Review of Palaeobotany and Palynology
Volume 141, Issues 1-2, August 2006, Pages 203-223
Proxy climate and vegetation changes during the last five millennia in NW
Iberia: Pollen and non-pollen palynomorph data from two ombrotrophic
peat bogs in the North Western Iberian Peninsula
T.M. Mighall, A. Martínez Cortizas, H. Biester and S.E. Turner
Pollen and non-pollen palynomorph data are presented from two radiocarbondated ombrotrophic peat bogs from the Xistral Mountains in the North Western
Iberian Peninsula. The results suggest that vegetation changes over the last five
millennia are the result of human disturbance and climate change. Four major
periods of forest disturbance are recorded: during the Late Neolithic, Metal Ages,
Roman period and culminating in the permanent decline of deciduous forests since
the Middle Ages, as agriculture and metallurgy intensified. Records of non-pollen
palynomorphs, particularly those derived from fungi, proved to be useful
indicators of climate change and human activity. Discriminant and cluster analysis
suggest that trends in certain pollen and NPP reflect changes in humidity and to a
lesser extent temperature. Cyperaceae and Types 18 and 18b increase during more
humid, wet phases, whilst Type 306 increases during drier phases. Various
ascospores, derived from coprophilous fungi, complement changes in pollen taxa
to infer human activity.
Keywords: ombrotrophic bog; proxy climate record; pollen; non-pollen
palynomorphs; NW Iberia
Linking changes in atmospheric dust deposition, vegetation change and human
activities in northwest Spain during the last 5300 years
Cortizas AM, Mighall T, Pombal XP, Munoz JCN, Varela EP, Rebolo RP
Volume: 15
Issue: 5
Pages: 698-706
Published: JUL
A high-resolution, 5300-yr record of pollen and lithogenic elements (K, Ca, Ti,
Rb, Sr, Y, Zr) from an ombrotrophic peat bog located in northwest Spain,
reveals that the variations in the fluxes of lithogenic elements supplied to the
bog by atmospheric deposition were coupled to the evolution of the vegetation
of the area. A strong negative correlation exists between the percentage of tree
pollen and the concentration of lithogenic elements. For example, the
correlation between total tree pollen and Sr concentrations is - 0.94. The main
phases of decline of the deciduous forest occurred during known cultural
periods (late Neolithic, the Metal Ages, the Roman Period, the Middle Ages and
the Industrial period) suggesting a close link between human activities (fires and
forest clearances), changes in the vegetation and soil erosion. The flux of
lithogenic elements seems to have increased before a significant variation in
pollen is detected, which may indicate that changes in soil erosion are reflected
earlier than the changes in vegetation in the bog record. Variations in the
composition of the deposited dust reflect impacts that occurred at different
spatial scales, with local sources dominant in the late Neolithic, the Metal Ages
and the Middle Ages, whilst regional sources are more important in the Roman
period and the Industrial Revolution. During the prehistoric period, arboreal
pollen percentages recovered to their former levels, suggesting that woodland
regenerated following a disturbance phase, but for the last 1400 years no
significant recovery took place until afforestation with Pines was introduced 200
years ago. While this must be the result of continuous clearances to convert
forest into arable land, a cumulative effect on soil degradation must also be
Science 7 May 1999:
Vol. 284 no. 5416 pp. 939-942
Mercury in a Spanish Peat Bog: Archive of Climate Change and Atmospheric
Metal Deposition
A. Martı́nez-Cortizas, X. Pontevedra-Pombal, E. Garcı́a-Rodeja, J. C. NóvoaMuñoz and W. Shotyk
A peat core from a bog in northwest Spain provides a record of the net
accumulation of atmospheric mercury since 4000 radiocarbon years before
the present. It was found that cold climates promoted an enhanced
accumulation and the preservation of mercury with low thermal stability,
and warm climates were characterized by a lower accumulation and the
predominance of mercury with moderate to high thermal stability. This
record can be separated into natural and anthropogenic components. The
substantial anthropogenic mercury component began ∼2500 radiocarbon
years before the present, which is near the time of the onset of mercury
mining in Spain. Anthropogenic mercury has dominated the deposition
record since the Islamic period (8th to 11th centuries A.D.). The results
shown here have implications for the global mercury cycle and also imply
that the thermal lability of the accumulated mercury can be used not only to
quantify the effects of human activity, but also as a new tool for quantitative
paleotemperature reconstruction.