere (+1.2 W/m
2 ). However, as noted above, the
comparison between these two values is of limited
Fig. 23.15 Left, sapropels within a sediment core recovered in 2001 during RV Meteor cruise M51-3 (Hemleben et al. 2003) (photograph by
Eelco. J. Rohling and Kristian.C. Emeis). Right, late Pliocene sapropel layers outcropping at Punta Piccola (Plancq et al. 2015)
23 Biogeochemical Cycles and Aerosols Over the Last Million Years
289