shallow or drying out (Rukwa, Victoria, Chad) (Williamson
et al. 1993), the whole intertropical zone has recorded major
and rapid changes in its water balance, linked mostly to
changes in regional temperature. The changes affected the
continental surfaces, the soils, the distribution and the biodiversity of terrestrial and aquatic ecosystems. For example,
the iron mineralogy of soils was modified, and variations of
several orders of magnitude of the concentration in magnetic
minerals are evidenced (Williamson et al. 1993).
Owing to unrivaled chronological and spatial resolution,
the data obtained from peat bogs or crater lakes, most
especially the molecular markers of microbial origin (Coffinet et al. 2014), show that these rapid changes in atmospheric circulation and in the composition of the atmosphere
(water, CO 2 ) were responsible for a fundamental reorganization of ecosystems, particularly with regard to the distribution of mountain ecosystems and most wetland areas.
These records confirm the dominant forcing of insolation
and monsoon circulation over tropical hydrology. At the
decennial to millennial scale, however, the depositional
record clearly indicates the coupling of the tropical climate
with the climate in the high latitudes, and with the activity of
the thermohaline circulation, particularly during the glacial
interval where the Dansgaard-Oeschger variability is identified in numerous hydrological records. New high resolution
chronological records are required to identify the mechanisms and the potential phase-lags linked with such changes
(Zhang et al. 2018).
Recent Anthropological Influence on Climate
Archives: Both a Proof and a Tool to Assess
the Impacts of Local and Regional
Development
Superimposed on natural climate stress, the human impact
on the hydrology and land-based environments of Africa
remains poorly documented, and presents a challenge to a
better understanding of the interactions between climate,
environment and society in developing countries. The first
large-scale human impacts on ecosystems (livestock
domestication and pastoralism) are recorded as early as ca.
4000 yr B.P., especially during the last 2500 yr with
deforestation and biomass burning (Thevenon et al. 2003)
being associated with iron metallurgy, the expansion of
farming activities and demography: rapid increases in the
fluxes of microcharcoal, detrital inputs (especially magnetic)
and pollen from ruderal vegetation (near habitations) and
pioneer taxa (Zhang et al. 2018). In East Africa, the
expansion of trade routes between the coast and the interior
at least 1300 years ago increased the abundance of exotic
plants, especially cultivated plants from Asia such as banana,
taro, rice, and, more recently, plants from the new world
such as maize, tobacco, tomatoes. However, it is only since
the late nineteenth century and especially after the Second
World War, that the archives show radical changes in the
environment caused by man (Marchant et al. 2018): the
organic components (on land and in water) and inorganic
components, dissolved or suspended (notably magnetic),
present in the environment are affected (Garcin et al. 2007).
In this context, just as changes in atmospheric composition have been reconstructed from ice cores, the land-based
‘pre-industrial’ archives recording changes in the climate
and the tropical environment are now the local and regional
references for environments relatively untouched by man,
from the decadal to the millennial scale. Such references are
required to establish a frame of reference so as to identify the
various controls of climate and society on the structural
changes in the landscape and in biodiversity, in vegetal
production, in erosional processes, or in stored material
(including pollutants), and thus to assess the extent and
sustainability of the changes imposed by humans on the
Earth’s surface.
References
Adegbie, A. T., Schneider, R. R., Röhl, U., & Wefer, G. (2003). Glacial
millennial-scale fluctuations in central African precipitation
recorded in terrigenous sediment supply and freshwater signals
offshore came.
Coffinet, S., Huguet, A., Williamson, D., Fosse, C., & Derenne, S.
(2014). Potential of GDGTs as a temperature proxy along an
altitudinal transect at Mount Rungwe (Tanzania). Organic Geochemistry, 68, 82–89.
DeMenocal, P., Ortiz, J., Guilderson, T., Adkins, J., Sarnthein, M.,
Baker, L., et al. (2000). Abrupt onset and termination of the African
humid period: Rapid climate responses to gradual insolation
forcing. Quaternary Science Reviews, 19, 347–361.
Garcin, Y., Williamson, D., Bergonzini, L., Radakovitch, O., Vincens,
A., Buchet, G., et al. (2007). Solar and anthropogenic imprints on
lake masoko (Southern Tanzania) during the last 500 years. Journal
of Paleolimnology, 37, 475–490.
Lézine, A. M., Casanova, J., & Hillaire-Marcel, C. (1990). Across an
early holocene humid phase in Western Sahara: Pollen and isotope
stratigraphy. Geology, 18, 264–267.
Little, M. G., Schneider, R. R., Kroon, D., Price, B., Summerhayes, C.
P., & Segl, M. (1997). Trade wind forcing of upwelling, seasonality,
and heinrich events as a response to sub-milankovitch climate
variability. Paleoceanography, 12, 568–576.
Marchant, R., Richer, S., Boles, O., Capitani, C., Courtney-Mustaphi,
C. J., Lane, P., et al. (2018). Drivers and trajectories of land cover
change in East Africa: Human and environmental interactions from
6000 years ago to present. Earth-Science Reviews, 178, 322–378.
Mayewski, P. A., Rohling, E. E., Stager, J. C., Karlén, W., Maasch, K.
A., Meeker, L. D., et al. (2004). Holocene climate variability.
Quaternary Research, 62, 243–255.
Petit-Maire, N., & Riser, J. (1981). Holocene lake deposits and
palaeoenvironments in central Sahara, Northeastern Mali. Palaeogeography Palaeoclimatology Palaeoecology, 35, 45–61.
18 Air-Ground Interface: Sediment Tracers in Tropical Lakes
211
et al. 1993), the whole intertropical zone has recorded major
and rapid changes in its water balance, linked mostly to
changes in regional temperature. The changes affected the
continental surfaces, the soils, the distribution and the biodiversity of terrestrial and aquatic ecosystems. For example,
the iron mineralogy of soils was modified, and variations of
several orders of magnitude of the concentration in magnetic
minerals are evidenced (Williamson et al. 1993).
Owing to unrivaled chronological and spatial resolution,
the data obtained from peat bogs or crater lakes, most
especially the molecular markers of microbial origin (Coffinet et al. 2014), show that these rapid changes in atmospheric circulation and in the composition of the atmosphere
(water, CO 2 ) were responsible for a fundamental reorganization of ecosystems, particularly with regard to the distribution of mountain ecosystems and most wetland areas.
These records confirm the dominant forcing of insolation
and monsoon circulation over tropical hydrology. At the
decennial to millennial scale, however, the depositional
record clearly indicates the coupling of the tropical climate
with the climate in the high latitudes, and with the activity of
the thermohaline circulation, particularly during the glacial
interval where the Dansgaard-Oeschger variability is identified in numerous hydrological records. New high resolution
chronological records are required to identify the mechanisms and the potential phase-lags linked with such changes
(Zhang et al. 2018).
Recent Anthropological Influence on Climate
Archives: Both a Proof and a Tool to Assess
the Impacts of Local and Regional
Development
Superimposed on natural climate stress, the human impact
on the hydrology and land-based environments of Africa
remains poorly documented, and presents a challenge to a
better understanding of the interactions between climate,
environment and society in developing countries. The first
large-scale human impacts on ecosystems (livestock
domestication and pastoralism) are recorded as early as ca.
4000 yr B.P., especially during the last 2500 yr with
deforestation and biomass burning (Thevenon et al. 2003)
being associated with iron metallurgy, the expansion of
farming activities and demography: rapid increases in the
fluxes of microcharcoal, detrital inputs (especially magnetic)
and pollen from ruderal vegetation (near habitations) and
pioneer taxa (Zhang et al. 2018). In East Africa, the
expansion of trade routes between the coast and the interior
at least 1300 years ago increased the abundance of exotic
plants, especially cultivated plants from Asia such as banana,
taro, rice, and, more recently, plants from the new world
such as maize, tobacco, tomatoes. However, it is only since
the late nineteenth century and especially after the Second
World War, that the archives show radical changes in the
environment caused by man (Marchant et al. 2018): the
organic components (on land and in water) and inorganic
components, dissolved or suspended (notably magnetic),
present in the environment are affected (Garcin et al. 2007).
In this context, just as changes in atmospheric composition have been reconstructed from ice cores, the land-based
‘pre-industrial’ archives recording changes in the climate
and the tropical environment are now the local and regional
references for environments relatively untouched by man,
from the decadal to the millennial scale. Such references are
required to establish a frame of reference so as to identify the
various controls of climate and society on the structural
changes in the landscape and in biodiversity, in vegetal
production, in erosional processes, or in stored material
(including pollutants), and thus to assess the extent and
sustainability of the changes imposed by humans on the
Earth’s surface.
References
Adegbie, A. T., Schneider, R. R., Röhl, U., & Wefer, G. (2003). Glacial
millennial-scale fluctuations in central African precipitation
recorded in terrigenous sediment supply and freshwater signals
offshore came.
Coffinet, S., Huguet, A., Williamson, D., Fosse, C., & Derenne, S.
(2014). Potential of GDGTs as a temperature proxy along an
altitudinal transect at Mount Rungwe (Tanzania). Organic Geochemistry, 68, 82–89.
DeMenocal, P., Ortiz, J., Guilderson, T., Adkins, J., Sarnthein, M.,
Baker, L., et al. (2000). Abrupt onset and termination of the African
humid period: Rapid climate responses to gradual insolation
forcing. Quaternary Science Reviews, 19, 347–361.
Garcin, Y., Williamson, D., Bergonzini, L., Radakovitch, O., Vincens,
A., Buchet, G., et al. (2007). Solar and anthropogenic imprints on
lake masoko (Southern Tanzania) during the last 500 years. Journal
of Paleolimnology, 37, 475–490.
Lézine, A. M., Casanova, J., & Hillaire-Marcel, C. (1990). Across an
early holocene humid phase in Western Sahara: Pollen and isotope
stratigraphy. Geology, 18, 264–267.
Little, M. G., Schneider, R. R., Kroon, D., Price, B., Summerhayes, C.
P., & Segl, M. (1997). Trade wind forcing of upwelling, seasonality,
and heinrich events as a response to sub-milankovitch climate
variability. Paleoceanography, 12, 568–576.
Marchant, R., Richer, S., Boles, O., Capitani, C., Courtney-Mustaphi,
C. J., Lane, P., et al. (2018). Drivers and trajectories of land cover
change in East Africa: Human and environmental interactions from
6000 years ago to present. Earth-Science Reviews, 178, 322–378.
Mayewski, P. A., Rohling, E. E., Stager, J. C., Karlén, W., Maasch, K.
A., Meeker, L. D., et al. (2004). Holocene climate variability.
Quaternary Research, 62, 243–255.
Petit-Maire, N., & Riser, J. (1981). Holocene lake deposits and
palaeoenvironments in central Sahara, Northeastern Mali. Palaeogeography Palaeoclimatology Palaeoecology, 35, 45–61.
18 Air-Ground Interface: Sediment Tracers in Tropical Lakes
211