Stable carbon isotope analysis on fossil Cedrus pollen shows summer aridification in Morocco during the last 5000 years

ABSTRACT Quantitative climate reconstructions from pollen typically rely on empirical relationships between pollen abundances or assemblages and climate, such as the modern analogue technique. However, these techniques may be problematic when applied to fossil sequences, as they cannot separate anth...

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Bibliographic Details
Published inJournal of quaternary science Vol. 34; no. 4-5; pp. 323 - 332
Main Authors Bell, Benjamin A., Fletcher, William J., Cornelissen, Henk L., Campbell, Jennifer F. E., Ryan, Peter, Grant, Helen, Zielhofer, Christoph
Format Journal Article
LanguageEnglish
Published Chichester Wiley Subscription Services, Inc 01.05.2019
Subjects
Anthropogenic factors
Aridification
Aridity
Carbon
Carbon isotopes
Cedrus
Cedrus atlantica
Climate
Climatic analysis
Empirical analysis
Fossils
Holocene
Human influences
Isotopes
mid‐Holocene
Moisture stress
Physiological responses
Pollen
stable isotopes
Summer
Vegetation
Morocco
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Summary:ABSTRACT Quantitative climate reconstructions from pollen typically rely on empirical relationships between pollen abundances or assemblages and climate, such as the modern analogue technique. However, these techniques may be problematic when applied to fossil sequences, as they cannot separate anthropogenic from climatic influence on pollen assemblages. Here, we reconstruct Mid‐ to Late Holocene summer aridity in the Middle Atlas, Morocco, using stable carbon isotope analysis of isolated fossil Cedrus pollen. This approach is based on well‐documented plant physiological responses to moisture stress and is therefore independent of vegetation composition. We find that there has been a general long‐term trend of increasing summer aridity in the region during the last 5000 years to the present day. The gradual decline of Cedrus atlantica forest in the Late Holocene follows this aridity trend. Additionally, we show how isolating a specific pollen type for carbon isotope analysis yields a robust climate signal, versus using pollen concentrates or bulk sediment. Our findings indicate that climate has become drier in the region and confirms the Mid‐ to Late Holocene aridification trend observed more widely in the western Mediterranean, using a novel proxy for this region with good potential for wider application in other environments.
ISSN:0267-8179
1099-1417
DOI:10.1002/jqs.3103